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Diffstat (limited to 'src')
| -rw-r--r-- | src/charon/doc/Todo-list.txt | 4 | ||||
| -rw-r--r-- | src/charon/doc/standards/draft-eronen-ipsec-ikev2-clarifications-09.txt | 3250 | ||||
| -rw-r--r-- | src/charon/doc/standards/draft-hoffman-ikev2-1-00.txt | 6720 | ||||
| -rw-r--r-- | src/charon/doc/standards/draft-hoffman-ikev2bis-00.txt | 6776 | ||||
| -rw-r--r-- | src/charon/doc/standards/draft-myers-ikev2-ocsp-03.txt | 785 | ||||
| -rw-r--r-- | src/charon/doc/standards/rfc4301.txt | 5659 | ||||
| -rw-r--r-- | src/charon/doc/standards/rfc4306.txt | 5547 | ||||
| -rw-r--r-- | src/charon/doc/standards/rfc4307.txt | 339 | ||||
| -rw-r--r-- | src/charon/doc/standards/rfc4478.txt | 283 |
9 files changed, 29363 insertions, 0 deletions
diff --git a/src/charon/doc/Todo-list.txt b/src/charon/doc/Todo-list.txt index 9d9debfca..7bb46438b 100644 --- a/src/charon/doc/Todo-list.txt +++ b/src/charon/doc/Todo-list.txt @@ -74,3 +74,7 @@ Todo-List for charon - add support for CERTREQs - proper handling of multiple certificate payloads (import order) - add a Rekey-Counter for SAs in "statusall" +- ipsec status: + - on one line: ip, id, spi + - no key age, rekey for IKE + - byte count
\ No newline at end of file diff --git a/src/charon/doc/standards/draft-eronen-ipsec-ikev2-clarifications-09.txt b/src/charon/doc/standards/draft-eronen-ipsec-ikev2-clarifications-09.txt new file mode 100644 index 000000000..00f50dc31 --- /dev/null +++ b/src/charon/doc/standards/draft-eronen-ipsec-ikev2-clarifications-09.txt @@ -0,0 +1,3250 @@ + + + + +Network Working Group P. Eronen +Internet-Draft Nokia +Intended status: Informational P. Hoffman +Expires: November 5, 2006 VPN Consortium + May 4, 2006 + + + IKEv2 Clarifications and Implementation Guidelines + draft-eronen-ipsec-ikev2-clarifications-09.txt + +Status of this Memo + + By submitting this Internet-Draft, each author represents that any + applicable patent or other IPR claims of which he or she is aware + have been or will be disclosed, and any of which he or she becomes + aware will be disclosed, in accordance with Section 6 of BCP 79. + + Internet-Drafts are working documents of the Internet Engineering + Task Force (IETF), its areas, and its working groups. Note that + other groups may also distribute working documents as Internet- + Drafts. + + Internet-Drafts are draft documents valid for a maximum of six months + and may be updated, replaced, or obsoleted by other documents at any + time. It is inappropriate to use Internet-Drafts as reference + material or to cite them other than as "work in progress." + + The list of current Internet-Drafts can be accessed at + http://www.ietf.org/ietf/1id-abstracts.txt. + + The list of Internet-Draft Shadow Directories can be accessed at + http://www.ietf.org/shadow.html. + + This Internet-Draft will expire on November 5, 2006. + +Copyright Notice + + Copyright (C) The Internet Society (2006). + +Abstract + + This document clarifies many areas of the IKEv2 specification. It + does not to introduce any changes to the protocol, but rather + provides descriptions that are less prone to ambiguous + interpretations. The purpose of this document is to encourage the + development of interoperable implementations. + + + + + +Eronen & Hoffman Expires November 5, 2006 [Page 1] + +Internet-Draft IKEv2 Clarifications May 2006 + + +Table of Contents + + 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 + 2. Creating the IKE_SA . . . . . . . . . . . . . . . . . . . . . 4 + 2.1. SPI values in IKE_SA_INIT exchange . . . . . . . . . . . . 4 + 2.2. Message IDs for IKE_SA_INIT messages . . . . . . . . . . . 5 + 2.3. Retransmissions of IKE_SA_INIT requests . . . . . . . . . 5 + 2.4. Interaction of COOKIE and INVALID_KE_PAYLOAD . . . . . . . 6 + 2.5. Invalid cookies . . . . . . . . . . . . . . . . . . . . . 8 + 3. Authentication . . . . . . . . . . . . . . . . . . . . . . . . 8 + 3.1. Data included in AUTH payload calculation . . . . . . . . 8 + 3.2. Hash function for RSA signatures . . . . . . . . . . . . . 9 + 3.3. Encoding method for RSA signatures . . . . . . . . . . . . 10 + 3.4. Identification type for EAP . . . . . . . . . . . . . . . 10 + 3.5. Identity for policy lookups when using EAP . . . . . . . . 11 + 3.6. Certificate encoding types . . . . . . . . . . . . . . . . 11 + 3.7. Shared key authentication and fixed PRF key size . . . . . 12 + 3.8. EAP authentication and fixed PRF key size . . . . . . . . 13 + 3.9. Matching ID payloads to certificate contents . . . . . . . 13 + 3.10. Message IDs for IKE_AUTH messages . . . . . . . . . . . . 13 + 4. Creating CHILD_SAs . . . . . . . . . . . . . . . . . . . . . . 13 + 4.1. Creating SAs with the CREATE_CHILD_SA exchange . . . . . . 13 + 4.2. Creating an IKE_SA without a CHILD_SA . . . . . . . . . . 16 + 4.3. Diffie-Hellman for first CHILD_SA . . . . . . . . . . . . 16 + 4.4. Extended Sequence Numbers (ESN) transform . . . . . . . . 16 + 4.5. Negotiation of ESP_TFC_PADDING_NOT_SUPPORTED . . . . . . . 17 + 4.6. Negotiation of NON_FIRST_FRAGMENTS_ALSO . . . . . . . . . 17 + 4.7. Semantics of complex traffic selector payloads . . . . . . 18 + 4.8. ICMP type/code in traffic selector payloads . . . . . . . 18 + 4.9. Mobility header in traffic selector payloads . . . . . . . 19 + 4.10. Narrowing the traffic selectors . . . . . . . . . . . . . 20 + 4.11. SINGLE_PAIR_REQUIRED . . . . . . . . . . . . . . . . . . . 20 + 4.12. Traffic selectors violating own policy . . . . . . . . . . 21 + 4.13. Traffic selector authorization . . . . . . . . . . . . . . 21 + 5. Rekeying and deleting SAs . . . . . . . . . . . . . . . . . . 22 + 5.1. Rekeying SAs with the CREATE_CHILD_SA exchange . . . . . . 23 + 5.2. Rekeying the IKE_SA vs. reauthentication . . . . . . . . . 24 + 5.3. SPIs when rekeying the IKE_SA . . . . . . . . . . . . . . 25 + 5.4. SPI when rekeying a CHILD_SA . . . . . . . . . . . . . . . 25 + 5.5. Changing PRFs when rekeying the IKE_SA . . . . . . . . . . 25 + 5.6. Deleting vs. closing SAs . . . . . . . . . . . . . . . . . 25 + 5.7. Deleting a CHILD_SA pair . . . . . . . . . . . . . . . . . 26 + 5.8. Deleting an IKE_SA . . . . . . . . . . . . . . . . . . . . 26 + 5.9. Who is the original initiator of IKE_SA . . . . . . . . . 26 + 5.10. Comparing nonces . . . . . . . . . . . . . . . . . . . . . 27 + 5.11. Exchange collisions . . . . . . . . . . . . . . . . . . . 27 + 5.12. Diffie-Hellman and rekeying the IKE_SA . . . . . . . . . . 36 + 6. Configuration payloads . . . . . . . . . . . . . . . . . . . . 36 + + + +Eronen & Hoffman Expires November 5, 2006 [Page 2] + +Internet-Draft IKEv2 Clarifications May 2006 + + + 6.1. Assigning IP addresses . . . . . . . . . . . . . . . . . . 36 + 6.2. Requesting any INTERNAL_IP4/IP6_ADDRESS . . . . . . . . . 37 + 6.3. INTERNAL_IP4_SUBNET/INTERNAL_IP6_SUBNET . . . . . . . . . 38 + 6.4. INTERNAL_IP4_NETMASK . . . . . . . . . . . . . . . . . . . 40 + 6.5. Configuration payloads for IPv6 . . . . . . . . . . . . . 41 + 6.6. INTERNAL_IP6_NBNS . . . . . . . . . . . . . . . . . . . . 43 + 6.7. INTERNAL_ADDRESS_EXPIRY . . . . . . . . . . . . . . . . . 43 + 6.8. Address assignment failures . . . . . . . . . . . . . . . 43 + 7. Miscellaneous issues . . . . . . . . . . . . . . . . . . . . . 44 + 7.1. Matching ID_IPV4_ADDR and ID_IPV6_ADDR . . . . . . . . . . 44 + 7.2. Relationship of IKEv2 to RFC4301 . . . . . . . . . . . . . 44 + 7.3. Reducing the window size . . . . . . . . . . . . . . . . . 45 + 7.4. Minimum size of nonces . . . . . . . . . . . . . . . . . . 45 + 7.5. Initial zero octets on port 4500 . . . . . . . . . . . . . 45 + 7.6. Destination port for NAT traversal . . . . . . . . . . . . 46 + 7.7. SPI values for messages outside of an IKE_SA . . . . . . . 46 + 7.8. Protocol ID/SPI fields in Notify payloads . . . . . . . . 47 + 7.9. Which message should contain INITIAL_CONTACT . . . . . . . 47 + 7.10. Alignment of payloads . . . . . . . . . . . . . . . . . . 47 + 7.11. Key length transform attribute . . . . . . . . . . . . . . 48 + 7.12. IPsec IANA considerations . . . . . . . . . . . . . . . . 48 + 7.13. Combining ESP and AH . . . . . . . . . . . . . . . . . . . 49 + 8. Implementation mistakes . . . . . . . . . . . . . . . . . . . 49 + 9. Security considerations . . . . . . . . . . . . . . . . . . . 50 + 10. IANA considerations . . . . . . . . . . . . . . . . . . . . . 50 + 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 50 + 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 50 + 12.1. Normative References . . . . . . . . . . . . . . . . . . . 50 + 12.2. Informative References . . . . . . . . . . . . . . . . . . 51 + Appendix A. Exchanges and payloads . . . . . . . . . . . . . . . 53 + A.1. IKE_SA_INIT exchange . . . . . . . . . . . . . . . . . . . 53 + A.2. IKE_AUTH exchange without EAP . . . . . . . . . . . . . . 54 + A.3. IKE_AUTH exchange with EAP . . . . . . . . . . . . . . . . 55 + A.4. CREATE_CHILD_SA exchange for creating/rekeying + CHILD_SAs . . . . . . . . . . . . . . . . . . . . . . . . 56 + A.5. CREATE_CHILD_SA exchange for rekeying the IKE_SA . . . . . 56 + A.6. INFORMATIONAL exchange . . . . . . . . . . . . . . . . . . 56 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 56 + Intellectual Property and Copyright Statements . . . . . . . . . . 58 + + + + + + + + + + + + +Eronen & Hoffman Expires November 5, 2006 [Page 3] + +Internet-Draft IKEv2 Clarifications May 2006 + + +1. Introduction + + This document clarifies many areas of the IKEv2 specification that + may be difficult to understand to developers not intimately familiar + with the specification and its history. The clarifications in this + document come from the discussion on the IPsec WG mailing list, from + experience in interoperability testing, and from implementation + issues that have been brought to the editors' attention. + + IKEv2/IPsec can be used for several different purposes, including + IPsec-based remote access (sometimes called the "road warrior" case), + site-to-site virtual private networks (VPNs), and host-to-host + protection of application traffic. While this document attempts to + consider all of these uses, the remote access scenario has perhaps + received more attention here than the other uses. + + This document does not place any requirements on anyone, and does not + use [RFC2119] keywords such as "MUST" and "SHOULD", except in + quotations from the original IKEv2 documents. The requirements are + given in the IKEv2 specification [IKEv2] and IKEv2 cryptographic + algorithms document [IKEv2ALG]. + + In this document, references to a numbered section (such as "Section + 2.15") mean that section in [IKEv2]. References to mailing list + messages or threads refer to the IPsec WG mailing list at + ipsec@ietf.org. Archives of the mailing list can be found at + <http://www.ietf.org/mail-archive/web/ipsec/index.html>. + + +2. Creating the IKE_SA + +2.1. SPI values in IKE_SA_INIT exchange + + Normal IKE messages include the initiator's and responder's SPIs, + both of which are non-zero, in the IKE header. However, there are + some corner cases where the IKEv2 specification is not fully + consistent about what values should be used. + + First, Section 3.1 says that the Responder's SPI "...MUST NOT be zero + in any other message" (than the first message of the IKE_SA_INIT + exchange). However, the figure in Section 2.6 shows the second + IKE_SA_INIT message as "HDR(A,0), N(COOKIE)", contradicting the text + in 3.1. + + Since the responder's SPI identifies security-related state held by + the responder, and in this case no state is created, sending a zero + value seems reasonable. + + + + +Eronen & Hoffman Expires November 5, 2006 [Page 4] + +Internet-Draft IKEv2 Clarifications May 2006 + + + Second, in addition to cookies, there are several other cases when + the IKE_SA_INIT exchange does not result in the creation of an IKE_SA + (for instance, INVALID_KE_PAYLOAD or NO_PROPOSAL_CHOSEN). What + responder SPI value should be used in the IKE_SA_INIT response in + this case? + + Since the IKE_SA_INIT request always has a zero responder SPI, the + value will not be actually used by the initiator. Thus, we think + sending a zero value is correct also in this case. + + If the responder sends a non-zero responder SPI, the initiator should + not reject the response only for that reason. However, when retrying + the IKE_SA_INIT request, the initiator will use a zero responder SPI, + as described in Section 3.1: "Responder's SPI [...] This value MUST + be zero in the first message of an IKE Initial Exchange (including + repeats of that message including a cookie) [...]". We believe the + intent was to cover repeats of that message due to other reasons, + such as INVALID_KE_PAYLOAD, as well. + + (References: "INVALID_KE_PAYLOAD and clarifications document" thread, + Sep-Oct 2005.) + +2.2. Message IDs for IKE_SA_INIT messages + + The Message ID for IKE_SA_INIT messages is always zero. This + includes retries of the message due to responses such as COOKIE and + INVALID_KE_PAYLOAD. + + This is because Message IDs are part of the IKE_SA state, and when + the responder replies to IKE_SA_INIT request with N(COOKIE) or + N(INVALID_KE_PAYLOAD), the responder does not allocate any state. + + (References: "Question about N(COOKIE) and N(INVALID_KE_PAYLOAD) + combination" thread, Oct 2004. Tero Kivinen's mail "Comments of + draft-eronen-ipsec-ikev2-clarifications-02.txt", 2005-04-05.) + +2.3. Retransmissions of IKE_SA_INIT requests + + When a responder receives an IKE_SA_INIT request, it has to determine + whether the packet is a retransmission belonging to an existing + "half-open" IKE_SA (in which case the responder retransmits the same + response), or a new request (in which case the responder creates a + new IKE_SA and sends a fresh response). + + The specification does not describe in detail how this determination + is done. In particular, it is not sufficient to use the initiator's + SPI and/or IP address for this purpose: two different peers behind a + single NAT could choose the same initiator SPI (and the probability + + + +Eronen & Hoffman Expires November 5, 2006 [Page 5] + +Internet-Draft IKEv2 Clarifications May 2006 + + + of this happening is not necessarily small, since IKEv2 does not + require SPIs to be chosen randomly). Instead, the responder should + do the IKE_SA lookup using the whole packet or its hash (or at the + minimum, the Ni payload which is always chosen randomly). + + For all other packets than IKE_SA_INIT requests, looking up right + IKE_SA is of course done based on the recipient's SPI (either the + initiator or responder SPI depending on the value of the Initiator + bit in the IKE header). + +2.4. Interaction of COOKIE and INVALID_KE_PAYLOAD + + There are two common reasons why the initiator may have to retry the + IKE_SA_INIT exchange: the responder requests a cookie or wants a + different Diffie-Hellman group than was included in the KEi payload. + Both of these cases are quite simple alone, but it is not totally + obvious what happens when they occur at the same time, that is, the + IKE_SA_INIT exchange is retried several times. + + The main question seems to be the following: if the initiator + receives a cookie from the responder, should it include the cookie in + only the next retry of the IKE_SA_INIT request, or in all subsequent + retries as well? Section 3.10.1 says that: + + "This notification MUST be included in an IKE_SA_INIT request + retry if a COOKIE notification was included in the initial + response." + + This could be interpreted as saying that when a cookie is received in + the initial response, it is included in all retries. On the other + hand, Section 2.6 says that: + + "Initiators who receive such responses MUST retry the + IKE_SA_INIT with a Notify payload of type COOKIE containing + the responder supplied cookie data as the first payload and + all other payloads unchanged." + + Including the same cookie in later retries makes sense only if the + "all other payloads unchanged" restriction applies only to the first + retry, but not to subsequent retries. + + It seems that both interpretations can peacefully co-exist. If the + initiator includes the cookie only in the next retry, one additional + roundtrip may be needed in some cases: + + + + + + + +Eronen & Hoffman Expires November 5, 2006 [Page 6] + +Internet-Draft IKEv2 Clarifications May 2006 + + + Initiator Responder + ----------- ----------- + HDR(A,0), SAi1, KEi, Ni --> + <-- HDR(A,0), N(COOKIE) + HDR(A,0), N(COOKIE), SAi1, KEi, Ni --> + <-- HDR(A,0), N(INVALID_KE_PAYLOAD) + HDR(A,0), SAi1, KEi', Ni --> + <-- HDR(A,0), N(COOKIE') + HDR(A,0), N(COOKIE'), SAi1, KEi',Ni --> + <-- HDR(A,B), SAr1, KEr, Nr + + An additional roundtrip is needed also if the initiator includes the + cookie in all retries, but the responder does not support this + functionality. For instance, if the responder includes the SAi1 and + KEi payloads in cookie calculation, it will reject the request by + sending a new cookie (see also Section 2.5 of this document for more + text about invalid cookies): + + Initiator Responder + ----------- ----------- + HDR(A,0), SAi1, KEi, Ni --> + <-- HDR(A,0), N(COOKIE) + HDR(A,0), N(COOKIE), SAi1, KEi, Ni --> + <-- HDR(A,0), N(INVALID_KE_PAYLOAD) + HDR(A,0), N(COOKIE), SAi1, KEi', Ni --> + <-- HDR(A,0), N(COOKIE') + HDR(A,0), N(COOKIE'), SAi1, KEi',Ni --> + <-- HDR(A,B), SAr1, KEr, Nr + + If both peers support including the cookie in all retries, a slightly + shorter exchange can happen: + + Initiator Responder + ----------- ----------- + HDR(A,0), SAi1, KEi, Ni --> + <-- HDR(A,0), N(COOKIE) + HDR(A,0), N(COOKIE), SAi1, KEi, Ni --> + <-- HDR(A,0), N(INVALID_KE_PAYLOAD) + HDR(A,0), N(COOKIE), SAi1, KEi', Ni --> + <-- HDR(A,B), SAr1, KEr, Nr + + This document recommends that implementations should support this + shorter exchange, but it must not be assumed the other peer also + supports the shorter exchange. + + + + + + + +Eronen & Hoffman Expires November 5, 2006 [Page 7] + +Internet-Draft IKEv2 Clarifications May 2006 + + + In theory, even this exchange has one unnecessary roundtrip, as both + the cookie and Diffie-Hellman group could be checked at the same + time: + + Initiator Responder + ----------- ----------- + HDR(A,0), SAi1, KEi, Ni --> + <-- HDR(A,0), N(COOKIE), + N(INVALID_KE_PAYLOAD) + HDR(A,0), N(COOKIE), SAi1, KEi',Ni --> + <-- HDR(A,B), SAr1, KEr, Nr + + However, it is clear that this case is not allowed by the text in + Section 2.6, since "all other payloads" clearly includes the KEi + payload as well. + + (References: "INVALID_KE_PAYLOAD and clarifications document" thread, + Sep-Oct 2005.) + +2.5. Invalid cookies + + There has been some confusion what should be done when an IKE_SA_INIT + request containing an invalid cookie is received ("invalid" in the + sense that its contents do not match the value expected by the + responder). + + The correct action is to ignore the cookie, and process the message + as if no cookie had been included (usually this means sending a + response containing a new cookie). This is shown in Section 2.6 when + it says "The responder in that case MAY reject the message by sending + another response with a new cookie [...]". + + Other possible actions, such as ignoring the whole request (or even + all requests from this IP address for some time), create strange + failure modes even in the absence of any malicious attackers, and do + not provide any additional protection against DoS attacks. + + (References: "Invalid Cookie" thread, Sep-Oct 2005.) + + +3. Authentication + +3.1. Data included in AUTH payload calculation + + Section 2.15 describes how the AUTH payloads are calculated; this + calculation involves values prf(SK_pi,IDi') and prf(SK_pr,IDr'). The + text describes the method in words, but does not give clear + definitions of what is signed or MACed. + + + +Eronen & Hoffman Expires November 5, 2006 [Page 8] + +Internet-Draft IKEv2 Clarifications May 2006 + + + The initiator's signed octets can be described as: + + InitiatorSignedOctets = RealMessage1 | NonceRData | MACedIDForI + GenIKEHDR = [ four octets 0 if using port 4500 ] | RealIKEHDR + RealIKEHDR = SPIi | SPIr | . . . | Length + RealMessage1 = RealIKEHDR | RestOfMessage1 + NonceRPayload = PayloadHeader | NonceRData + InitiatorIDPayload = PayloadHeader | RestOfIDPayload + RestOfInitIDPayload = IDType | RESERVED | InitIDData + MACedIDForI = prf(SK_pi, RestOfInitIDPayload) + + The responder's signed octets can be described as: + + ResponderSignedOctets = RealMessage2 | NonceIData | MACedIDForR + GenIKEHDR = [ four octets 0 if using port 4500 ] | RealIKEHDR + RealIKEHDR = SPIi | SPIr | . . . | Length + RealMessage2 = RealIKEHDR | RestOfMessage2 + NonceIPayload = PayloadHeader | NonceIData + ResponderIDPayload = PayloadHeader | RestOfIDPayload + RestOfRespIDPayload = IDType | RESERVED | InitIDData + MACedIDForR = prf(SK_pr, RestOfRespIDPayload) + +3.2. Hash function for RSA signatures + + Section 3.8 says that RSA digital signature is "Computed as specified + in section 2.15 using an RSA private key over a PKCS#1 padded hash." + + Unlike IKEv1, IKEv2 does not negotiate a hash function for the + IKE_SA. The algorithm for signatures is selected by the signing + party who, in general, may not know beforehand what algorithms the + verifying party supports. Furthermore, [IKEv2ALG] does not say what + algorithms implementations are required or recommended to support. + This clearly has a potential for causing interoperability problems, + since authentication will fail if the signing party selects an + algorithm that is not supported by the verifying party, or not + acceptable according to the verifying party's policy. + + This document recommends that all implementations support SHA-1, and + use SHA-1 as the default hash function when generating the + signatures, unless there are good reasons (such as explicit manual + configuration) to believe that the peer supports something else. + + Note that hash function collision attacks are not important for the + AUTH payloads, since they are not intended for third-party + verification, and the data includes fresh nonces. See [HashUse] for + more discussion about hash function attacks and IPsec. + + Another reasonable choice would be to use the hash function that was + + + +Eronen & Hoffman Expires November 5, 2006 [Page 9] + +Internet-Draft IKEv2 Clarifications May 2006 + + + used by the CA when signing the peer certificate. However, this does + not guarantee that the IKEv2 peer would be able to validate the AUTH + payload, because the same code might not be used to validate + certificate signatures and IKEv2 message signatures, and these two + routines may support a different set of hash algorithms. The peer + could be configured with a fingerprint of the certificate, or + certificate validation could be performed by an external entity using + [SCVP]. Furthermore, not all CERT payloads types include a + signature, and the certificate could be signed with some algorithm + other than RSA. + + Note that unlike IKEv1, IKEv2 uses the PKCS#1 v1.5 [PKCS1v20] + signature encoding method (see next section for details), which + includes the algorithm identifier for the hash algorithm. Thus, when + the verifying party receives the AUTH payload it can at least + determine which hash function was used. + + (References: Magnus Nystrom's mail "RE:", 2005-01-03. Pasi Eronen's + reply, 2005-01-04. Tero Kivinen's reply, 2005-01-04. "First draft + of IKEv2.1" thread, Dec 2005/Jan 2006.) + +3.3. Encoding method for RSA signatures + + Section 3.8 says that the RSA digital signature is "Computed as + specified in section 2.15 using an RSA private key over a PKCS#1 + padded hash." + + The PKCS#1 specification [PKCS1v21] defines two different encoding + methods (ways of "padding the hash") for signatures. However, the + Internet-Draft approved by the IESG had a reference to the older + PKCS#1 v2.0 [PKCS1v20]. That version has only one encoding method + for signatures (EMSA-PKCS1-v1_5), and thus there is no ambiguity. + + Note that this encoding method is different from the encoding method + used in IKEv1. If future revisions of IKEv2 provide support for + other encoding methods (such as EMSA-PSS), they will be given new + Auth Method numbers. + + (References: Pasi Eronen's mail "RE:", 2005-01-04.) + +3.4. Identification type for EAP + + Section 3.5 defines several different types for identification + payloads, including, e.g., ID_FQDN, ID_RFC822_ADDR, and ID_KEY_ID. + EAP [EAP] does not mandate the use of any particular type of + identifier, but often EAP is used with Network Access Identifiers + (NAIs) defined in [NAI]. Although NAIs look a bit like email + addresses (e.g., "joe@example.com"), the syntax is not exactly the + + + +Eronen & Hoffman Expires November 5, 2006 [Page 10] + +Internet-Draft IKEv2 Clarifications May 2006 + + + same as the syntax of email address in [RFC822]. This raises the + question of which identification type should be used. + + This document recommends that ID_RFC822_ADDR identification type is + used for those NAIs that include the realm component. Therefore, + responder implementations should not attempt to verify that the + contents actually conform to the exact syntax given in [RFC822] or + [RFC2822], but instead should accept any reasonable looking NAI. + + For NAIs that do not include the realm component, this document + recommends using the ID_KEY_ID identification type. + + (References: "need your help on this IKEv2/i18n/EAP issue" and "IKEv2 + identifier issue with EAP" threads, Aug 2004.) + +3.5. Identity for policy lookups when using EAP + + When the initiator authentication uses EAP, it is possible that the + contents of the IDi payload is used only for AAA routing purposes and + selecting which EAP method to use. This value may be different from + the identity authenticated by the EAP method (see [EAP], Sections 5.1 + and 7.3). + + It is important that policy lookups and access control decisions use + the actual authenticated identity. Often the EAP server is + implemented in a separate AAA server that communicates with the IKEv2 + responder using, e.g., RADIUS [RADEAP]. In this case, the + authenticated identity has to be sent from the AAA server to the + IKEv2 responder. + + (References: Pasi Eronen's mail "RE: Reauthentication in IKEv2", + 2004-10-28. "Policy lookups" thread, Oct/Nov 2004. RFC 3748, + Section 7.3.) + +3.6. Certificate encoding types + + Section 3.6 defines a total of twelve different certificate encoding + types, and continues that "Specific syntax is for some of the + certificate type codes above is not defined in this document." + However, the text does not provide references to other documents that + would contain information about the exact contents and use of those + values. + + + + + + + + + +Eronen & Hoffman Expires November 5, 2006 [Page 11] + +Internet-Draft IKEv2 Clarifications May 2006 + + + Without this information, it is not possible to develop interoperable + implementations. Therefore, this document recommends that the + following certificate encoding values should not be used before new + specifications that specify their use are available. + + PKCS #7 wrapped X.509 certificate 1 + PGP Certificate 2 + DNS Signed Key 3 + Kerberos Token 6 + SPKI Certificate 9 + + This document recommends that most implementations should use only + those values that are "MUST"/"SHOULD" requirements in [IKEv2]; i.e., + "X.509 Certificate - Signature" (4), "Raw RSA Key" (11), "Hash and + URL of X.509 certificate" (12), and "Hash and URL of X.509 bundle" + (13). + + Furthermore, Section 3.7 says that the "Certificate Encoding" field + for the Certificate Request payload uses the same values as for + Certificate payload. However, the contents of the "Certification + Authority" field are defined only for X.509 certificates (presumably + covering at least types 4, 10, 12, and 13). This document recommends + that other values should not be used before new specifications that + specify their use are available. + + The "Raw RSA Key" type needs one additional clarification. Section + 3.6 says it contains "a PKCS #1 encoded RSA key". What this means is + a DER-encoded RSAPublicKey structure from PKCS#1 [PKCS1v21]. + +3.7. Shared key authentication and fixed PRF key size + + Section 2.15 says that "If the negotiated prf takes a fixed-size key, + the shared secret MUST be of that fixed size". This statement is + correct: the shared secret must be of the correct size. If it is + not, it cannot be used; there is no padding, truncation, or other + processing involved to force it to that correct size. + + This requirement means that it is difficult to use these PRFs with + shared key authentication. The authors think this part of the + specification was very poorly thought out, and using PRFs with a + fixed key size is likely to result in interoperability problems. + Thus, we recommend that such PRFs should not be used with shared key + authentication. PRF_AES128_XCBC [RFC3664] originally used fixed key + sizes; that RFC has been updated to handle variable key sizes in + [RFC3664bis]. + + Note that Section 2.13 also contains text that is related to PRFs + with fixed key size: "When the key for the prf function has fixed + + + +Eronen & Hoffman Expires November 5, 2006 [Page 12] + +Internet-Draft IKEv2 Clarifications May 2006 + + + length, the data provided as a key is truncated or padded with zeros + as necessary unless exceptional processing is explained following the + formula". However, this text applies only to the prf+ construction, + so it does not contradict the text in Section 2.15. + + (References: Paul Hoffman's mail "Re: ikev2-07: last nits", + 2003-05-02. Hugo Krawczyk's reply, 2003-05-12. Thread "Question + about PRFs with fixed size key", Jan 2005.) + +3.8. EAP authentication and fixed PRF key size + + As described in the previous section, PRFs with a fixed key size + require a shared secret of exactly that size. This restriction + applies also to EAP authentication. For instance, a PRF that + requires a 128-bit key cannot be used with EAP since [EAP] specifies + that the MSK is at least 512 bits long. + + (References: Thread "Question about PRFs with fixed size key", Jan + 2005.) + +3.9. Matching ID payloads to certificate contents + + In IKEv1, there was some confusion about whether or not the + identities in certificates used to authenticate IKE were required to + match the contents of the ID payloads. The PKI4IPsec Working Group + produced the document [PKI4IPsec] which covers this topic in much + more detail. However, Section 3.5 of [IKEv2] explicitly says that + the ID payload "does not necessarily have to match anything in the + CERT payload". + +3.10. Message IDs for IKE_AUTH messages + + According to Section 2.2, "The IKE_SA initial setup messages will + always be numbered 0 and 1." That is true when the IKE_AUTH exchange + does not use EAP. When EAP is used, each pair of messages has their + message numbers incremented. The first pair of AUTH messages will + have an ID of 1, the second will be 2, and so on. + + (References: "Question about MsgID in AUTH exchange" thread, April + 2005.) + + +4. Creating CHILD_SAs + +4.1. Creating SAs with the CREATE_CHILD_SA exchange + + Section 1.3's organization does not lead to clear understanding of + what is needed in which environment. The section can be reorganized + + + +Eronen & Hoffman Expires November 5, 2006 [Page 13] + +Internet-Draft IKEv2 Clarifications May 2006 + + + with subsections for each use of the CREATE_CHILD_SA exchange + (creating child SAs, rekeying IKE SAs, and rekeying child SAs.) + + The new Section 1.3 with subsections and the above changes might look + like the following. + + NEW-1.3 The CREATE_CHILD_SA Exchange + + The CREATE_CHILD_SA Exchange is used to create new CHILD_SAs and + to rekey both IKE_SAs and CHILD_SAs. This exchange consists of + a single request/response pair, and some of its function was + referred to as a phase 2 exchange in IKEv1. It MAY be initiated + by either end of the IKE_SA after the initial exchanges are + completed. + + All messages following the initial exchange are + cryptographically protected using the cryptographic algorithms + and keys negotiated in the first two messages of the IKE + exchange. These subsequent messages use the syntax of the + Encrypted Payload described in section 3.14. All subsequent + messages include an Encrypted Payload, even if they are referred + to in the text as "empty". + + The CREATE_CHILD_SA is used for rekeying IKE_SAs and CHILD_SAs. + This section describes the first part of rekeying, the creation + of new SAs; Section 2.8 covers the mechanics of rekeying, + including moving traffic from old to new SAs and the deletion of + the old SAs. The two sections must be read together to + understand the entire process of rekeying. + + Either endpoint may initiate a CREATE_CHILD_SA exchange, so in + this section the term initiator refers to the endpoint + initiating this exchange. An implementation MAY refuse all + CREATE_CHILD_SA requests within an IKE_SA. + + The CREATE_CHILD_SA request MAY optionally contain a KE payload + for an additional Diffie-Hellman exchange to enable stronger + guarantees of forward secrecy for the CHILD_SA or IKE_SA. The + keying material for the SA is a function of SK_d established + during the establishment of the IKE_SA, the nonces exchanged + during the CREATE_CHILD_SA exchange, and the Diffie-Hellman + value (if KE payloads are included in the CREATE_CHILD_SA + exchange). The details are described in sections 2.17 and 2.18. + + If a CREATE_CHILD_SA exchange includes a KEi payload, at least + one of the SA offers MUST include the Diffie-Hellman group of + the KEi. The Diffie-Hellman group of the KEi MUST be an element + of the group the initiator expects the responder to accept + + + +Eronen & Hoffman Expires November 5, 2006 [Page 14] + +Internet-Draft IKEv2 Clarifications May 2006 + + + (additional Diffie-Hellman groups can be proposed). If the + responder rejects the Diffie-Hellman group of the KEi payload, + the responder MUST reject the request and indicate its preferred + Diffie-Hellman group in the INVALID_KE_PAYLOAD Notification + payload. In the case of such a rejection, the CREATE_CHILD_SA + exchange fails, and the initiator SHOULD retry the exchange with + a Diffie-Hellman proposal and KEi in the group that the + responder gave in the INVALID_KE_PAYLOAD. + + NEW-1.3.1 Creating New CHILD_SAs with the CREATE_CHILD_SA Exchange + + A CHILD_SA may be created by sending a CREATE_CHILD_SA request. + The CREATE_CHILD_SA request for creating a new CHILD_SA is: + + Initiator Responder + ----------- ----------- + HDR, SK {[N+], SA, Ni, [KEi], + TSi, TSr} --> + + The initiator sends SA offer(s) in the SA payload, a nonce in + the Ni payload, optionally a Diffie-Hellman value in the KEi + payload, and the proposed traffic selectors for the proposed + CHILD_SA in the TSi and TSr payloads. The request can also + contain Notify payloads that specify additional details for the + CHILD_SA: these include IPCOMP_SUPPORTED, USE_TRANSPORT_MODE, + ESP_TFC_PADDING_NOT_SUPPORTED, and NON_FIRST_FRAGMENTS_ALSO. + + The CREATE_CHILD_SA response for creating a new CHILD_SA is: + + <-- HDR, SK {[N+], SA, Nr, + [KEr], TSi, TSr} + + The responder replies with the accepted offer in an SA payload, + and a Diffie-Hellman value in the KEr payload if KEi was + included in the request and the selected cryptographic suite + includes that group. As with the request, optional Notification + payloads can specify additional details for the CHILD_SA. + + The traffic selectors for traffic to be sent on that SA are + specified in the TS payloads in the response, which may be a + subset of what the initiator of the CHILD_SA proposed. + + The text about rekeying SAs can be found in Section 5.1 of this + document. + + + + + + + +Eronen & Hoffman Expires November 5, 2006 [Page 15] + +Internet-Draft IKEv2 Clarifications May 2006 + + +4.2. Creating an IKE_SA without a CHILD_SA + + CHILD_SAs can be created either by being piggybacked on the IKE_AUTH + exchange, or using a separate CREATE_CHILD_SA exchange. The + specification is not clear about what happens if creating the + CHILD_SA during the IKE_AUTH exchange fails for some reason. + + Our recommendation in this sitation is that the IKE_SA is created as + usual. This is also in line with how the CREATE_CHILD_SA exchange + works: a failure to create a CHILD_SA does not close the IKE_SA. + + The list of responses in the IKE_AUTH exchange that do not prevent an + IKE_SA from being set up include at least the following: + NO_PROPOSAL_CHOSEN, TS_UNACCEPTABLE, SINGLE_PAIR_REQUIRED, + INTERNAL_ADDRESS_FAILURE, and FAILED_CP_REQUIRED. + + (References: "Questions about internal address" thread, April, 2005.) + +4.3. Diffie-Hellman for first CHILD_SA + + Section 1.2 shows that IKE_AUTH messages do not contain KEi/KEr or + Ni/Nr payloads. This implies that the SA payload in IKE_AUTH + exchange cannot contain Transform Type 4 (Diffie-Hellman Group) with + any other value than NONE. Implementations should probably leave the + transform out entirely in this case. + +4.4. Extended Sequence Numbers (ESN) transform + + The description of the ESN transform in Section 3.3 has be proved + difficult to understand. The ESN transform has the following + meaning: + + o A proposal containing one ESN transform with value 0 means "do not + use extended sequence numbers". + + o A proposal containing one ESN transform with value 1 means "use + extended sequence numbers". + + o A proposal containing two ESN transforms with values 0 and 1 means + "I support both normal and extended sequence numbers, you choose". + (Obviously this case is only allowed in requests; the response + will contain only one ESN transform.) + + In most cases, the exchange initiator will include either the first + or third alternative in its SA payload. The second alternative is + rarely useful for the initiator: it means that using normal sequence + numbers is not acceptable (so if the responder does not support ESNs, + the exchange will fail with NO_PROPOSAL_CHOSEN). + + + +Eronen & Hoffman Expires November 5, 2006 [Page 16] + +Internet-Draft IKEv2 Clarifications May 2006 + + + Note that including the ESN transform is mandatory when creating + ESP/AH SAs (it was optional in earlier drafts of the IKEv2 + specification). + + (References: "Technical change needed to IKEv2 before publication", + "STRAW POLL: Dealing with the ESN negotiation interop issue in IKEv2" + and "Results of straw poll regarding: IKEv2 interoperability issue" + threads, March-April 2005.) + +4.5. Negotiation of ESP_TFC_PADDING_NOT_SUPPORTED + + The description of ESP_TFC_PADDING_NOT_SUPPORTED notification in + Section 3.10.1 says that "This notification asserts that the sending + endpoint will NOT accept packets that contain Flow Confidentiality + (TFC) padding". + + However, the text does not say in which messages this notification + should be included, or whether the scope of this notification is a + single CHILD_SA or all CHILD_SAs of the peer. + + Our interpretation is that the scope is a single CHILD_SA, and thus + this notification is included in messages containing an SA payload + negotiating a CHILD_SA. If neither endpoint accepts TFC padding, + this notification will be included in both the request proposing an + SA and the response accepting it. If this notification is included + in only one of the messages, TFC padding can still be sent in one + direction. + +4.6. Negotiation of NON_FIRST_FRAGMENTS_ALSO + + NON_FIRST_FRAGMENTS_ALSO notification is described in Section 3.10.1 + simply as "Used for fragmentation control. See [RFC4301] for + explanation." + + [RFC4301] says "Implementations that will transmit non-initial + fragments on a tunnel mode SA that makes use of non-trivial port (or + ICMP type/code or MH type) selectors MUST notify a peer via the IKE + NOTIFY NON_FIRST_FRAGMENTS_ALSO payload. The peer MUST reject this + proposal if it will not accept non-initial fragments in this context. + If an implementation does not successfully negotiate transmission of + non-initial fragments for such an SA, it MUST NOT send such fragments + over the SA." + + However, it is not clear exactly how the negotiation works. Our + interpretation is that the negotiation works the same way as for + IPCOMP_SUPPORTED and USE_TRANSPORT_MODE: sending non-first fragments + is enabled only if NON_FIRST_FRAGMENTS_ALSO notification is included + in both the request proposing an SA and the response accepting it. + + + +Eronen & Hoffman Expires November 5, 2006 [Page 17] + +Internet-Draft IKEv2 Clarifications May 2006 + + + In other words, if the peer "rejects this proposal", it only omits + NON_FIRST_FRAGMENTS_ALSO notification from the response, but does not + reject the whole CHILD_SA creation. + +4.7. Semantics of complex traffic selector payloads + + As described in Section 3.13, the TSi/TSr payloads can include one or + more individual traffic selectors. + + There is no requirement that TSi and TSr contain the same number of + individual traffic selectors. Thus, they are interpreted as follows: + a packet matches a given TSi/TSr if it matches at least one of the + individual selectors in TSi, and at least one of the individual + selectors in TSr. + + For instance, the following traffic selectors: + + TSi = ((17, 100, 192.0.1.66-192.0.1.66), + (17, 200, 192.0.1.66-192.0.1.66)) + TSr = ((17, 300, 0.0.0.0-255.255.255.255), + (17, 400, 0.0.0.0-255.255.255.255)) + + would match UDP packets from 192.0.1.66 to anywhere, with any of the + four combinations of source/destination ports (100,300), (100,400), + (200,300), and (200, 400). + + This implies that some types of policies may require several CHILD_SA + pairs. For instance, a policy matching only source/destination ports + (100,300) and (200,400), but not the other two combinations, cannot + be negotiated as a single CHILD_SA pair using IKEv2. + + (References: "IKEv2 Traffic Selectors?" thread, Feb 2005.) + +4.8. ICMP type/code in traffic selector payloads + + The traffic selector types 7 and 8 can also refer to ICMP type and + code fields. As described in Section 3.13.1, "For the ICMP protocol, + the two one-octet fields Type and Code are treated as a single 16-bit + integer (with Type in the most significant eight bits and Code in the + least significant eight bits) port number for the purposes of + filtering based on this field." + + Since ICMP packets do not have separate source and destination port + fields, there is some room for confusion what exactly the four TS + payloads (two in the request, two in the response, each containing + both start and end port fields) should contain. + + The answer to this question can be found from [RFC4301] Section + + + +Eronen & Hoffman Expires November 5, 2006 [Page 18] + +Internet-Draft IKEv2 Clarifications May 2006 + + + 4.4.1.3. + + To give a concrete example, if a host at 192.0.1.234 wants to create + a transport mode SA for sending "Destination Unreachable" packets + (ICMPv4 type 3) to 192.0.2.155, but is not willing to receive them + over this SA pair, the CREATE_CHILD_SA exchange would look like this: + + Initiator Responder + ----------- ----------- + HDR, SK { N(USE_TRANSPORT_MODE), SA, Ni, + TSi(1, 0x0300-0x03FF, 192.0.1.234-192.0.1.234), + TSr(1, 65535-0, 192.0.2.155-192.0.2.155) } --> + + <-- HDR, SK { N(USE_TRANSPORT_MODE), SA, Nr, + TSi(1, 0x0300-0x03FF, 192.0.1.234-192.0.1.234), + TSr(1, 65535-0, 192.0.2.155-192.0.2.155) } + + Since IKEv2 always creates IPsec SAs in pairs, two SAs are also + created in this case, even though the second SA is never used for + data traffic. + + An exchange creating an SA pair that can be used both for sending and + receiving "Destination Unreachable" places the same value in all the + port: + + Initiator Responder + ----------- ----------- + HDR, SK { N(USE_TRANSPORT_MODE), SA, Ni, + TSi(1, 0x0300-0x03FF, 192.0.1.234-192.0.1.234), + TSr(1, 0x0300-0x03FF, 192.0.2.155-192.0.2.155) } --> + + <-- HDR, SK { N(USE_TRANSPORT_MODE), SA, Nr, + TSi(1, 0x0300-0x03FF, 192.0.1.234-192.0.1.234), + TSr(1, 0x0300-0x03FF, 192.0.2.155-192.0.2.155) } + + (References: "ICMP and MH TSs for IKEv2" thread, Sep 2005.) + +4.9. Mobility header in traffic selector payloads + + Traffic selectors can use IP Protocol ID 135 to match the IPv6 + mobility header [MIPv6]. However, the IKEv2 specification does not + define how to represent the "MH Type" field in traffic selectors. + + At some point, it was expected that this will be defined in a + separate document later. However, [RFC4301] says that "For IKE, the + IPv6 mobility header message type (MH type) is placed in the most + significant eight bits of the 16 bit local "port" selector". The + direction semantics of TSi/TSr port fields are the same as for ICMP, + + + +Eronen & Hoffman Expires November 5, 2006 [Page 19] + +Internet-Draft IKEv2 Clarifications May 2006 + + + and are described in the previous section. + + (References: Tero Kivinen's mail "Issue #86: Add IPv6 mobility header + message type as selector", 2003-10-14. "ICMP and MH TSs for IKEv2" + thread, Sep 2005.) + +4.10. Narrowing the traffic selectors + + Section 2.9 describes how traffic selectors are negotiated when + creating a CHILD_SA. A more concise summary of the narrowing process + is presented below. + + o If the responder's policy does not allow any part of the traffic + covered by TSi/TSr, it responds with TS_UNACCEPTABLE. + + o If the responder's policy allows the entire set of traffic covered + by TSi/TSr, no narrowing is necessary, and the responder can + return the same TSi/TSr values. + + o Otherwise, narrowing is needed. If the responder's policy allows + all traffic covered by TSi[1]/TSr[1] (the first traffic selectors + in TSi/TSr) but not entire TSi/TSr, the responder narrows to an + acceptable subset of TSi/TSr that includes TSi[1]/TSr[1]. + + o If the responder's policy does not allow all traffic covered by + TSi[1]/TSr[1], but does allow some parts of TSi/TSr, it narrows to + an acceptable subset of TSi/TSr. + + In the last two cases, there may be several subsets that are + acceptable (but their union is not); in this case, the responder + arbitrarily chooses one of them, and includes ADDITIONAL_TS_POSSIBLE + notification in the response. + +4.11. SINGLE_PAIR_REQUIRED + + The description of the SINGLE_PAIR_REQUIRED notify payload in + Sections 2.9 and 3.10.1 is not fully consistent. + + We do not attempt to describe this payload in this document either, + since it is expected that most implementations will not have policies + that require separate SAs for each address pair. + + Thus, if only some part (or parts) of the TSi/TSr proposed by the + initiator is (are) acceptable to the responder, most responders + should simply narrow TSi/TSr to an acceptable subset (as described in + the last two paragraphs of Section 2.9), rather than use + SINGLE_PAIR_REQUIRED. + + + + +Eronen & Hoffman Expires November 5, 2006 [Page 20] + +Internet-Draft IKEv2 Clarifications May 2006 + + +4.12. Traffic selectors violating own policy + + Section 2.9 describes traffic selector negotiation in great detail. + One aspect of this negotiation that may need some clarification is + that when creating a new SA, the initiator should not propose traffic + selectors that violate its own policy. If this rule is not followed, + valid traffic may be dropped. + + This is best illustrated by an example. Suppose that host A has a + policy whose effect is that traffic to 192.0.1.66 is sent via host B + encrypted using AES, and traffic to all other hosts in 192.0.1.0/24 + is also sent via B, but encrypted using 3DES. Suppose also that host + B accepts any combination of AES and 3DES. + + If host A now proposes an SA that uses 3DES, and includes TSr + containing (192.0.1.0-192.0.1.0.255), this will be accepted by host + B. Now, host B can also use this SA to send traffic from 192.0.1.66, + but those packets will be dropped by A since it requires the use of + AES for those traffic. Even if host A creates a new SA only for + 192.0.1.66 that uses AES, host B may freely continue to use the first + SA for the traffic. In this situation, when proposing the SA, host A + should have followed its own policy, and included a TSr containing + ((192.0.1.0-192.0.1.65),(192.0.1.67-192.0.1.255)) instead. + + In general, if (1) the initiator makes a proposal "for traffic X + (TSi/TSr), do SA", and (2) for some subset X' of X, the initiator + does not actually accept traffic X' with SA, and (3) the initiator + would be willing to accept traffic X' with some SA' (!=SA), valid + traffic can be unnecessarily dropped since the responder can apply + either SA or SA' to traffic X'. + + (References: "Question about "narrowing" ..." thread, Feb 2005. + "IKEv2 needs a "policy usage mode"..." thread, Feb 2005. "IKEv2 + Traffic Selectors?" thread, Feb 2005. "IKEv2 traffic selector + negotiation examples", 2004-08-08.) + +4.13. Traffic selector authorization + + IKEv2 relies on information in the Peer Authorization Database (PAD) + when determining what kind of IPsec SAs a peer is allowed to create. + This process is described in [RFC4301] Section 4.4.3. When a peer + requests the creation of an IPsec SA with some traffic selectors, the + PAD must contain "Child SA Authorization Data" linking the identity + authenticated by IKEv2 and the addresses permitted for traffic + selectors. + + For example, the PAD might be configured so that authenticated + identity "sgw23.example.com" is allowed to create IPsec SAs for + + + +Eronen & Hoffman Expires November 5, 2006 [Page 21] + +Internet-Draft IKEv2 Clarifications May 2006 + + + 192.0.2.0/24, meaning this security gateway is a valid + "representative" for these addresses. Host-to-host IPsec requires + similar entries, linking, for example, "fooserver4.example.com" with + 192.0.1.66/32, meaning this identity a valid "owner" or + "representative" of the address in question. + + As noted in [RFC4301], "It is necessary to impose these constraints + on creation of child SAs to prevent an authenticated peer from + spoofing IDs associated with other, legitimate peers." In the + example given above, a correct configuration of the PAD prevents + sgw23 from creating IPsec SAs with address 192.0.1.66, and prevents + fooserver4 from creating IPsec SAs with addresses from 192.0.2.0/24. + + It is important to note that simply sending IKEv2 packets using some + particular address does not imply a permission to create IPsec SAs + with that address in the traffic selectors. For example, even if + sgw23 would be able to spoof its IP address as 192.0.1.66, it could + not create IPsec SAs matching fooserver4's traffic. + + The IKEv2 specification does not specify how exactly IP address + assignment using configuration payloads interacts with the PAD. Our + interpretation is that when a security gateway assigns an address + using configuration payloads, it also creates a temporary PAD entry + linking the authenticated peer identity and the newly allocated inner + address. + + It has been recognized that configuring the PAD correctly may be + difficult in some environments. For instance, if IPsec is used + between a pair of hosts whose addresses are allocated dynamically + using DHCP, it is extremely difficult to ensure that the PAD + specifies the correct "owner" for each IP address. This would + require a mechanism to securely convey address assignments from the + DHCP server, and link them to identities authenticated using IKEv2. + + Due to this limitation, some vendors have been known to configure + their PADs to allow an authenticated peer to create IPsec SAs with + traffic selectors containing the same address that was used for the + IKEv2 packets. In environments where IP spoofing is possible (i.e., + almost everywhere) this essentially allows any peer to create IPsec + SAs with any traffic selectors. This is not an appropriate or secure + configuration in most circumstances. See [Aura05] for an extensive + discussion about this issue, and the limitations of host-to-host + IPsec in general. + + +5. Rekeying and deleting SAs + + + + + +Eronen & Hoffman Expires November 5, 2006 [Page 22] + +Internet-Draft IKEv2 Clarifications May 2006 + + +5.1. Rekeying SAs with the CREATE_CHILD_SA exchange + + Continued from Section 4.1 of this document. + + NEW-1.3.2 Rekeying IKE_SAs with the CREATE_CHILD_SA Exchange + + The CREATE_CHILD_SA request for rekeying an IKE_SA is: + + Initiator Responder + ----------- ----------- + HDR, SK {SA, Ni, [KEi]} --> + + The initiator sends SA offer(s) in the SA payload, a nonce in + the Ni payload, and optionally a Diffie-Hellman value in the KEi + payload. + + The CREATE_CHILD_SA response for rekeying an IKE_SA is: + + <-- HDR, SK {SA, Nr, [KEr]} + + The responder replies (using the same Message ID to respond) + with the accepted offer in an SA payload, a nonce in the Nr + payload, and, optionally, a Diffie-Hellman value in the KEr + payload. + + The new IKE_SA has its message counters set to 0, regardless of + what they were in the earlier IKE_SA. The window size starts at + 1 for any new IKE_SA. The new initiator and responder SPIs are + supplied in the SPI fields of the SA payloads. + + NEW-1.3.3 Rekeying CHILD_SAs with the CREATE_CHILD_SA Exchange + + The CREATE_CHILD_SA request for rekeying a CHILD_SA is: + + Initiator Responder + ----------- ----------- + HDR, SK {N(REKEY_SA), [N+], SA, + Ni, [KEi], TSi, TSr} --> + + The leading Notify payload of type REKEY_SA identifies the + CHILD_SA being rekeyed, and contains the SPI that the initiator + expects in the headers of inbound packets. In addition, the + initiator sends SA offer(s) in the SA payload, a nonce in the Ni + payload, optionally a Diffie-Hellman value in the KEi payload, + and the proposed traffic selectors in the TSi and TSr payloads. + The request can also contain Notify payloads that specify + additional details for the CHILD_SA. + + + + +Eronen & Hoffman Expires November 5, 2006 [Page 23] + +Internet-Draft IKEv2 Clarifications May 2006 + + + The CREATE_CHILD_SA response for rekeying a CHILD_SA is: + + <-- HDR, SK {[N+], SA, Nr, + [KEr], TSi, TSr} + + The responder replies with the accepted offer in an SA payload, + and a Diffie-Hellman value in the KEr payload if KEi was + included in the request and the selected cryptographic suite + includes that group. + + The traffic selectors for traffic to be sent on that SA are + specified in the TS payloads in the response, which may be a + subset of what the initiator of the CHILD_SA proposed. + +5.2. Rekeying the IKE_SA vs. reauthentication + + Rekeying the IKE_SA and reauthentication are different concepts in + IKEv2. Rekeying the IKE_SA establishes new keys for the IKE_SA and + resets the Message ID counters, but it does not authenticate the + parties again (no AUTH or EAP payloads are involved). + + While rekeying the IKE_SA may be important in some environments, + reauthentication (the verification that the parties still have access + to the long-term credentials) is often more important. + + IKEv2 does not have any special support for reauthentication. + Reauthentication is done by creating a new IKE_SA from scratch (using + IKE_SA_INIT/IKE_AUTH exchanges, without any REKEY_SA notify + payloads), creating new CHILD_SAs within the new IKE_SA (without + REKEY_SA notify payloads), and finally deleting the old IKE_SA (which + deletes the old CHILD_SAs as well). + + This means that reauthentication also establishes new keys for the + IKE_SA and CHILD_SAs. Therefore, while rekeying can be performed + more often than reauthentication, the situation where "authentication + lifetime" is shorter than "key lifetime" does not make sense. + + While creation of a new IKE_SA can be initiated by either party + (initiator or responder in the original IKE_SA), the use of EAP + authentication and/or configuration payloads means in practice that + reauthentication has to be initiated by the same party as the + original IKE_SA. IKEv2 does not currently allow the responder to + request reauthentication in this case; however, there is ongoing work + to add this functionality [ReAuth]. + + (References: "Reauthentication in IKEv2" thread, Oct/Nov 2004.) + + + + + +Eronen & Hoffman Expires November 5, 2006 [Page 24] + +Internet-Draft IKEv2 Clarifications May 2006 + + +5.3. SPIs when rekeying the IKE_SA + + Section 2.18 says that "New initiator and responder SPIs are supplied + in the SPI fields". This refers to the SPI fields in the Proposal + structures inside the Security Association (SA) payloads, not the SPI + fields in the IKE header. + + (References: Tom Stiemerling's mail "Rekey IKE SA", 2005-01-24. + Geoffrey Huang's reply, 2005-01-24.) + +5.4. SPI when rekeying a CHILD_SA + + Section 3.10.1 says that in REKEY_SA notifications, "The SPI field + identifies the SA being rekeyed." + + Since CHILD_SAs always exist in pairs, there are two different SPIs. + The SPI placed in the REKEY_SA notification is the SPI the exchange + initiator would expect in inbound ESP or AH packets (just as in + Delete payloads). + +5.5. Changing PRFs when rekeying the IKE_SA + + When rekeying the IKE_SA, Section 2.18 says that "SKEYSEED for the + new IKE_SA is computed using SK_d from the existing IKE_SA as + follows: + + SKEYSEED = prf(SK_d (old), [g^ir (new)] | Ni | Nr)" + + If the old and new IKE_SA selected a different PRF, it is not totally + clear which PRF should be used. + + Since the rekeying exchange belongs to the old IKE_SA, it is the old + IKE_SA's PRF that is used. This also follows the principle that the + same key (the old SK_d) should not be used with multiple + cryptographic algorithms. + + Note that this may work poorly if the new IKE_SA's PRF has a fixed + key size, since the output of the PRF may not be of the correct size. + This supports our opinion earlier in the document that the use of + PRFs with a fixed key size is a bad idea. + + (References: "Changing PRFs when rekeying the IKE_SA" thread, June + 2005.) + +5.6. Deleting vs. closing SAs + + The IKEv2 specification talks about "closing" and "deleting" SAs, but + it is not always clear what exactly is meant. However, other parts + + + +Eronen & Hoffman Expires November 5, 2006 [Page 25] + +Internet-Draft IKEv2 Clarifications May 2006 + + + of the specification make it clear that when local state related to a + CHILD_SA is removed, the SA must also be actively deleted with a + Delete payload. + + In particular, Section 2.4 says that "If an IKE endpoint chooses to + delete CHILD_SAs, it MUST send Delete payloads to the other end + notifying it of the deletion". Section 1.4 also explains that "ESP + and AH SAs always exist in pairs, with one SA in each direction. + When an SA is closed, both members of the pair MUST be closed." + +5.7. Deleting a CHILD_SA pair + + Section 1.4 describes how to delete SA pairs using the Informational + exchange: "To delete an SA, an INFORMATIONAL exchange with one or + more delete payloads is sent listing the SPIs (as they would be + expected in the headers of inbound packets) of the SAs to be deleted. + The recipient MUST close the designated SAs." + + The "one or more delete payloads" phrase has caused some confusion. + You never send delete payloads for the two sides of an SA in a single + message. If you have many SAs to delete at the same time (such as + the nested example given in that paragraph), you include delete + payloads for in inbound half of each SA in your Informational + exchange. + +5.8. Deleting an IKE_SA + + Since IKE_SAs do not exist in pairs, it is not totally clear what the + response message should contain when the request deleted the IKE_SA. + + Since there is no information that needs to be sent to the other side + (except that the request was received), an empty Informational + response seems like the most logical choice. + + (References: "Question about delete IKE SA" thread, May 2005.) + +5.9. Who is the original initiator of IKE_SA + + In the IKEv2 document, "initiator" refers to the party who initiated + the exchange being described, and "original initiator" refers to the + party who initiated the whole IKE_SA. However, there is some + potential for confusion because the IKE_SA can be rekeyed by either + party. + + To clear up this confusion, we propose that "original initiator" + always refers to the party who initiated the exchange which resulted + in the current IKE_SA. In other words, if the "original responder" + starts rekeying the IKE_SA, that party becomes the "original + + + +Eronen & Hoffman Expires November 5, 2006 [Page 26] + +Internet-Draft IKEv2 Clarifications May 2006 + + + initiator" of the new IKE_SA. + + (References: Paul Hoffman's mail "Original initiator in IKEv2", 2005- + 04-21.) + +5.10. Comparing nonces + + Section 2.8 about rekeying says that "If redundant SAs are created + though such a collision, the SA created with the lowest of the four + nonces used in the two exchanges SHOULD be closed by the endpoint + that created it." + + Here "lowest" uses an octet-by-octet (lexicographical) comparison + (instead of, for instance, comparing the nonces as large integers). + In other words, start by comparing the first octet; if they're equal, + move to the next octet, and so on. If you reach the end of one + nonce, that nonce is the lower one. + + (References: "IKEv2 rekeying question" thread, July 2005.) + +5.11. Exchange collisions + + Since IKEv2 exchanges can be initiated by both peers, it is possible + that two exchanges affecting the same SA partly overlap. This can + lead to a situation where the SA state information is temporarily not + synchronized, and a peer can receive a request it cannot process in a + normal fashion. Some of these corner cases are discussed in the + specification, some are not. + + Obviously, using a window size greater than one leads to infinitely + more complex situations, especially if requests are processed out of + order. In this section, we concentrate on problems that can arise + even with window size 1. + + (References: "IKEv2: invalid SPI in DELETE payload" thread, Dec 2005/ + Jan 2006. "Problem with exchanges collisions" thread, Dec 2005.) + +5.11.1. Simultaneous CHILD_SA close + + Probably the simplest case happens if both peers decide to close the + same CHILD_SA pair at the same time: + + + + + + + + + + +Eronen & Hoffman Expires November 5, 2006 [Page 27] + +Internet-Draft IKEv2 Clarifications May 2006 + + + Host A Host B + -------- -------- + send req1: D(SPIa) --> + <-- send req2: D(SPIb) + --> recv req1 + <-- send resp1: () + recv resp1 + recv req2 + send resp2: () --> + --> recv resp2 + + This case is described in Section 1.4, and is handled by omitting the + Delete payloads from the response messages. + +5.11.2. Simultaneous IKE_SA close + + Both peers can also decide to close the IKE_SA at the same time. The + desired end result is obvious; however, in certain cases the final + exchanges may not be fully completed. + + Host A Host B + -------- -------- + send req1: D() --> + <-- send req2: D() + --> recv req1 + + At this point, host B should reply as usual (with empty Informational + response), close the IKE_SA, and stop retransmitting req2. This is + because once host A receives resp1, it may not be able to reply any + longer. The situation is symmetric, so host A should behave the same + way. + + Host A Host B + -------- -------- + <-- send resp1: () + send resp2: () + + Even if neither resp1 nor resp2 ever arrives, the end result is still + correct: the IKE_SA is gone. The same happens if host A never + receives req2. + +5.11.3. Simultaneous CHILD_SA rekeying + + Another case that is described in the specification is simultaneous + rekeying. Section 2.8 says + + + + + + +Eronen & Hoffman Expires November 5, 2006 [Page 28] + +Internet-Draft IKEv2 Clarifications May 2006 + + + "If the two ends have the same lifetime policies, it is possible + that both will initiate a rekeying at the same time (which will + result in redundant SAs). To reduce the probability of this + happening, the timing of rekeying requests SHOULD be jittered + (delayed by a random amount of time after the need for rekeying is + noticed). + + This form of rekeying may temporarily result in multiple similar + SAs between the same pairs of nodes. When there are two SAs + eligible to receive packets, a node MUST accept incoming packets + through either SA. If redundant SAs are created though such a + collision, the SA created with the lowest of the four nonces used + in the two exchanges SHOULD be closed by the endpoint that created + it." + + However, a better explanation on what impact this has on + implementations is needed. Assume that hosts A and B have an + existing IPsec SA pair with SPIs (SPIa1,SPIb1), and both start + rekeying it at the same time: + + Host A Host B + -------- -------- + send req1: N(REKEY_SA,SPIa1), + SA(..,SPIa2,..),Ni1,.. --> + <-- send req2: N(REKEY_SA,SPIb1), + SA(..,SPIb2,..),Ni2,.. + recv req2 <-- + + At this point, A knows there is a simultaneous rekeying going on. + However, it cannot yet know which of the exchanges will have the + lowest nonce, so it will just note the situation and respond as + usual. + + send resp2: SA(..,SPIa3,..),Nr1,.. --> + --> recv req1 + + Now B also knows that simultaneous rekeying is going on. Similarly + as host A, it has to respond as usual. + + <-- send resp1: SA(..,SPIb3,..),Nr2,.. + recv resp1 <-- + --> recv resp2 + + At this point, there are three CHILD_SA pairs between A and B (the + old one and two new ones). A and B can now compare the nonces. + Suppose that the lowest nonce was Nr1 in message resp2; in this case, + B (the sender of req2) deletes the redundant new SA, and A (the node + that initiated the surviving rekeyed SA), deletes the old one. + + + +Eronen & Hoffman Expires November 5, 2006 [Page 29] + +Internet-Draft IKEv2 Clarifications May 2006 + + + send req3: D(SPIa1) --> + <-- send req4: D(SPIb2) + --> recv req3 + <-- send resp4: D(SPIb1) + recv req4 <-- + send resp4: D(SPIa3) --> + + The rekeying is now finished. + + However, there is a second possible sequence of events that can + happen if some packets are lost in the network, resulting in + retransmissions. The rekeying begins as usual, but A's first packet + (req1) is lost. + + Host A Host B + -------- -------- + send req1: N(REKEY_SA,SPIa1), + SA(..,SPIa2,..),Ni1,.. --> (lost) + <-- send req2: N(REKEY_SA,SPIb1), + SA(..,SPIb2,..),Ni2,.. + recv req2 <-- + send resp2: SA(..,SPIa3,..),Nr1,.. --> + --> recv resp2 + <-- send req3: D(SPIb1) + recv req3 <-- + send resp3: D(SPIa1) --> + --> recv resp3 + + From B's point of view, the rekeying is now completed, and since it + has not yet received A's req1, it does not even know that these was + simultaneous rekeying. However, A will continue retransmitting the + message, and eventually it will reach B. + + resend req1 --> + --> recv req1 + + What should B do in this point? To B, it looks like A is trying to + rekey an SA that no longer exists; thus failing the request with + something non-fatal such as NO_PROPOSAL_CHOSEN seems like a + reasonable approach. + + <-- send resp1: N(NO_PROPOSAL_CHOSEN) + recv resp1 <-- + + When A receives this error, it already knows there was simultaneous + rekeying, so it can ignore the error message. + + + + + +Eronen & Hoffman Expires November 5, 2006 [Page 30] + +Internet-Draft IKEv2 Clarifications May 2006 + + +5.11.4. Simultaneous IKE_SA rekeying + + Probably the most complex case occurs when both peers try to rekey + the IKE_SA at the same time. Basically, the text in Section 2.8 + applies to this case as well; however, it is important to ensure that + the CHILD_SAs are inherited by the right IKE_SA. + + The case where both endpoints notice the simultaneous rekeying works + the same way as with CHILD_SAs. After the CREATE_CHILD_SA exchanges, + three IKE_SAs exist between A and B; the one containing the lowest + nonce inherits the CHILD_SAs. + + However, there is a twist to the other case where one rekeying + finishes first: + + Host A Host B + -------- -------- + send req1: + SA(..,SPIa1,..),Ni1,.. --> + <-- send req2: SA(..,SPIb1,..),Ni2,.. + --> recv req1 + <-- send resp1: SA(..,SPIb2,..),Nr2,.. + recv resp1 <-- + send req3: D() --> + --> recv req3 + + At this point, host B sees a request to close the IKE_SA. There's + not much more to do than to reply as usual. However, at this point + host B should stop retransmitting req2, since once host A receives + resp3, it will delete all the state associated with the old IKE_SA, + and will not be able to reply to it. + + <-- send resp3: () + +5.11.5. Closing and rekeying a CHILD_SA + + A case similar to simultaneous rekeying can occur if one peer decides + to close an SA and the other peer tries to rekey it: + + Host A Host B + -------- -------- + send req1: D(SPIa) --> + <-- send req2: N(REKEY_SA,SPIb),SA,.. + --> recv req1 + + At this point, host B notices that host A is trying to close an SA + that host B is currently rekeying. Replying as usual is probably the + best choice: + + + +Eronen & Hoffman Expires November 5, 2006 [Page 31] + +Internet-Draft IKEv2 Clarifications May 2006 + + + <-- send resp1: D(SPIb) + + Depending on in which order req2 and resp1 arrive, host A sees either + a request to rekey an SA that it is currently closing, or a request + to rekey an SA that does not exist. In both cases, + NO_PROPOSAL_CHOSEN is probably fine. + + recv req2 + recv resp1 + send resp2: N(NO_PROPOSAL_CHOSEN) --> + --> recv resp2 + +5.11.6. Closing a new CHILD_SA + + Yet another case occurs when host A creates a CHILD_SA pair, but soon + thereafter host B decides to delete it (possible because its policy + changed): + + Host A Host B + -------- -------- + send req1: [N(REKEY_SA,SPIa1)], + SA(..,SPIa2,..),.. --> + --> recv req1 + (lost) <-- send resp1: SA(..,SPIb2,..),.. + + <-- send req2: D(SPIb2) + recv req2 + + At this point, host A has not yet received message resp1 (and is + retransmitting message req1), so it does not recognize SPIb in + message req2. What should host A do? + + One option would be to reply with an empty Informational response. + However, this same reply would also be sent if host A has received + resp1, but has already sent a new request to delete the SA that was + just created. This would lead to a situation where the peers are no + longer in sync about which SAs exist between them. However, host B + would eventually notice that the other half of the CHILD_SA pair has + not been deleted. Section 1.4 describes this case and notes that "a + node SHOULD regard half-closed connections as anomalous and audit + their existence should they persist", and continues that "if + connection state becomes sufficiently messed up, a node MAY close the + IKE_SA". + + Another solution that has been proposed is to reply with an + INVALID_SPI notification which contains SPIb. This would explicitly + tell host B that the SA was not deleted, so host B could try deleting + it again later. However, this usage is not part of the IKEv2 + + + +Eronen & Hoffman Expires November 5, 2006 [Page 32] + +Internet-Draft IKEv2 Clarifications May 2006 + + + specification, and would not be in line with normal use of the + INVALID_SPI notification where the data field contains the SPI the + recipient of the notification would put in outbound packets. + + Yet another solution would be to ignore req2 at this time, and wait + until we have received resp1. However, this alternative has not been + fully analyzed at this time; in general, ignoring valid requests is + always a bit dangerous, because both endpoints could do it, leading + to a deadlock. + + This document recommends the first alternative. + +5.11.7. Rekeying a new CHILD_SA + + Yet another case occurs when a CHILD_SA is rekeyed soon after it has + been created: + + Host A Host B + -------- -------- + send req1: [N(REKEY_SA,SPIa1)], + SA(..,SPIa2,..),.. --> + (lost) <-- send resp1: SA(..,SPIb2,..),.. + + <-- send req2: N(REKEY_SA,SPIb2), + SA(..,SPIb3,..),.. + recv req2 <-- + + To host A, this looks like a request to rekey an SA that does not + exist. Like in the simultaneous rekeying case, replying with + NO_PROPOSAL_CHOSEN is probably reasonable: + + send resp2: N(NO_PROPOSAL_CHOSEN) --> + recv resp1 + +5.11.8. Collisions with IKE_SA rekeying + + Another set of cases occur when one peer starts rekeying the IKE_SA + at the same time the other peer starts creating, rekeying, or closing + a CHILD_SA. Suppose that host B starts creating a CHILD_SA, and soon + after, host A starts rekeying the IKE_SA: + + Host A Host B + -------- -------- + <-- send req1: SA,Ni1,TSi,TSr + send req2: SA,Ni2,.. --> + --> recv req2 + + What should host B do at this point? Replying as usual would seem + + + +Eronen & Hoffman Expires November 5, 2006 [Page 33] + +Internet-Draft IKEv2 Clarifications May 2006 + + + like a reasonable choice: + + <-- send resp2: SA,Ni2,.. + recv resp2 <-- + send req3: D() --> + --> recv req3 + + Now, a problem arises: If host B now replies normally with an empty + Informational response, this will cause host A to delete state + associated with the IKE_SA. This means host B should stop + retransmitting req1. However, host B cannot know whether or not host + A has received req1. If host A did receive it, it will move the + CHILD_SA to the new IKE_SA as usual, and the state information will + then be out of sync. + + It seems this situation is tricky to handle correctly. Our proposal + is as follows: if a host receives a request to rekey the IKE_SA when + it has CHILD_SAs in "half-open" state (currently being created or + rekeyed), it should reply with NO_PROPOSAL_CHOSEN. If a host + receives a request to create or rekey a CHILD_SA after it has started + rekeying the IKE_SA, it should reply with NO_ADDITIONAL_SAS. + + The case where CHILD_SAs are being closed is even worse. Our + recommendation is that if a host receives a request to rekey the + IKE_SA when it has CHILD_SAs in "half-closed" state (currently being + closed), it should reply with NO_PROPOSAL_CHOSEN. And if a host + receives a request to close a CHILD_SA after it has started rekeying + the IKE_SA, it should reply with an empty Informational response. + This ensures that at least the other peer will eventually notice that + the CHILD_SA is still in "half-closed" state, and will start a new + IKE_SA from scratch. + +5.11.9. Closing and rekeying the IKE_SA + + The final case considered in this section occurs if one peer decides + to close the IKE_SA while the other peer tries to rekey it. + + Host A Host B + -------- -------- + send req1: SA(..,SPIa1,..),Ni1 --> + <-- send req2: D() + --> recv req1 + recv req2 <-- + + At this point, host B should probably reply with NO_PROPOSAL_CHOSEN, + and host A should reply as usual, close the IKE_SA, and stop + retransmitting req1. + + + + +Eronen & Hoffman Expires November 5, 2006 [Page 34] + +Internet-Draft IKEv2 Clarifications May 2006 + + + <-- send resp1: N(NO_PROPOSAL_CHOSEN) + send resp2: () + + If host A wants to continue communication with B, it can now start a + new IKE_SA. + +5.11.10. Summary + + If a host receives a request to rekey: + + o a CHILD_SA pair that the host is currently trying to close: reply + with NO_PROPOSAL_CHOSEN. + + o a CHILD_SA pair that the host is currently rekeying: reply as + usual, but prepare to close redundant SAs later based on the + nonces. + + o a CHILD_SA pair that does not exist: reply with + NO_PROPOSAL_CHOSEN. + + o the IKE_SA, and the host is currently rekeying the IKE_SA: reply + as usual, but prepare to close redundant SAs and move inherited + CHILD_SAs later based on the nonces. + + o the IKE_SA, and the host is currently creating, rekeying, or + closing a CHILD_SA: reply with NO_PROPOSAL_CHOSEN. + + o the IKE_SA, and the host is currently trying to close the IKE_SA: + reply with NO_PROPOSAL_CHOSEN. + + If a host receives a request to close: + + o a CHILD_SA pair that the host is currently trying to close: reply + without Delete payloads. + + o a CHILD_SA pair that the host is currently rekeying: reply as + usual, with Delete payload. + + o a CHILD_SA pair that does not exist: reply without Delete + payloads. + + o the IKE_SA, and the host is currently rekeying the IKE_SA: reply + as usual, and forget about our own rekeying request. + + o the IKE_SA, and the host is currently trying to close the IKE_SA: + reply as usual, and forget about our own close request. + + If a host receives a request to create or rekey a CHILD_SA when it is + + + +Eronen & Hoffman Expires November 5, 2006 [Page 35] + +Internet-Draft IKEv2 Clarifications May 2006 + + + currently rekeying the IKE_SA: reply with NO_ADDITIONAL_SAS. + + If a host receives a request to delete a CHILD_SA when it is + currently rekeying the IKE_SA: reply without Delete payloads. + +5.12. Diffie-Hellman and rekeying the IKE_SA + + There has been some confusion whether doing a new Diffie-Hellman + exchange is mandatory when the IKE_SA is rekeyed. + + It seems that this case is allowed by the IKEv2 specification. + Section 2.18 shows the Diffie-Hellman term (g^ir) in brackets. + Section 3.3.3 does not contradict this when it says that including + the D-H transform is mandatory: although including the transform is + mandatory, it can contain the value "NONE". + + However, having the option to skip the Diffie-Hellman exchange when + rekeying the IKE_SA does not add useful functionality to the + protocol. The main purpose of rekeying the IKE_SA is to ensure that + the compromise of old keying material does not provide information + about the current keys, or vice versa. This requires performing the + Diffie-Hellman exchange when rekeying. Furthermore, it is likely + that this option would have been removed from the protocol as + unnecessary complexity had it been discussed earlier. + + Given this, we recommend that implementations should have a hard- + coded policy that requires performing a new Diffie-Hellman exchange + when rekeying the IKE_SA. In other words, the initiator should not + propose the value "NONE" for the D-H transform, and the responder + should not accept such a proposal. This policy also implies that a + succesful exchange rekeying the IKE_SA always includes the KEi/KEr + payloads. + + (References: "Rekeying IKE_SAs with the CREATE_CHILD_SA exhange" + thread, Oct 2005. "Comments of + draft-eronen-ipsec-ikev2-clarifications-02.txt" thread, Apr 2005.) + + +6. Configuration payloads + +6.1. Assigning IP addresses + + Section 2.9 talks about traffic selector negotiation and mentions + that "In support of the scenario described in section 1.1.3, an + initiator may request that the responder assign an IP address and + tell the initiator what it is." + + This sentence is correct, but its placement is slightly confusing. + + + +Eronen & Hoffman Expires November 5, 2006 [Page 36] + +Internet-Draft IKEv2 Clarifications May 2006 + + + IKEv2 does allow the initiator to request assignment of an IP address + from the responder, but this is done using configuration payloads, + not traffic selector payloads. An address in a TSi payload in a + response does not mean that the responder has assigned that address + to the initiator; it only means that if packets matching these + traffic selectors are sent by the initiator, IPsec processing can be + performed as agreed for this SA. The TSi payload itself does not + give the initiator permission to configure the initiator's TCP/IP + stack with the address and use it as its source address. + + In other words, IKEv2 does not have two different mechanisms for + assigning addresses, but only one: configuration payloads. In the + scenario described in Section 1.1.3, both configuration and traffic + selector payloads are usually included in the same message, and often + contain the same information in the response message (see Section 6.3 + of this document for some examples). However, their semantics are + still different. + +6.2. Requesting any INTERNAL_IP4/IP6_ADDRESS + + When describing the INTERNAL_IP4/IP6_ADDRESS attributes, Section + 3.15.1 says that "In a request message, the address specified is a + requested address (or zero if no specific address is requested)". + The question here is that does "zero" mean an address "0.0.0.0" or a + zero length string? + + Earlier, the same section also says that "If an attribute in the + CFG_REQUEST Configuration Payload is not zero-length, it is taken as + a suggestion for that attribute". Also, the table of configuration + attributes shows that the length of INTERNAL_IP4_ADDRESS is either "0 + or 4 octets", and likewise, INTERNAL_IP6_ADDRESS is either "0 or 17 + octets". + + Thus, if the client does not request a specific address, it includes + a zero-length INTERNAL_IP4/IP6_ADDRESS attribute, not an attribute + containing an all-zeroes address. The example in 2.19 is thus + incorrect, since it shows the attribute as + "INTERNAL_ADDRESS(0.0.0.0)". + + However, since the value is only a suggestion, implementations are + recommended to ignore suggestions they do not accept; or in other + words, treat the same way a zero-length INTERNAL_IP4_ADDRESS, + "0.0.0.0", and any other addresses the implementation does not + recognize as a reasonable suggestion. + + + + + + + +Eronen & Hoffman Expires November 5, 2006 [Page 37] + +Internet-Draft IKEv2 Clarifications May 2006 + + +6.3. INTERNAL_IP4_SUBNET/INTERNAL_IP6_SUBNET + + Section 3.15.1 describes the INTERNAL_IP4_SUBNET as "The protected + sub-networks that this edge-device protects. This attribute is made + up of two fields: the first is an IP address and the second is a + netmask. Multiple sub-networks MAY be requested. The responder MAY + respond with zero or more sub-network attributes." + INTERNAL_IP6_SUBNET is defined in a similar manner. + + This raises two questions: first, since this information is usually + included in the TSr payload, what functionality does this attribute + add? And second, what does this attribute mean in CFG_REQUESTs? + + For the first question, there seem to be two sensible + interpretations. Clearly TSr (in IKE_AUTH or CREATE_CHILD_SA + response) indicates which subnets are accessible through the SA that + was just created. + + The first interpretation of the INTERNAL_IP4/6_SUBNET attributes is + that they indicate additional subnets that can be reached through + this gateway, but need a separate SA. According to this + interpretation, the INTERNAL_IP4/6_SUBNET attributes are useful + mainly when they contain addresses not included in TSr. + + The second interpretation is that the INTERNAL_IP4/6_SUBNET + attributes express the gateway's policy about what traffic should be + sent through the gateway. The client can choose whether other + traffic (covered by TSr, but not in INTERNAL_IP4/6_SUBNET) is sent + through the gateway or directly to the destination. According to + this interpretation, the attributes are useful mainly when TSr + contains addresses not included in the INTERNAL_IP4/6_SUBNET + attributes. + + It turns out that these two interpretations are not incompatible, but + rather two sides of the same principle: traffic to the addresses + listed in the INTERNAL_IP4/6_SUBNET attributes should be sent via + this gateway. If there are no existing IPsec SAs whose traffic + selectors cover the address in question, new SAs have to be created. + + A couple of examples are given below. For instance, if there are two + subnets, 192.0.1.0/26 and 192.0.2.0/24, and the client's request + contains the following: + + CP(CFG_REQUEST) = + INTERNAL_IP4_ADDRESS() + TSi = (0, 0-65535, 0.0.0.0-255.255.255.255) + TSr = (0, 0-65535, 0.0.0.0-255.255.255.255) + + + + +Eronen & Hoffman Expires November 5, 2006 [Page 38] + +Internet-Draft IKEv2 Clarifications May 2006 + + + Then a valid response could be the following (in which TSr and + INTERNAL_IP4_SUBNET contain the same information): + + CP(CFG_REPLY) = + INTERNAL_IP4_ADDRESS(192.0.1.234) + INTERNAL_IP4_SUBNET(192.0.1.0/255.255.255.192) + INTERNAL_IP4_SUBNET(192.0.2.0/255.255.255.0) + TSi = (0, 0-65535, 192.0.1.234-192.0.1.234) + TSr = ((0, 0-65535, 192.0.1.0-192.0.1.63), + (0, 0-65535, 192.0.2.0-192.0.2.255)) + + In these cases, the INTERNAL_IP4_SUBNET does not really carry any + useful information. Another possible reply would have been this: + + CP(CFG_REPLY) = + INTERNAL_IP4_ADDRESS(192.0.1.234) + INTERNAL_IP4_SUBNET(192.0.1.0/255.255.255.192) + INTERNAL_IP4_SUBNET(192.0.2.0/255.255.255.0) + TSi = (0, 0-65535, 192.0.1.234-192.0.1.234) + TSr = (0, 0-65535, 0.0.0.0-255.255.255.255) + + This would mean that the client can send all its traffic through the + gateway, but the gateway does not mind if the client sends traffic + not included by INTERNAL_IP4_SUBNET directly to the destination + (without going through the gateway). + + A different situation arises if the gateway has a policy that + requires the traffic for the two subnets to be carried in separate + SAs. Then a response like this would indicate to the client that if + it wants access to the second subnet, it needs to create a separate + SA: + + CP(CFG_REPLY) = + INTERNAL_IP4_ADDRESS(192.0.1.234) + INTERNAL_IP4_SUBNET(192.0.1.0/255.255.255.192) + INTERNAL_IP4_SUBNET(192.0.2.0/255.255.255.0) + TSi = (0, 0-65535, 192.0.1.234-192.0.1.234) + TSr = (0, 0-65535, 192.0.1.0-192.0.1.63) + + INTERNAL_IP4_SUBNET can also be useful if the client's TSr included + only part of the address space. For instance, if the client requests + the following: + + CP(CFG_REQUEST) = + INTERNAL_IP4_ADDRESS() + TSi = (0, 0-65535, 0.0.0.0-255.255.255.255) + TSr = (0, 0-65535, 192.0.2.155-192.0.2.155) + + + + +Eronen & Hoffman Expires November 5, 2006 [Page 39] + +Internet-Draft IKEv2 Clarifications May 2006 + + + Then the gateway's reply could be this: + + CP(CFG_REPLY) = + INTERNAL_IP4_ADDRESS(192.0.1.234) + INTERNAL_IP4_SUBNET(192.0.1.0/255.255.255.192) + INTERNAL_IP4_SUBNET(192.0.2.0/255.255.255.0) + TSi = (0, 0-65535, 192.0.1.234-192.0.1.234) + TSr = (0, 0-65535, 192.0.2.155-192.0.2.155) + + It is less clear what the attributes mean in CFG_REQUESTs, and + whether other lengths than zero make sense in this situation (but for + INTERNAL_IP6_SUBNET, zero length is not allowed at all!). Currently + this document recommends that implementations should not include + INTERNAL_IP4_SUBNET or INTERNAL_IP6_SUBNET attributes in + CFG_REQUESTs. + + For the IPv4 case, this document recommends using only netmasks + consisting of some amount of "1" bits followed by "0" bits; for + instance, "255.0.255.0" would not be a valid netmask for + INTERNAL_IP4_SUBNET. + + It is also worthwhile to note that the contents of the INTERNAL_IP4/ + 6_SUBNET attributes do not imply link boundaries. For instance, a + gateway providing access to a large company intranet using addresses + from the 10.0.0.0/8 block can send a single INTERNAL_IP4_SUBNET + attribute (10.0.0.0/255.0.0.0) even if the intranet has hundreds of + routers and separate links. + + (References: Tero Kivinen's mail "Intent of couple of attributes in + Configuration Payload in IKEv2?", 2004-11-19. Srinivasa Rao + Addepalli's mail "INTERNAL_IP4_SUBNET and INTERNAL_IP6_SUBNET in + IKEv2", 2004-09-10. Yoav Nir's mail "Re: New I-D: IKEv2 + Clarifications and Implementation Guidelines", 2005-02-07. + "Clarifications open issue: INTERNAL_IP4_SUBNET/NETMASK" thread, + April 2005.) + +6.4. INTERNAL_IP4_NETMASK + + Section 3.15.1 defines the INTERNAL_IP4_NETMASK attribute, and says + that "The internal network's netmask. Only one netmask is allowed in + the request and reply messages (e.g., 255.255.255.0) and it MUST be + used only with an INTERNAL_IP4_ADDRESS attribute". + + However, it is not clear what exactly this attribute means, as the + concept of "netmask" is not very well defined for point-to-point + links (unlike multi-access links, where it means "you can reach hosts + inside this netmask directly using layer 2, instead of sending + packets via a router"). Even if the operating system's TCP/IP stack + + + +Eronen & Hoffman Expires November 5, 2006 [Page 40] + +Internet-Draft IKEv2 Clarifications May 2006 + + + requires a netmask to be configured, for point-to-point links it + could be just set to 255.255.255.255. So, why is this information + sent in IKEv2? + + One possible interpretation would be that the host is given a whole + block of IP addresses instead of a single address. This is also what + Framed-IP-Netmask does in [RADIUS], the IPCP "subnet mask" extension + does in PPP [IPCPSubnet], and the prefix length in the IPv6 Framed- + IPv6-Prefix attribute does in [RADIUS6]. However, nothing in the + specification supports this interpretation, and discussions on the + IPsec WG mailing list have confirmed it was not intended. Section + 3.15.1 also says that multiple addresses are assigned using multiple + INTERNAL_IP4/6_ADDRESS attributes. + + Currently, this document's interpretation is the following: + INTERNAL_IP4_NETMASK in a CFG_REPLY means roughly the same thing as + INTERNAL_IP4_SUBNET containing the same information ("send traffic to + these addresses through me"), but also implies a link boundary. For + instance, the client could use its own address and the netmask to + calculate the broadcast address of the link. (Whether the gateway + will actually deliver broadcast packets to other VPN clients and/or + other nodes connected to this link is another matter.) + + An empty INTERNAL_IP4_NETMASK attribute can be included in a + CFG_REQUEST to request this information (although the gateway can + send the information even when not requested). However, it seems + that non-empty values for this attribute do not make sense in + CFG_REQUESTs. + + Fortunately, Section 4 clearly says that a minimal implementation + does not need to include or understand the INTERNAL_IP4_NETMASK + attribute, and thus this document recommends that implementations + should not use the INTERNAL_IP4_NETMASK attribute or assume that the + other peer supports it. + + (References: Charlie Kaufman's mail "RE: Proposed Last Call based + revisions to IKEv2", 2004-05-27. Email discussion with Tero Kivinen, + Jan 2005. Yoav Nir's mail "Re: New I-D: IKEv2 Clarifications and + Implementation Guidelines", 2005-02-07. "Clarifications open issue: + INTERNAL_IP4_SUBNET/NETMASK" thread, April 2005.) + +6.5. Configuration payloads for IPv6 + + IKEv2 also defines configuration payloads for IPv6. However, they + are based on the corresponding IPv4 payloads, and do not fully follow + the "normal IPv6 way of doing things". + + + + + +Eronen & Hoffman Expires November 5, 2006 [Page 41] + +Internet-Draft IKEv2 Clarifications May 2006 + + + A client can be assigned an IPv6 address using the + INTERNAL_IP6_ADDRESS configuration payload. A minimal exchange could + look like this: + + CP(CFG_REQUEST) = + INTERNAL_IP6_ADDRESS() + INTERNAL_IP6_DNS() + TSi = (0, 0-65535, :: - FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF) + TSr = (0, 0-65535, :: - FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF) + + CP(CFG_REPLY) = + INTERNAL_IP6_ADDRESS(2001:DB8:0:1:2:3:4:5/64) + INTERNAL_IP6_DNS(2001:DB8:99:88:77:66:55:44) + TSi = (0, 0-65535, 2001:DB8:0:1:2:3:4:5 - 2001:DB8:0:1:2:3:4:5) + TSr = (0, 0-65535, :: - FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF) + + In particular, IPv6 stateless autoconfiguration or router + advertisement messages are not used; neither is neighbor discovery. + + The client can also send a non-empty INTERNAL_IP6_ADDRESS attribute + in the CFG_REQUEST to request a specific address or interface + identifier. The gateway first checks if the specified address is + acceptable, and if it is, returns that one. If the address was not + acceptable, the gateway will attempt to use the interface identifier + with some other prefix; if even that fails, the gateway will select + another interface identifier. + + The INTERNAL_IP6_ADDRESS attribute also contains a prefix length + field. When used in a CFG_REPLY, this corresponds to the + INTERNAL_IP4_NETMASK attribute in the IPv4 case (and indeed, was + called INTERNAL_IP6_NETMASK in earlier versions of the IKEv2 draft). + See the previous section for more details. + + While this approach to configuring IPv6 addresses is reasonably + simple, it has some limitations: IPsec tunnels configured using IKEv2 + are not fully-featured "interfaces" in the IPv6 addressing + architecture [IPv6Addr] sense. In particular, they do not + necessarily have link-local addresses, and this may complicate the + use of protocols that assume them, such as [MLDv2]. (Whether they + are called "interfaces" in some particular operating system is a + different issue.) + + (References: "VPN remote host configuration IPv6 ?" thread, May 2004. + "Clarifications open issue: INTERNAL_IP4_SUBNET/NETMASK" thread, + April 2005.) + + + + + + +Eronen & Hoffman Expires November 5, 2006 [Page 42] + +Internet-Draft IKEv2 Clarifications May 2006 + + +6.6. INTERNAL_IP6_NBNS + + Section 3.15.1 defines the INTERNAL_IP6_NBNS attribute for sending + the IPv6 address of NetBIOS name servers. + + However, NetBIOS is not defined for IPv6, and probably never will be. + Thus, this attribute most likely does not make much sense. + + (Pointed out by Bernard Aboba in the IP Configuration Security (ICOS) + BoF at IETF62.) + +6.7. INTERNAL_ADDRESS_EXPIRY + + Section 3.15.1 defines the INTERNAL_ADDRESS_EXPIRY attribute as + "Specifies the number of seconds that the host can use the internal + IP address. The host MUST renew the IP address before this expiry + time. Only one of these attributes MAY be present in the reply." + + Expiry times and explicit renewals are primarily useful in + environments like DHCP, where the server cannot reliably know when + the client has gone away. However, in IKEv2 this is known, and the + gateway can simply free the address when the IKE_SA is deleted. + + Also, Section 4 says that supporting renewals is not mandatory. + Given that this functionality is usually not needed, we recommend + that gateways should not send the INTERNAL_ADDRESS_EXPIRY attribute. + (And since this attribute does not seem to make much sense for + CFG_REQUESTs, clients should not send it either.) + + Note that according to Section 4, clients are required to understand + INTERNAL_ADDRESS_EXPIRY if they receive it. A minimum implementation + would use the value to limit the lifetime of the IKE_SA. + + (References: Tero Kivinen's mail "Comments of + draft-eronen-ipsec-ikev2-clarifications-02.txt", 2005-04-05. + "Questions about internal address" thread, April 2005.) + +6.8. Address assignment failures + + If the responder encounters an error while attempting to assign an IP + address to the initiator, it responds with an + INTERNAL_ADDRESS_FAILURE notification as described in Section 3.10.1. + However, there are some more complex error cases. + + First, if the responder does not support configuration payloads at + all, it can simply ignore all configuration payloads. This type of + implementation never sends INTERNAL_ADDRESS_FAILURE notifications. + If the initiator requires the assignment of an IP address, it will + + + +Eronen & Hoffman Expires November 5, 2006 [Page 43] + +Internet-Draft IKEv2 Clarifications May 2006 + + + treat a response without CFG_REPLY as an error. + + A second case is where the responder does support configuration + payloads, but only for particular type of addresses (IPv4 or IPv6). + Section 4 says that "A minimal IPv4 responder implementation will + ignore the contents of the CP payload except to determine that it + includes an INTERNAL_IP4_ADDRESS attribute". If, for instance, the + initiator includes both INTERNAL_IP4_ADDRESS and INTERNAL_IP6_ADDRESS + in the CFG_REQUEST, an IPv4-only responder can thus simply ignore the + IPv6 part and process the IPv4 request as usual. + + A third case is where the initiator requests multiple addresses of a + type that the responder supports: what should happen if some (but not + all) of the requests fail? It seems that an optimistic approach + would be the best one here: if the responder is able to assign at + least one address, it replies with those; it sends + INTERNAL_ADDRESS_FAILURE only if no addresses can be assigned. + + (References: "ikev2 and internal_ivpn_address" thread, June 2005.) + + +7. Miscellaneous issues + +7.1. Matching ID_IPV4_ADDR and ID_IPV6_ADDR + + When using the ID_IPV4_ADDR/ID_IPV6_ADDR identity types in IDi/IDr + payloads, IKEv2 does not require this address to match the address in + the IP header (of IKEv2 packets), or anything in the TSi/TSr + payloads. The contents of IDi/IDr is used purely to fetch the policy + and authentication data related to the other party. + + (References: "Identities types IP address,FQDN/user FQDN and DN and + its usage in preshared key authentication" thread, Jan 2005.) + +7.2. Relationship of IKEv2 to RFC4301 + + The IKEv2 specification refers to [RFC4301], but it never makes + clearly defines the exact relationship is. + + However, there are some requirements in the specification that make + it clear that IKEv2 requires [RFC4301]. In other words, an + implementation that does IPsec processing strictly according to + [RFC2401] cannot be compliant with the IKEv2 specification. + + One such example can be found in Section 2.24: "Specifically, tunnel + encapsulators and decapsulators for all tunnel-mode SAs created by + IKEv2 [...] MUST implement the tunnel encapsulation and + decapsulation processing specified in [RFC4301] to prevent discarding + + + +Eronen & Hoffman Expires November 5, 2006 [Page 44] + +Internet-Draft IKEv2 Clarifications May 2006 + + + of ECN congestion indications." + + Nevertheless, the changes required to existing [RFC2401] + implementations are not very large, especially since supporting many + of the new features (such as Extended Sequence Numbers) is optional. + +7.3. Reducing the window size + + In IKEv2, the window size is assumed to be a (possibly configurable) + property of a particular implementation, and is not related to + congestion control (unlike the window size in TCP, for instance). + + In particular, it is not defined what the responder should do when it + receives a SET_WINDOW_SIZE notification containing a smaller value + than is currently in effect. Thus, there is currently no way to + reduce the window size of an existing IKE_SA. However, when rekeying + an IKE_SA, the new IKE_SA starts with window size 1 until it is + explicitly increased by sending a new SET_WINDOW_SIZE notification. + + (References: Tero Kivinen's mail "Comments of + draft-eronen-ipsec-ikev2-clarifications-02.txt", 2005-04-05.) + +7.4. Minimum size of nonces + + Section 2.10 says that "Nonces used in IKEv2 MUST be randomly chosen, + MUST be at least 128 bits in size, and MUST be at least half the key + size of the negotiated prf." + + However, the initiator chooses the nonce before the outcome of the + negotiation is known. In this case, the nonce has to be long enough + for all the PRFs being proposed. + +7.5. Initial zero octets on port 4500 + + It is not clear whether a peer sending an IKE_SA_INIT request on port + 4500 should include the initial four zero octets. Section 2.23 talks + about how to upgrade to tunneling over port 4500 after message 2, but + it does not say what to do if message 1 is sent on port 4500. + + + + + + + + + + + + + +Eronen & Hoffman Expires November 5, 2006 [Page 45] + +Internet-Draft IKEv2 Clarifications May 2006 + + + IKE MUST listen on port 4500 as well as port 500. + + [...] + + The IKE initiator MUST check these payloads if present and if + they do not match the addresses in the outer packet MUST tunnel + all future IKE and ESP packets associated with this IKE_SA over + UDP port 4500. + + To tunnel IKE packets over UDP port 4500, the IKE header has four + octets of zero prepended and the result immediately follows the + UDP header. [...] + + The very beginning of Section 2 says "... though IKE messages may + also be received on UDP port 4500 with a slightly different format + (see section 2.23)." + + That "slightly different format" is only described in discussing what + to do after changing to port 4500. However, [RFC3948] shows clearly + the format has the initial zeros even for initiators on port 4500. + Furthermore, without the initial zeros, the processing engine cannot + determine whether the packet is an IKE packet or an ESP packet. + + Thus, all packets sent on port 4500 need the four zero prefix; + otherwise, the receiver won't know how to handle them. + +7.6. Destination port for NAT traversal + + Section 2.23 says that "an IPsec endpoint that discovers a NAT + between it and its correspondent MUST send all subsequent traffic to + and from port 4500". + + This sentence is misleading. The peer "outside" the NAT uses source + port 4500 for the traffic it sends, but the destination port is, of + course, taken from packets sent by the peer behind the NAT. This + port number is usually dynamically allocated by the NAT. + +7.7. SPI values for messages outside of an IKE_SA + + The IKEv2 specification is not quite clear what SPI values should be + used in the IKE header for the small number of notifications that are + allowed to be sent outside of an IKE_SA. Note that such + notifications are explicitly not Informational exchanges; Section 1.5 + makes it clear that these are one-way messages that must not be + responded to. + + There are two cases when such a one-way notification can be sent: + INVALID_IKE_SPI and INVALID_SPI. + + + +Eronen & Hoffman Expires November 5, 2006 [Page 46] + +Internet-Draft IKEv2 Clarifications May 2006 + + + In case of INVALID_IKE_SPI, the message sent is a response message, + and Section 2.21 says that "If a response is sent, the response MUST + be sent to the IP address and port from whence it came with the same + IKE SPIs and the Message ID copied." + + In case of INVALID_SPI, however, there are no IKE SPI values that + would be meaningful to the recipient of such a notification. Also, + the message sent is now an INFORMATIONAL request. A strict + interpretation of the specification would require the sender to + invent garbage values for the SPI fields. However, we think this was + not the intention, and using zero values is acceptable. + + (References: "INVALID_IKE_SPI" thread, June 2005.) + +7.8. Protocol ID/SPI fields in Notify payloads + + Section 3.10 says that the Protocol ID field in Notify payloads "For + notifications that do not relate to an existing SA, this field MUST + be sent as zero and MUST be ignored on receipt". However, the + specification does not clearly say which notifications are related to + existing SAs and which are not. + + Since the main purpose of the Protocol ID field is to specify the + type of the SPI, our interpretation is that the Protocol ID field + should be non-zero only when the SPI field is non-empty. + + There are currently only two notifications where this is the case: + INVALID_SELECTORS and REKEY_SA. + +7.9. Which message should contain INITIAL_CONTACT + + The description of the INITIAL_CONTACT notification in Section 3.10.1 + says that "This notification asserts that this IKE_SA is the only + IKE_SA currently active between the authenticated identities". + However, neither Section 2.4 nor 3.10.1 says in which message this + payload should be placed. + + The general agreement is that INITIAL_CONTACT is best communicated in + the first IKE_AUTH request, not as a separate exchange afterwards. + + (References: "Clarifying the use of INITIAL_CONTACT in IKEv2" thread, + April 2005. "Initial Contact messages" thread, December 2004. + "IKEv2 and Initial Contact" thread, September 2004 and April 2005.) + +7.10. Alignment of payloads + + Many IKEv2 payloads contain fields marked as "RESERVED", mostly + because IKEv1 had them, and partly because they make the pictures + + + +Eronen & Hoffman Expires November 5, 2006 [Page 47] + +Internet-Draft IKEv2 Clarifications May 2006 + + + easier to draw. In particular, payloads in IKEv2 are not, in + general, aligned to 4-octet boundaries. (Note that payloads were not + aligned to 4-byte boundaries in IKEv1 either.) + + (References: "IKEv2: potential 4-byte alignment problem" thread, June + 2004.) + +7.11. Key length transform attribute + + Section 3.3.5 says that "The only algorithms defined in this document + that accept attributes are the AES based encryption, integrity, and + pseudo-random functions, which require a single attribute specifying + key width." + + This is incorrect. The AES-based integrity and pseudo-random + functions defined in [IKEv2] always use a 128-bit key. In fact, + there are currently no integrity or PRF algorithms that use the key + length attribute (and we recommend that they should not be defined in + the future either). + + For encryption algorithms, the situation is slightly more complex + since there are three different types of algorithms: + + o The key length attribute is never used with algorithms that use a + fixed length key, such as DES and IDEA. + + o The key length attribute is always included for the currently + defined AES-based algorithms (CBC, CTR, CCM and GCM). Omitting + the key length attribute is not allowed; if the proposal does not + contain it, the proposal has to be rejected. + + o For other algorithms, the key length attribute can be included but + is not mandatory. These algorithms include, e.g., RC5, CAST and + BLOWFISH. If the key length attribute is not included, the + default value specified in [RFC2451] is used. + +7.12. IPsec IANA considerations + + There are currently three different IANA registry files that contain + important numbers for IPsec: ikev2-registry, isakmp-registry, and + ipsec-registry. Implementors should note that IKEv2 may use numbers + different from IKEv1 for a particular algorithm. + + For instance, an encryption algorithm can have up to three different + numbers: the IKEv2 "Transform Type 1" identifier in ikev2-registry, + the IKEv1 phase 1 "Encryption Algorithm" identifier in ipsec- + registry, and the IKEv1 phase 2 "IPSEC ESP Transform Identifier" + isakmp-registry. Although some algorithms have the same number in + + + +Eronen & Hoffman Expires November 5, 2006 [Page 48] + +Internet-Draft IKEv2 Clarifications May 2006 + + + all three registries, the registries are not identical. + + Similarly, an integrity algorithm can have at least the IKEv2 + "Transform Type 3" identifier in ikev2-registry, the IKEv1 phase 2 + "IPSEC AH Transform Identifier" in isakmp-registry, and the IKEv1 + phase 2 ESP "Authentication Algorithm Security Association Attribute" + identifier in isakmp-registry. And there is also the IKEv1 phase 1 + "Hash Algorithm" list in ipsec-registry. + + This issue needs special care also when writing a specification for + how a new algorithm is used together with IPsec. + +7.13. Combining ESP and AH + + The IKEv2 specification contains some misleading text about how ESP + and AH can be combined. + + IKEv2 is based on [RFC4301] which does not include "SA bundles" that + were part of [RFC2401]. While a single packet can go through IPsec + processing multiple times, each of these passes uses a separate SA, + and the passes are coordinated by the forwarding tables. In IKEv2, + each of these SAs has to be created using a separate CREATE_CHILD_SA + exchange. Thus, the text in Section 2.7 about a single proposal + containing both ESP and AH is incorrect. + + Morever, the combination of ESP and AH (between the same endpoints) + become largely obsolete already in 1998 when RFC 2406 was published. + Our recommendation is that IKEv2 implementations should not support + this combination, and implementors should not assume the combination + can be made to work in interoperable manner. + + (References: "Rekeying SA bundles" thread, Oct 2005.) + + +8. Implementation mistakes + + Some implementers at the early IKEv2 bakeoffs didn't do everything + correctly. This may seem like an obvious statement, but it is + probably useful to list a few things that were clear in the document + and not needing clarification, that some implementors didn't do. All + of these things caused interoperability problems. + + o Some implementations continued to send traffic on a CHILD_SA after + it was rekeyed, even after receiving an DELETE payload. + + o After rekeying an IKE_SA, some implementations did not reset their + message counters to zero. One set the counter to 2, another did + not reset the counter at all. + + + +Eronen & Hoffman Expires November 5, 2006 [Page 49] + +Internet-Draft IKEv2 Clarifications May 2006 + + + o Some implementations could only handle a single pair of traffic + selectors, or would only process the first pair in the proposal. + + o Some implementations responded to a delete request by sending an + empty INFORMATIONAL response, and then initiated their own + INFORMATIONAL exchange with the pair of SAs to delete. + + o Although this did not happen at the bakeoff, from the discussion + there, it is clear that some people had not implemented message + window sizes correctly. Some implementations might have sent + messages that did not fit into the responder's message windows, + and some implementations may not have torn down an SA if they did + not ever receive a message that they know they should have. + + +9. Security considerations + + This document does not introduce any new security considerations to + IKEv2. If anything, clarifying complex areas of the specification + can reduce the likelihood of implementation problems that may have + security implications. + + +10. IANA considerations + + This document does not change or create any IANA-registered values. + + +11. Acknowledgments + + This document is mainly based on conversations on the IPsec WG + mailing list. The authors would especially like to thank Bernard + Aboba, Jari Arkko, Vijay Devarapalli, William Dixon, Francis Dupont, + Mika Joutsenvirta, Charlie Kaufman, Stephen Kent, Tero Kivinen, Yoav + Nir, Michael Richardson, and Joel Snyder for their contributions. + + In addition, the authors would like to thank all the participants of + the first public IKEv2 bakeoff, held in Santa Clara in February 2005, + for their questions and proposed clarifications. + + +12. References + +12.1. Normative References + + [IKEv2] Kaufman, C., Ed., "Internet Key Exchange (IKEv2) + Protocol", RFC 4306, December 2005. + + + + +Eronen & Hoffman Expires November 5, 2006 [Page 50] + +Internet-Draft IKEv2 Clarifications May 2006 + + + [IKEv2ALG] + Schiller, J., "Cryptographic Algorithms for Use in the + Internet Key Exchange Version 2 (IKEv2)", RFC 4307, + December 2005. + + [PKCS1v20] + Kaliski, B. and J. Staddon, "PKCS #1: RSA Cryptography + Specifications Version 2.0", RFC 2437, October 1998. + + [PKCS1v21] + Jonsson, J. and B. Kaliski, "Public-Key Cryptography + Standards (PKCS) #1: RSA Cryptography Specifications + Version 2.1", RFC 3447, February 2003. + + [RFC2401] Kent, S. and R. Atkinson, "Security Architecture for the + Internet Protocol", RFC 2401, November 1998. + + [RFC4301] Kent, S. and K. Seo, "Security Architecture for the + Internet Protocol", RFC 4301, December 2005. + +12.2. Informative References + + [Aura05] Aura, T., Roe, M., and A. Mohammed, "Experiences with + Host-to-Host IPsec", 13th International Workshop on + Security Protocols, Cambridge, UK, April 2005. + + [EAP] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. + Levkowetz, "Extensible Authentication Protocol (EAP)", + RFC 3748, June 2004. + + [HashUse] Hoffman, P., "Use of Hash Algorithms in IKE and IPsec", + draft-hoffman-ike-ipsec-hash-use-01 (work in progress), + December 2005. + + [IPCPSubnet] + Cisco Systems, Inc., "IPCP Subnet Mask Support + Enhancements", http://www.cisco.com/univercd/cc/td/doc/ + product/software/ios121/121newft/121limit/121dc/121dc3/ + ipcp_msk.htm, January 2003. + + [IPv6Addr] + Hinden, R. and S. Deering, "Internet Protocol Version 6 + (IPv6) Addressing Architecture", RFC 4291, April 2004. + + [MIPv6] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support + in IPv6", RFC 3775, June 2004. + + [MLDv2] Vida, R. and L. Costa, "Multicast Listener Discovery + + + +Eronen & Hoffman Expires November 5, 2006 [Page 51] + +Internet-Draft IKEv2 Clarifications May 2006 + + + Version 2 (MLDv2) for IPv6", RFC 3810, June 2004. + + [NAI] Aboba, B., Beadles, M., Arkko, J., and P. Eronen, "The + Network Access Identifier", RFC 4282, December 2005. + + [PKI4IPsec] + Korver, B., "Internet PKI Profile of IKEv1/ISAKMP, IKEv2, + and PKIX", draft-ietf-pki4ipsec-ikecert-profile (work in + progress), February 2006. + + [RADEAP] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication + Dial In User Service) Support For Extensible + Authentication Protocol (EAP)", RFC 3579, September 2003. + + [RADIUS] Rigney, C., Willens, S., Rubens, A., and W. Simpson, + "Remote Authentication Dial In User Service (RADIUS)", + RFC 2865, June 2000. + + [RADIUS6] Aboba, B., Zorn, G., and D. Mitton, "RADIUS and IPv6", + RFC 3162, August 2001. + + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", RFC 2119, March 1997. + + [RFC2451] Pereira, R. and R. Adams, "The ESP CBC-Mode Cipher + Algorithms", RFC 2451, November 1998. + + [RFC2822] Resnick, P., "Internet Message Format", RFC 2822, + April 2001. + + [RFC3664] Hoffman, P., "The AES-XCBC-PRF-128 Algorithm for the + Internet Key Exchange Protocol (IKE)", RFC 3664, + January 2004. + + [RFC3664bis] + Hoffman, P., "The AES-XCBC-PRF-128 Algorithm for the + Internet Key Exchange Protocol (IKE)", + draft-hoffman-rfc3664bis (work in progress), October 2005. + + [RFC3948] Huttunen, A., Swander, B., Volpe, V., DiBurro, L., and M. + Stenberg, "UDP Encapsulation of IPsec ESP Packets", + RFC 3948, January 2005. + + [RFC822] Crocker, D., "Standard for the format of ARPA Internet + text messages", RFC 822, August 1982. + + [ReAuth] Nir, Y., "Repeated Authentication in Internet Key Exchange + (IKEv2) Protocol", RFC 4478, April 2006. + + + +Eronen & Hoffman Expires November 5, 2006 [Page 52] + +Internet-Draft IKEv2 Clarifications May 2006 + + + [SCVP] Freeman, T., Housley, R., Malpani, A., Cooper, D., and T. + Polk, "Simple Certificate Validation Protocol (SCVP)", + draft-ietf-pkix-scvp-21 (work in progress), October 2005. + + +Appendix A. Exchanges and payloads + + This appendix contains a short summary of the IKEv2 exchanges, and + what payloads can appear in which message. This appendix is purely + informative; if it disagrees with the body of this document or the + IKEv2 specification, the other text is considered correct. + + Vendor-ID (V) payloads may be included in any place in any message. + This sequence shows what are, in our opinion, the most logical places + for them. + + The specification does not say which messages can contain + N(SET_WINDOW_SIZE). It can possibly be included in any message, but + it is not yet shown below. + +A.1. IKE_SA_INIT exchange + + request --> [N(COOKIE)], + SA, KE, Ni, + [N(NAT_DETECTION_SOURCE_IP)+, + N(NAT_DETECTION_DESTINATION_IP)], + [V+] + + normal response <-- SA, KE, Nr, + (no cookie) [N(NAT_DETECTION_SOURCE_IP), + N(NAT_DETECTION_DESTINATION_IP)], + [[N(HTTP_CERT_LOOKUP_SUPPORTED)], CERTREQ+], + [V+] + + + + + + + + + + + + + + + + + + +Eronen & Hoffman Expires November 5, 2006 [Page 53] + +Internet-Draft IKEv2 Clarifications May 2006 + + +A.2. IKE_AUTH exchange without EAP + + request --> IDi, [CERT+], + [N(INITIAL_CONTACT)], + [[N(HTTP_CERT_LOOKUP_SUPPORTED)], CERTREQ+], + [IDr], + AUTH, + [CP(CFG_REQUEST)], + [N(IPCOMP_SUPPORTED)+], + [N(USE_TRANSPORT_MODE)], + [N(ESP_TFC_PADDING_NOT_SUPPORTED)], + [N(NON_FIRST_FRAGMENTS_ALSO)], + SA, TSi, TSr, + [V+] + + response <-- IDr, [CERT+], + AUTH, + [CP(CFG_REPLY)], + [N(IPCOMP_SUPPORTED)], + [N(USE_TRANSPORT_MODE)], + [N(ESP_TFC_PADDING_NOT_SUPPORTED)], + [N(NON_FIRST_FRAGMENTS_ALSO)], + SA, TSi, TSr, + [N(ADDITIONAL_TS_POSSIBLE)], + [V+] + + + + + + + + + + + + + + + + + + + + + + + + + + +Eronen & Hoffman Expires November 5, 2006 [Page 54] + +Internet-Draft IKEv2 Clarifications May 2006 + + +A.3. IKE_AUTH exchange with EAP + + first request --> IDi, + [N(INITIAL_CONTACT)], + [[N(HTTP_CERT_LOOKUP_SUPPORTED)], CERTREQ+], + [IDr], + [CP(CFG_REQUEST)], + [N(IPCOMP_SUPPORTED)+], + [N(USE_TRANSPORT_MODE)], + [N(ESP_TFC_PADDING_NOT_SUPPORTED)], + [N(NON_FIRST_FRAGMENTS_ALSO)], + SA, TSi, TSr, + [V+] + + first response <-- IDr, [CERT+], AUTH, + EAP, + [V+] + + / --> EAP + repeat 1..N times | + \ <-- EAP + + last request --> AUTH + + last response <-- AUTH, + [CP(CFG_REPLY)], + [N(IPCOMP_SUPPORTED)], + [N(USE_TRANSPORT_MODE)], + [N(ESP_TFC_PADDING_NOT_SUPPORTED)], + [N(NON_FIRST_FRAGMENTS_ALSO)], + SA, TSi, TSr, + [N(ADDITIONAL_TS_POSSIBLE)], + [V+] + + + + + + + + + + + + + + + + + + +Eronen & Hoffman Expires November 5, 2006 [Page 55] + +Internet-Draft IKEv2 Clarifications May 2006 + + +A.4. CREATE_CHILD_SA exchange for creating/rekeying CHILD_SAs + + request --> [N(REKEY_SA)], + [N(IPCOMP_SUPPORTED)+], + [N(USE_TRANSPORT_MODE)], + [N(ESP_TFC_PADDING_NOT_SUPPORTED)], + [N(NON_FIRST_FRAGMENTS_ALSO)], + SA, Ni, [KEi], TSi, TSr + + response <-- [N(IPCOMP_SUPPORTED)], + [N(USE_TRANSPORT_MODE)], + [N(ESP_TFC_PADDING_NOT_SUPPORTED)], + [N(NON_FIRST_FRAGMENTS_ALSO)], + SA, Nr, [KEr], TSi, TSr, + [N(ADDITIONAL_TS_POSSIBLE)] + +A.5. CREATE_CHILD_SA exchange for rekeying the IKE_SA + + request --> SA, Ni, [KEi] + + response <-- SA, Nr, [KEr] + +A.6. INFORMATIONAL exchange + + request --> [N+], + [D+], + [CP(CFG_REQUEST)] + + response <-- [N+], + [D+], + [CP(CFG_REPLY)] + + +Authors' Addresses + + Pasi Eronen + Nokia Research Center + P.O. Box 407 + FIN-00045 Nokia Group + Finland + + Email: pasi.eronen@nokia.com + + + + + + + + + +Eronen & Hoffman Expires November 5, 2006 [Page 56] + +Internet-Draft IKEv2 Clarifications May 2006 + + + Paul Hoffman + VPN Consortium + 127 Segre Place + Santa Cruz, CA 95060 + USA + + Email: paul.hoffman@vpnc.org + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Eronen & Hoffman Expires November 5, 2006 [Page 57] + +Internet-Draft IKEv2 Clarifications May 2006 + + +Full Copyright Statement + + Copyright (C) The Internet Society (2006). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET + ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, + INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE + INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at + ietf-ipr@ietf.org. + + +Acknowledgment + + Funding for the RFC Editor function is provided by the IETF + Administrative Support Activity (IASA). + + + + + +Eronen & Hoffman Expires November 5, 2006 [Page 58] + + diff --git a/src/charon/doc/standards/draft-hoffman-ikev2-1-00.txt b/src/charon/doc/standards/draft-hoffman-ikev2-1-00.txt new file mode 100644 index 000000000..cd6b0ec22 --- /dev/null +++ b/src/charon/doc/standards/draft-hoffman-ikev2-1-00.txt @@ -0,0 +1,6720 @@ + + + +Network Working Group P. Hoffman +Internet-Draft VPN Consortium +Expires: July 5, 2006 January 2006 + + + Internet Key Exchange Protocol: IKEv2.1 + draft-hoffman-ikev2-1-00.txt + +Status of this Memo + + By submitting this Internet-Draft, each author represents that any + applicable patent or other IPR claims of which he or she is aware + have been or will be disclosed, and any of which he or she becomes + aware will be disclosed, in accordance with Section 6 of BCP 79. + + Internet-Drafts are working documents of the Internet Engineering + Task Force (IETF), its areas, and its working groups. Note that + other groups may also distribute working documents as Internet- + Drafts. + + Internet-Drafts are draft documents valid for a maximum of six months + and may be updated, replaced, or obsoleted by other documents at any + time. It is inappropriate to use Internet-Drafts as reference + material or to cite them other than as "work in progress." + + The list of current Internet-Drafts can be accessed at + http://www.ietf.org/ietf/1id-abstracts.txt. + + The list of Internet-Draft Shadow Directories can be accessed at + http://www.ietf.org/shadow.html. + + This Internet-Draft will expire on July 5, 2006. + +Copyright Notice + + Copyright (C) The Internet Society (2006). + +Abstract + + This document describes version 2.1 of the Internet Key Exchange + (IKE) protocol. IKEv2.1 is heavily based on IKEv2 from RFC 4306 + (edited by Charlie Kaufman), and includes all of the clarifications + from the "IKEv2 Clarifications" document (edited by Pasi Eronen and + Paul Hoffman). IKEv2.1 makes additional changes to those two + documents in places where IKEv2 was unclear and the clarifications + document did not commit to a particular protocol interpretation. + + + + + +Hoffman Expires July 5, 2006 [Page 1] + +Internet-Draft IKEv2 January 2006 + + +Table of Contents + + 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5 + 1.1. Usage Scenarios . . . . . . . . . . . . . . . . . . . . . 6 + 1.1.1. Security Gateway to Security Gateway Tunnel . . . . . 7 + 1.1.2. Endpoint-to-Endpoint Transport . . . . . . . . . . . 7 + 1.1.3. Endpoint to Security Gateway Tunnel . . . . . . . . . 8 + 1.1.4. Other Scenarios . . . . . . . . . . . . . . . . . . . 9 + 1.2. The Initial Exchanges . . . . . . . . . . . . . . . . . . 9 + 1.3. The CREATE_CHILD_SA Exchange . . . . . . . . . . . . . . 12 + 1.3.1. Creating New CHILD_SAs with the CREATE_CHILD_SA + Exchange . . . . . . . . . . . . . . . . . . . . . . 13 + 1.3.2. Rekeying IKE_SAs with the CREATE_CHILD_SA Exchange . 13 + 1.3.3. Rekeying CHILD_SAs with the CREATE_CHILD_SA + Exchange . . . . . . . . . . . . . . . . . . . . . . 14 + 1.4. The INFORMATIONAL Exchange . . . . . . . . . . . . . . . 15 + 1.5. Informational Messages outside of an IKE_SA . . . . . . . 16 + 1.6. Requirements Terminology . . . . . . . . . . . . . . . . 17 + 1.7. Introduction to IKEv2.1 . . . . . . . . . . . . . . . . . 17 + 2. IKE Protocol Details and Variations . . . . . . . . . . . . . 18 + 2.1. Use of Retransmission Timers . . . . . . . . . . . . . . 19 + 2.2. Use of Sequence Numbers for Message ID . . . . . . . . . 19 + 2.3. Window Size for Overlapping Requests . . . . . . . . . . 20 + 2.4. State Synchronization and Connection Timeouts . . . . . . 21 + 2.5. Version Numbers and Forward Compatibility . . . . . . . . 23 + 2.6. Cookies . . . . . . . . . . . . . . . . . . . . . . . . . 25 + 2.6.1. Interaction of COOKIE and INVALID_KE_PAYLOAD . . . . 27 + 2.7. Cryptographic Algorithm Negotiation . . . . . . . . . . . 28 + 2.8. Rekeying . . . . . . . . . . . . . . . . . . . . . . . . 29 + 2.8.1. Simultaneous CHILD_SA rekeying . . . . . . . . . . . 31 + 2.8.2. Rekeying the IKE_SA Versus Reauthentication . . . . . 33 + 2.9. Traffic Selector Negotiation . . . . . . . . . . . . . . 34 + 2.9.1. Traffic Selectors Violating Own Policy . . . . . . . 37 + 2.10. Nonces . . . . . . . . . . . . . . . . . . . . . . . . . 38 + 2.11. Address and Port Agility . . . . . . . . . . . . . . . . 38 + 2.12. Reuse of Diffie-Hellman Exponentials . . . . . . . . . . 38 + 2.13. Generating Keying Material . . . . . . . . . . . . . . . 39 + 2.14. Generating Keying Material for the IKE_SA . . . . . . . . 40 + 2.15. Authentication of the IKE_SA . . . . . . . . . . . . . . 41 + 2.16. Extensible Authentication Protocol Methods . . . . . . . 43 + 2.17. Generating Keying Material for CHILD_SAs . . . . . . . . 45 + 2.18. Rekeying IKE_SAs Using a CREATE_CHILD_SA Exchange . . . . 46 + 2.19. Requesting an Internal Address on a Remote Network . . . 47 + 2.20. Requesting the Peer's Version . . . . . . . . . . . . . . 48 + 2.21. Error Handling . . . . . . . . . . . . . . . . . . . . . 49 + 2.22. IPComp . . . . . . . . . . . . . . . . . . . . . . . . . 50 + 2.23. NAT Traversal . . . . . . . . . . . . . . . . . . . . . . 50 + 2.24. Explicit Congestion Notification (ECN) . . . . . . . . . 53 + + + +Hoffman Expires July 5, 2006 [Page 2] + +Internet-Draft IKEv2 January 2006 + + + 3. Header and Payload Formats . . . . . . . . . . . . . . . . . 53 + 3.1. The IKE Header . . . . . . . . . . . . . . . . . . . . . 53 + 3.2. Generic Payload Header . . . . . . . . . . . . . . . . . 56 + 3.3. Security Association Payload . . . . . . . . . . . . . . 58 + 3.3.1. Proposal Substructure . . . . . . . . . . . . . . . . 60 + 3.3.2. Transform Substructure . . . . . . . . . . . . . . . 62 + 3.3.3. Valid Transform Types by Protocol . . . . . . . . . . 64 + 3.3.4. Mandatory Transform IDs . . . . . . . . . . . . . . . 65 + 3.3.5. Transform Attributes . . . . . . . . . . . . . . . . 66 + 3.3.6. Attribute Negotiation . . . . . . . . . . . . . . . . 67 + 3.4. Key Exchange Payload . . . . . . . . . . . . . . . . . . 68 + 3.5. Identification Payloads . . . . . . . . . . . . . . . . . 69 + 3.6. Certificate Payload . . . . . . . . . . . . . . . . . . . 71 + 3.7. Certificate Request Payload . . . . . . . . . . . . . . . 74 + 3.8. Authentication Payload . . . . . . . . . . . . . . . . . 76 + 3.9. Nonce Payload . . . . . . . . . . . . . . . . . . . . . . 77 + 3.10. Notify Payload . . . . . . . . . . . . . . . . . . . . . 77 + 3.10.1. Notify Message Types . . . . . . . . . . . . . . . . 78 + 3.11. Delete Payload . . . . . . . . . . . . . . . . . . . . . 84 + 3.12. Vendor ID Payload . . . . . . . . . . . . . . . . . . . . 85 + 3.13. Traffic Selector Payload . . . . . . . . . . . . . . . . 86 + 3.13.1. Traffic Selector . . . . . . . . . . . . . . . . . . 88 + 3.14. Encrypted Payload . . . . . . . . . . . . . . . . . . . . 90 + 3.15. Configuration Payload . . . . . . . . . . . . . . . . . . 92 + 3.15.1. Configuration Attributes . . . . . . . . . . . . . . 94 + 3.15.2. Meaning of INTERNAL_IP4_SUBNET/INTERNAL_IP6_SUBNET . 97 + 3.15.3. Configuration payloads for IPv6 . . . . . . . . . . . 99 + 3.15.4. Address Assignment Failures . . . . . . . . . . . . . 100 + 3.16. Extensible Authentication Protocol (EAP) Payload . . . . 100 + 4. Conformance Requirements . . . . . . . . . . . . . . . . . . 102 + 5. Security Considerations . . . . . . . . . . . . . . . . . . . 104 + 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 107 + 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 107 + 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 108 + 8.1. Normative References . . . . . . . . . . . . . . . . . . 108 + 8.2. Informative References . . . . . . . . . . . . . . . . . 109 + Appendix A. Summary of changes from IKEv1 . . . . . . . . . . . 112 + Appendix B. Diffie-Hellman Groups . . . . . . . . . . . . . . . 114 + B.1. Group 1 - 768 Bit MODP . . . . . . . . . . . . . . . . . 114 + B.2. Group 2 - 1024 Bit MODP . . . . . . . . . . . . . . . . . 114 + Appendix C. Exchanges and Payloads . . . . . . . . . . . . . . . 115 + C.1. IKE_SA_INIT Exchange . . . . . . . . . . . . . . . . . . 115 + C.2. IKE_AUTH Exchange without EAP . . . . . . . . . . . . . . 116 + C.3. IKE_AUTH Exchange with EAP . . . . . . . . . . . . . . . 117 + C.4. CREATE_CHILD_SA Exchange for Creating or Rekeying + CHILD_SAs . . . . . . . . . . . . . . . . . . . . . . . . 118 + C.5. CREATE_CHILD_SA Exchange for Rekeying the IKE_SA . . . . 118 + C.6. INFORMATIONAL Exchange . . . . . . . . . . . . . . . . . 118 + + + +Hoffman Expires July 5, 2006 [Page 3] + +Internet-Draft IKEv2 January 2006 + + + Appendix D. Changes Between Internet Draft Versions . . . . . . 118 + D.1. Changes from IKEv2 to draft -00 . . . . . . . . . . . . . 118 + Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 119 + Intellectual Property and Copyright Statements . . . . . . . . . 119 + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Hoffman Expires July 5, 2006 [Page 4] + +Internet-Draft IKEv2 January 2006 + + +1. Introduction + + {{ An introduction to IKEv2.1 is given at the end of Section 1. It + is put there (instead of here) to preserve the section numbering of + the original IKEv2 document. }} + + IP Security (IPsec) provides confidentiality, data integrity, access + control, and data source authentication to IP datagrams. These + services are provided by maintaining shared state between the source + and the sink of an IP datagram. This state defines, among other + things, the specific services provided to the datagram, which + cryptographic algorithms will be used to provide the services, and + the keys used as input to the cryptographic algorithms. + + Establishing this shared state in a manual fashion does not scale + well. Therefore, a protocol to establish this state dynamically is + needed. This memo describes such a protocol -- the Internet Key + Exchange (IKE). This is version 2.1 of IKE. Version 1 of IKE was + defined in RFCs 2407 [DOI], 2408 [ISAKMP], and 2409 [IKEV1]. IKEv2 + was defined in [IKEV2]. This single document is intended to replace + all three of those RFCs. + + Definitions of the primitive terms in this document (such as Security + Association or SA) can be found in [IPSECARCH]. {{ Clarif-7.2 }} It + should be noted that parts of IKEv2 and IKEv2.1 rely on some of the + processing rules in [IPSECARCH], as described in various sections of + this document. + + IKE performs mutual authentication between two parties and + establishes an IKE security association (SA) that includes shared + secret information that can be used to efficiently establish SAs for + Encapsulating Security Payload (ESP) [ESP] and/or Authentication + Header (AH) [AH] and a set of cryptographic algorithms to be used by + the SAs to protect the traffic that they carry. In this document, + the term "suite" or "cryptographic suite" refers to a complete set of + algorithms used to protect an SA. An initiator proposes one or more + suites by listing supported algorithms that can be combined into + suites in a mix-and-match fashion. IKE can also negotiate use of IP + Compression (IPComp) [IPCOMP] in connection with an ESP and/or AH SA. + We call the IKE SA an "IKE_SA". The SAs for ESP and/or AH that get + set up through that IKE_SA we call "CHILD_SAs". + + All IKE communications consist of pairs of messages: a request and a + response. The pair is called an "exchange". We call the first + messages establishing an IKE_SA IKE_SA_INIT and IKE_AUTH exchanges + and subsequent IKE exchanges CREATE_CHILD_SA or INFORMATIONAL + exchanges. In the common case, there is a single IKE_SA_INIT + exchange and a single IKE_AUTH exchange (a total of four messages) to + + + +Hoffman Expires July 5, 2006 [Page 5] + +Internet-Draft IKEv2 January 2006 + + + establish the IKE_SA and the first CHILD_SA. In exceptional cases, + there may be more than one of each of these exchanges. In all cases, + all IKE_SA_INIT exchanges MUST complete before any other exchange + type, then all IKE_AUTH exchanges MUST complete, and following that + any number of CREATE_CHILD_SA and INFORMATIONAL exchanges may occur + in any order. In some scenarios, only a single CHILD_SA is needed + between the IPsec endpoints, and therefore there would be no + additional exchanges. Subsequent exchanges MAY be used to establish + additional CHILD_SAs between the same authenticated pair of endpoints + and to perform housekeeping functions. + + IKE message flow always consists of a request followed by a response. + It is the responsibility of the requester to ensure reliability. If + the response is not received within a timeout interval, the requester + needs to retransmit the request (or abandon the connection). + + The first request/response of an IKE session (IKE_SA_INIT) negotiates + security parameters for the IKE_SA, sends nonces, and sends Diffie- + Hellman values. + + The second request/response (IKE_AUTH) transmits identities, proves + knowledge of the secrets corresponding to the two identities, and + sets up an SA for the first (and often only) AH and/or ESP CHILD_SA. + + The types of subsequent exchanges are CREATE_CHILD_SA (which creates + a CHILD_SA) and INFORMATIONAL (which deletes an SA, reports error + conditions, or does other housekeeping). Every request requires a + response. An INFORMATIONAL request with no payloads (other than the + empty Encrypted payload required by the syntax) is commonly used as a + check for liveness. These subsequent exchanges cannot be used until + the initial exchanges have completed. + + In the description that follows, we assume that no errors occur. + Modifications to the flow should errors occur are described in + Section 2.21. + +1.1. Usage Scenarios + + IKE is expected to be used to negotiate ESP and/or AH SAs in a number + of different scenarios, each with its own special requirements. + + + + + + + + + + + +Hoffman Expires July 5, 2006 [Page 6] + +Internet-Draft IKEv2 January 2006 + + +1.1.1. Security Gateway to Security Gateway Tunnel + + +-+-+-+-+-+ +-+-+-+-+-+ + ! ! IPsec ! ! + Protected !Tunnel ! tunnel !Tunnel ! Protected + Subnet <-->!Endpoint !<---------->!Endpoint !<--> Subnet + ! ! ! ! + +-+-+-+-+-+ +-+-+-+-+-+ + + Figure 1: Security Gateway to Security Gateway Tunnel + + In this scenario, neither endpoint of the IP connection implements + IPsec, but network nodes between them protect traffic for part of the + way. Protection is transparent to the endpoints, and depends on + ordinary routing to send packets through the tunnel endpoints for + processing. Each endpoint would announce the set of addresses + "behind" it, and packets would be sent in tunnel mode where the inner + IP header would contain the IP addresses of the actual endpoints. + +1.1.2. Endpoint-to-Endpoint Transport + + +-+-+-+-+-+ +-+-+-+-+-+ + ! ! IPsec transport ! ! + !Protected! or tunnel mode SA !Protected! + !Endpoint !<---------------------------------------->!Endpoint ! + ! ! ! ! + +-+-+-+-+-+ +-+-+-+-+-+ + + Figure 2: Endpoint to Endpoint + + In this scenario, both endpoints of the IP connection implement + IPsec, as required of hosts in [IPSECARCH]. Transport mode will + commonly be used with no inner IP header. If there is an inner IP + header, the inner addresses will be the same as the outer addresses. + A single pair of addresses will be negotiated for packets to be + protected by this SA. These endpoints MAY implement application + layer access controls based on the IPsec authenticated identities of + the participants. This scenario enables the end-to-end security that + has been a guiding principle for the Internet since [ARCHPRINC], + [TRANSPARENCY], and a method of limiting the inherent problems with + complexity in networks noted by [ARCHGUIDEPHIL]. Although this + scenario may not be fully applicable to the IPv4 Internet, it has + been deployed successfully in specific scenarios within intranets + using IKEv1. It should be more broadly enabled during the transition + to IPv6 and with the adoption of IKEv2. + + It is possible in this scenario that one or both of the protected + endpoints will be behind a network address translation (NAT) node, in + + + +Hoffman Expires July 5, 2006 [Page 7] + +Internet-Draft IKEv2 January 2006 + + + which case the tunneled packets will have to be UDP encapsulated so + that port numbers in the UDP headers can be used to identify + individual endpoints "behind" the NAT (see Section 2.23). + +1.1.3. Endpoint to Security Gateway Tunnel + + +-+-+-+-+-+ +-+-+-+-+-+ + ! ! IPsec ! ! Protected + !Protected! tunnel !Tunnel ! Subnet + !Endpoint !<------------------------>!Endpoint !<--- and/or + ! ! ! ! Internet + +-+-+-+-+-+ +-+-+-+-+-+ + + Figure 3: Endpoint to Security Gateway Tunnel + + In this scenario, a protected endpoint (typically a portable roaming + computer) connects back to its corporate network through an IPsec- + protected tunnel. It might use this tunnel only to access + information on the corporate network, or it might tunnel all of its + traffic back through the corporate network in order to take advantage + of protection provided by a corporate firewall against Internet-based + attacks. In either case, the protected endpoint will want an IP + address associated with the security gateway so that packets returned + to it will go to the security gateway and be tunneled back. This IP + address may be static or may be dynamically allocated by the security + gateway. {{ Clarif-6.1 }} In support of the latter case, IKEv2 + includes a mechanism (namely, configuration payloads) for the + initiator to request an IP address owned by the security gateway for + use for the duration of its SA. + + In this scenario, packets will use tunnel mode. On each packet from + the protected endpoint, the outer IP header will contain the source + IP address associated with its current location (i.e., the address + that will get traffic routed to the endpoint directly), while the + inner IP header will contain the source IP address assigned by the + security gateway (i.e., the address that will get traffic routed to + the security gateway for forwarding to the endpoint). The outer + destination address will always be that of the security gateway, + while the inner destination address will be the ultimate destination + for the packet. + + In this scenario, it is possible that the protected endpoint will be + behind a NAT. In that case, the IP address as seen by the security + gateway will not be the same as the IP address sent by the protected + endpoint, and packets will have to be UDP encapsulated in order to be + routed properly. + + + + + +Hoffman Expires July 5, 2006 [Page 8] + +Internet-Draft IKEv2 January 2006 + + +1.1.4. Other Scenarios + + Other scenarios are possible, as are nested combinations of the + above. One notable example combines aspects of 1.1.1 and 1.1.3. A + subnet may make all external accesses through a remote security + gateway using an IPsec tunnel, where the addresses on the subnet are + routed to the security gateway by the rest of the Internet. An + example would be someone's home network being virtually on the + Internet with static IP addresses even though connectivity is + provided by an ISP that assigns a single dynamically assigned IP + address to the user's security gateway (where the static IP addresses + and an IPsec relay are provided by a third party located elsewhere). + +1.2. The Initial Exchanges + + Communication using IKE always begins with IKE_SA_INIT and IKE_AUTH + exchanges (known in IKEv1 as Phase 1). These initial exchanges + normally consist of four messages, though in some scenarios that + number can grow. All communications using IKE consist of request/ + response pairs. We'll describe the base exchange first, followed by + variations. The first pair of messages (IKE_SA_INIT) negotiate + cryptographic algorithms, exchange nonces, and do a Diffie-Hellman + exchange [DH]. + + The second pair of messages (IKE_AUTH) authenticate the previous + messages, exchange identities and certificates, and establish the + first CHILD_SA. Parts of these messages are encrypted and integrity + protected with keys established through the IKE_SA_INIT exchange, so + the identities are hidden from eavesdroppers and all fields in all + the messages are authenticated. + + In the following descriptions, the payloads contained in the message + are indicated by names as listed below. + + + + + + + + + + + + + + + + + + +Hoffman Expires July 5, 2006 [Page 9] + +Internet-Draft IKEv2 January 2006 + + + Notation Payload + ----------------------------------------- + AUTH Authentication + CERT Certificate + CERTREQ Certificate Request + CP Configuration + D Delete + E Encrypted + EAP Extensible Authentication + HDR IKE Header + IDi Identification - Initiator + IDr Identification - Responder + KE Key Exchange + Ni, Nr Nonce + N Notify + SA Security Association + TSi Traffic Selector - Initiator + TSr Traffic Selector - Responder + V Vendor ID + + The details of the contents of each payload are described in section + 3. Payloads that may optionally appear will be shown in brackets, + such as [CERTREQ], indicate that optionally a certificate request + payload can be included. + + {{ Clarif-7.10 }} Many payloads contain fields marked as "RESERVED" + Some payloads in IKEv2 (and historically in IKEv1) are not aligned to + 4-byte boundaries. + + The initial exchanges are as follows: + + Initiator Responder + ------------------------------------------------------------------- + HDR, SAi1, KEi, Ni --> + + HDR contains the Security Parameter Indexes (SPIs), version numbers, + and flags of various sorts. The SAi1 payload states the + cryptographic algorithms the initiator supports for the IKE_SA. The + KE payload sends the initiator's Diffie-Hellman value. Ni is the + initiator's nonce. + + <-- HDR, SAr1, KEr, Nr, [CERTREQ] + + The responder chooses a cryptographic suite from the initiator's + offered choices and expresses that choice in the SAr1 payload, + completes the Diffie-Hellman exchange with the KEr payload, and sends + its nonce in the Nr payload. + + + + +Hoffman Expires July 5, 2006 [Page 10] + +Internet-Draft IKEv2 January 2006 + + + At this point in the negotiation, each party can generate SKEYSEED, + from which all keys are derived for that IKE_SA. All but the headers + of all the messages that follow are encrypted and integrity + protected. The keys used for the encryption and integrity protection + are derived from SKEYSEED and are known as SK_e (encryption) and SK_a + (authentication, a.k.a. integrity protection). A separate SK_e and + SK_a is computed for each direction. In addition to the keys SK_e + and SK_a derived from the DH value for protection of the IKE_SA, + another quantity SK_d is derived and used for derivation of further + keying material for CHILD_SAs. The notation SK { ... } indicates + that these payloads are encrypted and integrity protected using that + direction's SK_e and SK_a. + + HDR, SK {IDi, [CERT,] [CERTREQ,] + [IDr,] AUTH, SAi2, + TSi, TSr} --> + + The initiator asserts its identity with the IDi payload, proves + knowledge of the secret corresponding to IDi and integrity protects + the contents of the first message using the AUTH payload (see + Section 2.15). It might also send its certificate(s) in CERT + payload(s) and a list of its trust anchors in CERTREQ payload(s). If + any CERT payloads are included, the first certificate provided MUST + contain the public key used to verify the AUTH field. The optional + payload IDr enables the initiator to specify which of the responder's + identities it wants to talk to. This is useful when the machine on + which the responder is running is hosting multiple identities at the + same IP address. The initiator begins negotiation of a CHILD_SA + using the SAi2 payload. The final fields (starting with SAi2) are + described in the description of the CREATE_CHILD_SA exchange. + + <-- HDR, SK {IDr, [CERT,] AUTH, + SAr2, TSi, TSr} + + The responder asserts its identity with the IDr payload, optionally + sends one or more certificates (again with the certificate containing + the public key used to verify AUTH listed first), authenticates its + identity and protects the integrity of the second message with the + AUTH payload, and completes negotiation of a CHILD_SA with the + additional fields described below in the CREATE_CHILD_SA exchange. + + The recipients of messages 3 and 4 MUST verify that all signatures + and MACs are computed correctly and that the names in the ID payloads + correspond to the keys used to generate the AUTH payload. + + {{ Clarif-4.2}} If creating the CHILD_SA during the IKE_AUTH exchange + fails for some reason, the IKE_SA is still created as usual. The + list of responses in the IKE_AUTH exchange that do not prevent an + + + +Hoffman Expires July 5, 2006 [Page 11] + +Internet-Draft IKEv2 January 2006 + + + IKE_SA from being set up include at least the following: + NO_PROPOSAL_CHOSEN, TS_UNACCEPTABLE, SINGLE_PAIR_REQUIRED, + INTERNAL_ADDRESS_FAILURE, and FAILED_CP_REQUIRED. + + {{ Clarif-4.3 }} Note that IKE_AUTH messages do not contain KEi/KEr + or Ni/Nr payloads. Thus, the SA payload in IKE_AUTH exchange cannot + contain Transform Type 4 (Diffie-Hellman Group) with any other value + than NONE. Implementations MUST leave the transform out entirely in + this case. + +1.3. The CREATE_CHILD_SA Exchange + + {{ This is a heavy rewrite of most of this section. The major + organization changes are described in Clarif-4.1 and Clarif-5.1. }} + + The CREATE_CHILD_SA exchange is used to create new CHILD_SAs and to + rekey both IKE_SAs and CHILD_SAs. This exchange consists of a single + request/response pair, and some of its function was referred to as a + phase 2 exchange in IKEv1. It MAY be initiated by either end of the + IKE_SA after the initial exchanges are completed. + + All messages following the initial exchange are cryptographically + protected using the cryptographic algorithms and keys negotiated in + the first two messages of the IKE exchange. These subsequent + messages use the syntax of the Encrypted Payload described in + Section 3.14. All subsequent messages included an Encrypted Payload, + even if they are referred to in the text as "empty". For both + messages in the CREATE_CHILD_SA, the message following the header is + encrypted and the message including the header is integrity protected + using the cryptographic algorithms negotiated for the IKE_SA. + + The CREATE_CHILD_SA is used for rekeying IKE_SAs and CHILD_SAs. This + section describes the first part of rekeying, the creation of new + SAs; Section 2.8 covers the mechanics of rekeying, including moving + traffic from old to new SAs and the deletion of the old SAs. The two + sections must be read together to understand the entire process of + rekeying. + + Either endpoint may initiate a CREATE_CHILD_SA exchange, so in this + section the term initiator refers to the endpoint initiating this + exchange. An implementation MAY refuse all CREATE_CHILD_SA requests + within an IKE_SA. + + The CREATE_CHILD_SA request MAY optionally contain a KE payload for + an additional Diffie-Hellman exchange to enable stronger guarantees + of forward secrecy for the CHILD_SA. The keying material for the + CHILD_SA is a function of SK_d established during the establishment + of the IKE_SA, the nonces exchanged during the CREATE_CHILD_SA + + + +Hoffman Expires July 5, 2006 [Page 12] + +Internet-Draft IKEv2 January 2006 + + + exchange, and the Diffie-Hellman value (if KE payloads are included + in the CREATE_CHILD_SA exchange). + + If a CREATE_CHILD_SA exchange includes a KEi payload, at least one of + the SA offers MUST include the Diffie-Hellman group of the KEi. The + Diffie-Hellman group of the KEi MUST be an element of the group the + initiator expects the responder to accept (additional Diffie-Hellman + groups can be proposed). If the responder rejects the Diffie-Hellman + group of the KEi payload, the responder MUST reject the request and + indicate its preferred Diffie-Hellman group in the INVALID_KE_PAYLOAD + Notification payload. In the case of such a rejection, the + CREATE_CHILD_SA exchange fails, and the initiator will probably retry + the exchange with a Diffie-Hellman proposal and KEi in the group that + the responder gave in the INVALID_KE_PAYLOAD. + +1.3.1. Creating New CHILD_SAs with the CREATE_CHILD_SA Exchange + + A CHILD_SA may be created by sending a CREATE_CHILD_SA request. The + CREATE_CHILD_SA request for creating a new CHILD_SA is: + + Initiator Responder + ------------------------------------------------------------------- + HDR, SK {SA, Ni, [KEi], + TSi, TSr} --> + + The initiator sends SA offer(s) in the SA payload, a nonce in the Ni + payload, optionally a Diffie-Hellman value in the KEi payload, and + the proposed traffic selectors for the proposed CHILD_SA in the TSi + and TSr payloads. + + The CREATE_CHILD_SA response for creating a new CHILD_SA is: + + <-- HDR, SK {SA, Nr, [KEr], + TSi, TSr} + + The responder replies (using the same Message ID to respond) with the + accepted offer in an SA payload, and a Diffie-Hellman value in the + KEr payload if KEi was included in the request and the selected + cryptographic suite includes that group. + + The traffic selectors for traffic to be sent on that SA are specified + in the TS payloads in the response, which may be a subset of what the + initiator of the CHILD_SA proposed. + +1.3.2. Rekeying IKE_SAs with the CREATE_CHILD_SA Exchange + + The CREATE_CHILD_SA request for rekeying an IKE_SA is: + + + + +Hoffman Expires July 5, 2006 [Page 13] + +Internet-Draft IKEv2 January 2006 + + + Initiator Responder + ------------------------------------------------------------------- + HDR, SK {SA, Ni, KEi} --> + + The initiator sends SA offer(s) in the SA payload, a nonce in the Ni + payload, and a Diffie-Hellman value in the KEi payload. New + initiator and responder SPIs are supplied in the SPI fields. + + The CREATE_CHILD_SA response for rekeying an IKE_SA is: + + <-- HDR, SK {SA, Nr, KEr} + + The responder replies (using the same Message ID to respond) with the + accepted offer in an SA payload, and a Diffie-Hellman value in the + KEr payload if the selected cryptographic suite includes that group. + + The new IKE_SA has its message counters set to 0, regardless of what + they were in the earlier IKE_SA. The window size starts at 1 for any + new IKE_SA. + + KEi and KEr are required for rekeying an IKE_SA. + +1.3.3. Rekeying CHILD_SAs with the CREATE_CHILD_SA Exchange + + The CREATE_CHILD_SA request for rekeying a CHILD_SA is: + + Initiator Responder + ------------------------------------------------------------------- + HDR, SK {N, SA, Ni, [KEi], + TSi, TSr} --> + + The initiator sends SA offer(s) in the SA payload, a nonce in the Ni + payload, optionally a Diffie-Hellman value in the KEi payload, and + the proposed traffic selectors for the proposed CHILD_SA in the TSi + and TSr payloads. When rekeying an existing CHILD_SA, the leading N + payload of type REKEY_SA MUST be included and MUST give the SPI (as + they would be expected in the headers of inbound packets) of the SAs + being rekeyed. + + The CREATE_CHILD_SA response for rekeying a CHILD_SA is: + + <-- HDR, SK {SA, Nr, [KEr], + Si, TSr} + + The responder replies (using the same Message ID to respond) with the + accepted offer in an SA payload, and a Diffie-Hellman value in the + KEr payload if KEi was included in the request and the selected + cryptographic suite includes that group. + + + +Hoffman Expires July 5, 2006 [Page 14] + +Internet-Draft IKEv2 January 2006 + + + The traffic selectors for traffic to be sent on that SA are specified + in the TS payloads in the response, which may be a subset of what the + initiator of the CHILD_SA proposed. + +1.4. The INFORMATIONAL Exchange + + At various points during the operation of an IKE_SA, peers may desire + to convey control messages to each other regarding errors or + notifications of certain events. To accomplish this, IKE defines an + INFORMATIONAL exchange. INFORMATIONAL exchanges MUST ONLY occur + after the initial exchanges and are cryptographically protected with + the negotiated keys. + + Control messages that pertain to an IKE_SA MUST be sent under that + IKE_SA. Control messages that pertain to CHILD_SAs MUST be sent + under the protection of the IKE_SA which generated them (or its + successor if the IKE_SA was replaced for the purpose of rekeying). + + Messages in an INFORMATIONAL exchange contain zero or more + Notification, Delete, and Configuration payloads. The Recipient of + an INFORMATIONAL exchange request MUST send some response (else the + Sender will assume the message was lost in the network and will + retransmit it). That response MAY be a message with no payloads. + The request message in an INFORMATIONAL exchange MAY also contain no + payloads. This is the expected way an endpoint can ask the other + endpoint to verify that it is alive. + + {{ Clarif-5.6 }} ESP and AH SAs always exist in pairs, with one SA in + each direction. When an SA is closed, both members of the pair MUST + be closed (that is, deleted). When SAs are nested, as when data (and + IP headers if in tunnel mode) are encapsulated first with IPComp, + then with ESP, and finally with AH between the same pair of + endpoints, all of the SAs MUST be deleted together. Each endpoint + MUST close its incoming SAs and allow the other endpoint to close the + other SA in each pair. To delete an SA, an INFORMATIONAL exchange + with one or more delete payloads is sent listing the SPIs (as they + would be expected in the headers of inbound packets) of the SAs to be + deleted. The recipient MUST close the designated SAs. {{ Clarif-5.7 + }} Note that you never send delete payloads for the two sides of an + SA in a single message. If you have many SAs to delete at the same + time (such as for nested SAs), you include delete payloads for in + inbound half of each SA in your Informational exchange. + + Normally, the reply in the INFORMATIONAL exchange will contain delete + payloads for the paired SAs going in the other direction. There is + one exception. If by chance both ends of a set of SAs independently + decide to close them, each may send a delete payload and the two + requests may cross in the network. If a node receives a delete + + + +Hoffman Expires July 5, 2006 [Page 15] + +Internet-Draft IKEv2 January 2006 + + + request for SAs for which it has already issued a delete request, it + MUST delete the outgoing SAs while processing the request and the + incoming SAs while processing the response. In that case, the + responses MUST NOT include delete payloads for the deleted SAs, since + that would result in duplicate deletion and could in theory delete + the wrong SA. + + {{ Demoted the SHOULD }} Half-closed connections are anomalous and, + and a node with auditing capability will probably audit their + existence if they persist. Note that this specification nowhere + specifies time periods, so it is up to individual endpoints to decide + how long to wait. A node MAY refuse to accept incoming data on half- + closed connections but MUST NOT unilaterally close them and reuse the + SPIs. If connection state becomes sufficiently messed up, a node MAY + close the IKE_SA; doing so will implicitly close all SAs negotiated + under it. It can then rebuild the SAs it needs on a clean base under + a new IKE_SA. {{ Clarif-5.8 }} The response to a request that deletes + the IKE_SA is an empty Informational response. + + The INFORMATIONAL exchange is defined as: + + Initiator Responder + ------------------------------------------------------------------- + HDR, SK {[N,] [D,] + [CP,] ...} --> + <-- HDR, SK {[N,] [D,] + [CP], ...} + + The processing of an INFORMATIONAL exchange is determined by its + component payloads. + +1.5. Informational Messages outside of an IKE_SA + + If an encrypted IKE packet arrives on port 500 or 4500 with an + unrecognized SPI, it could be because the receiving node has recently + crashed and lost state or because of some other system malfunction or + attack. If the receiving node has an active IKE_SA to the IP address + from whence the packet came, it MAY send a notification of the + wayward packet over that IKE_SA in an INFORMATIONAL exchange. If it + does not have such an IKE_SA, it MAY send an Informational message + without cryptographic protection to the source IP address. Such a + message is not part of an informational exchange, and the receiving + node MUST NOT respond to it. Doing so could cause a message loop. + + {{ Clarif-7.7 }} There are two cases when such a one-way notification + is sent: INVALID_IKE_SPI and INVALID_SPI. These notifications are + sent outside of an IKE_SA. Note that such notifications are + explicitly not Informational exchanges; these are one-way messages + + + +Hoffman Expires July 5, 2006 [Page 16] + +Internet-Draft IKEv2 January 2006 + + + that must not be responded to. In case of INVALID_IKE_SPI, the + message sent is a response message, and thus it is sent to the IP + address and port from whence it came with the same IKE SPIs and the + Message ID copied. In case of INVALID_SPI, however, there are no IKE + SPI values that would be meaningful to the recipient of such a + notification. Using zero values or random values are both + acceptable. + +1.6. Requirements Terminology + + Keywords "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT" and + "MAY" that appear in this document are to be interpreted as described + in [MUSTSHOULD]. + + The term "Expert Review" is to be interpreted as defined in + [IANACONS]. + +1.7. Introduction to IKEv2.1 + + IKEv2.1 is very similar to IKEv2. Most of the differences between + this document at [IKEV2] are clarifications, mostly based on + [Clarif]. The changes listed in that document were discussed in the + IPsec Working Group and, after the Working Group was disbanded, on + the IPsec mailing list. That document contains detailed explanations + of areas that were unclear in IKEv2, and is thus useful to + implementers of IKEv2 and IKEv2.1. + + In the body of this document, notes that are enclosed in double curly + braces {{ such as this }} point out changes from IKEv2. Changes that + come from [Clarif] are marked with the section from that document, + such as "{{ Clarif-2.10 }}". + + This document also make the figures and references a bit more regular + than in IKEv2. + + IKEv2 developers have noted that the SHOULD-level requirements are + often unclear in that they don't say when it is OK to not obey the + requirements. They also have noted that there are MUST-level + requirements that are not related to interoperability. This document + has more explanation of some of these SHOULD-level requirements, and + some SHOULD-level and MUST-level requirements have been changed to + better match the definitions in [MUSTSHOULD]. All non-capitalized + uses of the words SHOULD and MUST now mean their normal English + sense, not the interoperability sense of [MUSTSHOULD]. + + IKEv2 (and IKEv1) developers have noted that there is a great deal of + material in the tables of codes in Section 3.10. This leads to + implementers not having all the needed information in the main body + + + +Hoffman Expires July 5, 2006 [Page 17] + +Internet-Draft IKEv2 January 2006 + + + of the docment. A later version of this document may move much of + the material from those tables into the associated parts of the main + body of the document. + + A later version of this document will probably have all the {{ }} + comments removed from the body of the document and instead appear in + an appendix. + + +2. IKE Protocol Details and Variations + + IKE normally listens and sends on UDP port 500, though IKE messages + may also be received on UDP port 4500 with a slightly different + format (see Section 2.23). Since UDP is a datagram (unreliable) + protocol, IKE includes in its definition recovery from transmission + errors, including packet loss, packet replay, and packet forgery. + IKE is designed to function so long as (1) at least one of a series + of retransmitted packets reaches its destination before timing out; + and (2) the channel is not so full of forged and replayed packets so + as to exhaust the network or CPU capacities of either endpoint. Even + in the absence of those minimum performance requirements, IKE is + designed to fail cleanly (as though the network were broken). + + Although IKEv2 messages are intended to be short, they contain + structures with no hard upper bound on size (in particular, X.509 + certificates), and IKEv2 itself does not have a mechanism for + fragmenting large messages. IP defines a mechanism for fragmentation + of oversize UDP messages, but implementations vary in the maximum + message size supported. Furthermore, use of IP fragmentation opens + an implementation to denial of service attacks [DOSUDPPROT]. + Finally, some NAT and/or firewall implementations may block IP + fragments. + + All IKEv2 implementations MUST be able to send, receive, and process + IKE messages that are up to 1280 bytes long, and they SHOULD be able + to send, receive, and process messages that are up to 3000 bytes + long. {{ Demoted the SHOULD }} IKEv2 implementations need to be aware + of the maximum UDP message size supported and MAY shorten messages by + leaving out some certificates or cryptographic suite proposals if + that will keep messages below the maximum. Use of the "Hash and URL" + formats rather than including certificates in exchanges where + possible can avoid most problems. {{ Demoted the SHOULD }} + Implementations and configuration need to keep in mind, however, that + if the URL lookups are possible only after the IPsec SA is + established, recursion issues could prevent this technique from + working. + + + + + +Hoffman Expires July 5, 2006 [Page 18] + +Internet-Draft IKEv2 January 2006 + + +2.1. Use of Retransmission Timers + + All messages in IKE exist in pairs: a request and a response. The + setup of an IKE_SA normally consists of two request/response pairs. + Once the IKE_SA is set up, either end of the security association may + initiate requests at any time, and there can be many requests and + responses "in flight" at any given moment. But each message is + labeled as either a request or a response, and for each request/ + response pair one end of the security association is the initiator + and the other is the responder. + + For every pair of IKE messages, the initiator is responsible for + retransmission in the event of a timeout. The responder MUST never + retransmit a response unless it receives a retransmission of the + request. In that event, the responder MUST ignore the retransmitted + request except insofar as it triggers a retransmission of the + response. The initiator MUST remember each request until it receives + the corresponding response. The responder MUST remember each + response until it receives a request whose sequence number is larger + than the sequence number in the response plus its window size (see + Section 2.3). + + IKE is a reliable protocol, in the sense that the initiator MUST + retransmit a request until either it receives a corresponding reply + OR it deems the IKE security association to have failed and it + discards all state associated with the IKE_SA and any CHILD_SAs + negotiated using that IKE_SA. + + {{ Clarif-7.5 }} All packets sent on port 4500 MUST begin with the + prefix of four zeros; otherwise, the receiver won't know how to + handle them. + +2.2. Use of Sequence Numbers for Message ID + + Every IKE message contains a Message ID as part of its fixed header. + This Message ID is used to match up requests and responses, and to + identify retransmissions of messages. + + The Message ID is a 32-bit quantity, which is zero for the first IKE + request in each direction. {{ Clarif-3.11 }} When the IKE_AUTH + exchange does not use EAP, the IKE_SA initial setup messages will + always be numbered 0 and 1. When EAP is used, each pair of messages + have their message numbers incremented; the first pair of AUTH + messages will have an ID of 1, the second will be 2, and so on. + + Each endpoint in the IKE Security Association maintains two "current" + Message IDs: the next one to be used for a request it initiates and + the next one it expects to see in a request from the other end. + + + +Hoffman Expires July 5, 2006 [Page 19] + +Internet-Draft IKEv2 January 2006 + + + These counters increment as requests are generated and received. + Responses always contain the same message ID as the corresponding + request. That means that after the initial exchange, each integer n + may appear as the message ID in four distinct messages: the nth + request from the original IKE initiator, the corresponding response, + the nth request from the original IKE responder, and the + corresponding response. If the two ends make very different numbers + of requests, the Message IDs in the two directions can be very + different. There is no ambiguity in the messages, however, because + the (I)nitiator and (R)esponse bits in the message header specify + which of the four messages a particular one is. + + {{ Clarif-2.2 }} The Message ID for IKE_SA_INIT messages is always + zero, including for retries of the message due to responses such as + COOKIE and INVALID_KE_PAYLOAD. + + Note that Message IDs are cryptographically protected and provide + protection against message replays. In the unlikely event that + Message IDs grow too large to fit in 32 bits, the IKE_SA MUST be + closed. Rekeying an IKE_SA resets the sequence numbers. + + {{ Clarif-2.3 }} When a responder receives an IKE_SA_INIT request, it + has to determine whether the packet is a retransmission belonging to + an existing "half-open" IKE_SA (in which case the responder + retransmits the same response), or a new request (in which case the + responder creates a new IKE_SA and sends a fresh response). It is + not sufficient to use the initiator's SPI and/or IP address to + differentiate between the two cases because two different peers + behind a single NAT could choose the same initiator SPI. Instead, a + robust responder will do the IKE_SA lookup using the whole packet, + its hash, or the Ni payload. + +2.3. Window Size for Overlapping Requests + + In order to maximize IKE throughput, an IKE endpoint MAY issue + multiple requests before getting a response to any of them if the + other endpoint has indicated its ability to handle such requests. + For simplicity, an IKE implementation MAY choose to process requests + strictly in order and/or wait for a response to one request before + issuing another. Certain rules must be followed to ensure + interoperability between implementations using different strategies. + + After an IKE_SA is set up, either end can initiate one or more + requests. These requests may pass one another over the network. An + IKE endpoint MUST be prepared to accept and process a request while + it has a request outstanding in order to avoid a deadlock in this + situation. {{ Changed the SHOULD to MUST }} An IKE endpoint MUST be + prepared to accept and process multiple requests while it has a + + + +Hoffman Expires July 5, 2006 [Page 20] + +Internet-Draft IKEv2 January 2006 + + + request outstanding. + + An IKE endpoint MUST wait for a response to each of its messages + before sending a subsequent message unless it has received a + SET_WINDOW_SIZE Notify message from its peer informing it that the + peer is prepared to maintain state for multiple outstanding messages + in order to allow greater throughput. + + An IKE endpoint MUST NOT exceed the peer's stated window size for + transmitted IKE requests. In other words, if the responder stated + its window size is N, then when the initiator needs to make a request + X, it MUST wait until it has received responses to all requests up + through request X-N. An IKE endpoint MUST keep a copy of (or be able + to regenerate exactly) each request it has sent until it receives the + corresponding response. An IKE endpoint MUST keep a copy of (or be + able to regenerate exactly) the number of previous responses equal to + its declared window size in case its response was lost and the + initiator requests its retransmission by retransmitting the request. + + An IKE endpoint supporting a window size greater than one should be + capable of processing incoming requests out of order to maximize + performance in the event of network failures or packet reordering. + + {{ Clarif-7.3 }} The window size is assumed to be a (possibly + configurable) property of a particular implementation, and is not + related to congestion control (unlike the window size in TCP, for + example). In particular, it is not defined what the responder should + do when it receives a SET_WINDOW_SIZE notification containing a + smaller value than is currently in effect. Thus, there is currently + no way to reduce the window size of an existing IKE_SA; you can only + increase it. When rekeying an IKE_SA, the new IKE_SA starts with + window size 1 until it is explicitly increased by sending a new + SET_WINDOW_SIZE notification. + +2.4. State Synchronization and Connection Timeouts + + An IKE endpoint is allowed to forget all of its state associated with + an IKE_SA and the collection of corresponding CHILD_SAs at any time. + This is the anticipated behavior in the event of an endpoint crash + and restart. It is important when an endpoint either fails or + reinitializes its state that the other endpoint detect those + conditions and not continue to waste network bandwidth by sending + packets over discarded SAs and having them fall into a black hole. + + Since IKE is designed to operate in spite of Denial of Service (DoS) + attacks from the network, an endpoint MUST NOT conclude that the + other endpoint has failed based on any routing information (e.g., + ICMP messages) or IKE messages that arrive without cryptographic + + + +Hoffman Expires July 5, 2006 [Page 21] + +Internet-Draft IKEv2 January 2006 + + + protection (e.g., Notify messages complaining about unknown SPIs). + An endpoint MUST conclude that the other endpoint has failed only + when repeated attempts to contact it have gone unanswered for a + timeout period or when a cryptographically protected INITIAL_CONTACT + notification is received on a different IKE_SA to the same + authenticated identity. {{ Demoted the SHOULD }} An endpoint should + suspect that the other endpoint has failed based on routing + information and initiate a request to see whether the other endpoint + is alive. To check whether the other side is alive, IKE specifies an + empty INFORMATIONAL message that (like all IKE requests) requires an + acknowledgement (note that within the context of an IKE_SA, an + "empty" message consists of an IKE header followed by an Encrypted + payload that contains no payloads). If a cryptographically protected + message has been received from the other side recently, unprotected + notifications MAY be ignored. Implementations MUST limit the rate at + which they take actions based on unprotected messages. + + Numbers of retries and lengths of timeouts are not covered in this + specification because they do not affect interoperability. It is + suggested that messages be retransmitted at least a dozen times over + a period of at least several minutes before giving up on an SA, but + different environments may require different rules. To be a good + network citizen, retranmission times MUST increase exponentially to + avoid flooding the network and making an existing congestion + situation worse. If there has only been outgoing traffic on all of + the SAs associated with an IKE_SA, it is essential to confirm + liveness of the other endpoint to avoid black holes. If no + cryptographically protected messages have been received on an IKE_SA + or any of its CHILD_SAs recently, the system needs to perform a + liveness check in order to prevent sending messages to a dead peer. + Receipt of a fresh cryptographically protected message on an IKE_SA + or any of its CHILD_SAs ensures liveness of the IKE_SA and all of its + CHILD_SAs. Note that this places requirements on the failure modes + of an IKE endpoint. An implementation MUST NOT continue sending on + any SA if some failure prevents it from receiving on all of the + associated SAs. If CHILD_SAs can fail independently from one another + without the associated IKE_SA being able to send a delete message, + then they MUST be negotiated by separate IKE_SAs. + + There is a Denial of Service attack on the initiator of an IKE_SA + that can be avoided if the initiator takes the proper care. Since + the first two messages of an SA setup are not cryptographically + protected, an attacker could respond to the initiator's message + before the genuine responder and poison the connection setup attempt. + To prevent this, the initiator MAY be willing to accept multiple + responses to its first message, treat each as potentially legitimate, + respond to it, and then discard all the invalid half-open connections + when it receives a valid cryptographically protected response to any + + + +Hoffman Expires July 5, 2006 [Page 22] + +Internet-Draft IKEv2 January 2006 + + + one of its requests. Once a cryptographically valid response is + received, all subsequent responses should be ignored whether or not + they are cryptographically valid. + + Note that with these rules, there is no reason to negotiate and agree + upon an SA lifetime. If IKE presumes the partner is dead, based on + repeated lack of acknowledgement to an IKE message, then the IKE SA + and all CHILD_SAs set up through that IKE_SA are deleted. + + An IKE endpoint may at any time delete inactive CHILD_SAs to recover + resources used to hold their state. If an IKE endpoint chooses to + delete CHILD_SAs, it MUST send Delete payloads to the other end + notifying it of the deletion. It MAY similarly time out the IKE_SA. + {{ Clarified the SHOULD }} Closing the IKE_SA implicitly closes all + associated CHILD_SAs. In this case, an IKE endpoint SHOULD send a + Delete payload indicating that it has closed the IKE_SA unless the + other endpoint is no longer responding. + +2.5. Version Numbers and Forward Compatibility + + {{ The version number is changed in the following paragraph, and the + discussion of handling of multiple versions is also changed + throughout the section. }} + + This document describes version 2.1 of IKE, meaning the major version + number is 2 and the minor version number is 1. It is likely that + some implementations will want to support version 1.0 and version 2.0 + and version 2.1, and in the future, other versions. + + The major version number should be incremented only if the packet + formats or required actions have changed so dramatically that an + older version node would not be able to interoperate with a newer + version node if it simply ignored the fields it did not understand + and took the actions specified in the older specification. The minor + version number indicates new capabilities, and MUST be ignored by a + node with a smaller minor version number, but used for informational + purposes by the node with the larger minor version number. For + example, it might indicate the ability to process a newly defined + notification message. The node with the larger minor version number + would simply note that its correspondent would not be able to + understand that message and therefore would not send it. + + In the discussion of clarifications to IKEv2, it became clear that + there was a need for additional "MUST" and "SHOULD" requirements. + Some of those changes are reflected in IKEv2.1. Thus, the node with + the higher version number may also need to note that its + correspondent may not be following the same required actions, which + could affect interoperability. + + + +Hoffman Expires July 5, 2006 [Page 23] + +Internet-Draft IKEv2 January 2006 + + + {{ Promoted the SHOULD }} If an endpoint receives a message with a + higher major version number, it MUST drop the message and MUST send + an unauthenticated notification message containing the highest + version number it supports. If an endpoint supports major version n, + and major version m, it MUST support all versions between n and m. + If it receives a message with a major version that it supports, it + MUST respond with that version number. In order to prevent two nodes + from being tricked into corresponding with a lower major version + number than the maximum that they both support, IKE has a flag that + indicates that the node is capable of speaking a higher major version + number. + + Thus, the major version number in the IKE header indicates the + version number of the message, not the highest version number that + the transmitter supports. If the initiator is capable of speaking + versions n, n+1, and n+2, and the responder is capable of speaking + versions n and n+1, then they will negotiate speaking n+1, where the + initiator will set the flag indicating its ability to speak a higher + version. If they mistakenly (perhaps through an active attacker + sending error messages) negotiate to version n, then both will notice + that the other side can support a higher version number, and they + MUST break the connection and reconnect using version n+1. + + Note that IKEv1 does not follow these rules, because there is no way + in v1 of noting that you are capable of speaking a higher version + number. So an active attacker can trick two v2-capable nodes into + speaking v1. {{ Demoted the SHOULD }} When a v2-capable node + negotiates down to v1, it should note that fact in its logs. + + Also for forward compatibility, all fields marked RESERVED MUST be + set to zero by an implementation running version 2.0 or later, and + their content MUST be ignored by an implementation running version + 2.0 or later ("Be conservative in what you send and liberal in what + you receive"). In this way, future versions of the protocol can use + those fields in a way that is guaranteed to be ignored by + implementations that do not understand them. Similarly, payload + types that are not defined are reserved for future use; + implementations of a version where they are undefined MUST skip over + those payloads and ignore their contents. + + IKEv2 adds a "critical" flag to each payload header for further + flexibility for forward compatibility. If the critical flag is set + and the payload type is unrecognized, the message MUST be rejected + and the response to the IKE request containing that payload MUST + include a Notify payload UNSUPPORTED_CRITICAL_PAYLOAD, indicating an + unsupported critical payload was included. If the critical flag is + not set and the payload type is unsupported, that payload MUST be + ignored. + + + +Hoffman Expires July 5, 2006 [Page 24] + +Internet-Draft IKEv2 January 2006 + + + {{ Demoted the SHOULD }}Although new payload types may be added in + the future and may appear interleaved with the fields defined in this + specification, implementations MUST send the payloads defined in this + specification in the order shown in the figures in Section 2 and + implementations MAY reject as invalid a message with those payloads + in any other order. + +2.6. Cookies + + The term "cookies" originates with Karn and Simpson [PHOTURIS] in + Photuris, an early proposal for key management with IPsec, and it has + persisted. The Internet Security Association and Key Management + Protocol (ISAKMP) [ISAKMP] fixed message header includes two eight- + octet fields titled "cookies", and that syntax is used by both IKEv1 + and IKEv2 though in IKEv2 they are referred to as the IKE SPI and + there is a new separate field in a Notify payload holding the cookie. + The initial two eight-octet fields in the header are used as a + connection identifier at the beginning of IKE packets. {{ Promoted + the SHOULD }} Each endpoint chooses one of the two SPIs and MUST + choose them so as to be unique identifiers of an IKE_SA. An SPI + value of zero is special and indicates that the remote SPI value is + not yet known by the sender. + + Unlike ESP and AH where only the recipient's SPI appears in the + header of a message, in IKE the sender's SPI is also sent in every + message. Since the SPI chosen by the original initiator of the + IKE_SA is always sent first, an endpoint with multiple IKE_SAs open + that wants to find the appropriate IKE_SA using the SPI it assigned + must look at the I(nitiator) Flag bit in the header to determine + whether it assigned the first or the second eight octets. + + In the first message of an initial IKE exchange, the initiator will + not know the responder's SPI value and will therefore set that field + to zero. + + An expected attack against IKE is state and CPU exhaustion, where the + target is flooded with session initiation requests from forged IP + addresses. This attack can be made less effective if an + implementation of a responder uses minimal CPU and commits no state + to an SA until it knows the initiator can receive packets at the + address from which it claims to be sending them. To accomplish this, + a responder SHOULD -- when it detects a large number of half-open + IKE_SAs -- reject initial IKE messages unless they contain a Notify + payload of type COOKIE. {{ Clarified the SHOULD }} If the responder + wants to set up an SA, it SHOULD instead send an unprotected IKE + message as a response and include COOKIE Notify payload with the + cookie data to be returned. Initiators who receive such responses + MUST retry the IKE_SA_INIT with a Notify payload of type COOKIE + + + +Hoffman Expires July 5, 2006 [Page 25] + +Internet-Draft IKEv2 January 2006 + + + containing the responder supplied cookie data as the first payload + and all other payloads unchanged. The initial exchange will then be + as follows: + + Initiator Responder + ------------------------------------------------------------------- + HDR(A,0), SAi1, KEi, Ni --> + <-- HDR(A,0), N(COOKIE) + HDR(A,0), N(COOKIE), SAi1, + KEi, Ni --> + <-- HDR(A,B), SAr1, KEr, + Nr, [CERTREQ] + HDR(A,B), SK {IDi, [CERT,] + [CERTREQ,] [IDr,] AUTH, + SAi2, TSi, TSr} --> + <-- HDR(A,B), SK {IDr, [CERT,] + AUTH, SAr2, TSi, TSr} + + The first two messages do not affect any initiator or responder state + except for communicating the cookie. In particular, the message + sequence numbers in the first four messages will all be zero and the + message sequence numbers in the last two messages will be one. 'A' + is the SPI assigned by the initiator, while 'B' is the SPI assigned + by the responder. + + {{ Clarif-2.1 }} Because the responder's SPI identifies security- + related state held by the responder, and in this case no state is + created, the responder sends a zero value for the responder's SPI. + + {{ Demoted the SHOULD }} An IKE implementation should implement its + responder cookie generation in such a way as to not require any saved + state to recognize its valid cookie when the second IKE_SA_INIT + message arrives. The exact algorithms and syntax they use to + generate cookies do not affect interoperability and hence are not + specified here. The following is an example of how an endpoint could + use cookies to implement limited DOS protection. + + A good way to do this is to set the responder cookie to be: + + Cookie = <VersionIDofSecret> | Hash(Ni | IPi | SPIi | <secret>) + + where <secret> is a randomly generated secret known only to the + responder and periodically changed and | indicates concatenation. + <VersionIDofSecret> should be changed whenever <secret> is + regenerated. The cookie can be recomputed when the IKE_SA_INIT + arrives the second time and compared to the cookie in the received + message. If it matches, the responder knows that the cookie was + generated since the last change to <secret> and that IPi must be the + + + +Hoffman Expires July 5, 2006 [Page 26] + +Internet-Draft IKEv2 January 2006 + + + same as the source address it saw the first time. Incorporating SPIi + into the calculation ensures that if multiple IKE_SAs are being set + up in parallel they will all get different cookies (assuming the + initiator chooses unique SPIi's). Incorporating Ni into the hash + ensures that an attacker who sees only message 2 can't successfully + forge a message 3. + + If a new value for <secret> is chosen while there are connections in + the process of being initialized, an IKE_SA_INIT might be returned + with other than the current <VersionIDofSecret>. The responder in + that case MAY reject the message by sending another response with a + new cookie or it MAY keep the old value of <secret> around for a + short time and accept cookies computed from either one. {{ Demoted + the SHOULD NOT }} The responder should not accept cookies + indefinitely after <secret> is changed, since that would defeat part + of the denial of service protection. {{ Demoted the SHOULD }} The + responder should change the value of <secret> frequently, especially + if under attack. + + {{ Clarif-2.1 }} In addition to cookies, there are several cases + where the IKE_SA_INIT exchange does not result in the creation of an + IKE_SA (such as INVALID_KE_PAYLOAD or NO_PROPOSAL_CHOSEN). In such a + case, sending a zero value for the Responder's SPI is correct. If + the responder sends a non-zero responder SPI, the initiator should + not reject the response for only that reason. + + {{ Clarif-2.5 }} When one party receives an IKE_SA_INIT request + containing a cookie whose contents do not match the value expected, + that party MUST ignore the cookie and process the message as if no + cookie had been included; usually this means sending a response + containing a new cookie. + +2.6.1. Interaction of COOKIE and INVALID_KE_PAYLOAD + + {{ This section added by Clarif-2.4 }} + + There are two common reasons why the initiator may have to retry the + IKE_SA_INIT exchange: the responder requests a cookie or wants a + different Diffie-Hellman group than was included in the KEi payload. + If the initiator receives a cookie from the responder, the initiator + needs to decide whether or not tp include the cookie in only the next + retry of the IKE_SA_INIT request, or in all subsequent retries as + well. + + If the initiator includes the cookie only in the next retry, one + additional roundtrip may be needed in some cases. An additional + roundtrip is needed also if the initiator includes the cookie in all + retries, but the responder does not support this. For instance, if + + + +Hoffman Expires July 5, 2006 [Page 27] + +Internet-Draft IKEv2 January 2006 + + + the responder includes the SAi1 and KEi payloads in cookie + calculation, it will reject the request by sending a new cookie. + + If both peers support including the cookie in all retries, a slightly + shorter exchange can happen. Implementations MUST support this + shorter exchange, but MUST NOT assume other implementations also + supports this shorter exchange. + +2.7. Cryptographic Algorithm Negotiation + + The payload type known as "SA" indicates a proposal for a set of + choices of IPsec protocols (IKE, ESP, and/or AH) for the SA as well + as cryptographic algorithms associated with each protocol. + + An SA payload consists of one or more proposals. Each proposal + includes one or more protocols (usually one). Each protocol contains + one or more transforms -- each specifying a cryptographic algorithm. + Each transform contains zero or more attributes (attributes are + needed only if the transform identifier does not completely specify + the cryptographic algorithm). + + This hierarchical structure was designed to efficiently encode + proposals for cryptographic suites when the number of supported + suites is large because multiple values are acceptable for multiple + transforms. The responder MUST choose a single suite, which MAY be + any subset of the SA proposal following the rules below: + + Each proposal contains one or more protocols. If a proposal is + accepted, the SA response MUST contain the same protocols in the same + order as the proposal. The responder MUST accept a single proposal + or reject them all and return an error. (Example: if a single + proposal contains ESP and AH and that proposal is accepted, both ESP + and AH MUST be accepted. If ESP and AH are included in separate + proposals, the responder MUST accept only one of them). + + Each IPsec protocol proposal contains one or more transforms. Each + transform contains a transform type. The accepted cryptographic + suite MUST contain exactly one transform of each type included in the + proposal. For example: if an ESP proposal includes transforms + ENCR_3DES, ENCR_AES w/keysize 128, ENCR_AES w/keysize 256, + AUTH_HMAC_MD5, and AUTH_HMAC_SHA, the accepted suite MUST contain one + of the ENCR_ transforms and one of the AUTH_ transforms. Thus, six + combinations are acceptable. + + Since the initiator sends its Diffie-Hellman value in the + IKE_SA_INIT, it must guess the Diffie-Hellman group that the + responder will select from its list of supported groups. If the + initiator guesses wrong, the responder will respond with a Notify + + + +Hoffman Expires July 5, 2006 [Page 28] + +Internet-Draft IKEv2 January 2006 + + + payload of type INVALID_KE_PAYLOAD indicating the selected group. In + this case, the initiator MUST retry the IKE_SA_INIT with the + corrected Diffie-Hellman group. The initiator MUST again propose its + full set of acceptable cryptographic suites because the rejection + message was unauthenticated and otherwise an active attacker could + trick the endpoints into negotiating a weaker suite than a stronger + one that they both prefer. + +2.8. Rekeying + + {{ Demoted the SHOULD }} IKE, ESP, and AH security associations use + secret keys that should be used only for a limited amount of time and + to protect a limited amount of data. This limits the lifetime of the + entire security association. When the lifetime of a security + association expires, the security association MUST NOT be used. If + there is demand, new security associations MAY be established. + Reestablishment of security associations to take the place of ones + that expire is referred to as "rekeying". + + To allow for minimal IPsec implementations, the ability to rekey SAs + without restarting the entire IKE_SA is optional. An implementation + MAY refuse all CREATE_CHILD_SA requests within an IKE_SA. If an SA + has expired or is about to expire and rekeying attempts using the + mechanisms described here fail, an implementation MUST close the + IKE_SA and any associated CHILD_SAs and then MAY start new ones. {{ + Demoted the SHOULD }} Implementations should support in-place + rekeying of SAs, since doing so offers better performance and is + likely to reduce the number of packets lost during the transition. + + To rekey a CHILD_SA within an existing IKE_SA, create a new, + equivalent SA (see Section 2.17 below), and when the new one is + established, delete the old one. To rekey an IKE_SA, establish a new + equivalent IKE_SA (see Section 2.18 below) with the peer to whom the + old IKE_SA is shared using a CREATE_CHILD_SA within the existing + IKE_SA. An IKE_SA so created inherits all of the original IKE_SA's + CHILD_SAs. Use the new IKE_SA for all control messages needed to + maintain the CHILD_SAs created by the old IKE_SA, and delete the old + IKE_SA. The Delete payload to delete itself MUST be the last request + sent over an IKE_SA. + + {{ Demoted the SHOULD }} SAs should be rekeyed proactively, i.e., the + new SA should be established before the old one expires and becomes + unusable. Enough time should elapse between the time the new SA is + established and the old one becomes unusable so that traffic can be + switched over to the new SA. + + A difference between IKEv1 and IKEv2 is that in IKEv1 SA lifetimes + were negotiated. In IKEv2, each end of the SA is responsible for + + + +Hoffman Expires July 5, 2006 [Page 29] + +Internet-Draft IKEv2 January 2006 + + + enforcing its own lifetime policy on the SA and rekeying the SA when + necessary. If the two ends have different lifetime policies, the end + with the shorter lifetime will end up always being the one to request + the rekeying. If an SA bundle has been inactive for a long time and + if an endpoint would not initiate the SA in the absence of traffic, + the endpoint MAY choose to close the SA instead of rekeying it when + its lifetime expires. {{ Demoted the SHOULD }} It should do so if + there has been no traffic since the last time the SA was rekeyed. + + Note that IKEv2 deliberately allows parallel SAs with the same + traffic selectors between common endpoints. One of the purposes of + this is to support traffic quality of service (QoS) differences among + the SAs (see [DIFFSERVFIELD], [DIFFSERVARCH], and section 4.1 of + [DIFFTUNNEL]). Hence unlike IKEv1, the combination of the endpoints + and the traffic selectors may not uniquely identify an SA between + those endpoints, so the IKEv1 rekeying heuristic of deleting SAs on + the basis of duplicate traffic selectors SHOULD NOT be used. + + {{ Demoted the SHOULD }} The node that initiated the surviving + rekeyed SA should delete the replaced SA after the new one is + established. + + There are timing windows -- particularly in the presence of lost + packets -- where endpoints may not agree on the state of an SA. The + responder to a CREATE_CHILD_SA MUST be prepared to accept messages on + an SA before sending its response to the creation request, so there + is no ambiguity for the initiator. The initiator MAY begin sending + on an SA as soon as it processes the response. The initiator, + however, cannot receive on a newly created SA until it receives and + processes the response to its CREATE_CHILD_SA request. How, then, is + the responder to know when it is OK to send on the newly created SA? + + From a technical correctness and interoperability perspective, the + responder MAY begin sending on an SA as soon as it sends its response + to the CREATE_CHILD_SA request. In some situations, however, this + could result in packets unnecessarily being dropped, so an + implementation MAY want to defer such sending. + + The responder can be assured that the initiator is prepared to + receive messages on an SA if either (1) it has received a + cryptographically valid message on the new SA, or (2) the new SA + rekeys an existing SA and it receives an IKE request to close the + replaced SA. {{ Clarif-5.10 }} When rekeying an SA, the responder + SHOULD continue to send traffic on the old SA until one of those + events occurs. When establishing a new SA, the responder MAY defer + sending messages on a new SA until either it receives one or a + timeout has occurred. {{ Demoted the SHOULD }} If an initiator + receives a message on an SA for which it has not received a response + + + +Hoffman Expires July 5, 2006 [Page 30] + +Internet-Draft IKEv2 January 2006 + + + to its CREATE_CHILD_SA request, it should interpret that as a likely + packet loss and retransmit the CREATE_CHILD_SA request. An initiator + MAY send a dummy message on a newly created SA if it has no messages + queued in order to assure the responder that the initiator is ready + to receive messages. + + {{ Clarif-5.9 }} Throughout this document, "initiator" refers to the + party who initiated the exchange being described, and "original + initiator" refers to the party who initiated the whole IKE_SA. The + "original initiator" always refers to the party who initiated the + exchange which resulted in the current IKE_SA. In other words, if + the the "original responder" starts rekeying the IKE_SA, that party + becomes the "original initiator" of the new IKE_SA. + +2.8.1. Simultaneous CHILD_SA rekeying + + {{ The first two paragraphs were moved, and the rest was added, based + on Clarif-5.12 }} + + If the two ends have the same lifetime policies, it is possible that + both will initiate a rekeying at the same time (which will result in + redundant SAs). To reduce the probability of this happening, the + timing of rekeying requests SHOULD be jittered (delayed by a random + amount of time after the need for rekeying is noticed). + + This form of rekeying may temporarily result in multiple similar SAs + between the same pairs of nodes. When there are two SAs eligible to + receive packets, a node MUST accept incoming packets through either + SA. If redundant SAs are created though such a collision, the SA + created with the lowest of the four nonces used in the two exchanges + SHOULD be closed by the endpoint that created it. {{ Clarif-5.11 }} + "Lowest" means an octet-by-octet, lexicographical comparison (instead + of, for instance, comparing the nonces as large integers). In other + words, start by comparing the first octet; if they're equal, move to + the next octet, and so on. If you reach the end of one nonce, that + nonce is the lower one. + + The following is an explanation on the impact this has on + implementations. Assume that hosts A and B have an existing IPsec SA + pair with SPIs (SPIa1,SPIb1), and both start rekeying it at the same + time: + + Host A Host B + ------------------------------------------------------------------- + send req1: N(REKEY_SA,SPIa1), + SA(..,SPIa2,..),Ni1,.. --> + <-- send req2: N(REKEY_SA,SPIb1), + SA(..,SPIb2,..),Ni2 + + + +Hoffman Expires July 5, 2006 [Page 31] + +Internet-Draft IKEv2 January 2006 + + + recv req2 <-- + + At this point, A knows there is a simultaneous rekeying going on. + However, it cannot yet know which of the exchanges will have the + lowest nonce, so it will just note the situation and respond as + usual. + + send resp2: SA(..,SPIa3,..), + Nr1,.. --> + --> recv req1 + + Now B also knows that simultaneous rekeying is going on. It responds + as usual. + + <-- send resp1: SA(..,SPIb3,..), + Nr2,.. + recv resp1 <-- + --> recv resp2 + + At this point, there are three CHILD_SA pairs between A and B (the + old one and two new ones). A and B can now compare the nonces. + Suppose that the lowest nonce was Nr1 in message resp2; in this case, + B (the sender of req2) deletes the redundant new SA, and A (the node + that initiated the surviving rekeyed SA), deletes the old one. + + send req3: D(SPIa1) --> + <-- send req4: D(SPIb2) + --> recv req3 + <-- send resp4: D(SPIb1) + recv req4 <-- + send resp4: D(SPIa3) --> + + The rekeying is now finished. + + However, there is a second possible sequence of events that can + happen if some packets are lost in the network, resulting in + retransmissions. The rekeying begins as usual, but A's first packet + (req1) is lost. + + + + + + + + + + + + + +Hoffman Expires July 5, 2006 [Page 32] + +Internet-Draft IKEv2 January 2006 + + + Host A Host B + ------------------------------------------------------------------- + send req1: N(REKEY_SA,SPIa1), + SA(..,SPIa2,..), + Ni1,.. --> (lost) + <-- send req2: N(REKEY_SA,SPIb1), + SA(..,SPIb2,..),Ni2 + recv req2 <-- + send resp2: SA(..,SPIa3,..), + Nr1,.. --> + --> recv resp2 + <-- send req3: D(SPIb1) + recv req3 <-- + send resp3: D(SPIa1) --> + --> recv resp3 + + From B's point of view, the rekeying is now completed, and since it + has not yet received A's req1, it does not even know that these was + simultaneous rekeying. However, A will continue retransmitting the + message, and eventually it will reach B. + + resend req1 --> + --> recv req1 + + To B, it looks like A is trying to rekey an SA that no longer exists; + thus, B responds to the request with something non-fatal such as + NO_PROPOSAL_CHOSEN. + + <-- send resp1: N(NO_PROPOSAL_CHOSEN) + recv resp1 <-- + + When A receives this error, it already knows there was simultaneous + rekeying, so it can ignore the error message. + +2.8.2. Rekeying the IKE_SA Versus Reauthentication + + {{ Added this section from Clarif-5.2 }} + + Rekeying the IKE_SA and reauthentication are different concepts in + IKEv2. Rekeying the IKE_SA establishes new keys for the IKE_SA and + resets the Message ID counters, but it does not authenticate the + parties again (no AUTH or EAP payloads are involved). + + Although rekeying the IKE_SA may be important in some environments, + reauthentication (the verification that the parties still have access + to the long-term credentials) is often more important. + + IKEv2 does not have any special support for reauthentication. + + + +Hoffman Expires July 5, 2006 [Page 33] + +Internet-Draft IKEv2 January 2006 + + + Reauthentication is done by creating a new IKE_SA from scratch (using + IKE_SA_INIT/IKE_AUTH exchanges, without any REKEY_SA notify + payloads), creating new CHILD_SAs within the new IKE_SA (without + REKEY_SA notify payloads), and finally deleting the old IKE_SA (which + deletes the old CHILD_SAs as well). + + This means that reauthentication also establishes new keys for the + IKE_SA and CHILD_SAs. Therefore, while rekeying can be performed + more often than reauthentication, the situation where "authentication + lifetime" is shorter than "key lifetime" does not make sense. + + While creation of a new IKE_SA can be initiated by either party + (initiator or responder in the original IKE_SA), the use of EAP + authentication and/or configuration payloads means in practice that + reauthentication has to be initiated by the same party as the + original IKE_SA. IKEv2 does not currently allow the responder to + request reauthentication in this case; however, there is ongoing work + to add this functionality [REAUTH]. + +2.9. Traffic Selector Negotiation + + {{ Clarif-7.2 }} When an RFC4301-compliant IPsec subsystem receives + an IP packet and matches a "protect" selector in its Security Policy + Database (SPD), the subsystem protects that packet with IPsec. When + no SA exists yet, it is the task of IKE to create it. Maintenance of + a system's SPD is outside the scope of IKE (see [PFKEY] for an + example protocol), though some implementations might update their SPD + in connection with the running of IKE (for an example scenario, see + Section 1.1.3). + + Traffic Selector (TS) payloads allow endpoints to communicate some of + the information from their SPD to their peers. TS payloads specify + the selection criteria for packets that will be forwarded over the + newly set up SA. This can serve as a consistency check in some + scenarios to assure that the SPDs are consistent. In others, it + guides the dynamic update of the SPD. + + Two TS payloads appear in each of the messages in the exchange that + creates a CHILD_SA pair. Each TS payload contains one or more + Traffic Selectors. Each Traffic Selector consists of an address + range (IPv4 or IPv6), a port range, and an IP protocol ID. In + support of the scenario described in Section 1.1.3, an initiator may + request that the responder assign an IP address and tell the + initiator what it is. {{ Clarif-6.1 }} That request is done using + configuration payloads, not traffic selectors. An address in a TSi + payload in a response does not mean that the responder has assigned + that address to the initiator: it only means that if packets matching + these traffic selectors are sent by the initiator, IPsec processing + + + +Hoffman Expires July 5, 2006 [Page 34] + +Internet-Draft IKEv2 January 2006 + + + can be performed as agreed for this SA. + + IKEv2 allows the responder to choose a subset of the traffic proposed + by the initiator. This could happen when the configurations of the + two endpoints are being updated but only one end has received the new + information. Since the two endpoints may be configured by different + people, the incompatibility may persist for an extended period even + in the absence of errors. It also allows for intentionally different + configurations, as when one end is configured to tunnel all addresses + and depends on the other end to have the up-to-date list. + + The first of the two TS payloads is known as TSi (Traffic Selector- + initiator). The second is known as TSr (Traffic Selector-responder). + TSi specifies the source address of traffic forwarded from (or the + destination address of traffic forwarded to) the initiator of the + CHILD_SA pair. TSr specifies the destination address of the traffic + forwarded to (or the source address of the traffic forwarded from) + the responder of the CHILD_SA pair. For example, if the original + initiator request the creation of a CHILD_SA pair, and wishes to + tunnel all traffic from subnet 192.0.1.* on the initiator's side to + subnet 192.0.2.* on the responder's side, the initiator would include + a single traffic selector in each TS payload. TSi would specify the + address range (192.0.1.0 - 192.0.1.255) and TSr would specify the + address range (192.0.2.0 - 192.0.2.255). Assuming that proposal was + acceptable to the responder, it would send identical TS payloads + back. (Note: The IP address range 192.0.2.* has been reserved for + use in examples in RFCs and similar documents. This document needed + two such ranges, and so also used 192.0.1.*. This should not be + confused with any actual address.) + + The responder is allowed to narrow the choices by selecting a subset + of the traffic, for instance by eliminating or narrowing the range of + one or more members of the set of traffic selectors, provided the set + does not become the NULL set. + + It is possible for the responder's policy to contain multiple smaller + ranges, all encompassed by the initiator's traffic selector, and with + the responder's policy being that each of those ranges should be sent + over a different SA. Continuing the example above, the responder + might have a policy of being willing to tunnel those addresses to and + from the initiator, but might require that each address pair be on a + separately negotiated CHILD_SA. If the initiator generated its + request in response to an incoming packet from 192.0.1.43 to + 192.0.2.123, there would be no way for the responder to determine + which pair of addresses should be included in this tunnel, and it + would have to make a guess or reject the request with a status of + SINGLE_PAIR_REQUIRED. + + + + +Hoffman Expires July 5, 2006 [Page 35] + +Internet-Draft IKEv2 January 2006 + + + {{ Clarif-4.11 }} Few implementations will have policies that require + separate SAs for each address pair. Because of this, if only some + part (or parts) of the TSi/TSr proposed by the initiator is (are) + acceptable to the responder, responders SHOULD narrow TSi/TSr to an + acceptable subset rather than use SINGLE_PAIR_REQUIRED. + + To enable the responder to choose the appropriate range in this case, + if the initiator has requested the SA due to a data packet, the + initiator SHOULD include as the first traffic selector in each of TSi + and TSr a very specific traffic selector including the addresses in + the packet triggering the request. In the example, the initiator + would include in TSi two traffic selectors: the first containing the + address range (192.0.1.43 - 192.0.1.43) and the source port and IP + protocol from the packet and the second containing (192.0.1.0 - + 192.0.1.255) with all ports and IP protocols. The initiator would + similarly include two traffic selectors in TSr. + + If the responder's policy does not allow it to accept the entire set + of traffic selectors in the initiator's request, but does allow him + to accept the first selector of TSi and TSr, then the responder MUST + narrow the traffic selectors to a subset that includes the + initiator's first choices. In this example, the responder might + respond with TSi being (192.0.1.43 - 192.0.1.43) with all ports and + IP protocols. + + If the initiator creates the CHILD_SA pair not in response to an + arriving packet, but rather, say, upon startup, then there may be no + specific addresses the initiator prefers for the initial tunnel over + any other. In that case, the first values in TSi and TSr MAY be + ranges rather than specific values, and the responder chooses a + subset of the initiator's TSi and TSr that are acceptable. If more + than one subset is acceptable but their union is not, the responder + MUST accept some subset and MAY include a Notify payload of type + ADDITIONAL_TS_POSSIBLE to indicate that the initiator might want to + try again. This case will occur only when the initiator and + responder are configured differently from one another. If the + initiator and responder agree on the granularity of tunnels, the + initiator will never request a tunnel wider than the responder will + accept. {{ Demoted the SHOULD }} Such misconfigurations should be + recorded in error logs. + + {{ Clarif-4.10 }} A concise summary of the narrowing process is: + + o If the responder's policy does not allow any part of the traffic + covered by TSi/TSr, it responds with TS_UNACCEPTABLE. + + o If the responder's policy allows the entire set of traffic covered + by TSi/TSr, no narrowing is necessary, and the responder can + + + +Hoffman Expires July 5, 2006 [Page 36] + +Internet-Draft IKEv2 January 2006 + + + return the same TSi/TSr values. + + o Otherwise, narrowing is needed. If the responder's policy allows + all traffic covered by TSi[1]/TSr[1] (the first traffic selectors + in TSi/TSr) but not entire TSi/TSr, the responder narrows to an + acceptable subset of TSi/TSr that includes TSi[1]/TSr[1]. + + o If the responder's policy does not allow all traffic covered by + TSi[1]/TSr[1], but does allow some parts of TSi/TSr, it narrows to + an acceptable subset of TSi/TSr. + + In the last two cases, there may be several subsets that are + acceptable (but their union is not); in this case, the responder + arbitrarily chooses one of them, and includes ADDITIONAL_TS_POSSIBLE + notification in the response. + +2.9.1. Traffic Selectors Violating Own Policy + + {{ Clarif-4.12 }} + + When creating a new SA, the initiator should not propose traffic + selectors that violate its own policy. If this rule is not followed, + valid traffic may be dropped. + + This is best illustrated by an example. Suppose that host A has a + policy whose effect is that traffic to 192.0.1.66 is sent via host B + encrypted using AES, and traffic to all other hosts in 192.0.1.0/24 + is also sent via B, but must use 3DES. Suppose also that host B + accepts any combination of AES and 3DES. + + If host A now proposes an SA that uses 3DES, and includes TSr + containing (192.0.1.0-192.0.1.0.255), this will be accepted by host + B. Now, host B can also use this SA to send traffic from 192.0.1.66, + but those packets will be dropped by A since it requires the use of + AES for those traffic. Even if host A creates a new SA only for + 192.0.1.66 that uses AES, host B may freely continue to use the first + SA for the traffic. In this situation, when proposing the SA, host A + should have followed its own policy, and included a TSr containing + ((192.0.1.0-192.0.1.65),(192.0.1.67-192.0.1.255)) instead. + + In general, if (1) the initiator makes a proposal "for traffic X + (TSi/TSr), do SA", and (2) for some subset X' of X, the initiator + does not actually accept traffic X' with SA, and (3) the initiator + would be willing to accept traffic X' with some SA' (!=SA), valid + traffic can be unnecessarily dropped since the responder can apply + either SA or SA' to traffic X'. + + + + + +Hoffman Expires July 5, 2006 [Page 37] + +Internet-Draft IKEv2 January 2006 + + +2.10. Nonces + + The IKE_SA_INIT messages each contain a nonce. These nonces are used + as inputs to cryptographic functions. The CREATE_CHILD_SA request + and the CREATE_CHILD_SA response also contain nonces. These nonces + are used to add freshness to the key derivation technique used to + obtain keys for CHILD_SA, and to ensure creation of strong pseudo- + random bits from the Diffie-Hellman key. Nonces used in IKEv2 MUST + be randomly chosen, MUST be at least 128 bits in size, and MUST be at + least half the key size of the negotiated prf. ("prf" refers to + "pseudo-random function", one of the cryptographic algorithms + negotiated in the IKE exchange.) {{ Clarif-7.4 }} However, the + initiator chooses the nonce before the outcome of the negotiation is + known. Because of that, the nonce has to be long enough for all the + PRFs being proposed. If the same random number source is used for + both keys and nonces, care must be taken to ensure that the latter + use does not compromise the former. + +2.11. Address and Port Agility + + IKE runs over UDP ports 500 and 4500, and implicitly sets up ESP and + AH associations for the same IP addresses it runs over. The IP + addresses and ports in the outer header are, however, not themselves + cryptographically protected, and IKE is designed to work even through + Network Address Translation (NAT) boxes. An implementation MUST + accept incoming requests even if the source port is not 500 or 4500, + and MUST respond to the address and port from which the request was + received. It MUST specify the address and port at which the request + was received as the source address and port in the response. IKE + functions identically over IPv4 or IPv6. + +2.12. Reuse of Diffie-Hellman Exponentials + + IKE generates keying material using an ephemeral Diffie-Hellman + exchange in order to gain the property of "perfect forward secrecy". + This means that once a connection is closed and its corresponding + keys are forgotten, even someone who has recorded all of the data + from the connection and gets access to all of the long-term keys of + the two endpoints cannot reconstruct the keys used to protect the + conversation without doing a brute force search of the session key + space. + + Achieving perfect forward secrecy requires that when a connection is + closed, each endpoint MUST forget not only the keys used by the + connection but also any information that could be used to recompute + those keys. In particular, it MUST forget the secrets used in the + Diffie-Hellman calculation and any state that may persist in the + state of a pseudo-random number generator that could be used to + + + +Hoffman Expires July 5, 2006 [Page 38] + +Internet-Draft IKEv2 January 2006 + + + recompute the Diffie-Hellman secrets. + + Since the computing of Diffie-Hellman exponentials is computationally + expensive, an endpoint may find it advantageous to reuse those + exponentials for multiple connection setups. There are several + reasonable strategies for doing this. An endpoint could choose a new + exponential only periodically though this could result in less-than- + perfect forward secrecy if some connection lasts for less than the + lifetime of the exponential. Or it could keep track of which + exponential was used for each connection and delete the information + associated with the exponential only when some corresponding + connection was closed. This would allow the exponential to be reused + without losing perfect forward secrecy at the cost of maintaining + more state. + + Decisions as to whether and when to reuse Diffie-Hellman exponentials + is a private decision in the sense that it will not affect + interoperability. An implementation that reuses exponentials MAY + choose to remember the exponential used by the other endpoint on past + exchanges and if one is reused to avoid the second half of the + calculation. + +2.13. Generating Keying Material + + In the context of the IKE_SA, four cryptographic algorithms are + negotiated: an encryption algorithm, an integrity protection + algorithm, a Diffie-Hellman group, and a pseudo-random function + (prf). The pseudo-random function is used for the construction of + keying material for all of the cryptographic algorithms used in both + the IKE_SA and the CHILD_SAs. + + We assume that each encryption algorithm and integrity protection + algorithm uses a fixed-size key and that any randomly chosen value of + that fixed size can serve as an appropriate key. For algorithms that + accept a variable length key, a fixed key size MUST be specified as + part of the cryptographic transform negotiated. For algorithms for + which not all values are valid keys (such as DES or 3DES with key + parity), the algorithm by which keys are derived from arbitrary + values MUST be specified by the cryptographic transform. For + integrity protection functions based on Hashed Message Authentication + Code (HMAC), the fixed key size is the size of the output of the + underlying hash function. When the prf function takes a variable + length key, variable length data, and produces a fixed-length output + (e.g., when using HMAC), the formulas in this document apply. When + the key for the prf function has fixed length, the data provided as a + key is truncated or padded with zeros as necessary unless exceptional + processing is explained following the formula. + + + + +Hoffman Expires July 5, 2006 [Page 39] + +Internet-Draft IKEv2 January 2006 + + + Keying material will always be derived as the output of the + negotiated prf algorithm. Since the amount of keying material needed + may be greater than the size of the output of the prf algorithm, we + will use the prf iteratively. We will use the terminology prf+ to + describe the function that outputs a pseudo-random stream based on + the inputs to a prf as follows: (where | indicates concatenation) + + prf+ (K,S) = T1 | T2 | T3 | T4 | ... + + where: + T1 = prf (K, S | 0x01) + T2 = prf (K, T1 | S | 0x02) + T3 = prf (K, T2 | S | 0x03) + T4 = prf (K, T3 | S | 0x04) + + continuing as needed to compute all required keys. The keys are + taken from the output string without regard to boundaries (e.g., if + the required keys are a 256-bit Advanced Encryption Standard (AES) + key and a 160-bit HMAC key, and the prf function generates 160 bits, + the AES key will come from T1 and the beginning of T2, while the HMAC + key will come from the rest of T2 and the beginning of T3). + + The constant concatenated to the end of each string feeding the prf + is a single octet. prf+ in this document is not defined beyond 255 + times the size of the prf output. + +2.14. Generating Keying Material for the IKE_SA + + The shared keys are computed as follows. A quantity called SKEYSEED + is calculated from the nonces exchanged during the IKE_SA_INIT + exchange and the Diffie-Hellman shared secret established during that + exchange. SKEYSEED is used to calculate seven other secrets: SK_d + used for deriving new keys for the CHILD_SAs established with this + IKE_SA; SK_ai and SK_ar used as a key to the integrity protection + algorithm for authenticating the component messages of subsequent + exchanges; SK_ei and SK_er used for encrypting (and of course + decrypting) all subsequent exchanges; and SK_pi and SK_pr, which are + used when generating an AUTH payload. + + SKEYSEED and its derivatives are computed as follows: + + SKEYSEED = prf(Ni | Nr, g^ir) + + {SK_d | SK_ai | SK_ar | SK_ei | SK_er | SK_pi | SK_pr } + = prf+ (SKEYSEED, Ni | Nr | SPIi | SPIr ) + + (indicating that the quantities SK_d, SK_ai, SK_ar, SK_ei, SK_er, + SK_pi, and SK_pr are taken in order from the generated bits of the + + + +Hoffman Expires July 5, 2006 [Page 40] + +Internet-Draft IKEv2 January 2006 + + + prf+). g^ir is the shared secret from the ephemeral Diffie-Hellman + exchange. g^ir is represented as a string of octets in big endian + order padded with zeros if necessary to make it the length of the + modulus. Ni and Nr are the nonces, stripped of any headers. If the + negotiated prf takes a fixed-length key and the lengths of Ni and Nr + do not add up to that length, half the bits must come from Ni and + half from Nr, taking the first bits of each. + + The two directions of traffic flow use different keys. The keys used + to protect messages from the original initiator are SK_ai and SK_ei. + The keys used to protect messages in the other direction are SK_ar + and SK_er. Each algorithm takes a fixed number of bits of keying + material, which is specified as part of the algorithm. For integrity + algorithms based on a keyed hash, the key size is always equal to the + length of the output of the underlying hash function. + +2.15. Authentication of the IKE_SA + + When not using extensible authentication (see Section 2.16), the + peers are authenticated by having each sign (or MAC using a shared + secret as the key) a block of data. For the responder, the octets to + be signed start with the first octet of the first SPI in the header + of the second message and end with the last octet of the last payload + in the second message. Appended to this (for purposes of computing + the signature) are the initiator's nonce Ni (just the value, not the + payload containing it), and the value prf(SK_pr,IDr') where IDr' is + the responder's ID payload excluding the fixed header. Note that + neither the nonce Ni nor the value prf(SK_pr,IDr') are transmitted. + Similarly, the initiator signs the first message, starting with the + first octet of the first SPI in the header and ending with the last + octet of the last payload. Appended to this (for purposes of + computing the signature) are the responder's nonce Nr, and the value + prf(SK_pi,IDi'). In the above calculation, IDi' and IDr' are the + entire ID payloads excluding the fixed header. It is critical to the + security of the exchange that each side sign the other side's nonce. + + {{ Clarif-3.1 }} + + The initiator's signed octets can be described as: + + InitiatorSignedOctets = RealMessage1 | NonceRData | MACedIDForI + GenIKEHDR = [ four octets 0 if using port 4500 ] | RealIKEHDR + RealIKEHDR = SPIi | SPIr | . . . | Length + RealMessage1 = RealIKEHDR | RestOfMessage1 + NonceRPayload = PayloadHeader | NonceRData + InitiatorIDPayload = PayloadHeader | RestOfIDPayload + RestOfInitIDPayload = IDType | RESERVED | InitIDData + MACedIDForI = prf(SK_pi, RestOfInitIDPayload) + + + +Hoffman Expires July 5, 2006 [Page 41] + +Internet-Draft IKEv2 January 2006 + + + The responder's signed octets can be described as: + + ResponderSignedOctets = RealMessage2 | NonceIData | MACedIDForR + GenIKEHDR = [ four octets 0 if using port 4500 ] | RealIKEHDR + RealIKEHDR = SPIi | SPIr | . . . | Length + RealMessage2 = RealIKEHDR | RestOfMessage2 + NonceIPayload = PayloadHeader | NonceIData + ResponderIDPayload = PayloadHeader | RestOfIDPayload + RestOfRespIDPayload = IDType | RESERVED | InitIDData + MACedIDForR = prf(SK_pr, RestOfRespIDPayload) + + Note that all of the payloads are included under the signature, + including any payload types not defined in this document. If the + first message of the exchange is sent twice (the second time with a + responder cookie and/or a different Diffie-Hellman group), it is the + second version of the message that is signed. + + Optionally, messages 3 and 4 MAY include a certificate, or + certificate chain providing evidence that the key used to compute a + digital signature belongs to the name in the ID payload. The + signature or MAC will be computed using algorithms dictated by the + type of key used by the signer, and specified by the Auth Method + field in the Authentication payload. There is no requirement that + the initiator and responder sign with the same cryptographic + algorithms. The choice of cryptographic algorithms depends on the + type of key each has. In particular, the initiator may be using a + shared key while the responder may have a public signature key and + certificate. It will commonly be the case (but it is not required) + that if a shared secret is used for authentication that the same key + is used in both directions. Note that it is a common but typically + insecure practice to have a shared key derived solely from a user- + chosen password without incorporating another source of randomness. + + This is typically insecure because user-chosen passwords are unlikely + to have sufficient unpredictability to resist dictionary attacks and + these attacks are not prevented in this authentication method. + (Applications using password-based authentication for bootstrapping + and IKE_SA should use the authentication method in Section 2.16, + which is designed to prevent off-line dictionary attacks.) {{ Demoted + the SHOULD }} The pre-shared key needs to contain as much + unpredictability as the strongest key being negotiated. In the case + of a pre-shared key, the AUTH value is computed as: + + AUTH = prf(prf(Shared Secret,"Key Pad for IKEv2"), <msg octets>) + + where the string "Key Pad for IKEv2" is 17 ASCII characters without + null termination. The shared secret can be variable length. The pad + string is added so that if the shared secret is derived from a + + + +Hoffman Expires July 5, 2006 [Page 42] + +Internet-Draft IKEv2 January 2006 + + + password, the IKE implementation need not store the password in + cleartext, but rather can store the value prf(Shared Secret,"Key Pad + for IKEv2"), which could not be used as a password equivalent for + protocols other than IKEv2. As noted above, deriving the shared + secret from a password is not secure. This construction is used + because it is anticipated that people will do it anyway. The + management interface by which the Shared Secret is provided MUST + accept ASCII strings of at least 64 octets and MUST NOT add a null + terminator before using them as shared secrets. It MUST also accept + a HEX encoding of the Shared Secret. The management interface MAY + accept other encodings if the algorithm for translating the encoding + to a binary string is specified. + + {{ Clarif-3.8 }} If the negotiated prf takes a fixed-size key, the + shared secret MUST be of that fixed size. This requirement means + that it is difficult to use these PRFs with shared key authentication + because it limits the shared secrets that can be used. Thus, PRFs + that require a fixed-size key SHOULD NOT be used with shared key + authentication. For example, PRF_AES128_CBC [PRFAES128CBC] + originally used fixed key sizes; that RFC has been updated to handle + variable key sizes in [PRFAES128CBC-bis]. Note that Section 2.13 + also contains text that is related to PRFs with fixed key size. + However, the text in that section applies only to the prf+ + construction. + +2.16. Extensible Authentication Protocol Methods + + In addition to authentication using public key signatures and shared + secrets, IKE supports authentication using methods defined in RFC + 3748 [EAP]. Typically, these methods are asymmetric (designed for a + user authenticating to a server), and they may not be mutual. For + this reason, these protocols are typically used to authenticate the + initiator to the responder and MUST be used in conjunction with a + public key signature based authentication of the responder to the + initiator. These methods are often associated with mechanisms + referred to as "Legacy Authentication" mechanisms. + + While this memo references [EAP] with the intent that new methods can + be added in the future without updating this specification, some + simpler variations are documented here and in Section 3.16. [EAP] + defines an authentication protocol requiring a variable number of + messages. Extensible Authentication is implemented in IKE as + additional IKE_AUTH exchanges that MUST be completed in order to + initialize the IKE_SA. + + An initiator indicates a desire to use extensible authentication by + leaving out the AUTH payload from message 3. By including an IDi + payload but not an AUTH payload, the initiator has declared an + + + +Hoffman Expires July 5, 2006 [Page 43] + +Internet-Draft IKEv2 January 2006 + + + identity but has not proven it. If the responder is willing to use + an extensible authentication method, it will place an Extensible + Authentication Protocol (EAP) payload in message 4 and defer sending + SAr2, TSi, and TSr until initiator authentication is complete in a + subsequent IKE_AUTH exchange. In the case of a minimal extensible + authentication, the initial SA establishment will appear as follows: + + Initiator Responder + ------------------------------------------------------------------- + HDR, SAi1, KEi, Ni --> + <-- HDR, SAr1, KEr, Nr, [CERTREQ] + HDR, SK {IDi, [CERTREQ,] + [IDr,] SAi2, + TSi, TSr} --> + <-- HDR, SK {IDr, [CERT,] AUTH, + EAP } + HDR, SK {EAP} --> + <-- HDR, SK {EAP (success)} + HDR, SK {AUTH} --> + <-- HDR, SK {AUTH, SAr2, TSi, TSr } + + {{ Clarif-3.11 }} As described in Section 2.2, when EAP is used, each + pair of IKE_SA initial setup messages will have their message numbers + incremented; the first pair of AUTH messages will have an ID of 1, + the second will be 2, and so on. + + For EAP methods that create a shared key as a side effect of + authentication, that shared key MUST be used by both the initiator + and responder to generate AUTH payloads in messages 7 and 8 using the + syntax for shared secrets specified in Section 2.15. The shared key + from EAP is the field from the EAP specification named MSK. The + shared key generated during an IKE exchange MUST NOT be used for any + other purpose. + + EAP methods that do not establish a shared key SHOULD NOT be used, as + they are subject to a number of man-in-the-middle attacks [EAPMITM] + if these EAP methods are used in other protocols that do not use a + server-authenticated tunnel. Please see the Security Considerations + section for more details. If EAP methods that do not generate a + shared key are used, the AUTH payloads in messages 7 and 8 MUST be + generated using SK_pi and SK_pr, respectively. + + {{ Demoted the SHOULD }} The initiator of an IKE_SA using EAP needs + to be capable of extending the initial protocol exchange to at least + ten IKE_AUTH exchanges in the event the responder sends notification + messages and/or retries the authentication prompt. Once the protocol + exchange defined by the chosen EAP authentication method has + successfully terminated, the responder MUST send an EAP payload + + + +Hoffman Expires July 5, 2006 [Page 44] + +Internet-Draft IKEv2 January 2006 + + + containing the Success message. Similarly, if the authentication + method has failed, the responder MUST send an EAP payload containing + the Failure message. The responder MAY at any time terminate the IKE + exchange by sending an EAP payload containing the Failure message. + + Following such an extended exchange, the EAP AUTH payloads MUST be + included in the two messages following the one containing the EAP + Success message. + + {{ Clarif-3.5 }} When the initiator authentication uses EAP, it is + possible that the contents of the IDi payload is used only for AAA + routing purposes and selecting which EAP method to use. This value + may be different from the identity authenticated by the EAP method. + It is important that policy lookups and access control decisions use + the actual authenticated identity. Often the EAP server is + implemented in a separate AAA server that communicates with the IKEv2 + responder. In this case, the authenticated identity has to be sent + from the AAA server to the IKEv2 responder. + + {{ Clarif-3.9 }} The information in Section 2.17 about PRFs with + fixed-size keys also applies to EAP authentication. For instance, a + PRF that requires a 128-bit key cannot be used with EAP because + specifies that the MSK is at least 512 bits long. + +2.17. Generating Keying Material for CHILD_SAs + + A single CHILD_SA is created by the IKE_AUTH exchange, and additional + CHILD_SAs can optionally be created in CREATE_CHILD_SA exchanges. + Keying material for them is generated as follows: + + KEYMAT = prf+(SK_d, Ni | Nr) + + Where Ni and Nr are the nonces from the IKE_SA_INIT exchange if this + request is the first CHILD_SA created or the fresh Ni and Nr from the + CREATE_CHILD_SA exchange if this is a subsequent creation. + + For CREATE_CHILD_SA exchanges including an optional Diffie-Hellman + exchange, the keying material is defined as: + + KEYMAT = prf+(SK_d, g^ir (new) | Ni | Nr ) + + where g^ir (new) is the shared secret from the ephemeral Diffie- + Hellman exchange of this CREATE_CHILD_SA exchange (represented as an + octet string in big endian order padded with zeros in the high-order + bits if necessary to make it the length of the modulus). + + A single CHILD_SA negotiation may result in multiple security + associations. ESP and AH SAs exist in pairs (one in each direction), + + + +Hoffman Expires July 5, 2006 [Page 45] + +Internet-Draft IKEv2 January 2006 + + + and four SAs could be created in a single CHILD_SA negotiation if a + combination of ESP and AH is being negotiated. + + Keying material MUST be taken from the expanded KEYMAT in the + following order: + + o All keys for SAs carrying data from the initiator to the responder + are taken before SAs going in the reverse direction. + + o If multiple IPsec protocols are negotiated, keying material is + taken in the order in which the protocol headers will appear in + the encapsulated packet. + + o If a single protocol has both encryption and authentication keys, + the encryption key is taken from the first octets of KEYMAT and + the authentication key is taken from the next octets. + + Each cryptographic algorithm takes a fixed number of bits of keying + material specified as part of the algorithm. + +2.18. Rekeying IKE_SAs Using a CREATE_CHILD_SA Exchange + + The CREATE_CHILD_SA exchange can be used to rekey an existing IKE_SA + (see Section 2.8). {{ Clarif-5.3 }} New initiator and responder SPIs + are supplied in the SPI fields in the Proposal structures inside the + Security Association (SA) payloads (not the SPI fields in the IKE + header). The TS payloads are omitted when rekeying an IKE_SA. + SKEYSEED for the new IKE_SA is computed using SK_d from the existing + IKE_SA as follows: + + SKEYSEED = prf(SK_d (old), [g^ir (new)] | Ni | Nr) + + where g^ir (new) is the shared secret from the ephemeral Diffie- + Hellman exchange of this CREATE_CHILD_SA exchange (represented as an + octet string in big endian order padded with zeros if necessary to + make it the length of the modulus) and Ni and Nr are the two nonces + stripped of any headers. + + {{ Clarif-5.5 }} The old and new IKE_SA may have selected a different + PRF. Because the rekeying exchange belongs to the old IKE_SA, it is + the old IKE_SA's PRF that is used. Note that this may not work if + the new IKE_SA's PRF has a fixed key size because the output of the + PRF may not be of the correct size. + + The new IKE_SA MUST reset its message counters to 0. + + SK_d, SK_ai, SK_ar, SK_ei, and SK_er are computed from SKEYSEED as + specified in Section 2.14. + + + +Hoffman Expires July 5, 2006 [Page 46] + +Internet-Draft IKEv2 January 2006 + + +2.19. Requesting an Internal Address on a Remote Network + + Most commonly occurring in the endpoint-to-security-gateway scenario, + an endpoint may need an IP address in the network protected by the + security gateway and may need to have that address dynamically + assigned. A request for such a temporary address can be included in + any request to create a CHILD_SA (including the implicit request in + message 3) by including a CP payload. + + This function provides address allocation to an IPsec Remote Access + Client (IRAC) trying to tunnel into a network protected by an IPsec + Remote Access Server (IRAS). Since the IKE_AUTH exchange creates an + IKE_SA and a CHILD_SA, the IRAC MUST request the IRAS-controlled + address (and optionally other information concerning the protected + network) in the IKE_AUTH exchange. The IRAS may procure an address + for the IRAC from any number of sources such as a DHCP/BOOTP server + or its own address pool. + + Initiator Responder + ------------------------------------------------------------------- + HDR, SK {IDi, [CERT,] + [CERTREQ,] [IDr,] AUTH, + CP(CFG_REQUEST), SAi2, + TSi, TSr} --> + <-- HDR, SK {IDr, [CERT,] AUTH, + CP(CFG_REPLY), SAr2, + TSi, TSr} + + In all cases, the CP payload MUST be inserted before the SA payload. + In variations of the protocol where there are multiple IKE_AUTH + exchanges, the CP payloads MUST be inserted in the messages + containing the SA payloads. + + CP(CFG_REQUEST) MUST contain at least an INTERNAL_ADDRESS attribute + (either IPv4 or IPv6) but MAY contain any number of additional + attributes the initiator wants returned in the response. + + For example, message from initiator to responder: + + {{ Clarif-6.3 }} + + CP(CFG_REQUEST)= + INTERNAL_ADDRESS() + TSi = (0, 0-65535,0.0.0.0-255.255.255.255) + TSr = (0, 0-65535,0.0.0.0-255.255.255.255) + + NOTE: Traffic Selectors contain (protocol, port range, address + range). + + + +Hoffman Expires July 5, 2006 [Page 47] + +Internet-Draft IKEv2 January 2006 + + + Message from responder to initiator: + + CP(CFG_REPLY)= + INTERNAL_ADDRESS(192.0.2.202) + INTERNAL_NETMASK(255.255.255.0) + INTERNAL_SUBNET(192.0.2.0/255.255.255.0) + TSi = (0, 0-65535,192.0.2.202-192.0.2.202) + TSr = (0, 0-65535,192.0.2.0-192.0.2.255) + + All returned values will be implementation dependent. As can be seen + in the above example, the IRAS MAY also send other attributes that + were not included in CP(CFG_REQUEST) and MAY ignore the non- + mandatory attributes that it does not support. + + The responder MUST NOT send a CFG_REPLY without having first received + a CP(CFG_REQUEST) from the initiator, because we do not want the IRAS + to perform an unnecessary configuration lookup if the IRAC cannot + process the REPLY. In the case where the IRAS's configuration + requires that CP be used for a given identity IDi, but IRAC has + failed to send a CP(CFG_REQUEST), IRAS MUST fail the request, and + terminate the IKE exchange with a FAILED_CP_REQUIRED error. + +2.20. Requesting the Peer's Version + + An IKE peer wishing to inquire about the other peer's IKE software + version information MAY use the method below. This is an example of + a configuration request within an INFORMATIONAL exchange, after the + IKE_SA and first CHILD_SA have been created. + + An IKE implementation MAY decline to give out version information + prior to authentication or even after authentication to prevent + trolling in case some implementation is known to have some security + weakness. In that case, it MUST either return an empty string or no + CP payload if CP is not supported. + + Initiator Responder + ------------------------------------------------------------------- + HDR, SK{CP(CFG_REQUEST)} --> + <-- HDR, SK{CP(CFG_REPLY)} + + CP(CFG_REQUEST)= + APPLICATION_VERSION("") + + CP(CFG_REPLY) APPLICATION_VERSION("foobar v1.3beta, (c) Foo Bar + Inc.") + + + + + + +Hoffman Expires July 5, 2006 [Page 48] + +Internet-Draft IKEv2 January 2006 + + +2.21. Error Handling + + There are many kinds of errors that can occur during IKE processing. + If a request is received that is badly formatted or unacceptable for + reasons of policy (e.g., no matching cryptographic algorithms), the + response MUST contain a Notify payload indicating the error. If an + error occurs outside the context of an IKE request (e.g., the node is + getting ESP messages on a nonexistent SPI), the node SHOULD initiate + an INFORMATIONAL exchange with a Notify payload describing the + problem. + + Errors that occur before a cryptographically protected IKE_SA is + established must be handled very carefully. There is a trade-off + between wanting to be helpful in diagnosing a problem and responding + to it and wanting to avoid being a dupe in a denial of service attack + based on forged messages. + + If a node receives a message on UDP port 500 or 4500 outside the + context of an IKE_SA known to it (and not a request to start one), it + may be the result of a recent crash of the node. If the message is + marked as a response, the node MAY audit the suspicious event but + MUST NOT respond. If the message is marked as a request, the node + MAY audit the suspicious event and MAY send a response. If a + response is sent, the response MUST be sent to the IP address and + port from whence it came with the same IKE SPIs and the Message ID + copied. The response MUST NOT be cryptographically protected and + MUST contain a Notify payload indicating INVALID_IKE_SPI. + + A node receiving such an unprotected Notify payload MUST NOT respond + and MUST NOT change the state of any existing SAs. The message might + be a forgery or might be a response the genuine correspondent was + tricked into sending. {{ Demoted two SHOULDs }} A node should treat + such a message (and also a network message like ICMP destination + unreachable) as a hint that there might be problems with SAs to that + IP address and should initiate a liveness test for any such IKE_SA. + An implementation SHOULD limit the frequency of such tests to avoid + being tricked into participating in a denial of service attack. + + A node receiving a suspicious message from an IP address with which + it has an IKE_SA MAY send an IKE Notify payload in an IKE + INFORMATIONAL exchange over that SA. {{ Demoted the SHOULD }} The + recipient MUST NOT change the state of any SAs as a result but may + wish to audit the event to aid in diagnosing malfunctions. A node + MUST limit the rate at which it will send messages in response to + unprotected messages. + + + + + + +Hoffman Expires July 5, 2006 [Page 49] + +Internet-Draft IKEv2 January 2006 + + +2.22. IPComp + + Use of IP compression [IPCOMP] can be negotiated as part of the setup + of a CHILD_SA. While IP compression involves an extra header in each + packet and a compression parameter index (CPI), the virtual + "compression association" has no life outside the ESP or AH SA that + contains it. Compression associations disappear when the + corresponding ESP or AH SA goes away. It is not explicitly mentioned + in any DELETE payload. + + Negotiation of IP compression is separate from the negotiation of + cryptographic parameters associated with a CHILD_SA. A node + requesting a CHILD_SA MAY advertise its support for one or more + compression algorithms through one or more Notify payloads of type + IPCOMP_SUPPORTED. The response MAY indicate acceptance of a single + compression algorithm with a Notify payload of type IPCOMP_SUPPORTED. + These payloads MUST NOT occur in messages that do not contain SA + payloads. + + Although there has been discussion of allowing multiple compression + algorithms to be accepted and to have different compression + algorithms available for the two directions of a CHILD_SA, + implementations of this specification MUST NOT accept an IPComp + algorithm that was not proposed, MUST NOT accept more than one, and + MUST NOT compress using an algorithm other than one proposed and + accepted in the setup of the CHILD_SA. + + A side effect of separating the negotiation of IPComp from + cryptographic parameters is that it is not possible to propose + multiple cryptographic suites and propose IP compression with some of + them but not others. + +2.23. NAT Traversal + + Network Address Translation (NAT) gateways are a controversial + subject. This section briefly describes what they are and how they + are likely to act on IKE traffic. Many people believe that NATs are + evil and that we should not design our protocols so as to make them + work better. IKEv2 does specify some unintuitive processing rules in + order that NATs are more likely to work. + + NATs exist primarily because of the shortage of IPv4 addresses, + though there are other rationales. IP nodes that are "behind" a NAT + have IP addresses that are not globally unique, but rather are + assigned from some space that is unique within the network behind the + NAT but that are likely to be reused by nodes behind other NATs. + Generally, nodes behind NATs can communicate with other nodes behind + the same NAT and with nodes with globally unique addresses, but not + + + +Hoffman Expires July 5, 2006 [Page 50] + +Internet-Draft IKEv2 January 2006 + + + with nodes behind other NATs. There are exceptions to that rule. + When those nodes make connections to nodes on the real Internet, the + NAT gateway "translates" the IP source address to an address that + will be routed back to the gateway. Messages to the gateway from the + Internet have their destination addresses "translated" to the + internal address that will route the packet to the correct endnode. + + NATs are designed to be "transparent" to endnodes. Neither software + on the node behind the NAT nor the node on the Internet requires + modification to communicate through the NAT. Achieving this + transparency is more difficult with some protocols than with others. + Protocols that include IP addresses of the endpoints within the + payloads of the packet will fail unless the NAT gateway understands + the protocol and modifies the internal references as well as those in + the headers. Such knowledge is inherently unreliable, is a network + layer violation, and often results in subtle problems. + + Opening an IPsec connection through a NAT introduces special + problems. If the connection runs in transport mode, changing the IP + addresses on packets will cause the checksums to fail and the NAT + cannot correct the checksums because they are cryptographically + protected. Even in tunnel mode, there are routing problems because + transparently translating the addresses of AH and ESP packets + requires special logic in the NAT and that logic is heuristic and + unreliable in nature. For that reason, IKEv2 can negotiate UDP + encapsulation of IKE and ESP packets. This encoding is slightly less + efficient but is easier for NATs to process. In addition, firewalls + may be configured to pass IPsec traffic over UDP but not ESP/AH or + vice versa. + + It is a common practice of NATs to translate TCP and UDP port numbers + as well as addresses and use the port numbers of inbound packets to + decide which internal node should get a given packet. For this + reason, even though IKE packets MUST be sent from and to UDP port + 500, they MUST be accepted coming from any port and responses MUST be + sent to the port from whence they came. This is because the ports + may be modified as the packets pass through NATs. Similarly, IP + addresses of the IKE endpoints are generally not included in the IKE + payloads because the payloads are cryptographically protected and + could not be transparently modified by NATs. + + Port 4500 is reserved for UDP-encapsulated ESP and IKE. When working + through a NAT, it is generally better to pass IKE packets over port + 4500 because some older NATs handle IKE traffic on port 500 cleverly + in an attempt to transparently establish IPsec connections between + endpoints that don't handle NAT traversal themselves. Such NATs may + interfere with the straightforward NAT traversal envisioned by this + document. {{ Clarif-7.6 }} An IPsec endpoint that discovers a NAT + + + +Hoffman Expires July 5, 2006 [Page 51] + +Internet-Draft IKEv2 January 2006 + + + between it and its correspondent MUST send all subsequent traffic + from port 4500, which NATs should not treat specially (as they might + with port 500). + + The specific requirements for supporting NAT traversal [NATREQ] are + listed below. Support for NAT traversal is optional. In this + section only, requirements listed as MUST apply only to + implementations supporting NAT traversal. + + o IKE MUST listen on port 4500 as well as port 500. IKE MUST + respond to the IP address and port from which packets arrived. + + o Both IKE initiator and responder MUST include in their IKE_SA_INIT + packets Notify payloads of type NAT_DETECTION_SOURCE_IP and + NAT_DETECTION_DESTINATION_IP. Those payloads can be used to + detect if there is NAT between the hosts, and which end is behind + the NAT. The location of the payloads in the IKE_SA_INIT packets + are just after the Ni and Nr payloads (before the optional CERTREQ + payload). + + o If none of the NAT_DETECTION_SOURCE_IP payload(s) received matches + the hash of the source IP and port found from the IP header of the + packet containing the payload, it means that the other end is + behind NAT (i.e., someone along the route changed the source + address of the original packet to match the address of the NAT + box). In this case, this end should allow dynamic update of the + other ends IP address, as described later. + + o If the NAT_DETECTION_DESTINATION_IP payload received does not + match the hash of the destination IP and port found from the IP + header of the packet containing the payload, it means that this + end is behind a NAT. In this case, this end SHOULD start sending + keepalive packets as explained in [UDPENCAPS]. + + o The IKE initiator MUST check these payloads if present and if they + do not match the addresses in the outer packet MUST tunnel all + future IKE and ESP packets associated with this IKE_SA over UDP + port 4500. + + o To tunnel IKE packets over UDP port 4500, the IKE header has four + octets of zero prepended and the result immediately follows the + UDP header. To tunnel ESP packets over UDP port 4500, the ESP + header immediately follows the UDP header. Since the first four + bytes of the ESP header contain the SPI, and the SPI cannot + validly be zero, it is always possible to distinguish ESP and IKE + messages. + + + + + +Hoffman Expires July 5, 2006 [Page 52] + +Internet-Draft IKEv2 January 2006 + + + o The original source and destination IP address required for the + transport mode TCP and UDP packet checksum fixup (see [UDPENCAPS]) + are obtained from the Traffic Selectors associated with the + exchange. In the case of NAT traversal, the Traffic Selectors + MUST contain exactly one IP address, which is then used as the + original IP address. + + o There are cases where a NAT box decides to remove mappings that + are still alive (for example, the keepalive interval is too long, + or the NAT box is rebooted). To recover in these cases, hosts + that are not behind a NAT SHOULD send all packets (including + retransmission packets) to the IP address and port from the last + valid authenticated packet from the other end (i.e., dynamically + update the address). {{ Promoted the SHOULD }} A host behind a NAT + MUST NOT do this because it opens a DoS attack possibility. Any + authenticated IKE packet or any authenticated UDP-encapsulated ESP + packet can be used to detect that the IP address or the port has + changed. + + Note that similar but probably not identical actions will likely be + needed to make IKE work with Mobile IP, but such processing is not + addressed by this document. + +2.24. Explicit Congestion Notification (ECN) + + When IPsec tunnels behave as originally specified in [IPSECARCH-OLD], + ECN usage is not appropriate for the outer IP headers because tunnel + decapsulation processing discards ECN congestion indications to the + detriment of the network. ECN support for IPsec tunnels for IKEv1- + based IPsec requires multiple operating modes and negotiation (see + [ECN]). IKEv2 simplifies this situation by requiring that ECN be + usable in the outer IP headers of all tunnel-mode IPsec SAs created + by IKEv2. Specifically, tunnel encapsulators and decapsulators for + all tunnel-mode SAs created by IKEv2 MUST support the ECN full- + functionality option for tunnels specified in [ECN] and MUST + implement the tunnel encapsulation and decapsulation processing + specified in [IPSECARCH] to prevent discarding of ECN congestion + indications. + + +3. Header and Payload Formats + +3.1. The IKE Header + + IKE messages use UDP ports 500 and/or 4500, with one IKE message per + UDP datagram. Information from the beginning of the packet through + the UDP header is largely ignored except that the IP addresses and + UDP ports from the headers are reversed and used for return packets. + + + +Hoffman Expires July 5, 2006 [Page 53] + +Internet-Draft IKEv2 January 2006 + + + When sent on UDP port 500, IKE messages begin immediately following + the UDP header. When sent on UDP port 4500, IKE messages have + prepended four octets of zero. These four octets of zero are not + part of the IKE message and are not included in any of the length + fields or checksums defined by IKE. Each IKE message begins with the + IKE header, denoted HDR in this memo. Following the header are one + or more IKE payloads each identified by a "Next Payload" field in the + preceding payload. Payloads are processed in the order in which they + appear in an IKE message by invoking the appropriate processing + routine according to the "Next Payload" field in the IKE header and + subsequently according to the "Next Payload" field in the IKE payload + itself until a "Next Payload" field of zero indicates that no + payloads follow. If a payload of type "Encrypted" is found, that + payload is decrypted and its contents parsed as additional payloads. + An Encrypted payload MUST be the last payload in a packet and an + Encrypted payload MUST NOT contain another Encrypted payload. + + The Recipient SPI in the header identifies an instance of an IKE + security association. It is therefore possible for a single instance + of IKE to multiplex distinct sessions with multiple peers. + + All multi-octet fields representing integers are laid out in big + endian order (aka most significant byte first, or network byte + order). + + The format of the IKE header is shown in Figure 4. + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! IKE_SA Initiator's SPI ! + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! IKE_SA Responder's SPI ! + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload ! MjVer ! MnVer ! Exchange Type ! Flags ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Message ID ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 4: IKE Header Format + + o Initiator's SPI (8 octets) - A value chosen by the initiator to + identify a unique IKE security association. This value MUST NOT + be zero. + + + +Hoffman Expires July 5, 2006 [Page 54] + +Internet-Draft IKEv2 January 2006 + + + o Responder's SPI (8 octets) - A value chosen by the responder to + identify a unique IKE security association. This value MUST be + zero in the first message of an IKE Initial Exchange (including + repeats of that message including a cookie). {{ The phrase "and + MUST NOT be zero in any other message" was removed; Clarif-2.1 }} + + o Next Payload (1 octet) - Indicates the type of payload that + immediately follows the header. The format and value of each + payload are defined below. + + o Major Version (4 bits) - Indicates the major version of the IKE + protocol in use. Implementations based on this version of IKE + MUST set the Major Version to 2. Implementations based on + previous versions of IKE and ISAKMP MUST set the Major Version to + 1. Implementations based on this version of IKE MUST reject or + ignore messages containing a version number greater than 2. + + o Minor Version (4 bits) - Indicates the minor version of the IKE + protocol in use. Implementations based on this version of IKE + MUST set the Minor Version to 0. They MUST ignore the minor + version number of received messages. + + o Exchange Type (1 octet) - Indicates the type of exchange being + used. This constrains the payloads sent in each message and + orderings of messages in an exchange. + + Exchange Type Value + ---------------------------------- + RESERVED 0-33 + IKE_SA_INIT 34 + IKE_AUTH 35 + CREATE_CHILD_SA 36 + INFORMATIONAL 37 + RESERVED TO IANA 38-239 + Reserved for private use 240-255 + + o Flags (1 octet) - Indicates specific options that are set for the + message. Presence of options are indicated by the appropriate bit + in the flags field being set. The bits are defined LSB first, so + bit 0 would be the least significant bit of the Flags octet. In + the description below, a bit being 'set' means its value is '1', + while 'cleared' means its value is '0'. + + * X(reserved) (bits 0-2) - These bits MUST be cleared when + sending and MUST be ignored on receipt. + + * I(nitiator) (bit 3 of Flags) - This bit MUST be set in messages + sent by the original initiator of the IKE_SA and MUST be + + + +Hoffman Expires July 5, 2006 [Page 55] + +Internet-Draft IKEv2 January 2006 + + + cleared in messages sent by the original responder. It is used + by the recipient to determine which eight octets of the SPI + were generated by the recipient. + + * V(ersion) (bit 4 of Flags) - This bit indicates that the + transmitter is capable of speaking a higher major version + number of the protocol than the one indicated in the major + version number field. Implementations of IKEv2 must clear this + bit when sending and MUST ignore it in incoming messages. + + * R(esponse) (bit 5 of Flags) - This bit indicates that this + message is a response to a message containing the same message + ID. This bit MUST be cleared in all request messages and MUST + be set in all responses. An IKE endpoint MUST NOT generate a + response to a message that is marked as being a response. + + * X(reserved) (bits 6-7 of Flags) - These bits MUST be cleared + when sending and MUST be ignored on receipt. + + o Message ID (4 octets) - Message identifier used to control + retransmission of lost packets and matching of requests and + responses. It is essential to the security of the protocol + because it is used to prevent message replay attacks. See + Section 2.1 and Section 2.2. + + o Length (4 octets) - Length of total message (header + payloads) in + octets. + +3.2. Generic Payload Header + + Each IKE payload defined in Section 3.3 through Section 3.16 begins + with a generic payload header, shown in Figure 5. Figures for each + payload below will include the generic payload header, but for + brevity the description of each field will be omitted. + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 5: Generic Payload Header + + The Generic Payload Header fields are defined as follows: + + o Next Payload (1 octet) - Identifier for the payload type of the + next payload in the message. If the current payload is the last + in the message, then this field will be 0. This field provides a + + + +Hoffman Expires July 5, 2006 [Page 56] + +Internet-Draft IKEv2 January 2006 + + + "chaining" capability whereby additional payloads can be added to + a message by appending it to the end of the message and setting + the "Next Payload" field of the preceding payload to indicate the + new payload's type. An Encrypted payload, which must always be + the last payload of a message, is an exception. It contains data + structures in the format of additional payloads. In the header of + an Encrypted payload, the Next Payload field is set to the payload + type of the first contained payload (instead of 0). The payload + type values are: + + Next Payload Type Notation Value + -------------------------------------------------- + No Next Payload 0 + RESERVED 1-32 + Security Association SA 33 + Key Exchange KE 34 + Identification - Initiator IDi 35 + Identification - Responder IDr 36 + Certificate CERT 37 + Certificate Request CERTREQ 38 + Authentication AUTH 39 + Nonce Ni, Nr 40 + Notify N 41 + Delete D 42 + Vendor ID V 43 + Traffic Selector - Initiator TSi 44 + Traffic Selector - Responder TSr 45 + Encrypted E 46 + Configuration CP 47 + Extensible Authentication EAP 48 + RESERVED TO IANA 49-127 + PRIVATE USE 128-255 + + (Payload type values 1-32 should not be assigned in the + future so that there is no overlap with the code assignments + for IKEv1.) + + o Critical (1 bit) - MUST be set to zero if the sender wants the + recipient to skip this payload if it does not understand the + payload type code in the Next Payload field of the previous + payload. MUST be set to one if the sender wants the recipient to + reject this entire message if it does not understand the payload + type. MUST be ignored by the recipient if the recipient + understands the payload type code. MUST be set to zero for + payload types defined in this document. Note that the critical + bit applies to the current payload rather than the "next" payload + whose type code appears in the first octet. The reasoning behind + not setting the critical bit for payloads defined in this document + + + +Hoffman Expires July 5, 2006 [Page 57] + +Internet-Draft IKEv2 January 2006 + + + is that all implementations MUST understand all payload types + defined in this document and therefore must ignore the Critical + bit's value. Skipped payloads are expected to have valid Next + Payload and Payload Length fields. + + o RESERVED (7 bits) - MUST be sent as zero; MUST be ignored on + receipt. + + o Payload Length (2 octets) - Length in octets of the current + payload, including the generic payload header. + +3.3. Security Association Payload + + The Security Association Payload, denoted SA in this memo, is used to + negotiate attributes of a security association. Assembly of Security + Association Payloads requires great peace of mind. An SA payload MAY + contain multiple proposals. If there is more than one, they MUST be + ordered from most preferred to least preferred. Each proposal may + contain multiple IPsec protocols (where a protocol is IKE, ESP, or + AH), each protocol MAY contain multiple transforms, and each + transform MAY contain multiple attributes. When parsing an SA, an + implementation MUST check that the total Payload Length is consistent + with the payload's internal lengths and counts. Proposals, + Transforms, and Attributes each have their own variable length + encodings. They are nested such that the Payload Length of an SA + includes the combined contents of the SA, Proposal, Transform, and + Attribute information. The length of a Proposal includes the lengths + of all Transforms and Attributes it contains. The length of a + Transform includes the lengths of all Attributes it contains. + + The syntax of Security Associations, Proposals, Transforms, and + Attributes is based on ISAKMP; however the semantics are somewhat + different. The reason for the complexity and the hierarchy is to + allow for multiple possible combinations of algorithms to be encoded + in a single SA. Sometimes there is a choice of multiple algorithms, + whereas other times there is a combination of algorithms. For + example, an initiator might want to propose using (AH w/MD5 and ESP + w/3DES) OR (ESP w/MD5 and 3DES). + + One of the reasons the semantics of the SA payload has changed from + ISAKMP and IKEv1 is to make the encodings more compact in common + cases. + + The Proposal structure contains within it a Proposal # and an IPsec + protocol ID. Each structure MUST have the same Proposal # as the + previous one or be one (1) greater. The first Proposal MUST have a + Proposal # of one (1). If two successive structures have the same + Proposal number, it means that the proposal consists of the first + + + +Hoffman Expires July 5, 2006 [Page 58] + +Internet-Draft IKEv2 January 2006 + + + structure AND the second. So a proposal of AH AND ESP would have two + proposal structures, one for AH and one for ESP and both would have + Proposal #1. A proposal of AH OR ESP would have two proposal + structures, one for AH with Proposal #1 and one for ESP with Proposal + #2. + + Each Proposal/Protocol structure is followed by one or more transform + structures. The number of different transforms is generally + determined by the Protocol. AH generally has a single transform: an + integrity check algorithm. ESP generally has two: an encryption + algorithm and an integrity check algorithm. IKE generally has four + transforms: a Diffie-Hellman group, an integrity check algorithm, a + prf algorithm, and an encryption algorithm. If an algorithm that + combines encryption and integrity protection is proposed, it MUST be + proposed as an encryption algorithm and an integrity protection + algorithm MUST NOT be proposed. For each Protocol, the set of + permissible transforms is assigned transform ID numbers, which appear + in the header of each transform. + + If there are multiple transforms with the same Transform Type, the + proposal is an OR of those transforms. If there are multiple + Transforms with different Transform Types, the proposal is an AND of + the different groups. For example, to propose ESP with (3DES or + IDEA) and (HMAC_MD5 or HMAC_SHA), the ESP proposal would contain two + Transform Type 1 candidates (one for 3DES and one for IDEA) and two + Transform Type 2 candidates (one for HMAC_MD5 and one for HMAC_SHA). + This effectively proposes four combinations of algorithms. If the + initiator wanted to propose only a subset of those, for example (3DES + and HMAC_MD5) or (IDEA and HMAC_SHA), there is no way to encode that + as multiple transforms within a single Proposal. Instead, the + initiator would have to construct two different Proposals, each with + two transforms. + + A given transform MAY have one or more Attributes. Attributes are + necessary when the transform can be used in more than one way, as + when an encryption algorithm has a variable key size. The transform + would specify the algorithm and the attribute would specify the key + size. Most transforms do not have attributes. A transform MUST NOT + have multiple attributes of the same type. To propose alternate + values for an attribute (for example, multiple key sizes for the AES + encryption algorithm), and implementation MUST include multiple + Transforms with the same Transform Type each with a single Attribute. + + Note that the semantics of Transforms and Attributes are quite + different from those in IKEv1. In IKEv1, a single Transform carried + multiple algorithms for a protocol with one carried in the Transform + and the others carried in the Attributes. + + + + +Hoffman Expires July 5, 2006 [Page 59] + +Internet-Draft IKEv2 January 2006 + + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ <Proposals> ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 6: Security Association Payload + + o Proposals (variable) - One or more proposal substructures. + + The payload type for the Security Association Payload is thirty three + (33). + +3.3.1. Proposal Substructure + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! 0 (last) or 2 ! RESERVED ! Proposal Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Proposal # ! Protocol ID ! SPI Size !# of Transforms! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ~ SPI (variable) ~ + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ <Transforms> ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 7: Proposal Substructure + + o 0 (last) or 2 (more) (1 octet) - Specifies whether this is the + last Proposal Substructure in the SA. This syntax is inherited + from ISAKMP, but is unnecessary because the last Proposal could be + identified from the length of the SA. The value (2) corresponds + to a Payload Type of Proposal in IKEv1, and the first four octets + of the Proposal structure are designed to look somewhat like the + header of a Payload. + + o RESERVED (1 octet) - MUST be sent as zero; MUST be ignored on + receipt. + + o Proposal Length (2 octets) - Length of this proposal, including + all transforms and attributes that follow. + + + +Hoffman Expires July 5, 2006 [Page 60] + +Internet-Draft IKEv2 January 2006 + + + o Proposal # (1 octet) - When a proposal is made, the first proposal + in an SA payload MUST be #1, and subsequent proposals MUST either + be the same as the previous proposal (indicating an AND of the two + proposals) or one more than the previous proposal (indicating an + OR of the two proposals). When a proposal is accepted, all of the + proposal numbers in the SA payload MUST be the same and MUST match + the number on the proposal sent that was accepted. + + o Protocol ID (1 octet) - Specifies the IPsec protocol identifier + for the current negotiation. The defined values are: + + Protocol Protocol ID + ----------------------------------- + RESERVED 0 + IKE 1 + AH 2 + ESP 3 + RESERVED TO IANA 4-200 + PRIVATE USE 201-255 + + o SPI Size (1 octet) - For an initial IKE_SA negotiation, this field + MUST be zero; the SPI is obtained from the outer header. During + subsequent negotiations, it is equal to the size, in octets, of + the SPI of the corresponding protocol (8 for IKE, 4 for ESP and + AH). + + o # of Transforms (1 octet) - Specifies the number of transforms in + this proposal. + + o SPI (variable) - The sending entity's SPI. Even if the SPI Size + is not a multiple of 4 octets, there is no padding applied to the + payload. When the SPI Size field is zero, this field is not + present in the Security Association payload. + + o Transforms (variable) - One or more transform substructures. + + + + + + + + + + + + + + + + +Hoffman Expires July 5, 2006 [Page 61] + +Internet-Draft IKEv2 January 2006 + + +3.3.2. Transform Substructure + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! 0 (last) or 3 ! RESERVED ! Transform Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + !Transform Type ! RESERVED ! Transform ID ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ Transform Attributes ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 8: Transform Substructure + + o 0 (last) or 3 (more) (1 octet) - Specifies whether this is the + last Transform Substructure in the Proposal. This syntax is + inherited from ISAKMP, but is unnecessary because the last + Proposal could be identified from the length of the SA. The value + (3) corresponds to a Payload Type of Transform in IKEv1, and the + first four octets of the Transform structure are designed to look + somewhat like the header of a Payload. + + o RESERVED - MUST be sent as zero; MUST be ignored on receipt. + + o Transform Length - The length (in octets) of the Transform + Substructure including Header and Attributes. + + o Transform Type (1 octet) - The type of transform being specified + in this transform. Different protocols support different + transform types. For some protocols, some of the transforms may + be optional. If a transform is optional and the initiator wishes + to propose that the transform be omitted, no transform of the + given type is included in the proposal. If the initiator wishes + to make use of the transform optional to the responder, it + includes a transform substructure with transform ID = 0 as one of + the options. + + o Transform ID (2 octets) - The specific instance of the transform + type being proposed. + + The tranform type values are: + + + + + + + + +Hoffman Expires July 5, 2006 [Page 62] + +Internet-Draft IKEv2 January 2006 + + + Description Trans. Used In + Type + ------------------------------------------------------------------ + RESERVED 0 + Encryption Algorithm (ENCR) 1 IKE and ESP + Pseudo-random Function (PRF) 2 IKE + Integrity Algorithm (INTEG) 3 IKE, AH, optional in ESP + Diffie-Hellman Group (D-H) 4 IKE, optional in AH & ESP + Extended Sequence Numbers (ESN) 5 AH and ESP + RESERVED TO IANA 6-240 + PRIVATE USE 241-255 + + For Transform Type 1 (Encryption Algorithm), defined Transform IDs + are: + + Name Number Defined In + --------------------------------------------------- + RESERVED 0 + ENCR_DES_IV64 1 (RFC1827) + ENCR_DES 2 (RFC2405), [DES] + ENCR_3DES 3 (RFC2451) + ENCR_RC5 4 (RFC2451) + ENCR_IDEA 5 (RFC2451), [IDEA] + ENCR_CAST 6 (RFC2451) + ENCR_BLOWFISH 7 (RFC2451) + ENCR_3IDEA 8 (RFC2451) + ENCR_DES_IV32 9 + RESERVED 10 + ENCR_NULL 11 (RFC2410) + ENCR_AES_CBC 12 (RFC3602) + ENCR_AES_CTR 13 (RFC3664) + RESERVED TO IANA 14-1023 + PRIVATE USE 1024-65535 + + For Transform Type 2 (Pseudo-random Function), defined Transform IDs + are: + + Name Number Defined In + ------------------------------------------------------ + RESERVED 0 + PRF_HMAC_MD5 1 (RFC2104), [MD5] + PRF_HMAC_SHA1 2 (RFC2104), [SHA] + PRF_HMAC_TIGER 3 (RFC2104) + PRF_AES128_XCBC 4 (RFC3664) + RESERVED TO IANA 5-1023 + PRIVATE USE 1024-65535 + + For Transform Type 3 (Integrity Algorithm), defined Transform IDs + + + +Hoffman Expires July 5, 2006 [Page 63] + +Internet-Draft IKEv2 January 2006 + + + are: + + Name Number Defined In + ---------------------------------------- + NONE 0 + AUTH_HMAC_MD5_96 1 (RFC2403) + AUTH_HMAC_SHA1_96 2 (RFC2404) + AUTH_DES_MAC 3 + AUTH_KPDK_MD5 4 (RFC1826) + AUTH_AES_XCBC_96 5 (RFC3566) + RESERVED TO IANA 6-1023 + PRIVATE USE 1024-65535 + + For Transform Type 4 (Diffie-Hellman Group), defined Transform IDs + are: + + Name Number + -------------------------------------- + NONE 0 + Defined in Appendix B 1 - 2 + RESERVED 3 - 4 + Defined in [ADDGROUP] 5 + RESERVED TO IANA 6 - 13 + Defined in [ADDGROUP] 14 - 18 + RESERVED TO IANA 19 - 1023 + PRIVATE USE 1024-65535 + + For Transform Type 5 (Extended Sequence Numbers), defined Transform + IDs are: + + Name Number + -------------------------------------------- + No Extended Sequence Numbers 0 + Extended Sequence Numbers 1 + RESERVED 2 - 65535 + +3.3.3. Valid Transform Types by Protocol + + The number and type of transforms that accompany an SA payload are + dependent on the protocol in the SA itself. An SA payload proposing + the establishment of an SA has the following mandatory and optional + transform types. A compliant implementation MUST understand all + mandatory and optional types for each protocol it supports (though it + need not accept proposals with unacceptable suites). A proposal MAY + omit the optional types if the only value for them it will accept is + NONE. + + + + + +Hoffman Expires July 5, 2006 [Page 64] + +Internet-Draft IKEv2 January 2006 + + + Protocol Mandatory Types Optional Types + --------------------------------------------------- + IKE ENCR, PRF, INTEG, D-H + ESP ENCR, ESN INTEG, D-H + AH INTEG, ESN D-H + +3.3.4. Mandatory Transform IDs + + The specification of suites that MUST and SHOULD be supported for + interoperability has been removed from this document because they are + likely to change more rapidly than this document evolves. + + An important lesson learned from IKEv1 is that no system should only + implement the mandatory algorithms and expect them to be the best + choice for all customers. For example, at the time that this + document was written, many IKEv1 implementers were starting to + migrate to AES in Cipher Block Chaining (CBC) mode for Virtual + Private Network (VPN) applications. Many IPsec systems based on + IKEv2 will implement AES, additional Diffie-Hellman groups, and + additional hash algorithms, and some IPsec customers already require + these algorithms in addition to the ones listed above. + + It is likely that IANA will add additional transforms in the future, + and some users may want to use private suites, especially for IKE + where implementations should be capable of supporting different + parameters, up to certain size limits. In support of this goal, all + implementations of IKEv2 SHOULD include a management facility that + allows specification (by a user or system administrator) of Diffie- + Hellman (DH) parameters (the generator, modulus, and exponent lengths + and values) for new DH groups. Implementations SHOULD provide a + management interface through which these parameters and the + associated transform IDs may be entered (by a user or system + administrator), to enable negotiating such groups. + + All implementations of IKEv2 MUST include a management facility that + enables a user or system administrator to specify the suites that are + acceptable for use with IKE. Upon receipt of a payload with a set of + transform IDs, the implementation MUST compare the transmitted + transform IDs against those locally configured via the management + controls, to verify that the proposed suite is acceptable based on + local policy. The implementation MUST reject SA proposals that are + not authorized by these IKE suite controls. Note that cryptographic + suites that MUST be implemented need not be configured as acceptable + to local policy. + + + + + + + +Hoffman Expires July 5, 2006 [Page 65] + +Internet-Draft IKEv2 January 2006 + + +3.3.5. Transform Attributes + + Each transform in a Security Association payload may include + attributes that modify or complete the specification of the + transform. These attributes are type/value pairs and are defined + below. For example, if an encryption algorithm has a variable-length + key, the key length to be used may be specified as an attribute. + Attributes can have a value with a fixed two octet length or a + variable-length value. For the latter, the attribute is encoded as + type/length/value. + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + !A! Attribute Type ! AF=0 Attribute Length ! + !F! ! AF=1 Attribute Value ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! AF=0 Attribute Value ! + ! AF=1 Not Transmitted ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 9: Data Attributes + + o Attribute Type (2 octets) - Unique identifier for each type of + attribute (see below). The most significant bit of this field is + the Attribute Format bit (AF). It indicates whether the data + attributes follow the Type/Length/Value (TLV) format or a + shortened Type/Value (TV) format. If the AF bit is zero (0), then + the Data Attributes are of the Type/Length/Value (TLV) form. If + the AF bit is a one (1), then the Data Attributes are of the Type/ + Value form. + + o Attribute Length (2 octets) - Length in octets of the Attribute + Value. When the AF bit is a one (1), the Attribute Value is only + 2 octets and the Attribute Length field is not present. + + o Attribute Value (variable length) - Value of the Attribute + associated with the Attribute Type. If the AF bit is a zero (0), + this field has a variable length defined by the Attribute Length + field. If the AF bit is a one (1), the Attribute Value has a + length of 2 octets. + + o Key Length - When using an Encryption Algorithm that has a + variable-length key, this attribute specifies the key length in + bits (MUST use network byte order). This attribute MUST NOT be + used when the specified Encryption Algorithm uses a fixed-length + key. + + + + +Hoffman Expires July 5, 2006 [Page 66] + +Internet-Draft IKEv2 January 2006 + + + Note that only a single attribute type (Key Length) is defined, and + it is fixed length. The variable-length encoding specification is + included only for future extensions. {{ Clarif-7.11 removed the + sentence that listed, incorrectly, the algorithms defined in the + document that accept attributes. }} + + Attributes described as basic MUST NOT be encoded using the variable- + length encoding. Variable-length attributes MUST NOT be encoded as + basic even if their value can fit into two octets. NOTE: This is a + change from IKEv1, where increased flexibility may have simplified + the composer of messages but certainly complicated the parser. + + Attribute Type Value Attribute Format + ------------------------------------------------------------ + RESERVED 0-13 + Key Length (in bits) 14 TV + RESERVED 15-17 + RESERVED TO IANA 18-16383 + PRIVATE USE 16384-32767 + Values 0-13 and 15-17 were used in a similar context in + IKEv1, and should not be assigned except to matching values. + +3.3.6. Attribute Negotiation + + During security association negotiation initiators present offers to + responders. Responders MUST select a single complete set of + parameters from the offers (or reject all offers if none are + acceptable). If there are multiple proposals, the responder MUST + choose a single proposal number and return all of the Proposal + substructures with that Proposal number. If there are multiple + Transforms with the same type, the responder MUST choose a single + one. Any attributes of a selected transform MUST be returned + unmodified. The initiator of an exchange MUST check that the + accepted offer is consistent with one of its proposals, and if not + that response MUST be rejected. + + Negotiating Diffie-Hellman groups presents some special challenges. + SA offers include proposed attributes and a Diffie-Hellman public + number (KE) in the same message. If in the initial exchange the + initiator offers to use one of several Diffie-Hellman groups, it + SHOULD pick the one the responder is most likely to accept and + include a KE corresponding to that group. If the guess turns out to + be wrong, the responder will indicate the correct group in the + response and the initiator SHOULD pick an element of that group for + its KE value when retrying the first message. It SHOULD, however, + continue to propose its full supported set of groups in order to + prevent a man-in-the-middle downgrade attack. + + + + +Hoffman Expires July 5, 2006 [Page 67] + +Internet-Draft IKEv2 January 2006 + + + Implementation Note: + + Certain negotiable attributes can have ranges or could have multiple + acceptable values. These include the key length of a variable key + length symmetric cipher. To further interoperability and to support + upgrading endpoints independently, implementers of this protocol + SHOULD accept values that they deem to supply greater security. For + instance, if a peer is configured to accept a variable-length cipher + with a key length of X bits and is offered that cipher with a larger + key length, the implementation SHOULD accept the offer if it supports + use of the longer key. + + Support of this capability allows an implementation to express a + concept of "at least" a certain level of security-- "a key length of + _at least_ X bits for cipher Y". + +3.4. Key Exchange Payload + + The Key Exchange Payload, denoted KE in this memo, is used to + exchange Diffie-Hellman public numbers as part of a Diffie-Hellman + key exchange. The Key Exchange Payload consists of the IKE generic + payload header followed by the Diffie-Hellman public value itself. + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! DH Group # ! RESERVED ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ Key Exchange Data ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 10: Key Exchange Payload Format + + A key exchange payload is constructed by copying one's Diffie-Hellman + public value into the "Key Exchange Data" portion of the payload. + The length of the Diffie-Hellman public value MUST be equal to the + length of the prime modulus over which the exponentiation was + performed, prepending zero bits to the value if necessary. + + The DH Group # identifies the Diffie-Hellman group in which the Key + Exchange Data was computed (see Section 3.3.2). If the selected + proposal uses a different Diffie-Hellman group, the message MUST be + rejected with a Notify payload of type INVALID_KE_PAYLOAD. + + + + +Hoffman Expires July 5, 2006 [Page 68] + +Internet-Draft IKEv2 January 2006 + + + The payload type for the Key Exchange payload is thirty four (34). + +3.5. Identification Payloads + + The Identification Payloads, denoted IDi and IDr in this memo, allow + peers to assert an identity to one another. This identity may be + used for policy lookup, but does not necessarily have to match + anything in the CERT payload; both fields may be used by an + implementation to perform access control decisions. {{ Clarif-7.1 }} + When using the ID_IPV4_ADDR/ID_IPV6_ADDR identity types in IDi/IDr + payloads, IKEv2 does not require this address to match the address in + the IP header of IKEv2 packets, or anything in the TSi/TSr payloads. + The contents of IDi/IDr is used purely to fetch the policy and + authentication data related to the other party. + + NOTE: In IKEv1, two ID payloads were used in each direction to hold + Traffic Selector (TS) information for data passing over the SA. In + IKEv2, this information is carried in TS payloads (see Section 3.13). + + The Identification Payload consists of the IKE generic payload header + followed by identification fields as follows: + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ID Type ! RESERVED | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ Identification Data ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 11: Identification Payload Format + + o ID Type (1 octet) - Specifies the type of Identification being + used. + + o RESERVED - MUST be sent as zero; MUST be ignored on receipt. + + o Identification Data (variable length) - Value, as indicated by the + Identification Type. The length of the Identification Data is + computed from the size in the ID payload header. + + The payload types for the Identification Payload are thirty five (35) + for IDi and thirty six (36) for IDr. + + + + +Hoffman Expires July 5, 2006 [Page 69] + +Internet-Draft IKEv2 January 2006 + + + The following table lists the assigned values for the Identification + Type field: + + ID Type Value + ------------------------------------------------------------------- + RESERVED 0 + + ID_IPV4_ADDR 1 + A single four (4) octet IPv4 address. + + ID_FQDN 2 + A fully-qualified domain name string. An example of a ID_FQDN + is, "example.com". The string MUST not contain any terminators + (e.g., NULL, CR, etc.). + + ID_RFC822_ADDR 3 + A fully-qualified RFC822 email address string, An example of a + ID_RFC822_ADDR is, "jsmith@example.com". The string MUST not + contain any terminators. + + RESERVED TO IANA 4 + + ID_IPV6_ADDR 5 + A single sixteen (16) octet IPv6 address. + + RESERVED TO IANA 6 - 8 + + ID_DER_ASN1_DN 9 + The binary Distinguished Encoding Rules (DER) encoding of an + ASN.1 X.500 Distinguished Name [X.501]. + + ID_DER_ASN1_GN 10 + The binary DER encoding of an ASN.1 X.500 GeneralName [X.509]. + + ID_KEY_ID 11 + An opaque octet stream which may be used to pass vendor- + specific information necessary to do certain proprietary + types of identification. + + RESERVED TO IANA 12-200 + + PRIVATE USE 201-255 + + Two implementations will interoperate only if each can generate a + type of ID acceptable to the other. To assure maximum + interoperability, implementations MUST be configurable to send at + least one of ID_IPV4_ADDR, ID_FQDN, ID_RFC822_ADDR, or ID_KEY_ID, and + MUST be configurable to accept all of these types. Implementations + + + +Hoffman Expires July 5, 2006 [Page 70] + +Internet-Draft IKEv2 January 2006 + + + SHOULD be capable of generating and accepting all of these types. + IPv6-capable implementations MUST additionally be configurable to + accept ID_IPV6_ADDR. IPv6-only implementations MAY be configurable + to send only ID_IPV6_ADDR. + + {{ Clarif-3.4 }} EAP [EAP] does not mandate the use of any particular + type of identifier, but often EAP is used with Network Access + Identifiers (NAIs) defined in [NAI]. Although NAIs look a bit like + email addresses (e.g., "joe@example.com"), the syntax is not exactly + the same as the syntax of email address in [MAILFORMAT]. For those + NAIs that include the realm component, the ID_RFC822_ADDR + identification type SHOULD be used. Responder implementations should + not attempt to verify that the contents actually conform to the exact + syntax given in [MAILFORMAT], but instead should accept any + reasonable-looking NAI. For NAIs that do not include the realm + component,the ID_KEY_ID identification type SHOULD be used. + +3.6. Certificate Payload + + The Certificate Payload, denoted CERT in this memo, provides a means + to transport certificates or other authentication-related information + via IKE. Certificate payloads SHOULD be included in an exchange if + certificates are available to the sender unless the peer has + indicated an ability to retrieve this information from elsewhere + using an HTTP_CERT_LOOKUP_SUPPORTED Notify payload. Note that the + term "Certificate Payload" is somewhat misleading, because not all + authentication mechanisms use certificates and data other than + certificates may be passed in this payload. + + The Certificate Payload is defined as follows: + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Cert Encoding ! ! + +-+-+-+-+-+-+-+-+ ! + ~ Certificate Data ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 12: Certificate Payload Format + + o Certificate Encoding (1 octet) - This field indicates the type of + certificate or certificate-related information contained in the + Certificate Data field. + + + + +Hoffman Expires July 5, 2006 [Page 71] + +Internet-Draft IKEv2 January 2006 + + + Certificate Encoding Value + ------------------------------------------------- + RESERVED 0 + PKCS #7 wrapped X.509 certificate 1 + PGP Certificate 2 + DNS Signed Key 3 + X.509 Certificate - Signature 4 + Kerberos Token 6 + Certificate Revocation List (CRL) 7 + Authority Revocation List (ARL) 8 + SPKI Certificate 9 + X.509 Certificate - Attribute 10 + Raw RSA Key 11 + Hash and URL of X.509 certificate 12 + Hash and URL of X.509 bundle 13 + RESERVED to IANA 14 - 200 + PRIVATE USE 201 - 255 + + o Certificate Data (variable length) - Actual encoding of + certificate data. The type of certificate is indicated by the + Certificate Encoding field. + + The payload type for the Certificate Payload is thirty seven (37). + + Specific syntax is for some of the certificate type codes above is + not defined in this document. The types whose syntax is defined in + this document are: + + o X.509 Certificate - Signature (4) contains a DER encoded X.509 + certificate whose public key is used to validate the sender's AUTH + payload. + + o Certificate Revocation List (7) contains a DER encoded X.509 + certificate revocation list. + + o {{ Added "DER-encoded RSAPublicKey structure" from Clarif-3.7 }} + Raw RSA Key (11) contains a PKCS #1 encoded RSA key, that is, a + DER-encoded RSAPublicKey structure (see [RSA] and [PKCS1]). + + o Hash and URL encodings (12-13) allow IKE messages to remain short + by replacing long data structures with a 20 octet SHA-1 hash (see + [SHA]) of the replaced value followed by a variable-length URL + that resolves to the DER encoded data structure itself. This + improves efficiency when the endpoints have certificate data + cached and makes IKE less subject to denial of service attacks + that become easier to mount when IKE messages are large enough to + require IP fragmentation [DOSUDPPROT]. + + + + +Hoffman Expires July 5, 2006 [Page 72] + +Internet-Draft IKEv2 January 2006 + + + Use the following ASN.1 definition for an X.509 bundle: + + CertBundle + { iso(1) identified-organization(3) dod(6) internet(1) + security(5) mechanisms(5) pkix(7) id-mod(0) + id-mod-cert-bundle(34) } + + DEFINITIONS EXPLICIT TAGS ::= + BEGIN + + IMPORTS + Certificate, CertificateList + FROM PKIX1Explicit88 + { iso(1) identified-organization(3) dod(6) + internet(1) security(5) mechanisms(5) pkix(7) + id-mod(0) id-pkix1-explicit(18) } ; + + CertificateOrCRL ::= CHOICE { + cert [0] Certificate, + crl [1] CertificateList } + + CertificateBundle ::= SEQUENCE OF CertificateOrCRL + + END + + Implementations MUST be capable of being configured to send and + accept up to four X.509 certificates in support of authentication, + and also MUST be capable of being configured to send and accept the + first two Hash and URL formats (with HTTP URLs). Implementations + SHOULD be capable of being configured to send and accept Raw RSA + keys. If multiple certificates are sent, the first certificate MUST + contain the public key used to sign the AUTH payload. The other + certificates may be sent in any order. + + {{ Clarif-3.7 }} Because the contents and use of some of the + certificate types are not defined, they SHOULD NOT be used. In + specific, implementations SHOULD NOT use the following types unless + they are later defined in a standards-track document: + + PKCS #7 wrapped X.509 certificate 1 + PGP Certificate 2 + DNS Signed Key 3 + Kerberos Token 6 + SPKI Certificate 9 + + + + + + + +Hoffman Expires July 5, 2006 [Page 73] + +Internet-Draft IKEv2 January 2006 + + +3.7. Certificate Request Payload + + The Certificate Request Payload, denoted CERTREQ in this memo, + provides a means to request preferred certificates via IKE and can + appear in the IKE_INIT_SA response and/or the IKE_AUTH request. + Certificate Request payloads MAY be included in an exchange when the + sender needs to get the certificate of the receiver. If multiple CAs + are trusted and the cert encoding does not allow a list, then + multiple Certificate Request payloads SHOULD be transmitted. + + The Certificate Request Payload is defined as follows: + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Cert Encoding ! ! + +-+-+-+-+-+-+-+-+ ! + ~ Certification Authority ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 13: Certificate Request Payload Format + + o Certificate Encoding (1 octet) - Contains an encoding of the type + or format of certificate requested. Values are listed in + Section 3.6. + + o Certification Authority (variable length) - Contains an encoding + of an acceptable certification authority for the type of + certificate requested. + + The payload type for the Certificate Request Payload is thirty eight + (38). + + The Certificate Encoding field has the same values as those defined + in Section 3.6. The Certification Authority field contains an + indicator of trusted authorities for this certificate type. The + Certification Authority value is a concatenated list of SHA-1 hashes + of the public keys of trusted Certification Authorities (CAs). Each + is encoded as the SHA-1 hash of the Subject Public Key Info element + (see section 4.1.2.7 of [PKIX]) from each Trust Anchor certificate. + The twenty-octet hashes are concatenated and included with no other + formatting. + + {{ Clarif-3.7 }} The contents of the "Certification Authority" field + are defined only for X.509 certificates, which are types 4, 10, 12, + + + +Hoffman Expires July 5, 2006 [Page 74] + +Internet-Draft IKEv2 January 2006 + + + and 13. Other values SHOULD NOT be used until standards-track + specifications that specify their use are published. + + Note that the term "Certificate Request" is somewhat misleading, in + that values other than certificates are defined in a "Certificate" + payload and requests for those values can be present in a Certificate + Request Payload. The syntax of the Certificate Request payload in + such cases is not defined in this document. + + The Certificate Request Payload is processed by inspecting the "Cert + Encoding" field to determine whether the processor has any + certificates of this type. If so, the "Certification Authority" + field is inspected to determine if the processor has any certificates + that can be validated up to one of the specified certification + authorities. This can be a chain of certificates. + + If an end-entity certificate exists that satisfies the criteria + specified in the CERTREQ, a certificate or certificate chain SHOULD + be sent back to the certificate requestor if the recipient of the + CERTREQ: + + o is configured to use certificate authentication, + + o is allowed to send a CERT payload, + + o has matching CA trust policy governing the current negotiation, + and + + o has at least one time-wise and usage appropriate end-entity + certificate chaining to a CA provided in the CERTREQ. + + Certificate revocation checking must be considered during the + chaining process used to select a certificate. Note that even if two + peers are configured to use two different CAs, cross-certification + relationships should be supported by appropriate selection logic. + + The intent is not to prevent communication through the strict + adherence of selection of a certificate based on CERTREQ, when an + alternate certificate could be selected by the sender that would + still enable the recipient to successfully validate and trust it + through trust conveyed by cross-certification, CRLs, or other out-of- + band configured means. Thus, the processing of a CERTREQ should be + seen as a suggestion for a certificate to select, not a mandated one. + If no certificates exist, then the CERTREQ is ignored. This is not + an error condition of the protocol. There may be cases where there + is a preferred CA sent in the CERTREQ, but an alternate might be + acceptable (perhaps after prompting a human operator). + + + + +Hoffman Expires July 5, 2006 [Page 75] + +Internet-Draft IKEv2 January 2006 + + +3.8. Authentication Payload + + The Authentication Payload, denoted AUTH in this memo, contains data + used for authentication purposes. The syntax of the Authentication + data varies according to the Auth Method as specified below. + + The Authentication Payload is defined as follows: + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Auth Method ! RESERVED ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ Authentication Data ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 14: Authentication Payload Format + + o Auth Method (1 octet) - Specifies the method of authentication + used. Values defined are: + + * RSA Digital Signature (1) - Computed as specified in + Section 2.15 using an RSA private key over a PKCS#1 padded hash + (see [RSA] and [PKCS1]). {{ Clarif-3.2 }} To promote + interoperability, implementations that support this type SHOULD + support signatures that use SHA-1 as the hash function and + SHOULD use SHA-1 as the default hash function when generating + signatures. {{ Clarif-3.3 }} A newer version of PKCS#1 (v2.1) + defines two different encoding methods (ways of "padding the + hash") for signatures. However, IKEv2 and this document point + specifically to the PKCS#1 v2.0 which has only one encoding + method for signatures (EMSA-PKCS1- v1_5). + + * Shared Key Message Integrity Code (2) - Computed as specified + in Section 2.15 using the shared key associated with the + identity in the ID payload and the negotiated prf function + + * DSS Digital Signature (3) - Computed as specified in + Section 2.15 using a DSS private key (see [DSS]) over a SHA-1 + hash. + + * The values 0 and 4-200 are reserved to IANA. The values 201- + 255 are available for private use. + + + + +Hoffman Expires July 5, 2006 [Page 76] + +Internet-Draft IKEv2 January 2006 + + + o Authentication Data (variable length) - see Section 2.15. + + The payload type for the Authentication Payload is thirty nine (39). + +3.9. Nonce Payload + + The Nonce Payload, denoted Ni and Nr in this memo for the initiator's + and responder's nonce respectively, contains random data used to + guarantee liveness during an exchange and protect against replay + attacks. + + The Nonce Payload is defined as follows: + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ Nonce Data ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 15: Nonce Payload Format + + o Nonce Data (variable length) - Contains the random data generated + by the transmitting entity. + + The payload type for the Nonce Payload is forty (40). + + The size of a Nonce MUST be between 16 and 256 octets inclusive. + Nonce values MUST NOT be reused. + +3.10. Notify Payload + + The Notify Payload, denoted N in this document, is used to transmit + informational data, such as error conditions and state transitions, + to an IKE peer. A Notify Payload may appear in a response message + (usually specifying why a request was rejected), in an INFORMATIONAL + Exchange (to report an error not in an IKE request), or in any other + message to indicate sender capabilities or to modify the meaning of + the request. + + The Notify Payload is defined as follows: + + + + + + + +Hoffman Expires July 5, 2006 [Page 77] + +Internet-Draft IKEv2 January 2006 + + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Protocol ID ! SPI Size ! Notify Message Type ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ Security Parameter Index (SPI) ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ Notification Data ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 16: Notify Payload Format + + o Protocol ID (1 octet) - If this notification concerns an existing + SA, this field indicates the type of that SA. For IKE_SA + notifications, this field MUST be one (1). For notifications + concerning IPsec SAs this field MUST contain either (2) to + indicate AH or (3) to indicate ESP. {{ Clarif-7.8 }} For + notifications that do not relate to an existing SA, this field + MUST be sent as zero and MUST be ignored on receipt; this is only + true for the INVALID_SELECTORS and REKEY_SA notifications. . All + other values for this field are reserved to IANA for future + assignment. + + o SPI Size (1 octet) - Length in octets of the SPI as defined by the + IPsec protocol ID or zero if no SPI is applicable. For a + notification concerning the IKE_SA, the SPI Size MUST be zero. + + o Notify Message Type (2 octets) - Specifies the type of + notification message. + + o SPI (variable length) - Security Parameter Index. + + o Notification Data (variable length) - Informational or error data + transmitted in addition to the Notify Message Type. Values for + this field are type specific (see below). + + The payload type for the Notify Payload is forty one (41). + +3.10.1. Notify Message Types + + Notification information can be error messages specifying why an SA + could not be established. It can also be status data that a process + + + +Hoffman Expires July 5, 2006 [Page 78] + +Internet-Draft IKEv2 January 2006 + + + managing an SA database wishes to communicate with a peer process. + The table below lists the Notification messages and their + corresponding values. The number of different error statuses was + greatly reduced from IKEv1 both for simplification and to avoid + giving configuration information to probers. + + Types in the range 0 - 16383 are intended for reporting errors. An + implementation receiving a Notify payload with one of these types + that it does not recognize in a response MUST assume that the + corresponding request has failed entirely. {{ Demoted the SHOULD }} + Unrecognized error types in a request and status types in a request + or response MUST be ignored, and they should be logged. + + Notify payloads with status types MAY be added to any message and + MUST be ignored if not recognized. They are intended to indicate + capabilities, and as part of SA negotiation are used to negotiate + non-cryptographic parameters. + + NOTIFY messages: error types Value + ------------------------------------------------------------------- + + RESERVED 0 + + UNSUPPORTED_CRITICAL_PAYLOAD 1 + Sent if the payload has the "critical" bit set and the payload + type is not recognized. Notification Data contains the one-octet + payload type. + + INVALID_IKE_SPI 4 + Indicates an IKE message was received with an unrecognized + destination SPI. This usually indicates that the recipient has + rebooted and forgotten the existence of an IKE_SA. + + INVALID_MAJOR_VERSION 5 + Indicates the recipient cannot handle the version of IKE + specified in the header. The closest version number that the + recipient can support will be in the reply header. + + INVALID_SYNTAX 7 + Indicates the IKE message that was received was invalid because + some type, length, or value was out of range or because the + request was rejected for policy reasons. To avoid a denial of + service attack using forged messages, this status may only be + returned for and in an encrypted packet if the message ID and + cryptographic checksum were valid. To avoid leaking information + to someone probing a node, this status MUST be sent in response + to any error not covered by one of the other status types. + {{ Demoted the SHOULD }} To aid debugging, more detailed error + + + +Hoffman Expires July 5, 2006 [Page 79] + +Internet-Draft IKEv2 January 2006 + + + information should be written to a console or log. + + INVALID_MESSAGE_ID 9 + Sent when an IKE message ID outside the supported window is + received. This Notify MUST NOT be sent in a response; the invalid + request MUST NOT be acknowledged. Instead, inform the other side + by initiating an INFORMATIONAL exchange with Notification data + containing the four octet invalid message ID. Sending this + notification is optional, and notifications of this type MUST be + rate limited. + + INVALID_SPI 11 + MAY be sent in an IKE INFORMATIONAL exchange when a node receives + an ESP or AH packet with an invalid SPI. The Notification Data + contains the SPI of the invalid packet. This usually indicates a + node has rebooted and forgotten an SA. If this Informational + Message is sent outside the context of an IKE_SA, it should only + be used by the recipient as a "hint" that something might be + wrong (because it could easily be forged). + + NO_PROPOSAL_CHOSEN 14 + None of the proposed crypto suites was acceptable. + + INVALID_KE_PAYLOAD 17 + The D-H Group # field in the KE payload is not the group # + selected by the responder for this exchange. There are two octets + of data associated with this notification: the accepted D-H Group + # in big endian order. + + AUTHENTICATION_FAILED 24 + Sent in the response to an IKE_AUTH message when for some reason + the authentication failed. There is no associated data. + + SINGLE_PAIR_REQUIRED 34 + This error indicates that a CREATE_CHILD_SA request is + unacceptable because its sender is only willing to accept traffic + selectors specifying a single pair of addresses. The requestor is + expected to respond by requesting an SA for only the specific + traffic it is trying to forward. + + NO_ADDITIONAL_SAS 35 + This error indicates that a CREATE_CHILD_SA request is + unacceptable because the responder is unwilling to accept any + more CHILD_SAs on this IKE_SA. Some minimal implementations may + only accept a single CHILD_SA setup in the context of an initial + IKE exchange and reject any subsequent attempts to add more. + + INTERNAL_ADDRESS_FAILURE 36 + + + +Hoffman Expires July 5, 2006 [Page 80] + +Internet-Draft IKEv2 January 2006 + + + Indicates an error assigning an internal address (i.e., + INTERNAL_IP4_ADDRESS or INTERNAL_IP6_ADDRESS) during the + processing of a Configuration Payload by a responder. If this + error is generated within an IKE_AUTH exchange, no CHILD_SA will + be created. + + FAILED_CP_REQUIRED 37 + Sent by responder in the case where CP(CFG_REQUEST) was expected + but not received, and so is a conflict with locally configured + policy. There is no associated data. + + TS_UNACCEPTABLE 38 + Indicates that none of the addresses/protocols/ports in the + supplied traffic selectors is acceptable. + + INVALID_SELECTORS 39 + MAY be sent in an IKE INFORMATIONAL exchange when a node receives + an ESP or AH packet whose selectors do not match those of the SA + on which it was delivered (and that caused the packet to be + dropped). The Notification Data contains the start of the + offending packet (as in ICMP messages) and the SPI field of the + notification is set to match the SPI of the IPsec SA. + + RESERVED TO IANA 40-8191 + + PRIVATE USE 8192-16383 + + + NOTIFY messages: status types Value + ------------------------------------------------------------------- + + INITIAL_CONTACT 16384 + This notification asserts that this IKE_SA is the only IKE_SA + currently active between the authenticated identities. It MAY be + sent when an IKE_SA is established after a crash, and the + recipient MAY use this information to delete any other IKE_SAs it + has to the same authenticated identity without waiting for a + timeout. This notification MUST NOT be sent by an entity that may + be replicated (e.g., a roaming user's credentials where the user + is allowed to connect to the corporate firewall from two remote + systems at the same time). {{ Clarif-7.9 }} The INITIAL_CONTACT + notification, if sent, MUST be in the first IKE_AUTH request, + not as a separate exchange afterwards. + + SET_WINDOW_SIZE 16385 + This notification asserts that the sending endpoint is capable of + keeping state for multiple outstanding exchanges, permitting the + recipient to send multiple requests before getting a response to + + + +Hoffman Expires July 5, 2006 [Page 81] + +Internet-Draft IKEv2 January 2006 + + + the first. The data associated with a SET_WINDOW_SIZE + notification MUST be 4 octets long and contain the big endian + representation of the number of messages the sender promises to + keep. Window size is always one until the initial exchanges + complete. + + ADDITIONAL_TS_POSSIBLE 16386 + This notification asserts that the sending endpoint narrowed the + proposed traffic selectors but that other traffic selectors would + also have been acceptable, though only in a separate SA (see + section 2.9). There is no data associated with this Notify type. + It may be sent only as an additional payload in a message + including accepted TSs. + + IPCOMP_SUPPORTED 16387 + This notification may be included only in a message containing an + SA payload negotiating a CHILD_SA and indicates a willingness by + its sender to use IPComp on this SA. The data associated with + this notification includes a two-octet IPComp CPI followed by a + one-octet transform ID optionally followed by attributes whose + length and format are defined by that transform ID. A message + proposing an SA may contain multiple IPCOMP_SUPPORTED + notifications to indicate multiple supported algorithms. A + message accepting an SA may contain at most one. + + The transform IDs currently defined are: + + Name Number Defined In + ------------------------------------- + RESERVED 0 + IPCOMP_OUI 1 + IPCOMP_DEFLATE 2 RFC 2394 + IPCOMP_LZS 3 RFC 2395 + IPCOMP_LZJH 4 RFC 3051 + RESERVED TO IANA 5-240 + PRIVATE USE 241-255 + + NAT_DETECTION_SOURCE_IP 16388 + This notification is used by its recipient to determine whether + the source is behind a NAT box. The data associated with this + notification is a SHA-1 digest of the SPIs (in the order they + appear in the header), IP address, and port on which this packet + was sent. There MAY be multiple Notify payloads of this type in a + message if the sender does not know which of several network + attachments will be used to send the packet. The recipient of + this notification MAY compare the supplied value to a SHA-1 hash + of the SPIs, source IP address, and port, and if they don't match + it SHOULD enable NAT traversal (see section 2.23). Alternately, + + + +Hoffman Expires July 5, 2006 [Page 82] + +Internet-Draft IKEv2 January 2006 + + + it MAY reject the connection attempt if NAT traversal is not + supported. + + NAT_DETECTION_DESTINATION_IP 16389 + This notification is used by its recipient to determine whether + it is behind a NAT box. The data associated with this + notification is a SHA-1 digest of the SPIs (in the order they + appear in the header), IP address, and port to which this packet + was sent. The recipient of this notification MAY compare the + supplied value to a hash of the SPIs, destination IP address, and + port, and if they don't match it SHOULD invoke NAT traversal (see + section 2.23). If they don't match, it means that this end is + behind a NAT and this end SHOULD start sending keepalive packets + as defined in [UDPENCAPS]. Alternately, it MAY reject the + connection attempt if NAT traversal is not supported. + + COOKIE 16390 + This notification MAY be included in an IKE_SA_INIT response. It + indicates that the request should be retried with a copy of this + notification as the first payload. This notification MUST be + included in an IKE_SA_INIT request retry if a COOKIE notification + was included in the initial response. The data associated with + this notification MUST be between 1 and 64 octets in length + (inclusive). + + USE_TRANSPORT_MODE 16391 + This notification MAY be included in a request message that also + includes an SA payload requesting a CHILD_SA. It requests that + the CHILD_SA use transport mode rather than tunnel mode for the + SA created. If the request is accepted, the response MUST also + include a notification of type USE_TRANSPORT_MODE. If the + responder declines the request, the CHILD_SA will be established + in tunnel mode. If this is unacceptable to the initiator, the + initiator MUST delete the SA. Note: Except when using this option + to negotiate transport mode, all CHILD_SAs will use tunnel mode. + + Note: The ECN decapsulation modifications specified in + [IPSECARCH] MUST be performed for every tunnel mode SA created + by IKEv2. + + HTTP_CERT_LOOKUP_SUPPORTED 16392 + This notification MAY be included in any message that can include + a CERTREQ payload and indicates that the sender is capable of + looking up certificates based on an HTTP-based URL (and hence + presumably would prefer to receive certificate specifications in + that format). + + REKEY_SA 16393 + + + +Hoffman Expires July 5, 2006 [Page 83] + +Internet-Draft IKEv2 January 2006 + + + This notification MUST be included in a CREATE_CHILD_SA exchange + if the purpose of the exchange is to replace an existing ESP or + AH SA. The SPI field identifies the SA being rekeyed. + {{ Clarif-5.4 }} The SPI placed in the REKEY_SA + notification is the SPI the exchange initiator would expect in + inbound ESP or AH packets. There is no data. + + ESP_TFC_PADDING_NOT_SUPPORTED 16394 + This notification asserts that the sending endpoint will NOT + accept packets that contain Flow Confidentiality (TFC) padding. + {{ Clarif-4.5 }} The scope of this message is a single + CHILD_SA, and thus this notification is included in messages + containing an SA payload negotiating a CHILD_SA. If neither + endpoint accepts TFC padding, this notification SHOULD be + included in both the request proposing an SA and the response + accepting it. If this notification is included in only one of + the messages, TFC padding can still be sent in the other + direction. + + NON_FIRST_FRAGMENTS_ALSO 16395 + Used for fragmentation control. See [IPSECARCH] for explanation. + {{ Clarif-4.6 }} Sending non-first fragments is + enabled only if NON_FIRST_FRAGMENTS_ALSO notification is + included in both the request proposing an SA and the response + accepting it. If the peer rejects this proposal, the peer only + omits NON_FIRST_FRAGMENTS_ALSO notification from the response, + but does not reject the whole CHILD_SA creation. + + RESERVED TO IANA 16396-40959 + + PRIVATE USE 40960-65535 + +3.11. Delete Payload + + The Delete Payload, denoted D in this memo, contains a protocol + specific security association identifier that the sender has removed + from its security association database and is, therefore, no longer + valid. Figure 17 shows the format of the Delete Payload. It is + possible to send multiple SPIs in a Delete payload; however, each SPI + MUST be for the same protocol. Mixing of protocol identifiers MUST + NOT be performed in the Delete payload. It is permitted, however, to + include multiple Delete payloads in a single INFORMATIONAL exchange + where each Delete payload lists SPIs for a different protocol. + + Deletion of the IKE_SA is indicated by a protocol ID of 1 (IKE) but + no SPIs. Deletion of a CHILD_SA, such as ESP or AH, will contain the + IPsec protocol ID of that protocol (2 for AH, 3 for ESP), and the SPI + is the SPI the sending endpoint would expect in inbound ESP or AH + + + +Hoffman Expires July 5, 2006 [Page 84] + +Internet-Draft IKEv2 January 2006 + + + packets. + + The Delete Payload is defined as follows: + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Protocol ID ! SPI Size ! # of SPIs ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ Security Parameter Index(es) (SPI) ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 17: Delete Payload Format + + o Protocol ID (1 octet) - Must be 1 for an IKE_SA, 2 for AH, or 3 + for ESP. + + o SPI Size (1 octet) - Length in octets of the SPI as defined by the + protocol ID. It MUST be zero for IKE (SPI is in message header) + or four for AH and ESP. + + o # of SPIs (2 octets) - The number of SPIs contained in the Delete + payload. The size of each SPI is defined by the SPI Size field. + + o Security Parameter Index(es) (variable length) - Identifies the + specific security association(s) to delete. The length of this + field is determined by the SPI Size and # of SPIs fields. + + The payload type for the Delete Payload is forty two (42). + +3.12. Vendor ID Payload + + The Vendor ID Payload, denoted V in this memo, contains a vendor + defined constant. The constant is used by vendors to identify and + recognize remote instances of their implementations. This mechanism + allows a vendor to experiment with new features while maintaining + backward compatibility. + + A Vendor ID payload MAY announce that the sender is capable to + accepting certain extensions to the protocol, or it MAY simply + identify the implementation as an aid in debugging. A Vendor ID + payload MUST NOT change the interpretation of any information defined + in this specification (i.e., the critical bit MUST be set to 0). + Multiple Vendor ID payloads MAY be sent. An implementation is NOT + + + +Hoffman Expires July 5, 2006 [Page 85] + +Internet-Draft IKEv2 January 2006 + + + REQUIRED to send any Vendor ID payload at all. + + A Vendor ID payload may be sent as part of any message. Reception of + a familiar Vendor ID payload allows an implementation to make use of + Private USE numbers described throughout this memo-- private + payloads, private exchanges, private notifications, etc. Unfamiliar + Vendor IDs MUST be ignored. + + Writers of Internet-Drafts who wish to extend this protocol MUST + define a Vendor ID payload to announce the ability to implement the + extension in the Internet-Draft. It is expected that Internet-Drafts + that gain acceptance and are standardized will be given "magic + numbers" out of the Future Use range by IANA, and the requirement to + use a Vendor ID will go away. + + The Vendor ID Payload fields are defined as follows: + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ Vendor ID (VID) ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 18: Vendor ID Payload Format + + o Vendor ID (variable length) - It is the responsibility of the + person choosing the Vendor ID to assure its uniqueness in spite of + the absence of any central registry for IDs. Good practice is to + include a company name, a person name, or some such. If you want + to show off, you might include the latitude and longitude and time + where you were when you chose the ID and some random input. A + message digest of a long unique string is preferable to the long + unique string itself. + + The payload type for the Vendor ID Payload is forty three (43). + +3.13. Traffic Selector Payload + + The Traffic Selector Payload, denoted TS in this memo, allows peers + to identify packet flows for processing by IPsec security services. + The Traffic Selector Payload consists of the IKE generic payload + header followed by individual traffic selectors as follows: + + + + + +Hoffman Expires July 5, 2006 [Page 86] + +Internet-Draft IKEv2 January 2006 + + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Number of TSs ! RESERVED ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ <Traffic Selectors> ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 19: Traffic Selectors Payload Format + + o Number of TSs (1 octet) - Number of traffic selectors being + provided. + + o RESERVED - This field MUST be sent as zero and MUST be ignored on + receipt. + + o Traffic Selectors (variable length) - One or more individual + traffic selectors. + + The length of the Traffic Selector payload includes the TS header and + all the traffic selectors. + + The payload type for the Traffic Selector payload is forty four (44) + for addresses at the initiator's end of the SA and forty five (45) + for addresses at the responder's end. + + {{ Clarif-4.7 }} There is no requirement that TSi and TSr contain the + same number of individual traffic selectors. Thus, they are + interpreted as follows: a packet matches a given TSi/TSr if it + matches at least one of the individual selectors in TSi, and at least + one of the individual selectors in TSr. + + For instance, the following traffic selectors: + + TSi = ((17, 100, 192.0.1.66-192.0.1.66), + (17, 200, 192.0.1.66-192.0.1.66)) + TSr = ((17, 300, 0.0.0.0-255.255.255.255), + (17, 400, 0.0.0.0-255.255.255.255)) + + would match UDP packets from 192.0.1.66 to anywhere, with any of the + four combinations of source/destination ports (100,300), (100,400), + (200,300), and (200, 400). + + Thus, some types of policies may require several CHILD_SA pairs. For + + + +Hoffman Expires July 5, 2006 [Page 87] + +Internet-Draft IKEv2 January 2006 + + + instance, a policy matching only source/destination ports (100,300) + and (200,400), but not the other two combinations, cannot be + negotiated as a single CHILD_SA pair. + +3.13.1. Traffic Selector + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! TS Type !IP Protocol ID*| Selector Length | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Start Port* | End Port* | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ Starting Address* ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ Ending Address* ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 20: Traffic Selector + + *Note: All fields other than TS Type and Selector Length depend on + the TS Type. The fields shown are for TS Types 7 and 8, the only two + values currently defined. + + o TS Type (one octet) - Specifies the type of traffic selector. + + o IP protocol ID (1 octet) - Value specifying an associated IP + protocol ID (e.g., UDP/TCP/ICMP). A value of zero means that the + protocol ID is not relevant to this traffic selector-- the SA can + carry all protocols. + + o Selector Length - Specifies the length of this Traffic Selector + Substructure including the header. + + o Start Port (2 octets) - Value specifying the smallest port number + allowed by this Traffic Selector. For protocols for which port is + undefined, or if all ports are allowed, this field MUST be zero. + For the ICMP protocol, the two one-octet fields Type and Code are + treated as a single 16-bit integer (with Type in the most + significant eight bits and Code in the least significant eight + bits) port number for the purposes of filtering based on this + field. + + + + + +Hoffman Expires July 5, 2006 [Page 88] + +Internet-Draft IKEv2 January 2006 + + + o End Port (2 octets) - Value specifying the largest port number + allowed by this Traffic Selector. For protocols for which port is + undefined, or if all ports are allowed, this field MUST be 65535. + For the ICMP protocol, the two one-octet fields Type and Code are + treated as a single 16-bit integer (with Type in the most + significant eight bits and Code in the least significant eight + bits) port number for the purposed of filtering based on this + field. + + o Starting Address - The smallest address included in this Traffic + Selector (length determined by TS type). + + o Ending Address - The largest address included in this Traffic + Selector (length determined by TS type). + + Systems that are complying with [IPSECARCH] that wish to indicate + "ANY" ports MUST set the start port to 0 and the end port to 65535; + note that according to [IPSECARCH], "ANY" includes "OPAQUE". Systems + working with [IPSECARCH] that wish to indicate "OPAQUE" ports, but + not "ANY" ports, MUST set the start port to 65535 and the end port to + 0. + + {{ Added from Clarif-4.8 }} The traffic selector types 7 and 8 can + also refer to ICMP type and code fields. Note, however, that ICMP + packets do not have separate source and destination port fields. The + method for specifying the traffic selectors for ICMP is shown by + example in Section 4.4.1.3 of [IPSECARCH]. + + {{ Added from Clarif-4.9 }} Traffic selectors can use IP Protocol ID + 135 to match the IPv6 mobility header [MIPV6]. This document does + not specify how to represent the "MH Type" field in traffic + selectors, although it is likely that a different document will + specify this in the future. Note that [IPSECARCH] says that the IPv6 + mobility header (MH) message type is placed in the most significant + eight bits of the 16-bit local port selector. The direction + semantics of TSi/TSr port fields are the same as for ICMP. + + The following table lists the assigned values for the Traffic + Selector Type field and the corresponding Address Selector Data. + + + + + + + + + + + + +Hoffman Expires July 5, 2006 [Page 89] + +Internet-Draft IKEv2 January 2006 + + + TS Type Value + ------------------------------------------------------------------- + RESERVED 0-6 + + TS_IPV4_ADDR_RANGE 7 + + A range of IPv4 addresses, represented by two four-octet + values. The first value is the beginning IPv4 address + (inclusive) and the second value is the ending IPv4 address + (inclusive). All addresses falling between the two specified + addresses are considered to be within the list. + + TS_IPV6_ADDR_RANGE 8 + + A range of IPv6 addresses, represented by two sixteen-octet + values. The first value is the beginning IPv6 address + (inclusive) and the second value is the ending IPv6 address + (inclusive). All addresses falling between the two specified + addresses are considered to be within the list. + + RESERVED TO IANA 9-240 + PRIVATE USE 241-255 + +3.14. Encrypted Payload + + The Encrypted Payload, denoted SK{...} or E in this memo, contains + other payloads in encrypted form. The Encrypted Payload, if present + in a message, MUST be the last payload in the message. Often, it is + the only payload in the message. + + The algorithms for encryption and integrity protection are negotiated + during IKE_SA setup, and the keys are computed as specified in + Section 2.14 and Section 2.18. + + The encryption and integrity protection algorithms are modeled after + the ESP algorithms described in RFCs 2104 [HMAC], 4303 [ESP], and + 2451 [ESPCBC]. This document completely specifies the cryptographic + processing of IKE data, but those documents should be consulted for + design rationale. We require a block cipher with a fixed block size + and an integrity check algorithm that computes a fixed-length + checksum over a variable size message. + + The payload type for an Encrypted payload is forty six (46). The + Encrypted Payload consists of the IKE generic payload header followed + by individual fields as follows: + + + + + + +Hoffman Expires July 5, 2006 [Page 90] + +Internet-Draft IKEv2 January 2006 + + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Initialization Vector ! + ! (length is block size for encryption algorithm) ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ~ Encrypted IKE Payloads ~ + + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! Padding (0-255 octets) ! + +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+ + ! ! Pad Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ~ Integrity Checksum Data ~ + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 21: Encrypted Payload Format + + o Next Payload - The payload type of the first embedded payload. + Note that this is an exception in the standard header format, + since the Encrypted payload is the last payload in the message and + therefore the Next Payload field would normally be zero. But + because the content of this payload is embedded payloads and there + was no natural place to put the type of the first one, that type + is placed here. + + o Payload Length - Includes the lengths of the header, IV, Encrypted + IKE Payloads, Padding, Pad Length, and Integrity Checksum Data. + + o Initialization Vector - A randomly chosen value whose length is + equal to the block length of the underlying encryption algorithm. + Recipients MUST accept any value. Senders SHOULD either pick this + value pseudo-randomly and independently for each message or use + the final ciphertext block of the previous message sent. Senders + MUST NOT use the same value for each message, use a sequence of + values with low hamming distance (e.g., a sequence number), or use + ciphertext from a received message. + + o IKE Payloads are as specified earlier in this section. This field + is encrypted with the negotiated cipher. + + o Padding MAY contain any value chosen by the sender, and MUST have + a length that makes the combination of the Payloads, the Padding, + and the Pad Length to be a multiple of the encryption block size. + This field is encrypted with the negotiated cipher. + + + + + +Hoffman Expires July 5, 2006 [Page 91] + +Internet-Draft IKEv2 January 2006 + + + o Pad Length is the length of the Padding field. The sender SHOULD + set the Pad Length to the minimum value that makes the combination + of the Payloads, the Padding, and the Pad Length a multiple of the + block size, but the recipient MUST accept any length that results + in proper alignment. This field is encrypted with the negotiated + cipher. + + o Integrity Checksum Data is the cryptographic checksum of the + entire message starting with the Fixed IKE Header through the Pad + Length. The checksum MUST be computed over the encrypted message. + Its length is determined by the integrity algorithm negotiated. + +3.15. Configuration Payload + + The Configuration payload, denoted CP in this document, is used to + exchange configuration information between IKE peers. The exchange + is for an IRAC to request an internal IP address from an IRAS and to + exchange other information of the sort that one would acquire with + Dynamic Host Configuration Protocol (DHCP) if the IRAC were directly + connected to a LAN. + + Configuration payloads are of type CFG_REQUEST/CFG_REPLY or CFG_SET/ + CFG_ACK (see CFG Type in the payload description below). CFG_REQUEST + and CFG_SET payloads may optionally be added to any IKE request. The + IKE response MUST include either a corresponding CFG_REPLY or CFG_ACK + or a Notify payload with an error type indicating why the request + could not be honored. An exception is that a minimal implementation + MAY ignore all CFG_REQUEST and CFG_SET payloads, so a response + message without a corresponding CFG_REPLY or CFG_ACK MUST be accepted + as an indication that the request was not supported. + + "CFG_REQUEST/CFG_REPLY" allows an IKE endpoint to request information + from its peer. If an attribute in the CFG_REQUEST Configuration + Payload is not zero-length, it is taken as a suggestion for that + attribute. The CFG_REPLY Configuration Payload MAY return that + value, or a new one. It MAY also add new attributes and not include + some requested ones. Requestors MUST ignore returned attributes that + they do not recognize. + + Some attributes MAY be multi-valued, in which case multiple attribute + values of the same type are sent and/or returned. Generally, all + values of an attribute are returned when the attribute is requested. + For some attributes (in this version of the specification only + internal addresses), multiple requests indicates a request that + multiple values be assigned. For these attributes, the number of + values returned SHOULD NOT exceed the number requested. + + If the data type requested in a CFG_REQUEST is not recognized or not + + + +Hoffman Expires July 5, 2006 [Page 92] + +Internet-Draft IKEv2 January 2006 + + + supported, the responder MUST NOT return an error type but rather + MUST either send a CFG_REPLY that MAY be empty or a reply not + containing a CFG_REPLY payload at all. Error returns are reserved + for cases where the request is recognized but cannot be performed as + requested or the request is badly formatted. + + "CFG_SET/CFG_ACK" allows an IKE endpoint to push configuration data + to its peer. In this case, the CFG_SET Configuration Payload + contains attributes the initiator wants its peer to alter. The + responder MUST return a Configuration Payload if it accepted any of + the configuration data and it MUST contain the attributes that the + responder accepted with zero-length data. Those attributes that it + did not accept MUST NOT be in the CFG_ACK Configuration Payload. If + no attributes were accepted, the responder MUST return either an + empty CFG_ACK payload or a response message without a CFG_ACK + payload. There are currently no defined uses for the CFG_SET/CFG_ACK + exchange, though they may be used in connection with extensions based + on Vendor IDs. An minimal implementation of this specification MAY + ignore CFG_SET payloads. + + {{ Demoted the SHOULD }} Extensions via the CP payload should not be + used for general purpose management. Its main intent is to provide a + bootstrap mechanism to exchange information within IPsec from IRAS to + IRAC. While it MAY be useful to use such a method to exchange + information between some Security Gateways (SGW) or small networks, + existing management protocols such as DHCP [DHCP], RADIUS [RADIUS], + SNMP, or LDAP [LDAP] should be preferred for enterprise management as + well as subsequent information exchanges. + + The Configuration Payload is defined as follows: + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! CFG Type ! RESERVED ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ Configuration Attributes ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 22: Configuration Payload Format + + The payload type for the Configuration Payload is forty seven (47). + + + + + +Hoffman Expires July 5, 2006 [Page 93] + +Internet-Draft IKEv2 January 2006 + + + o CFG Type (1 octet) - The type of exchange represented by the + Configuration Attributes. + + CFG Type Value + -------------------------- + RESERVED 0 + CFG_REQUEST 1 + CFG_REPLY 2 + CFG_SET 3 + CFG_ACK 4 + RESERVED TO IANA 5-127 + PRIVATE USE 128-255 + + o RESERVED (3 octets) - MUST be sent as zero; MUST be ignored on + receipt. + + o Configuration Attributes (variable length) - These are type length + values specific to the Configuration Payload and are defined + below. There may be zero or more Configuration Attributes in this + payload. + +3.15.1. Configuration Attributes + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + !R| Attribute Type ! Length | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + ~ Value ~ + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 23: Configuration Attribute Format + + o Reserved (1 bit) - This bit MUST be set to zero and MUST be + ignored on receipt. + + o Attribute Type (15 bits) - A unique identifier for each of the + Configuration Attribute Types. + + o Length (2 octets) - Length in octets of Value. + + o Value (0 or more octets) - The variable-length value of this + Configuration Attribute. The following attribute types have been + defined: + + + + + +Hoffman Expires July 5, 2006 [Page 94] + +Internet-Draft IKEv2 January 2006 + + + Multi- + Attribute Type Value Valued Length + ------------------------------------------------------- + RESERVED 0 + INTERNAL_IP4_ADDRESS 1 YES* 0 or 4 octets + INTERNAL_IP4_NETMASK 2 NO 0 or 4 octets + INTERNAL_IP4_DNS 3 YES 0 or 4 octets + INTERNAL_IP4_NBNS 4 YES 0 or 4 octets + INTERNAL_ADDRESS_EXPIRY 5 NO 0 or 4 octets + INTERNAL_IP4_DHCP 6 YES 0 or 4 octets + APPLICATION_VERSION 7 NO 0 or more + INTERNAL_IP6_ADDRESS 8 YES* 0 or 17 octets + RESERVED 9 + INTERNAL_IP6_DNS 10 YES 0 or 16 octets + INTERNAL_IP6_NBNS 11 YES 0 or 16 octets + INTERNAL_IP6_DHCP 12 YES 0 or 16 octets + INTERNAL_IP4_SUBNET 13 YES 0 or 8 octets + SUPPORTED_ATTRIBUTES 14 NO Multiple of 2 + INTERNAL_IP6_SUBNET 15 YES 17 octets + RESERVED TO IANA 16-16383 + PRIVATE USE 16384-32767 + + * These attributes may be multi-valued on return only if + multiple values were requested. + + o INTERNAL_IP4_ADDRESS, INTERNAL_IP6_ADDRESS - An address on the + internal network, sometimes called a red node address or private + address and MAY be a private address on the Internet. {{ + Clarif-6.3}} In a request message, the address specified is a + requested address (or a zero-length address if no specific address + is requested). If a specific address is requested, it likely + indicates that a previous connection existed with this address and + the requestor would like to reuse that address. With IPv6, a + requestor MAY supply the low-order address bytes it wants to use. + Multiple internal addresses MAY be requested by requesting + multiple internal address attributes. The responder MAY only send + up to the number of addresses requested. The INTERNAL_IP6_ADDRESS + is made up of two fields: the first is a 16-octet IPv6 address, + and the second is a one-octet prefix-length as defined in + [ADDRIPV6]. + + The requested address is valid until the expiry time defined with + the INTERNAL_ADDRESS_EXPIRY attribute or there are no IKE_SAs + between the peers. + + o INTERNAL_IP4_NETMASK - The internal network's netmask. Only one + netmask is allowed in the request and reply messages (e.g., + 255.255.255.0), and it MUST be used only with an + + + +Hoffman Expires July 5, 2006 [Page 95] + +Internet-Draft IKEv2 January 2006 + + + INTERNAL_IP4_ADDRESS attribute. {{ Clarif-6.5 }} + INTERNAL_IP4_NETMASK in a CFG_REPLY means roughly the same thing + as INTERNAL_IP4_SUBNET containing the same information ("send + traffic to these addresses through me"), but also implies a link + boundary. For instance, the client could use its own address and + the netmask to calculate the broadcast address of the link. An + empty INTERNAL_IP4_NETMASK attribute can be included in a + CFG_REQUEST to request this information (although the gateway can + send the information even when not requested). Non-empty values + for this attribute in a CFG_REQUEST do not make sense and thus + MUST NOT be included. + + o INTERNAL_IP4_DNS, INTERNAL_IP6_DNS - Specifies an address of a DNS + server within the network. Multiple DNS servers MAY be requested. + The responder MAY respond with zero or more DNS server attributes. + + o INTERNAL_IP4_NBNS, INTERNAL_IP6_NBNS - Specifies an address of a + NetBios Name Server (WINS) within the network. Multiple NBNS + servers MAY be requested. The responder MAY respond with zero or + more NBNS server attributes. {{ Clarif-6.7 }} NetBIOS is not + defined for IPv6; therefore, INTERNAL_IP6_NBNS SHOULD NOT be used. + + o INTERNAL_ADDRESS_EXPIRY - Specifies the number of seconds that the + host can use the internal IP address. The host MUST renew the IP + address before this expiry time. Only one of these attributes MAY + be present in the reply. {{ Clarif-6.8 }} Expiry times and + explicit renewals are primarily useful in environments like DHCP, + where the server cannot reliably know when the client has gone + away. However, in IKEv2, this is known, and the gateway can + simply free the address when the IKE_SA is deleted. Further, + supporting renewals is not mandatory. Thus + INTERNAL_ADDRESS_EXPIRY attribute MUST NOT be used. + + o INTERNAL_IP4_DHCP, INTERNAL_IP6_DHCP - Instructs the host to send + any internal DHCP requests to the address contained within the + attribute. Multiple DHCP servers MAY be requested. The responder + MAY respond with zero or more DHCP server attributes. + + o APPLICATION_VERSION - The version or application information of + the IPsec host. This is a string of printable ASCII characters + that is NOT null terminated. + + o INTERNAL_IP4_SUBNET - The protected sub-networks that this edge- + device protects. This attribute is made up of two fields: the + first being an IP address and the second being a netmask. + Multiple sub-networks MAY be requested. The responder MAY respond + with zero or more sub-network attributes. + + + + +Hoffman Expires July 5, 2006 [Page 96] + +Internet-Draft IKEv2 January 2006 + + + o SUPPORTED_ATTRIBUTES - When used within a Request, this attribute + MUST be zero-length and specifies a query to the responder to + reply back with all of the attributes that it supports. The + response contains an attribute that contains a set of attribute + identifiers each in 2 octets. The length divided by 2 (octets) + would state the number of supported attributes contained in the + response. + + o INTERNAL_IP6_SUBNET - The protected sub-networks that this edge- + device protects. This attribute is made up of two fields: the + first is a 16-octet IPv6 address, and the second is a one-octet + prefix-length as defined in [ADDRIPV6]. Multiple sub-networks MAY + be requested. The responder MAY respond with zero or more sub- + network attributes. + + Note that no recommendations are made in this document as to how an + implementation actually figures out what information to send in a + reply. That is, we do not recommend any specific method of an IRAS + determining which DNS server should be returned to a requesting IRAC. + +3.15.2. Meaning of INTERNAL_IP4_SUBNET/INTERNAL_IP6_SUBNET + + {{ Section added based on Clarif-6.4 }} + + INTERNAL_IP4/6_SUBNET attributes can indicate additional subnets, + ones that need one or more separate SAs, that can be reached through + the gateway that announces the attributes. INTERNAL_IP4/6_SUBNET + attributes may also express the gateway's policy about what traffic + should be sent through the gateway; the client can choose whether + other traffic (covered by TSr, but not in INTERNAL_IP4/6_SUBNET) is + sent through the gateway or directly to the destination. Thus, + traffic to the addresses listed in the INTERNAL_IP4/6_SUBNET + attributes should be sent through the gateway that announces the + attributes. If there are no existing IPsec SAs whose traffic + selectors cover the address in question, new SAs need to be created. + + For instance, if there are two subnets, 192.0.1.0/26 and + 192.0.2.0/24, and the client's request contains the following: + + CP(CFG_REQUEST) = + INTERNAL_IP4_ADDRESS() + TSi = (0, 0-65535, 0.0.0.0-255.255.255.255) + TSr = (0, 0-65535, 0.0.0.0-255.255.255.255) + + then a valid response could be the following (in which TSr and + INTERNAL_IP4_SUBNET contain the same information): + + + + + +Hoffman Expires July 5, 2006 [Page 97] + +Internet-Draft IKEv2 January 2006 + + + CP(CFG_REPLY) = + INTERNAL_IP4_ADDRESS(192.0.1.234) + INTERNAL_IP4_SUBNET(192.0.1.0/255.255.255.192) + INTERNAL_IP4_SUBNET(192.0.2.0/255.255.255.0) + TSi = (0, 0-65535, 192.0.1.234-192.0.1.234) + TSr = ((0, 0-65535, 192.0.1.0-192.0.1.63), + (0, 0-65535, 192.0.2.0-192.0.2.255)) + + In these cases, the INTERNAL_IP4_SUBNET does not really carry any + useful information. + + A different possible reply would have been this: + + CP(CFG_REPLY) = + INTERNAL_IP4_ADDRESS(192.0.1.234) + INTERNAL_IP4_SUBNET(192.0.1.0/255.255.255.192) + INTERNAL_IP4_SUBNET(192.0.2.0/255.255.255.0) + TSi = (0, 0-65535, 192.0.1.234-192.0.1.234) + TSr = (0, 0-65535, 0.0.0.0-255.255.255.255) + + That reply would mean that the client can send all its traffic + through the gateway, but the gateway does not mind if the client + sends traffic not included by INTERNAL_IP4_SUBNET directly to the + destination (without going through the gateway). + + A different situation arises if the gateway has a policy that + requires the traffic for the two subnets to be carried in separate + SAs. Then a response like this would indicate to the client that if + it wants access to the second subnet, it needs to create a separate + SA: + + CP(CFG_REPLY) = + INTERNAL_IP4_ADDRESS(192.0.1.234) + INTERNAL_IP4_SUBNET(192.0.1.0/255.255.255.192) + INTERNAL_IP4_SUBNET(192.0.2.0/255.255.255.0) + TSi = (0, 0-65535, 192.0.1.234-192.0.1.234) + TSr = (0, 0-65535, 192.0.1.0-192.0.1.63) + + INTERNAL_IP4_SUBNET can also be useful if the client's TSr included + only part of the address space. For instance, if the client requests + the following: + + CP(CFG_REQUEST) = + INTERNAL_IP4_ADDRESS() + TSi = (0, 0-65535, 0.0.0.0-255.255.255.255) + TSr = (0, 0-65535, 192.0.2.155-192.0.2.155) + + then the gateway's reply might be: + + + +Hoffman Expires July 5, 2006 [Page 98] + +Internet-Draft IKEv2 January 2006 + + + CP(CFG_REPLY) = + INTERNAL_IP4_ADDRESS(192.0.1.234) + INTERNAL_IP4_SUBNET(192.0.1.0/255.255.255.192) + INTERNAL_IP4_SUBNET(192.0.2.0/255.255.255.0) + TSi = (0, 0-65535, 192.0.1.234-192.0.1.234) + TSr = (0, 0-65535, 192.0.2.155-192.0.2.155) + + Because the meaning of INTERNAL_IP4_SUBNET/INTERNAL_IP6_SUBNET is in + CFG_REQUESTs is unclear, they MUST NOT be used in CFG_REQUESTs. + +3.15.3. Configuration payloads for IPv6 + + {{ Added this section from Clarif-6.6 }} + + The configuration payloads for IPv6 are based on the corresponding + IPv4 payloads, and do not fully follow the "normal IPv6 way of doing + things". In particular, IPv6 stateless autoconfiguration or router + advertisement messages are not used; neither is neighbor discovery. + + A client can be assigned an IPv6 address using the + INTERNAL_IP6_ADDRESS configuration payload. A minimal exchange might + look like this: + + CP(CFG_REQUEST) = + INTERNAL_IP6_ADDRESS() + INTERNAL_IP6_DNS() + TSi = (0, 0-65535, :: - FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF) + TSr = (0, 0-65535, :: - FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF) + + CP(CFG_REPLY) = + INTERNAL_IP6_ADDRESS(2001:DB8:0:1:2:3:4:5/64) + INTERNAL_IP6_DNS(2001:DB8:99:88:77:66:55:44) + TSi = (0, 0-65535, 2001:DB8:0:1:2:3:4:5 - 2001:DB8:0:1:2:3:4:5) + TSr = (0, 0-65535, :: - FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF) + + The client MAY send a non-empty INTERNAL_IP6_ADDRESS attribute in the + CFG_REQUEST to request a specific address or interface identifier. + The gateway first checks if the specified address is acceptable, and + if it is, returns that one. If the address was not acceptable, the + gateway attempts to use the interface identifier with some other + prefix; if even that fails, the gateway selects another interface + identifier. + + The INTERNAL_IP6_ADDRESS attribute also contains a prefix length + field. When used in a CFG_REPLY, this corresponds to the + INTERNAL_IP4_NETMASK attribute in the IPv4 case. + + Although this approach to configuring IPv6 addresses is reasonably + + + +Hoffman Expires July 5, 2006 [Page 99] + +Internet-Draft IKEv2 January 2006 + + + simple, it has some limitations. IPsec tunnels configured using + IKEv2 are not fully-featured "interfaces" in the IPv6 addressing + architecture sense [IPV6ADDR]. In particular, they do not + necessarily have link-local addresses, and this may complicate the + use of protocols that assume them, such as [MLDV2]. + +3.15.4. Address Assignment Failures + + {{ Added this section from Clarif-6.9 }} + + If the responder encounters an error while attempting to assign an IP + address to the initiator, it responds with an + INTERNAL_ADDRESS_FAILURE notification. However, there are some more + complex error cases. + + If the responder does not support configuration payloads at all, it + can simply ignore all configuration payloads. This type of + implementation never sends INTERNAL_ADDRESS_FAILURE notifications. + If the initiator requires the assignment of an IP address, it will + treat a response without CFG_REPLY as an error. + + The initiator may request a particular type of address (IPv4 or IPv6) + that the responder does not support, even though the responder + supports configuration payloads. In this case, the responder simply + ignores the type of address it does not support and processes the + rest of the request as usual. + + If the initiator requests multiple addresses of a type that the + responder supports, and some (but not all) of the requests fail, the + responder replies with the successful addresses only. The responder + sends INTERNAL_ADDRESS_FAILURE only if no addresses can be assigned. + +3.16. Extensible Authentication Protocol (EAP) Payload + + The Extensible Authentication Protocol Payload, denoted EAP in this + memo, allows IKE_SAs to be authenticated using the protocol defined + in RFC 3748 [EAP] and subsequent extensions to that protocol. The + full set of acceptable values for the payload is defined elsewhere, + but a short summary of RFC 3748 is included here to make this + document stand alone in the common cases. + + + + + + + + + + + +Hoffman Expires July 5, 2006 [Page 100] + +Internet-Draft IKEv2 January 2006 + + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ EAP Message ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 24: EAP Payload Format + + The payload type for an EAP Payload is forty eight (48). + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Code ! Identifier ! Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Type ! Type_Data... + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- + + Figure 25: EAP Message Format + + o Code (1 octet) indicates whether this message is a Request (1), + Response (2), Success (3), or Failure (4). + + o Identifier (1 octet) is used in PPP to distinguish replayed + messages from repeated ones. Since in IKE, EAP runs over a + reliable protocol, it serves no function here. In a response + message, this octet MUST be set to match the identifier in the + corresponding request. In other messages, this field MAY be set + to any value. + + o Length (2 octets) is the length of the EAP message and MUST be + four less than the Payload Length of the encapsulating payload. + + o Type (1 octet) is present only if the Code field is Request (1) or + Response (2). For other codes, the EAP message length MUST be + four octets and the Type and Type_Data fields MUST NOT be present. + In a Request (1) message, Type indicates the data being requested. + In a Response (2) message, Type MUST either be Nak or match the + type of the data requested. The following types are defined in + RFC 3748: + + + + + + + +Hoffman Expires July 5, 2006 [Page 101] + +Internet-Draft IKEv2 January 2006 + + + 1 Identity + 2 Notification + 3 Nak (Response Only) + 4 MD5-Challenge + 5 One-Time Password (OTP) + 6 Generic Token Card + + o Type_Data (Variable Length) varies with the Type of Request and + the associated Response. For the documentation of the EAP + methods, see [EAP]. + + {{ Demoted the SHOULD NOT and SHOULD }} Note that since IKE passes an + indication of initiator identity in message 3 of the protocol, the + responder should not send EAP Identity requests. The initiator may, + however, respond to such requests if it receives them. + + +4. Conformance Requirements + + In order to assure that all implementations of IKEv2 can + interoperate, there are "MUST support" requirements in addition to + those listed elsewhere. Of course, IKEv2 is a security protocol, and + one of its major functions is to allow only authorized parties to + successfully complete establishment of SAs. So a particular + implementation may be configured with any of a number of restrictions + concerning algorithms and trusted authorities that will prevent + universal interoperability. + + IKEv2 is designed to permit minimal implementations that can + interoperate with all compliant implementations. There are a series + of optional features that can easily be ignored by a particular + implementation if it does not support that feature. Those features + include: + + o Ability to negotiate SAs through a NAT and tunnel the resulting + ESP SA over UDP. + + o Ability to request (and respond to a request for) a temporary IP + address on the remote end of a tunnel. + + o Ability to support various types of legacy authentication. + + o Ability to support window sizes greater than one. + + o Ability to establish multiple ESP and/or AH SAs within a single + IKE_SA. + + + + + +Hoffman Expires July 5, 2006 [Page 102] + +Internet-Draft IKEv2 January 2006 + + + o Ability to rekey SAs. + + To assure interoperability, all implementations MUST be capable of + parsing all payload types (if only to skip over them) and to ignore + payload types that it does not support unless the critical bit is set + in the payload header. If the critical bit is set in an unsupported + payload header, all implementations MUST reject the messages + containing those payloads. + + Every implementation MUST be capable of doing four-message + IKE_SA_INIT and IKE_AUTH exchanges establishing two SAs (one for IKE, + one for ESP and/or AH). Implementations MAY be initiate-only or + respond-only if appropriate for their platform. Every implementation + MUST be capable of responding to an INFORMATIONAL exchange, but a + minimal implementation MAY respond to any INFORMATIONAL message with + an empty INFORMATIONAL reply (note that within the context of an + IKE_SA, an "empty" message consists of an IKE header followed by an + Encrypted payload with no payloads contained in it). A minimal + implementation MAY support the CREATE_CHILD_SA exchange only in so + far as to recognize requests and reject them with a Notify payload of + type NO_ADDITIONAL_SAS. A minimal implementation need not be able to + initiate CREATE_CHILD_SA or INFORMATIONAL exchanges. When an SA + expires (based on locally configured values of either lifetime or + octets passed), and implementation MAY either try to renew it with a + CREATE_CHILD_SA exchange or it MAY delete (close) the old SA and + create a new one. If the responder rejects the CREATE_CHILD_SA + request with a NO_ADDITIONAL_SAS notification, the implementation + MUST be capable of instead deleting the old SA and creating a new + one. + + Implementations are not required to support requesting temporary IP + addresses or responding to such requests. If an implementation does + support issuing such requests, it MUST include a CP payload in + message 3 containing at least a field of type INTERNAL_IP4_ADDRESS or + INTERNAL_IP6_ADDRESS. All other fields are optional. If an + implementation supports responding to such requests, it MUST parse + the CP payload of type CFG_REQUEST in message 3 and recognize a field + of type INTERNAL_IP4_ADDRESS or INTERNAL_IP6_ADDRESS. If it supports + leasing an address of the appropriate type, it MUST return a CP + payload of type CFG_REPLY containing an address of the requested + type. {{ Demoted the SHOULD }} The responder may include any other + related attributes. + + A minimal IPv4 responder implementation will ignore the contents of + the CP payload except to determine that it includes an + INTERNAL_IP4_ADDRESS attribute and will respond with the address and + other related attributes regardless of whether the initiator + requested them. + + + +Hoffman Expires July 5, 2006 [Page 103] + +Internet-Draft IKEv2 January 2006 + + + A minimal IPv4 initiator will generate a CP payload containing only + an INTERNAL_IP4_ADDRESS attribute and will parse the response + ignoring attributes it does not know how to use. {{ Clarif-6.8 + removes the sentence about processing INTERNAL_ADDRESS_EXPIRY. }} + Minimal initiators need not be able to request lease renewals and + minimal responders need not respond to them. + + For an implementation to be called conforming to this specification, + it MUST be possible to configure it to accept the following: + + o PKIX Certificates containing and signed by RSA keys of size 1024 + or 2048 bits, where the ID passed is any of ID_KEY_ID, ID_FQDN, + ID_RFC822_ADDR, or ID_DER_ASN1_DN. + + o Shared key authentication where the ID passes is any of ID_KEY_ID, + ID_FQDN, or ID_RFC822_ADDR. + + o Authentication where the responder is authenticated using PKIX + Certificates and the initiator is authenticated using shared key + authentication. + + +5. Security Considerations + + While this protocol is designed to minimize disclosure of + configuration information to unauthenticated peers, some such + disclosure is unavoidable. One peer or the other must identify + itself first and prove its identity first. To avoid probing, the + initiator of an exchange is required to identify itself first, and + usually is required to authenticate itself first. The initiator can, + however, learn that the responder supports IKE and what cryptographic + protocols it supports. The responder (or someone impersonating the + responder) can probe the initiator not only for its identity, but + using CERTREQ payloads may be able to determine what certificates the + initiator is willing to use. + + Use of EAP authentication changes the probing possibilities somewhat. + When EAP authentication is used, the responder proves its identity + before the initiator does, so an initiator that knew the name of a + valid initiator could probe the responder for both its name and + certificates. + + Repeated rekeying using CREATE_CHILD_SA without additional Diffie- + Hellman exchanges leaves all SAs vulnerable to cryptanalysis of a + single key or overrun of either endpoint. Implementers should take + note of this fact and set a limit on CREATE_CHILD_SA exchanges + between exponentiations. This memo does not prescribe such a limit. + + + + +Hoffman Expires July 5, 2006 [Page 104] + +Internet-Draft IKEv2 January 2006 + + + The strength of a key derived from a Diffie-Hellman exchange using + any of the groups defined here depends on the inherent strength of + the group, the size of the exponent used, and the entropy provided by + the random number generator used. Due to these inputs, it is + difficult to determine the strength of a key for any of the defined + groups. Diffie-Hellman group number two, when used with a strong + random number generator and an exponent no less than 200 bits, is + common for use with 3DES. Group five provides greater security than + group two. Group one is for historic purposes only and does not + provide sufficient strength except for use with DES, which is also + for historic use only. Implementations should make note of these + estimates when establishing policy and negotiating security + parameters. + + Note that these limitations are on the Diffie-Hellman groups + themselves. There is nothing in IKE that prohibits using stronger + groups nor is there anything that will dilute the strength obtained + from stronger groups (limited by the strength of the other algorithms + negotiated including the prf function). In fact, the extensible + framework of IKE encourages the definition of more groups; use of + elliptical curve groups may greatly increase strength using much + smaller numbers. + + It is assumed that all Diffie-Hellman exponents are erased from + memory after use. In particular, these exponents MUST NOT be derived + from long-lived secrets like the seed to a pseudo-random generator + that is not erased after use. + + The strength of all keys is limited by the size of the output of the + negotiated prf function. For this reason, a prf function whose + output is less than 128 bits (e.g., 3DES-CBC) MUST NOT be used with + this protocol. + + The security of this protocol is critically dependent on the + randomness of the randomly chosen parameters. These should be + generated by a strong random or properly seeded pseudo-random source + (see [RANDOMNESS]). Implementers should take care to ensure that use + of random numbers for both keys and nonces is engineered in a fashion + that does not undermine the security of the keys. + + For information on the rationale of many of the cryptographic design + choices in this protocol, see [SIGMA] and [SKEME]. Though the + security of negotiated CHILD_SAs does not depend on the strength of + the encryption and integrity protection negotiated in the IKE_SA, + implementations MUST NOT negotiate NONE as the IKE integrity + protection algorithm or ENCR_NULL as the IKE encryption algorithm. + + When using pre-shared keys, a critical consideration is how to assure + + + +Hoffman Expires July 5, 2006 [Page 105] + +Internet-Draft IKEv2 January 2006 + + + the randomness of these secrets. The strongest practice is to ensure + that any pre-shared key contain as much randomness as the strongest + key being negotiated. Deriving a shared secret from a password, + name, or other low-entropy source is not secure. These sources are + subject to dictionary and social engineering attacks, among others. + + The NAT_DETECTION_*_IP notifications contain a hash of the addresses + and ports in an attempt to hide internal IP addresses behind a NAT. + Since the IPv4 address space is only 32 bits, and it is usually very + sparse, it would be possible for an attacker to find out the internal + address used behind the NAT box by trying all possible IP addresses + and trying to find the matching hash. The port numbers are normally + fixed to 500, and the SPIs can be extracted from the packet. This + reduces the number of hash calculations to 2^32. With an educated + guess of the use of private address space, the number of hash + calculations is much smaller. Designers should therefore not assume + that use of IKE will not leak internal address information. + + When using an EAP authentication method that does not generate a + shared key for protecting a subsequent AUTH payload, certain man-in- + the-middle and server impersonation attacks are possible [EAPMITM]. + These vulnerabilities occur when EAP is also used in protocols that + are not protected with a secure tunnel. Since EAP is a general- + purpose authentication protocol, which is often used to provide + single-signon facilities, a deployed IPsec solution that relies on an + EAP authentication method that does not generate a shared key (also + known as a non-key-generating EAP method) can become compromised due + to the deployment of an entirely unrelated application that also + happens to use the same non-key-generating EAP method, but in an + unprotected fashion. Note that this vulnerability is not limited to + just EAP, but can occur in other scenarios where an authentication + infrastructure is reused. For example, if the EAP mechanism used by + IKEv2 utilizes a token authenticator, a man-in-the-middle attacker + could impersonate the web server, intercept the token authentication + exchange, and use it to initiate an IKEv2 connection. For this + reason, use of non-key-generating EAP methods SHOULD be avoided where + possible. Where they are used, it is extremely important that all + usages of these EAP methods SHOULD utilize a protected tunnel, where + the initiator validates the responder's certificate before initiating + the EAP exchange. {{ Demoted the SHOULD }} Implementers should + describe the vulnerabilities of using non-key-generating EAP methods + in the documentation of their implementations so that the + administrators deploying IPsec solutions are aware of these dangers. + + An implementation using EAP MUST also use a public-key-based + authentication of the server to the client before the EAP exchange + begins, even if the EAP method offers mutual authentication. This + avoids having additional IKEv2 protocol variations and protects the + + + +Hoffman Expires July 5, 2006 [Page 106] + +Internet-Draft IKEv2 January 2006 + + + EAP data from active attackers. + + If the messages of IKEv2 are long enough that IP-level fragmentation + is necessary, it is possible that attackers could prevent the + exchange from completing by exhausting the reassembly buffers. The + chances of this can be minimized by using the Hash and URL encodings + instead of sending certificates (see Section 3.6). Additional + mitigations are discussed in [DOSUDPPROT]. + + +6. IANA Considerations + + {{ This section was changed to not re-define any new IANA registries. + }} + + [IKEV2] defined many field types and values. IANA has already + registered those types and values, so the are not listed here again. + No new types or values are registered in IKEv2.1. + + +7. Acknowledgements + + {{ Added new acknowledgements. }} + + Charlie Kaufman did a huge amount of work on the original IKEv2 + document, on which this document is primarily based. Pasi Eronen + worked hard on the clarifications document, which is the basis for + the differences between IKEv2 and IKEv2.1. The individuals on the + IPsec mailing list was very helpful in both pointing out where + clarifications and changes were needed, as well as in reviewing the + clarifications suggested by others. + + The acknowledgements from the IKEv2 document were: + + This document is a collaborative effort of the entire IPsec WG. If + there were no limit to the number of authors that could appear on an + RFC, the following, in alphabetical order, would have been listed: + Bill Aiello, Stephane Beaulieu, Steve Bellovin, Sara Bitan, Matt + Blaze, Ran Canetti, Darren Dukes, Dan Harkins, Paul Hoffman, John + Ioannidis, Charlie Kaufman, Steve Kent, Angelos Keromytis, Tero + Kivinen, Hugo Krawczyk, Andrew Krywaniuk, Radia Perlman, Omer + Reingold, and Michael Richardson. Many other people contributed to + the design. It is an evolution of IKEv1, ISAKMP, and the IPsec DOI, + each of which has its own list of authors. Hugh Daniel suggested the + feature of having the initiator, in message 3, specify a name for the + responder, and gave the feature the cute name "You Tarzan, Me Jane". + David Faucher and Valery Smyzlov helped refine the design of the + traffic selector negotiation. + + + +Hoffman Expires July 5, 2006 [Page 107] + +Internet-Draft IKEv2 January 2006 + + + This paragraph lists references that appear only in figures. The + section is only here to keep the 'xml2rfc' program happy, and will be + removed when the document is published. Feel free to ignore it. + [DES] [IDEA] [MD5] [X.501] [X.509] + + +8. References + +8.1. Normative References + + [ADDGROUP] + Kivinen, T. and M. Kojo, "More Modular Exponential (MODP) + Diffie-Hellman groups for Internet Key Exchange (IKE)", + RFC 3526, May 2003. + + [ADDRIPV6] + Hinden, R. and S. Deering, "Internet Protocol Version 6 + (IPv6) Addressing Architecture", RFC 3513, April 2003. + + [Clarif] "IKEv2 Clarifications and Implementation Guidelines", + draft-eronen-ipsec-ikev2-clarifications (work in + progress). + + [EAP] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. + Levkowetz, "Extensible Authentication Protocol (EAP)", + RFC 3748, June 2004. + + [ECN] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition + of Explicit Congestion Notification (ECN) to IP", + RFC 3168, September 2001. + + [ESPCBC] Pereira, R. and R. Adams, "The ESP CBC-Mode Cipher + Algorithms", RFC 2451, November 1998. + + [IANACONS] + Narten, T. and H. Alvestrand, "Guidelines for Writing an + IANA Considerations Section in RFCs", BCP 26, RFC 2434. + + [IKEV2] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", + RFC 4306, December 2005. + + [IPSECARCH] + Kent, S. and K. Seo, "Security Architecture for the + Internet Protocol", RFC 4301, December 2005. + + [MUSTSHOULD] + Bradner, S., "Key Words for use in RFCs to indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + + +Hoffman Expires July 5, 2006 [Page 108] + +Internet-Draft IKEv2 January 2006 + + + [PKIX] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet + X.509 Public Key Infrastructure Certificate and + Certificate Revocation List (CRL) Profile", RFC 3280, + April 2002. + + [UDPENCAPS] + Huttunen, A., Swander, B., Volpe, V., DiBurro, L., and M. + Stenberg, "UDP Encapsulation of IPsec ESP Packets", + RFC 3948, January 2005. + +8.2. Informative References + + [AH] Kent, S., "IP Authentication Header", RFC 4302, + December 2005. + + [ARCHGUIDEPHIL] + Bush, R. and D. Meyer, "Some Internet Architectural + Guidelines and Philosophy", RFC 3439, December 2002. + + [ARCHPRINC] + Carpenter, B., "Architectural Principles of the Internet", + RFC 1958, June 1996. + + [DES] American National Standards Institute, "American National + Standard for Information Systems-Data Link Encryption", + ANSI X3.106, 1983. + + [DH] Diffie, W. and M. Hellman, "New Directions in + Cryptography", IEEE Transactions on Information Theory, + V.IT-22 n. 6, June 1977. + + [DHCP] Droms, R., "Dynamic Host Configuration Protocol", + RFC 2131, March 1997. + + [DIFFSERVARCH] + Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z., + and W. Weiss, "An Architecture for Differentiated + Services", RFC 2475. + + [DIFFSERVFIELD] + Nichols, K., Blake, S., Baker, F., and D. Black, + "Definition of the Differentiated Services Field (DS + Field) in the IPv4 and IPv6 Headers", RFC 2474, + December 1998. + + [DIFFTUNNEL] + Black, D., "Differentiated Services and Tunnels", + RFC 2983, October 2000. + + + +Hoffman Expires July 5, 2006 [Page 109] + +Internet-Draft IKEv2 January 2006 + + + [DOI] Piper, D., "The Internet IP Security Domain of + Interpretation for ISAKMP", RFC 2407, November 1998. + + [DOSUDPPROT] + C. Kaufman, R. Perlman, and B. Sommerfeld, "DoS protection + for UDP-based protocols", ACM Conference on Computer and + Communications Security , October 2003. + + [DSS] National Institute of Standards and Technology, U.S. + Department of Commerce, "Digital Signature Standard", + FIPS 186, May 1994. + + [EAPMITM] N. Asokan, V. Nierni, and K. Nyberg, "Man-in-the-Middle in + Tunneled Authentication Protocols", November 2002, + <http://eprint.iacr.org/2002/163>. + + [ESP] Kent, S., "IP Encapsulating Security Payload (ESP)", + RFC 4303, December 2005. + + [EXCHANGEANALYSIS] + R. Perlman and C. Kaufman, "Analysis of the IPsec key + exchange Standard", WET-ICE Security Conference, MIT , + 2001, + <http://sec.femto.org/wetice-2001/papers/radia-paper.pdf>. + + [HMAC] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- + Hashing for Message Authentication", RFC 2104, + February 1997. + + [IDEA] X. Lai, "On the Design and Security of Block Ciphers", ETH + Series in Information Processing, v. 1, Konstanz: Hartung- + Gorre Verlag, 1992. + + [IKEV1] Harkins, D. and D. Carrel, "The Internet Key Exchange + (IKE)", RFC 2409, November 1998. + + [IPCOMP] Shacham, A., Monsour, B., Pereira, R., and M. Thomas, "IP + Payload Compression Protocol (IPComp)", RFC 3173, + September 2001. + + [IPSECARCH-OLD] + Kent, S. and R. Atkinson, "Security Architecture for the + Internet Protocol", RFC 2401, November 1998. + + [IPV6ADDR] + Hinden, R. and S. Deering, "Internet Protocol Version 6 + (IPv6) Addressing Architecture", RFC 3513, April 2003. + + + + +Hoffman Expires July 5, 2006 [Page 110] + +Internet-Draft IKEv2 January 2006 + + + [ISAKMP] Maughan, D., Schneider, M., and M. Schertler, "Internet + Security Association and Key Management Protocol + (ISAKMP)", RFC 2408, November 1998. + + [LDAP] Wahl, M., Howes, T., and S. Kille, "Lightweight Directory + Access Protocol (v3)", RFC 2251, December 1997. + + [MAILFORMAT] + Resnick, P., "Internet Message Format", RFC 2822, + April 2001. + + [MD5] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, + April 1992. + + [MIPV6] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support + in IPv6", RFC 3775, June 2004. + + [MLDV2] Vida, R. and L. Costa, "Multicast Listener Discovery + Version 2 (MLDv2) for IPv6", RFC 3810, June 2004. + + [NAI] Aboba, B. and M. Beadles, "The Network Access Identifier", + RFC 2486, January 1999. + + [NATREQ] Aboba, B. and W. Dixon, "IPsec-Network Address Translation + (NAT) Compatibility Requirements", RFC 3715, March 2004. + + [OAKLEY] Orman, H., "The OAKLEY Key Determination Protocol", + RFC 2412, November 1998. + + [PFKEY] McDonald, D., Metz, C., and B. Phan, "PF_KEY Key + Management API, Version 2", RFC 2367, July 1998. + + [PHOTURIS] + Karn, P. and W. Simpson, "Photuris: Session-Key Management + Protocol", RFC 2522, March 1999. + + [PKCS1] B. Kaliski and J. Staddon, "PKCS #1: RSA Cryptography + Specifications Version 2", September 1998. + + [PRFAES128CBC] + Hoffman, P., "The AES-XCBC-PRF-128 Algorithm for the + Internet Key Exchange Protocol (IKE)", RFC 3664, + January 2004. + + [PRFAES128CBC-bis] + Hoffman, P., "The AES-XCBC-PRF-128 Algorithm for the + Internet Key Exchange Protocol (IKE)", + draft-hoffman-rfc3664bis (work in progress), October 2005. + + + +Hoffman Expires July 5, 2006 [Page 111] + +Internet-Draft IKEv2 January 2006 + + + [RADIUS] Rigney, C., Rubens, A., Simpson, W., and S. Willens, + "Remote Authentication Dial In User Service (RADIUS)", + RFC 2138, April 1997. + + [RANDOMNESS] + Eastlake, D., Schiller, J., and S. Crocker, "Randomness + Requirements for Security", BCP 106, RFC 4086, June 2005. + + [REAUTH] Nir, Y., ""Repeated Authentication in IKEv2", + draft-nir-ikev2-auth-lt (work in progress), May 2005. + + [RSA] R. Rivest, A. Shamir, and L. Adleman, "A Method for + Obtaining Digital Signatures and Public-Key + Cryptosystems", February 1978. + + [SHA] National Institute of Standards and Technology, U.S. + Department of Commerce, "Secure Hash Standard", + FIPS 180-1, May 1994. + + [SIGMA] H. Krawczyk, "SIGMA: the `SIGn-and-MAc' Approach to + Authenticated Diffie-Hellman and its Use in the IKE + Protocols", Advances in Cryptography - CRYPTO 2003 + Proceedings LNCS 2729, 2003, <http:// + www.informatik.uni-trier.de/~ley/db/conf/crypto/ + crypto2003.html>. + + [SKEME] H. Krawczyk, "SKEME: A Versatile Secure Key Exchange + Mechanism for Internet", IEEE Proceedings of the 1996 + Symposium on Network and Distributed Systems Security , + 1996. + + [TRANSPARENCY] + Carpenter, B., "Internet Transparency", RFC 2775, + February 2000. + + [X.501] ITU-T, "Recommendation X.501: Information Technology - + Open Systems Interconnection - The Directory: Models", + 1993. + + [X.509] ITU-T, "Recommendation X.509 (1997 E): Information + Technology - Open Systems Interconnection - The Directory: + Authentication Framework", 1997. + + +Appendix A. Summary of changes from IKEv1 + + The goals of this revision to IKE are: + + + + +Hoffman Expires July 5, 2006 [Page 112] + +Internet-Draft IKEv2 January 2006 + + + 1. To define the entire IKE protocol in a single document, + replacing RFCs 2407, 2408, and 2409 and incorporating subsequent + changes to support NAT Traversal, Extensible Authentication, and + Remote Address acquisition; + + 2. To simplify IKE by replacing the eight different initial + exchanges with a single four-message exchange (with changes in + authentication mechanisms affecting only a single AUTH payload + rather than restructuring the entire exchange) see + [EXCHANGEANALYSIS]; + + 3. To remove the Domain of Interpretation (DOI), Situation (SIT), + and Labeled Domain Identifier fields, and the Commit and + Authentication only bits; + + 4. To decrease IKE's latency in the common case by making the + initial exchange be 2 round trips (4 messages), and allowing the + ability to piggyback setup of a CHILD_SA on that exchange; + + 5. To replace the cryptographic syntax for protecting the IKE + messages themselves with one based closely on ESP to simplify + implementation and security analysis; + + 6. To reduce the number of possible error states by making the + protocol reliable (all messages are acknowledged) and sequenced. + This allows shortening CREATE_CHILD_SA exchanges from 3 messages + to 2; + + 7. To increase robustness by allowing the responder to not do + significant processing until it receives a message proving that + the initiator can receive messages at its claimed IP address, + and not commit any state to an exchange until the initiator can + be cryptographically authenticated; + + 8. To fix cryptographic weaknesses such as the problem with + symmetries in hashes used for authentication documented by Tero + Kivinen; + + 9. To specify Traffic Selectors in their own payloads type rather + than overloading ID payloads, and making more flexible the + Traffic Selectors that may be specified; + + 10. To specify required behavior under certain error conditions or + when data that is not understood is received in order to make it + easier to make future revisions in a way that does not break + backwards compatibility; + + + + + +Hoffman Expires July 5, 2006 [Page 113] + +Internet-Draft IKEv2 January 2006 + + + 11. To simplify and clarify how shared state is maintained in the + presence of network failures and Denial of Service attacks; and + + 12. To maintain existing syntax and magic numbers to the extent + possible to make it likely that implementations of IKEv1 can be + enhanced to support IKEv2 with minimum effort. + + +Appendix B. Diffie-Hellman Groups + + There are two Diffie-Hellman groups defined here for use in IKE. + These groups were generated by Richard Schroeppel at the University + of Arizona. Properties of these primes are described in [OAKLEY]. + + The strength supplied by group one may not be sufficient for the + mandatory-to-implement encryption algorithm and is here for historic + reasons. + + Additional Diffie-Hellman groups have been defined in [ADDGROUP]. + +B.1. Group 1 - 768 Bit MODP + + This group is assigned id 1 (one). + + The prime is: 2^768 - 2 ^704 - 1 + 2^64 * { [2^638 pi] + 149686 } + Its hexadecimal value is: + + FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1 + 29024E08 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD + EF9519B3 CD3A431B 302B0A6D F25F1437 4FE1356D 6D51C245 + E485B576 625E7EC6 F44C42E9 A63A3620 FFFFFFFF FFFFFFFF + + The generator is 2. + +B.2. Group 2 - 1024 Bit MODP + + This group is assigned id 2 (two). + + The prime is 2^1024 - 2^960 - 1 + 2^64 * { [2^894 pi] + 129093 }. + Its hexadecimal value is: + + FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1 + 29024E08 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD + EF9519B3 CD3A431B 302B0A6D F25F1437 4FE1356D 6D51C245 + E485B576 625E7EC6 F44C42E9 A637ED6B 0BFF5CB6 F406B7ED + EE386BFB 5A899FA5 AE9F2411 7C4B1FE6 49286651 ECE65381 + FFFFFFFF FFFFFFFF + + + + +Hoffman Expires July 5, 2006 [Page 114] + +Internet-Draft IKEv2 January 2006 + + + The generator is 2. + + +Appendix C. Exchanges and Payloads + + {{ Clarif-AppA }} + + This appendix contains a short summary of the IKEv2 exchanges, and + what payloads can appear in which message. This appendix is purely + informative; if it disagrees with the body of this document, the + other text is considered correct. + + Vendor-ID (V) payloads may be included in any place in any message. + This sequence here shows what are the most logical places for them. + +C.1. IKE_SA_INIT Exchange + + request --> [N(COOKIE)], + SA, KE, Ni, + [N(NAT_DETECTION_SOURCE_IP)+, + N(NAT_DETECTION_DESTINATION_IP)], + [V+] + + normal response <-- SA, KE, Nr, + (no cookie) [N(NAT_DETECTION_SOURCE_IP), + N(NAT_DETECTION_DESTINATION_IP)], + [[N(HTTP_CERT_LOOKUP_SUPPORTED)], CERTREQ+], + [V+] + + + + + + + + + + + + + + + + + + + + + + + +Hoffman Expires July 5, 2006 [Page 115] + +Internet-Draft IKEv2 January 2006 + + +C.2. IKE_AUTH Exchange without EAP + + request --> IDi, [CERT+], + [N(INITIAL_CONTACT)], + [[N(HTTP_CERT_LOOKUP_SUPPORTED)], CERTREQ+], + [IDr], + AUTH, + [CP(CFG_REQUEST)], + [N(IPCOMP_SUPPORTED)+], + [N(USE_TRANSPORT_MODE)], + [N(ESP_TFC_PADDING_NOT_SUPPORTED)], + [N(NON_FIRST_FRAGMENTS_ALSO)], + SA, TSi, TSr, + [V+] + + response <-- IDr, [CERT+], + AUTH, + [CP(CFG_REPLY)], + [N(IPCOMP_SUPPORTED)], + [N(USE_TRANSPORT_MODE)], + [N(ESP_TFC_PADDING_NOT_SUPPORTED)], + [N(NON_FIRST_FRAGMENTS_ALSO)], + SA, TSi, TSr, + [N(ADDITIONAL_TS_POSSIBLE)], + [V+] + + + + + + + + + + + + + + + + + + + + + + + + + + +Hoffman Expires July 5, 2006 [Page 116] + +Internet-Draft IKEv2 January 2006 + + +C.3. IKE_AUTH Exchange with EAP + + first request --> IDi, + [N(INITIAL_CONTACT)], + [[N(HTTP_CERT_LOOKUP_SUPPORTED)], CERTREQ+], + [IDr], + [CP(CFG_REQUEST)], + [N(IPCOMP_SUPPORTED)+], + [N(USE_TRANSPORT_MODE)], + [N(ESP_TFC_PADDING_NOT_SUPPORTED)], + [N(NON_FIRST_FRAGMENTS_ALSO)], + SA, TSi, TSr, + [V+] + + first response <-- IDr, [CERT+], AUTH, + EAP, + [V+] + + / --> EAP + repeat 1..N times | + \ <-- EAP + + last request --> AUTH + + last response <-- AUTH, + [CP(CFG_REPLY)], + [N(IPCOMP_SUPPORTED)], + [N(USE_TRANSPORT_MODE)], + [N(ESP_TFC_PADDING_NOT_SUPPORTED)], + [N(NON_FIRST_FRAGMENTS_ALSO)], + SA, TSi, TSr, + [N(ADDITIONAL_TS_POSSIBLE)], + [V+] + + + + + + + + + + + + + + + + + + +Hoffman Expires July 5, 2006 [Page 117] + +Internet-Draft IKEv2 January 2006 + + +C.4. CREATE_CHILD_SA Exchange for Creating or Rekeying CHILD_SAs + + request --> [N(REKEY_SA)], + [N(IPCOMP_SUPPORTED)+], + [N(USE_TRANSPORT_MODE)], + [N(ESP_TFC_PADDING_NOT_SUPPORTED)], + [N(NON_FIRST_FRAGMENTS_ALSO)], + SA, Ni, [KEi], TSi, TSr + + response <-- [N(IPCOMP_SUPPORTED)], + [N(USE_TRANSPORT_MODE)], + [N(ESP_TFC_PADDING_NOT_SUPPORTED)], + [N(NON_FIRST_FRAGMENTS_ALSO)], + SA, Nr, [KEr], TSi, TSr, + [N(ADDITIONAL_TS_POSSIBLE)] + +C.5. CREATE_CHILD_SA Exchange for Rekeying the IKE_SA + + request --> SA, Ni, [KEi] + + response <-- SA, Nr, [KEr] + +C.6. INFORMATIONAL Exchange + + request --> [N+], + [D+], + [CP(CFG_REQUEST)] + + response <-- [N+], + [D+], + [CP(CFG_REPLY)] + + +Appendix D. Changes Between Internet Draft Versions + + This section will be removed before publication as an RFC. + +D.1. Changes from IKEv2 to draft -00 + + There were a zillion additions from the Clarifications document. + These are noted with "{{ Clarif-nn }}". + + Cleaned up many of the figures. Made the table headings consistent. + Made some tables easier to read by removing blank spaces. Removed + the "reserved to IANA" and "private use" text wording and moved it + into the tables. + + Changed many SHOULD and MUST requirements to better match RFC 2119. + + + +Hoffman Expires July 5, 2006 [Page 118] + +Internet-Draft IKEv2 January 2006 + + +Author's Address + + Paul Hoffman + VPN Consortium + 127 Segre Place + Santa Cruz, CA 95060 + US + + Phone: 1-831-426-9827 + Email: paul.hoffman@vpnc.org + + +Full Copyright Statement + + Copyright (C) The Internet Society (2006). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET + ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, + INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE + INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + + + +Hoffman Expires July 5, 2006 [Page 119] + +Internet-Draft IKEv2 January 2006 + + + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at + ietf-ipr@ietf.org. + + +Acknowledgment + + Funding for the RFC Editor function is currently provided by the + Internet Society. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Hoffman Expires July 5, 2006 [Page 120] + diff --git a/src/charon/doc/standards/draft-hoffman-ikev2bis-00.txt b/src/charon/doc/standards/draft-hoffman-ikev2bis-00.txt new file mode 100644 index 000000000..9d1b9d74d --- /dev/null +++ b/src/charon/doc/standards/draft-hoffman-ikev2bis-00.txt @@ -0,0 +1,6776 @@ + + + +Network Working Group C. Kaufman +Internet-Draft Microsoft +Expires: August 27, 2006 P. Hoffman + VPN Consortium + P. Eronen + Nokia + February 23, 2006 + + + Internet Key Exchange Protocol: IKEv2 + draft-hoffman-ikev2bis-00.txt + +Status of this Memo + + By submitting this Internet-Draft, each author represents that any + applicable patent or other IPR claims of which he or she is aware + have been or will be disclosed, and any of which he or she becomes + aware will be disclosed, in accordance with Section 6 of BCP 79. + + Internet-Drafts are working documents of the Internet Engineering + Task Force (IETF), its areas, and its working groups. Note that + other groups may also distribute working documents as Internet- + Drafts. + + Internet-Drafts are draft documents valid for a maximum of six months + and may be updated, replaced, or obsoleted by other documents at any + time. It is inappropriate to use Internet-Drafts as reference + material or to cite them other than as "work in progress." + + The list of current Internet-Drafts can be accessed at + http://www.ietf.org/ietf/1id-abstracts.txt. + + The list of Internet-Draft Shadow Directories can be accessed at + http://www.ietf.org/shadow.html. + + This Internet-Draft will expire on August 27, 2006. + +Copyright Notice + + Copyright (C) The Internet Society (2006). + +Abstract + + This document describes version 2 of the Internet Key Exchange (IKE) + protocol. It is a restatement of RFC 4306, and includes all of the + clarifications from the "IKEv2 Clarifications" document. + + + + + +Kaufman, et al. Expires August 27, 2006 [Page 1] + +Internet-Draft IKEv2bis February 2006 + + +Table of Contents + + 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5 + 1.1. Usage Scenarios . . . . . . . . . . . . . . . . . . . . . 6 + 1.1.1. Security Gateway to Security Gateway Tunnel . . . . . 7 + 1.1.2. Endpoint-to-Endpoint Transport . . . . . . . . . . . 7 + 1.1.3. Endpoint to Security Gateway Tunnel . . . . . . . . . 8 + 1.1.4. Other Scenarios . . . . . . . . . . . . . . . . . . . 9 + 1.2. The Initial Exchanges . . . . . . . . . . . . . . . . . . 9 + 1.3. The CREATE_CHILD_SA Exchange . . . . . . . . . . . . . . 12 + 1.3.1. Creating New CHILD_SAs with the CREATE_CHILD_SA + Exchange . . . . . . . . . . . . . . . . . . . . . . 13 + 1.3.2. Rekeying IKE_SAs with the CREATE_CHILD_SA Exchange . 14 + 1.3.3. Rekeying CHILD_SAs with the CREATE_CHILD_SA + Exchange . . . . . . . . . . . . . . . . . . . . . . 14 + 1.4. The INFORMATIONAL Exchange . . . . . . . . . . . . . . . 15 + 1.5. Informational Messages outside of an IKE_SA . . . . . . . 16 + 1.6. Requirements Terminology . . . . . . . . . . . . . . . . 17 + 1.7. Differences Between RFC 4306 and This Document . . . . . 17 + 2. IKE Protocol Details and Variations . . . . . . . . . . . . . 18 + 2.1. Use of Retransmission Timers . . . . . . . . . . . . . . 19 + 2.2. Use of Sequence Numbers for Message ID . . . . . . . . . 19 + 2.3. Window Size for Overlapping Requests . . . . . . . . . . 20 + 2.4. State Synchronization and Connection Timeouts . . . . . . 21 + 2.5. Version Numbers and Forward Compatibility . . . . . . . . 23 + 2.6. Cookies . . . . . . . . . . . . . . . . . . . . . . . . . 25 + 2.6.1. Interaction of COOKIE and INVALID_KE_PAYLOAD . . . . 27 + 2.7. Cryptographic Algorithm Negotiation . . . . . . . . . . . 28 + 2.8. Rekeying . . . . . . . . . . . . . . . . . . . . . . . . 29 + 2.8.1. Simultaneous CHILD_SA rekeying . . . . . . . . . . . 31 + 2.8.2. Rekeying the IKE_SA Versus Reauthentication . . . . . 33 + 2.9. Traffic Selector Negotiation . . . . . . . . . . . . . . 34 + 2.9.1. Traffic Selectors Violating Own Policy . . . . . . . 37 + 2.10. Nonces . . . . . . . . . . . . . . . . . . . . . . . . . 38 + 2.11. Address and Port Agility . . . . . . . . . . . . . . . . 38 + 2.12. Reuse of Diffie-Hellman Exponentials . . . . . . . . . . 38 + 2.13. Generating Keying Material . . . . . . . . . . . . . . . 39 + 2.14. Generating Keying Material for the IKE_SA . . . . . . . . 40 + 2.15. Authentication of the IKE_SA . . . . . . . . . . . . . . 41 + 2.16. Extensible Authentication Protocol Methods . . . . . . . 43 + 2.17. Generating Keying Material for CHILD_SAs . . . . . . . . 45 + 2.18. Rekeying IKE_SAs Using a CREATE_CHILD_SA Exchange . . . . 46 + 2.19. Requesting an Internal Address on a Remote Network . . . 47 + 2.20. Requesting the Peer's Version . . . . . . . . . . . . . . 48 + 2.21. Error Handling . . . . . . . . . . . . . . . . . . . . . 49 + 2.22. IPComp . . . . . . . . . . . . . . . . . . . . . . . . . 50 + 2.23. NAT Traversal . . . . . . . . . . . . . . . . . . . . . . 50 + 2.24. Explicit Congestion Notification (ECN) . . . . . . . . . 53 + + + +Kaufman, et al. Expires August 27, 2006 [Page 2] + +Internet-Draft IKEv2bis February 2006 + + + 3. Header and Payload Formats . . . . . . . . . . . . . . . . . 53 + 3.1. The IKE Header . . . . . . . . . . . . . . . . . . . . . 53 + 3.2. Generic Payload Header . . . . . . . . . . . . . . . . . 56 + 3.3. Security Association Payload . . . . . . . . . . . . . . 58 + 3.3.1. Proposal Substructure . . . . . . . . . . . . . . . . 60 + 3.3.2. Transform Substructure . . . . . . . . . . . . . . . 62 + 3.3.3. Valid Transform Types by Protocol . . . . . . . . . . 64 + 3.3.4. Mandatory Transform IDs . . . . . . . . . . . . . . . 65 + 3.3.5. Transform Attributes . . . . . . . . . . . . . . . . 66 + 3.3.6. Attribute Negotiation . . . . . . . . . . . . . . . . 67 + 3.4. Key Exchange Payload . . . . . . . . . . . . . . . . . . 68 + 3.5. Identification Payloads . . . . . . . . . . . . . . . . . 69 + 3.6. Certificate Payload . . . . . . . . . . . . . . . . . . . 71 + 3.7. Certificate Request Payload . . . . . . . . . . . . . . . 74 + 3.8. Authentication Payload . . . . . . . . . . . . . . . . . 76 + 3.9. Nonce Payload . . . . . . . . . . . . . . . . . . . . . . 77 + 3.10. Notify Payload . . . . . . . . . . . . . . . . . . . . . 77 + 3.10.1. Notify Message Types . . . . . . . . . . . . . . . . 78 + 3.11. Delete Payload . . . . . . . . . . . . . . . . . . . . . 84 + 3.12. Vendor ID Payload . . . . . . . . . . . . . . . . . . . . 85 + 3.13. Traffic Selector Payload . . . . . . . . . . . . . . . . 86 + 3.13.1. Traffic Selector . . . . . . . . . . . . . . . . . . 88 + 3.14. Encrypted Payload . . . . . . . . . . . . . . . . . . . . 90 + 3.15. Configuration Payload . . . . . . . . . . . . . . . . . . 92 + 3.15.1. Configuration Attributes . . . . . . . . . . . . . . 94 + 3.15.2. Meaning of INTERNAL_IP4_SUBNET/INTERNAL_IP6_SUBNET . 97 + 3.15.3. Configuration payloads for IPv6 . . . . . . . . . . . 99 + 3.15.4. Address Assignment Failures . . . . . . . . . . . . . 100 + 3.16. Extensible Authentication Protocol (EAP) Payload . . . . 100 + 4. Conformance Requirements . . . . . . . . . . . . . . . . . . 102 + 5. Security Considerations . . . . . . . . . . . . . . . . . . . 104 + 5.1. Traffic selector authorization . . . . . . . . . . . . . 107 + 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 108 + 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 108 + 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 109 + 8.1. Normative References . . . . . . . . . . . . . . . . . . 109 + 8.2. Informative References . . . . . . . . . . . . . . . . . 110 + Appendix A. Summary of changes from IKEv1 . . . . . . . . . . . 114 + Appendix B. Diffie-Hellman Groups . . . . . . . . . . . . . . . 115 + B.1. Group 1 - 768 Bit MODP . . . . . . . . . . . . . . . . . 115 + B.2. Group 2 - 1024 Bit MODP . . . . . . . . . . . . . . . . . 115 + Appendix C. Exchanges and Payloads . . . . . . . . . . . . . . . 116 + C.1. IKE_SA_INIT Exchange . . . . . . . . . . . . . . . . . . 116 + C.2. IKE_AUTH Exchange without EAP . . . . . . . . . . . . . . 117 + C.3. IKE_AUTH Exchange with EAP . . . . . . . . . . . . . . . 118 + C.4. CREATE_CHILD_SA Exchange for Creating or Rekeying + CHILD_SAs . . . . . . . . . . . . . . . . . . . . . . . . 119 + C.5. CREATE_CHILD_SA Exchange for Rekeying the IKE_SA . . . . 119 + + + +Kaufman, et al. Expires August 27, 2006 [Page 3] + +Internet-Draft IKEv2bis February 2006 + + + C.6. INFORMATIONAL Exchange . . . . . . . . . . . . . . . . . 119 + Appendix D. Changes Between Internet Draft Versions . . . . . . 119 + D.1. Changes from IKEv2 to draft -00 . . . . . . . . . . . . . 119 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 120 + Intellectual Property and Copyright Statements . . . . . . . . . 120 + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Kaufman, et al. Expires August 27, 2006 [Page 4] + +Internet-Draft IKEv2bis February 2006 + + +1. Introduction + + {{ An introduction to the differences between RFC 4306 [IKEV2] and + this document is given at the end of Section 1. It is put there + (instead of here) to preserve the section numbering of the original + IKEv2 document. }} + + IP Security (IPsec) provides confidentiality, data integrity, access + control, and data source authentication to IP datagrams. These + services are provided by maintaining shared state between the source + and the sink of an IP datagram. This state defines, among other + things, the specific services provided to the datagram, which + cryptographic algorithms will be used to provide the services, and + the keys used as input to the cryptographic algorithms. + + Establishing this shared state in a manual fashion does not scale + well. Therefore, a protocol to establish this state dynamically is + needed. This memo describes such a protocol -- the Internet Key + Exchange (IKE). Version 1 of IKE was defined in RFCs 2407 [DOI], + 2408 [ISAKMP], and 2409 [IKEV1]. IKEv2 was defined in [IKEV2]. This + single document is intended to replace all three of those RFCs. + + Definitions of the primitive terms in this document (such as Security + Association or SA) can be found in [IPSECARCH]. {{ Clarif-7.2 }} It + should be noted that parts of IKEv2 rely on some of the processing + rules in [IPSECARCH], as described in various sections of this + document. + + IKE performs mutual authentication between two parties and + establishes an IKE security association (SA) that includes shared + secret information that can be used to efficiently establish SAs for + Encapsulating Security Payload (ESP) [ESP] and/or Authentication + Header (AH) [AH] and a set of cryptographic algorithms to be used by + the SAs to protect the traffic that they carry. In this document, + the term "suite" or "cryptographic suite" refers to a complete set of + algorithms used to protect an SA. An initiator proposes one or more + suites by listing supported algorithms that can be combined into + suites in a mix-and-match fashion. IKE can also negotiate use of IP + Compression (IPComp) [IPCOMP] in connection with an ESP and/or AH SA. + We call the IKE SA an "IKE_SA". The SAs for ESP and/or AH that get + set up through that IKE_SA we call "CHILD_SAs". + + All IKE communications consist of pairs of messages: a request and a + response. The pair is called an "exchange". We call the first + messages establishing an IKE_SA IKE_SA_INIT and IKE_AUTH exchanges + and subsequent IKE exchanges CREATE_CHILD_SA or INFORMATIONAL + exchanges. In the common case, there is a single IKE_SA_INIT + exchange and a single IKE_AUTH exchange (a total of four messages) to + + + +Kaufman, et al. Expires August 27, 2006 [Page 5] + +Internet-Draft IKEv2bis February 2006 + + + establish the IKE_SA and the first CHILD_SA. In exceptional cases, + there may be more than one of each of these exchanges. In all cases, + all IKE_SA_INIT exchanges MUST complete before any other exchange + type, then all IKE_AUTH exchanges MUST complete, and following that + any number of CREATE_CHILD_SA and INFORMATIONAL exchanges may occur + in any order. In some scenarios, only a single CHILD_SA is needed + between the IPsec endpoints, and therefore there would be no + additional exchanges. Subsequent exchanges MAY be used to establish + additional CHILD_SAs between the same authenticated pair of endpoints + and to perform housekeeping functions. + + IKE message flow always consists of a request followed by a response. + It is the responsibility of the requester to ensure reliability. If + the response is not received within a timeout interval, the requester + needs to retransmit the request (or abandon the connection). + + The first request/response of an IKE session (IKE_SA_INIT) negotiates + security parameters for the IKE_SA, sends nonces, and sends Diffie- + Hellman values. + + The second request/response (IKE_AUTH) transmits identities, proves + knowledge of the secrets corresponding to the two identities, and + sets up an SA for the first (and often only) AH and/or ESP CHILD_SA. + + The types of subsequent exchanges are CREATE_CHILD_SA (which creates + a CHILD_SA) and INFORMATIONAL (which deletes an SA, reports error + conditions, or does other housekeeping). Every request requires a + response. An INFORMATIONAL request with no payloads (other than the + empty Encrypted payload required by the syntax) is commonly used as a + check for liveness. These subsequent exchanges cannot be used until + the initial exchanges have completed. + + In the description that follows, we assume that no errors occur. + Modifications to the flow should errors occur are described in + Section 2.21. + +1.1. Usage Scenarios + + IKE is expected to be used to negotiate ESP and/or AH SAs in a number + of different scenarios, each with its own special requirements. + + + + + + + + + + + +Kaufman, et al. Expires August 27, 2006 [Page 6] + +Internet-Draft IKEv2bis February 2006 + + +1.1.1. Security Gateway to Security Gateway Tunnel + + +-+-+-+-+-+ +-+-+-+-+-+ + ! ! IPsec ! ! + Protected !Tunnel ! tunnel !Tunnel ! Protected + Subnet <-->!Endpoint !<---------->!Endpoint !<--> Subnet + ! ! ! ! + +-+-+-+-+-+ +-+-+-+-+-+ + + Figure 1: Security Gateway to Security Gateway Tunnel + + In this scenario, neither endpoint of the IP connection implements + IPsec, but network nodes between them protect traffic for part of the + way. Protection is transparent to the endpoints, and depends on + ordinary routing to send packets through the tunnel endpoints for + processing. Each endpoint would announce the set of addresses + "behind" it, and packets would be sent in tunnel mode where the inner + IP header would contain the IP addresses of the actual endpoints. + +1.1.2. Endpoint-to-Endpoint Transport + + +-+-+-+-+-+ +-+-+-+-+-+ + ! ! IPsec transport ! ! + !Protected! or tunnel mode SA !Protected! + !Endpoint !<---------------------------------------->!Endpoint ! + ! ! ! ! + +-+-+-+-+-+ +-+-+-+-+-+ + + Figure 2: Endpoint to Endpoint + + In this scenario, both endpoints of the IP connection implement + IPsec, as required of hosts in [IPSECARCH]. Transport mode will + commonly be used with no inner IP header. If there is an inner IP + header, the inner addresses will be the same as the outer addresses. + A single pair of addresses will be negotiated for packets to be + protected by this SA. These endpoints MAY implement application + layer access controls based on the IPsec authenticated identities of + the participants. This scenario enables the end-to-end security that + has been a guiding principle for the Internet since [ARCHPRINC], + [TRANSPARENCY], and a method of limiting the inherent problems with + complexity in networks noted by [ARCHGUIDEPHIL]. Although this + scenario may not be fully applicable to the IPv4 Internet, it has + been deployed successfully in specific scenarios within intranets + using IKEv1. It should be more broadly enabled during the transition + to IPv6 and with the adoption of IKEv2. + + It is possible in this scenario that one or both of the protected + endpoints will be behind a network address translation (NAT) node, in + + + +Kaufman, et al. Expires August 27, 2006 [Page 7] + +Internet-Draft IKEv2bis February 2006 + + + which case the tunneled packets will have to be UDP encapsulated so + that port numbers in the UDP headers can be used to identify + individual endpoints "behind" the NAT (see Section 2.23). + +1.1.3. Endpoint to Security Gateway Tunnel + + +-+-+-+-+-+ +-+-+-+-+-+ + ! ! IPsec ! ! Protected + !Protected! tunnel !Tunnel ! Subnet + !Endpoint !<------------------------>!Endpoint !<--- and/or + ! ! ! ! Internet + +-+-+-+-+-+ +-+-+-+-+-+ + + Figure 3: Endpoint to Security Gateway Tunnel + + In this scenario, a protected endpoint (typically a portable roaming + computer) connects back to its corporate network through an IPsec- + protected tunnel. It might use this tunnel only to access + information on the corporate network, or it might tunnel all of its + traffic back through the corporate network in order to take advantage + of protection provided by a corporate firewall against Internet-based + attacks. In either case, the protected endpoint will want an IP + address associated with the security gateway so that packets returned + to it will go to the security gateway and be tunneled back. This IP + address may be static or may be dynamically allocated by the security + gateway. {{ Clarif-6.1 }} In support of the latter case, IKEv2 + includes a mechanism (namely, configuration payloads) for the + initiator to request an IP address owned by the security gateway for + use for the duration of its SA. + + In this scenario, packets will use tunnel mode. On each packet from + the protected endpoint, the outer IP header will contain the source + IP address associated with its current location (i.e., the address + that will get traffic routed to the endpoint directly), while the + inner IP header will contain the source IP address assigned by the + security gateway (i.e., the address that will get traffic routed to + the security gateway for forwarding to the endpoint). The outer + destination address will always be that of the security gateway, + while the inner destination address will be the ultimate destination + for the packet. + + In this scenario, it is possible that the protected endpoint will be + behind a NAT. In that case, the IP address as seen by the security + gateway will not be the same as the IP address sent by the protected + endpoint, and packets will have to be UDP encapsulated in order to be + routed properly. + + + + + +Kaufman, et al. Expires August 27, 2006 [Page 8] + +Internet-Draft IKEv2bis February 2006 + + +1.1.4. Other Scenarios + + Other scenarios are possible, as are nested combinations of the + above. One notable example combines aspects of 1.1.1 and 1.1.3. A + subnet may make all external accesses through a remote security + gateway using an IPsec tunnel, where the addresses on the subnet are + routed to the security gateway by the rest of the Internet. An + example would be someone's home network being virtually on the + Internet with static IP addresses even though connectivity is + provided by an ISP that assigns a single dynamically assigned IP + address to the user's security gateway (where the static IP addresses + and an IPsec relay are provided by a third party located elsewhere). + +1.2. The Initial Exchanges + + Communication using IKE always begins with IKE_SA_INIT and IKE_AUTH + exchanges (known in IKEv1 as Phase 1). These initial exchanges + normally consist of four messages, though in some scenarios that + number can grow. All communications using IKE consist of request/ + response pairs. We'll describe the base exchange first, followed by + variations. The first pair of messages (IKE_SA_INIT) negotiate + cryptographic algorithms, exchange nonces, and do a Diffie-Hellman + exchange [DH]. + + The second pair of messages (IKE_AUTH) authenticate the previous + messages, exchange identities and certificates, and establish the + first CHILD_SA. Parts of these messages are encrypted and integrity + protected with keys established through the IKE_SA_INIT exchange, so + the identities are hidden from eavesdroppers and all fields in all + the messages are authenticated. + + In the following descriptions, the payloads contained in the message + are indicated by names as listed below. + + + + + + + + + + + + + + + + + + +Kaufman, et al. Expires August 27, 2006 [Page 9] + +Internet-Draft IKEv2bis February 2006 + + + Notation Payload + ----------------------------------------- + AUTH Authentication + CERT Certificate + CERTREQ Certificate Request + CP Configuration + D Delete + E Encrypted + EAP Extensible Authentication + HDR IKE Header + IDi Identification - Initiator + IDr Identification - Responder + KE Key Exchange + Ni, Nr Nonce + N Notify + SA Security Association + TSi Traffic Selector - Initiator + TSr Traffic Selector - Responder + V Vendor ID + + The details of the contents of each payload are described in section + 3. Payloads that may optionally appear will be shown in brackets, + such as [CERTREQ], indicate that optionally a certificate request + payload can be included. + + {{ Clarif-7.10 }} Many payloads contain fields marked as "RESERVED". + Some payloads in IKEv2 (and historically in IKEv1) are not aligned to + 4-byte boundaries. + + The initial exchanges are as follows: + + Initiator Responder + ------------------------------------------------------------------- + HDR, SAi1, KEi, Ni --> + + HDR contains the Security Parameter Indexes (SPIs), version numbers, + and flags of various sorts. The SAi1 payload states the + cryptographic algorithms the initiator supports for the IKE_SA. The + KE payload sends the initiator's Diffie-Hellman value. Ni is the + initiator's nonce. + + <-- HDR, SAr1, KEr, Nr, [CERTREQ] + + The responder chooses a cryptographic suite from the initiator's + offered choices and expresses that choice in the SAr1 payload, + completes the Diffie-Hellman exchange with the KEr payload, and sends + its nonce in the Nr payload. + + + + +Kaufman, et al. Expires August 27, 2006 [Page 10] + +Internet-Draft IKEv2bis February 2006 + + + At this point in the negotiation, each party can generate SKEYSEED, + from which all keys are derived for that IKE_SA. All but the headers + of all the messages that follow are encrypted and integrity + protected. The keys used for the encryption and integrity protection + are derived from SKEYSEED and are known as SK_e (encryption) and SK_a + (authentication, a.k.a. integrity protection). A separate SK_e and + SK_a is computed for each direction. In addition to the keys SK_e + and SK_a derived from the DH value for protection of the IKE_SA, + another quantity SK_d is derived and used for derivation of further + keying material for CHILD_SAs. The notation SK { ... } indicates + that these payloads are encrypted and integrity protected using that + direction's SK_e and SK_a. + + HDR, SK {IDi, [CERT,] [CERTREQ,] + [IDr,] AUTH, SAi2, + TSi, TSr} --> + + The initiator asserts its identity with the IDi payload, proves + knowledge of the secret corresponding to IDi and integrity protects + the contents of the first message using the AUTH payload (see + Section 2.15). It might also send its certificate(s) in CERT + payload(s) and a list of its trust anchors in CERTREQ payload(s). If + any CERT payloads are included, the first certificate provided MUST + contain the public key used to verify the AUTH field. The optional + payload IDr enables the initiator to specify which of the responder's + identities it wants to talk to. This is useful when the machine on + which the responder is running is hosting multiple identities at the + same IP address. The initiator begins negotiation of a CHILD_SA + using the SAi2 payload. The final fields (starting with SAi2) are + described in the description of the CREATE_CHILD_SA exchange. + + <-- HDR, SK {IDr, [CERT,] AUTH, + SAr2, TSi, TSr} + + The responder asserts its identity with the IDr payload, optionally + sends one or more certificates (again with the certificate containing + the public key used to verify AUTH listed first), authenticates its + identity and protects the integrity of the second message with the + AUTH payload, and completes negotiation of a CHILD_SA with the + additional fields described below in the CREATE_CHILD_SA exchange. + + The recipients of messages 3 and 4 MUST verify that all signatures + and MACs are computed correctly and that the names in the ID payloads + correspond to the keys used to generate the AUTH payload. + + {{ Clarif-4.2}} If creating the CHILD_SA during the IKE_AUTH exchange + fails for some reason, the IKE_SA is still created as usual. The + list of responses in the IKE_AUTH exchange that do not prevent an + + + +Kaufman, et al. Expires August 27, 2006 [Page 11] + +Internet-Draft IKEv2bis February 2006 + + + IKE_SA from being set up include at least the following: + NO_PROPOSAL_CHOSEN, TS_UNACCEPTABLE, SINGLE_PAIR_REQUIRED, + INTERNAL_ADDRESS_FAILURE, and FAILED_CP_REQUIRED. + + {{ Clarif-4.3 }} Note that IKE_AUTH messages do not contain KEi/KEr + or Ni/Nr payloads. Thus, the SA payload in IKE_AUTH exchange cannot + contain Transform Type 4 (Diffie-Hellman Group) with any value other + than NONE. Implementations SHOULD NOT send such a transform because + it cannot be interpreted consistently, and implementations SHOULD + ignore any such tranforms they receive. + +1.3. The CREATE_CHILD_SA Exchange + + {{ This is a heavy rewrite of most of this section. The major + organization changes are described in Clarif-4.1 and Clarif-5.1. }} + + The CREATE_CHILD_SA exchange is used to create new CHILD_SAs and to + rekey both IKE_SAs and CHILD_SAs. This exchange consists of a single + request/response pair, and some of its function was referred to as a + phase 2 exchange in IKEv1. It MAY be initiated by either end of the + IKE_SA after the initial exchanges are completed. + + All messages following the initial exchange are cryptographically + protected using the cryptographic algorithms and keys negotiated in + the first two messages of the IKE exchange. These subsequent + messages use the syntax of the Encrypted Payload described in + Section 3.14. All subsequent messages include an Encrypted Payload, + even if they are referred to in the text as "empty". For both + messages in the CREATE_CHILD_SA, the message following the header is + encrypted and the message including the header is integrity protected + using the cryptographic algorithms negotiated for the IKE_SA. + + The CREATE_CHILD_SA is also used for rekeying IKE_SAs and CHILD_SAs. + An SA is rekeyed by creating a new SA and then deleting the old one. + This section describes the first part of rekeying, the creation of + new SAs; Section 2.8 covers the mechanics of rekeying, including + moving traffic from old to new SAs and the deletion of the old SAs. + The two sections must be read together to understand the entire + process of rekeying. + + Either endpoint may initiate a CREATE_CHILD_SA exchange, so in this + section the term initiator refers to the endpoint initiating this + exchange. An implementation MAY refuse all CREATE_CHILD_SA requests + within an IKE_SA. + + The CREATE_CHILD_SA request MAY optionally contain a KE payload for + an additional Diffie-Hellman exchange to enable stronger guarantees + of forward secrecy for the CHILD_SA. The keying material for the + + + +Kaufman, et al. Expires August 27, 2006 [Page 12] + +Internet-Draft IKEv2bis February 2006 + + + CHILD_SA is a function of SK_d established during the establishment + of the IKE_SA, the nonces exchanged during the CREATE_CHILD_SA + exchange, and the Diffie-Hellman value (if KE payloads are included + in the CREATE_CHILD_SA exchange). + + If a CREATE_CHILD_SA exchange includes a KEi payload, at least one of + the SA offers MUST include the Diffie-Hellman group of the KEi. The + Diffie-Hellman group of the KEi MUST be an element of the group the + initiator expects the responder to accept (additional Diffie-Hellman + groups can be proposed). If the responder rejects the Diffie-Hellman + group of the KEi payload, the responder MUST reject the request and + indicate its preferred Diffie-Hellman group in the INVALID_KE_PAYLOAD + Notification payload. In the case of such a rejection, the + CREATE_CHILD_SA exchange fails, and the initiator will probably retry + the exchange with a Diffie-Hellman proposal and KEi in the group that + the responder gave in the INVALID_KE_PAYLOAD. + +1.3.1. Creating New CHILD_SAs with the CREATE_CHILD_SA Exchange + + A CHILD_SA may be created by sending a CREATE_CHILD_SA request. The + CREATE_CHILD_SA request for creating a new CHILD_SA is: + + Initiator Responder + ------------------------------------------------------------------- + HDR, SK {SA, Ni, [KEi], + TSi, TSr} --> + + The initiator sends SA offer(s) in the SA payload, a nonce in the Ni + payload, optionally a Diffie-Hellman value in the KEi payload, and + the proposed traffic selectors for the proposed CHILD_SA in the TSi + and TSr payloads. + + The CREATE_CHILD_SA response for creating a new CHILD_SA is: + + <-- HDR, SK {SA, Nr, [KEr], + TSi, TSr} + + The responder replies (using the same Message ID to respond) with the + accepted offer in an SA payload, and a Diffie-Hellman value in the + KEr payload if KEi was included in the request and the selected + cryptographic suite includes that group. + + The traffic selectors for traffic to be sent on that SA are specified + in the TS payloads in the response, which may be a subset of what the + initiator of the CHILD_SA proposed. + + + + + + +Kaufman, et al. Expires August 27, 2006 [Page 13] + +Internet-Draft IKEv2bis February 2006 + + +1.3.2. Rekeying IKE_SAs with the CREATE_CHILD_SA Exchange + + The CREATE_CHILD_SA request for rekeying an IKE_SA is: + + Initiator Responder + ------------------------------------------------------------------- + HDR, SK {SA, Ni, KEi} --> + + The initiator sends SA offer(s) in the SA payload, a nonce in the Ni + payload, and a Diffie-Hellman value in the KEi payload. New + initiator and responder SPIs are supplied in the SPI fields. + + The CREATE_CHILD_SA response for rekeying an IKE_SA is: + + <-- HDR, SK {SA, Nr, KEr} + + The responder replies (using the same Message ID to respond) with the + accepted offer in an SA payload, and a Diffie-Hellman value in the + KEr payload if the selected cryptographic suite includes that group. + + The new IKE_SA has its message counters set to 0, regardless of what + they were in the earlier IKE_SA. The window size starts at 1 for any + new IKE_SA. + + KEi and KEr are required for rekeying an IKE_SA. + +1.3.3. Rekeying CHILD_SAs with the CREATE_CHILD_SA Exchange + + The CREATE_CHILD_SA request for rekeying a CHILD_SA is: + + Initiator Responder + ------------------------------------------------------------------- + HDR, SK {N, SA, Ni, [KEi], + TSi, TSr} --> + + The initiator sends SA offer(s) in the SA payload, a nonce in the Ni + payload, optionally a Diffie-Hellman value in the KEi payload, and + the proposed traffic selectors for the proposed CHILD_SA in the TSi + and TSr payloads. When rekeying an existing CHILD_SA, the leading N + payload of type REKEY_SA MUST be included and MUST give the SPI (as + they would be expected in the headers of inbound packets) of the SAs + being rekeyed. + + The CREATE_CHILD_SA response for rekeying a CHILD_SA is: + + <-- HDR, SK {SA, Nr, [KEr], + Si, TSr} + + + + +Kaufman, et al. Expires August 27, 2006 [Page 14] + +Internet-Draft IKEv2bis February 2006 + + + The responder replies (using the same Message ID to respond) with the + accepted offer in an SA payload, and a Diffie-Hellman value in the + KEr payload if KEi was included in the request and the selected + cryptographic suite includes that group. + + The traffic selectors for traffic to be sent on that SA are specified + in the TS payloads in the response, which may be a subset of what the + initiator of the CHILD_SA proposed. + +1.4. The INFORMATIONAL Exchange + + At various points during the operation of an IKE_SA, peers may desire + to convey control messages to each other regarding errors or + notifications of certain events. To accomplish this, IKE defines an + INFORMATIONAL exchange. INFORMATIONAL exchanges MUST ONLY occur + after the initial exchanges and are cryptographically protected with + the negotiated keys. + + Control messages that pertain to an IKE_SA MUST be sent under that + IKE_SA. Control messages that pertain to CHILD_SAs MUST be sent + under the protection of the IKE_SA which generated them (or its + successor if the IKE_SA was replaced for the purpose of rekeying). + + Messages in an INFORMATIONAL exchange contain zero or more + Notification, Delete, and Configuration payloads. The Recipient of + an INFORMATIONAL exchange request MUST send some response (else the + Sender will assume the message was lost in the network and will + retransmit it). That response MAY be a message with no payloads. + The request message in an INFORMATIONAL exchange MAY also contain no + payloads. This is the expected way an endpoint can ask the other + endpoint to verify that it is alive. + + {{ Clarif-5.6 }} ESP and AH SAs always exist in pairs, with one SA in + each direction. When an SA is closed, both members of the pair MUST + be closed (that is, deleted). When SAs are nested, as when data (and + IP headers if in tunnel mode) are encapsulated first with IPComp, + then with ESP, and finally with AH between the same pair of + endpoints, all of the SAs MUST be deleted together. Each endpoint + MUST close its incoming SAs and allow the other endpoint to close the + other SA in each pair. To delete an SA, an INFORMATIONAL exchange + with one or more delete payloads is sent listing the SPIs (as they + would be expected in the headers of inbound packets) of the SAs to be + deleted. The recipient MUST close the designated SAs. {{ Clarif-5.7 + }} Note that one never sends delete payloads for the two sides of an + SA in a single message. If there are many SAs to delete at the same + time (such as for nested SAs), one includes delete payloads for in + inbound half of each SA pair in your Informational exchange. + + + + +Kaufman, et al. Expires August 27, 2006 [Page 15] + +Internet-Draft IKEv2bis February 2006 + + + Normally, the reply in the INFORMATIONAL exchange will contain delete + payloads for the paired SAs going in the other direction. There is + one exception. If by chance both ends of a set of SAs independently + decide to close them, each may send a delete payload and the two + requests may cross in the network. If a node receives a delete + request for SAs for which it has already issued a delete request, it + MUST delete the outgoing SAs while processing the request and the + incoming SAs while processing the response. In that case, the + responses MUST NOT include delete payloads for the deleted SAs, since + that would result in duplicate deletion and could in theory delete + the wrong SA. + + {{ Demoted the SHOULD }} Half-closed connections are anomalous, and a + node with auditing capability should probably audit their existence + if they persist. Note that this specification nowhere specifies time + periods, so it is up to individual endpoints to decide how long to + wait. A node MAY refuse to accept incoming data on half-closed + connections but MUST NOT unilaterally close them and reuse the SPIs. + If connection state becomes sufficiently messed up, a node MAY close + the IKE_SA; doing so will implicitly close all SAs negotiated under + it. It can then rebuild the SAs it needs on a clean base under a new + IKE_SA. {{ Clarif-5.8 }} The response to a request that deletes the + IKE_SA is an empty Informational response. + + The INFORMATIONAL exchange is defined as: + + Initiator Responder + ------------------------------------------------------------------- + HDR, SK {[N,] [D,] + [CP,] ...} --> + <-- HDR, SK {[N,] [D,] + [CP], ...} + + The processing of an INFORMATIONAL exchange is determined by its + component payloads. + +1.5. Informational Messages outside of an IKE_SA + + If an encrypted IKE packet arrives on port 500 or 4500 with an + unrecognized SPI, it could be because the receiving node has recently + crashed and lost state or because of some other system malfunction or + attack. If the receiving node has an active IKE_SA to the IP address + from whence the packet came, it MAY send a notification of the + wayward packet over that IKE_SA in an INFORMATIONAL exchange. If it + does not have such an IKE_SA, it MAY send an Informational message + without cryptographic protection to the source IP address. Such a + message is not part of an informational exchange, and the receiving + node MUST NOT respond to it. Doing so could cause a message loop. + + + +Kaufman, et al. Expires August 27, 2006 [Page 16] + +Internet-Draft IKEv2bis February 2006 + + + {{ Clarif-7.7 }} There are two cases when such a one-way notification + is sent: INVALID_IKE_SPI and INVALID_SPI. These notifications are + sent outside of an IKE_SA. Note that such notifications are + explicitly not Informational exchanges; these are one-way messages + that must not be responded to. In case of INVALID_IKE_SPI, the + message sent is a response message, and thus it is sent to the IP + address and port from whence it came with the same IKE SPIs and the + Message ID copied. In case of INVALID_SPI, however, there are no IKE + SPI values that would be meaningful to the recipient of such a + notification. Using zero values or random values are both + acceptable. + +1.6. Requirements Terminology + + Keywords "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT" and + "MAY" that appear in this document are to be interpreted as described + in [MUSTSHOULD]. + + The term "Expert Review" is to be interpreted as defined in + [IANACONS]. + +1.7. Differences Between RFC 4306 and This Document + + {{ Added this entire section, including this recursive remark. }} + + This document contains clarifications and amplifications to IKEv2 + [IKEV2]. The clarifications are mostly based on [Clarif]. The + changes listed in that document were discussed in the IPsec Working + Group and, after the Working Group was disbanded, on the IPsec + mailing list. That document contains detailed explanations of areas + that were unclear in IKEv2, and is thus useful to implementers of + IKEv2. + + The protocol described in this document retains the same major + version number (2) and minor version number (0) as was used in RFC + 4306. + + In the body of this document, notes that are enclosed in double curly + braces {{ such as this }} point out changes from IKEv2. Changes that + come from [Clarif] are marked with the section from that document, + such as "{{ Clarif-2.10 }}". + + This document also make the figures and references a bit more regular + than in [IKEV2]. + + IKEv2 developers have noted that the SHOULD-level requirements are + often unclear in that they don't say when it is OK to not obey the + requirements. They also have noted that there are MUST-level + + + +Kaufman, et al. Expires August 27, 2006 [Page 17] + +Internet-Draft IKEv2bis February 2006 + + + requirements that are not related to interoperability. This document + has more explanation of some of these requirements. All non- + capitalized uses of the words SHOULD and MUST now mean their normal + English sense, not the interoperability sense of [MUSTSHOULD]. + + IKEv2 (and IKEv1) developers have noted that there is a great deal of + material in the tables of codes in Section 3.10. This leads to + implementers not having all the needed information in the main body + of the docment. A later version of this document may move much of + the material from those tables into the associated parts of the main + body of the document. + + A later version of this document will probably have all the {{ }} + comments removed from the body of the document and instead appear in + an appendix. + + +2. IKE Protocol Details and Variations + + IKE normally listens and sends on UDP port 500, though IKE messages + may also be received on UDP port 4500 with a slightly different + format (see Section 2.23). Since UDP is a datagram (unreliable) + protocol, IKE includes in its definition recovery from transmission + errors, including packet loss, packet replay, and packet forgery. + IKE is designed to function so long as (1) at least one of a series + of retransmitted packets reaches its destination before timing out; + and (2) the channel is not so full of forged and replayed packets so + as to exhaust the network or CPU capacities of either endpoint. Even + in the absence of those minimum performance requirements, IKE is + designed to fail cleanly (as though the network were broken). + + Although IKEv2 messages are intended to be short, they contain + structures with no hard upper bound on size (in particular, X.509 + certificates), and IKEv2 itself does not have a mechanism for + fragmenting large messages. IP defines a mechanism for fragmentation + of oversize UDP messages, but implementations vary in the maximum + message size supported. Furthermore, use of IP fragmentation opens + an implementation to denial of service attacks [DOSUDPPROT]. + Finally, some NAT and/or firewall implementations may block IP + fragments. + + All IKEv2 implementations MUST be able to send, receive, and process + IKE messages that are up to 1280 bytes long, and they SHOULD be able + to send, receive, and process messages that are up to 3000 bytes + long. {{ Demoted the SHOULD }} IKEv2 implementations need to be aware + of the maximum UDP message size supported and MAY shorten messages by + leaving out some certificates or cryptographic suite proposals if + that will keep messages below the maximum. Use of the "Hash and URL" + + + +Kaufman, et al. Expires August 27, 2006 [Page 18] + +Internet-Draft IKEv2bis February 2006 + + + formats rather than including certificates in exchanges where + possible can avoid most problems. {{ Demoted the SHOULD }} + Implementations and configuration need to keep in mind, however, that + if the URL lookups are possible only after the IPsec SA is + established, recursion issues could prevent this technique from + working. + + {{ Clarif-7.5 }} All packets sent on port 4500 MUST begin with the + prefix of four zeros; otherwise, the receiver won't know how to + handle them. + +2.1. Use of Retransmission Timers + + All messages in IKE exist in pairs: a request and a response. The + setup of an IKE_SA normally consists of two request/response pairs. + Once the IKE_SA is set up, either end of the security association may + initiate requests at any time, and there can be many requests and + responses "in flight" at any given moment. But each message is + labeled as either a request or a response, and for each request/ + response pair one end of the security association is the initiator + and the other is the responder. + + For every pair of IKE messages, the initiator is responsible for + retransmission in the event of a timeout. The responder MUST never + retransmit a response unless it receives a retransmission of the + request. In that event, the responder MUST ignore the retransmitted + request except insofar as it triggers a retransmission of the + response. The initiator MUST remember each request until it receives + the corresponding response. The responder MUST remember each + response until it receives a request whose sequence number is larger + than the sequence number in the response plus its window size (see + Section 2.3). + + IKE is a reliable protocol, in the sense that the initiator MUST + retransmit a request until either it receives a corresponding reply + OR it deems the IKE security association to have failed and it + discards all state associated with the IKE_SA and any CHILD_SAs + negotiated using that IKE_SA. + +2.2. Use of Sequence Numbers for Message ID + + Every IKE message contains a Message ID as part of its fixed header. + This Message ID is used to match up requests and responses, and to + identify retransmissions of messages. + + The Message ID is a 32-bit quantity, which is zero for the first IKE + request in each direction. {{ Clarif-3.10 }} When the IKE_AUTH + exchange does not use EAP, the IKE_SA initial setup messages will + + + +Kaufman, et al. Expires August 27, 2006 [Page 19] + +Internet-Draft IKEv2bis February 2006 + + + always be numbered 0 and 1. When EAP is used, each pair of messages + have their message numbers incremented; the first pair of AUTH + messages will have an ID of 1, the second will be 2, and so on. + + Each endpoint in the IKE Security Association maintains two "current" + Message IDs: the next one to be used for a request it initiates and + the next one it expects to see in a request from the other end. + These counters increment as requests are generated and received. + Responses always contain the same message ID as the corresponding + request. That means that after the initial exchange, each integer n + may appear as the message ID in four distinct messages: the nth + request from the original IKE initiator, the corresponding response, + the nth request from the original IKE responder, and the + corresponding response. If the two ends make very different numbers + of requests, the Message IDs in the two directions can be very + different. There is no ambiguity in the messages, however, because + the (I)nitiator and (R)esponse bits in the message header specify + which of the four messages a particular one is. + + {{ Clarif-2.2 }} The Message ID for IKE_SA_INIT messages is always + zero, including for retries of the message due to responses such as + COOKIE and INVALID_KE_PAYLOAD. + + Note that Message IDs are cryptographically protected and provide + protection against message replays. In the unlikely event that + Message IDs grow too large to fit in 32 bits, the IKE_SA MUST be + closed. Rekeying an IKE_SA resets the sequence numbers. + + {{ Clarif-2.3 }} When a responder receives an IKE_SA_INIT request, it + has to determine whether the packet is a retransmission belonging to + an existing "half-open" IKE_SA (in which case the responder + retransmits the same response), or a new request (in which case the + responder creates a new IKE_SA and sends a fresh response), or it is + a retransmission of a now-opened IKE_SA (in whcih case the responder + ignores it). It is not sufficient to use the initiator's SPI and/or + IP address to differentiate between the two cases because two + different peers behind a single NAT could choose the same initiator + SPI. Instead, a robust responder will do the IKE_SA lookup using the + whole packet, its hash, or the Ni payload. + +2.3. Window Size for Overlapping Requests + + In order to maximize IKE throughput, an IKE endpoint MAY issue + multiple requests before getting a response to any of them if the + other endpoint has indicated its ability to handle such requests. + For simplicity, an IKE implementation MAY choose to process requests + strictly in order and/or wait for a response to one request before + issuing another. Certain rules must be followed to ensure + + + +Kaufman, et al. Expires August 27, 2006 [Page 20] + +Internet-Draft IKEv2bis February 2006 + + + interoperability between implementations using different strategies. + + After an IKE_SA is set up, either end can initiate one or more + requests. These requests may pass one another over the network. An + IKE endpoint MUST be prepared to accept and process a request while + it has a request outstanding in order to avoid a deadlock in this + situation. {{ Downgraded the SHOULD }} An IKE endpoint may also + accept and process multiple requests while it has a request + outstanding. + + An IKE endpoint MUST wait for a response to each of its messages + before sending a subsequent message unless it has received a + SET_WINDOW_SIZE Notify message from its peer informing it that the + peer is prepared to maintain state for multiple outstanding messages + in order to allow greater throughput. + + An IKE endpoint MUST NOT exceed the peer's stated window size for + transmitted IKE requests. In other words, if the responder stated + its window size is N, then when the initiator needs to make a request + X, it MUST wait until it has received responses to all requests up + through request X-N. An IKE endpoint MUST keep a copy of (or be able + to regenerate exactly) each request it has sent until it receives the + corresponding response. An IKE endpoint MUST keep a copy of (or be + able to regenerate exactly) the number of previous responses equal to + its declared window size in case its response was lost and the + initiator requests its retransmission by retransmitting the request. + + An IKE endpoint supporting a window size greater than one ought to be + capable of processing incoming requests out of order to maximize + performance in the event of network failures or packet reordering. + + {{ Clarif-7.3 }} The window size is normally a (possibly + configurable) property of a particular implementation, and is not + related to congestion control (unlike the window size in TCP, for + example). In particular, it is not defined what the responder should + do when it receives a SET_WINDOW_SIZE notification containing a + smaller value than is currently in effect. Thus, there is currently + no way to reduce the window size of an existing IKE_SA; you can only + increase it. When rekeying an IKE_SA, the new IKE_SA starts with + window size 1 until it is explicitly increased by sending a new + SET_WINDOW_SIZE notification. + +2.4. State Synchronization and Connection Timeouts + + An IKE endpoint is allowed to forget all of its state associated with + an IKE_SA and the collection of corresponding CHILD_SAs at any time. + This is the anticipated behavior in the event of an endpoint crash + and restart. It is important when an endpoint either fails or + + + +Kaufman, et al. Expires August 27, 2006 [Page 21] + +Internet-Draft IKEv2bis February 2006 + + + reinitializes its state that the other endpoint detect those + conditions and not continue to waste network bandwidth by sending + packets over discarded SAs and having them fall into a black hole. + + Since IKE is designed to operate in spite of Denial of Service (DoS) + attacks from the network, an endpoint MUST NOT conclude that the + other endpoint has failed based on any routing information (e.g., + ICMP messages) or IKE messages that arrive without cryptographic + protection (e.g., Notify messages complaining about unknown SPIs). + An endpoint MUST conclude that the other endpoint has failed only + when repeated attempts to contact it have gone unanswered for a + timeout period or when a cryptographically protected INITIAL_CONTACT + notification is received on a different IKE_SA to the same + authenticated identity. {{ Demoted the SHOULD }} An endpoint should + suspect that the other endpoint has failed based on routing + information and initiate a request to see whether the other endpoint + is alive. To check whether the other side is alive, IKE specifies an + empty INFORMATIONAL message that (like all IKE requests) requires an + acknowledgement (note that within the context of an IKE_SA, an + "empty" message consists of an IKE header followed by an Encrypted + payload that contains no payloads). If a cryptographically protected + message has been received from the other side recently, unprotected + notifications MAY be ignored. Implementations MUST limit the rate at + which they take actions based on unprotected messages. + + Numbers of retries and lengths of timeouts are not covered in this + specification because they do not affect interoperability. It is + suggested that messages be retransmitted at least a dozen times over + a period of at least several minutes before giving up on an SA, but + different environments may require different rules. To be a good + network citizen, retranmission times MUST increase exponentially to + avoid flooding the network and making an existing congestion + situation worse. If there has only been outgoing traffic on all of + the SAs associated with an IKE_SA, it is essential to confirm + liveness of the other endpoint to avoid black holes. If no + cryptographically protected messages have been received on an IKE_SA + or any of its CHILD_SAs recently, the system needs to perform a + liveness check in order to prevent sending messages to a dead peer. + Receipt of a fresh cryptographically protected message on an IKE_SA + or any of its CHILD_SAs ensures liveness of the IKE_SA and all of its + CHILD_SAs. Note that this places requirements on the failure modes + of an IKE endpoint. An implementation MUST NOT continue sending on + any SA if some failure prevents it from receiving on all of the + associated SAs. If CHILD_SAs can fail independently from one another + without the associated IKE_SA being able to send a delete message, + then they MUST be negotiated by separate IKE_SAs. + + There is a Denial of Service attack on the initiator of an IKE_SA + + + +Kaufman, et al. Expires August 27, 2006 [Page 22] + +Internet-Draft IKEv2bis February 2006 + + + that can be avoided if the initiator takes the proper care. Since + the first two messages of an SA setup are not cryptographically + protected, an attacker could respond to the initiator's message + before the genuine responder and poison the connection setup attempt. + To prevent this, the initiator MAY be willing to accept multiple + responses to its first message, treat each as potentially legitimate, + respond to it, and then discard all the invalid half-open connections + when it receives a valid cryptographically protected response to any + one of its requests. Once a cryptographically valid response is + received, all subsequent responses should be ignored whether or not + they are cryptographically valid. + + Note that with these rules, there is no reason to negotiate and agree + upon an SA lifetime. If IKE presumes the partner is dead, based on + repeated lack of acknowledgement to an IKE message, then the IKE SA + and all CHILD_SAs set up through that IKE_SA are deleted. + + An IKE endpoint may at any time delete inactive CHILD_SAs to recover + resources used to hold their state. If an IKE endpoint chooses to + delete CHILD_SAs, it MUST send Delete payloads to the other end + notifying it of the deletion. It MAY similarly time out the IKE_SA. + {{ Clarified the SHOULD }} Closing the IKE_SA implicitly closes all + associated CHILD_SAs. In this case, an IKE endpoint SHOULD send a + Delete payload indicating that it has closed the IKE_SA unless the + other endpoint is no longer responding. + +2.5. Version Numbers and Forward Compatibility + + This document describes version 2.0 of IKE, meaning the major version + number is 2 and the minor version number is 0. {{ Restated the + relationship to RFC 4306 }} This document is a clarification of + [IKEV2]. It is likely that some implementations will want to support + version 1.0 and version 2.0, and in the future, other versions. + + The major version number should be incremented only if the packet + formats or required actions have changed so dramatically that an + older version node would not be able to interoperate with a newer + version node if it simply ignored the fields it did not understand + and took the actions specified in the older specification. The minor + version number indicates new capabilities, and MUST be ignored by a + node with a smaller minor version number, but used for informational + purposes by the node with the larger minor version number. For + example, it might indicate the ability to process a newly defined + notification message. The node with the larger minor version number + would simply note that its correspondent would not be able to + understand that message and therefore would not send it. + + If an endpoint receives a message with a higher major version number, + + + +Kaufman, et al. Expires August 27, 2006 [Page 23] + +Internet-Draft IKEv2bis February 2006 + + + it MUST drop the message and SHOULD send an unauthenticated + notification message containing the highest version number it + supports. If an endpoint supports major version n, and major version + m, it MUST support all versions between n and m. If it receives a + message with a major version that it supports, it MUST respond with + that version number. In order to prevent two nodes from being + tricked into corresponding with a lower major version number than the + maximum that they both support, IKE has a flag that indicates that + the node is capable of speaking a higher major version number. + + Thus, the major version number in the IKE header indicates the + version number of the message, not the highest version number that + the transmitter supports. If the initiator is capable of speaking + versions n, n+1, and n+2, and the responder is capable of speaking + versions n and n+1, then they will negotiate speaking n+1, where the + initiator will set the flag indicating its ability to speak a higher + version. If they mistakenly (perhaps through an active attacker + sending error messages) negotiate to version n, then both will notice + that the other side can support a higher version number, and they + MUST break the connection and reconnect using version n+1. + + Note that IKEv1 does not follow these rules, because there is no way + in v1 of noting that you are capable of speaking a higher version + number. So an active attacker can trick two v2-capable nodes into + speaking v1. {{ Demoted the SHOULD }} When a v2-capable node + negotiates down to v1, it should note that fact in its logs. + + Also for forward compatibility, all fields marked RESERVED MUST be + set to zero by an implementation running version 2.0 or later, and + their content MUST be ignored by an implementation running version + 2.0 or later ("Be conservative in what you send and liberal in what + you receive"). In this way, future versions of the protocol can use + those fields in a way that is guaranteed to be ignored by + implementations that do not understand them. Similarly, payload + types that are not defined are reserved for future use; + implementations of a version where they are undefined MUST skip over + those payloads and ignore their contents. + + IKEv2 adds a "critical" flag to each payload header for further + flexibility for forward compatibility. If the critical flag is set + and the payload type is unrecognized, the message MUST be rejected + and the response to the IKE request containing that payload MUST + include a Notify payload UNSUPPORTED_CRITICAL_PAYLOAD, indicating an + unsupported critical payload was included. If the critical flag is + not set and the payload type is unsupported, that payload MUST be + ignored. + + {{ Demoted the SHOULD in the second clause }}Although new payload + + + +Kaufman, et al. Expires August 27, 2006 [Page 24] + +Internet-Draft IKEv2bis February 2006 + + + types may be added in the future and may appear interleaved with the + fields defined in this specification, implementations MUST send the + payloads defined in this specification in the order shown in the + figures in Section 2; implementations are explicitly allowed to + reject as invalid a message with those payloads in any other order. + +2.6. Cookies + + The term "cookies" originates with Karn and Simpson [PHOTURIS] in + Photuris, an early proposal for key management with IPsec, and it has + persisted. The Internet Security Association and Key Management + Protocol (ISAKMP) [ISAKMP] fixed message header includes two eight- + octet fields titled "cookies", and that syntax is used by both IKEv1 + and IKEv2 though in IKEv2 they are referred to as the IKE SPI and + there is a new separate field in a Notify payload holding the cookie. + The initial two eight-octet fields in the header are used as a + connection identifier at the beginning of IKE packets. {{ Demoted the + SHOULD }} Each endpoint chooses one of the two SPIs and needs to + choose them so as to be unique identifiers of an IKE_SA. An SPI + value of zero is special and indicates that the remote SPI value is + not yet known by the sender. + + Unlike ESP and AH where only the recipient's SPI appears in the + header of a message, in IKE the sender's SPI is also sent in every + message. Since the SPI chosen by the original initiator of the + IKE_SA is always sent first, an endpoint with multiple IKE_SAs open + that wants to find the appropriate IKE_SA using the SPI it assigned + must look at the I(nitiator) Flag bit in the header to determine + whether it assigned the first or the second eight octets. + + In the first message of an initial IKE exchange, the initiator will + not know the responder's SPI value and will therefore set that field + to zero. + + An expected attack against IKE is state and CPU exhaustion, where the + target is flooded with session initiation requests from forged IP + addresses. This attack can be made less effective if an + implementation of a responder uses minimal CPU and commits no state + to an SA until it knows the initiator can receive packets at the + address from which it claims to be sending them. To accomplish this, + a responder SHOULD -- when it detects a large number of half-open + IKE_SAs -- reject initial IKE messages unless they contain a Notify + payload of type COOKIE. {{ Clarified the SHOULD }} If the responder + wants to set up an SA, it SHOULD instead send an unprotected IKE + message as a response and include COOKIE Notify payload with the + cookie data to be returned. Initiators who receive such responses + MUST retry the IKE_SA_INIT with a Notify payload of type COOKIE + containing the responder supplied cookie data as the first payload + + + +Kaufman, et al. Expires August 27, 2006 [Page 25] + +Internet-Draft IKEv2bis February 2006 + + + and all other payloads unchanged. The initial exchange will then be + as follows: + + Initiator Responder + ------------------------------------------------------------------- + HDR(A,0), SAi1, KEi, Ni --> + <-- HDR(A,0), N(COOKIE) + HDR(A,0), N(COOKIE), SAi1, + KEi, Ni --> + <-- HDR(A,B), SAr1, KEr, + Nr, [CERTREQ] + HDR(A,B), SK {IDi, [CERT,] + [CERTREQ,] [IDr,] AUTH, + SAi2, TSi, TSr} --> + <-- HDR(A,B), SK {IDr, [CERT,] + AUTH, SAr2, TSi, TSr} + + The first two messages do not affect any initiator or responder state + except for communicating the cookie. In particular, the message + sequence numbers in the first four messages will all be zero and the + message sequence numbers in the last two messages will be one. 'A' + is the SPI assigned by the initiator, while 'B' is the SPI assigned + by the responder. + + {{ Clarif-2.1 }} Because the responder's SPI identifies security- + related state held by the responder, and in this case no state is + created, the responder sends a zero value for the responder's SPI. + + {{ Demoted the SHOULD }} An IKE implementation should implement its + responder cookie generation in such a way as to not require any saved + state to recognize its valid cookie when the second IKE_SA_INIT + message arrives. The exact algorithms and syntax they use to + generate cookies do not affect interoperability and hence are not + specified here. The following is an example of how an endpoint could + use cookies to implement limited DOS protection. + + A good way to do this is to set the responder cookie to be: + + Cookie = <VersionIDofSecret> | Hash(Ni | IPi | SPIi | <secret>) + + where <secret> is a randomly generated secret known only to the + responder and periodically changed and | indicates concatenation. + <VersionIDofSecret> should be changed whenever <secret> is + regenerated. The cookie can be recomputed when the IKE_SA_INIT + arrives the second time and compared to the cookie in the received + message. If it matches, the responder knows that the cookie was + generated since the last change to <secret> and that IPi must be the + same as the source address it saw the first time. Incorporating SPIi + + + +Kaufman, et al. Expires August 27, 2006 [Page 26] + +Internet-Draft IKEv2bis February 2006 + + + into the calculation ensures that if multiple IKE_SAs are being set + up in parallel they will all get different cookies (assuming the + initiator chooses unique SPIi's). Incorporating Ni into the hash + ensures that an attacker who sees only message 2 can't successfully + forge a message 3. + + If a new value for <secret> is chosen while there are connections in + the process of being initialized, an IKE_SA_INIT might be returned + with other than the current <VersionIDofSecret>. The responder in + that case MAY reject the message by sending another response with a + new cookie or it MAY keep the old value of <secret> around for a + short time and accept cookies computed from either one. {{ Demoted + the SHOULD NOT }} The responder should not accept cookies + indefinitely after <secret> is changed, since that would defeat part + of the denial of service protection. {{ Demoted the SHOULD }} The + responder should change the value of <secret> frequently, especially + if under attack. + + {{ Clarif-2.1 }} In addition to cookies, there are several cases + where the IKE_SA_INIT exchange does not result in the creation of an + IKE_SA (such as INVALID_KE_PAYLOAD or NO_PROPOSAL_CHOSEN). In such a + case, sending a zero value for the Responder's SPI is correct. If + the responder sends a non-zero responder SPI, the initiator should + not reject the response for only that reason. + + {{ Clarif-2.5 }} When one party receives an IKE_SA_INIT request + containing a cookie whose contents do not match the value expected, + that party MUST ignore the cookie and process the message as if no + cookie had been included; usually this means sending a response + containing a new cookie. + +2.6.1. Interaction of COOKIE and INVALID_KE_PAYLOAD + + {{ This section added by Clarif-2.4 }} + + There are two common reasons why the initiator may have to retry the + IKE_SA_INIT exchange: the responder requests a cookie or wants a + different Diffie-Hellman group than was included in the KEi payload. + If the initiator receives a cookie from the responder, the initiator + needs to decide whether or not to include the cookie in only the next + retry of the IKE_SA_INIT request, or in all subsequent retries as + well. + + If the initiator includes the cookie only in the next retry, one + additional roundtrip may be needed in some cases. An additional + roundtrip is needed also if the initiator includes the cookie in all + retries, but the responder does not support this. For instance, if + the responder includes the SAi1 and KEi payloads in cookie + + + +Kaufman, et al. Expires August 27, 2006 [Page 27] + +Internet-Draft IKEv2bis February 2006 + + + calculation, it will reject the request by sending a new cookie. + + If both peers support including the cookie in all retries, a slightly + shorter exchange can happen. Implementations SHOULD support this + shorter exchange, but MUST NOT fail if other implementations do not + support this shorter exchange. + +2.7. Cryptographic Algorithm Negotiation + + The payload type known as "SA" indicates a proposal for a set of + choices of IPsec protocols (IKE, ESP, and/or AH) for the SA as well + as cryptographic algorithms associated with each protocol. + + An SA payload consists of one or more proposals. Each proposal + includes one or more protocols (usually one). Each protocol contains + one or more transforms -- each specifying a cryptographic algorithm. + Each transform contains zero or more attributes (attributes are + needed only if the transform identifier does not completely specify + the cryptographic algorithm). + + This hierarchical structure was designed to efficiently encode + proposals for cryptographic suites when the number of supported + suites is large because multiple values are acceptable for multiple + transforms. The responder MUST choose a single suite, which MAY be + any subset of the SA proposal following the rules below: + + Each proposal contains one or more protocols. If a proposal is + accepted, the SA response MUST contain the same protocols in the same + order as the proposal. The responder MUST accept a single proposal + or reject them all and return an error. (Example: if a single + proposal contains ESP and AH and that proposal is accepted, both ESP + and AH MUST be accepted. If ESP and AH are included in separate + proposals, the responder MUST accept only one of them). + + Each IPsec protocol proposal contains one or more transforms. Each + transform contains a transform type. The accepted cryptographic + suite MUST contain exactly one transform of each type included in the + proposal. For example: if an ESP proposal includes transforms + ENCR_3DES, ENCR_AES w/keysize 128, ENCR_AES w/keysize 256, + AUTH_HMAC_MD5, and AUTH_HMAC_SHA, the accepted suite MUST contain one + of the ENCR_ transforms and one of the AUTH_ transforms. Thus, six + combinations are acceptable. + + Since the initiator sends its Diffie-Hellman value in the + IKE_SA_INIT, it must guess the Diffie-Hellman group that the + responder will select from its list of supported groups. If the + initiator guesses wrong, the responder will respond with a Notify + payload of type INVALID_KE_PAYLOAD indicating the selected group. In + + + +Kaufman, et al. Expires August 27, 2006 [Page 28] + +Internet-Draft IKEv2bis February 2006 + + + this case, the initiator MUST retry the IKE_SA_INIT with the + corrected Diffie-Hellman group. The initiator MUST again propose its + full set of acceptable cryptographic suites because the rejection + message was unauthenticated and otherwise an active attacker could + trick the endpoints into negotiating a weaker suite than a stronger + one that they both prefer. + +2.8. Rekeying + + {{ Demoted the SHOULD }} IKE, ESP, and AH security associations use + secret keys that should be used only for a limited amount of time and + to protect a limited amount of data. This limits the lifetime of the + entire security association. When the lifetime of a security + association expires, the security association MUST NOT be used. If + there is demand, new security associations MAY be established. + Reestablishment of security associations to take the place of ones + that expire is referred to as "rekeying". + + To allow for minimal IPsec implementations, the ability to rekey SAs + without restarting the entire IKE_SA is optional. An implementation + MAY refuse all CREATE_CHILD_SA requests within an IKE_SA. If an SA + has expired or is about to expire and rekeying attempts using the + mechanisms described here fail, an implementation MUST close the + IKE_SA and any associated CHILD_SAs and then MAY start new ones. {{ + Demoted the SHOULD }} Implementations may wish to support in-place + rekeying of SAs, since doing so offers better performance and is + likely to reduce the number of packets lost during the transition. + + To rekey a CHILD_SA within an existing IKE_SA, create a new, + equivalent SA (see Section 2.17 below), and when the new one is + established, delete the old one. To rekey an IKE_SA, establish a new + equivalent IKE_SA (see Section 2.18 below) with the peer to whom the + old IKE_SA is shared using a CREATE_CHILD_SA within the existing + IKE_SA. An IKE_SA so created inherits all of the original IKE_SA's + CHILD_SAs. Use the new IKE_SA for all control messages needed to + maintain the CHILD_SAs created by the old IKE_SA, and delete the old + IKE_SA. The Delete payload to delete itself MUST be the last request + sent over an IKE_SA. + + {{ Demoted the SHOULD }} SAs should be rekeyed proactively, i.e., the + new SA should be established before the old one expires and becomes + unusable. Enough time should elapse between the time the new SA is + established and the old one becomes unusable so that traffic can be + switched over to the new SA. + + A difference between IKEv1 and IKEv2 is that in IKEv1 SA lifetimes + were negotiated. In IKEv2, each end of the SA is responsible for + enforcing its own lifetime policy on the SA and rekeying the SA when + + + +Kaufman, et al. Expires August 27, 2006 [Page 29] + +Internet-Draft IKEv2bis February 2006 + + + necessary. If the two ends have different lifetime policies, the end + with the shorter lifetime will end up always being the one to request + the rekeying. If an SA bundle has been inactive for a long time and + if an endpoint would not initiate the SA in the absence of traffic, + the endpoint MAY choose to close the SA instead of rekeying it when + its lifetime expires. {{ Demoted the SHOULD }} It should do so if + there has been no traffic since the last time the SA was rekeyed. + + Note that IKEv2 deliberately allows parallel SAs with the same + traffic selectors between common endpoints. One of the purposes of + this is to support traffic quality of service (QoS) differences among + the SAs (see [DIFFSERVFIELD], [DIFFSERVARCH], and section 4.1 of + [DIFFTUNNEL]). Hence unlike IKEv1, the combination of the endpoints + and the traffic selectors may not uniquely identify an SA between + those endpoints, so the IKEv1 rekeying heuristic of deleting SAs on + the basis of duplicate traffic selectors SHOULD NOT be used. + + {{ Demoted the SHOULD }} The node that initiated the surviving + rekeyed SA should delete the replaced SA after the new one is + established. + + There are timing windows -- particularly in the presence of lost + packets -- where endpoints may not agree on the state of an SA. The + responder to a CREATE_CHILD_SA MUST be prepared to accept messages on + an SA before sending its response to the creation request, so there + is no ambiguity for the initiator. The initiator MAY begin sending + on an SA as soon as it processes the response. The initiator, + however, cannot receive on a newly created SA until it receives and + processes the response to its CREATE_CHILD_SA request. How, then, is + the responder to know when it is OK to send on the newly created SA? + + From a technical correctness and interoperability perspective, the + responder MAY begin sending on an SA as soon as it sends its response + to the CREATE_CHILD_SA request. In some situations, however, this + could result in packets unnecessarily being dropped, so an + implementation MAY want to defer such sending. + + The responder can be assured that the initiator is prepared to + receive messages on an SA if either (1) it has received a + cryptographically valid message on the new SA, or (2) the new SA + rekeys an existing SA and it receives an IKE request to close the + replaced SA. When rekeying an SA, the responder continues to send + traffic on the old SA until one of those events occurs. When + establishing a new SA, the responder MAY defer sending messages on a + new SA until either it receives one or a timeout has occurred. {{ + Demoted the SHOULD }} If an initiator receives a message on an SA for + which it has not received a response to its CREATE_CHILD_SA request, + it interprets that as a likely packet loss and retransmits the + + + +Kaufman, et al. Expires August 27, 2006 [Page 30] + +Internet-Draft IKEv2bis February 2006 + + + CREATE_CHILD_SA request. An initiator MAY send a dummy message on a + newly created SA if it has no messages queued in order to assure the + responder that the initiator is ready to receive messages. + + {{ Clarif-5.9 }} Throughout this document, "initiator" refers to the + party who initiated the exchange being described, and "original + initiator" refers to the party who initiated the whole IKE_SA. The + "original initiator" always refers to the party who initiated the + exchange which resulted in the current IKE_SA. In other words, if + the the "original responder" starts rekeying the IKE_SA, that party + becomes the "original initiator" of the new IKE_SA. + +2.8.1. Simultaneous CHILD_SA rekeying + + {{ The first two paragraphs were moved, and the rest was added, based + on Clarif-5.11 }} + + If the two ends have the same lifetime policies, it is possible that + both will initiate a rekeying at the same time (which will result in + redundant SAs). To reduce the probability of this happening, the + timing of rekeying requests SHOULD be jittered (delayed by a random + amount of time after the need for rekeying is noticed). + + This form of rekeying may temporarily result in multiple similar SAs + between the same pairs of nodes. When there are two SAs eligible to + receive packets, a node MUST accept incoming packets through either + SA. If redundant SAs are created though such a collision, the SA + created with the lowest of the four nonces used in the two exchanges + SHOULD be closed by the endpoint that created it. {{ Clarif-5.10 }} + "Lowest" means an octet-by-octet, lexicographical comparison (instead + of, for instance, comparing the nonces as large integers). In other + words, start by comparing the first octet; if they're equal, move to + the next octet, and so on. If you reach the end of one nonce, that + nonce is the lower one. + + The following is an explanation on the impact this has on + implementations. Assume that hosts A and B have an existing IPsec SA + pair with SPIs (SPIa1,SPIb1), and both start rekeying it at the same + time: + + Host A Host B + ------------------------------------------------------------------- + send req1: N(REKEY_SA,SPIa1), + SA(..,SPIa2,..),Ni1,.. --> + <-- send req2: N(REKEY_SA,SPIb1), + SA(..,SPIb2,..),Ni2 + recv req2 <-- + + + + +Kaufman, et al. Expires August 27, 2006 [Page 31] + +Internet-Draft IKEv2bis February 2006 + + + At this point, A knows there is a simultaneous rekeying going on. + However, it cannot yet know which of the exchanges will have the + lowest nonce, so it will just note the situation and respond as + usual. + + send resp2: SA(..,SPIa3,..), + Nr1,.. --> + --> recv req1 + + Now B also knows that simultaneous rekeying is going on. It responds + as usual. + + <-- send resp1: SA(..,SPIb3,..), + Nr2,.. + recv resp1 <-- + --> recv resp2 + + At this point, there are three CHILD_SA pairs between A and B (the + old one and two new ones). A and B can now compare the nonces. + Suppose that the lowest nonce was Nr1 in message resp2; in this case, + B (the sender of req2) deletes the redundant new SA, and A (the node + that initiated the surviving rekeyed SA), deletes the old one. + + send req3: D(SPIa1) --> + <-- send req4: D(SPIb2) + --> recv req3 + <-- send resp4: D(SPIb1) + recv req4 <-- + send resp4: D(SPIa3) --> + + The rekeying is now finished. + + However, there is a second possible sequence of events that can + happen if some packets are lost in the network, resulting in + retransmissions. The rekeying begins as usual, but A's first packet + (req1) is lost. + + + + + + + + + + + + + + + +Kaufman, et al. Expires August 27, 2006 [Page 32] + +Internet-Draft IKEv2bis February 2006 + + + Host A Host B + ------------------------------------------------------------------- + send req1: N(REKEY_SA,SPIa1), + SA(..,SPIa2,..), + Ni1,.. --> (lost) + <-- send req2: N(REKEY_SA,SPIb1), + SA(..,SPIb2,..),Ni2 + recv req2 <-- + send resp2: SA(..,SPIa3,..), + Nr1,.. --> + --> recv resp2 + <-- send req3: D(SPIb1) + recv req3 <-- + send resp3: D(SPIa1) --> + --> recv resp3 + + From B's point of view, the rekeying is now completed, and since it + has not yet received A's req1, it does not even know that there was + simultaneous rekeying. However, A will continue retransmitting the + message, and eventually it will reach B. + + resend req1 --> + --> recv req1 + + To B, it looks like A is trying to rekey an SA that no longer exists; + thus, B responds to the request with something non-fatal such as + NO_PROPOSAL_CHOSEN. + + <-- send resp1: N(NO_PROPOSAL_CHOSEN) + recv resp1 <-- + + When A receives this error, it already knows there was simultaneous + rekeying, so it can ignore the error message. + +2.8.2. Rekeying the IKE_SA Versus Reauthentication + + {{ Added this section from Clarif-5.2 }} + + Rekeying the IKE_SA and reauthentication are different concepts in + IKEv2. Rekeying the IKE_SA establishes new keys for the IKE_SA and + resets the Message ID counters, but it does not authenticate the + parties again (no AUTH or EAP payloads are involved). + + Although rekeying the IKE_SA may be important in some environments, + reauthentication (the verification that the parties still have access + to the long-term credentials) is often more important. + + IKEv2 does not have any special support for reauthentication. + + + +Kaufman, et al. Expires August 27, 2006 [Page 33] + +Internet-Draft IKEv2bis February 2006 + + + Reauthentication is done by creating a new IKE_SA from scratch (using + IKE_SA_INIT/IKE_AUTH exchanges, without any REKEY_SA notify + payloads), creating new CHILD_SAs within the new IKE_SA (without + REKEY_SA notify payloads), and finally deleting the old IKE_SA (which + deletes the old CHILD_SAs as well). + + This means that reauthentication also establishes new keys for the + IKE_SA and CHILD_SAs. Therefore, while rekeying can be performed + more often than reauthentication, the situation where "authentication + lifetime" is shorter than "key lifetime" does not make sense. + + While creation of a new IKE_SA can be initiated by either party + (initiator or responder in the original IKE_SA), the use of EAP + authentication and/or configuration payloads means in practice that + reauthentication has to be initiated by the same party as the + original IKE_SA. IKEv2 does not currently allow the responder to + request reauthentication in this case; however, there is ongoing work + to add this functionality [REAUTH]. + +2.9. Traffic Selector Negotiation + + {{ Clarif-7.2 }} When an RFC4301-compliant IPsec subsystem receives + an IP packet and matches a "protect" selector in its Security Policy + Database (SPD), the subsystem protects that packet with IPsec. When + no SA exists yet, it is the task of IKE to create it. Maintenance of + a system's SPD is outside the scope of IKE (see [PFKEY] for an + example protocol), though some implementations might update their SPD + in connection with the running of IKE (for an example scenario, see + Section 1.1.3). + + Traffic Selector (TS) payloads allow endpoints to communicate some of + the information from their SPD to their peers. TS payloads specify + the selection criteria for packets that will be forwarded over the + newly set up SA. This can serve as a consistency check in some + scenarios to assure that the SPDs are consistent. In others, it + guides the dynamic update of the SPD. + + Two TS payloads appear in each of the messages in the exchange that + creates a CHILD_SA pair. Each TS payload contains one or more + Traffic Selectors. Each Traffic Selector consists of an address + range (IPv4 or IPv6), a port range, and an IP protocol ID. In + support of the scenario described in Section 1.1.3, an initiator may + request that the responder assign an IP address and tell the + initiator what it is. {{ Clarif-6.1 }} That request is done using + configuration payloads, not traffic selectors. An address in a TSi + payload in a response does not mean that the responder has assigned + that address to the initiator: it only means that if packets matching + these traffic selectors are sent by the initiator, IPsec processing + + + +Kaufman, et al. Expires August 27, 2006 [Page 34] + +Internet-Draft IKEv2bis February 2006 + + + can be performed as agreed for this SA. + + IKEv2 allows the responder to choose a subset of the traffic proposed + by the initiator. This could happen when the configurations of the + two endpoints are being updated but only one end has received the new + information. Since the two endpoints may be configured by different + people, the incompatibility may persist for an extended period even + in the absence of errors. It also allows for intentionally different + configurations, as when one end is configured to tunnel all addresses + and depends on the other end to have the up-to-date list. + + The first of the two TS payloads is known as TSi (Traffic Selector- + initiator). The second is known as TSr (Traffic Selector-responder). + TSi specifies the source address of traffic forwarded from (or the + destination address of traffic forwarded to) the initiator of the + CHILD_SA pair. TSr specifies the destination address of the traffic + forwarded to (or the source address of the traffic forwarded from) + the responder of the CHILD_SA pair. For example, if the original + initiator request the creation of a CHILD_SA pair, and wishes to + tunnel all traffic from subnet 192.0.1.* on the initiator's side to + subnet 192.0.2.* on the responder's side, the initiator would include + a single traffic selector in each TS payload. TSi would specify the + address range (192.0.1.0 - 192.0.1.255) and TSr would specify the + address range (192.0.2.0 - 192.0.2.255). Assuming that proposal was + acceptable to the responder, it would send identical TS payloads + back. (Note: The IP address range 192.0.2.* has been reserved for + use in examples in RFCs and similar documents. This document needed + two such ranges, and so also used 192.0.1.*. This should not be + confused with any actual address.) + + The responder is allowed to narrow the choices by selecting a subset + of the traffic, for instance by eliminating or narrowing the range of + one or more members of the set of traffic selectors, provided the set + does not become the NULL set. + + It is possible for the responder's policy to contain multiple smaller + ranges, all encompassed by the initiator's traffic selector, and with + the responder's policy being that each of those ranges should be sent + over a different SA. Continuing the example above, the responder + might have a policy of being willing to tunnel those addresses to and + from the initiator, but might require that each address pair be on a + separately negotiated CHILD_SA. If the initiator generated its + request in response to an incoming packet from 192.0.1.43 to + 192.0.2.123, there would be no way for the responder to determine + which pair of addresses should be included in this tunnel, and it + would have to make a guess or reject the request with a status of + SINGLE_PAIR_REQUIRED. + + + + +Kaufman, et al. Expires August 27, 2006 [Page 35] + +Internet-Draft IKEv2bis February 2006 + + + {{ Clarif-4.11 }} Few implementations will have policies that require + separate SAs for each address pair. Because of this, if only some + part (or parts) of the TSi/TSr proposed by the initiator is (are) + acceptable to the responder, responders SHOULD narrow TSi/TSr to an + acceptable subset rather than use SINGLE_PAIR_REQUIRED. + + To enable the responder to choose the appropriate range in this case, + if the initiator has requested the SA due to a data packet, the + initiator SHOULD include as the first traffic selector in each of TSi + and TSr a very specific traffic selector including the addresses in + the packet triggering the request. In the example, the initiator + would include in TSi two traffic selectors: the first containing the + address range (192.0.1.43 - 192.0.1.43) and the source port and IP + protocol from the packet and the second containing (192.0.1.0 - + 192.0.1.255) with all ports and IP protocols. The initiator would + similarly include two traffic selectors in TSr. + + If the responder's policy does not allow it to accept the entire set + of traffic selectors in the initiator's request, but does allow him + to accept the first selector of TSi and TSr, then the responder MUST + narrow the traffic selectors to a subset that includes the + initiator's first choices. In this example, the responder might + respond with TSi being (192.0.1.43 - 192.0.1.43) with all ports and + IP protocols. + + If the initiator creates the CHILD_SA pair not in response to an + arriving packet, but rather, say, upon startup, then there may be no + specific addresses the initiator prefers for the initial tunnel over + any other. In that case, the first values in TSi and TSr MAY be + ranges rather than specific values, and the responder chooses a + subset of the initiator's TSi and TSr that are acceptable. If more + than one subset is acceptable but their union is not, the responder + MUST accept some subset and MAY include a Notify payload of type + ADDITIONAL_TS_POSSIBLE to indicate that the initiator might want to + try again. This case will occur only when the initiator and + responder are configured differently from one another. If the + initiator and responder agree on the granularity of tunnels, the + initiator will never request a tunnel wider than the responder will + accept. {{ Demoted the SHOULD }} Such misconfigurations should be + recorded in error logs. + + {{ Clarif-4.10 }} A concise summary of the narrowing process is: + + o If the responder's policy does not allow any part of the traffic + covered by TSi/TSr, it responds with TS_UNACCEPTABLE. + + o If the responder's policy allows the entire set of traffic covered + by TSi/TSr, no narrowing is necessary, and the responder can + + + +Kaufman, et al. Expires August 27, 2006 [Page 36] + +Internet-Draft IKEv2bis February 2006 + + + return the same TSi/TSr values. + + o Otherwise, narrowing is needed. If the responder's policy allows + all traffic covered by TSi[1]/TSr[1] (the first traffic selectors + in TSi/TSr) but not entire TSi/TSr, the responder narrows to an + acceptable subset of TSi/TSr that includes TSi[1]/TSr[1]. + + o If the responder's policy does not allow all traffic covered by + TSi[1]/TSr[1], but does allow some parts of TSi/TSr, it narrows to + an acceptable subset of TSi/TSr. + + In the last two cases, there may be several subsets that are + acceptable (but their union is not); in this case, the responder + arbitrarily chooses one of them, and includes ADDITIONAL_TS_POSSIBLE + notification in the response. + +2.9.1. Traffic Selectors Violating Own Policy + + {{ Clarif-4.12 }} + + When creating a new SA, the initiator needs to avoid proposing + traffic selectors that violate its own policy. If this rule is not + followed, valid traffic may be dropped. + + This is best illustrated by an example. Suppose that host A has a + policy whose effect is that traffic to 192.0.1.66 is sent via host B + encrypted using AES, and traffic to all other hosts in 192.0.1.0/24 + is also sent via B, but must use 3DES. Suppose also that host B + accepts any combination of AES and 3DES. + + If host A now proposes an SA that uses 3DES, and includes TSr + containing (192.0.1.0-192.0.1.0.255), this will be accepted by host + B. Now, host B can also use this SA to send traffic from 192.0.1.66, + but those packets will be dropped by A since it requires the use of + AES for those traffic. Even if host A creates a new SA only for + 192.0.1.66 that uses AES, host B may freely continue to use the first + SA for the traffic. In this situation, when proposing the SA, host A + should have followed its own policy, and included a TSr containing + ((192.0.1.0-192.0.1.65),(192.0.1.67-192.0.1.255)) instead. + + In general, if (1) the initiator makes a proposal "for traffic X + (TSi/TSr), do SA", and (2) for some subset X' of X, the initiator + does not actually accept traffic X' with SA, and (3) the initiator + would be willing to accept traffic X' with some SA' (!=SA), valid + traffic can be unnecessarily dropped since the responder can apply + either SA or SA' to traffic X'. + + + + + +Kaufman, et al. Expires August 27, 2006 [Page 37] + +Internet-Draft IKEv2bis February 2006 + + +2.10. Nonces + + The IKE_SA_INIT messages each contain a nonce. These nonces are used + as inputs to cryptographic functions. The CREATE_CHILD_SA request + and the CREATE_CHILD_SA response also contain nonces. These nonces + are used to add freshness to the key derivation technique used to + obtain keys for CHILD_SA, and to ensure creation of strong pseudo- + random bits from the Diffie-Hellman key. Nonces used in IKEv2 MUST + be randomly chosen, MUST be at least 128 bits in size, and MUST be at + least half the key size of the negotiated prf. ("prf" refers to + "pseudo-random function", one of the cryptographic algorithms + negotiated in the IKE exchange.) {{ Clarif-7.4 }} However, the + initiator chooses the nonce before the outcome of the negotiation is + known. Because of that, the nonce has to be long enough for all the + PRFs being proposed. If the same random number source is used for + both keys and nonces, care must be taken to ensure that the latter + use does not compromise the former. + +2.11. Address and Port Agility + + IKE runs over UDP ports 500 and 4500, and implicitly sets up ESP and + AH associations for the same IP addresses it runs over. The IP + addresses and ports in the outer header are, however, not themselves + cryptographically protected, and IKE is designed to work even through + Network Address Translation (NAT) boxes. An implementation MUST + accept incoming requests even if the source port is not 500 or 4500, + and MUST respond to the address and port from which the request was + received. It MUST specify the address and port at which the request + was received as the source address and port in the response. IKE + functions identically over IPv4 or IPv6. + +2.12. Reuse of Diffie-Hellman Exponentials + + IKE generates keying material using an ephemeral Diffie-Hellman + exchange in order to gain the property of "perfect forward secrecy". + This means that once a connection is closed and its corresponding + keys are forgotten, even someone who has recorded all of the data + from the connection and gets access to all of the long-term keys of + the two endpoints cannot reconstruct the keys used to protect the + conversation without doing a brute force search of the session key + space. + + Achieving perfect forward secrecy requires that when a connection is + closed, each endpoint MUST forget not only the keys used by the + connection but also any information that could be used to recompute + those keys. In particular, it MUST forget the secrets used in the + Diffie-Hellman calculation and any state that may persist in the + state of a pseudo-random number generator that could be used to + + + +Kaufman, et al. Expires August 27, 2006 [Page 38] + +Internet-Draft IKEv2bis February 2006 + + + recompute the Diffie-Hellman secrets. + + Since the computing of Diffie-Hellman exponentials is computationally + expensive, an endpoint may find it advantageous to reuse those + exponentials for multiple connection setups. There are several + reasonable strategies for doing this. An endpoint could choose a new + exponential only periodically though this could result in less-than- + perfect forward secrecy if some connection lasts for less than the + lifetime of the exponential. Or it could keep track of which + exponential was used for each connection and delete the information + associated with the exponential only when some corresponding + connection was closed. This would allow the exponential to be reused + without losing perfect forward secrecy at the cost of maintaining + more state. + + Decisions as to whether and when to reuse Diffie-Hellman exponentials + is a private decision in the sense that it will not affect + interoperability. An implementation that reuses exponentials MAY + choose to remember the exponential used by the other endpoint on past + exchanges and if one is reused to avoid the second half of the + calculation. + +2.13. Generating Keying Material + + In the context of the IKE_SA, four cryptographic algorithms are + negotiated: an encryption algorithm, an integrity protection + algorithm, a Diffie-Hellman group, and a pseudo-random function + (prf). The pseudo-random function is used for the construction of + keying material for all of the cryptographic algorithms used in both + the IKE_SA and the CHILD_SAs. + + We assume that each encryption algorithm and integrity protection + algorithm uses a fixed-size key and that any randomly chosen value of + that fixed size can serve as an appropriate key. For algorithms that + accept a variable length key, a fixed key size MUST be specified as + part of the cryptographic transform negotiated. For algorithms for + which not all values are valid keys (such as DES or 3DES with key + parity), the algorithm by which keys are derived from arbitrary + values MUST be specified by the cryptographic transform. For + integrity protection functions based on Hashed Message Authentication + Code (HMAC), the fixed key size is the size of the output of the + underlying hash function. When the prf function takes a variable + length key, variable length data, and produces a fixed-length output + (e.g., when using HMAC), the formulas in this document apply. When + the key for the prf function has fixed length, the data provided as a + key is truncated or padded with zeros as necessary unless exceptional + processing is explained following the formula. + + + + +Kaufman, et al. Expires August 27, 2006 [Page 39] + +Internet-Draft IKEv2bis February 2006 + + + Keying material will always be derived as the output of the + negotiated prf algorithm. Since the amount of keying material needed + may be greater than the size of the output of the prf algorithm, we + will use the prf iteratively. We will use the terminology prf+ to + describe the function that outputs a pseudo-random stream based on + the inputs to a prf as follows: (where | indicates concatenation) + + prf+ (K,S) = T1 | T2 | T3 | T4 | ... + + where: + T1 = prf (K, S | 0x01) + T2 = prf (K, T1 | S | 0x02) + T3 = prf (K, T2 | S | 0x03) + T4 = prf (K, T3 | S | 0x04) + + continuing as needed to compute all required keys. The keys are + taken from the output string without regard to boundaries (e.g., if + the required keys are a 256-bit Advanced Encryption Standard (AES) + key and a 160-bit HMAC key, and the prf function generates 160 bits, + the AES key will come from T1 and the beginning of T2, while the HMAC + key will come from the rest of T2 and the beginning of T3). + + The constant concatenated to the end of each string feeding the prf + is a single octet. prf+ in this document is not defined beyond 255 + times the size of the prf output. + +2.14. Generating Keying Material for the IKE_SA + + The shared keys are computed as follows. A quantity called SKEYSEED + is calculated from the nonces exchanged during the IKE_SA_INIT + exchange and the Diffie-Hellman shared secret established during that + exchange. SKEYSEED is used to calculate seven other secrets: SK_d + used for deriving new keys for the CHILD_SAs established with this + IKE_SA; SK_ai and SK_ar used as a key to the integrity protection + algorithm for authenticating the component messages of subsequent + exchanges; SK_ei and SK_er used for encrypting (and of course + decrypting) all subsequent exchanges; and SK_pi and SK_pr, which are + used when generating an AUTH payload. + + SKEYSEED and its derivatives are computed as follows: + + SKEYSEED = prf(Ni | Nr, g^ir) + + {SK_d | SK_ai | SK_ar | SK_ei | SK_er | SK_pi | SK_pr } + = prf+ (SKEYSEED, Ni | Nr | SPIi | SPIr ) + + (indicating that the quantities SK_d, SK_ai, SK_ar, SK_ei, SK_er, + SK_pi, and SK_pr are taken in order from the generated bits of the + + + +Kaufman, et al. Expires August 27, 2006 [Page 40] + +Internet-Draft IKEv2bis February 2006 + + + prf+). g^ir is the shared secret from the ephemeral Diffie-Hellman + exchange. g^ir is represented as a string of octets in big endian + order padded with zeros if necessary to make it the length of the + modulus. Ni and Nr are the nonces, stripped of any headers. If the + negotiated prf takes a fixed-length key and the lengths of Ni and Nr + do not add up to that length, half the bits must come from Ni and + half from Nr, taking the first bits of each. + + The two directions of traffic flow use different keys. The keys used + to protect messages from the original initiator are SK_ai and SK_ei. + The keys used to protect messages in the other direction are SK_ar + and SK_er. Each algorithm takes a fixed number of bits of keying + material, which is specified as part of the algorithm. For integrity + algorithms based on a keyed hash, the key size is always equal to the + length of the output of the underlying hash function. + +2.15. Authentication of the IKE_SA + + When not using extensible authentication (see Section 2.16), the + peers are authenticated by having each sign (or MAC using a shared + secret as the key) a block of data. For the responder, the octets to + be signed start with the first octet of the first SPI in the header + of the second message and end with the last octet of the last payload + in the second message. Appended to this (for purposes of computing + the signature) are the initiator's nonce Ni (just the value, not the + payload containing it), and the value prf(SK_pr,IDr') where IDr' is + the responder's ID payload excluding the fixed header. Note that + neither the nonce Ni nor the value prf(SK_pr,IDr') are transmitted. + Similarly, the initiator signs the first message, starting with the + first octet of the first SPI in the header and ending with the last + octet of the last payload. Appended to this (for purposes of + computing the signature) are the responder's nonce Nr, and the value + prf(SK_pi,IDi'). In the above calculation, IDi' and IDr' are the + entire ID payloads excluding the fixed header. It is critical to the + security of the exchange that each side sign the other side's nonce. + + {{ Clarif-3.1 }} + + The initiator's signed octets can be described as: + + InitiatorSignedOctets = RealMessage1 | NonceRData | MACedIDForI + GenIKEHDR = [ four octets 0 if using port 4500 ] | RealIKEHDR + RealIKEHDR = SPIi | SPIr | . . . | Length + RealMessage1 = RealIKEHDR | RestOfMessage1 + NonceRPayload = PayloadHeader | NonceRData + InitiatorIDPayload = PayloadHeader | RestOfIDPayload + RestOfInitIDPayload = IDType | RESERVED | InitIDData + MACedIDForI = prf(SK_pi, RestOfInitIDPayload) + + + +Kaufman, et al. Expires August 27, 2006 [Page 41] + +Internet-Draft IKEv2bis February 2006 + + + The responder's signed octets can be described as: + + ResponderSignedOctets = RealMessage2 | NonceIData | MACedIDForR + GenIKEHDR = [ four octets 0 if using port 4500 ] | RealIKEHDR + RealIKEHDR = SPIi | SPIr | . . . | Length + RealMessage2 = RealIKEHDR | RestOfMessage2 + NonceIPayload = PayloadHeader | NonceIData + ResponderIDPayload = PayloadHeader | RestOfIDPayload + RestOfRespIDPayload = IDType | RESERVED | InitIDData + MACedIDForR = prf(SK_pr, RestOfRespIDPayload) + + Note that all of the payloads are included under the signature, + including any payload types not defined in this document. If the + first message of the exchange is sent twice (the second time with a + responder cookie and/or a different Diffie-Hellman group), it is the + second version of the message that is signed. + + Optionally, messages 3 and 4 MAY include a certificate, or + certificate chain providing evidence that the key used to compute a + digital signature belongs to the name in the ID payload. The + signature or MAC will be computed using algorithms dictated by the + type of key used by the signer, and specified by the Auth Method + field in the Authentication payload. There is no requirement that + the initiator and responder sign with the same cryptographic + algorithms. The choice of cryptographic algorithms depends on the + type of key each has. In particular, the initiator may be using a + shared key while the responder may have a public signature key and + certificate. It will commonly be the case (but it is not required) + that if a shared secret is used for authentication that the same key + is used in both directions. Note that it is a common but typically + insecure practice to have a shared key derived solely from a user- + chosen password without incorporating another source of randomness. + + This is typically insecure because user-chosen passwords are unlikely + to have sufficient unpredictability to resist dictionary attacks and + these attacks are not prevented in this authentication method. + (Applications using password-based authentication for bootstrapping + and IKE_SA should use the authentication method in Section 2.16, + which is designed to prevent off-line dictionary attacks.) {{ Demoted + the SHOULD }} The pre-shared key needs to contain as much + unpredictability as the strongest key being negotiated. In the case + of a pre-shared key, the AUTH value is computed as: + + AUTH = prf(prf(Shared Secret,"Key Pad for IKEv2"), <msg octets>) + + where the string "Key Pad for IKEv2" is 17 ASCII characters without + null termination. The shared secret can be variable length. The pad + string is added so that if the shared secret is derived from a + + + +Kaufman, et al. Expires August 27, 2006 [Page 42] + +Internet-Draft IKEv2bis February 2006 + + + password, the IKE implementation need not store the password in + cleartext, but rather can store the value prf(Shared Secret,"Key Pad + for IKEv2"), which could not be used as a password equivalent for + protocols other than IKEv2. As noted above, deriving the shared + secret from a password is not secure. This construction is used + because it is anticipated that people will do it anyway. The + management interface by which the Shared Secret is provided MUST + accept ASCII strings of at least 64 octets and MUST NOT add a null + terminator before using them as shared secrets. It MUST also accept + a hex encoding of the Shared Secret. The management interface MAY + accept other encodings if the algorithm for translating the encoding + to a binary string is specified. + + {{ Clarif-3.7 }} If the negotiated prf takes a fixed-size key, the + shared secret MUST be of that fixed size. This requirement means + that it is difficult to use these PRFs with shared key authentication + because it limits the shared secrets that can be used. Thus, PRFs + that require a fixed-size key SHOULD NOT be used with shared key + authentication. For example, PRF_AES128_CBC [PRFAES128CBC] + originally used fixed key sizes; that RFC has been updated to handle + variable key sizes in [PRFAES128CBC-bis]. Note that Section 2.13 + also contains text that is related to PRFs with fixed key size. + However, the text in that section applies only to the prf+ + construction. + +2.16. Extensible Authentication Protocol Methods + + In addition to authentication using public key signatures and shared + secrets, IKE supports authentication using methods defined in RFC + 3748 [EAP]. Typically, these methods are asymmetric (designed for a + user authenticating to a server), and they may not be mutual. {{ In + the next sentence, changed "public key signature based" to "strong" + }} For this reason, these protocols are typically used to + authenticate the initiator to the responder and MUST be used in + conjunction with a strong authentication of the responder to the + initiator. These methods are often associated with mechanisms + referred to as "Legacy Authentication" mechanisms. + + While this memo references [EAP] with the intent that new methods can + be added in the future without updating this specification, some + simpler variations are documented here and in Section 3.16. [EAP] + defines an authentication protocol requiring a variable number of + messages. Extensible Authentication is implemented in IKE as + additional IKE_AUTH exchanges that MUST be completed in order to + initialize the IKE_SA. + + An initiator indicates a desire to use extensible authentication by + leaving out the AUTH payload from message 3. By including an IDi + + + +Kaufman, et al. Expires August 27, 2006 [Page 43] + +Internet-Draft IKEv2bis February 2006 + + + payload but not an AUTH payload, the initiator has declared an + identity but has not proven it. If the responder is willing to use + an extensible authentication method, it will place an Extensible + Authentication Protocol (EAP) payload in message 4 and defer sending + SAr2, TSi, and TSr until initiator authentication is complete in a + subsequent IKE_AUTH exchange. In the case of a minimal extensible + authentication, the initial SA establishment will appear as follows: + + Initiator Responder + ------------------------------------------------------------------- + HDR, SAi1, KEi, Ni --> + <-- HDR, SAr1, KEr, Nr, [CERTREQ] + HDR, SK {IDi, [CERTREQ,] + [IDr,] SAi2, + TSi, TSr} --> + <-- HDR, SK {IDr, [CERT,] AUTH, + EAP } + HDR, SK {EAP} --> + <-- HDR, SK {EAP (success)} + HDR, SK {AUTH} --> + <-- HDR, SK {AUTH, SAr2, TSi, TSr } + + {{ Clarif-3.10 }} As described in Section 2.2, when EAP is used, each + pair of IKE_SA initial setup messages will have their message numbers + incremented; the first pair of AUTH messages will have an ID of 1, + the second will be 2, and so on. + + For EAP methods that create a shared key as a side effect of + authentication, that shared key MUST be used by both the initiator + and responder to generate AUTH payloads in messages 7 and 8 using the + syntax for shared secrets specified in Section 2.15. The shared key + from EAP is the field from the EAP specification named MSK. The + shared key generated during an IKE exchange MUST NOT be used for any + other purpose. + + EAP methods that do not establish a shared key SHOULD NOT be used, as + they are subject to a number of man-in-the-middle attacks [EAPMITM] + if these EAP methods are used in other protocols that do not use a + server-authenticated tunnel. Please see the Security Considerations + section for more details. If EAP methods that do not generate a + shared key are used, the AUTH payloads in messages 7 and 8 MUST be + generated using SK_pi and SK_pr, respectively. + + {{ Demoted the SHOULD }} The initiator of an IKE_SA using EAP needs + to be capable of extending the initial protocol exchange to at least + ten IKE_AUTH exchanges in the event the responder sends notification + messages and/or retries the authentication prompt. Once the protocol + exchange defined by the chosen EAP authentication method has + + + +Kaufman, et al. Expires August 27, 2006 [Page 44] + +Internet-Draft IKEv2bis February 2006 + + + successfully terminated, the responder MUST send an EAP payload + containing the Success message. Similarly, if the authentication + method has failed, the responder MUST send an EAP payload containing + the Failure message. The responder MAY at any time terminate the IKE + exchange by sending an EAP payload containing the Failure message. + + Following such an extended exchange, the EAP AUTH payloads MUST be + included in the two messages following the one containing the EAP + Success message. + + {{ Clarif-3.5 }} When the initiator authentication uses EAP, it is + possible that the contents of the IDi payload is used only for AAA + routing purposes and selecting which EAP method to use. This value + may be different from the identity authenticated by the EAP method. + It is important that policy lookups and access control decisions use + the actual authenticated identity. Often the EAP server is + implemented in a separate AAA server that communicates with the IKEv2 + responder. In this case, the authenticated identity has to be sent + from the AAA server to the IKEv2 responder. + + {{ Clarif-3.8 }} The information in Section 2.17 about PRFs with + fixed-size keys also applies to EAP authentication. For instance, a + PRF that requires a 128-bit key cannot be used with EAP because + specifies that the MSK is at least 512 bits long. + +2.17. Generating Keying Material for CHILD_SAs + + A single CHILD_SA is created by the IKE_AUTH exchange, and additional + CHILD_SAs can optionally be created in CREATE_CHILD_SA exchanges. + Keying material for them is generated as follows: + + KEYMAT = prf+(SK_d, Ni | Nr) + + Where Ni and Nr are the nonces from the IKE_SA_INIT exchange if this + request is the first CHILD_SA created or the fresh Ni and Nr from the + CREATE_CHILD_SA exchange if this is a subsequent creation. + + For CREATE_CHILD_SA exchanges including an optional Diffie-Hellman + exchange, the keying material is defined as: + + KEYMAT = prf+(SK_d, g^ir (new) | Ni | Nr ) + + where g^ir (new) is the shared secret from the ephemeral Diffie- + Hellman exchange of this CREATE_CHILD_SA exchange (represented as an + octet string in big endian order padded with zeros in the high-order + bits if necessary to make it the length of the modulus). + + A single CHILD_SA negotiation may result in multiple security + + + +Kaufman, et al. Expires August 27, 2006 [Page 45] + +Internet-Draft IKEv2bis February 2006 + + + associations. ESP and AH SAs exist in pairs (one in each direction), + and four SAs could be created in a single CHILD_SA negotiation if a + combination of ESP and AH is being negotiated. + + Keying material MUST be taken from the expanded KEYMAT in the + following order: + + o All keys for SAs carrying data from the initiator to the responder + are taken before SAs going in the reverse direction. + + o If multiple IPsec protocols are negotiated, keying material is + taken in the order in which the protocol headers will appear in + the encapsulated packet. + + o If a single protocol has both encryption and authentication keys, + the encryption key is taken from the first octets of KEYMAT and + the authentication key is taken from the next octets. + + Each cryptographic algorithm takes a fixed number of bits of keying + material specified as part of the algorithm. + +2.18. Rekeying IKE_SAs Using a CREATE_CHILD_SA Exchange + + The CREATE_CHILD_SA exchange can be used to rekey an existing IKE_SA + (see Section 2.8). {{ Clarif-5.3 }} New initiator and responder SPIs + are supplied in the SPI fields in the Proposal structures inside the + Security Association (SA) payloads (not the SPI fields in the IKE + header). The TS payloads are omitted when rekeying an IKE_SA. + SKEYSEED for the new IKE_SA is computed using SK_d from the existing + IKE_SA as follows: + + SKEYSEED = prf(SK_d (old), [g^ir (new)] | Ni | Nr) + + where g^ir (new) is the shared secret from the ephemeral Diffie- + Hellman exchange of this CREATE_CHILD_SA exchange (represented as an + octet string in big endian order padded with zeros if necessary to + make it the length of the modulus) and Ni and Nr are the two nonces + stripped of any headers. + + {{ Clarif-5.5 }} The old and new IKE_SA may have selected a different + PRF. Because the rekeying exchange belongs to the old IKE_SA, it is + the old IKE_SA's PRF that is used. Note that this may not work if + the new IKE_SA's PRF has a fixed key size because the output of the + PRF may not be of the correct size. + + The new IKE_SA MUST reset its message counters to 0. + + SK_d, SK_ai, SK_ar, SK_ei, and SK_er are computed from SKEYSEED as + + + +Kaufman, et al. Expires August 27, 2006 [Page 46] + +Internet-Draft IKEv2bis February 2006 + + + specified in Section 2.14. + +2.19. Requesting an Internal Address on a Remote Network + + Most commonly occurring in the endpoint-to-security-gateway scenario, + an endpoint may need an IP address in the network protected by the + security gateway and may need to have that address dynamically + assigned. A request for such a temporary address can be included in + any request to create a CHILD_SA (including the implicit request in + message 3) by including a CP payload. + + This function provides address allocation to an IPsec Remote Access + Client (IRAC) trying to tunnel into a network protected by an IPsec + Remote Access Server (IRAS). Since the IKE_AUTH exchange creates an + IKE_SA and a CHILD_SA, the IRAC MUST request the IRAS-controlled + address (and optionally other information concerning the protected + network) in the IKE_AUTH exchange. The IRAS may procure an address + for the IRAC from any number of sources such as a DHCP/BOOTP server + or its own address pool. + + Initiator Responder + ------------------------------------------------------------------- + HDR, SK {IDi, [CERT,] + [CERTREQ,] [IDr,] AUTH, + CP(CFG_REQUEST), SAi2, + TSi, TSr} --> + <-- HDR, SK {IDr, [CERT,] AUTH, + CP(CFG_REPLY), SAr2, + TSi, TSr} + + In all cases, the CP payload MUST be inserted before the SA payload. + In variations of the protocol where there are multiple IKE_AUTH + exchanges, the CP payloads MUST be inserted in the messages + containing the SA payloads. + + CP(CFG_REQUEST) MUST contain at least an INTERNAL_ADDRESS attribute + (either IPv4 or IPv6) but MAY contain any number of additional + attributes the initiator wants returned in the response. + + For example, message from initiator to responder: + + CP(CFG_REQUEST)= + INTERNAL_ADDRESS() + TSi = (0, 0-65535,0.0.0.0-255.255.255.255) + TSr = (0, 0-65535,0.0.0.0-255.255.255.255) + + NOTE: Traffic Selectors contain (protocol, port range, address + range). + + + +Kaufman, et al. Expires August 27, 2006 [Page 47] + +Internet-Draft IKEv2bis February 2006 + + + Message from responder to initiator: + + CP(CFG_REPLY)= + INTERNAL_ADDRESS(192.0.2.202) + INTERNAL_NETMASK(255.255.255.0) + INTERNAL_SUBNET(192.0.2.0/255.255.255.0) + TSi = (0, 0-65535,192.0.2.202-192.0.2.202) + TSr = (0, 0-65535,192.0.2.0-192.0.2.255) + + All returned values will be implementation dependent. As can be seen + in the above example, the IRAS MAY also send other attributes that + were not included in CP(CFG_REQUEST) and MAY ignore the non- + mandatory attributes that it does not support. + + The responder MUST NOT send a CFG_REPLY without having first received + a CP(CFG_REQUEST) from the initiator, because we do not want the IRAS + to perform an unnecessary configuration lookup if the IRAC cannot + process the REPLY. In the case where the IRAS's configuration + requires that CP be used for a given identity IDi, but IRAC has + failed to send a CP(CFG_REQUEST), IRAS MUST fail the request, and + terminate the IKE exchange with a FAILED_CP_REQUIRED error. + +2.20. Requesting the Peer's Version + + An IKE peer wishing to inquire about the other peer's IKE software + version information MAY use the method below. This is an example of + a configuration request within an INFORMATIONAL exchange, after the + IKE_SA and first CHILD_SA have been created. + + An IKE implementation MAY decline to give out version information + prior to authentication or even after authentication to prevent + trolling in case some implementation is known to have some security + weakness. In that case, it MUST either return an empty string or no + CP payload if CP is not supported. + + Initiator Responder + ------------------------------------------------------------------- + HDR, SK{CP(CFG_REQUEST)} --> + <-- HDR, SK{CP(CFG_REPLY)} + + CP(CFG_REQUEST)= + APPLICATION_VERSION("") + + CP(CFG_REPLY) APPLICATION_VERSION("foobar v1.3beta, (c) Foo Bar + Inc.") + + + + + + +Kaufman, et al. Expires August 27, 2006 [Page 48] + +Internet-Draft IKEv2bis February 2006 + + +2.21. Error Handling + + There are many kinds of errors that can occur during IKE processing. + If a request is received that is badly formatted or unacceptable for + reasons of policy (e.g., no matching cryptographic algorithms), the + response MUST contain a Notify payload indicating the error. If an + error occurs outside the context of an IKE request (e.g., the node is + getting ESP messages on a nonexistent SPI), the node SHOULD initiate + an INFORMATIONAL exchange with a Notify payload describing the + problem. + + Errors that occur before a cryptographically protected IKE_SA is + established must be handled very carefully. There is a trade-off + between wanting to be helpful in diagnosing a problem and responding + to it and wanting to avoid being a dupe in a denial of service attack + based on forged messages. + + If a node receives a message on UDP port 500 or 4500 outside the + context of an IKE_SA known to it (and not a request to start one), it + may be the result of a recent crash of the node. If the message is + marked as a response, the node MAY audit the suspicious event but + MUST NOT respond. If the message is marked as a request, the node + MAY audit the suspicious event and MAY send a response. If a + response is sent, the response MUST be sent to the IP address and + port from whence it came with the same IKE SPIs and the Message ID + copied. The response MUST NOT be cryptographically protected and + MUST contain a Notify payload indicating INVALID_IKE_SPI. + + A node receiving such an unprotected Notify payload MUST NOT respond + and MUST NOT change the state of any existing SAs. The message might + be a forgery or might be a response the genuine correspondent was + tricked into sending. {{ Demoted two SHOULDs }} A node should treat + such a message (and also a network message like ICMP destination + unreachable) as a hint that there might be problems with SAs to that + IP address and should initiate a liveness test for any such IKE_SA. + An implementation SHOULD limit the frequency of such tests to avoid + being tricked into participating in a denial of service attack. + + A node receiving a suspicious message from an IP address with which + it has an IKE_SA MAY send an IKE Notify payload in an IKE + INFORMATIONAL exchange over that SA. {{ Demoted the SHOULD }} The + recipient MUST NOT change the state of any SAs as a result, but may + wish to audit the event to aid in diagnosing malfunctions. A node + MUST limit the rate at which it will send messages in response to + unprotected messages. + + + + + + +Kaufman, et al. Expires August 27, 2006 [Page 49] + +Internet-Draft IKEv2bis February 2006 + + +2.22. IPComp + + Use of IP compression [IPCOMP] can be negotiated as part of the setup + of a CHILD_SA. While IP compression involves an extra header in each + packet and a compression parameter index (CPI), the virtual + "compression association" has no life outside the ESP or AH SA that + contains it. Compression associations disappear when the + corresponding ESP or AH SA goes away. It is not explicitly mentioned + in any DELETE payload. + + Negotiation of IP compression is separate from the negotiation of + cryptographic parameters associated with a CHILD_SA. A node + requesting a CHILD_SA MAY advertise its support for one or more + compression algorithms through one or more Notify payloads of type + IPCOMP_SUPPORTED. The response MAY indicate acceptance of a single + compression algorithm with a Notify payload of type IPCOMP_SUPPORTED. + These payloads MUST NOT occur in messages that do not contain SA + payloads. + + Although there has been discussion of allowing multiple compression + algorithms to be accepted and to have different compression + algorithms available for the two directions of a CHILD_SA, + implementations of this specification MUST NOT accept an IPComp + algorithm that was not proposed, MUST NOT accept more than one, and + MUST NOT compress using an algorithm other than one proposed and + accepted in the setup of the CHILD_SA. + + A side effect of separating the negotiation of IPComp from + cryptographic parameters is that it is not possible to propose + multiple cryptographic suites and propose IP compression with some of + them but not others. + +2.23. NAT Traversal + + Network Address Translation (NAT) gateways are a controversial + subject. This section briefly describes what they are and how they + are likely to act on IKE traffic. Many people believe that NATs are + evil and that we should not design our protocols so as to make them + work better. IKEv2 does specify some unintuitive processing rules in + order that NATs are more likely to work. + + NATs exist primarily because of the shortage of IPv4 addresses, + though there are other rationales. IP nodes that are "behind" a NAT + have IP addresses that are not globally unique, but rather are + assigned from some space that is unique within the network behind the + NAT but that are likely to be reused by nodes behind other NATs. + Generally, nodes behind NATs can communicate with other nodes behind + the same NAT and with nodes with globally unique addresses, but not + + + +Kaufman, et al. Expires August 27, 2006 [Page 50] + +Internet-Draft IKEv2bis February 2006 + + + with nodes behind other NATs. There are exceptions to that rule. + When those nodes make connections to nodes on the real Internet, the + NAT gateway "translates" the IP source address to an address that + will be routed back to the gateway. Messages to the gateway from the + Internet have their destination addresses "translated" to the + internal address that will route the packet to the correct endnode. + + NATs are designed to be "transparent" to endnodes. Neither software + on the node behind the NAT nor the node on the Internet requires + modification to communicate through the NAT. Achieving this + transparency is more difficult with some protocols than with others. + Protocols that include IP addresses of the endpoints within the + payloads of the packet will fail unless the NAT gateway understands + the protocol and modifies the internal references as well as those in + the headers. Such knowledge is inherently unreliable, is a network + layer violation, and often results in subtle problems. + + Opening an IPsec connection through a NAT introduces special + problems. If the connection runs in transport mode, changing the IP + addresses on packets will cause the checksums to fail and the NAT + cannot correct the checksums because they are cryptographically + protected. Even in tunnel mode, there are routing problems because + transparently translating the addresses of AH and ESP packets + requires special logic in the NAT and that logic is heuristic and + unreliable in nature. For that reason, IKEv2 can negotiate UDP + encapsulation of IKE and ESP packets. This encoding is slightly less + efficient but is easier for NATs to process. In addition, firewalls + may be configured to pass IPsec traffic over UDP but not ESP/AH or + vice versa. + + It is a common practice of NATs to translate TCP and UDP port numbers + as well as addresses and use the port numbers of inbound packets to + decide which internal node should get a given packet. For this + reason, even though IKE packets MUST be sent from and to UDP port + 500, they MUST be accepted coming from any port and responses MUST be + sent to the port from whence they came. This is because the ports + may be modified as the packets pass through NATs. Similarly, IP + addresses of the IKE endpoints are generally not included in the IKE + payloads because the payloads are cryptographically protected and + could not be transparently modified by NATs. + + Port 4500 is reserved for UDP-encapsulated ESP and IKE. When working + through a NAT, it is generally better to pass IKE packets over port + 4500 because some older NATs handle IKE traffic on port 500 cleverly + in an attempt to transparently establish IPsec connections between + endpoints that don't handle NAT traversal themselves. Such NATs may + interfere with the straightforward NAT traversal envisioned by this + document. {{ Clarif-7.6 }} An IPsec endpoint that discovers a NAT + + + +Kaufman, et al. Expires August 27, 2006 [Page 51] + +Internet-Draft IKEv2bis February 2006 + + + between it and its correspondent MUST send all subsequent traffic + from port 4500, which NATs should not treat specially (as they might + with port 500). + + The specific requirements for supporting NAT traversal [NATREQ] are + listed below. Support for NAT traversal is optional. In this + section only, requirements listed as MUST apply only to + implementations supporting NAT traversal. + + o IKE MUST listen on port 4500 as well as port 500. IKE MUST + respond to the IP address and port from which packets arrived. + + o Both IKE initiator and responder MUST include in their IKE_SA_INIT + packets Notify payloads of type NAT_DETECTION_SOURCE_IP and + NAT_DETECTION_DESTINATION_IP. Those payloads can be used to + detect if there is NAT between the hosts, and which end is behind + the NAT. The location of the payloads in the IKE_SA_INIT packets + are just after the Ni and Nr payloads (before the optional CERTREQ + payload). + + o If none of the NAT_DETECTION_SOURCE_IP payload(s) received matches + the hash of the source IP and port found from the IP header of the + packet containing the payload, it means that the other end is + behind NAT (i.e., someone along the route changed the source + address of the original packet to match the address of the NAT + box). In this case, this end should allow dynamic update of the + other ends IP address, as described later. + + o If the NAT_DETECTION_DESTINATION_IP payload received does not + match the hash of the destination IP and port found from the IP + header of the packet containing the payload, it means that this + end is behind a NAT. In this case, this end SHOULD start sending + keepalive packets as explained in [UDPENCAPS]. + + o The IKE initiator MUST check these payloads if present and if they + do not match the addresses in the outer packet MUST tunnel all + future IKE and ESP packets associated with this IKE_SA over UDP + port 4500. + + o To tunnel IKE packets over UDP port 4500, the IKE header has four + octets of zero prepended and the result immediately follows the + UDP header. To tunnel ESP packets over UDP port 4500, the ESP + header immediately follows the UDP header. Since the first four + bytes of the ESP header contain the SPI, and the SPI cannot + validly be zero, it is always possible to distinguish ESP and IKE + messages. + + + + + +Kaufman, et al. Expires August 27, 2006 [Page 52] + +Internet-Draft IKEv2bis February 2006 + + + o The original source and destination IP address required for the + transport mode TCP and UDP packet checksum fixup (see [UDPENCAPS]) + are obtained from the Traffic Selectors associated with the + exchange. In the case of NAT traversal, the Traffic Selectors + MUST contain exactly one IP address, which is then used as the + original IP address. + + o There are cases where a NAT box decides to remove mappings that + are still alive (for example, the keepalive interval is too long, + or the NAT box is rebooted). To recover in these cases, hosts + that are not behind a NAT SHOULD send all packets (including + retransmission packets) to the IP address and port from the last + valid authenticated packet from the other end (i.e., dynamically + update the address). A host behind a NAT SHOULD NOT do this + because it opens a DoS attack possibility. Any authenticated IKE + packet or any authenticated UDP-encapsulated ESP packet can be + used to detect that the IP address or the port has changed. + + Note that similar but probably not identical actions will likely be + needed to make IKE work with Mobile IP, but such processing is not + addressed by this document. + +2.24. Explicit Congestion Notification (ECN) + + When IPsec tunnels behave as originally specified in [IPSECARCH-OLD], + ECN usage is not appropriate for the outer IP headers because tunnel + decapsulation processing discards ECN congestion indications to the + detriment of the network. ECN support for IPsec tunnels for IKEv1- + based IPsec requires multiple operating modes and negotiation (see + [ECN]). IKEv2 simplifies this situation by requiring that ECN be + usable in the outer IP headers of all tunnel-mode IPsec SAs created + by IKEv2. Specifically, tunnel encapsulators and decapsulators for + all tunnel-mode SAs created by IKEv2 MUST support the ECN full- + functionality option for tunnels specified in [ECN] and MUST + implement the tunnel encapsulation and decapsulation processing + specified in [IPSECARCH] to prevent discarding of ECN congestion + indications. + + +3. Header and Payload Formats + +3.1. The IKE Header + + IKE messages use UDP ports 500 and/or 4500, with one IKE message per + UDP datagram. Information from the beginning of the packet through + the UDP header is largely ignored except that the IP addresses and + UDP ports from the headers are reversed and used for return packets. + When sent on UDP port 500, IKE messages begin immediately following + + + +Kaufman, et al. Expires August 27, 2006 [Page 53] + +Internet-Draft IKEv2bis February 2006 + + + the UDP header. When sent on UDP port 4500, IKE messages have + prepended four octets of zero. These four octets of zero are not + part of the IKE message and are not included in any of the length + fields or checksums defined by IKE. Each IKE message begins with the + IKE header, denoted HDR in this memo. Following the header are one + or more IKE payloads each identified by a "Next Payload" field in the + preceding payload. Payloads are processed in the order in which they + appear in an IKE message by invoking the appropriate processing + routine according to the "Next Payload" field in the IKE header and + subsequently according to the "Next Payload" field in the IKE payload + itself until a "Next Payload" field of zero indicates that no + payloads follow. If a payload of type "Encrypted" is found, that + payload is decrypted and its contents parsed as additional payloads. + An Encrypted payload MUST be the last payload in a packet and an + Encrypted payload MUST NOT contain another Encrypted payload. + + The Recipient SPI in the header identifies an instance of an IKE + security association. It is therefore possible for a single instance + of IKE to multiplex distinct sessions with multiple peers. + + All multi-octet fields representing integers are laid out in big + endian order (aka most significant byte first, or network byte + order). + + The format of the IKE header is shown in Figure 4. + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! IKE_SA Initiator's SPI ! + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! IKE_SA Responder's SPI ! + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload ! MjVer ! MnVer ! Exchange Type ! Flags ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Message ID ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 4: IKE Header Format + + o Initiator's SPI (8 octets) - A value chosen by the initiator to + identify a unique IKE security association. This value MUST NOT + be zero. + + + + +Kaufman, et al. Expires August 27, 2006 [Page 54] + +Internet-Draft IKEv2bis February 2006 + + + o Responder's SPI (8 octets) - A value chosen by the responder to + identify a unique IKE security association. This value MUST be + zero in the first message of an IKE Initial Exchange (including + repeats of that message including a cookie). {{ The phrase "and + MUST NOT be zero in any other message" was removed; Clarif-2.1 }} + + o Next Payload (1 octet) - Indicates the type of payload that + immediately follows the header. The format and value of each + payload are defined below. + + o Major Version (4 bits) - Indicates the major version of the IKE + protocol in use. Implementations based on this version of IKE + MUST set the Major Version to 2. Implementations based on + previous versions of IKE and ISAKMP MUST set the Major Version to + 1. Implementations based on this version of IKE MUST reject or + ignore messages containing a version number greater than 2. + + o Minor Version (4 bits) - Indicates the minor version of the IKE + protocol in use. Implementations based on this version of IKE + MUST set the Minor Version to 0. They MUST ignore the minor + version number of received messages. + + o Exchange Type (1 octet) - Indicates the type of exchange being + used. This constrains the payloads sent in each message and + orderings of messages in an exchange. + + Exchange Type Value + ---------------------------------- + RESERVED 0-33 + IKE_SA_INIT 34 + IKE_AUTH 35 + CREATE_CHILD_SA 36 + INFORMATIONAL 37 + RESERVED TO IANA 38-239 + Reserved for private use 240-255 + + o Flags (1 octet) - Indicates specific options that are set for the + message. Presence of options are indicated by the appropriate bit + in the flags field being set. The bits are defined LSB first, so + bit 0 would be the least significant bit of the Flags octet. In + the description below, a bit being 'set' means its value is '1', + while 'cleared' means its value is '0'. + + * X(reserved) (bits 0-2) - These bits MUST be cleared when + sending and MUST be ignored on receipt. + + * I(nitiator) (bit 3 of Flags) - This bit MUST be set in messages + sent by the original initiator of the IKE_SA and MUST be + + + +Kaufman, et al. Expires August 27, 2006 [Page 55] + +Internet-Draft IKEv2bis February 2006 + + + cleared in messages sent by the original responder. It is used + by the recipient to determine which eight octets of the SPI + were generated by the recipient. + + * V(ersion) (bit 4 of Flags) - This bit indicates that the + transmitter is capable of speaking a higher major version + number of the protocol than the one indicated in the major + version number field. Implementations of IKEv2 must clear this + bit when sending and MUST ignore it in incoming messages. + + * R(esponse) (bit 5 of Flags) - This bit indicates that this + message is a response to a message containing the same message + ID. This bit MUST be cleared in all request messages and MUST + be set in all responses. An IKE endpoint MUST NOT generate a + response to a message that is marked as being a response. + + * X(reserved) (bits 6-7 of Flags) - These bits MUST be cleared + when sending and MUST be ignored on receipt. + + o Message ID (4 octets) - Message identifier used to control + retransmission of lost packets and matching of requests and + responses. It is essential to the security of the protocol + because it is used to prevent message replay attacks. See + Section 2.1 and Section 2.2. + + o Length (4 octets) - Length of total message (header + payloads) in + octets. + +3.2. Generic Payload Header + + Each IKE payload defined in Section 3.3 through Section 3.16 begins + with a generic payload header, shown in Figure 5. Figures for each + payload below will include the generic payload header, but for + brevity the description of each field will be omitted. + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 5: Generic Payload Header + + The Generic Payload Header fields are defined as follows: + + o Next Payload (1 octet) - Identifier for the payload type of the + next payload in the message. If the current payload is the last + in the message, then this field will be 0. This field provides a + + + +Kaufman, et al. Expires August 27, 2006 [Page 56] + +Internet-Draft IKEv2bis February 2006 + + + "chaining" capability whereby additional payloads can be added to + a message by appending it to the end of the message and setting + the "Next Payload" field of the preceding payload to indicate the + new payload's type. An Encrypted payload, which must always be + the last payload of a message, is an exception. It contains data + structures in the format of additional payloads. In the header of + an Encrypted payload, the Next Payload field is set to the payload + type of the first contained payload (instead of 0). The payload + type values are: + + Next Payload Type Notation Value + -------------------------------------------------- + No Next Payload 0 + RESERVED 1-32 + Security Association SA 33 + Key Exchange KE 34 + Identification - Initiator IDi 35 + Identification - Responder IDr 36 + Certificate CERT 37 + Certificate Request CERTREQ 38 + Authentication AUTH 39 + Nonce Ni, Nr 40 + Notify N 41 + Delete D 42 + Vendor ID V 43 + Traffic Selector - Initiator TSi 44 + Traffic Selector - Responder TSr 45 + Encrypted E 46 + Configuration CP 47 + Extensible Authentication EAP 48 + RESERVED TO IANA 49-127 + PRIVATE USE 128-255 + + (Payload type values 1-32 should not be assigned in the + future so that there is no overlap with the code assignments + for IKEv1.) + + o Critical (1 bit) - MUST be set to zero if the sender wants the + recipient to skip this payload if it does not understand the + payload type code in the Next Payload field of the previous + payload. MUST be set to one if the sender wants the recipient to + reject this entire message if it does not understand the payload + type. MUST be ignored by the recipient if the recipient + understands the payload type code. MUST be set to zero for + payload types defined in this document. Note that the critical + bit applies to the current payload rather than the "next" payload + whose type code appears in the first octet. The reasoning behind + not setting the critical bit for payloads defined in this document + + + +Kaufman, et al. Expires August 27, 2006 [Page 57] + +Internet-Draft IKEv2bis February 2006 + + + is that all implementations MUST understand all payload types + defined in this document and therefore must ignore the Critical + bit's value. Skipped payloads are expected to have valid Next + Payload and Payload Length fields. + + o RESERVED (7 bits) - MUST be sent as zero; MUST be ignored on + receipt. + + o Payload Length (2 octets) - Length in octets of the current + payload, including the generic payload header. + +3.3. Security Association Payload + + The Security Association Payload, denoted SA in this memo, is used to + negotiate attributes of a security association. Assembly of Security + Association Payloads requires great peace of mind. An SA payload MAY + contain multiple proposals. If there is more than one, they MUST be + ordered from most preferred to least preferred. Each proposal may + contain multiple IPsec protocols (where a protocol is IKE, ESP, or + AH), each protocol MAY contain multiple transforms, and each + transform MAY contain multiple attributes. When parsing an SA, an + implementation MUST check that the total Payload Length is consistent + with the payload's internal lengths and counts. Proposals, + Transforms, and Attributes each have their own variable length + encodings. They are nested such that the Payload Length of an SA + includes the combined contents of the SA, Proposal, Transform, and + Attribute information. The length of a Proposal includes the lengths + of all Transforms and Attributes it contains. The length of a + Transform includes the lengths of all Attributes it contains. + + The syntax of Security Associations, Proposals, Transforms, and + Attributes is based on ISAKMP; however the semantics are somewhat + different. The reason for the complexity and the hierarchy is to + allow for multiple possible combinations of algorithms to be encoded + in a single SA. Sometimes there is a choice of multiple algorithms, + whereas other times there is a combination of algorithms. For + example, an initiator might want to propose using (AH w/MD5 and ESP + w/3DES) OR (ESP w/MD5 and 3DES). + + One of the reasons the semantics of the SA payload has changed from + ISAKMP and IKEv1 is to make the encodings more compact in common + cases. + + The Proposal structure contains within it a Proposal # and an IPsec + protocol ID. Each structure MUST have the same Proposal # as the + previous one or be one (1) greater. The first Proposal MUST have a + Proposal # of one (1). If two successive structures have the same + Proposal number, it means that the proposal consists of the first + + + +Kaufman, et al. Expires August 27, 2006 [Page 58] + +Internet-Draft IKEv2bis February 2006 + + + structure AND the second. So a proposal of AH AND ESP would have two + proposal structures, one for AH and one for ESP and both would have + Proposal #1. A proposal of AH OR ESP would have two proposal + structures, one for AH with Proposal #1 and one for ESP with Proposal + #2. + + Each Proposal/Protocol structure is followed by one or more transform + structures. The number of different transforms is generally + determined by the Protocol. AH generally has a single transform: an + integrity check algorithm. ESP generally has two: an encryption + algorithm and an integrity check algorithm. IKE generally has four + transforms: a Diffie-Hellman group, an integrity check algorithm, a + prf algorithm, and an encryption algorithm. If an algorithm that + combines encryption and integrity protection is proposed, it MUST be + proposed as an encryption algorithm and an integrity protection + algorithm MUST NOT be proposed. For each Protocol, the set of + permissible transforms is assigned transform ID numbers, which appear + in the header of each transform. + + If there are multiple transforms with the same Transform Type, the + proposal is an OR of those transforms. If there are multiple + Transforms with different Transform Types, the proposal is an AND of + the different groups. For example, to propose ESP with (3DES or + IDEA) and (HMAC_MD5 or HMAC_SHA), the ESP proposal would contain two + Transform Type 1 candidates (one for 3DES and one for IDEA) and two + Transform Type 2 candidates (one for HMAC_MD5 and one for HMAC_SHA). + This effectively proposes four combinations of algorithms. If the + initiator wanted to propose only a subset of those, for example (3DES + and HMAC_MD5) or (IDEA and HMAC_SHA), there is no way to encode that + as multiple transforms within a single Proposal. Instead, the + initiator would have to construct two different Proposals, each with + two transforms. + + A given transform MAY have one or more Attributes. Attributes are + necessary when the transform can be used in more than one way, as + when an encryption algorithm has a variable key size. The transform + would specify the algorithm and the attribute would specify the key + size. Most transforms do not have attributes. A transform MUST NOT + have multiple attributes of the same type. To propose alternate + values for an attribute (for example, multiple key sizes for the AES + encryption algorithm), and implementation MUST include multiple + Transforms with the same Transform Type each with a single Attribute. + + Note that the semantics of Transforms and Attributes are quite + different from those in IKEv1. In IKEv1, a single Transform carried + multiple algorithms for a protocol with one carried in the Transform + and the others carried in the Attributes. + + + + +Kaufman, et al. Expires August 27, 2006 [Page 59] + +Internet-Draft IKEv2bis February 2006 + + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ <Proposals> ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 6: Security Association Payload + + o Proposals (variable) - One or more proposal substructures. + + The payload type for the Security Association Payload is thirty three + (33). + +3.3.1. Proposal Substructure + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! 0 (last) or 2 ! RESERVED ! Proposal Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Proposal # ! Protocol ID ! SPI Size !# of Transforms! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ~ SPI (variable) ~ + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ <Transforms> ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 7: Proposal Substructure + + o 0 (last) or 2 (more) (1 octet) - Specifies whether this is the + last Proposal Substructure in the SA. This syntax is inherited + from ISAKMP, but is unnecessary because the last Proposal could be + identified from the length of the SA. The value (2) corresponds + to a Payload Type of Proposal in IKEv1, and the first four octets + of the Proposal structure are designed to look somewhat like the + header of a Payload. + + o RESERVED (1 octet) - MUST be sent as zero; MUST be ignored on + receipt. + + o Proposal Length (2 octets) - Length of this proposal, including + all transforms and attributes that follow. + + + +Kaufman, et al. Expires August 27, 2006 [Page 60] + +Internet-Draft IKEv2bis February 2006 + + + o Proposal # (1 octet) - When a proposal is made, the first proposal + in an SA payload MUST be #1, and subsequent proposals MUST either + be the same as the previous proposal (indicating an AND of the two + proposals) or one more than the previous proposal (indicating an + OR of the two proposals). When a proposal is accepted, all of the + proposal numbers in the SA payload MUST be the same and MUST match + the number on the proposal sent that was accepted. + + o Protocol ID (1 octet) - Specifies the IPsec protocol identifier + for the current negotiation. The defined values are: + + Protocol Protocol ID + ----------------------------------- + RESERVED 0 + IKE 1 + AH 2 + ESP 3 + RESERVED TO IANA 4-200 + PRIVATE USE 201-255 + + o SPI Size (1 octet) - For an initial IKE_SA negotiation, this field + MUST be zero; the SPI is obtained from the outer header. During + subsequent negotiations, it is equal to the size, in octets, of + the SPI of the corresponding protocol (8 for IKE, 4 for ESP and + AH). + + o # of Transforms (1 octet) - Specifies the number of transforms in + this proposal. + + o SPI (variable) - The sending entity's SPI. Even if the SPI Size + is not a multiple of 4 octets, there is no padding applied to the + payload. When the SPI Size field is zero, this field is not + present in the Security Association payload. + + o Transforms (variable) - One or more transform substructures. + + + + + + + + + + + + + + + + +Kaufman, et al. Expires August 27, 2006 [Page 61] + +Internet-Draft IKEv2bis February 2006 + + +3.3.2. Transform Substructure + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! 0 (last) or 3 ! RESERVED ! Transform Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + !Transform Type ! RESERVED ! Transform ID ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ Transform Attributes ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 8: Transform Substructure + + o 0 (last) or 3 (more) (1 octet) - Specifies whether this is the + last Transform Substructure in the Proposal. This syntax is + inherited from ISAKMP, but is unnecessary because the last + Proposal could be identified from the length of the SA. The value + (3) corresponds to a Payload Type of Transform in IKEv1, and the + first four octets of the Transform structure are designed to look + somewhat like the header of a Payload. + + o RESERVED - MUST be sent as zero; MUST be ignored on receipt. + + o Transform Length - The length (in octets) of the Transform + Substructure including Header and Attributes. + + o Transform Type (1 octet) - The type of transform being specified + in this transform. Different protocols support different + transform types. For some protocols, some of the transforms may + be optional. If a transform is optional and the initiator wishes + to propose that the transform be omitted, no transform of the + given type is included in the proposal. If the initiator wishes + to make use of the transform optional to the responder, it + includes a transform substructure with transform ID = 0 as one of + the options. + + o Transform ID (2 octets) - The specific instance of the transform + type being proposed. + + The tranform type values are: + + + + + + + + +Kaufman, et al. Expires August 27, 2006 [Page 62] + +Internet-Draft IKEv2bis February 2006 + + + Description Trans. Used In + Type + ------------------------------------------------------------------ + RESERVED 0 + Encryption Algorithm (ENCR) 1 IKE and ESP + Pseudo-random Function (PRF) 2 IKE + Integrity Algorithm (INTEG) 3 IKE, AH, optional in ESP + Diffie-Hellman Group (D-H) 4 IKE, optional in AH & ESP + Extended Sequence Numbers (ESN) 5 AH and ESP + RESERVED TO IANA 6-240 + PRIVATE USE 241-255 + + For Transform Type 1 (Encryption Algorithm), defined Transform IDs + are: + + Name Number Defined In + --------------------------------------------------- + RESERVED 0 + ENCR_DES_IV64 1 (RFC1827) + ENCR_DES 2 (RFC2405), [DES] + ENCR_3DES 3 (RFC2451) + ENCR_RC5 4 (RFC2451) + ENCR_IDEA 5 (RFC2451), [IDEA] + ENCR_CAST 6 (RFC2451) + ENCR_BLOWFISH 7 (RFC2451) + ENCR_3IDEA 8 (RFC2451) + ENCR_DES_IV32 9 + RESERVED 10 + ENCR_NULL 11 (RFC2410) + ENCR_AES_CBC 12 (RFC3602) + ENCR_AES_CTR 13 (RFC3664) + RESERVED TO IANA 14-1023 + PRIVATE USE 1024-65535 + + For Transform Type 2 (Pseudo-random Function), defined Transform IDs + are: + + Name Number Defined In + ------------------------------------------------------ + RESERVED 0 + PRF_HMAC_MD5 1 (RFC2104), [MD5] + PRF_HMAC_SHA1 2 (RFC2104), [SHA] + PRF_HMAC_TIGER 3 (RFC2104) + PRF_AES128_XCBC 4 (RFC3664) + RESERVED TO IANA 5-1023 + PRIVATE USE 1024-65535 + + For Transform Type 3 (Integrity Algorithm), defined Transform IDs + + + +Kaufman, et al. Expires August 27, 2006 [Page 63] + +Internet-Draft IKEv2bis February 2006 + + + are: + + Name Number Defined In + ---------------------------------------- + NONE 0 + AUTH_HMAC_MD5_96 1 (RFC2403) + AUTH_HMAC_SHA1_96 2 (RFC2404) + AUTH_DES_MAC 3 + AUTH_KPDK_MD5 4 (RFC1826) + AUTH_AES_XCBC_96 5 (RFC3566) + RESERVED TO IANA 6-1023 + PRIVATE USE 1024-65535 + + For Transform Type 4 (Diffie-Hellman Group), defined Transform IDs + are: + + Name Number + -------------------------------------- + NONE 0 + Defined in Appendix B 1 - 2 + RESERVED 3 - 4 + Defined in [ADDGROUP] 5 + RESERVED TO IANA 6 - 13 + Defined in [ADDGROUP] 14 - 18 + RESERVED TO IANA 19 - 1023 + PRIVATE USE 1024-65535 + + For Transform Type 5 (Extended Sequence Numbers), defined Transform + IDs are: + + Name Number + -------------------------------------------- + No Extended Sequence Numbers 0 + Extended Sequence Numbers 1 + RESERVED 2 - 65535 + +3.3.3. Valid Transform Types by Protocol + + The number and type of transforms that accompany an SA payload are + dependent on the protocol in the SA itself. An SA payload proposing + the establishment of an SA has the following mandatory and optional + transform types. A compliant implementation MUST understand all + mandatory and optional types for each protocol it supports (though it + need not accept proposals with unacceptable suites). A proposal MAY + omit the optional types if the only value for them it will accept is + NONE. + + + + + +Kaufman, et al. Expires August 27, 2006 [Page 64] + +Internet-Draft IKEv2bis February 2006 + + + Protocol Mandatory Types Optional Types + --------------------------------------------------- + IKE ENCR, PRF, INTEG, D-H + ESP ENCR, ESN INTEG, D-H + AH INTEG, ESN D-H + +3.3.4. Mandatory Transform IDs + + The specification of suites that MUST and SHOULD be supported for + interoperability has been removed from this document because they are + likely to change more rapidly than this document evolves. + + An important lesson learned from IKEv1 is that no system should only + implement the mandatory algorithms and expect them to be the best + choice for all customers. For example, at the time that this + document was written, many IKEv1 implementers were starting to + migrate to AES in Cipher Block Chaining (CBC) mode for Virtual + Private Network (VPN) applications. Many IPsec systems based on + IKEv2 will implement AES, additional Diffie-Hellman groups, and + additional hash algorithms, and some IPsec customers already require + these algorithms in addition to the ones listed above. + + It is likely that IANA will add additional transforms in the future, + and some users may want to use private suites, especially for IKE + where implementations should be capable of supporting different + parameters, up to certain size limits. In support of this goal, all + implementations of IKEv2 SHOULD include a management facility that + allows specification (by a user or system administrator) of Diffie- + Hellman (DH) parameters (the generator, modulus, and exponent lengths + and values) for new DH groups. Implementations SHOULD provide a + management interface through which these parameters and the + associated transform IDs may be entered (by a user or system + administrator), to enable negotiating such groups. + + All implementations of IKEv2 MUST include a management facility that + enables a user or system administrator to specify the suites that are + acceptable for use with IKE. Upon receipt of a payload with a set of + transform IDs, the implementation MUST compare the transmitted + transform IDs against those locally configured via the management + controls, to verify that the proposed suite is acceptable based on + local policy. The implementation MUST reject SA proposals that are + not authorized by these IKE suite controls. Note that cryptographic + suites that MUST be implemented need not be configured as acceptable + to local policy. + + + + + + + +Kaufman, et al. Expires August 27, 2006 [Page 65] + +Internet-Draft IKEv2bis February 2006 + + +3.3.5. Transform Attributes + + Each transform in a Security Association payload may include + attributes that modify or complete the specification of the + transform. These attributes are type/value pairs and are defined + below. For example, if an encryption algorithm has a variable-length + key, the key length to be used may be specified as an attribute. + Attributes can have a value with a fixed two octet length or a + variable-length value. For the latter, the attribute is encoded as + type/length/value. + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + !A! Attribute Type ! AF=0 Attribute Length ! + !F! ! AF=1 Attribute Value ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! AF=0 Attribute Value ! + ! AF=1 Not Transmitted ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 9: Data Attributes + + o Attribute Type (2 octets) - Unique identifier for each type of + attribute (see below). The most significant bit of this field is + the Attribute Format bit (AF). It indicates whether the data + attributes follow the Type/Length/Value (TLV) format or a + shortened Type/Value (TV) format. If the AF bit is zero (0), then + the Data Attributes are of the Type/Length/Value (TLV) form. If + the AF bit is a one (1), then the Data Attributes are of the Type/ + Value form. + + o Attribute Length (2 octets) - Length in octets of the Attribute + Value. When the AF bit is a one (1), the Attribute Value is only + 2 octets and the Attribute Length field is not present. + + o Attribute Value (variable length) - Value of the Attribute + associated with the Attribute Type. If the AF bit is a zero (0), + this field has a variable length defined by the Attribute Length + field. If the AF bit is a one (1), the Attribute Value has a + length of 2 octets. + + o Key Length - When using an Encryption Algorithm that has a + variable-length key, this attribute specifies the key length in + bits (MUST use network byte order). This attribute MUST NOT be + used when the specified Encryption Algorithm uses a fixed-length + key. + + + + +Kaufman, et al. Expires August 27, 2006 [Page 66] + +Internet-Draft IKEv2bis February 2006 + + + Note that only a single attribute type (Key Length) is defined, and + it is fixed length. The variable-length encoding specification is + included only for future extensions. {{ Clarif-7.11 removed the + sentence that listed, incorrectly, the algorithms defined in the + document that accept attributes. }} + + Attributes described as basic MUST NOT be encoded using the variable- + length encoding. Variable-length attributes MUST NOT be encoded as + basic even if their value can fit into two octets. NOTE: This is a + change from IKEv1, where increased flexibility may have simplified + the composer of messages but certainly complicated the parser. + + Attribute Type Value Attribute Format + ------------------------------------------------------------ + RESERVED 0-13 + Key Length (in bits) 14 TV + RESERVED 15-17 + RESERVED TO IANA 18-16383 + PRIVATE USE 16384-32767 + Values 0-13 and 15-17 were used in a similar context in + IKEv1, and should not be assigned except to matching values. + +3.3.6. Attribute Negotiation + + During security association negotiation initiators present offers to + responders. Responders MUST select a single complete set of + parameters from the offers (or reject all offers if none are + acceptable). If there are multiple proposals, the responder MUST + choose a single proposal number and return all of the Proposal + substructures with that Proposal number. If there are multiple + Transforms with the same type, the responder MUST choose a single + one. Any attributes of a selected transform MUST be returned + unmodified. The initiator of an exchange MUST check that the + accepted offer is consistent with one of its proposals, and if not + that response MUST be rejected. + + Negotiating Diffie-Hellman groups presents some special challenges. + SA offers include proposed attributes and a Diffie-Hellman public + number (KE) in the same message. If in the initial exchange the + initiator offers to use one of several Diffie-Hellman groups, it + SHOULD pick the one the responder is most likely to accept and + include a KE corresponding to that group. If the guess turns out to + be wrong, the responder will indicate the correct group in the + response and the initiator SHOULD pick an element of that group for + its KE value when retrying the first message. It SHOULD, however, + continue to propose its full supported set of groups in order to + prevent a man-in-the-middle downgrade attack. + + + + +Kaufman, et al. Expires August 27, 2006 [Page 67] + +Internet-Draft IKEv2bis February 2006 + + + Implementation Note: + + Certain negotiable attributes can have ranges or could have multiple + acceptable values. These include the key length of a variable key + length symmetric cipher. To further interoperability and to support + upgrading endpoints independently, implementers of this protocol + SHOULD accept values that they deem to supply greater security. For + instance, if a peer is configured to accept a variable-length cipher + with a key length of X bits and is offered that cipher with a larger + key length, the implementation SHOULD accept the offer if it supports + use of the longer key. + + Support of this capability allows an implementation to express a + concept of "at least" a certain level of security-- "a key length of + _at least_ X bits for cipher Y". + +3.4. Key Exchange Payload + + The Key Exchange Payload, denoted KE in this memo, is used to + exchange Diffie-Hellman public numbers as part of a Diffie-Hellman + key exchange. The Key Exchange Payload consists of the IKE generic + payload header followed by the Diffie-Hellman public value itself. + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! DH Group # ! RESERVED ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ Key Exchange Data ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 10: Key Exchange Payload Format + + A key exchange payload is constructed by copying one's Diffie-Hellman + public value into the "Key Exchange Data" portion of the payload. + The length of the Diffie-Hellman public value MUST be equal to the + length of the prime modulus over which the exponentiation was + performed, prepending zero bits to the value if necessary. + + The DH Group # identifies the Diffie-Hellman group in which the Key + Exchange Data was computed (see Section 3.3.2). If the selected + proposal uses a different Diffie-Hellman group, the message MUST be + rejected with a Notify payload of type INVALID_KE_PAYLOAD. + + + + +Kaufman, et al. Expires August 27, 2006 [Page 68] + +Internet-Draft IKEv2bis February 2006 + + + The payload type for the Key Exchange payload is thirty four (34). + +3.5. Identification Payloads + + The Identification Payloads, denoted IDi and IDr in this memo, allow + peers to assert an identity to one another. This identity may be + used for policy lookup, but does not necessarily have to match + anything in the CERT payload; both fields may be used by an + implementation to perform access control decisions. {{ Clarif-7.1 }} + When using the ID_IPV4_ADDR/ID_IPV6_ADDR identity types in IDi/IDr + payloads, IKEv2 does not require this address to match the address in + the IP header of IKEv2 packets, or anything in the TSi/TSr payloads. + The contents of IDi/IDr is used purely to fetch the policy and + authentication data related to the other party. + + NOTE: In IKEv1, two ID payloads were used in each direction to hold + Traffic Selector (TS) information for data passing over the SA. In + IKEv2, this information is carried in TS payloads (see Section 3.13). + + The Identification Payload consists of the IKE generic payload header + followed by identification fields as follows: + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ID Type ! RESERVED | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ Identification Data ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 11: Identification Payload Format + + o ID Type (1 octet) - Specifies the type of Identification being + used. + + o RESERVED - MUST be sent as zero; MUST be ignored on receipt. + + o Identification Data (variable length) - Value, as indicated by the + Identification Type. The length of the Identification Data is + computed from the size in the ID payload header. + + The payload types for the Identification Payload are thirty five (35) + for IDi and thirty six (36) for IDr. + + + + +Kaufman, et al. Expires August 27, 2006 [Page 69] + +Internet-Draft IKEv2bis February 2006 + + + The following table lists the assigned values for the Identification + Type field: + + ID Type Value + ------------------------------------------------------------------- + RESERVED 0 + + ID_IPV4_ADDR 1 + A single four (4) octet IPv4 address. + + ID_FQDN 2 + A fully-qualified domain name string. An example of a ID_FQDN + is, "example.com". The string MUST not contain any terminators + (e.g., NULL, CR, etc.). + + ID_RFC822_ADDR 3 + A fully-qualified RFC822 email address string, An example of a + ID_RFC822_ADDR is, "jsmith@example.com". The string MUST not + contain any terminators. + + RESERVED TO IANA 4 + + ID_IPV6_ADDR 5 + A single sixteen (16) octet IPv6 address. + + RESERVED TO IANA 6 - 8 + + ID_DER_ASN1_DN 9 + The binary Distinguished Encoding Rules (DER) encoding of an + ASN.1 X.500 Distinguished Name [X.501]. + + ID_DER_ASN1_GN 10 + The binary DER encoding of an ASN.1 X.500 GeneralName [X.509]. + + ID_KEY_ID 11 + An opaque octet stream which may be used to pass vendor- + specific information necessary to do certain proprietary + types of identification. + + RESERVED TO IANA 12-200 + + PRIVATE USE 201-255 + + Two implementations will interoperate only if each can generate a + type of ID acceptable to the other. To assure maximum + interoperability, implementations MUST be configurable to send at + least one of ID_IPV4_ADDR, ID_FQDN, ID_RFC822_ADDR, or ID_KEY_ID, and + MUST be configurable to accept all of these types. Implementations + + + +Kaufman, et al. Expires August 27, 2006 [Page 70] + +Internet-Draft IKEv2bis February 2006 + + + SHOULD be capable of generating and accepting all of these types. + IPv6-capable implementations MUST additionally be configurable to + accept ID_IPV6_ADDR. IPv6-only implementations MAY be configurable + to send only ID_IPV6_ADDR. + + {{ Clarif-3.4 }} EAP [EAP] does not mandate the use of any particular + type of identifier, but often EAP is used with Network Access + Identifiers (NAIs) defined in [NAI]. Although NAIs look a bit like + email addresses (e.g., "joe@example.com"), the syntax is not exactly + the same as the syntax of email address in [MAILFORMAT]. For those + NAIs that include the realm component, the ID_RFC822_ADDR + identification type SHOULD be used. Responder implementations should + not attempt to verify that the contents actually conform to the exact + syntax given in [MAILFORMAT], but instead should accept any + reasonable-looking NAI. For NAIs that do not include the realm + component,the ID_KEY_ID identification type SHOULD be used. + +3.6. Certificate Payload + + The Certificate Payload, denoted CERT in this memo, provides a means + to transport certificates or other authentication-related information + via IKE. Certificate payloads SHOULD be included in an exchange if + certificates are available to the sender unless the peer has + indicated an ability to retrieve this information from elsewhere + using an HTTP_CERT_LOOKUP_SUPPORTED Notify payload. Note that the + term "Certificate Payload" is somewhat misleading, because not all + authentication mechanisms use certificates and data other than + certificates may be passed in this payload. + + The Certificate Payload is defined as follows: + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Cert Encoding ! ! + +-+-+-+-+-+-+-+-+ ! + ~ Certificate Data ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 12: Certificate Payload Format + + o Certificate Encoding (1 octet) - This field indicates the type of + certificate or certificate-related information contained in the + Certificate Data field. + + + + +Kaufman, et al. Expires August 27, 2006 [Page 71] + +Internet-Draft IKEv2bis February 2006 + + + Certificate Encoding Value + ------------------------------------------------- + RESERVED 0 + PKCS #7 wrapped X.509 certificate 1 + PGP Certificate 2 + DNS Signed Key 3 + X.509 Certificate - Signature 4 + Kerberos Token 6 + Certificate Revocation List (CRL) 7 + Authority Revocation List (ARL) 8 + SPKI Certificate 9 + X.509 Certificate - Attribute 10 + Raw RSA Key 11 + Hash and URL of X.509 certificate 12 + Hash and URL of X.509 bundle 13 + RESERVED to IANA 14 - 200 + PRIVATE USE 201 - 255 + + o Certificate Data (variable length) - Actual encoding of + certificate data. The type of certificate is indicated by the + Certificate Encoding field. + + The payload type for the Certificate Payload is thirty seven (37). + + Specific syntax is for some of the certificate type codes above is + not defined in this document. The types whose syntax is defined in + this document are: + + o X.509 Certificate - Signature (4) contains a DER encoded X.509 + certificate whose public key is used to validate the sender's AUTH + payload. + + o Certificate Revocation List (7) contains a DER encoded X.509 + certificate revocation list. + + o {{ Added "DER-encoded RSAPublicKey structure" from Clarif-3.6 }} + Raw RSA Key (11) contains a PKCS #1 encoded RSA key, that is, a + DER-encoded RSAPublicKey structure (see [RSA] and [PKCS1]). + + o Hash and URL encodings (12-13) allow IKE messages to remain short + by replacing long data structures with a 20 octet SHA-1 hash (see + [SHA]) of the replaced value followed by a variable-length URL + that resolves to the DER encoded data structure itself. This + improves efficiency when the endpoints have certificate data + cached and makes IKE less subject to denial of service attacks + that become easier to mount when IKE messages are large enough to + require IP fragmentation [DOSUDPPROT]. + + + + +Kaufman, et al. Expires August 27, 2006 [Page 72] + +Internet-Draft IKEv2bis February 2006 + + + Use the following ASN.1 definition for an X.509 bundle: + + CertBundle + { iso(1) identified-organization(3) dod(6) internet(1) + security(5) mechanisms(5) pkix(7) id-mod(0) + id-mod-cert-bundle(34) } + + DEFINITIONS EXPLICIT TAGS ::= + BEGIN + + IMPORTS + Certificate, CertificateList + FROM PKIX1Explicit88 + { iso(1) identified-organization(3) dod(6) + internet(1) security(5) mechanisms(5) pkix(7) + id-mod(0) id-pkix1-explicit(18) } ; + + CertificateOrCRL ::= CHOICE { + cert [0] Certificate, + crl [1] CertificateList } + + CertificateBundle ::= SEQUENCE OF CertificateOrCRL + + END + + Implementations MUST be capable of being configured to send and + accept up to four X.509 certificates in support of authentication, + and also MUST be capable of being configured to send and accept the + first two Hash and URL formats (with HTTP URLs). Implementations + SHOULD be capable of being configured to send and accept Raw RSA + keys. If multiple certificates are sent, the first certificate MUST + contain the public key used to sign the AUTH payload. The other + certificates may be sent in any order. + + {{ Clarif-3.6 }} Because the contents and use of some of the + certificate types are not defined, they SHOULD NOT be used. In + specific, implementations SHOULD NOT use the following types unless + they are later defined in a standards-track document: + + PKCS #7 wrapped X.509 certificate 1 + PGP Certificate 2 + DNS Signed Key 3 + Kerberos Token 6 + SPKI Certificate 9 + + + + + + + +Kaufman, et al. Expires August 27, 2006 [Page 73] + +Internet-Draft IKEv2bis February 2006 + + +3.7. Certificate Request Payload + + The Certificate Request Payload, denoted CERTREQ in this memo, + provides a means to request preferred certificates via IKE and can + appear in the IKE_INIT_SA response and/or the IKE_AUTH request. + Certificate Request payloads MAY be included in an exchange when the + sender needs to get the certificate of the receiver. If multiple CAs + are trusted and the cert encoding does not allow a list, then + multiple Certificate Request payloads SHOULD be transmitted. + + The Certificate Request Payload is defined as follows: + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Cert Encoding ! ! + +-+-+-+-+-+-+-+-+ ! + ~ Certification Authority ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 13: Certificate Request Payload Format + + o Certificate Encoding (1 octet) - Contains an encoding of the type + or format of certificate requested. Values are listed in + Section 3.6. + + o Certification Authority (variable length) - Contains an encoding + of an acceptable certification authority for the type of + certificate requested. + + The payload type for the Certificate Request Payload is thirty eight + (38). + + The Certificate Encoding field has the same values as those defined + in Section 3.6. The Certification Authority field contains an + indicator of trusted authorities for this certificate type. The + Certification Authority value is a concatenated list of SHA-1 hashes + of the public keys of trusted Certification Authorities (CAs). Each + is encoded as the SHA-1 hash of the Subject Public Key Info element + (see section 4.1.2.7 of [PKIX]) from each Trust Anchor certificate. + The twenty-octet hashes are concatenated and included with no other + formatting. + + {{ Clarif-3.6 }} The contents of the "Certification Authority" field + are defined only for X.509 certificates, which are types 4, 10, 12, + + + +Kaufman, et al. Expires August 27, 2006 [Page 74] + +Internet-Draft IKEv2bis February 2006 + + + and 13. Other values SHOULD NOT be used until standards-track + specifications that specify their use are published. + + Note that the term "Certificate Request" is somewhat misleading, in + that values other than certificates are defined in a "Certificate" + payload and requests for those values can be present in a Certificate + Request Payload. The syntax of the Certificate Request payload in + such cases is not defined in this document. + + The Certificate Request Payload is processed by inspecting the "Cert + Encoding" field to determine whether the processor has any + certificates of this type. If so, the "Certification Authority" + field is inspected to determine if the processor has any certificates + that can be validated up to one of the specified certification + authorities. This can be a chain of certificates. + + If an end-entity certificate exists that satisfies the criteria + specified in the CERTREQ, a certificate or certificate chain SHOULD + be sent back to the certificate requestor if the recipient of the + CERTREQ: + + o is configured to use certificate authentication, + + o is allowed to send a CERT payload, + + o has matching CA trust policy governing the current negotiation, + and + + o has at least one time-wise and usage appropriate end-entity + certificate chaining to a CA provided in the CERTREQ. + + Certificate revocation checking must be considered during the + chaining process used to select a certificate. Note that even if two + peers are configured to use two different CAs, cross-certification + relationships should be supported by appropriate selection logic. + + The intent is not to prevent communication through the strict + adherence of selection of a certificate based on CERTREQ, when an + alternate certificate could be selected by the sender that would + still enable the recipient to successfully validate and trust it + through trust conveyed by cross-certification, CRLs, or other out-of- + band configured means. Thus, the processing of a CERTREQ should be + seen as a suggestion for a certificate to select, not a mandated one. + If no certificates exist, then the CERTREQ is ignored. This is not + an error condition of the protocol. There may be cases where there + is a preferred CA sent in the CERTREQ, but an alternate might be + acceptable (perhaps after prompting a human operator). + + + + +Kaufman, et al. Expires August 27, 2006 [Page 75] + +Internet-Draft IKEv2bis February 2006 + + +3.8. Authentication Payload + + The Authentication Payload, denoted AUTH in this memo, contains data + used for authentication purposes. The syntax of the Authentication + data varies according to the Auth Method as specified below. + + The Authentication Payload is defined as follows: + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Auth Method ! RESERVED ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ Authentication Data ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 14: Authentication Payload Format + + o Auth Method (1 octet) - Specifies the method of authentication + used. Values defined are: + + * RSA Digital Signature (1) - Computed as specified in + Section 2.15 using an RSA private key over a PKCS#1 padded hash + (see [RSA] and [PKCS1]). {{ Clarif-3.2 }} To promote + interoperability, implementations that support this type SHOULD + support signatures that use SHA-1 as the hash function and + SHOULD use SHA-1 as the default hash function when generating + signatures. {{ Clarif-3.3 }} A newer version of PKCS#1 (v2.1) + defines two different encoding methods (ways of "padding the + hash") for signatures. However, IKEv2 and this document point + specifically to the PKCS#1 v2.0 which has only one encoding + method for signatures (EMSA-PKCS1- v1_5). + + * Shared Key Message Integrity Code (2) - Computed as specified + in Section 2.15 using the shared key associated with the + identity in the ID payload and the negotiated prf function + + * DSS Digital Signature (3) - Computed as specified in + Section 2.15 using a DSS private key (see [DSS]) over a SHA-1 + hash. + + * The values 0 and 4-200 are reserved to IANA. The values 201- + 255 are available for private use. + + + + +Kaufman, et al. Expires August 27, 2006 [Page 76] + +Internet-Draft IKEv2bis February 2006 + + + o Authentication Data (variable length) - see Section 2.15. + + The payload type for the Authentication Payload is thirty nine (39). + +3.9. Nonce Payload + + The Nonce Payload, denoted Ni and Nr in this memo for the initiator's + and responder's nonce respectively, contains random data used to + guarantee liveness during an exchange and protect against replay + attacks. + + The Nonce Payload is defined as follows: + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ Nonce Data ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 15: Nonce Payload Format + + o Nonce Data (variable length) - Contains the random data generated + by the transmitting entity. + + The payload type for the Nonce Payload is forty (40). + + The size of a Nonce MUST be between 16 and 256 octets inclusive. + Nonce values MUST NOT be reused. + +3.10. Notify Payload + + The Notify Payload, denoted N in this document, is used to transmit + informational data, such as error conditions and state transitions, + to an IKE peer. A Notify Payload may appear in a response message + (usually specifying why a request was rejected), in an INFORMATIONAL + Exchange (to report an error not in an IKE request), or in any other + message to indicate sender capabilities or to modify the meaning of + the request. + + The Notify Payload is defined as follows: + + + + + + + +Kaufman, et al. Expires August 27, 2006 [Page 77] + +Internet-Draft IKEv2bis February 2006 + + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Protocol ID ! SPI Size ! Notify Message Type ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ Security Parameter Index (SPI) ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ Notification Data ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 16: Notify Payload Format + + o Protocol ID (1 octet) - If this notification concerns an existing + SA, this field indicates the type of that SA. For IKE_SA + notifications, this field MUST be one (1). For notifications + concerning IPsec SAs this field MUST contain either (2) to + indicate AH or (3) to indicate ESP. {{ Clarif-7.8 }} For + notifications that do not relate to an existing SA, this field + MUST be sent as zero and MUST be ignored on receipt; this is + currently only true for the INVALID_SELECTORS and REKEY_SA + notifications. All other values for this field are reserved to + IANA for future assignment. + + o SPI Size (1 octet) - Length in octets of the SPI as defined by the + IPsec protocol ID or zero if no SPI is applicable. For a + notification concerning the IKE_SA, the SPI Size MUST be zero. + + o Notify Message Type (2 octets) - Specifies the type of + notification message. + + o SPI (variable length) - Security Parameter Index. + + o Notification Data (variable length) - Informational or error data + transmitted in addition to the Notify Message Type. Values for + this field are type specific (see below). + + The payload type for the Notify Payload is forty one (41). + +3.10.1. Notify Message Types + + Notification information can be error messages specifying why an SA + could not be established. It can also be status data that a process + + + +Kaufman, et al. Expires August 27, 2006 [Page 78] + +Internet-Draft IKEv2bis February 2006 + + + managing an SA database wishes to communicate with a peer process. + The table below lists the Notification messages and their + corresponding values. The number of different error statuses was + greatly reduced from IKEv1 both for simplification and to avoid + giving configuration information to probers. + + Types in the range 0 - 16383 are intended for reporting errors. An + implementation receiving a Notify payload with one of these types + that it does not recognize in a response MUST assume that the + corresponding request has failed entirely. {{ Demoted the SHOULD }} + Unrecognized error types in a request and status types in a request + or response MUST be ignored, and they should be logged. + + Notify payloads with status types MAY be added to any message and + MUST be ignored if not recognized. They are intended to indicate + capabilities, and as part of SA negotiation are used to negotiate + non-cryptographic parameters. + + NOTIFY messages: error types Value + ------------------------------------------------------------------- + + RESERVED 0 + + UNSUPPORTED_CRITICAL_PAYLOAD 1 + Sent if the payload has the "critical" bit set and the payload + type is not recognized. Notification Data contains the one-octet + payload type. + + INVALID_IKE_SPI 4 + Indicates an IKE message was received with an unrecognized + destination SPI. This usually indicates that the recipient has + rebooted and forgotten the existence of an IKE_SA. + + INVALID_MAJOR_VERSION 5 + Indicates the recipient cannot handle the version of IKE + specified in the header. The closest version number that the + recipient can support will be in the reply header. + + INVALID_SYNTAX 7 + Indicates the IKE message that was received was invalid because + some type, length, or value was out of range or because the + request was rejected for policy reasons. To avoid a denial of + service attack using forged messages, this status may only be + returned for and in an encrypted packet if the message ID and + cryptographic checksum were valid. To avoid leaking information + to someone probing a node, this status MUST be sent in response + to any error not covered by one of the other status types. + {{ Demoted the SHOULD }} To aid debugging, more detailed error + + + +Kaufman, et al. Expires August 27, 2006 [Page 79] + +Internet-Draft IKEv2bis February 2006 + + + information should be written to a console or log. + + INVALID_MESSAGE_ID 9 + Sent when an IKE message ID outside the supported window is + received. This Notify MUST NOT be sent in a response; the invalid + request MUST NOT be acknowledged. Instead, inform the other side + by initiating an INFORMATIONAL exchange with Notification data + containing the four octet invalid message ID. Sending this + notification is optional, and notifications of this type MUST be + rate limited. + + INVALID_SPI 11 + MAY be sent in an IKE INFORMATIONAL exchange when a node receives + an ESP or AH packet with an invalid SPI. The Notification Data + contains the SPI of the invalid packet. This usually indicates a + node has rebooted and forgotten an SA. If this Informational + Message is sent outside the context of an IKE_SA, it should only + be used by the recipient as a "hint" that something might be + wrong (because it could easily be forged). + + NO_PROPOSAL_CHOSEN 14 + None of the proposed crypto suites was acceptable. + + INVALID_KE_PAYLOAD 17 + The D-H Group # field in the KE payload is not the group # + selected by the responder for this exchange. There are two octets + of data associated with this notification: the accepted D-H Group + # in big endian order. + + AUTHENTICATION_FAILED 24 + Sent in the response to an IKE_AUTH message when for some reason + the authentication failed. There is no associated data. + + SINGLE_PAIR_REQUIRED 34 + This error indicates that a CREATE_CHILD_SA request is + unacceptable because its sender is only willing to accept traffic + selectors specifying a single pair of addresses. The requestor is + expected to respond by requesting an SA for only the specific + traffic it is trying to forward. + + NO_ADDITIONAL_SAS 35 + This error indicates that a CREATE_CHILD_SA request is + unacceptable because the responder is unwilling to accept any + more CHILD_SAs on this IKE_SA. Some minimal implementations may + only accept a single CHILD_SA setup in the context of an initial + IKE exchange and reject any subsequent attempts to add more. + + INTERNAL_ADDRESS_FAILURE 36 + + + +Kaufman, et al. Expires August 27, 2006 [Page 80] + +Internet-Draft IKEv2bis February 2006 + + + Indicates an error assigning an internal address (i.e., + INTERNAL_IP4_ADDRESS or INTERNAL_IP6_ADDRESS) during the + processing of a Configuration Payload by a responder. If this + error is generated within an IKE_AUTH exchange, no CHILD_SA will + be created. + + FAILED_CP_REQUIRED 37 + Sent by responder in the case where CP(CFG_REQUEST) was expected + but not received, and so is a conflict with locally configured + policy. There is no associated data. + + TS_UNACCEPTABLE 38 + Indicates that none of the addresses/protocols/ports in the + supplied traffic selectors is acceptable. + + INVALID_SELECTORS 39 + MAY be sent in an IKE INFORMATIONAL exchange when a node receives + an ESP or AH packet whose selectors do not match those of the SA + on which it was delivered (and that caused the packet to be + dropped). The Notification Data contains the start of the + offending packet (as in ICMP messages) and the SPI field of the + notification is set to match the SPI of the IPsec SA. + + RESERVED TO IANA 40-8191 + + PRIVATE USE 8192-16383 + + + NOTIFY messages: status types Value + ------------------------------------------------------------------- + + INITIAL_CONTACT 16384 + This notification asserts that this IKE_SA is the only IKE_SA + currently active between the authenticated identities. It MAY be + sent when an IKE_SA is established after a crash, and the + recipient MAY use this information to delete any other IKE_SAs it + has to the same authenticated identity without waiting for a + timeout. This notification MUST NOT be sent by an entity that may + be replicated (e.g., a roaming user's credentials where the user + is allowed to connect to the corporate firewall from two remote + systems at the same time). {{ Clarif-7.9 }} The INITIAL_CONTACT + notification, if sent, SHOULD be in the first IKE_AUTH request, + not as a separate exchange afterwards; however, receiving + parties need to deal with it in other requests. + + SET_WINDOW_SIZE 16385 + This notification asserts that the sending endpoint is capable of + keeping state for multiple outstanding exchanges, permitting the + + + +Kaufman, et al. Expires August 27, 2006 [Page 81] + +Internet-Draft IKEv2bis February 2006 + + + recipient to send multiple requests before getting a response to + the first. The data associated with a SET_WINDOW_SIZE + notification MUST be 4 octets long and contain the big endian + representation of the number of messages the sender promises to + keep. Window size is always one until the initial exchanges + complete. + + ADDITIONAL_TS_POSSIBLE 16386 + This notification asserts that the sending endpoint narrowed the + proposed traffic selectors but that other traffic selectors would + also have been acceptable, though only in a separate SA (see + section 2.9). There is no data associated with this Notify type. + It may be sent only as an additional payload in a message + including accepted TSs. + + IPCOMP_SUPPORTED 16387 + This notification may be included only in a message containing an + SA payload negotiating a CHILD_SA and indicates a willingness by + its sender to use IPComp on this SA. The data associated with + this notification includes a two-octet IPComp CPI followed by a + one-octet transform ID optionally followed by attributes whose + length and format are defined by that transform ID. A message + proposing an SA may contain multiple IPCOMP_SUPPORTED + notifications to indicate multiple supported algorithms. A + message accepting an SA may contain at most one. + + The transform IDs currently defined are: + + Name Number Defined In + ------------------------------------- + RESERVED 0 + IPCOMP_OUI 1 + IPCOMP_DEFLATE 2 RFC 2394 + IPCOMP_LZS 3 RFC 2395 + IPCOMP_LZJH 4 RFC 3051 + RESERVED TO IANA 5-240 + PRIVATE USE 241-255 + + NAT_DETECTION_SOURCE_IP 16388 + This notification is used by its recipient to determine whether + the source is behind a NAT box. The data associated with this + notification is a SHA-1 digest of the SPIs (in the order they + appear in the header), IP address, and port on which this packet + was sent. There MAY be multiple Notify payloads of this type in a + message if the sender does not know which of several network + attachments will be used to send the packet. The recipient of + this notification MAY compare the supplied value to a SHA-1 hash + of the SPIs, source IP address, and port, and if they don't match + + + +Kaufman, et al. Expires August 27, 2006 [Page 82] + +Internet-Draft IKEv2bis February 2006 + + + it SHOULD enable NAT traversal (see section 2.23). Alternately, + it MAY reject the connection attempt if NAT traversal is not + supported. + + NAT_DETECTION_DESTINATION_IP 16389 + This notification is used by its recipient to determine whether + it is behind a NAT box. The data associated with this + notification is a SHA-1 digest of the SPIs (in the order they + appear in the header), IP address, and port to which this packet + was sent. The recipient of this notification MAY compare the + supplied value to a hash of the SPIs, destination IP address, and + port, and if they don't match it SHOULD invoke NAT traversal (see + section 2.23). If they don't match, it means that this end is + behind a NAT and this end SHOULD start sending keepalive packets + as defined in [UDPENCAPS]. Alternately, it MAY reject the + connection attempt if NAT traversal is not supported. + + COOKIE 16390 + This notification MAY be included in an IKE_SA_INIT response. It + indicates that the request should be retried with a copy of this + notification as the first payload. This notification MUST be + included in an IKE_SA_INIT request retry if a COOKIE notification + was included in the initial response. The data associated with + this notification MUST be between 1 and 64 octets in length + (inclusive). + + USE_TRANSPORT_MODE 16391 + This notification MAY be included in a request message that also + includes an SA payload requesting a CHILD_SA. It requests that + the CHILD_SA use transport mode rather than tunnel mode for the + SA created. If the request is accepted, the response MUST also + include a notification of type USE_TRANSPORT_MODE. If the + responder declines the request, the CHILD_SA will be established + in tunnel mode. If this is unacceptable to the initiator, the + initiator MUST delete the SA. Note: Except when using this option + to negotiate transport mode, all CHILD_SAs will use tunnel mode. + + Note: The ECN decapsulation modifications specified in + [IPSECARCH] MUST be performed for every tunnel mode SA created + by IKEv2. + + HTTP_CERT_LOOKUP_SUPPORTED 16392 + This notification MAY be included in any message that can include + a CERTREQ payload and indicates that the sender is capable of + looking up certificates based on an HTTP-based URL (and hence + presumably would prefer to receive certificate specifications in + that format). + + + + +Kaufman, et al. Expires August 27, 2006 [Page 83] + +Internet-Draft IKEv2bis February 2006 + + + REKEY_SA 16393 + This notification MUST be included in a CREATE_CHILD_SA exchange + if the purpose of the exchange is to replace an existing ESP or + AH SA. The SPI field identifies the SA being rekeyed. + {{ Clarif-5.4 }} The SPI placed in the REKEY_SA + notification is the SPI the exchange initiator would expect in + inbound ESP or AH packets. There is no data. + + ESP_TFC_PADDING_NOT_SUPPORTED 16394 + This notification asserts that the sending endpoint will NOT + accept packets that contain Flow Confidentiality (TFC) padding. + {{ Clarif-4.5 }} The scope of this message is a single + CHILD_SA, and thus this notification is included in messages + containing an SA payload negotiating a CHILD_SA. If neither + endpoint accepts TFC padding, this notification SHOULD be + included in both the request proposing an SA and the response + accepting it. If this notification is included in only one of + the messages, TFC padding can still be sent in the other + direction. + + NON_FIRST_FRAGMENTS_ALSO 16395 + Used for fragmentation control. See [IPSECARCH] for explanation. + {{ Clarif-4.6 }} Sending non-first fragments is + enabled only if NON_FIRST_FRAGMENTS_ALSO notification is + included in both the request proposing an SA and the response + accepting it. If the peer rejects this proposal, the peer only + omits NON_FIRST_FRAGMENTS_ALSO notification from the response, + but does not reject the whole CHILD_SA creation. + + RESERVED TO IANA 16396-40959 + + PRIVATE USE 40960-65535 + +3.11. Delete Payload + + The Delete Payload, denoted D in this memo, contains a protocol + specific security association identifier that the sender has removed + from its security association database and is, therefore, no longer + valid. Figure 17 shows the format of the Delete Payload. It is + possible to send multiple SPIs in a Delete payload; however, each SPI + MUST be for the same protocol. Mixing of protocol identifiers MUST + NOT be performed in the Delete payload. It is permitted, however, to + include multiple Delete payloads in a single INFORMATIONAL exchange + where each Delete payload lists SPIs for a different protocol. + + Deletion of the IKE_SA is indicated by a protocol ID of 1 (IKE) but + no SPIs. Deletion of a CHILD_SA, such as ESP or AH, will contain the + IPsec protocol ID of that protocol (2 for AH, 3 for ESP), and the SPI + + + +Kaufman, et al. Expires August 27, 2006 [Page 84] + +Internet-Draft IKEv2bis February 2006 + + + is the SPI the sending endpoint would expect in inbound ESP or AH + packets. + + The Delete Payload is defined as follows: + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Protocol ID ! SPI Size ! # of SPIs ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ Security Parameter Index(es) (SPI) ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 17: Delete Payload Format + + o Protocol ID (1 octet) - Must be 1 for an IKE_SA, 2 for AH, or 3 + for ESP. + + o SPI Size (1 octet) - Length in octets of the SPI as defined by the + protocol ID. It MUST be zero for IKE (SPI is in message header) + or four for AH and ESP. + + o # of SPIs (2 octets) - The number of SPIs contained in the Delete + payload. The size of each SPI is defined by the SPI Size field. + + o Security Parameter Index(es) (variable length) - Identifies the + specific security association(s) to delete. The length of this + field is determined by the SPI Size and # of SPIs fields. + + The payload type for the Delete Payload is forty two (42). + +3.12. Vendor ID Payload + + The Vendor ID Payload, denoted V in this memo, contains a vendor + defined constant. The constant is used by vendors to identify and + recognize remote instances of their implementations. This mechanism + allows a vendor to experiment with new features while maintaining + backward compatibility. + + A Vendor ID payload MAY announce that the sender is capable to + accepting certain extensions to the protocol, or it MAY simply + identify the implementation as an aid in debugging. A Vendor ID + payload MUST NOT change the interpretation of any information defined + in this specification (i.e., the critical bit MUST be set to 0). + + + +Kaufman, et al. Expires August 27, 2006 [Page 85] + +Internet-Draft IKEv2bis February 2006 + + + Multiple Vendor ID payloads MAY be sent. An implementation is NOT + REQUIRED to send any Vendor ID payload at all. + + A Vendor ID payload may be sent as part of any message. Reception of + a familiar Vendor ID payload allows an implementation to make use of + Private USE numbers described throughout this memo-- private + payloads, private exchanges, private notifications, etc. Unfamiliar + Vendor IDs MUST be ignored. + + Writers of Internet-Drafts who wish to extend this protocol MUST + define a Vendor ID payload to announce the ability to implement the + extension in the Internet-Draft. It is expected that Internet-Drafts + that gain acceptance and are standardized will be given "magic + numbers" out of the Future Use range by IANA, and the requirement to + use a Vendor ID will go away. + + The Vendor ID Payload fields are defined as follows: + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ Vendor ID (VID) ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 18: Vendor ID Payload Format + + o Vendor ID (variable length) - It is the responsibility of the + person choosing the Vendor ID to assure its uniqueness in spite of + the absence of any central registry for IDs. Good practice is to + include a company name, a person name, or some such. If you want + to show off, you might include the latitude and longitude and time + where you were when you chose the ID and some random input. A + message digest of a long unique string is preferable to the long + unique string itself. + + The payload type for the Vendor ID Payload is forty three (43). + +3.13. Traffic Selector Payload + + The Traffic Selector Payload, denoted TS in this memo, allows peers + to identify packet flows for processing by IPsec security services. + The Traffic Selector Payload consists of the IKE generic payload + header followed by individual traffic selectors as follows: + + + + +Kaufman, et al. Expires August 27, 2006 [Page 86] + +Internet-Draft IKEv2bis February 2006 + + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Number of TSs ! RESERVED ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ <Traffic Selectors> ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 19: Traffic Selectors Payload Format + + o Number of TSs (1 octet) - Number of traffic selectors being + provided. + + o RESERVED - This field MUST be sent as zero and MUST be ignored on + receipt. + + o Traffic Selectors (variable length) - One or more individual + traffic selectors. + + The length of the Traffic Selector payload includes the TS header and + all the traffic selectors. + + The payload type for the Traffic Selector payload is forty four (44) + for addresses at the initiator's end of the SA and forty five (45) + for addresses at the responder's end. + + {{ Clarif-4.7 }} There is no requirement that TSi and TSr contain the + same number of individual traffic selectors. Thus, they are + interpreted as follows: a packet matches a given TSi/TSr if it + matches at least one of the individual selectors in TSi, and at least + one of the individual selectors in TSr. + + For instance, the following traffic selectors: + + TSi = ((17, 100, 192.0.1.66-192.0.1.66), + (17, 200, 192.0.1.66-192.0.1.66)) + TSr = ((17, 300, 0.0.0.0-255.255.255.255), + (17, 400, 0.0.0.0-255.255.255.255)) + + would match UDP packets from 192.0.1.66 to anywhere, with any of the + four combinations of source/destination ports (100,300), (100,400), + (200,300), and (200, 400). + + Thus, some types of policies may require several CHILD_SA pairs. For + + + +Kaufman, et al. Expires August 27, 2006 [Page 87] + +Internet-Draft IKEv2bis February 2006 + + + instance, a policy matching only source/destination ports (100,300) + and (200,400), but not the other two combinations, cannot be + negotiated as a single CHILD_SA pair. + +3.13.1. Traffic Selector + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! TS Type !IP Protocol ID*| Selector Length | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Start Port* | End Port* | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ Starting Address* ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ Ending Address* ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 20: Traffic Selector + + *Note: All fields other than TS Type and Selector Length depend on + the TS Type. The fields shown are for TS Types 7 and 8, the only two + values currently defined. + + o TS Type (one octet) - Specifies the type of traffic selector. + + o IP protocol ID (1 octet) - Value specifying an associated IP + protocol ID (e.g., UDP/TCP/ICMP). A value of zero means that the + protocol ID is not relevant to this traffic selector-- the SA can + carry all protocols. + + o Selector Length - Specifies the length of this Traffic Selector + Substructure including the header. + + o Start Port (2 octets) - Value specifying the smallest port number + allowed by this Traffic Selector. For protocols for which port is + undefined, or if all ports are allowed, this field MUST be zero. + For the ICMP protocol, the two one-octet fields Type and Code are + treated as a single 16-bit integer (with Type in the most + significant eight bits and Code in the least significant eight + bits) port number for the purposes of filtering based on this + field. + + + + + +Kaufman, et al. Expires August 27, 2006 [Page 88] + +Internet-Draft IKEv2bis February 2006 + + + o End Port (2 octets) - Value specifying the largest port number + allowed by this Traffic Selector. For protocols for which port is + undefined, or if all ports are allowed, this field MUST be 65535. + For the ICMP protocol, the two one-octet fields Type and Code are + treated as a single 16-bit integer (with Type in the most + significant eight bits and Code in the least significant eight + bits) port number for the purposed of filtering based on this + field. + + o Starting Address - The smallest address included in this Traffic + Selector (length determined by TS type). + + o Ending Address - The largest address included in this Traffic + Selector (length determined by TS type). + + Systems that are complying with [IPSECARCH] that wish to indicate + "ANY" ports MUST set the start port to 0 and the end port to 65535; + note that according to [IPSECARCH], "ANY" includes "OPAQUE". Systems + working with [IPSECARCH] that wish to indicate "OPAQUE" ports, but + not "ANY" ports, MUST set the start port to 65535 and the end port to + 0. + + {{ Added from Clarif-4.8 }} The traffic selector types 7 and 8 can + also refer to ICMP type and code fields. Note, however, that ICMP + packets do not have separate source and destination port fields. The + method for specifying the traffic selectors for ICMP is shown by + example in Section 4.4.1.3 of [IPSECARCH]. + + {{ Added from Clarif-4.9 }} Traffic selectors can use IP Protocol ID + 135 to match the IPv6 mobility header [MIPV6]. This document does + not specify how to represent the "MH Type" field in traffic + selectors, although it is likely that a different document will + specify this in the future. Note that [IPSECARCH] says that the IPv6 + mobility header (MH) message type is placed in the most significant + eight bits of the 16-bit local port selector. The direction + semantics of TSi/TSr port fields are the same as for ICMP. + + The following table lists the assigned values for the Traffic + Selector Type field and the corresponding Address Selector Data. + + + + + + + + + + + + +Kaufman, et al. Expires August 27, 2006 [Page 89] + +Internet-Draft IKEv2bis February 2006 + + + TS Type Value + ------------------------------------------------------------------- + RESERVED 0-6 + + TS_IPV4_ADDR_RANGE 7 + + A range of IPv4 addresses, represented by two four-octet + values. The first value is the beginning IPv4 address + (inclusive) and the second value is the ending IPv4 address + (inclusive). All addresses falling between the two specified + addresses are considered to be within the list. + + TS_IPV6_ADDR_RANGE 8 + + A range of IPv6 addresses, represented by two sixteen-octet + values. The first value is the beginning IPv6 address + (inclusive) and the second value is the ending IPv6 address + (inclusive). All addresses falling between the two specified + addresses are considered to be within the list. + + RESERVED TO IANA 9-240 + PRIVATE USE 241-255 + +3.14. Encrypted Payload + + The Encrypted Payload, denoted SK{...} or E in this memo, contains + other payloads in encrypted form. The Encrypted Payload, if present + in a message, MUST be the last payload in the message. Often, it is + the only payload in the message. + + The algorithms for encryption and integrity protection are negotiated + during IKE_SA setup, and the keys are computed as specified in + Section 2.14 and Section 2.18. + + The encryption and integrity protection algorithms are modeled after + the ESP algorithms described in RFCs 2104 [HMAC], 4303 [ESP], and + 2451 [ESPCBC]. This document completely specifies the cryptographic + processing of IKE data, but those documents should be consulted for + design rationale. We require a block cipher with a fixed block size + and an integrity check algorithm that computes a fixed-length + checksum over a variable size message. + + The payload type for an Encrypted payload is forty six (46). The + Encrypted Payload consists of the IKE generic payload header followed + by individual fields as follows: + + + + + + +Kaufman, et al. Expires August 27, 2006 [Page 90] + +Internet-Draft IKEv2bis February 2006 + + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Initialization Vector ! + ! (length is block size for encryption algorithm) ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ~ Encrypted IKE Payloads ~ + + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! Padding (0-255 octets) ! + +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+ + ! ! Pad Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ~ Integrity Checksum Data ~ + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 21: Encrypted Payload Format + + o Next Payload - The payload type of the first embedded payload. + Note that this is an exception in the standard header format, + since the Encrypted payload is the last payload in the message and + therefore the Next Payload field would normally be zero. But + because the content of this payload is embedded payloads and there + was no natural place to put the type of the first one, that type + is placed here. + + o Payload Length - Includes the lengths of the header, IV, Encrypted + IKE Payloads, Padding, Pad Length, and Integrity Checksum Data. + + o Initialization Vector - A randomly chosen value whose length is + equal to the block length of the underlying encryption algorithm. + Recipients MUST accept any value. Senders SHOULD either pick this + value pseudo-randomly and independently for each message or use + the final ciphertext block of the previous message sent. Senders + MUST NOT use the same value for each message, use a sequence of + values with low hamming distance (e.g., a sequence number), or use + ciphertext from a received message. + + o IKE Payloads are as specified earlier in this section. This field + is encrypted with the negotiated cipher. + + o Padding MAY contain any value chosen by the sender, and MUST have + a length that makes the combination of the Payloads, the Padding, + and the Pad Length to be a multiple of the encryption block size. + This field is encrypted with the negotiated cipher. + + + + + +Kaufman, et al. Expires August 27, 2006 [Page 91] + +Internet-Draft IKEv2bis February 2006 + + + o Pad Length is the length of the Padding field. The sender SHOULD + set the Pad Length to the minimum value that makes the combination + of the Payloads, the Padding, and the Pad Length a multiple of the + block size, but the recipient MUST accept any length that results + in proper alignment. This field is encrypted with the negotiated + cipher. + + o Integrity Checksum Data is the cryptographic checksum of the + entire message starting with the Fixed IKE Header through the Pad + Length. The checksum MUST be computed over the encrypted message. + Its length is determined by the integrity algorithm negotiated. + +3.15. Configuration Payload + + The Configuration payload, denoted CP in this document, is used to + exchange configuration information between IKE peers. The exchange + is for an IRAC to request an internal IP address from an IRAS and to + exchange other information of the sort that one would acquire with + Dynamic Host Configuration Protocol (DHCP) if the IRAC were directly + connected to a LAN. + + Configuration payloads are of type CFG_REQUEST/CFG_REPLY or CFG_SET/ + CFG_ACK (see CFG Type in the payload description below). CFG_REQUEST + and CFG_SET payloads may optionally be added to any IKE request. The + IKE response MUST include either a corresponding CFG_REPLY or CFG_ACK + or a Notify payload with an error type indicating why the request + could not be honored. An exception is that a minimal implementation + MAY ignore all CFG_REQUEST and CFG_SET payloads, so a response + message without a corresponding CFG_REPLY or CFG_ACK MUST be accepted + as an indication that the request was not supported. + + "CFG_REQUEST/CFG_REPLY" allows an IKE endpoint to request information + from its peer. If an attribute in the CFG_REQUEST Configuration + Payload is not zero-length, it is taken as a suggestion for that + attribute. The CFG_REPLY Configuration Payload MAY return that + value, or a new one. It MAY also add new attributes and not include + some requested ones. Requestors MUST ignore returned attributes that + they do not recognize. + + Some attributes MAY be multi-valued, in which case multiple attribute + values of the same type are sent and/or returned. Generally, all + values of an attribute are returned when the attribute is requested. + For some attributes (in this version of the specification only + internal addresses), multiple requests indicates a request that + multiple values be assigned. For these attributes, the number of + values returned SHOULD NOT exceed the number requested. + + If the data type requested in a CFG_REQUEST is not recognized or not + + + +Kaufman, et al. Expires August 27, 2006 [Page 92] + +Internet-Draft IKEv2bis February 2006 + + + supported, the responder MUST NOT return an error type but rather + MUST either send a CFG_REPLY that MAY be empty or a reply not + containing a CFG_REPLY payload at all. Error returns are reserved + for cases where the request is recognized but cannot be performed as + requested or the request is badly formatted. + + "CFG_SET/CFG_ACK" allows an IKE endpoint to push configuration data + to its peer. In this case, the CFG_SET Configuration Payload + contains attributes the initiator wants its peer to alter. The + responder MUST return a Configuration Payload if it accepted any of + the configuration data and it MUST contain the attributes that the + responder accepted with zero-length data. Those attributes that it + did not accept MUST NOT be in the CFG_ACK Configuration Payload. If + no attributes were accepted, the responder MUST return either an + empty CFG_ACK payload or a response message without a CFG_ACK + payload. There are currently no defined uses for the CFG_SET/CFG_ACK + exchange, though they may be used in connection with extensions based + on Vendor IDs. An minimal implementation of this specification MAY + ignore CFG_SET payloads. + + {{ Demoted the SHOULD }} Extensions via the CP payload should not be + used for general purpose management. Its main intent is to provide a + bootstrap mechanism to exchange information within IPsec from IRAS to + IRAC. While it MAY be useful to use such a method to exchange + information between some Security Gateways (SGW) or small networks, + existing management protocols such as DHCP [DHCP], RADIUS [RADIUS], + SNMP, or LDAP [LDAP] should be preferred for enterprise management as + well as subsequent information exchanges. + + The Configuration Payload is defined as follows: + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! CFG Type ! RESERVED ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ Configuration Attributes ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 22: Configuration Payload Format + + The payload type for the Configuration Payload is forty seven (47). + + + + + +Kaufman, et al. Expires August 27, 2006 [Page 93] + +Internet-Draft IKEv2bis February 2006 + + + o CFG Type (1 octet) - The type of exchange represented by the + Configuration Attributes. + + CFG Type Value + -------------------------- + RESERVED 0 + CFG_REQUEST 1 + CFG_REPLY 2 + CFG_SET 3 + CFG_ACK 4 + RESERVED TO IANA 5-127 + PRIVATE USE 128-255 + + o RESERVED (3 octets) - MUST be sent as zero; MUST be ignored on + receipt. + + o Configuration Attributes (variable length) - These are type length + values specific to the Configuration Payload and are defined + below. There may be zero or more Configuration Attributes in this + payload. + +3.15.1. Configuration Attributes + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + !R| Attribute Type ! Length | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + ~ Value ~ + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 23: Configuration Attribute Format + + o Reserved (1 bit) - This bit MUST be set to zero and MUST be + ignored on receipt. + + o Attribute Type (15 bits) - A unique identifier for each of the + Configuration Attribute Types. + + o Length (2 octets) - Length in octets of Value. + + o Value (0 or more octets) - The variable-length value of this + Configuration Attribute. The following attribute types have been + defined: + + + + + +Kaufman, et al. Expires August 27, 2006 [Page 94] + +Internet-Draft IKEv2bis February 2006 + + + Multi- + Attribute Type Value Valued Length + ------------------------------------------------------- + RESERVED 0 + INTERNAL_IP4_ADDRESS 1 YES* 0 or 4 octets + INTERNAL_IP4_NETMASK 2 NO 0 or 4 octets + INTERNAL_IP4_DNS 3 YES 0 or 4 octets + INTERNAL_IP4_NBNS 4 YES 0 or 4 octets + INTERNAL_ADDRESS_EXPIRY 5 NO 0 or 4 octets + INTERNAL_IP4_DHCP 6 YES 0 or 4 octets + APPLICATION_VERSION 7 NO 0 or more + INTERNAL_IP6_ADDRESS 8 YES* 0 or 17 octets + RESERVED 9 + INTERNAL_IP6_DNS 10 YES 0 or 16 octets + INTERNAL_IP6_NBNS 11 YES 0 or 16 octets + INTERNAL_IP6_DHCP 12 YES 0 or 16 octets + INTERNAL_IP4_SUBNET 13 YES 0 or 8 octets + SUPPORTED_ATTRIBUTES 14 NO Multiple of 2 + INTERNAL_IP6_SUBNET 15 YES 17 octets + RESERVED TO IANA 16-16383 + PRIVATE USE 16384-32767 + + * These attributes may be multi-valued on return only if + multiple values were requested. + + o INTERNAL_IP4_ADDRESS, INTERNAL_IP6_ADDRESS - An address on the + internal network, sometimes called a red node address or private + address and MAY be a private address on the Internet. {{ + Clarif-6.2}} In a request message, the address specified is a + requested address (or a zero-length address if no specific address + is requested). If a specific address is requested, it likely + indicates that a previous connection existed with this address and + the requestor would like to reuse that address. With IPv6, a + requestor MAY supply the low-order address bytes it wants to use. + Multiple internal addresses MAY be requested by requesting + multiple internal address attributes. The responder MAY only send + up to the number of addresses requested. The INTERNAL_IP6_ADDRESS + is made up of two fields: the first is a 16-octet IPv6 address, + and the second is a one-octet prefix-length as defined in + [ADDRIPV6]. + + The requested address is valid until the expiry time defined with + the INTERNAL_ADDRESS_EXPIRY attribute or there are no IKE_SAs + between the peers. + + o INTERNAL_IP4_NETMASK - The internal network's netmask. Only one + netmask is allowed in the request and reply messages (e.g., + 255.255.255.0), and it MUST be used only with an + + + +Kaufman, et al. Expires August 27, 2006 [Page 95] + +Internet-Draft IKEv2bis February 2006 + + + INTERNAL_IP4_ADDRESS attribute. {{ Clarif-6.4 }} + INTERNAL_IP4_NETMASK in a CFG_REPLY means roughly the same thing + as INTERNAL_IP4_SUBNET containing the same information ("send + traffic to these addresses through me"), but also implies a link + boundary. For instance, the client could use its own address and + the netmask to calculate the broadcast address of the link. An + empty INTERNAL_IP4_NETMASK attribute can be included in a + CFG_REQUEST to request this information (although the gateway can + send the information even when not requested). Non-empty values + for this attribute in a CFG_REQUEST do not make sense and thus + MUST NOT be included. + + o INTERNAL_IP4_DNS, INTERNAL_IP6_DNS - Specifies an address of a DNS + server within the network. Multiple DNS servers MAY be requested. + The responder MAY respond with zero or more DNS server attributes. + + o INTERNAL_IP4_NBNS, INTERNAL_IP6_NBNS - Specifies an address of a + NetBios Name Server (WINS) within the network. Multiple NBNS + servers MAY be requested. The responder MAY respond with zero or + more NBNS server attributes. {{ Clarif-6.6 }} NetBIOS is not + defined for IPv6; therefore, INTERNAL_IP6_NBNS SHOULD NOT be used. + + o INTERNAL_ADDRESS_EXPIRY - Specifies the number of seconds that the + host can use the internal IP address. The host MUST renew the IP + address before this expiry time. Only one of these attributes MAY + be present in the reply. {{ Clarif-6.7 }} Expiry times and + explicit renewals are primarily useful in environments like DHCP, + where the server cannot reliably know when the client has gone + away. However, in IKEv2, this is known, and the gateway can + simply free the address when the IKE_SA is deleted. Further, + supporting renewals is not mandatory. Thus + INTERNAL_ADDRESS_EXPIRY attribute MUST NOT be used. + + o INTERNAL_IP4_DHCP, INTERNAL_IP6_DHCP - Instructs the host to send + any internal DHCP requests to the address contained within the + attribute. Multiple DHCP servers MAY be requested. The responder + MAY respond with zero or more DHCP server attributes. + + o APPLICATION_VERSION - The version or application information of + the IPsec host. This is a string of printable ASCII characters + that is NOT null terminated. + + o INTERNAL_IP4_SUBNET - The protected sub-networks that this edge- + device protects. This attribute is made up of two fields: the + first being an IP address and the second being a netmask. + Multiple sub-networks MAY be requested. The responder MAY respond + with zero or more sub-network attributes. + + + + +Kaufman, et al. Expires August 27, 2006 [Page 96] + +Internet-Draft IKEv2bis February 2006 + + + o SUPPORTED_ATTRIBUTES - When used within a Request, this attribute + MUST be zero-length and specifies a query to the responder to + reply back with all of the attributes that it supports. The + response contains an attribute that contains a set of attribute + identifiers each in 2 octets. The length divided by 2 (octets) + would state the number of supported attributes contained in the + response. + + o INTERNAL_IP6_SUBNET - The protected sub-networks that this edge- + device protects. This attribute is made up of two fields: the + first is a 16-octet IPv6 address, and the second is a one-octet + prefix-length as defined in [ADDRIPV6]. Multiple sub-networks MAY + be requested. The responder MAY respond with zero or more sub- + network attributes. + + Note that no recommendations are made in this document as to how an + implementation actually figures out what information to send in a + reply. That is, we do not recommend any specific method of an IRAS + determining which DNS server should be returned to a requesting IRAC. + +3.15.2. Meaning of INTERNAL_IP4_SUBNET/INTERNAL_IP6_SUBNET + + {{ Section added based on Clarif-6.3 }} + + INTERNAL_IP4/6_SUBNET attributes can indicate additional subnets, + ones that need one or more separate SAs, that can be reached through + the gateway that announces the attributes. INTERNAL_IP4/6_SUBNET + attributes may also express the gateway's policy about what traffic + should be sent through the gateway; the client can choose whether + other traffic (covered by TSr, but not in INTERNAL_IP4/6_SUBNET) is + sent through the gateway or directly to the destination. Thus, + traffic to the addresses listed in the INTERNAL_IP4/6_SUBNET + attributes should be sent through the gateway that announces the + attributes. If there are no existing IPsec SAs whose traffic + selectors cover the address in question, new SAs need to be created. + + For instance, if there are two subnets, 192.0.1.0/26 and + 192.0.2.0/24, and the client's request contains the following: + + CP(CFG_REQUEST) = + INTERNAL_IP4_ADDRESS() + TSi = (0, 0-65535, 0.0.0.0-255.255.255.255) + TSr = (0, 0-65535, 0.0.0.0-255.255.255.255) + + then a valid response could be the following (in which TSr and + INTERNAL_IP4_SUBNET contain the same information): + + + + + +Kaufman, et al. Expires August 27, 2006 [Page 97] + +Internet-Draft IKEv2bis February 2006 + + + CP(CFG_REPLY) = + INTERNAL_IP4_ADDRESS(192.0.1.234) + INTERNAL_IP4_SUBNET(192.0.1.0/255.255.255.192) + INTERNAL_IP4_SUBNET(192.0.2.0/255.255.255.0) + TSi = (0, 0-65535, 192.0.1.234-192.0.1.234) + TSr = ((0, 0-65535, 192.0.1.0-192.0.1.63), + (0, 0-65535, 192.0.2.0-192.0.2.255)) + + In these cases, the INTERNAL_IP4_SUBNET does not really carry any + useful information. + + A different possible reply would have been this: + + CP(CFG_REPLY) = + INTERNAL_IP4_ADDRESS(192.0.1.234) + INTERNAL_IP4_SUBNET(192.0.1.0/255.255.255.192) + INTERNAL_IP4_SUBNET(192.0.2.0/255.255.255.0) + TSi = (0, 0-65535, 192.0.1.234-192.0.1.234) + TSr = (0, 0-65535, 0.0.0.0-255.255.255.255) + + That reply would mean that the client can send all its traffic + through the gateway, but the gateway does not mind if the client + sends traffic not included by INTERNAL_IP4_SUBNET directly to the + destination (without going through the gateway). + + A different situation arises if the gateway has a policy that + requires the traffic for the two subnets to be carried in separate + SAs. Then a response like this would indicate to the client that if + it wants access to the second subnet, it needs to create a separate + SA: + + CP(CFG_REPLY) = + INTERNAL_IP4_ADDRESS(192.0.1.234) + INTERNAL_IP4_SUBNET(192.0.1.0/255.255.255.192) + INTERNAL_IP4_SUBNET(192.0.2.0/255.255.255.0) + TSi = (0, 0-65535, 192.0.1.234-192.0.1.234) + TSr = (0, 0-65535, 192.0.1.0-192.0.1.63) + + INTERNAL_IP4_SUBNET can also be useful if the client's TSr included + only part of the address space. For instance, if the client requests + the following: + + CP(CFG_REQUEST) = + INTERNAL_IP4_ADDRESS() + TSi = (0, 0-65535, 0.0.0.0-255.255.255.255) + TSr = (0, 0-65535, 192.0.2.155-192.0.2.155) + + then the gateway's reply might be: + + + +Kaufman, et al. Expires August 27, 2006 [Page 98] + +Internet-Draft IKEv2bis February 2006 + + + CP(CFG_REPLY) = + INTERNAL_IP4_ADDRESS(192.0.1.234) + INTERNAL_IP4_SUBNET(192.0.1.0/255.255.255.192) + INTERNAL_IP4_SUBNET(192.0.2.0/255.255.255.0) + TSi = (0, 0-65535, 192.0.1.234-192.0.1.234) + TSr = (0, 0-65535, 192.0.2.155-192.0.2.155) + + Because the meaning of INTERNAL_IP4_SUBNET/INTERNAL_IP6_SUBNET is in + CFG_REQUESTs is unclear, they cannot be used reliably in + CFG_REQUESTs. + +3.15.3. Configuration payloads for IPv6 + + {{ Added this section from Clarif-6.5 }} + + The configuration payloads for IPv6 are based on the corresponding + IPv4 payloads, and do not fully follow the "normal IPv6 way of doing + things". In particular, IPv6 stateless autoconfiguration or router + advertisement messages are not used; neither is neighbor discovery. + + A client can be assigned an IPv6 address using the + INTERNAL_IP6_ADDRESS configuration payload. A minimal exchange might + look like this: + + CP(CFG_REQUEST) = + INTERNAL_IP6_ADDRESS() + INTERNAL_IP6_DNS() + TSi = (0, 0-65535, :: - FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF) + TSr = (0, 0-65535, :: - FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF) + + CP(CFG_REPLY) = + INTERNAL_IP6_ADDRESS(2001:DB8:0:1:2:3:4:5/64) + INTERNAL_IP6_DNS(2001:DB8:99:88:77:66:55:44) + TSi = (0, 0-65535, 2001:DB8:0:1:2:3:4:5 - 2001:DB8:0:1:2:3:4:5) + TSr = (0, 0-65535, :: - FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF) + + The client MAY send a non-empty INTERNAL_IP6_ADDRESS attribute in the + CFG_REQUEST to request a specific address or interface identifier. + The gateway first checks if the specified address is acceptable, and + if it is, returns that one. If the address was not acceptable, the + gateway attempts to use the interface identifier with some other + prefix; if even that fails, the gateway selects another interface + identifier. + + The INTERNAL_IP6_ADDRESS attribute also contains a prefix length + field. When used in a CFG_REPLY, this corresponds to the + INTERNAL_IP4_NETMASK attribute in the IPv4 case. + + + + +Kaufman, et al. Expires August 27, 2006 [Page 99] + +Internet-Draft IKEv2bis February 2006 + + + Although this approach to configuring IPv6 addresses is reasonably + simple, it has some limitations. IPsec tunnels configured using + IKEv2 are not fully-featured "interfaces" in the IPv6 addressing + architecture sense [IPV6ADDR]. In particular, they do not + necessarily have link-local addresses, and this may complicate the + use of protocols that assume them, such as [MLDV2]. + +3.15.4. Address Assignment Failures + + {{ Added this section from Clarif-6.8 }} + + If the responder encounters an error while attempting to assign an IP + address to the initiator, it responds with an + INTERNAL_ADDRESS_FAILURE notification. However, there are some more + complex error cases. + + If the responder does not support configuration payloads at all, it + can simply ignore all configuration payloads. This type of + implementation never sends INTERNAL_ADDRESS_FAILURE notifications. + If the initiator requires the assignment of an IP address, it will + treat a response without CFG_REPLY as an error. + + The initiator may request a particular type of address (IPv4 or IPv6) + that the responder does not support, even though the responder + supports configuration payloads. In this case, the responder simply + ignores the type of address it does not support and processes the + rest of the request as usual. + + If the initiator requests multiple addresses of a type that the + responder supports, and some (but not all) of the requests fail, the + responder replies with the successful addresses only. The responder + sends INTERNAL_ADDRESS_FAILURE only if no addresses can be assigned. + +3.16. Extensible Authentication Protocol (EAP) Payload + + The Extensible Authentication Protocol Payload, denoted EAP in this + memo, allows IKE_SAs to be authenticated using the protocol defined + in RFC 3748 [EAP] and subsequent extensions to that protocol. The + full set of acceptable values for the payload is defined elsewhere, + but a short summary of RFC 3748 is included here to make this + document stand alone in the common cases. + + + + + + + + + + +Kaufman, et al. Expires August 27, 2006 [Page 100] + +Internet-Draft IKEv2bis February 2006 + + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ EAP Message ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 24: EAP Payload Format + + The payload type for an EAP Payload is forty eight (48). + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Code ! Identifier ! Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Type ! Type_Data... + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- + + Figure 25: EAP Message Format + + o Code (1 octet) indicates whether this message is a Request (1), + Response (2), Success (3), or Failure (4). + + o Identifier (1 octet) is used in PPP to distinguish replayed + messages from repeated ones. Since in IKE, EAP runs over a + reliable protocol, it serves no function here. In a response + message, this octet MUST be set to match the identifier in the + corresponding request. In other messages, this field MAY be set + to any value. + + o Length (2 octets) is the length of the EAP message and MUST be + four less than the Payload Length of the encapsulating payload. + + o Type (1 octet) is present only if the Code field is Request (1) or + Response (2). For other codes, the EAP message length MUST be + four octets and the Type and Type_Data fields MUST NOT be present. + In a Request (1) message, Type indicates the data being requested. + In a Response (2) message, Type MUST either be Nak or match the + type of the data requested. The following types are defined in + RFC 3748: + + + + + + + +Kaufman, et al. Expires August 27, 2006 [Page 101] + +Internet-Draft IKEv2bis February 2006 + + + 1 Identity + 2 Notification + 3 Nak (Response Only) + 4 MD5-Challenge + 5 One-Time Password (OTP) + 6 Generic Token Card + + o Type_Data (Variable Length) varies with the Type of Request and + the associated Response. For the documentation of the EAP + methods, see [EAP]. + + {{ Demoted the SHOULD NOT and SHOULD }} Note that since IKE passes an + indication of initiator identity in message 3 of the protocol, the + responder should not send EAP Identity requests. The initiator may, + however, respond to such requests if it receives them. + + +4. Conformance Requirements + + In order to assure that all implementations of IKEv2 can + interoperate, there are "MUST support" requirements in addition to + those listed elsewhere. Of course, IKEv2 is a security protocol, and + one of its major functions is to allow only authorized parties to + successfully complete establishment of SAs. So a particular + implementation may be configured with any of a number of restrictions + concerning algorithms and trusted authorities that will prevent + universal interoperability. + + IKEv2 is designed to permit minimal implementations that can + interoperate with all compliant implementations. There are a series + of optional features that can easily be ignored by a particular + implementation if it does not support that feature. Those features + include: + + o Ability to negotiate SAs through a NAT and tunnel the resulting + ESP SA over UDP. + + o Ability to request (and respond to a request for) a temporary IP + address on the remote end of a tunnel. + + o Ability to support various types of legacy authentication. + + o Ability to support window sizes greater than one. + + o Ability to establish multiple ESP and/or AH SAs within a single + IKE_SA. + + + + + +Kaufman, et al. Expires August 27, 2006 [Page 102] + +Internet-Draft IKEv2bis February 2006 + + + o Ability to rekey SAs. + + To assure interoperability, all implementations MUST be capable of + parsing all payload types (if only to skip over them) and to ignore + payload types that it does not support unless the critical bit is set + in the payload header. If the critical bit is set in an unsupported + payload header, all implementations MUST reject the messages + containing those payloads. + + Every implementation MUST be capable of doing four-message + IKE_SA_INIT and IKE_AUTH exchanges establishing two SAs (one for IKE, + one for ESP and/or AH). Implementations MAY be initiate-only or + respond-only if appropriate for their platform. Every implementation + MUST be capable of responding to an INFORMATIONAL exchange, but a + minimal implementation MAY respond to any INFORMATIONAL message with + an empty INFORMATIONAL reply (note that within the context of an + IKE_SA, an "empty" message consists of an IKE header followed by an + Encrypted payload with no payloads contained in it). A minimal + implementation MAY support the CREATE_CHILD_SA exchange only in so + far as to recognize requests and reject them with a Notify payload of + type NO_ADDITIONAL_SAS. A minimal implementation need not be able to + initiate CREATE_CHILD_SA or INFORMATIONAL exchanges. When an SA + expires (based on locally configured values of either lifetime or + octets passed), and implementation MAY either try to renew it with a + CREATE_CHILD_SA exchange or it MAY delete (close) the old SA and + create a new one. If the responder rejects the CREATE_CHILD_SA + request with a NO_ADDITIONAL_SAS notification, the implementation + MUST be capable of instead deleting the old SA and creating a new + one. + + Implementations are not required to support requesting temporary IP + addresses or responding to such requests. If an implementation does + support issuing such requests, it MUST include a CP payload in + message 3 containing at least a field of type INTERNAL_IP4_ADDRESS or + INTERNAL_IP6_ADDRESS. All other fields are optional. If an + implementation supports responding to such requests, it MUST parse + the CP payload of type CFG_REQUEST in message 3 and recognize a field + of type INTERNAL_IP4_ADDRESS or INTERNAL_IP6_ADDRESS. If it supports + leasing an address of the appropriate type, it MUST return a CP + payload of type CFG_REPLY containing an address of the requested + type. {{ Demoted the SHOULD }} The responder may include any other + related attributes. + + A minimal IPv4 responder implementation will ignore the contents of + the CP payload except to determine that it includes an + INTERNAL_IP4_ADDRESS attribute and will respond with the address and + other related attributes regardless of whether the initiator + requested them. + + + +Kaufman, et al. Expires August 27, 2006 [Page 103] + +Internet-Draft IKEv2bis February 2006 + + + A minimal IPv4 initiator will generate a CP payload containing only + an INTERNAL_IP4_ADDRESS attribute and will parse the response + ignoring attributes it does not know how to use. {{ Clarif-6.7 + removes the sentence about processing INTERNAL_ADDRESS_EXPIRY. }} + Minimal initiators need not be able to request lease renewals and + minimal responders need not respond to them. + + For an implementation to be called conforming to this specification, + it MUST be possible to configure it to accept the following: + + o PKIX Certificates containing and signed by RSA keys of size 1024 + or 2048 bits, where the ID passed is any of ID_KEY_ID, ID_FQDN, + ID_RFC822_ADDR, or ID_DER_ASN1_DN. + + o Shared key authentication where the ID passes is any of ID_KEY_ID, + ID_FQDN, or ID_RFC822_ADDR. + + o Authentication where the responder is authenticated using PKIX + Certificates and the initiator is authenticated using shared key + authentication. + + +5. Security Considerations + + While this protocol is designed to minimize disclosure of + configuration information to unauthenticated peers, some such + disclosure is unavoidable. One peer or the other must identify + itself first and prove its identity first. To avoid probing, the + initiator of an exchange is required to identify itself first, and + usually is required to authenticate itself first. The initiator can, + however, learn that the responder supports IKE and what cryptographic + protocols it supports. The responder (or someone impersonating the + responder) can probe the initiator not only for its identity, but + using CERTREQ payloads may be able to determine what certificates the + initiator is willing to use. + + Use of EAP authentication changes the probing possibilities somewhat. + When EAP authentication is used, the responder proves its identity + before the initiator does, so an initiator that knew the name of a + valid initiator could probe the responder for both its name and + certificates. + + Repeated rekeying using CREATE_CHILD_SA without additional Diffie- + Hellman exchanges leaves all SAs vulnerable to cryptanalysis of a + single key or overrun of either endpoint. Implementers should take + note of this fact and set a limit on CREATE_CHILD_SA exchanges + between exponentiations. This memo does not prescribe such a limit. + + + + +Kaufman, et al. Expires August 27, 2006 [Page 104] + +Internet-Draft IKEv2bis February 2006 + + + The strength of a key derived from a Diffie-Hellman exchange using + any of the groups defined here depends on the inherent strength of + the group, the size of the exponent used, and the entropy provided by + the random number generator used. Due to these inputs, it is + difficult to determine the strength of a key for any of the defined + groups. Diffie-Hellman group number two, when used with a strong + random number generator and an exponent no less than 200 bits, is + common for use with 3DES. Group five provides greater security than + group two. Group one is for historic purposes only and does not + provide sufficient strength except for use with DES, which is also + for historic use only. Implementations should make note of these + estimates when establishing policy and negotiating security + parameters. + + Note that these limitations are on the Diffie-Hellman groups + themselves. There is nothing in IKE that prohibits using stronger + groups nor is there anything that will dilute the strength obtained + from stronger groups (limited by the strength of the other algorithms + negotiated including the prf function). In fact, the extensible + framework of IKE encourages the definition of more groups; use of + elliptical curve groups may greatly increase strength using much + smaller numbers. + + It is assumed that all Diffie-Hellman exponents are erased from + memory after use. In particular, these exponents MUST NOT be derived + from long-lived secrets like the seed to a pseudo-random generator + that is not erased after use. + + The strength of all keys is limited by the size of the output of the + negotiated prf function. For this reason, a prf function whose + output is less than 128 bits (e.g., 3DES-CBC) MUST NOT be used with + this protocol. + + The security of this protocol is critically dependent on the + randomness of the randomly chosen parameters. These should be + generated by a strong random or properly seeded pseudo-random source + (see [RANDOMNESS]). Implementers should take care to ensure that use + of random numbers for both keys and nonces is engineered in a fashion + that does not undermine the security of the keys. + + For information on the rationale of many of the cryptographic design + choices in this protocol, see [SIGMA] and [SKEME]. Though the + security of negotiated CHILD_SAs does not depend on the strength of + the encryption and integrity protection negotiated in the IKE_SA, + implementations MUST NOT negotiate NONE as the IKE integrity + protection algorithm or ENCR_NULL as the IKE encryption algorithm. + + When using pre-shared keys, a critical consideration is how to assure + + + +Kaufman, et al. Expires August 27, 2006 [Page 105] + +Internet-Draft IKEv2bis February 2006 + + + the randomness of these secrets. The strongest practice is to ensure + that any pre-shared key contain as much randomness as the strongest + key being negotiated. Deriving a shared secret from a password, + name, or other low-entropy source is not secure. These sources are + subject to dictionary and social engineering attacks, among others. + + The NAT_DETECTION_*_IP notifications contain a hash of the addresses + and ports in an attempt to hide internal IP addresses behind a NAT. + Since the IPv4 address space is only 32 bits, and it is usually very + sparse, it would be possible for an attacker to find out the internal + address used behind the NAT box by trying all possible IP addresses + and trying to find the matching hash. The port numbers are normally + fixed to 500, and the SPIs can be extracted from the packet. This + reduces the number of hash calculations to 2^32. With an educated + guess of the use of private address space, the number of hash + calculations is much smaller. Designers should therefore not assume + that use of IKE will not leak internal address information. + + When using an EAP authentication method that does not generate a + shared key for protecting a subsequent AUTH payload, certain man-in- + the-middle and server impersonation attacks are possible [EAPMITM]. + These vulnerabilities occur when EAP is also used in protocols that + are not protected with a secure tunnel. Since EAP is a general- + purpose authentication protocol, which is often used to provide + single-signon facilities, a deployed IPsec solution that relies on an + EAP authentication method that does not generate a shared key (also + known as a non-key-generating EAP method) can become compromised due + to the deployment of an entirely unrelated application that also + happens to use the same non-key-generating EAP method, but in an + unprotected fashion. Note that this vulnerability is not limited to + just EAP, but can occur in other scenarios where an authentication + infrastructure is reused. For example, if the EAP mechanism used by + IKEv2 utilizes a token authenticator, a man-in-the-middle attacker + could impersonate the web server, intercept the token authentication + exchange, and use it to initiate an IKEv2 connection. For this + reason, use of non-key-generating EAP methods SHOULD be avoided where + possible. Where they are used, it is extremely important that all + usages of these EAP methods SHOULD utilize a protected tunnel, where + the initiator validates the responder's certificate before initiating + the EAP exchange. {{ Demoted the SHOULD }} Implementers should + describe the vulnerabilities of using non-key-generating EAP methods + in the documentation of their implementations so that the + administrators deploying IPsec solutions are aware of these dangers. + + An implementation using EAP MUST also use a public-key-based + authentication of the server to the client before the EAP exchange + begins, even if the EAP method offers mutual authentication. This + avoids having additional IKEv2 protocol variations and protects the + + + +Kaufman, et al. Expires August 27, 2006 [Page 106] + +Internet-Draft IKEv2bis February 2006 + + + EAP data from active attackers. + + If the messages of IKEv2 are long enough that IP-level fragmentation + is necessary, it is possible that attackers could prevent the + exchange from completing by exhausting the reassembly buffers. The + chances of this can be minimized by using the Hash and URL encodings + instead of sending certificates (see Section 3.6). Additional + mitigations are discussed in [DOSUDPPROT]. + +5.1. Traffic selector authorization + + {{ Added this section from Clarif-4.13 }} + + IKEv2 relies on information in the Peer Authorization Database (PAD) + when determining what kind of IPsec SAs a peer is allowed to create. + This process is described in [IPSECARCH] Section 4.4.3. When a peer + requests the creation of an IPsec SA with some traffic selectors, the + PAD must contain "Child SA Authorization Data" linking the identity + authenticated by IKEv2 and the addresses permitted for traffic + selectors. + + For example, the PAD might be configured so that authenticated + identity "sgw23.example.com" is allowed to create IPsec SAs for + 192.0.2.0/24, meaning this security gateway is a valid + "representative" for these addresses. Host-to-host IPsec requires + similar entries, linking, for example, "fooserver4.example.com" with + 192.0.1.66/32, meaning this identity a valid "owner" or + "representative" of the address in question. + + As noted in [IPSECARCH], "It is necessary to impose these constraints + on creation of child SAs to prevent an authenticated peer from + spoofing IDs associated with other, legitimate peers." In the + example given above, a correct configuration of the PAD prevents + sgw23 from creating IPsec SAs with address 192.0.1.66, and prevents + fooserver4 from creating IPsec SAs with addresses from 192.0.2.0/24. + + It is important to note that simply sending IKEv2 packets using some + particular address does not imply a permission to create IPsec SAs + with that address in the traffic selectors. For example, even if + sgw23 would be able to spoof its IP address as 192.0.1.66, it could + not create IPsec SAs matching fooserver4's traffic. + + The IKEv2 specification does not specify how exactly IP address + assignment using configuration payloads interacts with the PAD. Our + interpretation is that when a security gateway assigns an address + using configuration payloads, it also creates a temporary PAD entry + linking the authenticated peer identity and the newly allocated inner + address. + + + +Kaufman, et al. Expires August 27, 2006 [Page 107] + +Internet-Draft IKEv2bis February 2006 + + + It has been recognized that configuring the PAD correctly may be + difficult in some environments. For instance, if IPsec is used + between a pair of hosts whose addresses are allocated dynamically + using DHCP, it is extremely difficult to ensure that the PAD + specifies the correct "owner" for each IP address. This would + require a mechanism to securely convey address assignments from the + DHCP server, and link them to identities authenticated using IKEv2. + + Due to this limitation, some vendors have been known to configure + their PADs to allow an authenticated peer to create IPsec SAs with + traffic selectors containing the same address that was used for the + IKEv2 packets. In environments where IP spoofing is possible (i.e., + almost everywhere) this essentially allows any peer to create IPsec + SAs with any traffic selectors. This is not an appropriate or secure + configuration in most circumstances. See [H2HIPSEC] for an extensive + discussion about this issue, and the limitations of host-to-host + IPsec in general. + + +6. IANA Considerations + + {{ This section was changed to not re-define any new IANA registries. + }} + + [IKEV2] defined many field types and values. IANA has already + registered those types and values, so the are not listed here again. + No new types or values are registered in this document. + + +7. Acknowledgements + + The acknowledgements from the IKEv2 document were: + + This document is a collaborative effort of the entire IPsec WG. If + there were no limit to the number of authors that could appear on an + RFC, the following, in alphabetical order, would have been listed: + Bill Aiello, Stephane Beaulieu, Steve Bellovin, Sara Bitan, Matt + Blaze, Ran Canetti, Darren Dukes, Dan Harkins, Paul Hoffman, John + Ioannidis, Charlie Kaufman, Steve Kent, Angelos Keromytis, Tero + Kivinen, Hugo Krawczyk, Andrew Krywaniuk, Radia Perlman, Omer + Reingold, and Michael Richardson. Many other people contributed to + the design. It is an evolution of IKEv1, ISAKMP, and the IPsec DOI, + each of which has its own list of authors. Hugh Daniel suggested the + feature of having the initiator, in message 3, specify a name for the + responder, and gave the feature the cute name "You Tarzan, Me Jane". + David Faucher and Valery Smyzlov helped refine the design of the + traffic selector negotiation. + + + + +Kaufman, et al. Expires August 27, 2006 [Page 108] + +Internet-Draft IKEv2bis February 2006 + + + This paragraph lists references that appear only in figures. The + section is only here to keep the 'xml2rfc' program happy, and will be + removed when the document is published. Feel free to ignore it. + [DES] [IDEA] [MD5] [X.501] [X.509] + + +8. References + +8.1. Normative References + + [ADDGROUP] + Kivinen, T. and M. Kojo, "More Modular Exponential (MODP) + Diffie-Hellman groups for Internet Key Exchange (IKE)", + RFC 3526, May 2003. + + [ADDRIPV6] + Hinden, R. and S. Deering, "Internet Protocol Version 6 + (IPv6) Addressing Architecture", RFC 3513, April 2003. + + [Clarif] "IKEv2 Clarifications and Implementation Guidelines", + draft-eronen-ipsec-ikev2-clarifications (work in + progress). + + [EAP] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. + Levkowetz, "Extensible Authentication Protocol (EAP)", + RFC 3748, June 2004. + + [ECN] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition + of Explicit Congestion Notification (ECN) to IP", + RFC 3168, September 2001. + + [ESPCBC] Pereira, R. and R. Adams, "The ESP CBC-Mode Cipher + Algorithms", RFC 2451, November 1998. + + [IANACONS] + Narten, T. and H. Alvestrand, "Guidelines for Writing an + IANA Considerations Section in RFCs", BCP 26, RFC 2434. + + [IKEV2] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", + RFC 4306, December 2005. + + [IPSECARCH] + Kent, S. and K. Seo, "Security Architecture for the + Internet Protocol", RFC 4301, December 2005. + + [MUSTSHOULD] + Bradner, S., "Key Words for use in RFCs to indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + + +Kaufman, et al. Expires August 27, 2006 [Page 109] + +Internet-Draft IKEv2bis February 2006 + + + [PKIX] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet + X.509 Public Key Infrastructure Certificate and + Certificate Revocation List (CRL) Profile", RFC 3280, + April 2002. + + [UDPENCAPS] + Huttunen, A., Swander, B., Volpe, V., DiBurro, L., and M. + Stenberg, "UDP Encapsulation of IPsec ESP Packets", + RFC 3948, January 2005. + +8.2. Informative References + + [AH] Kent, S., "IP Authentication Header", RFC 4302, + December 2005. + + [ARCHGUIDEPHIL] + Bush, R. and D. Meyer, "Some Internet Architectural + Guidelines and Philosophy", RFC 3439, December 2002. + + [ARCHPRINC] + Carpenter, B., "Architectural Principles of the Internet", + RFC 1958, June 1996. + + [DES] American National Standards Institute, "American National + Standard for Information Systems-Data Link Encryption", + ANSI X3.106, 1983. + + [DH] Diffie, W. and M. Hellman, "New Directions in + Cryptography", IEEE Transactions on Information Theory, + V.IT-22 n. 6, June 1977. + + [DHCP] Droms, R., "Dynamic Host Configuration Protocol", + RFC 2131, March 1997. + + [DIFFSERVARCH] + Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z., + and W. Weiss, "An Architecture for Differentiated + Services", RFC 2475. + + [DIFFSERVFIELD] + Nichols, K., Blake, S., Baker, F., and D. Black, + "Definition of the Differentiated Services Field (DS + Field) in the IPv4 and IPv6 Headers", RFC 2474, + December 1998. + + [DIFFTUNNEL] + Black, D., "Differentiated Services and Tunnels", + RFC 2983, October 2000. + + + +Kaufman, et al. Expires August 27, 2006 [Page 110] + +Internet-Draft IKEv2bis February 2006 + + + [DOI] Piper, D., "The Internet IP Security Domain of + Interpretation for ISAKMP", RFC 2407, November 1998. + + [DOSUDPPROT] + C. Kaufman, R. Perlman, and B. Sommerfeld, "DoS protection + for UDP-based protocols", ACM Conference on Computer and + Communications Security , October 2003. + + [DSS] National Institute of Standards and Technology, U.S. + Department of Commerce, "Digital Signature Standard", + FIPS 186, May 1994. + + [EAPMITM] N. Asokan, V. Nierni, and K. Nyberg, "Man-in-the-Middle in + Tunneled Authentication Protocols", November 2002, + <http://eprint.iacr.org/2002/163>. + + [ESP] Kent, S., "IP Encapsulating Security Payload (ESP)", + RFC 4303, December 2005. + + [EXCHANGEANALYSIS] + R. Perlman and C. Kaufman, "Analysis of the IPsec key + exchange Standard", WET-ICE Security Conference, MIT , + 2001, + <http://sec.femto.org/wetice-2001/papers/radia-paper.pdf>. + + [H2HIPSEC] + Aura, T., Roe, M., and A. Mohammed, "Experiences with + Host-to-Host IPsec", 13th International Workshop on + Security Protocols, Cambridge, UK, April 2005. + + [HMAC] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- + Hashing for Message Authentication", RFC 2104, + February 1997. + + [IDEA] X. Lai, "On the Design and Security of Block Ciphers", ETH + Series in Information Processing, v. 1, Konstanz: Hartung- + Gorre Verlag, 1992. + + [IKEV1] Harkins, D. and D. Carrel, "The Internet Key Exchange + (IKE)", RFC 2409, November 1998. + + [IPCOMP] Shacham, A., Monsour, B., Pereira, R., and M. Thomas, "IP + Payload Compression Protocol (IPComp)", RFC 3173, + September 2001. + + [IPSECARCH-OLD] + Kent, S. and R. Atkinson, "Security Architecture for the + Internet Protocol", RFC 2401, November 1998. + + + +Kaufman, et al. Expires August 27, 2006 [Page 111] + +Internet-Draft IKEv2bis February 2006 + + + [IPV6ADDR] + Hinden, R. and S. Deering, "Internet Protocol Version 6 + (IPv6) Addressing Architecture", RFC 3513, April 2003. + + [ISAKMP] Maughan, D., Schneider, M., and M. Schertler, "Internet + Security Association and Key Management Protocol + (ISAKMP)", RFC 2408, November 1998. + + [LDAP] Wahl, M., Howes, T., and S. Kille, "Lightweight Directory + Access Protocol (v3)", RFC 2251, December 1997. + + [MAILFORMAT] + Resnick, P., "Internet Message Format", RFC 2822, + April 2001. + + [MD5] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, + April 1992. + + [MIPV6] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support + in IPv6", RFC 3775, June 2004. + + [MLDV2] Vida, R. and L. Costa, "Multicast Listener Discovery + Version 2 (MLDv2) for IPv6", RFC 3810, June 2004. + + [NAI] Aboba, B. and M. Beadles, "The Network Access Identifier", + RFC 2486, January 1999. + + [NATREQ] Aboba, B. and W. Dixon, "IPsec-Network Address Translation + (NAT) Compatibility Requirements", RFC 3715, March 2004. + + [OAKLEY] Orman, H., "The OAKLEY Key Determination Protocol", + RFC 2412, November 1998. + + [PFKEY] McDonald, D., Metz, C., and B. Phan, "PF_KEY Key + Management API, Version 2", RFC 2367, July 1998. + + [PHOTURIS] + Karn, P. and W. Simpson, "Photuris: Session-Key Management + Protocol", RFC 2522, March 1999. + + [PKCS1] B. Kaliski and J. Staddon, "PKCS #1: RSA Cryptography + Specifications Version 2", September 1998. + + [PRFAES128CBC] + Hoffman, P., "The AES-XCBC-PRF-128 Algorithm for the + Internet Key Exchange Protocol (IKE)", RFC 3664, + January 2004. + + + + +Kaufman, et al. Expires August 27, 2006 [Page 112] + +Internet-Draft IKEv2bis February 2006 + + + [PRFAES128CBC-bis] + Hoffman, P., "The AES-XCBC-PRF-128 Algorithm for the + Internet Key Exchange Protocol (IKE)", + draft-hoffman-rfc3664bis (work in progress), October 2005. + + [RADIUS] Rigney, C., Rubens, A., Simpson, W., and S. Willens, + "Remote Authentication Dial In User Service (RADIUS)", + RFC 2138, April 1997. + + [RANDOMNESS] + Eastlake, D., Schiller, J., and S. Crocker, "Randomness + Requirements for Security", BCP 106, RFC 4086, June 2005. + + [REAUTH] Nir, Y., ""Repeated Authentication in IKEv2", + draft-nir-ikev2-auth-lt (work in progress), May 2005. + + [RSA] R. Rivest, A. Shamir, and L. Adleman, "A Method for + Obtaining Digital Signatures and Public-Key + Cryptosystems", February 1978. + + [SHA] National Institute of Standards and Technology, U.S. + Department of Commerce, "Secure Hash Standard", + FIPS 180-1, May 1994. + + [SIGMA] H. Krawczyk, "SIGMA: the `SIGn-and-MAc' Approach to + Authenticated Diffie-Hellman and its Use in the IKE + Protocols", Advances in Cryptography - CRYPTO 2003 + Proceedings LNCS 2729, 2003, <http:// + www.informatik.uni-trier.de/~ley/db/conf/crypto/ + crypto2003.html>. + + [SKEME] H. Krawczyk, "SKEME: A Versatile Secure Key Exchange + Mechanism for Internet", IEEE Proceedings of the 1996 + Symposium on Network and Distributed Systems Security , + 1996. + + [TRANSPARENCY] + Carpenter, B., "Internet Transparency", RFC 2775, + February 2000. + + [X.501] ITU-T, "Recommendation X.501: Information Technology - + Open Systems Interconnection - The Directory: Models", + 1993. + + [X.509] ITU-T, "Recommendation X.509 (1997 E): Information + Technology - Open Systems Interconnection - The Directory: + Authentication Framework", 1997. + + + + +Kaufman, et al. Expires August 27, 2006 [Page 113] + +Internet-Draft IKEv2bis February 2006 + + +Appendix A. Summary of changes from IKEv1 + + The goals of this revision to IKE are: + + 1. To define the entire IKE protocol in a single document, + replacing RFCs 2407, 2408, and 2409 and incorporating subsequent + changes to support NAT Traversal, Extensible Authentication, and + Remote Address acquisition; + + 2. To simplify IKE by replacing the eight different initial + exchanges with a single four-message exchange (with changes in + authentication mechanisms affecting only a single AUTH payload + rather than restructuring the entire exchange) see + [EXCHANGEANALYSIS]; + + 3. To remove the Domain of Interpretation (DOI), Situation (SIT), + and Labeled Domain Identifier fields, and the Commit and + Authentication only bits; + + 4. To decrease IKE's latency in the common case by making the + initial exchange be 2 round trips (4 messages), and allowing the + ability to piggyback setup of a CHILD_SA on that exchange; + + 5. To replace the cryptographic syntax for protecting the IKE + messages themselves with one based closely on ESP to simplify + implementation and security analysis; + + 6. To reduce the number of possible error states by making the + protocol reliable (all messages are acknowledged) and sequenced. + This allows shortening CREATE_CHILD_SA exchanges from 3 messages + to 2; + + 7. To increase robustness by allowing the responder to not do + significant processing until it receives a message proving that + the initiator can receive messages at its claimed IP address, + and not commit any state to an exchange until the initiator can + be cryptographically authenticated; + + 8. To fix cryptographic weaknesses such as the problem with + symmetries in hashes used for authentication documented by Tero + Kivinen; + + 9. To specify Traffic Selectors in their own payloads type rather + than overloading ID payloads, and making more flexible the + Traffic Selectors that may be specified; + + 10. To specify required behavior under certain error conditions or + when data that is not understood is received in order to make it + + + +Kaufman, et al. Expires August 27, 2006 [Page 114] + +Internet-Draft IKEv2bis February 2006 + + + easier to make future revisions in a way that does not break + backwards compatibility; + + 11. To simplify and clarify how shared state is maintained in the + presence of network failures and Denial of Service attacks; and + + 12. To maintain existing syntax and magic numbers to the extent + possible to make it likely that implementations of IKEv1 can be + enhanced to support IKEv2 with minimum effort. + + +Appendix B. Diffie-Hellman Groups + + There are two Diffie-Hellman groups defined here for use in IKE. + These groups were generated by Richard Schroeppel at the University + of Arizona. Properties of these primes are described in [OAKLEY]. + + The strength supplied by group one may not be sufficient for the + mandatory-to-implement encryption algorithm and is here for historic + reasons. + + Additional Diffie-Hellman groups have been defined in [ADDGROUP]. + +B.1. Group 1 - 768 Bit MODP + + This group is assigned id 1 (one). + + The prime is: 2^768 - 2 ^704 - 1 + 2^64 * { [2^638 pi] + 149686 } + Its hexadecimal value is: + + FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1 + 29024E08 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD + EF9519B3 CD3A431B 302B0A6D F25F1437 4FE1356D 6D51C245 + E485B576 625E7EC6 F44C42E9 A63A3620 FFFFFFFF FFFFFFFF + + The generator is 2. + +B.2. Group 2 - 1024 Bit MODP + + This group is assigned id 2 (two). + + + + + + + + + + + +Kaufman, et al. Expires August 27, 2006 [Page 115] + +Internet-Draft IKEv2bis February 2006 + + + The prime is 2^1024 - 2^960 - 1 + 2^64 * { [2^894 pi] + 129093 }. + Its hexadecimal value is: + + FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1 + 29024E08 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD + EF9519B3 CD3A431B 302B0A6D F25F1437 4FE1356D 6D51C245 + E485B576 625E7EC6 F44C42E9 A637ED6B 0BFF5CB6 F406B7ED + EE386BFB 5A899FA5 AE9F2411 7C4B1FE6 49286651 ECE65381 + FFFFFFFF FFFFFFFF + + The generator is 2. + + +Appendix C. Exchanges and Payloads + + {{ Clarif-AppA }} + + This appendix contains a short summary of the IKEv2 exchanges, and + what payloads can appear in which message. This appendix is purely + informative; if it disagrees with the body of this document, the + other text is considered correct. + + Vendor-ID (V) payloads may be included in any place in any message. + This sequence here shows what are the most logical places for them. + +C.1. IKE_SA_INIT Exchange + + request --> [N(COOKIE)], + SA, KE, Ni, + [N(NAT_DETECTION_SOURCE_IP)+, + N(NAT_DETECTION_DESTINATION_IP)], + [V+] + + normal response <-- SA, KE, Nr, + (no cookie) [N(NAT_DETECTION_SOURCE_IP), + N(NAT_DETECTION_DESTINATION_IP)], + [[N(HTTP_CERT_LOOKUP_SUPPORTED)], CERTREQ+], + [V+] + + + + + + + + + + + + + +Kaufman, et al. Expires August 27, 2006 [Page 116] + +Internet-Draft IKEv2bis February 2006 + + +C.2. IKE_AUTH Exchange without EAP + + request --> IDi, [CERT+], + [N(INITIAL_CONTACT)], + [[N(HTTP_CERT_LOOKUP_SUPPORTED)], CERTREQ+], + [IDr], + AUTH, + [CP(CFG_REQUEST)], + [N(IPCOMP_SUPPORTED)+], + [N(USE_TRANSPORT_MODE)], + [N(ESP_TFC_PADDING_NOT_SUPPORTED)], + [N(NON_FIRST_FRAGMENTS_ALSO)], + SA, TSi, TSr, + [V+] + + response <-- IDr, [CERT+], + AUTH, + [CP(CFG_REPLY)], + [N(IPCOMP_SUPPORTED)], + [N(USE_TRANSPORT_MODE)], + [N(ESP_TFC_PADDING_NOT_SUPPORTED)], + [N(NON_FIRST_FRAGMENTS_ALSO)], + SA, TSi, TSr, + [N(ADDITIONAL_TS_POSSIBLE)], + [V+] + + + + + + + + + + + + + + + + + + + + + + + + + + +Kaufman, et al. Expires August 27, 2006 [Page 117] + +Internet-Draft IKEv2bis February 2006 + + +C.3. IKE_AUTH Exchange with EAP + + first request --> IDi, + [N(INITIAL_CONTACT)], + [[N(HTTP_CERT_LOOKUP_SUPPORTED)], CERTREQ+], + [IDr], + [CP(CFG_REQUEST)], + [N(IPCOMP_SUPPORTED)+], + [N(USE_TRANSPORT_MODE)], + [N(ESP_TFC_PADDING_NOT_SUPPORTED)], + [N(NON_FIRST_FRAGMENTS_ALSO)], + SA, TSi, TSr, + [V+] + + first response <-- IDr, [CERT+], AUTH, + EAP, + [V+] + + / --> EAP + repeat 1..N times | + \ <-- EAP + + last request --> AUTH + + last response <-- AUTH, + [CP(CFG_REPLY)], + [N(IPCOMP_SUPPORTED)], + [N(USE_TRANSPORT_MODE)], + [N(ESP_TFC_PADDING_NOT_SUPPORTED)], + [N(NON_FIRST_FRAGMENTS_ALSO)], + SA, TSi, TSr, + [N(ADDITIONAL_TS_POSSIBLE)], + [V+] + + + + + + + + + + + + + + + + + + +Kaufman, et al. Expires August 27, 2006 [Page 118] + +Internet-Draft IKEv2bis February 2006 + + +C.4. CREATE_CHILD_SA Exchange for Creating or Rekeying CHILD_SAs + + request --> [N(REKEY_SA)], + [N(IPCOMP_SUPPORTED)+], + [N(USE_TRANSPORT_MODE)], + [N(ESP_TFC_PADDING_NOT_SUPPORTED)], + [N(NON_FIRST_FRAGMENTS_ALSO)], + SA, Ni, [KEi], TSi, TSr + + response <-- [N(IPCOMP_SUPPORTED)], + [N(USE_TRANSPORT_MODE)], + [N(ESP_TFC_PADDING_NOT_SUPPORTED)], + [N(NON_FIRST_FRAGMENTS_ALSO)], + SA, Nr, [KEr], TSi, TSr, + [N(ADDITIONAL_TS_POSSIBLE)] + +C.5. CREATE_CHILD_SA Exchange for Rekeying the IKE_SA + + request --> SA, Ni, [KEi] + + response <-- SA, Nr, [KEr] + +C.6. INFORMATIONAL Exchange + + request --> [N+], + [D+], + [CP(CFG_REQUEST)] + + response <-- [N+], + [D+], + [CP(CFG_REPLY)] + + +Appendix D. Changes Between Internet Draft Versions + + This section will be removed before publication as an RFC. + +D.1. Changes from IKEv2 to draft -00 + + There were a zillion additions from the Clarifications document. + These are noted with "{{ Clarif-nn }}". The numbers used in the text + of this version are based on + draft-eronen-ipsec-ikev2-clarifications-08.txt, which has different + numbers than earlier versions of that draft. + + Cleaned up many of the figures. Made the table headings consistent. + Made some tables easier to read by removing blank spaces. Removed + the "reserved to IANA" and "private use" text wording and moved it + + + +Kaufman, et al. Expires August 27, 2006 [Page 119] + +Internet-Draft IKEv2bis February 2006 + + + into the tables. + + Changed many SHOULD requirements to better match RFC 2119. These are + also marked with comments such as "{{ Demoted the SHOULD }}". + + In Section 2.16, changed the MUST requirement of authenticating the + responder from "public key signature based" to "strong" because that + is what most current IKEv2 implementations do, and it better matches + the actual security requirement. + + +Authors' Addresses + + Charlie Kaufman + Microsoft + 1 Microsoft Way + Redmond, WA 98052 + US + + Phone: 1-425-707-3335 + Email: charliek@microsoft.com + + + Paul Hoffman + VPN Consortium + 127 Segre Place + Santa Cruz, CA 95060 + US + + Phone: 1-831-426-9827 + Email: paul.hoffman@vpnc.org + + + Pasi Eronen + Nokia Research Center + P.O. Box 407 + FIN-00045 Nokia Group + Finland + + Email: pasi.eronen@nokia.com + + +Full Copyright Statement + + Copyright (C) The Internet Society (2006). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + + + +Kaufman, et al. Expires August 27, 2006 [Page 120] + +Internet-Draft IKEv2bis February 2006 + + + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET + ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, + INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE + INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at + ietf-ipr@ietf.org. + + +Acknowledgment + + Funding for the RFC Editor function is currently provided by the + Internet Society. + + + + + + + + + + + +Kaufman, et al. Expires August 27, 2006 [Page 121] + diff --git a/src/charon/doc/standards/draft-myers-ikev2-ocsp-03.txt b/src/charon/doc/standards/draft-myers-ikev2-ocsp-03.txt new file mode 100644 index 000000000..fb59fc958 --- /dev/null +++ b/src/charon/doc/standards/draft-myers-ikev2-ocsp-03.txt @@ -0,0 +1,785 @@ + + + +Network Working Group M. Myers +Internet-Draft TraceRoute Security LLC +Expires: January 12, 2007 H. Tschofenig + Siemens + July 11, 2006 + + + OCSP Extensions to IKEv2 + draft-myers-ikev2-ocsp-03.txt + +Status of this Memo + + By submitting this Internet-Draft, each author represents that any + applicable patent or other IPR claims of which he or she is aware + have been or will be disclosed, and any of which he or she becomes + aware will be disclosed, in accordance with Section 6 of BCP 79. + + Internet-Drafts are working documents of the Internet Engineering + Task Force (IETF), its areas, and its working groups. Note that + other groups may also distribute working documents as Internet- + Drafts. + + Internet-Drafts are draft documents valid for a maximum of six months + and may be updated, replaced, or obsoleted by other documents at any + time. It is inappropriate to use Internet-Drafts as reference + material or to cite them other than as "work in progress." + + The list of current Internet-Drafts can be accessed at + http://www.ietf.org/ietf/1id-abstracts.txt. + + The list of Internet-Draft Shadow Directories can be accessed at + http://www.ietf.org/shadow.html. + + This Internet-Draft will expire on January 12, 2007. + +Copyright Notice + + Copyright (C) The Internet Society (2006). + +Abstract + + While IKEv2 supports public key based authentication (PKI), the + corresponding use of in-band CRLs is problematic due to unbounded CRL + size. The size of an OCSP response is however well-bounded and + small. This document defines the "OCSP Content" extension to IKEv2. + A CERTREQ payload with "OCSP Content" identifies one or more trusted + OCSP responders and is a request for inclusion of an OCSP response in + the IKEv2 handshake. A cooperative recipient of such a request + + + +Myers & Tschofenig Expires January 12, 2007 [Page 1] + +Internet-Draft OCSP Extensions to IKEv2 July 2006 + + + responds with a CERT payload containing the appropriate OCSP + response. This content is recognizable via the same "OCSP Content" + identifier. + + When certificates are used with IKEv2, the communicating peers need a + mechanism to determine the revocation status of the peer's + certificate. OCSP is one such mechanism. This document applies when + OCSP is desired and security policy prevents one of the IKEv2 peers + from accessing the relevant OCSP responder directly. Firewalls are + often deployed in a manner that prevents such access by IKEv2 peers + outside of an enterprise network. + + +Table of Contents + + 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 + 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 + 3. Extension Definition . . . . . . . . . . . . . . . . . . . . . 5 + 3.1. OCSP Request . . . . . . . . . . . . . . . . . . . . . . . 5 + 3.2. OCSP Response . . . . . . . . . . . . . . . . . . . . . . 5 + 4. Extension Requirements . . . . . . . . . . . . . . . . . . . . 6 + 4.1. OCSP Request . . . . . . . . . . . . . . . . . . . . . . . 6 + 4.2. OCSP Response . . . . . . . . . . . . . . . . . . . . . . 6 + 5. Examples and Discussion . . . . . . . . . . . . . . . . . . . 8 + 5.1. Peer to Peer . . . . . . . . . . . . . . . . . . . . . . . 8 + 5.2. Extended Authentication Protocol (EAP) . . . . . . . . . . 9 + 6. Security Considerations . . . . . . . . . . . . . . . . . . . 10 + 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 + 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12 + 9. Normative References . . . . . . . . . . . . . . . . . . . . . 12 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13 + Intellectual Property and Copyright Statements . . . . . . . . . . 14 + + + + + + + + + + + + + + + + + + + +Myers & Tschofenig Expires January 12, 2007 [Page 2] + +Internet-Draft OCSP Extensions to IKEv2 July 2006 + + +1. Introduction + + Version 2 of the Internet Key Exchange (IKE) protocol [IKEv2] + supports a range of authentication mechanisms, including the use of + public key based authentication. Confirmation of certificate + reliability is essential to achieve the security assurances public + key cryptography provides. One fundamental element of such + confirmation is reference to certificate revocation status (see + [RFC3280] for additional detail). + + The historic means of determining certificate revocation status is + through the use of Certificate Revocation Lists (CRLs). IKEv2 allows + CRLs to be exchanged in-band via the CERT payload. + + CRLs can however grow unbounded in size. Many real-world examples + exist to demonstrate the impracticality of including a multi-megabyte + file in an IKE exchange. This constraint is particularly acute in + bandwidth limited environments (e.g., mobile communications). The + net effect is exclusion of in-band CRLs in favor of out-of-band (OOB) + acquisition of these data, should they even be used at all. + + Reliance on OOB methods can be further complicated if access to + revocation data requires use of IPsec (and therefore IKE) to + establish secure and authorized access to the CRLs of an IKE + participant. Such network access deadlock further contributes to a + reduced reliance on certificate revocation status in favor of blind + trust. + + OCSP [RFC2560] offers a useful alternative. The size of an OCSP + response is bounded and small and therefore suitable for in-band + IKEv2 signaling of a certificate's revocation status. + + This document defines an extension to IKEv2 that enables the use of + OCSP for in-band signaling of certificate revocation status. A new + content encoding is defined for use in the CERTREQ and CERT payloads. + A CERTREQ payload with "OCSP Content" identifies one or more trusted + OCSP responders and is a request for inclusion of an OCSP response in + the IKEv2 handshake. A cooperative recipient of such a request + responds with a CERT payload containing the appropriate OCSP + response. This content is recognizable via the same "OCSP Content" + identifier. + + + + + + + + + + +Myers & Tschofenig Expires January 12, 2007 [Page 3] + +Internet-Draft OCSP Extensions to IKEv2 July 2006 + + +2. Terminology + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in RFC 2119 [RFC2119]. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Myers & Tschofenig Expires January 12, 2007 [Page 4] + +Internet-Draft OCSP Extensions to IKEv2 July 2006 + + +3. Extension Definition + + With reference to Section 3.6 of [IKEv2], the values for the Cert + Encoding field of the CERT payload are extended as follows (see also + the IANA Considerations section of this document): + + Certificate Encoding Value + -------------------- ----- + OCSP Content 14 + +3.1. OCSP Request + + A value of OCSP Content (14) in the Cert Encoding field of a CERTREQ + Payload indicates the presence of one or more OCSP Responder + certificate hashes in the Certificate Authority field of the CERTREQ + payload. + + The presence of OCSP Content (14) in a CERTREQ message: + + 1. identifies one or more OCSP responders trusted by the sender; + + 2. notifies the recipient of sender's support for the OCSP extension + to IKEv2; and + + 3. notifies the recipient of sender's desire to receive OCSP + confirmation in a subsequent CERT payload. + +3.2. OCSP Response + + A value of OCSP Content (14) in the Cert Encoding field of a CERT + Payload indicates the presence of an OCSP Response in the Certificate + Data field of the CERT payload. + + Correlation between an OCSP Response CERT payload and a corresponding + CERT payload carrying a certificate can be achieved by matching the + OCSP response CertID field to the certificate. See [RFC2560] for the + definition of OCSP response content. + + + + + + + + + + + + + + +Myers & Tschofenig Expires January 12, 2007 [Page 5] + +Internet-Draft OCSP Extensions to IKEv2 July 2006 + + +4. Extension Requirements + +4.1. OCSP Request + + Section 3.7 of [IKEv2] allows for the concatenation of trust anchor + hashes as the Certification Authority value of a single CERTREQ + message. There is no means however to indicate which among those + hashes relates to the certificate of a trusted OCSP responder. + + Therefore an OCSP Request as defined in Section 3.1 above SHALL be + transmitted separate from any other CERTREQ payloads in an IKEv2 + exchange. + + Where it is useful to identify more than one trusted OCSP responder, + each such identification SHALL be concatenated in a manner identical + to the method documented in Section 3.7 of [IKEv2] regarding the + assembly of multiple trust anchor hashes. + + The Certification Authority value in an OCSP Request CERTREQ SHALL be + computed and produced in a manner identical to that of trust anchor + hashes as documented in Section 3.7 of [IKEv2]. + + Upon receipt of an OCSP Response CERT payload corresponding to a + prior OCSP Request CERTREQ, the CERTREQ sender SHALL incorporate the + OCSP response into path validation logic defined by [RFC3280]. + + The sender of an OCSP Request CERTREQ MAY abort an IKEv2 exchange if + either: + + 1. the corresponding OCSP Response CERT payload indicates that the + subject certificate is revoked; OR + + 2. the corresponding OCSP Response CERT payload indicates an OCSP + error (e.g., malformedRequest, internalError, tryLater, + sigRequired, unauthorized, etc.). + + The sender of an OCSP Request CERTREQ SHOULD accept an IKEv2 exchange + if a corresponding OCSP Response CERT payload is not received. This + might be an indication that this OCSP extension is not supported. + +4.2. OCSP Response + + Upon receipt of an OCSP Request CERTREQ payload, the recipient SHOULD + acquire the related OCSP-based assertion and produce and transmit an + OCSP Response CERT payload corresponding to the certificate needed to + verify its signature on IKEv2 payloads. + + An OCSP Response CERT payload SHALL be transmitted separate from any + + + +Myers & Tschofenig Expires January 12, 2007 [Page 6] + +Internet-Draft OCSP Extensions to IKEv2 July 2006 + + + other CERT payload in an IKEv2 exchange. + + The means by which an OCSP response may be acquired for production of + an OCSP Response CERT payload is out of scope of this document. + + The structure and encoding of the Certificate Data field of an OCSP + Response CERT payload SHALL be identical to that defined in + [RFC2560]. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Myers & Tschofenig Expires January 12, 2007 [Page 7] + +Internet-Draft OCSP Extensions to IKEv2 July 2006 + + +5. Examples and Discussion + + This section shows the standard IKEv2 message examples with both + peers, the initiator and the responder, using public key based + authentication, CERTREQ and CERT payloads. The first instance + corresponds to Section 1.2 of [IKEv2], the illustrations of which are + reproduced below for reference. + +5.1. Peer to Peer + + Application of the IKEv2 extensions defined in this document to the + peer-to-peer exchange defined in Section 1.2 of [IKEv2] is as + follows. Messages are numbered for ease of reference. + + + Initiator Responder + ----------- ----------- + (1) HDR, SAi1, KEi, Ni --> + + (2) <-- HDR, SAr1, KEr, Nr, + CERTREQ(OCSP Request) + (3) HDR, SK {IDi, CERT(certificate),--> + CERT(OCSP Response), + CERTREQ(OCSP Request), + [IDr,] AUTH, SAi2, TSi, TSr} + + (4) <-- HDR, SK {IDr, + CERT(certificate), + CERT(OCSP Response), + AUTH, SAr2, TSi, TSr} + + In (2) Responder sends an OCSP Request CERTREQ payload identifying + one or more OCSP responders trusted by Responder. In response, + Initiator sends in (3) both a CERT payload carrying its certificate + and an OCSP Response CERT payload covering that certificate. In (3) + Initiator also requests an OCSP response via the OCSP Request CERTREQ + payload. In (4) Responder returns its certificate and a separate + OCSP Response CERT payload covering that certificate. + + It is important to note that in this scenario, the Responder in (2) + does not yet possess the Initiator's certificate and therefore cannot + form an OCSP request. [RFC2560] allows for pre-produced responses. + It is thus easily inferred that OCSP responses can be produced in the + absence of a corresponding request (OCSP nonces notwithstanding). In + such instances OCSP Requests are simply index values into these data. + + It is also important in extending IKEv2 towards OCSP in this scenario + that the Initiator has certain knowledge that the Responder is + + + +Myers & Tschofenig Expires January 12, 2007 [Page 8] + +Internet-Draft OCSP Extensions to IKEv2 July 2006 + + + capable of and willing to participate in the extension. Yet the + Responder will only trust one or more OCSP responder signatures. + These factors motivate the definition of OCSP Responder Hash + extension. + +5.2. Extended Authentication Protocol (EAP) + + Another scenario of pressing interest is the use of EAP to + accommodate multiple end users seeking enterprise access to an IPsec + gateway. As with the preceding section, the following illustration + is extracted from [IKEv2]. In the event of a conflict between this + document and[IKEv2] regarding these illustrations, [IKEv2] SHALL + dominate. + + + Initiator Responder + ----------- ----------- + (1) HDR, SAi1, KEi, Ni --> + (2) <-- HDR, SAr1, KEr, Nr + (3) HDR, SK {IDi, --> + CERTREQ(OCSP Request), + [IDr,] AUTH, SAi2, TSi, TSr} + (4) <-- HDR, SK {IDr, + CERT(certificate), + CERT(OCSP Response), + AUTH, EAP} + (5) HDR, SK {EAP} --> + + (6) <-- HDR, SK {EAP (success)} + + (7) HDR, SK {AUTH} --> + + (8) <-- HDR, SK {AUTH, SAr2, TSi, + TSr } + + In the EAP scenario, messages (5) through (8) are not relevant to + this document. Note that while [IKEv2] allows for the optional + inclusion of a CERTREQ in (2), this document asserts no need of its + use. It is assumed that environments including this optional payload + and yet wishing to implement the OCSP extension to IKEv2 are + sufficiently robust as to accommodate this redundant payload. + + + + + + + + + + +Myers & Tschofenig Expires January 12, 2007 [Page 9] + +Internet-Draft OCSP Extensions to IKEv2 July 2006 + + +6. Security Considerations + + For the reasons noted above, OCSP request as defined in Section 3.1 + is used in place of OCSP request syntax to trigger production and + transmission of an OCSP response. OCSP as defined in [RFC2560] may + contain a nonce request extension to improve security against replay + attacks (see Section 4.4.1 of [RFC2560] for further details). The + OCSP Request defined by this document cannot accommodate nonces. + [RFC2560] deals with this aspect by allowing pre-produced responses. + + [RFC2560] points to this replay vulnerability and indicates: "The use + of precomputed responses allows replay attacks in which an old (good) + response is replayed prior to its expiration date but after the + certificate has been revoked. Deployments of OCSP should carefully + evaluate the benefit of precomputed responses against the probability + of a replay attack and the costs associated with its successful + execution." Nodes SHOULD make the required freshness of an OCSP + Response configurable. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Myers & Tschofenig Expires January 12, 2007 [Page 10] + +Internet-Draft OCSP Extensions to IKEv2 July 2006 + + +7. IANA Considerations + + This document defines one new field type for use in the IKEv2 Cert + Encoding field of the Certificate Payload format. Official + assignment of the "OCSP Content" extension to the Cert Encoding table + of Section 3.6 of [IKEv2] needs to be acquired from IANA. + + Certificate Encoding Value + -------------------- ----- + OCSP Content 14 + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Myers & Tschofenig Expires January 12, 2007 [Page 11] + +Internet-Draft OCSP Extensions to IKEv2 July 2006 + + +8. Acknowledgements + + The authors would like to thank Russ Housley for his support. + Additionally, we would like to thank Pasi Eronen, Nicolas Williams, + Liqiang (Larry) Zhu, Lakshminath Dondeti and Paul Hoffman for their + review. + +9. Normative References + + [IKEv2] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", + RFC 4306, December 2005. + + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [RFC2560] Myers, M., Ankney, R., Malpani, A., Galperin, S., and C. + Adams, "X.509 Internet Public Key Infrastructure Online + Certificate Status Protocol - OCSP", RFC 2560, June 1999. + + [RFC3280] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet + X.509 Public Key Infrastructure Certificate and + Certificate Revocation List (CRL) Profile", RFC 3280, + April 2002. + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Myers & Tschofenig Expires January 12, 2007 [Page 12] + +Internet-Draft OCSP Extensions to IKEv2 July 2006 + + +Authors' Addresses + + Michael Myers + TraceRoute Security LLC + + + Email: mmyers@fastq.com + + + Hannes Tschofenig + Siemens + Otto-Hahn-Ring 6 + Munich, Bavaria 81739 + Germany + + Email: Hannes.Tschofenig@siemens.com + URI: http://www.tschofenig.com + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Myers & Tschofenig Expires January 12, 2007 [Page 13] + +Internet-Draft OCSP Extensions to IKEv2 July 2006 + + +Intellectual Property Statement + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at + ietf-ipr@ietf.org. + + +Disclaimer of Validity + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET + ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, + INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE + INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + + +Copyright Statement + + Copyright (C) The Internet Society (2006). This document is subject + to the rights, licenses and restrictions contained in BCP 78, and + except as set forth therein, the authors retain all their rights. + + +Acknowledgment + + Funding for the RFC Editor function is currently provided by the + Internet Society. + + + + +Myers & Tschofenig Expires January 12, 2007 [Page 14] + + diff --git a/src/charon/doc/standards/rfc4301.txt b/src/charon/doc/standards/rfc4301.txt new file mode 100644 index 000000000..4a8eba975 --- /dev/null +++ b/src/charon/doc/standards/rfc4301.txt @@ -0,0 +1,5659 @@ + + + + + + +Network Working Group S. Kent +Request for Comments: 4301 K. Seo +Obsoletes: 2401 BBN Technologies +Category: Standards Track December 2005 + + + Security Architecture for the Internet Protocol + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (C) The Internet Society (2005). + +Abstract + + This document describes an updated version of the "Security + Architecture for IP", which is designed to provide security services + for traffic at the IP layer. This document obsoletes RFC 2401 + (November 1998). + +Dedication + + This document is dedicated to the memory of Charlie Lynn, a long-time + senior colleague at BBN, who made very significant contributions to + the IPsec documents. + + + + + + + + + + + + + + + + + + + +Kent & Seo Standards Track [Page 1] + +RFC 4301 Security Architecture for IP December 2005 + + +Table of Contents + + 1. Introduction ....................................................4 + 1.1. Summary of Contents of Document ............................4 + 1.2. Audience ...................................................4 + 1.3. Related Documents ..........................................5 + 2. Design Objectives ...............................................5 + 2.1. Goals/Objectives/Requirements/Problem Description ..........5 + 2.2. Caveats and Assumptions ....................................6 + 3. System Overview .................................................7 + 3.1. What IPsec Does ............................................7 + 3.2. How IPsec Works ............................................9 + 3.3. Where IPsec Can Be Implemented ............................10 + 4. Security Associations ..........................................11 + 4.1. Definition and Scope ......................................12 + 4.2. SA Functionality ..........................................16 + 4.3. Combining SAs .............................................17 + 4.4. Major IPsec Databases .....................................18 + 4.4.1. The Security Policy Database (SPD) .................19 + 4.4.1.1. Selectors .................................26 + 4.4.1.2. Structure of an SPD Entry .................30 + 4.4.1.3. More Regarding Fields Associated + with Next Layer Protocols .................32 + 4.4.2. Security Association Database (SAD) ................34 + 4.4.2.1. Data Items in the SAD .....................36 + 4.4.2.2. Relationship between SPD, PFP + flag, packet, and SAD .....................38 + 4.4.3. Peer Authorization Database (PAD) ..................43 + 4.4.3.1. PAD Entry IDs and Matching Rules ..........44 + 4.4.3.2. IKE Peer Authentication Data ..............45 + 4.4.3.3. Child SA Authorization Data ...............46 + 4.4.3.4. How the PAD Is Used .......................46 + 4.5. SA and Key Management .....................................47 + 4.5.1. Manual Techniques ..................................48 + 4.5.2. Automated SA and Key Management ....................48 + 4.5.3. Locating a Security Gateway ........................49 + 4.6. SAs and Multicast .........................................50 + 5. IP Traffic Processing ..........................................50 + 5.1. Outbound IP Traffic Processing + (protected-to-unprotected) ................................52 + 5.1.1. Handling an Outbound Packet That Must Be + Discarded ..........................................54 + 5.1.2. Header Construction for Tunnel Mode ................55 + 5.1.2.1. IPv4: Header Construction for + Tunnel Mode ...............................57 + 5.1.2.2. IPv6: Header Construction for + Tunnel Mode ...............................59 + 5.2. Processing Inbound IP Traffic (unprotected-to-protected) ..59 + + + +Kent & Seo Standards Track [Page 2] + +RFC 4301 Security Architecture for IP December 2005 + + + 6. ICMP Processing ................................................63 + 6.1. Processing ICMP Error Messages Directed to an + IPsec Implementation ......................................63 + 6.1.1. ICMP Error Messages Received on the + Unprotected Side of the Boundary ...................63 + 6.1.2. ICMP Error Messages Received on the + Protected Side of the Boundary .....................64 + 6.2. Processing Protected, Transit ICMP Error Messages .........64 + 7. Handling Fragments (on the protected side of the IPsec + boundary) ......................................................66 + 7.1. Tunnel Mode SAs that Carry Initial and Non-Initial + Fragments .................................................67 + 7.2. Separate Tunnel Mode SAs for Non-Initial Fragments ........67 + 7.3. Stateful Fragment Checking ................................68 + 7.4. BYPASS/DISCARD Traffic ....................................69 + 8. Path MTU/DF Processing .........................................69 + 8.1. DF Bit ....................................................69 + 8.2. Path MTU (PMTU) Discovery .................................70 + 8.2.1. Propagation of PMTU ................................70 + 8.2.2. PMTU Aging .........................................71 + 9. Auditing .......................................................71 + 10. Conformance Requirements ......................................71 + 11. Security Considerations .......................................72 + 12. IANA Considerations ...........................................72 + 13. Differences from RFC 2401 .....................................72 + 14. Acknowledgements ..............................................75 + Appendix A: Glossary ..............................................76 + Appendix B: Decorrelation .........................................79 + B.1. Decorrelation Algorithm ...................................79 + Appendix C: ASN.1 for an SPD Entry ................................82 + Appendix D: Fragment Handling Rationale ...........................88 + D.1. Transport Mode and Fragments ..............................88 + D.2. Tunnel Mode and Fragments .................................89 + D.3. The Problem of Non-Initial Fragments ......................90 + D.4. BYPASS/DISCARD Traffic ....................................93 + D.5. Just say no to ports? .....................................94 + D.6. Other Suggested Solutions..................................94 + D.7. Consistency................................................95 + D.8. Conclusions................................................95 + Appendix E: Example of Supporting Nested SAs via SPD and + Forwarding Table Entries...............................96 + References.........................................................98 + Normative References............................................98 + Informative References..........................................99 + + + + + + + +Kent & Seo Standards Track [Page 3] + +RFC 4301 Security Architecture for IP December 2005 + + +1. Introduction + +1.1. Summary of Contents of Document + + This document specifies the base architecture for IPsec-compliant + systems. It describes how to provide a set of security services for + traffic at the IP layer, in both the IPv4 [Pos81a] and IPv6 [DH98] + environments. This document describes the requirements for systems + that implement IPsec, the fundamental elements of such systems, and + how the elements fit together and fit into the IP environment. It + also describes the security services offered by the IPsec protocols, + and how these services can be employed in the IP environment. This + document does not address all aspects of the IPsec architecture. + Other documents address additional architectural details in + specialized environments, e.g., use of IPsec in Network Address + Translation (NAT) environments and more comprehensive support for IP + multicast. The fundamental components of the IPsec security + architecture are discussed in terms of their underlying, required + functionality. Additional RFCs (see Section 1.3 for pointers to + other documents) define the protocols in (a), (c), and (d). + + a. Security Protocols -- Authentication Header (AH) and + Encapsulating Security Payload (ESP) + b. Security Associations -- what they are and how they work, + how they are managed, associated processing + c. Key Management -- manual and automated (The Internet Key + Exchange (IKE)) + d. Cryptographic algorithms for authentication and encryption + + This document is not a Security Architecture for the Internet; it + addresses security only at the IP layer, provided through the use of + a combination of cryptographic and protocol security mechanisms. + + The spelling "IPsec" is preferred and used throughout this and all + related IPsec standards. All other capitalizations of IPsec (e.g., + IPSEC, IPSec, ipsec) are deprecated. However, any capitalization of + the sequence of letters "IPsec" should be understood to refer to the + IPsec protocols. + + The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, + SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this + document, are to be interpreted as described in RFC 2119 [Bra97]. + +1.2. Audience + + The target audience for this document is primarily individuals who + implement this IP security technology or who architect systems that + will use this technology. Technically adept users of this technology + + + +Kent & Seo Standards Track [Page 4] + +RFC 4301 Security Architecture for IP December 2005 + + + (end users or system administrators) also are part of the target + audience. A glossary is provided in Appendix A to help fill in gaps + in background/vocabulary. This document assumes that the reader is + familiar with the Internet Protocol (IP), related networking + technology, and general information system security terms and + concepts. + +1.3. Related Documents + + As mentioned above, other documents provide detailed definitions of + some of the components of IPsec and of their interrelationship. They + include RFCs on the following topics: + + a. security protocols -- RFCs describing the Authentication + Header (AH) [Ken05b] and Encapsulating Security Payload + (ESP) [Ken05a] protocols. + b. cryptographic algorithms for integrity and encryption -- one + RFC that defines the mandatory, default algorithms for use + with AH and ESP [Eas05], a similar RFC that defines the + mandatory algorithms for use with IKEv2 [Sch05] plus a + separate RFC for each cryptographic algorithm. + c. automatic key management -- RFCs on "The Internet Key + Exchange (IKEv2) Protocol" [Kau05] and "Cryptographic + Algorithms for Use in the Internet Key Exchange Version 2 + (IKEv2)" [Sch05]. + +2. Design Objectives + +2.1. Goals/Objectives/Requirements/Problem Description + + IPsec is designed to provide interoperable, high quality, + cryptographically-based security for IPv4 and IPv6. The set of + security services offered includes access control, connectionless + integrity, data origin authentication, detection and rejection of + replays (a form of partial sequence integrity), confidentiality (via + encryption), and limited traffic flow confidentiality. These + services are provided at the IP layer, offering protection in a + standard fashion for all protocols that may be carried over IP + (including IP itself). + + IPsec includes a specification for minimal firewall functionality, + since that is an essential aspect of access control at the IP layer. + Implementations are free to provide more sophisticated firewall + mechanisms, and to implement the IPsec-mandated functionality using + those more sophisticated mechanisms. (Note that interoperability may + suffer if additional firewall constraints on traffic flows are + imposed by an IPsec implementation but cannot be negotiated based on + the traffic selector features defined in this document and negotiated + + + +Kent & Seo Standards Track [Page 5] + +RFC 4301 Security Architecture for IP December 2005 + + + via IKEv2.) The IPsec firewall function makes use of the + cryptographically-enforced authentication and integrity provided for + all IPsec traffic to offer better access control than could be + obtained through use of a firewall (one not privy to IPsec internal + parameters) plus separate cryptographic protection. + + Most of the security services are provided through use of two traffic + security protocols, the Authentication Header (AH) and the + Encapsulating Security Payload (ESP), and through the use of + cryptographic key management procedures and protocols. The set of + IPsec protocols employed in a context, and the ways in which they are + employed, will be determined by the users/administrators in that + context. It is the goal of the IPsec architecture to ensure that + compliant implementations include the services and management + interfaces needed to meet the security requirements of a broad user + population. + + When IPsec is correctly implemented and deployed, it ought not + adversely affect users, hosts, and other Internet components that do + not employ IPsec for traffic protection. IPsec security protocols + (AH and ESP, and to a lesser extent, IKE) are designed to be + cryptographic algorithm independent. This modularity permits + selection of different sets of cryptographic algorithms as + appropriate, without affecting the other parts of the implementation. + For example, different user communities may select different sets of + cryptographic algorithms (creating cryptographically-enforced + cliques) if required. + + To facilitate interoperability in the global Internet, a set of + default cryptographic algorithms for use with AH and ESP is specified + in [Eas05] and a set of mandatory-to-implement algorithms for IKEv2 + is specified in [Sch05]. [Eas05] and [Sch05] will be periodically + updated to keep pace with computational and cryptologic advances. By + specifying these algorithms in documents that are separate from the + AH, ESP, and IKEv2 specifications, these algorithms can be updated or + replaced without affecting the standardization progress of the rest + of the IPsec document suite. The use of these cryptographic + algorithms, in conjunction with IPsec traffic protection and key + management protocols, is intended to permit system and application + developers to deploy high quality, Internet-layer, cryptographic + security technology. + +2.2. Caveats and Assumptions + + The suite of IPsec protocols and associated default cryptographic + algorithms are designed to provide high quality security for Internet + traffic. However, the security offered by use of these protocols + ultimately depends on the quality of their implementation, which is + + + +Kent & Seo Standards Track [Page 6] + +RFC 4301 Security Architecture for IP December 2005 + + + outside the scope of this set of standards. Moreover, the security + of a computer system or network is a function of many factors, + including personnel, physical, procedural, compromising emanations, + and computer security practices. Thus, IPsec is only one part of an + overall system security architecture. + + Finally, the security afforded by the use of IPsec is critically + dependent on many aspects of the operating environment in which the + IPsec implementation executes. For example, defects in OS security, + poor quality of random number sources, sloppy system management + protocols and practices, etc., can all degrade the security provided + by IPsec. As above, none of these environmental attributes are + within the scope of this or other IPsec standards. + +3. System Overview + + This section provides a high level description of how IPsec works, + the components of the system, and how they fit together to provide + the security services noted above. The goal of this description is + to enable the reader to "picture" the overall process/system, see how + it fits into the IP environment, and to provide context for later + sections of this document, which describe each of the components in + more detail. + + An IPsec implementation operates in a host, as a security gateway + (SG), or as an independent device, affording protection to IP + traffic. (A security gateway is an intermediate system implementing + IPsec, e.g., a firewall or router that has been IPsec-enabled.) More + detail on these classes of implementations is provided later, in + Section 3.3. The protection offered by IPsec is based on requirements + defined by a Security Policy Database (SPD) established and + maintained by a user or system administrator, or by an application + operating within constraints established by either of the above. In + general, packets are selected for one of three processing actions + based on IP and next layer header information ("Selectors", Section + 4.4.1.1) matched against entries in the SPD. Each packet is either + PROTECTed using IPsec security services, DISCARDed, or allowed to + BYPASS IPsec protection, based on the applicable SPD policies + identified by the Selectors. + +3.1. What IPsec Does + + IPsec creates a boundary between unprotected and protected + interfaces, for a host or a network (see Figure 1 below). Traffic + traversing the boundary is subject to the access controls specified + by the user or administrator responsible for the IPsec configuration. + These controls indicate whether packets cross the boundary unimpeded, + are afforded security services via AH or ESP, or are discarded. + + + +Kent & Seo Standards Track [Page 7] + +RFC 4301 Security Architecture for IP December 2005 + + + IPsec security services are offered at the IP layer through selection + of appropriate security protocols, cryptographic algorithms, and + cryptographic keys. IPsec can be used to protect one or more "paths" + (a) between a pair of hosts, (b) between a pair of security gateways, + or (c) between a security gateway and a host. A compliant host + implementation MUST support (a) and (c) and a compliant security + gateway must support all three of these forms of connectivity, since + under certain circumstances a security gateway acts as a host. + + Unprotected + ^ ^ + | | + +-------------|-------|-------+ + | +-------+ | | | + | |Discard|<--| V | + | +-------+ |B +--------+ | + ................|y..| AH/ESP |..... IPsec Boundary + | +---+ |p +--------+ | + | |IKE|<----|a ^ | + | +---+ |s | | + | +-------+ |s | | + | |Discard|<--| | | + | +-------+ | | | + +-------------|-------|-------+ + | | + V V + Protected + + Figure 1. Top Level IPsec Processing Model + + In this diagram, "unprotected" refers to an interface that might also + be described as "black" or "ciphertext". Here, "protected" refers to + an interface that might also be described as "red" or "plaintext". + The protected interface noted above may be internal, e.g., in a host + implementation of IPsec, the protected interface may link to a socket + layer interface presented by the OS. In this document, the term + "inbound" refers to traffic entering an IPsec implementation via the + unprotected interface or emitted by the implementation on the + unprotected side of the boundary and directed towards the protected + interface. The term "outbound" refers to traffic entering the + implementation via the protected interface, or emitted by the + implementation on the protected side of the boundary and directed + toward the unprotected interface. An IPsec implementation may + support more than one interface on either or both sides of the + boundary. + + + + + + +Kent & Seo Standards Track [Page 8] + +RFC 4301 Security Architecture for IP December 2005 + + + Note the facilities for discarding traffic on either side of the + IPsec boundary, the BYPASS facility that allows traffic to transit + the boundary without cryptographic protection, and the reference to + IKE as a protected-side key and security management function. + + IPsec optionally supports negotiation of IP compression [SMPT01], + motivated in part by the observation that when encryption is employed + within IPsec, it prevents effective compression by lower protocol + layers. + +3.2. How IPsec Works + + IPsec uses two protocols to provide traffic security services -- + Authentication Header (AH) and Encapsulating Security Payload (ESP). + Both protocols are described in detail in their respective RFCs + [Ken05b, Ken05a]. IPsec implementations MUST support ESP and MAY + support AH. (Support for AH has been downgraded to MAY because + experience has shown that there are very few contexts in which ESP + cannot provide the requisite security services. Note that ESP can be + used to provide only integrity, without confidentiality, making it + comparable to AH in most contexts.) + + o The IP Authentication Header (AH) [Ken05b] offers integrity and + data origin authentication, with optional (at the discretion of + the receiver) anti-replay features. + + o The Encapsulating Security Payload (ESP) protocol [Ken05a] offers + the same set of services, and also offers confidentiality. Use of + ESP to provide confidentiality without integrity is NOT + RECOMMENDED. When ESP is used with confidentiality enabled, there + are provisions for limited traffic flow confidentiality, i.e., + provisions for concealing packet length, and for facilitating + efficient generation and discard of dummy packets. This + capability is likely to be effective primarily in virtual private + network (VPN) and overlay network contexts. + + o Both AH and ESP offer access control, enforced through the + distribution of cryptographic keys and the management of traffic + flows as dictated by the Security Policy Database (SPD, Section + 4.4.1). + + These protocols may be applied individually or in combination with + each other to provide IPv4 and IPv6 security services. However, most + security requirements can be met through the use of ESP by itself. + Each protocol supports two modes of use: transport mode and tunnel + mode. In transport mode, AH and ESP provide protection primarily for + + + + + +Kent & Seo Standards Track [Page 9] + +RFC 4301 Security Architecture for IP December 2005 + + + next layer protocols; in tunnel mode, AH and ESP are applied to + tunneled IP packets. The differences between the two modes are + discussed in Section 4.1. + + IPsec allows the user (or system administrator) to control the + granularity at which a security service is offered. For example, one + can create a single encrypted tunnel to carry all the traffic between + two security gateways, or a separate encrypted tunnel can be created + for each TCP connection between each pair of hosts communicating + across these gateways. IPsec, through the SPD management paradigm, + incorporates facilities for specifying: + + o which security protocol (AH or ESP) to employ, the mode (transport + or tunnel), security service options, what cryptographic + algorithms to use, and in what combinations to use the specified + protocols and services, and + + o the granularity at which protection should be applied. + + Because most of the security services provided by IPsec require the + use of cryptographic keys, IPsec relies on a separate set of + mechanisms for putting these keys in place. This document requires + support for both manual and automated distribution of keys. It + specifies a specific public-key based approach (IKEv2 [Kau05]) for + automated key management, but other automated key distribution + techniques MAY be used. + + Note: This document mandates support for several features for which + support is available in IKEv2 but not in IKEv1, e.g., negotiation of + an SA representing ranges of local and remote ports or negotiation of + multiple SAs with the same selectors. Therefore, this document + assumes use of IKEv2 or a key and security association management + system with comparable features. + +3.3. Where IPsec Can Be Implemented + + There are many ways in which IPsec may be implemented in a host, or + in conjunction with a router or firewall to create a security + gateway, or as an independent security device. + + a. IPsec may be integrated into the native IP stack. This requires + access to the IP source code and is applicable to both hosts and + security gateways, although native host implementations benefit + the most from this strategy, as explained later (Section 4.4.1, + paragraph 6; Section 4.4.1.1, last paragraph). + + + + + + +Kent & Seo Standards Track [Page 10] + +RFC 4301 Security Architecture for IP December 2005 + + + b. In a "bump-in-the-stack" (BITS) implementation, IPsec is + implemented "underneath" an existing implementation of an IP + protocol stack, between the native IP and the local network + drivers. Source code access for the IP stack is not required in + this context, making this implementation approach appropriate for + use with legacy systems. This approach, when it is adopted, is + usually employed in hosts. + + c. The use of a dedicated, inline security protocol processor is a + common design feature of systems used by the military, and of some + commercial systems as well. It is sometimes referred to as a + "bump-in-the-wire" (BITW) implementation. Such implementations + may be designed to serve either a host or a gateway. Usually, the + BITW device is itself IP addressable. When supporting a single + host, it may be quite analogous to a BITS implementation, but in + supporting a router or firewall, it must operate like a security + gateway. + + This document often talks in terms of use of IPsec by a host or a + security gateway, without regard to whether the implementation is + native, BITS, or BITW. When the distinctions among these + implementation options are significant, the document makes reference + to specific implementation approaches. + + A host implementation of IPsec may appear in devices that might not + be viewed as "hosts". For example, a router might employ IPsec to + protect routing protocols (e.g., BGP) and management functions (e.g., + Telnet), without affecting subscriber traffic traversing the router. + A security gateway might employ separate IPsec implementations to + protect its management traffic and subscriber traffic. The + architecture described in this document is very flexible. For + example, a computer with a full-featured, compliant, native OS IPsec + implementation should be capable of being configured to protect + resident (host) applications and to provide security gateway + protection for traffic traversing the computer. Such configuration + would make use of the forwarding tables and the SPD selection + function described in Sections 5.1 and 5.2. + +4. Security Associations + + This section defines Security Association management requirements for + all IPv6 implementations and for those IPv4 implementations that + implement AH, ESP, or both AH and ESP. The concept of a "Security + Association" (SA) is fundamental to IPsec. Both AH and ESP make use + of SAs, and a major function of IKE is the establishment and + maintenance of SAs. All implementations of AH or ESP MUST support + the concept of an SA as described below. The remainder of this + + + + +Kent & Seo Standards Track [Page 11] + +RFC 4301 Security Architecture for IP December 2005 + + + section describes various aspects of SA management, defining required + characteristics for SA policy management and SA management + techniques. + +4.1. Definition and Scope + + An SA is a simplex "connection" that affords security services to the + traffic carried by it. Security services are afforded to an SA by + the use of AH, or ESP, but not both. If both AH and ESP protection + are applied to a traffic stream, then two SAs must be created and + coordinated to effect protection through iterated application of the + security protocols. To secure typical, bi-directional communication + between two IPsec-enabled systems, a pair of SAs (one in each + direction) is required. IKE explicitly creates SA pairs in + recognition of this common usage requirement. + + For an SA used to carry unicast traffic, the Security Parameters + Index (SPI) by itself suffices to specify an SA. (For information on + the SPI, see Appendix A and the AH and ESP specifications [Ken05b, + Ken05a].) However, as a local matter, an implementation may choose + to use the SPI in conjunction with the IPsec protocol type (AH or + ESP) for SA identification. If an IPsec implementation supports + multicast, then it MUST support multicast SAs using the algorithm + below for mapping inbound IPsec datagrams to SAs. Implementations + that support only unicast traffic need not implement this de- + multiplexing algorithm. + + In many secure multicast architectures, e.g., [RFC3740], a central + Group Controller/Key Server unilaterally assigns the Group Security + Association's (GSA's) SPI. This SPI assignment is not negotiated or + coordinated with the key management (e.g., IKE) subsystems that + reside in the individual end systems that constitute the group. + Consequently, it is possible that a GSA and a unicast SA can + simultaneously use the same SPI. A multicast-capable IPsec + implementation MUST correctly de-multiplex inbound traffic even in + the context of SPI collisions. + + Each entry in the SA Database (SAD) (Section 4.4.2) must indicate + whether the SA lookup makes use of the destination IP address, or the + destination and source IP addresses, in addition to the SPI. For + multicast SAs, the protocol field is not employed for SA lookups. + For each inbound, IPsec-protected packet, an implementation must + conduct its search of the SAD such that it finds the entry that + matches the "longest" SA identifier. In this context, if two or more + SAD entries match based on the SPI value, then the entry that also + matches based on destination address, or destination and source + address (as indicated in the SAD entry) is the "longest" match. This + implies a logical ordering of the SAD search as follows: + + + +Kent & Seo Standards Track [Page 12] + +RFC 4301 Security Architecture for IP December 2005 + + + 1. Search the SAD for a match on the combination of SPI, + destination address, and source address. If an SAD entry + matches, then process the inbound packet with that + matching SAD entry. Otherwise, proceed to step 2. + + 2. Search the SAD for a match on both SPI and destination address. + If the SAD entry matches, then process the inbound packet + with that matching SAD entry. Otherwise, proceed to step 3. + + 3. Search the SAD for a match on only SPI if the receiver has + chosen to maintain a single SPI space for AH and ESP, and on + both SPI and protocol, otherwise. If an SAD entry matches, + then process the inbound packet with that matching SAD entry. + Otherwise, discard the packet and log an auditable event. + + In practice, an implementation may choose any method (or none at all) + to accelerate this search, although its externally visible behavior + MUST be functionally equivalent to having searched the SAD in the + above order. For example, a software-based implementation could + index into a hash table by the SPI. The SAD entries in each hash + table bucket's linked list could be kept sorted to have those SAD + entries with the longest SA identifiers first in that linked list. + Those SAD entries having the shortest SA identifiers could be sorted + so that they are the last entries in the linked list. A + hardware-based implementation may be able to effect the longest match + search intrinsically, using commonly available Ternary + Content-Addressable Memory (TCAM) features. + + The indication of whether source and destination address matching is + required to map inbound IPsec traffic to SAs MUST be set either as a + side effect of manual SA configuration or via negotiation using an SA + management protocol, e.g., IKE or Group Domain of Interpretation + (GDOI) [RFC3547]. Typically, Source-Specific Multicast (SSM) [HC03] + groups use a 3-tuple SA identifier composed of an SPI, a destination + multicast address, and source address. An Any-Source Multicast group + SA requires only an SPI and a destination multicast address as an + identifier. + + If different classes of traffic (distinguished by Differentiated + Services Code Point (DSCP) bits [NiBlBaBL98], [Gro02]) are sent on + the same SA, and if the receiver is employing the optional + anti-replay feature available in both AH and ESP, this could result + in inappropriate discarding of lower priority packets due to the + windowing mechanism used by this feature. Therefore, a sender SHOULD + put traffic of different classes, but with the same selector values, + on different SAs to support Quality of Service (QoS) appropriately. + To permit this, the IPsec implementation MUST permit establishment + and maintenance of multiple SAs between a given sender and receiver, + + + +Kent & Seo Standards Track [Page 13] + +RFC 4301 Security Architecture for IP December 2005 + + + with the same selectors. Distribution of traffic among these + parallel SAs to support QoS is locally determined by the sender and + is not negotiated by IKE. The receiver MUST process the packets from + the different SAs without prejudice. These requirements apply to + both transport and tunnel mode SAs. In the case of tunnel mode SAs, + the DSCP values in question appear in the inner IP header. In + transport mode, the DSCP value might change en route, but this should + not cause problems with respect to IPsec processing since the value + is not employed for SA selection and MUST NOT be checked as part of + SA/packet validation. However, if significant re-ordering of packets + occurs in an SA, e.g., as a result of changes to DSCP values en + route, this may trigger packet discarding by a receiver due to + application of the anti-replay mechanism. + + DISCUSSION: Although the DSCP [NiBlBaBL98, Gro02] and Explicit + Congestion Notification (ECN) [RaFlBl01] fields are not "selectors", + as that term in used in this architecture, the sender will need a + mechanism to direct packets with a given (set of) DSCP values to the + appropriate SA. This mechanism might be termed a "classifier". + + As noted above, two types of SAs are defined: transport mode and + tunnel mode. IKE creates pairs of SAs, so for simplicity, we choose + to require that both SAs in a pair be of the same mode, transport or + tunnel. + + A transport mode SA is an SA typically employed between a pair of + hosts to provide end-to-end security services. When security is + desired between two intermediate systems along a path (vs. end-to-end + use of IPsec), transport mode MAY be used between security gateways + or between a security gateway and a host. In the case where + transport mode is used between security gateways or between a + security gateway and a host, transport mode may be used to support + in-IP tunneling (e.g., IP-in-IP [Per96] or Generic Routing + Encapsulation (GRE) tunneling [FaLiHaMeTr00] or dynamic routing + [ToEgWa04]) over transport mode SAs. To clarify, the use of + transport mode by an intermediate system (e.g., a security gateway) + is permitted only when applied to packets whose source address (for + outbound packets) or destination address (for inbound packets) is an + address belonging to the intermediate system itself. The access + control functions that are an important part of IPsec are + significantly limited in this context, as they cannot be applied to + the end-to-end headers of the packets that traverse a transport mode + SA used in this fashion. Thus, this way of using transport mode + should be evaluated carefully before being employed in a specific + context. + + + + + + +Kent & Seo Standards Track [Page 14] + +RFC 4301 Security Architecture for IP December 2005 + + + In IPv4, a transport mode security protocol header appears + immediately after the IP header and any options, and before any next + layer protocols (e.g., TCP or UDP). In IPv6, the security protocol + header appears after the base IP header and selected extension + headers, but may appear before or after destination options; it MUST + appear before next layer protocols (e.g., TCP, UDP, Stream Control + Transmission Protocol (SCTP)). In the case of ESP, a transport mode + SA provides security services only for these next layer protocols, + not for the IP header or any extension headers preceding the ESP + header. In the case of AH, the protection is also extended to + selected portions of the IP header preceding it, selected portions of + extension headers, and selected options (contained in the IPv4 + header, IPv6 Hop-by-Hop extension header, or IPv6 Destination + extension headers). For more details on the coverage afforded by AH, + see the AH specification [Ken05b]. + + A tunnel mode SA is essentially an SA applied to an IP tunnel, with + the access controls applied to the headers of the traffic inside the + tunnel. Two hosts MAY establish a tunnel mode SA between themselves. + Aside from the two exceptions below, whenever either end of a + security association is a security gateway, the SA MUST be tunnel + mode. Thus, an SA between two security gateways is typically a + tunnel mode SA, as is an SA between a host and a security gateway. + The two exceptions are as follows. + + o Where traffic is destined for a security gateway, e.g., Simple + Network Management Protocol (SNMP) commands, the security gateway + is acting as a host and transport mode is allowed. In this case, + the SA terminates at a host (management) function within a + security gateway and thus merits different treatment. + + o As noted above, security gateways MAY support a transport mode SA + to provide security for IP traffic between two intermediate + systems along a path, e.g., between a host and a security gateway + or between two security gateways. + + Several concerns motivate the use of tunnel mode for an SA involving + a security gateway. For example, if there are multiple paths (e.g., + via different security gateways) to the same destination behind a + security gateway, it is important that an IPsec packet be sent to the + security gateway with which the SA was negotiated. Similarly, a + packet that might be fragmented en route must have all the fragments + delivered to the same IPsec instance for reassembly prior to + cryptographic processing. Also, when a fragment is processed by + IPsec and transmitted, then fragmented en route, it is critical that + there be inner and outer headers to retain the fragmentation state + data for the pre- and post-IPsec packet formats. Hence there are + several reasons for employing tunnel mode when either end of an SA is + + + +Kent & Seo Standards Track [Page 15] + +RFC 4301 Security Architecture for IP December 2005 + + + a security gateway. (Use of an IP-in-IP tunnel in conjunction with + transport mode can also address these fragmentation issues. However, + this configuration limits the ability of IPsec to enforce access + control policies on traffic.) + + Note: AH and ESP cannot be applied using transport mode to IPv4 + packets that are fragments. Only tunnel mode can be employed in such + cases. For IPv6, it would be feasible to carry a plaintext fragment + on a transport mode SA; however, for simplicity, this restriction + also applies to IPv6 packets. See Section 7 for more details on + handling plaintext fragments on the protected side of the IPsec + barrier. + + For a tunnel mode SA, there is an "outer" IP header that specifies + the IPsec processing source and destination, plus an "inner" IP + header that specifies the (apparently) ultimate source and + destination for the packet. The security protocol header appears + after the outer IP header, and before the inner IP header. If AH is + employed in tunnel mode, portions of the outer IP header are afforded + protection (as above), as well as all of the tunneled IP packet + (i.e., all of the inner IP header is protected, as well as next layer + protocols). If ESP is employed, the protection is afforded only to + the tunneled packet, not to the outer header. + + In summary, + + a) A host implementation of IPsec MUST support both transport and + tunnel mode. This is true for native, BITS, and BITW + implementations for hosts. + + b) A security gateway MUST support tunnel mode and MAY support + transport mode. If it supports transport mode, that should be + used only when the security gateway is acting as a host, e.g., for + network management, or to provide security between two + intermediate systems along a path. + +4.2. SA Functionality + + The set of security services offered by an SA depends on the security + protocol selected, the SA mode, the endpoints of the SA, and the + election of optional services within the protocol. + + For example, both AH and ESP offer integrity and authentication + services, but the coverage differs for each protocol and differs for + transport vs. tunnel mode. If the integrity of an IPv4 option or + IPv6 extension header must be protected en route between sender and + receiver, AH can provide this service, except for IP or extension + headers that may change in a fashion not predictable by the sender. + + + +Kent & Seo Standards Track [Page 16] + +RFC 4301 Security Architecture for IP December 2005 + + + However, the same security may be achieved in some contexts by + applying ESP to a tunnel carrying a packet. + + The granularity of access control provided is determined by the + choice of the selectors that define each SA. Moreover, the + authentication means employed by IPsec peers, e.g., during creation + of an IKE (vs. child) SA also affects the granularity of the access + control afforded. + + If confidentiality is selected, then an ESP (tunnel mode) SA between + two security gateways can offer partial traffic flow confidentiality. + The use of tunnel mode allows the inner IP headers to be encrypted, + concealing the identities of the (ultimate) traffic source and + destination. Moreover, ESP payload padding also can be invoked to + hide the size of the packets, further concealing the external + characteristics of the traffic. Similar traffic flow confidentiality + services may be offered when a mobile user is assigned a dynamic IP + address in a dialup context, and establishes a (tunnel mode) ESP SA + to a corporate firewall (acting as a security gateway). Note that + fine-granularity SAs generally are more vulnerable to traffic + analysis than coarse-granularity ones that are carrying traffic from + many subscribers. + + Note: A compliant implementation MUST NOT allow instantiation of an + ESP SA that employs both NULL encryption and no integrity algorithm. + An attempt to negotiate such an SA is an auditable event by both + initiator and responder. The audit log entry for this event SHOULD + include the current date/time, local IKE IP address, and remote IKE + IP address. The initiator SHOULD record the relevant SPD entry. + +4.3. Combining SAs + + This document does not require support for nested security + associations or for what RFC 2401 [RFC2401] called "SA bundles". + These features still can be effected by appropriate configuration of + both the SPD and the local forwarding functions (for inbound and + outbound traffic), but this capability is outside of the IPsec module + and thus the scope of this specification. As a result, management of + nested/bundled SAs is potentially more complex and less assured than + under the model implied by RFC 2401 [RFC2401]. An implementation + that provides support for nested SAs SHOULD provide a management + interface that enables a user or administrator to express the nesting + requirement, and then create the appropriate SPD entries and + forwarding table entries to effect the requisite processing. (See + Appendix E for an example of how to configure nested SAs.) + + + + + + +Kent & Seo Standards Track [Page 17] + +RFC 4301 Security Architecture for IP December 2005 + + +4.4. Major IPsec Databases + + Many of the details associated with processing IP traffic in an IPsec + implementation are largely a local matter, not subject to + standardization. However, some external aspects of the processing + must be standardized to ensure interoperability and to provide a + minimum management capability that is essential for productive use of + IPsec. This section describes a general model for processing IP + traffic relative to IPsec functionality, in support of these + interoperability and functionality goals. The model described below + is nominal; implementations need not match details of this model as + presented, but the external behavior of implementations MUST + correspond to the externally observable characteristics of this model + in order to be compliant. + + There are three nominal databases in this model: the Security Policy + Database (SPD), the Security Association Database (SAD), and the Peer + Authorization Database (PAD). The first specifies the policies that + determine the disposition of all IP traffic inbound or outbound from + a host or security gateway (Section 4.4.1). The second database + contains parameters that are associated with each established (keyed) + SA (Section 4.4.2). The third database, the PAD, provides a link + between an SA management protocol (such as IKE) and the SPD (Section + 4.4.3). + + Multiple Separate IPsec Contexts + + If an IPsec implementation acts as a security gateway for multiple + subscribers, it MAY implement multiple separate IPsec contexts. + Each context MAY have and MAY use completely independent + identities, policies, key management SAs, and/or IPsec SAs. This + is for the most part a local implementation matter. However, a + means for associating inbound (SA) proposals with local contexts + is required. To this end, if supported by the key management + protocol in use, context identifiers MAY be conveyed from + initiator to responder in the signaling messages, with the result + that IPsec SAs are created with a binding to a particular context. + For example, a security gateway that provides VPN service to + multiple customers will be able to associate each customer's + traffic with the correct VPN. + + Forwarding vs Security Decisions + + The IPsec model described here embodies a clear separation between + forwarding (routing) and security decisions, to accommodate a wide + range of contexts where IPsec may be employed. Forwarding may be + trivial, in the case where there are only two interfaces, or it + may be complex, e.g., if the context in which IPsec is implemented + + + +Kent & Seo Standards Track [Page 18] + +RFC 4301 Security Architecture for IP December 2005 + + + employs a sophisticated forwarding function. IPsec assumes only + that outbound and inbound traffic that has passed through IPsec + processing is forwarded in a fashion consistent with the context + in which IPsec is implemented. Support for nested SAs is + optional; if required, it requires coordination between forwarding + tables and SPD entries to cause a packet to traverse the IPsec + boundary more than once. + + "Local" vs "Remote" + + In this document, with respect to IP addresses and ports, the + terms "Local" and "Remote" are used for policy rules. "Local" + refers to the entity being protected by an IPsec implementation, + i.e., the "source" address/port of outbound packets or the + "destination" address/port of inbound packets. "Remote" refers to + a peer entity or peer entities. The terms "source" and + "destination" are used for packet header fields. + + "Non-initial" vs "Initial" Fragments + + Throughout this document, the phrase "non-initial fragments" is + used to mean fragments that do not contain all of the selector + values that may be needed for access control (e.g., they might not + contain Next Layer Protocol, source and destination ports, ICMP + message type/code, Mobility Header type). And the phrase "initial + fragment" is used to mean a fragment that contains all the + selector values needed for access control. However, it should be + noted that for IPv6, which fragment contains the Next Layer + Protocol and ports (or ICMP message type/code or Mobility Header + type [Mobip]) will depend on the kind and number of extension + headers present. The "initial fragment" might not be the first + fragment, in this context. + +4.4.1. The Security Policy Database (SPD) + + An SA is a management construct used to enforce security policy for + traffic crossing the IPsec boundary. Thus, an essential element of + SA processing is an underlying Security Policy Database (SPD) that + specifies what services are to be offered to IP datagrams and in what + fashion. The form of the database and its interface are outside the + scope of this specification. However, this section specifies minimum + management functionality that must be provided, to allow a user or + system administrator to control whether and how IPsec is applied to + traffic transmitted or received by a host or transiting a security + gateway. The SPD, or relevant caches, must be consulted during the + processing of all traffic (inbound and outbound), including traffic + not protected by IPsec, that traverses the IPsec boundary. This + includes IPsec management traffic such as IKE. An IPsec + + + +Kent & Seo Standards Track [Page 19] + +RFC 4301 Security Architecture for IP December 2005 + + + implementation MUST have at least one SPD, and it MAY support + multiple SPDs, if appropriate for the context in which the IPsec + implementation operates. There is no requirement to maintain SPDs on + a per-interface basis, as was specified in RFC 2401 [RFC2401]. + However, if an implementation supports multiple SPDs, then it MUST + include an explicit SPD selection function that is invoked to select + the appropriate SPD for outbound traffic processing. The inputs to + this function are the outbound packet and any local metadata (e.g., + the interface via which the packet arrived) required to effect the + SPD selection function. The output of the function is an SPD + identifier (SPD-ID). + + The SPD is an ordered database, consistent with the use of Access + Control Lists (ACLs) or packet filters in firewalls, routers, etc. + The ordering requirement arises because entries often will overlap + due to the presence of (non-trivial) ranges as values for selectors. + Thus, a user or administrator MUST be able to order the entries to + express a desired access control policy. There is no way to impose a + general, canonical order on SPD entries, because of the allowed use + of wildcards for selector values and because the different types of + selectors are not hierarchically related. + + Processing Choices: DISCARD, BYPASS, PROTECT + + An SPD must discriminate among traffic that is afforded IPsec + protection and traffic that is allowed to bypass IPsec. This + applies to the IPsec protection to be applied by a sender and to + the IPsec protection that must be present at the receiver. For + any outbound or inbound datagram, three processing choices are + possible: DISCARD, BYPASS IPsec, or PROTECT using IPsec. The + first choice refers to traffic that is not allowed to traverse the + IPsec boundary (in the specified direction). The second choice + refers to traffic that is allowed to cross the IPsec boundary + without IPsec protection. The third choice refers to traffic that + is afforded IPsec protection, and for such traffic the SPD must + specify the security protocols to be employed, their mode, + security service options, and the cryptographic algorithms to be + used. + + SPD-S, SPD-I, SPD-O + + An SPD is logically divided into three pieces. The SPD-S (secure + traffic) contains entries for all traffic subject to IPsec + protection. SPD-O (outbound) contains entries for all outbound + traffic that is to be bypassed or discarded. SPD-I (inbound) is + applied to inbound traffic that will be bypassed or discarded. + All three of these can be decorrelated (with the exception noted + above for native host implementations) to facilitate caching. If + + + +Kent & Seo Standards Track [Page 20] + +RFC 4301 Security Architecture for IP December 2005 + + + an IPsec implementation supports only one SPD, then the SPD + consists of all three parts. If multiple SPDs are supported, some + of them may be partial, e.g., some SPDs might contain only SPD-I + entries, to control inbound bypassed traffic on a per-interface + basis. The split allows SPD-I to be consulted without having to + consult SPD-S, for such traffic. Since the SPD-I is just a part + of the SPD, if a packet that is looked up in the SPD-I cannot be + matched to an entry there, then the packet MUST be discarded. + Note that for outbound traffic, if a match is not found in SPD-S, + then SPD-O must be checked to see if the traffic should be + bypassed. Similarly, if SPD-O is checked first and no match is + found, then SPD-S must be checked. In an ordered, + non-decorrelated SPD, the entries for the SPD-S, SPD-I, and SPD-O + are interleaved. So there is one lookup in the SPD. + + SPD Entries + + Each SPD entry specifies packet disposition as BYPASS, DISCARD, or + PROTECT. The entry is keyed by a list of one or more selectors. + The SPD contains an ordered list of these entries. The required + selector types are defined in Section 4.4.1.1. These selectors are + used to define the granularity of the SAs that are created in + response to an outbound packet or in response to a proposal from a + peer. The detailed structure of an SPD entry is described in + Section 4.4.1.2. Every SPD SHOULD have a nominal, final entry that + matches anything that is otherwise unmatched, and discards it. + + The SPD MUST permit a user or administrator to specify policy + entries as follows: + + - SPD-I: For inbound traffic that is to be bypassed or discarded, + the entry consists of the values of the selectors that apply to + the traffic to be bypassed or discarded. + + - SPD-O: For outbound traffic that is to be bypassed or + discarded, the entry consists of the values of the selectors + that apply to the traffic to be bypassed or discarded. + + - SPD-S: For traffic that is to be protected using IPsec, the + entry consists of the values of the selectors that apply to the + traffic to be protected via AH or ESP, controls on how to + create SAs based on these selectors, and the parameters needed + to effect this protection (e.g., algorithms, modes, etc.). Note + that an SPD-S entry also contains information such as "populate + from packet" (PFP) flag (see paragraphs below on "How To Derive + the Values for an SAD entry") and bits indicating whether the + + + + + +Kent & Seo Standards Track [Page 21] + +RFC 4301 Security Architecture for IP December 2005 + + + SA lookup makes use of the local and remote IP addresses in + addition to the SPI (see AH [Ken05b] or ESP [Ken05a] + specifications). + + Representing Directionality in an SPD Entry + + For traffic protected by IPsec, the Local and Remote address and + ports in an SPD entry are swapped to represent directionality, + consistent with IKE conventions. In general, the protocols that + IPsec deals with have the property of requiring symmetric SAs with + flipped Local/Remote IP addresses. However, for ICMP, there is + often no such bi-directional authorization requirement. + Nonetheless, for the sake of uniformity and simplicity, SPD + entries for ICMP are specified in the same way as for other + protocols. Note also that for ICMP, Mobility Header, and + non-initial fragments, there are no port fields in these packets. + ICMP has message type and code and Mobility Header has mobility + header type. Thus, SPD entries have provisions for expressing + access controls appropriate for these protocols, in lieu of the + normal port field controls. For bypassed or discarded traffic, + separate inbound and outbound entries are supported, e.g., to + permit unidirectional flows if required. + + OPAQUE and ANY + + For each selector in an SPD entry, in addition to the literal + values that define a match, there are two special values: ANY and + OPAQUE. ANY is a wildcard that matches any value in the + corresponding field of the packet, or that matches packets where + that field is not present or is obscured. OPAQUE indicates that + the corresponding selector field is not available for examination + because it may not be present in a fragment, it does not exist for + the given Next Layer Protocol, or prior application of IPsec may + have encrypted the value. The ANY value encompasses the OPAQUE + value. Thus, OPAQUE need be used only when it is necessary to + distinguish between the case of any allowed value for a field, vs. + the absence or unavailability (e.g., due to encryption) of the + field. + + How to Derive the Values for an SAD Entry + + For each selector in an SPD entry, the entry specifies how to + derive the corresponding values for a new SA Database (SAD, see + Section 4.4.2) entry from those in the SPD and the packet. The + goal is to allow an SAD entry and an SPD cache entry to be created + based on specific selector values from the packet, or from the + matching SPD entry. For outbound traffic, there are SPD-S cache + entries and SPD-O cache entries. For inbound traffic not + + + +Kent & Seo Standards Track [Page 22] + +RFC 4301 Security Architecture for IP December 2005 + + + protected by IPsec, there are SPD-I cache entries and there is the + SAD, which represents the cache for inbound IPsec-protected + traffic (see Section 4.4.2). If IPsec processing is specified for + an entry, a "populate from packet" (PFP) flag may be asserted for + one or more of the selectors in the SPD entry (Local IP address; + Remote IP address; Next Layer Protocol; and, depending on Next + Layer Protocol, Local port and Remote port, or ICMP type/code, or + Mobility Header type). If asserted for a given selector X, the + flag indicates that the SA to be created should take its value for + X from the value in the packet. Otherwise, the SA should take its + value(s) for X from the value(s) in the SPD entry. Note: In the + non-PFP case, the selector values negotiated by the SA management + protocol (e.g., IKEv2) may be a subset of those in the SPD entry, + depending on the SPD policy of the peer. Also, whether a single + flag is used for, e.g., source port, ICMP type/code, and Mobility + Header (MH) type, or a separate flag is used for each, is a local + matter. + + The following example illustrates the use of the PFP flag in the + context of a security gateway or a BITS/BITW implementation. + Consider an SPD entry where the allowed value for Remote address + is a range of IPv4 addresses: 192.0.2.1 to 192.0.2.10. Suppose an + outbound packet arrives with a destination address of 192.0.2.3, + and there is no extant SA to carry this packet. The value used + for the SA created to transmit this packet could be either of the + two values shown below, depending on what the SPD entry for this + selector says is the source of the selector value: + + PFP flag value example of new + for the Remote SAD dest. address + addr. selector selector value + --------------- ------------ + a. PFP TRUE 192.0.2.3 (one host) + b. PFP FALSE 192.0.2.1 to 192.0.2.10 (range of hosts) + + Note that if the SPD entry above had a value of ANY for the Remote + address, then the SAD selector value would have to be ANY for case + (b), but would still be as illustrated for case (a). Thus, the + PFP flag can be used to prohibit sharing of an SA, even among + packets that match the same SPD entry. + + Management Interface + + For every IPsec implementation, there MUST be a management + interface that allows a user or system administrator to manage the + SPD. The interface must allow the user (or administrator) to + specify the security processing to be applied to every packet that + traverses the IPsec boundary. (In a native host IPsec + + + +Kent & Seo Standards Track [Page 23] + +RFC 4301 Security Architecture for IP December 2005 + + + implementation making use of a socket interface, the SPD may not + need to be consulted on a per-packet basis, as noted at the end of + Section 4.4.1.1 and in Section 5.) The management interface for + the SPD MUST allow creation of entries consistent with the + selectors defined in Section 4.4.1.1, and MUST support (total) + ordering of these entries, as seen via this interface. The SPD + entries' selectors are analogous to the ACL or packet filters + commonly found in a stateless firewall or packet filtering router + and which are currently managed this way. + + In host systems, applications MAY be allowed to create SPD + entries. (The means of signaling such requests to the IPsec + implementation are outside the scope of this standard.) However, + the system administrator MUST be able to specify whether or not a + user or application can override (default) system policies. The + form of the management interface is not specified by this document + and may differ for hosts vs. security gateways, and within hosts + the interface may differ for socket-based vs. BITS + implementations. However, this document does specify a standard + set of SPD elements that all IPsec implementations MUST support. + + Decorrelation + + The processing model described in this document assumes the + ability to decorrelate overlapping SPD entries to permit caching, + which enables more efficient processing of outbound traffic in + security gateways and BITS/BITW implementations. Decorrelation + [CoSa04] is only a means of improving performance and simplifying + the processing description. This RFC does not require a compliant + implementation to make use of decorrelation. For example, native + host implementations typically make use of caching implicitly + because they bind SAs to socket interfaces, and thus there is no + requirement to be able to decorrelate SPD entries in these + implementations. + + Note: Unless otherwise qualified, the use of "SPD" refers to the + body of policy information in both ordered or decorrelated + (unordered) state. Appendix B provides an algorithm that can be + used to decorrelate SPD entries, but any algorithm that produces + equivalent output may be used. Note that when an SPD entry is + decorrelated all the resulting entries MUST be linked together, so + that all members of the group derived from an individual, SPD + entry (prior to decorrelation) can all be placed into caches and + into the SAD at the same time. For example, suppose one starts + with an entry A (from an ordered SPD) that when decorrelated, + yields entries A1, A2, and A3. When a packet comes along that + matches, say A2, and triggers the creation of an SA, the SA + management protocol (e.g., IKEv2) negotiates A. And all 3 + + + +Kent & Seo Standards Track [Page 24] + +RFC 4301 Security Architecture for IP December 2005 + + + decorrelated entries, A1, A2, and A3, are placed in the + appropriate SPD-S cache and linked to the SA. The intent is that + use of a decorrelated SPD ought not to create more SAs than would + have resulted from use of a not-decorrelated SPD. + + If a decorrelated SPD is employed, there are three options for + what an initiator sends to a peer via an SA management protocol + (e.g., IKE). By sending the complete set of linked, decorrelated + entries that were selected from the SPD, a peer is given the best + possible information to enable selection of the appropriate SPD + entry at its end, especially if the peer has also decorrelated its + SPD. However, if a large number of decorrelated entries are + linked, this may create large packets for SA negotiation, and + hence fragmentation problems for the SA management protocol. + + Alternatively, the original entry from the (correlated) SPD may be + retained and passed to the SA management protocol. Passing the + correlated SPD entry keeps the use of a decorrelated SPD a local + matter, not visible to peers, and avoids possible fragmentation + concerns, although it provides less precise information to a + responder for matching against the responder's SPD. + + An intermediate approach is to send a subset of the complete set + of linked, decorrelated SPD entries. This approach can avoid the + fragmentation problems cited above yet provide better information + than the original, correlated entry. The major shortcoming of + this approach is that it may cause additional SAs to be created + later, since only a subset of the linked, decorrelated entries are + sent to a peer. Implementers are free to employ any of the + approaches cited above. + + A responder uses the traffic selector proposals it receives via an + SA management protocol to select an appropriate entry in its SPD. + The intent of the matching is to select an SPD entry and create an + SA that most closely matches the intent of the initiator, so that + traffic traversing the resulting SA will be accepted at both ends. + If the responder employs a decorrelated SPD, it SHOULD use the + decorrelated SPD entries for matching, as this will generally + result in creation of SAs that are more likely to match the intent + of both peers. If the responder has a correlated SPD, then it + SHOULD match the proposals against the correlated entries. For + IKEv2, use of a decorrelated SPD offers the best opportunity for a + responder to generate a "narrowed" response. + + In all cases, when a decorrelated SPD is available, the + decorrelated entries are used to populate the SPD-S cache. If the + SPD is not decorrelated, caching is not allowed and an ordered + + + + +Kent & Seo Standards Track [Page 25] + +RFC 4301 Security Architecture for IP December 2005 + + + search of SPD MUST be performed to verify that inbound traffic + arriving on an SA is consistent with the access control policy + expressed in the SPD. + + Handling Changes to the SPD While the System Is Running + + If a change is made to the SPD while the system is running, a + check SHOULD be made of the effect of this change on extant SAs. + An implementation SHOULD check the impact of an SPD change on + extant SAs and SHOULD provide a user/administrator with a + mechanism for configuring what actions to take, e.g., delete an + affected SA, allow an affected SA to continue unchanged, etc. + +4.4.1.1. Selectors + + An SA may be fine-grained or coarse-grained, depending on the + selectors used to define the set of traffic for the SA. For example, + all traffic between two hosts may be carried via a single SA, and + afforded a uniform set of security services. Alternatively, traffic + between a pair of hosts might be spread over multiple SAs, depending + on the applications being used (as defined by the Next Layer Protocol + and related fields, e.g., ports), with different security services + offered by different SAs. Similarly, all traffic between a pair of + security gateways could be carried on a single SA, or one SA could be + assigned for each communicating host pair. The following selector + parameters MUST be supported by all IPsec implementations to + facilitate control of SA granularity. Note that both Local and + Remote addresses should either be IPv4 or IPv6, but not a mix of + address types. Also, note that the Local/Remote port selectors (and + ICMP message type and code, and Mobility Header type) may be labeled + as OPAQUE to accommodate situations where these fields are + inaccessible due to packet fragmentation. + + - Remote IP Address(es) (IPv4 or IPv6): This is a list of ranges + of IP addresses (unicast, broadcast (IPv4 only)). This + structure allows expression of a single IP address (via a + trivial range), or a list of addresses (each a trivial range), + or a range of addresses (low and high values, inclusive), as + well as the most generic form of a list of ranges. Address + ranges are used to support more than one remote system sharing + the same SA, e.g., behind a security gateway. + + - Local IP Address(es) (IPv4 or IPv6): This is a list of ranges of + IP addresses (unicast, broadcast (IPv4 only)). This structure + allows expression of a single IP address (via a trivial range), + or a list of addresses (each a trivial range), or a range of + addresses (low and high values, inclusive), as well as the most + generic form of a list of ranges. Address ranges are used to + + + +Kent & Seo Standards Track [Page 26] + +RFC 4301 Security Architecture for IP December 2005 + + + support more than one source system sharing the same SA, e.g., + behind a security gateway. Local refers to the address(es) + being protected by this implementation (or policy entry). + + Note: The SPD does not include support for multicast address + entries. To support multicast SAs, an implementation should + make use of a Group SPD (GSPD) as defined in [RFC3740]. GSPD + entries require a different structure, i.e., one cannot use the + symmetric relationship associated with local and remote address + values for unicast SAs in a multicast context. Specifically, + outbound traffic directed to a multicast address on an SA would + not be received on a companion, inbound SA with the multicast + address as the source. + + - Next Layer Protocol: Obtained from the IPv4 "Protocol" or the + IPv6 "Next Header" fields. This is an individual protocol + number, ANY, or for IPv6 only, OPAQUE. The Next Layer Protocol + is whatever comes after any IP extension headers that are + present. To simplify locating the Next Layer Protocol, there + SHOULD be a mechanism for configuring which IPv6 extension + headers to skip. The default configuration for which protocols + to skip SHOULD include the following protocols: 0 (Hop-by-hop + options), 43 (Routing Header), 44 (Fragmentation Header), and 60 + (Destination Options). Note: The default list does NOT include + 51 (AH) or 50 (ESP). From a selector lookup point of view, + IPsec treats AH and ESP as Next Layer Protocols. + + Several additional selectors depend on the Next Layer Protocol + value: + + * If the Next Layer Protocol uses two ports (as do TCP, UDP, + SCTP, and others), then there are selectors for Local and + Remote Ports. Each of these selectors has a list of ranges + of values. Note that the Local and Remote ports may not be + available in the case of receipt of a fragmented packet or if + the port fields have been protected by IPsec (encrypted); + thus, a value of OPAQUE also MUST be supported. Note: In a + non-initial fragment, port values will not be available. If + a port selector specifies a value other than ANY or OPAQUE, + it cannot match packets that are non-initial fragments. If + the SA requires a port value other than ANY or OPAQUE, an + arriving fragment without ports MUST be discarded. (See + Section 7, "Handling Fragments".) + + * If the Next Layer Protocol is a Mobility Header, then there + is a selector for IPv6 Mobility Header message type (MH type) + [Mobip]. This is an 8-bit value that identifies a particular + mobility message. Note that the MH type may not be available + + + +Kent & Seo Standards Track [Page 27] + +RFC 4301 Security Architecture for IP December 2005 + + + in the case of receipt of a fragmented packet. (See Section + 7, "Handling Fragments".) For IKE, the IPv6 Mobility Header + message type (MH type) is placed in the most significant + eight bits of the 16-bit local "port" selector. + + * If the Next Layer Protocol value is ICMP, then there is a + 16-bit selector for the ICMP message type and code. The + message type is a single 8-bit value, which defines the type + of an ICMP message, or ANY. The ICMP code is a single 8-bit + value that defines a specific subtype for an ICMP message. + For IKE, the message type is placed in the most significant 8 + bits of the 16-bit selector and the code is placed in the + least significant 8 bits. This 16-bit selector can contain a + single type and a range of codes, a single type and ANY code, + and ANY type and ANY code. Given a policy entry with a range + of Types (T-start to T-end) and a range of Codes (C-start to + C-end), and an ICMP packet with Type t and Code c, an + implementation MUST test for a match using + + (T-start*256) + C-start <= (t*256) + c <= (T-end*256) + + C-end + + Note that the ICMP message type and code may not be available + in the case of receipt of a fragmented packet. (See Section + 7, "Handling Fragments".) + + - Name: This is not a selector like the others above. It is not + acquired from a packet. A name may be used as a symbolic + identifier for an IPsec Local or Remote address. Named SPD + entries are used in two ways: + + 1. A named SPD entry is used by a responder (not an initiator) + in support of access control when an IP address would not be + appropriate for the Remote IP address selector, e.g., for + "road warriors". The name used to match this field is + communicated during the IKE negotiation in the ID payload. + In this context, the initiator's Source IP address (inner IP + header in tunnel mode) is bound to the Remote IP address in + the SAD entry created by the IKE negotiation. This address + overrides the Remote IP address value in the SPD, when the + SPD entry is selected in this fashion. All IPsec + implementations MUST support this use of names. + + 2. A named SPD entry may be used by an initiator to identify a + user for whom an IPsec SA will be created (or for whom + traffic may be bypassed). The initiator's IP source address + (from inner IP header in tunnel mode) is used to replace the + following if and when they are created: + + + +Kent & Seo Standards Track [Page 28] + +RFC 4301 Security Architecture for IP December 2005 + + + - local address in the SPD cache entry + - local address in the outbound SAD entry + - remote address in the inbound SAD entry + + Support for this use is optional for multi-user, native host + implementations and not applicable to other implementations. + Note that this name is used only locally; it is not + communicated by the key management protocol. Also, name + forms other than those used for case 1 above (responder) are + applicable in the initiator context (see below). + + An SPD entry can contain both a name (or a list of names) and + also values for the Local or Remote IP address. + + For case 1, responder, the identifiers employed in named SPD + entries are one of the following four types: + + a. a fully qualified user name string (email), e.g., + mozart@foo.example.com + (this corresponds to ID_RFC822_ADDR in IKEv2) + + b. a fully qualified DNS name, e.g., + foo.example.com + (this corresponds to ID_FQDN in IKEv2) + + c. X.500 distinguished name, e.g., [WaKiHo97], + CN = Stephen T. Kent, O = BBN Technologies, + SP = MA, C = US + (this corresponds to ID_DER_ASN1_DN in IKEv2, after + decoding) + + d. a byte string + (this corresponds to Key_ID in IKEv2) + + For case 2, initiator, the identifiers employed in named SPD + entries are of type byte string. They are likely to be Unix + UIDs, Windows security IDs, or something similar, but could + also be a user name or account name. In all cases, this + identifier is only of local concern and is not transmitted. + + The IPsec implementation context determines how selectors are used. + For example, a native host implementation typically makes use of a + socket interface. When a new connection is established, the SPD can + be consulted and an SA bound to the socket. Thus, traffic sent via + that socket need not result in additional lookups to the SPD (SPD-O + and SPD-S) cache. In contrast, a BITS, BITW, or security gateway + implementation needs to look at each packet and perform an + SPD-O/SPD-S cache lookup based on the selectors. + + + +Kent & Seo Standards Track [Page 29] + +RFC 4301 Security Architecture for IP December 2005 + + +4.4.1.2. Structure of an SPD Entry + + This section contains a prose description of an SPD entry. Also, + Appendix C provides an example of an ASN.1 definition of an SPD + entry. + + This text describes the SPD in a fashion that is intended to map + directly into IKE payloads to ensure that the policy required by SPD + entries can be negotiated through IKE. Unfortunately, the semantics + of the version of IKEv2 published concurrently with this document + [Kau05] do not align precisely with those defined for the SPD. + Specifically, IKEv2 does not enable negotiation of a single SA that + binds multiple pairs of local and remote addresses and ports to a + single SA. Instead, when multiple local and remote addresses and + ports are negotiated for an SA, IKEv2 treats these not as pairs, but + as (unordered) sets of local and remote values that can be + arbitrarily paired. Until IKE provides a facility that conveys the + semantics that are expressed in the SPD via selector sets (as + described below), users MUST NOT include multiple selector sets in a + single SPD entry unless the access control intent aligns with the IKE + "mix and match" semantics. An implementation MAY warn users, to + alert them to this problem if users create SPD entries with multiple + selector sets, the syntax of which indicates possible conflicts with + current IKE semantics. + + The management GUI can offer the user other forms of data entry and + display, e.g., the option of using address prefixes as well as + ranges, and symbolic names for protocols, ports, etc. (Do not confuse + the use of symbolic names in a management interface with the SPD + selector "Name".) Note that Remote/Local apply only to IP addresses + and ports, not to ICMP message type/code or Mobility Header type. + Also, if the reserved, symbolic selector value OPAQUE or ANY is + employed for a given selector type, only that value may appear in the + list for that selector, and it must appear only once in the list for + that selector. Note that ANY and OPAQUE are local syntax conventions + -- IKEv2 negotiates these values via the ranges indicated below: + + ANY: start = 0 end = <max> + OPAQUE: start = <max> end = 0 + + An SPD is an ordered list of entries each of which contains the + following fields. + + o Name -- a list of IDs. This quasi-selector is optional. + The forms that MUST be supported are described above in + Section 4.4.1.1 under "Name". + + + + + +Kent & Seo Standards Track [Page 30] + +RFC 4301 Security Architecture for IP December 2005 + + + o PFP flags -- one per traffic selector. A given flag, e.g., + for Next Layer Protocol, applies to the relevant selector + across all "selector sets" (see below) contained in an SPD + entry. When creating an SA, each flag specifies for the + corresponding traffic selector whether to instantiate the + selector from the corresponding field in the packet that + triggered the creation of the SA or from the value(s) in + the corresponding SPD entry (see Section 4.4.1, "How to + Derive the Values for an SAD Entry"). Whether a single + flag is used for, e.g., source port, ICMP type/code, and + MH type, or a separate flag is used for each, is a local + matter. There are PFP flags for: + - Local Address + - Remote Address + - Next Layer Protocol + - Local Port, or ICMP message type/code or Mobility + Header type (depending on the next layer protocol) + - Remote Port, or ICMP message type/code or Mobility + Header type (depending on the next layer protocol) + + o One to N selector sets that correspond to the "condition" + for applying a particular IPsec action. Each selector set + contains: + - Local Address + - Remote Address + - Next Layer Protocol + - Local Port, or ICMP message type/code or Mobility + Header type (depending on the next layer protocol) + - Remote Port, or ICMP message type/code or Mobility + Header type (depending on the next layer protocol) + + Note: The "next protocol" selector is an individual value + (unlike the local and remote IP addresses) in a selector + set entry. This is consistent with how IKEv2 negotiates + the Traffic Selector (TS) values for an SA. It also makes + sense because one may need to associate different port + fields with different protocols. It is possible to + associate multiple protocols (and ports) with a single SA + by specifying multiple selector sets for that SA. + + o Processing info -- which action is required -- PROTECT, + BYPASS, or DISCARD. There is just one action that goes + with all the selector sets, not a separate action for each + set. If the required processing is PROTECT, the entry + contains the following information. + - IPsec mode -- tunnel or transport + + + + + +Kent & Seo Standards Track [Page 31] + +RFC 4301 Security Architecture for IP December 2005 + + + - (if tunnel mode) local tunnel address -- For a + non-mobile host, if there is just one interface, this + is straightforward; if there are multiple + interfaces, this must be statically configured. For a + mobile host, the specification of the local address + is handled externally to IPsec. + - (if tunnel mode) remote tunnel address -- There is no + standard way to determine this. See 4.5.3, "Locating + a Security Gateway". + - Extended Sequence Number -- Is this SA using extended + sequence numbers? + - stateful fragment checking -- Is this SA using + stateful fragment checking? (See Section 7 for more + details.) + - Bypass DF bit (T/F) -- applicable to tunnel mode SAs + - Bypass DSCP (T/F) or map to unprotected DSCP values + (array) if needed to restrict bypass of DSCP values -- + applicable to tunnel mode SAs + - IPsec protocol -- AH or ESP + - algorithms -- which ones to use for AH, which ones to + use for ESP, which ones to use for combined mode, + ordered by decreasing priority + + It is a local matter as to what information is kept with regard to + handling extant SAs when the SPD is changed. + +4.4.1.3. More Regarding Fields Associated with Next Layer Protocols + + Additional selectors are often associated with fields in the Next + Layer Protocol header. A particular Next Layer Protocol can have + zero, one, or two selectors. There may be situations where there + aren't both local and remote selectors for the fields that are + dependent on the Next Layer Protocol. The IPv6 Mobility Header has + only a Mobility Header message type. AH and ESP have no further + selector fields. A system may be willing to send an ICMP message + type and code that it does not want to receive. In the descriptions + below, "port" is used to mean a field that is dependent on the Next + Layer Protocol. + + A. If a Next Layer Protocol has no "port" selectors, then + the Local and Remote "port" selectors are set to OPAQUE in + the relevant SPD entry, e.g., + + Local's + next layer protocol = AH + "port" selector = OPAQUE + + + + + +Kent & Seo Standards Track [Page 32] + +RFC 4301 Security Architecture for IP December 2005 + + + Remote's + next layer protocol = AH + "port" selector = OPAQUE + + B. Even if a Next Layer Protocol has only one selector, e.g., + Mobility Header type, then the Local and Remote "port" + selectors are used to indicate whether a system is + willing to send and/or receive traffic with the specified + "port" values. For example, if Mobility Headers of a + specified type are allowed to be sent and received via an + SA, then the relevant SPD entry would be set as follows: + + Local's + next layer protocol = Mobility Header + "port" selector = Mobility Header message type + + Remote's + next layer protocol = Mobility Header + "port" selector = Mobility Header message type + + If Mobility Headers of a specified type are allowed to be + sent but NOT received via an SA, then the relevant SPD + entry would be set as follows: + + Local's + next layer protocol = Mobility Header + "port" selector = Mobility Header message type + + Remote's + next layer protocol = Mobility Header + "port" selector = OPAQUE + + If Mobility Headers of a specified type are allowed to be + received but NOT sent via an SA, then the relevant SPD + entry would be set as follows: + + Local's + next layer protocol = Mobility Header + "port" selector = OPAQUE + + Remote's + next layer protocol = Mobility Header + "port" selector = Mobility Header message type + + C. If a system is willing to send traffic with a particular + "port" value but NOT receive traffic with that kind of + port value, the system's traffic selectors are set as + follows in the relevant SPD entry: + + + +Kent & Seo Standards Track [Page 33] + +RFC 4301 Security Architecture for IP December 2005 + + + Local's + next layer protocol = ICMP + "port" selector = <specific ICMP type & code> + + Remote's + next layer protocol = ICMP + "port" selector = OPAQUE + + D. To indicate that a system is willing to receive traffic + with a particular "port" value but NOT send that kind of + traffic, the system's traffic selectors are set as follows + in the relevant SPD entry: + + Local's + next layer protocol = ICMP + "port" selector = OPAQUE + + Remote's + next layer protocol = ICMP + "port" selector = <specific ICMP type & code> + + For example, if a security gateway is willing to allow + systems behind it to send ICMP traceroutes, but is not + willing to let outside systems run ICMP traceroutes to + systems behind it, then the security gateway's traffic + selectors are set as follows in the relevant SPD entry: + + Local's + next layer protocol = 1 (ICMPv4) + "port" selector = 30 (traceroute) + + Remote's + next layer protocol = 1 (ICMPv4) + "port" selector = OPAQUE + +4.4.2. Security Association Database (SAD) + + In each IPsec implementation, there is a nominal Security Association + Database (SAD), in which each entry defines the parameters associated + with one SA. Each SA has an entry in the SAD. For outbound + processing, each SAD entry is pointed to by entries in the SPD-S part + of the SPD cache. For inbound processing, for unicast SAs, the SPI + is used either alone to look up an SA or in conjunction with the + IPsec protocol type. If an IPsec implementation supports multicast, + the SPI plus destination address, or SPI plus destination and source + addresses are used to look up the SA. (See Section 4.1 for details on + the algorithm that MUST be used for mapping inbound IPsec datagrams + to SAs.) The following parameters are associated with each entry in + + + +Kent & Seo Standards Track [Page 34] + +RFC 4301 Security Architecture for IP December 2005 + + + the SAD. They should all be present except where otherwise noted, + e.g., AH Authentication algorithm. This description does not purport + to be a MIB, only a specification of the minimal data items required + to support an SA in an IPsec implementation. + + For each of the selectors defined in Section 4.4.1.1, the entry for + an inbound SA in the SAD MUST be initially populated with the value + or values negotiated at the time the SA was created. (See the + paragraph in Section 4.4.1 under "Handling Changes to the SPD while + the System is Running" for guidance on the effect of SPD changes on + extant SAs.) For a receiver, these values are used to check that the + header fields of an inbound packet (after IPsec processing) match the + selector values negotiated for the SA. Thus, the SAD acts as a cache + for checking the selectors of inbound traffic arriving on SAs. For + the receiver, this is part of verifying that a packet arriving on an + SA is consistent with the policy for the SA. (See Section 6 for rules + for ICMP messages.) These fields can have the form of specific + values, ranges, ANY, or OPAQUE, as described in Section 4.4.1.1, + "Selectors". Note also that there are a couple of situations in + which the SAD can have entries for SAs that do not have corresponding + entries in the SPD. Since this document does not mandate that the + SAD be selectively cleared when the SPD is changed, SAD entries can + remain when the SPD entries that created them are changed or deleted. + Also, if a manually keyed SA is created, there could be an SAD entry + for this SA that does not correspond to any SPD entry. + + Note: The SAD can support multicast SAs, if manually configured. An + outbound multicast SA has the same structure as a unicast SA. The + source address is that of the sender, and the destination address is + the multicast group address. An inbound, multicast SA must be + configured with the source addresses of each peer authorized to + transmit to the multicast SA in question. The SPI value for a + multicast SA is provided by a multicast group controller, not by the + receiver, as for a unicast SA. Because an SAD entry may be required + to accommodate multiple, individual IP source addresses that were + part of an SPD entry (for unicast SAs), the required facility for + inbound, multicast SAs is a feature already present in an IPsec + implementation. However, because the SPD has no provisions for + accommodating multicast entries, this document does not specify an + automated way to create an SAD entry for a multicast, inbound SA. + Only manually configured SAD entries can be created to accommodate + inbound, multicast traffic. + + Implementation Guidance: This document does not specify how an SPD-S + entry refers to the corresponding SAD entry, as this is an + implementation-specific detail. However, some implementations (based + on experience from RFC 2401) are known to have problems in this + regard. In particular, simply storing the (remote tunnel header IP + + + +Kent & Seo Standards Track [Page 35] + +RFC 4301 Security Architecture for IP December 2005 + + + address, remote SPI) pair in the SPD cache is not sufficient, since + the pair does not always uniquely identify a single SAD entry. For + instance, two hosts behind the same NAT could choose the same SPI + value. The situation also may arise if a host is assigned an IP + address (e.g., via DHCP) previously used by some other host, and the + SAs associated with the old host have not yet been deleted via dead + peer detection mechanisms. This may lead to packets being sent over + the wrong SA or, if key management ensures the pair is unique, + denying the creation of otherwise valid SAs. Thus, implementors + should implement links between the SPD cache and the SAD in a way + that does not engender such problems. + +4.4.2.1. Data Items in the SAD + + The following data items MUST be in the SAD: + + o Security Parameter Index (SPI): a 32-bit value selected by the + receiving end of an SA to uniquely identify the SA. In an SAD + entry for an outbound SA, the SPI is used to construct the + packet's AH or ESP header. In an SAD entry for an inbound SA, the + SPI is used to map traffic to the appropriate SA (see text on + unicast/multicast in Section 4.1). + + o Sequence Number Counter: a 64-bit counter used to generate the + Sequence Number field in AH or ESP headers. 64-bit sequence + numbers are the default, but 32-bit sequence numbers are also + supported if negotiated. + + o Sequence Counter Overflow: a flag indicating whether overflow of + the sequence number counter should generate an auditable event and + prevent transmission of additional packets on the SA, or whether + rollover is permitted. The audit log entry for this event SHOULD + include the SPI value, current date/time, Local Address, Remote + Address, and the selectors from the relevant SAD entry. + + o Anti-Replay Window: a 64-bit counter and a bit-map (or equivalent) + used to determine whether an inbound AH or ESP packet is a replay. + + Note: If anti-replay has been disabled by the receiver for an SA, + e.g., in the case of a manually keyed SA, then the Anti-Replay + Window is ignored for the SA in question. 64-bit sequence numbers + are the default, but this counter size accommodates 32-bit + sequence numbers as well. + + o AH Authentication algorithm, key, etc. This is required only if + AH is supported. + + + + + +Kent & Seo Standards Track [Page 36] + +RFC 4301 Security Architecture for IP December 2005 + + + o ESP Encryption algorithm, key, mode, IV, etc. If a combined mode + algorithm is used, these fields will not be applicable. + + o ESP integrity algorithm, keys, etc. If the integrity service is + not selected, these fields will not be applicable. If a combined + mode algorithm is used, these fields will not be applicable. + + o ESP combined mode algorithms, key(s), etc. This data is used when + a combined mode (encryption and integrity) algorithm is used with + ESP. If a combined mode algorithm is not used, these fields are + not applicable. + + o Lifetime of this SA: a time interval after which an SA must be + replaced with a new SA (and new SPI) or terminated, plus an + indication of which of these actions should occur. This may be + expressed as a time or byte count, or a simultaneous use of both + with the first lifetime to expire taking precedence. A compliant + implementation MUST support both types of lifetimes, and MUST + support a simultaneous use of both. If time is employed, and if + IKE employs X.509 certificates for SA establishment, the SA + lifetime must be constrained by the validity intervals of the + certificates, and the NextIssueDate of the Certificate Revocation + Lists (CRLs) used in the IKE exchange for the SA. Both initiator + and responder are responsible for constraining the SA lifetime in + this fashion. Note: The details of how to handle the refreshing + of keys when SAs expire is a local matter. However, one + reasonable approach is: + + (a) If byte count is used, then the implementation SHOULD count the + number of bytes to which the IPsec cryptographic algorithm is + applied. For ESP, this is the encryption algorithm (including + Null encryption) and for AH, this is the authentication + algorithm. This includes pad bytes, etc. Note that + implementations MUST be able to handle having the counters at + the ends of an SA get out of synch, e.g., because of packet + loss or because the implementations at each end of the SA + aren't doing things the same way. + + (b) There SHOULD be two kinds of lifetime -- a soft lifetime that + warns the implementation to initiate action such as setting up + a replacement SA, and a hard lifetime when the current SA ends + and is destroyed. + + (c) If the entire packet does not get delivered during the SA's + lifetime, the packet SHOULD be discarded. + + o IPsec protocol mode: tunnel or transport. Indicates which mode of + AH or ESP is applied to traffic on this SA. + + + +Kent & Seo Standards Track [Page 37] + +RFC 4301 Security Architecture for IP December 2005 + + + o Stateful fragment checking flag. Indicates whether or not + stateful fragment checking applies to this SA. + + o Bypass DF bit (T/F) -- applicable to tunnel mode SAs where both + inner and outer headers are IPv4. + + o DSCP values -- the set of DSCP values allowed for packets carried + over this SA. If no values are specified, no DSCP-specific + filtering is applied. If one or more values are specified, these + are used to select one SA among several that match the traffic + selectors for an outbound packet. Note that these values are NOT + checked against inbound traffic arriving on the SA. + + o Bypass DSCP (T/F) or map to unprotected DSCP values (array) if + needed to restrict bypass of DSCP values -- applicable to tunnel + mode SAs. This feature maps DSCP values from an inner header to + values in an outer header, e.g., to address covert channel + signaling concerns. + + o Path MTU: any observed path MTU and aging variables. + + o Tunnel header IP source and destination address -- both addresses + must be either IPv4 or IPv6 addresses. The version implies the + type of IP header to be used. Only used when the IPsec protocol + mode is tunnel. + +4.4.2.2. Relationship between SPD, PFP flag, packet, and SAD + + For each selector, the following tables show the relationship + between the value in the SPD, the PFP flag, the value in the + triggering packet, and the resulting value in the SAD. Note that + the administrative interface for IPsec can use various syntactic + options to make it easier for the administrator to enter rules. + For example, although a list of ranges is what IKEv2 sends, it + might be clearer and less error prone for the user to enter a + single IP address or IP address prefix. + + + + + + + + + + + + + + + +Kent & Seo Standards Track [Page 38] + +RFC 4301 Security Architecture for IP December 2005 + + + Value in + Triggering Resulting SAD + Selector SPD Entry PFP Packet Entry + -------- ---------------- --- ------------ -------------- + loc addr list of ranges 0 IP addr "S" list of ranges + ANY 0 IP addr "S" ANY + list of ranges 1 IP addr "S" "S" + ANY 1 IP addr "S" "S" + + rem addr list of ranges 0 IP addr "D" list of ranges + ANY 0 IP addr "D" ANY + list of ranges 1 IP addr "D" "D" + ANY 1 IP addr "D" "D" + + protocol list of prot's* 0 prot. "P" list of prot's* + ANY** 0 prot. "P" ANY + OPAQUE**** 0 prot. "P" OPAQUE + + list of prot's* 0 not avail. discard packet + ANY** 0 not avail. ANY + OPAQUE**** 0 not avail. OPAQUE + + list of prot's* 1 prot. "P" "P" + ANY** 1 prot. "P" "P" + OPAQUE**** 1 prot. "P" *** + + list of prot's* 1 not avail. discard packet + ANY** 1 not avail. discard packet + OPAQUE**** 1 not avail. *** + + + + + + + + + + + + + + + + + + + + + + +Kent & Seo Standards Track [Page 39] + +RFC 4301 Security Architecture for IP December 2005 + + + If the protocol is one that has two ports, then there will be + selectors for both Local and Remote ports. + + Value in + Triggering Resulting SAD + Selector SPD Entry PFP Packet Entry + -------- ---------------- --- ------------ -------------- + loc port list of ranges 0 src port "s" list of ranges + ANY 0 src port "s" ANY + OPAQUE 0 src port "s" OPAQUE + + list of ranges 0 not avail. discard packet + ANY 0 not avail. ANY + OPAQUE 0 not avail. OPAQUE + + list of ranges 1 src port "s" "s" + ANY 1 src port "s" "s" + OPAQUE 1 src port "s" *** + + list of ranges 1 not avail. discard packet + ANY 1 not avail. discard packet + OPAQUE 1 not avail. *** + + + rem port list of ranges 0 dst port "d" list of ranges + ANY 0 dst port "d" ANY + OPAQUE 0 dst port "d" OPAQUE + + list of ranges 0 not avail. discard packet + ANY 0 not avail. ANY + OPAQUE 0 not avail. OPAQUE + + list of ranges 1 dst port "d" "d" + ANY 1 dst port "d" "d" + OPAQUE 1 dst port "d" *** + + list of ranges 1 not avail. discard packet + ANY 1 not avail. discard packet + OPAQUE 1 not avail. *** + + + + + + + + + + + + +Kent & Seo Standards Track [Page 40] + +RFC 4301 Security Architecture for IP December 2005 + + + If the protocol is mobility header, then there will be a selector + for mh type. + + Value in + Triggering Resulting SAD + Selector SPD Entry PFP Packet Entry + -------- ---------------- --- ------------ -------------- + mh type list of ranges 0 mh type "T" list of ranges + ANY 0 mh type "T" ANY + OPAQUE 0 mh type "T" OPAQUE + + list of ranges 0 not avail. discard packet + ANY 0 not avail. ANY + OPAQUE 0 not avail. OPAQUE + + list of ranges 1 mh type "T" "T" + ANY 1 mh type "T" "T" + OPAQUE 1 mh type "T" *** + + list of ranges 1 not avail. discard packet + ANY 1 not avail. discard packet + OPAQUE 1 not avail. *** + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Kent & Seo Standards Track [Page 41] + +RFC 4301 Security Architecture for IP December 2005 + + + If the protocol is ICMP, then there will be a 16-bit selector for + ICMP type and ICMP code. Note that the type and code are bound to + each other, i.e., the codes apply to the particular type. This + 16-bit selector can contain a single type and a range of codes, a + single type and ANY code, and ANY type and ANY code. + + Value in + Triggering Resulting SAD + Selector SPD Entry PFP Packet Entry + --------- ---------------- --- ------------ -------------- + ICMP type a single type & 0 type "t" & single type & + and code range of codes code "c" range of codes + a single type & 0 type "t" & single type & + ANY code code "c" ANY code + ANY type & ANY 0 type "t" & ANY type & + code code "c" ANY code + OPAQUE 0 type "t" & OPAQUE + code "c" + + a single type & 0 not avail. discard packet + range of codes + a single type & 0 not avail. discard packet + ANY code + ANY type & 0 not avail. ANY type & + ANY code ANY code + OPAQUE 0 not avail. OPAQUE + + a single type & 1 type "t" & "t" and "c" + range of codes code "c" + a single type & 1 type "t" & "t" and "c" + ANY code code "c" + ANY type & 1 type "t" & "t" and "c" + ANY code code "c" + OPAQUE 1 type "t" & *** + code "c" + + a single type & 1 not avail. discard packet + range of codes + a single type & 1 not avail. discard packet + ANY code + ANY type & 1 not avail. discard packet + ANY code + OPAQUE 1 not avail. *** + + + + + + + + +Kent & Seo Standards Track [Page 42] + +RFC 4301 Security Architecture for IP December 2005 + + + If the name selector is used: + + Value in + Triggering Resulting SAD + Selector SPD Entry PFP Packet Entry + --------- ---------------- --- ------------ -------------- + name list of user or N/A N/A N/A + system names + + * "List of protocols" is the information, not the way + that the SPD or SAD or IKEv2 have to represent this + information. + ** 0 (zero) is used by IKE to indicate ANY for + protocol. + *** Use of PFP=1 with an OPAQUE value is an error and + SHOULD be prohibited by an IPsec implementation. + **** The protocol field cannot be OPAQUE in IPv4. This + table entry applies only to IPv6. + +4.4.3. Peer Authorization Database (PAD) + + The Peer Authorization Database (PAD) provides the link between the + SPD and a security association management protocol such as IKE. It + embodies several critical functions: + + o identifies the peers or groups of peers that are authorized + to communicate with this IPsec entity + o specifies the protocol and method used to authenticate each + peer + o provides the authentication data for each peer + o constrains the types and values of IDs that can be asserted + by a peer with regard to child SA creation, to ensure that the + peer does not assert identities for lookup in the SPD that it + is not authorized to represent, when child SAs are created + o peer gateway location info, e.g., IP address(es) or DNS names, + MAY be included for peers that are known to be "behind" a + security gateway + + The PAD provides these functions for an IKE peer when the peer acts + as either the initiator or the responder. + + To perform these functions, the PAD contains an entry for each peer + or group of peers with which the IPsec entity will communicate. An + entry names an individual peer (a user, end system or security + gateway) or specifies a group of peers (using ID matching rules + defined below). The entry specifies the authentication protocol + (e.g., IKEv1, IKEv2, KINK) method used (e.g., certificates or pre- + shared secrets) and the authentication data (e.g., the pre-shared + + + +Kent & Seo Standards Track [Page 43] + +RFC 4301 Security Architecture for IP December 2005 + + + secret or the trust anchor relative to which the peer's certificate + will be validated). For certificate-based authentication, the entry + also may provide information to assist in verifying the revocation + status of the peer, e.g., a pointer to a CRL repository or the name + of an Online Certificate Status Protocol (OCSP) server associated + with the peer or with the trust anchor associated with the peer. + + Each entry also specifies whether the IKE ID payload will be used as + a symbolic name for SPD lookup, or whether the remote IP address + provided in traffic selector payloads will be used for SPD lookups + when child SAs are created. + + Note that the PAD information MAY be used to support creation of more + than one tunnel mode SA at a time between two peers, e.g., two + tunnels to protect the same addresses/hosts, but with different + tunnel endpoints. + +4.4.3.1. PAD Entry IDs and Matching Rules + + The PAD is an ordered database, where the order is defined by an + administrator (or a user in the case of a single-user end system). + Usually, the same administrator will be responsible for both the PAD + and SPD, since the two databases must be coordinated. The ordering + requirement for the PAD arises for the same reason as for the SPD, + i.e., because use of "star name" entries allows for overlaps in the + set of IKE IDs that could match a specific entry. + + Six types of IDs are supported for entries in the PAD, consistent + with the symbolic name types and IP addresses used to identify SPD + entries. The ID for each entry acts as the index for the PAD, i.e., + it is the value used to select an entry. All of these ID types can + be used to match IKE ID payload types. The six types are: + + o DNS name (specific or partial) + o Distinguished Name (complete or sub-tree constrained) + o RFC 822 email address (complete or partially qualified) + o IPv4 address (range) + o IPv6 address (range) + o Key ID (exact match only) + + The first three name types can accommodate sub-tree matching as well + as exact matches. A DNS name may be fully qualified and thus match + exactly one name, e.g., foo.example.com. Alternatively, the name may + encompass a group of peers by being partially specified, e.g., the + string ".example.com" could be used to match any DNS name ending in + these two domain name components. + + + + + +Kent & Seo Standards Track [Page 44] + +RFC 4301 Security Architecture for IP December 2005 + + + Similarly, a Distinguished Name may specify a complete Distinguished + Name to match exactly one entry, e.g., CN = Stephen, O = BBN + Technologies, SP = MA, C = US. Alternatively, an entry may encompass + a group of peers by specifying a sub-tree, e.g., an entry of the form + "C = US, SP = MA" might be used to match all DNs that contain these + two attributes as the top two Relative Distinguished Names (RDNs). + + For an RFC 822 e-mail addresses, the same options exist. A complete + address such as foo@example.com matches one entity, but a sub-tree + name such as "@example.com" could be used to match all the entities + with names ending in those two domain names to the right of the @. + + The specific syntax used by an implementation to accommodate sub-tree + matching for distinguished names, domain names or RFC 822 e-mail + addresses is a local matter. But, at a minimum, sub-tree matching of + the sort described above MUST be supported. (Substring matching + within a DN, DNS name, or RFC 822 address MAY be supported, but is + not required.) + + For IPv4 and IPv6 addresses, the same address range syntax used for + SPD entries MUST be supported. This allows specification of an + individual address (via a trivial range), an address prefix (by + choosing a range that adheres to Classless Inter-Domain Routing + (CIDR)-style prefixes), or an arbitrary address range. + + The Key ID field is defined as an OCTET string in IKE. For this name + type, only exact-match syntax MUST be supported (since there is no + explicit structure for this ID type). Additional matching functions + MAY be supported for this ID type. + +4.4.3.2. IKE Peer Authentication Data + + Once an entry is located based on an ordered search of the PAD based + on ID field matching, it is necessary to verify the asserted + identity, i.e., to authenticate the asserted ID. For each PAD entry, + there is an indication of the type of authentication to be performed. + This document requires support for two required authentication data + types: + + - X.509 certificate + - pre-shared secret + + For authentication based on an X.509 certificate, the PAD entry + contains a trust anchor via which the end entity (EE) certificate for + the peer must be verifiable, either directly or via a certificate + path. See RFC 3280 for the definition of a trust anchor. An entry + used with certificate-based authentication MAY include additional + data to facilitate certificate revocation status, e.g., a list of + + + +Kent & Seo Standards Track [Page 45] + +RFC 4301 Security Architecture for IP December 2005 + + + appropriate OCSP responders or CRL repositories, and associated + authentication data. For authentication based on a pre-shared + secret, the PAD contains the pre-shared secret to be used by IKE. + + This document does not require that the IKE ID asserted by a peer be + syntactically related to a specific field in an end entity + certificate that is employed to authenticate the identity of that + peer. However, it often will be appropriate to impose such a + requirement, e.g., when a single entry represents a set of peers each + of whom may have a distinct SPD entry. Thus, implementations MUST + provide a means for an administrator to require a match between an + asserted IKE ID and the subject name or subject alt name in a + certificate. The former is applicable to IKE IDs expressed as + distinguished names; the latter is appropriate for DNS names, RFC 822 + e-mail addresses, and IP addresses. Since KEY ID is intended for + identifying a peer authenticated via a pre-shared secret, there is no + requirement to match this ID type to a certificate field. + + See IKEv1 [HarCar98] and IKEv2 [Kau05] for details of how IKE + performs peer authentication using certificates or pre-shared + secrets. + + This document does not mandate support for any other authentication + methods, although such methods MAY be employed. + +4.4.3.3. Child SA Authorization Data + + Once an IKE peer is authenticated, child SAs may be created. Each + PAD entry contains data to constrain the set of IDs that can be + asserted by an IKE peer, for matching against the SPD. Each PAD + entry indicates whether the IKE ID is to be used as a symbolic name + for SPD matching, or whether an IP address asserted in a traffic + selector payload is to be used. + + If the entry indicates that the IKE ID is to be used, then the PAD + entry ID field defines the authorized set of IDs. If the entry + indicates that child SAs traffic selectors are to be used, then an + additional data element is required, in the form of IPv4 and/or IPv6 + address ranges. (A peer may be authorized for both address types, so + there MUST be provision for both a v4 and a v6 address range.) + +4.4.3.4. How the PAD Is Used + + During the initial IKE exchange, the initiator and responder each + assert their identity via the IKE ID payload and send an AUTH payload + to verify the asserted identity. One or more CERT payloads may be + transmitted to facilitate the verification of each asserted identity. + + + + +Kent & Seo Standards Track [Page 46] + +RFC 4301 Security Architecture for IP December 2005 + + + When an IKE entity receives an IKE ID payload, it uses the asserted + ID to locate an entry in the PAD, using the matching rules described + above. The PAD entry specifies the authentication method to be + employed for the identified peer. This ensures that the right method + is used for each peer and that different methods can be used for + different peers. The entry also specifies the authentication data + that will be used to verify the asserted identity. This data is + employed in conjunction with the specified method to authenticate the + peer, before any CHILD SAs are created. + + Child SAs are created based on the exchange of traffic selector + payloads, either at the end of the initial IKE exchange or in + subsequent CREATE_CHILD_SA exchanges. The PAD entry for the (now + authenticated) IKE peer is used to constrain creation of child SAs; + specifically, the PAD entry specifies how the SPD is searched using a + traffic selector proposal from a peer. There are two choices: either + the IKE ID asserted by the peer is used to find an SPD entry via its + symbolic name, or peer IP addresses asserted in traffic selector + payloads are used for SPD lookups based on the remote IP address + field portion of an SPD entry. It is necessary to impose these + constraints on creation of child SAs to prevent an authenticated peer + from spoofing IDs associated with other, legitimate peers. + + Note that because the PAD is checked before searching for an SPD + entry, this safeguard protects an initiator against spoofing attacks. + For example, assume that IKE A receives an outbound packet destined + for IP address X, a host served by a security gateway. RFC 2401 + [RFC2401] and this document do not specify how A determines the + address of the IKE peer serving X. However, any peer contacted by A + as the presumed representative for X must be registered in the PAD in + order to allow the IKE exchange to be authenticated. Moreover, when + the authenticated peer asserts that it represents X in its traffic + selector exchange, the PAD will be consulted to determine if the peer + in question is authorized to represent X. Thus, the PAD provides a + binding of address ranges (or name sub-spaces) to peers, to counter + such attacks. + +4.5. SA and Key Management + + All IPsec implementations MUST support both manual and automated SA + and cryptographic key management. The IPsec protocols, AH and ESP, + are largely independent of the associated SA management techniques, + although the techniques involved do affect some of the security + services offered by the protocols. For example, the optional + anti-replay service available for AH and ESP requires automated SA + management. Moreover, the granularity of key distribution employed + with IPsec determines the granularity of authentication provided. In + general, data origin authentication in AH and ESP is limited by the + + + +Kent & Seo Standards Track [Page 47] + +RFC 4301 Security Architecture for IP December 2005 + + + extent to which secrets used with the integrity algorithm (or with a + key management protocol that creates such secrets) are shared among + multiple possible sources. + + The following text describes the minimum requirements for both types + of SA management. + +4.5.1. Manual Techniques + + The simplest form of management is manual management, in which a + person manually configures each system with keying material and SA + management data relevant to secure communication with other systems. + Manual techniques are practical in small, static environments but + they do not scale well. For example, a company could create a + virtual private network (VPN) using IPsec in security gateways at + several sites. If the number of sites is small, and since all the + sites come under the purview of a single administrative domain, this + might be a feasible context for manual management techniques. In + this case, the security gateway might selectively protect traffic to + and from other sites within the organization using a manually + configured key, while not protecting traffic for other destinations. + It also might be appropriate when only selected communications need + to be secured. A similar argument might apply to use of IPsec + entirely within an organization for a small number of hosts and/or + gateways. Manual management techniques often employ statically + configured, symmetric keys, though other options also exist. + +4.5.2. Automated SA and Key Management + + Widespread deployment and use of IPsec requires an Internet-standard, + scalable, automated, SA management protocol. Such support is + required to facilitate use of the anti-replay features of AH and ESP, + and to accommodate on-demand creation of SAs, e.g., for user- and + session-oriented keying. (Note that the notion of "rekeying" an SA + actually implies creation of a new SA with a new SPI, a process that + generally implies use of an automated SA/key management protocol.) + + The default automated key management protocol selected for use with + IPsec is IKEv2 [Kau05]. This document assumes the availability of + certain functions from the key management protocol that are not + supported by IKEv1. Other automated SA management protocols MAY be + employed. + + When an automated SA/key management protocol is employed, the output + from this protocol is used to generate multiple keys for a single SA. + This also occurs because distinct keys are used for each of the two + + + + + +Kent & Seo Standards Track [Page 48] + +RFC 4301 Security Architecture for IP December 2005 + + + SAs created by IKE. If both integrity and confidentiality are + employed, then a minimum of four keys are required. Additionally, + some cryptographic algorithms may require multiple keys, e.g., 3DES. + + The Key Management System may provide a separate string of bits for + each key or it may generate one string of bits from which all keys + are extracted. If a single string of bits is provided, care needs to + be taken to ensure that the parts of the system that map the string + of bits to the required keys do so in the same fashion at both ends + of the SA. To ensure that the IPsec implementations at each end of + the SA use the same bits for the same keys, and irrespective of which + part of the system divides the string of bits into individual keys, + the encryption keys MUST be taken from the first (left-most, + high-order) bits and the integrity keys MUST be taken from the + remaining bits. The number of bits for each key is defined in the + relevant cryptographic algorithm specification RFC. In the case of + multiple encryption keys or multiple integrity keys, the + specification for the cryptographic algorithm must specify the order + in which they are to be selected from a single string of bits + provided to the cryptographic algorithm. + +4.5.3. Locating a Security Gateway + + This section discusses issues relating to how a host learns about the + existence of relevant security gateways and, once a host has + contacted these security gateways, how it knows that these are the + correct security gateways. The details of where the required + information is stored is a local matter, but the Peer Authorization + Database (PAD) described in Section 4.4 is the most likely candidate. + (Note: S* indicates a system that is running IPsec, e.g., SH1 and SG2 + below.) + + Consider a situation in which a remote host (SH1) is using the + Internet to gain access to a server or other machine (H2) and there + is a security gateway (SG2), e.g., a firewall, through which H1's + traffic must pass. An example of this situation would be a mobile + host crossing the Internet to his home organization's firewall (SG2). + This situation raises several issues: + + 1. How does SH1 know/learn about the existence of the security + gateway SG2? + + 2. How does it authenticate SG2, and once it has authenticated SG2, + how does it confirm that SG2 has been authorized to represent H2? + + 3. How does SG2 authenticate SH1 and verify that SH1 is authorized to + contact H2? + + + + +Kent & Seo Standards Track [Page 49] + +RFC 4301 Security Architecture for IP December 2005 + + + 4. How does SH1 know/learn about any additional gateways that provide + alternate paths to H2? + + To address these problems, an IPsec-supporting host or security + gateway MUST have an administrative interface that allows the + user/administrator to configure the address of one or more security + gateways for ranges of destination addresses that require its use. + This includes the ability to configure information for locating and + authenticating one or more security gateways and verifying the + authorization of these gateways to represent the destination host. + (The authorization function is implied in the PAD.) This document + does not address the issue of how to automate the + discovery/verification of security gateways. + +4.6. SAs and Multicast + + The receiver-orientation of the SA implies that, in the case of + unicast traffic, the destination system will select the SPI value. + By having the destination select the SPI value, there is no potential + for manually configured SAs to conflict with automatically configured + (e.g., via a key management protocol) SAs or for SAs from multiple + sources to conflict with each other. For multicast traffic, there + are multiple destination systems associated with a single SA. So + some system or person will need to coordinate among all multicast + groups to select an SPI or SPIs on behalf of each multicast group and + then communicate the group's IPsec information to all of the + legitimate members of that multicast group via mechanisms not defined + here. + + Multiple senders to a multicast group SHOULD use a single Security + Association (and hence SPI) for all traffic to that group when a + symmetric key encryption or integrity algorithm is employed. In such + circumstances, the receiver knows only that the message came from a + system possessing the key for that multicast group. In such + circumstances, a receiver generally will not be able to authenticate + which system sent the multicast traffic. Specifications for other, + more general multicast approaches are deferred to the IETF Multicast + Security Working Group. + +5. IP Traffic Processing + + As mentioned in Section 4.4.1, "The Security Policy Database (SPD)", + the SPD (or associated caches) MUST be consulted during the + processing of all traffic that crosses the IPsec protection boundary, + including IPsec management traffic. If no policy is found in the SPD + that matches a packet (for either inbound or outbound traffic), the + packet MUST be discarded. To simplify processing, and to allow for + very fast SA lookups (for SG/BITS/BITW), this document introduces the + + + +Kent & Seo Standards Track [Page 50] + +RFC 4301 Security Architecture for IP December 2005 + + + notion of an SPD cache for all outbound traffic (SPD-O plus SPD-S), + and a cache for inbound, non-IPsec-protected traffic (SPD-I). (As + mentioned earlier, the SAD acts as a cache for checking the selectors + of inbound IPsec-protected traffic arriving on SAs.) There is + nominally one cache per SPD. For the purposes of this specification, + it is assumed that each cached entry will map to exactly one SA. + Note, however, exceptions arise when one uses multiple SAs to carry + traffic of different priorities (e.g., as indicated by distinct DSCP + values) but the same selectors. Note also, that there are a couple + of situations in which the SAD can have entries for SAs that do not + have corresponding entries in the SPD. Since this document does not + mandate that the SAD be selectively cleared when the SPD is changed, + SAD entries can remain when the SPD entries that created them are + changed or deleted. Also, if a manually keyed SA is created, there + could be an SAD entry for this SA that does not correspond to any SPD + entry. + + Since SPD entries may overlap, one cannot safely cache these entries + in general. Simple caching might result in a match against a cache + entry, whereas an ordered search of the SPD would have resulted in a + match against a different entry. But, if the SPD entries are first + decorrelated, then the resulting entries can safely be cached. Each + cached entry will indicate that matching traffic should be bypassed + or discarded, appropriately. (Note: The original SPD entry might + result in multiple SAs, e.g., because of PFP.) Unless otherwise + noted, all references below to the "SPD" or "SPD cache" or "cache" + are to a decorrelated SPD (SPD-I, SPD-O, SPD-S) or the SPD cache + containing entries from the decorrelated SPD. + + Note: In a host IPsec implementation based on sockets, the SPD will + be consulted whenever a new socket is created to determine what, if + any, IPsec processing will be applied to the traffic that will flow + on that socket. This provides an implicit caching mechanism, and the + portions of the preceding discussion that address caching can be + ignored in such implementations. + + Note: It is assumed that one starts with a correlated SPD because + that is how users and administrators are accustomed to managing these + sorts of access control lists or firewall filter rules. Then the + decorrelation algorithm is applied to build a list of cache-able SPD + entries. The decorrelation is invisible at the management interface. + + For inbound IPsec traffic, the SAD entry selected by the SPI serves + as the cache for the selectors to be matched against arriving IPsec + packets, after AH or ESP processing has been performed. + + + + + + +Kent & Seo Standards Track [Page 51] + +RFC 4301 Security Architecture for IP December 2005 + + +5.1. Outbound IP Traffic Processing (protected-to-unprotected) + + First consider the path for traffic entering the implementation via a + protected interface and exiting via an unprotected interface. + + Unprotected Interface + ^ + | + (nested SAs) +----------+ + -------------------|Forwarding|<-----+ + | +----------+ | + | ^ | + | | BYPASS | + V +-----+ | + +-------+ | SPD | +--------+ + ...| SPD-I |.................|Cache|.....|PROCESS |...IPsec + | (*) | | (*) |---->|(AH/ESP)| boundary + +-------+ +-----+ +--------+ + | +-------+ / ^ + | |DISCARD| <--/ | + | +-------+ | + | | + | +-------------+ + |---------------->|SPD Selection| + +-------------+ + ^ + | +------+ + | -->| ICMP | + | / +------+ + |/ + | + | + Protected Interface + + + Figure 2. Processing Model for Outbound Traffic + (*) = The SPD caches are shown here. If there + is a cache miss, then the SPD is checked. + There is no requirement that an + implementation buffer the packet if + there is a cache miss. + + + + + + + + + + +Kent & Seo Standards Track [Page 52] + +RFC 4301 Security Architecture for IP December 2005 + + + IPsec MUST perform the following steps when processing outbound + packets: + + 1. When a packet arrives from the subscriber (protected) interface, + invoke the SPD selection function to obtain the SPD-ID needed to + choose the appropriate SPD. (If the implementation uses only one + SPD, this step is a no-op.) + + 2. Match the packet headers against the cache for the SPD specified + by the SPD-ID from step 1. Note that this cache contains entries + from SPD-O and SPD-S. + + 3a. If there is a match, then process the packet as specified by the + matching cache entry, i.e., BYPASS, DISCARD, or PROTECT using AH + or ESP. If IPsec processing is applied, there is a link from the + SPD cache entry to the relevant SAD entry (specifying the mode, + cryptographic algorithms, keys, SPI, PMTU, etc.). IPsec + processing is as previously defined, for tunnel or transport + modes and for AH or ESP, as specified in their respective RFCs + [Ken05b, Ken05a]. Note that the SA PMTU value, plus the value of + the stateful fragment checking flag (and the DF bit in the IP + header of the outbound packet) determine whether the packet can + (must) be fragmented prior to or after IPsec processing, or if it + must be discarded and an ICMP PMTU message is sent. + + 3b. If no match is found in the cache, search the SPD (SPD-S and + SPD-O parts) specified by SPD-ID. If the SPD entry calls for + BYPASS or DISCARD, create one or more new outbound SPD cache + entries and if BYPASS, create one or more new inbound SPD cache + entries. (More than one cache entry may be created since a + decorrelated SPD entry may be linked to other such entries that + were created as a side effect of the decorrelation process.) If + the SPD entry calls for PROTECT, i.e., creation of an SA, the key + management mechanism (e.g., IKEv2) is invoked to create the SA. + If SA creation succeeds, a new outbound (SPD-S) cache entry is + created, along with outbound and inbound SAD entries, otherwise + the packet is discarded. (A packet that triggers an SPD lookup + MAY be discarded by the implementation, or it MAY be processed + against the newly created cache entry, if one is created.) Since + SAs are created in pairs, an SAD entry for the corresponding + inbound SA also is created, and it contains the selector values + derived from the SPD entry (and packet, if any PFP flags were + "true") used to create the inbound SA, for use in checking + inbound traffic delivered via the SA. + + 4. The packet is passed to the outbound forwarding function + (operating outside of the IPsec implementation), to select the + interface to which the packet will be directed. This function + + + +Kent & Seo Standards Track [Page 53] + +RFC 4301 Security Architecture for IP December 2005 + + + may cause the packet to be passed back across the IPsec boundary, + for additional IPsec processing, e.g., in support of nested SAs. + If so, there MUST be an entry in SPD-I database that permits + inbound bypassing of the packet, otherwise the packet will be + discarded. If necessary, i.e., if there is more than one SPD-I, + the traffic being looped back MAY be tagged as coming from this + internal interface. This would allow the use of a different + SPD-I for "real" external traffic vs. looped traffic, if needed. + + Note: With the exception of IPv4 and IPv6 transport mode, an SG, + BITS, or BITW implementation MAY fragment packets before applying + IPsec. (This applies only to IPv4. For IPv6 packets, only the + originator is allowed to fragment them.) The device SHOULD have a + configuration setting to disable this. The resulting fragments are + evaluated against the SPD in the normal manner. Thus, fragments not + containing port numbers (or ICMP message type and code, or Mobility + Header type) will only match rules having port (or ICMP message type + and code, or MH type) selectors of OPAQUE or ANY. (See Section 7 for + more details.) + + Note: With regard to determining and enforcing the PMTU of an SA, the + IPsec system MUST follow the steps described in Section 8.2. + +5.1.1. Handling an Outbound Packet That Must Be Discarded + + If an IPsec system receives an outbound packet that it finds it must + discard, it SHOULD be capable of generating and sending an ICMP + message to indicate to the sender of the outbound packet that the + packet was discarded. The type and code of the ICMP message will + depend on the reason for discarding the packet, as specified below. + The reason SHOULD be recorded in the audit log. The audit log entry + for this event SHOULD include the reason, current date/time, and the + selector values from the packet. + + a. The selectors of the packet matched an SPD entry requiring the + packet to be discarded. + + IPv4 Type = 3 (destination unreachable) Code = 13 + (Communication Administratively Prohibited) + + IPv6 Type = 1 (destination unreachable) Code = 1 + (Communication with destination administratively + prohibited) + + b1. The IPsec system successfully reached the remote peer but was + unable to negotiate the SA required by the SPD entry matching the + packet because, for example, the remote peer is administratively + prohibited from communicating with the initiator, the initiating + + + +Kent & Seo Standards Track [Page 54] + +RFC 4301 Security Architecture for IP December 2005 + + + peer was unable to authenticate itself to the remote peer, the + remote peer was unable to authenticate itself to the initiating + peer, or the SPD at the remote peer did not have a suitable + entry. + + IPv4 Type = 3 (destination unreachable) Code = 13 + (Communication Administratively Prohibited) + + IPv6 Type = 1 (destination unreachable) Code = 1 + (Communication with destination administratively + prohibited) + + b2. The IPsec system was unable to set up the SA required by the SPD + entry matching the packet because the IPsec peer at the other end + of the exchange could not be contacted. + + IPv4 Type = 3 (destination unreachable) Code = 1 (host + unreachable) + + IPv6 Type = 1 (destination unreachable) Code = 3 (address + unreachable) + + Note that an attacker behind a security gateway could send packets + with a spoofed source address, W.X.Y.Z, to an IPsec entity causing it + to send ICMP messages to W.X.Y.Z. This creates an opportunity for a + denial of service (DoS) attack among hosts behind a security gateway. + To address this, a security gateway SHOULD include a management + control to allow an administrator to configure an IPsec + implementation to send or not send the ICMP messages under these + circumstances, and if this facility is selected, to rate limit the + transmission of such ICMP responses. + +5.1.2. Header Construction for Tunnel Mode + + This section describes the handling of the inner and outer IP + headers, extension headers, and options for AH and ESP tunnels, with + regard to outbound traffic processing. This includes how to + construct the encapsulating (outer) IP header, how to process fields + in the inner IP header, and what other actions should be taken for + outbound, tunnel mode traffic. The general processing described here + is modeled after RFC 2003, "IP Encapsulation within IP" [Per96]: + + o The outer IP header Source Address and Destination Address + identify the "endpoints" of the tunnel (the encapsulator and + decapsulator). The inner IP header Source Address and Destination + Addresses identify the original sender and recipient of the + datagram (from the perspective of this tunnel), respectively. + + + + +Kent & Seo Standards Track [Page 55] + +RFC 4301 Security Architecture for IP December 2005 + + + (See footnote 3 after the table in 5.1.2.1 for more details on the + encapsulating source IP address.) + + o The inner IP header is not changed except as noted below for TTL + (or Hop Limit) and the DS/ECN Fields. The inner IP header + otherwise remains unchanged during its delivery to the tunnel exit + point. + + o No change to IP options or extension headers in the inner header + occurs during delivery of the encapsulated datagram through the + tunnel. + + Note: IPsec tunnel mode is different from IP-in-IP tunneling (RFC + 2003 [Per96]) in several ways: + + o IPsec offers certain controls to a security administrator to + manage covert channels (which would not normally be a concern for + tunneling) and to ensure that the receiver examines the right + portions of the received packet with respect to application of + access controls. An IPsec implementation MAY be configurable with + regard to how it processes the outer DS field for tunnel mode for + transmitted packets. For outbound traffic, one configuration + setting for the outer DS field will operate as described in the + following sections on IPv4 and IPv6 header processing for IPsec + tunnels. Another will allow the outer DS field to be mapped to a + fixed value, which MAY be configured on a per-SA basis. (The value + might really be fixed for all traffic outbound from a device, but + per-SA granularity allows that as well.) This configuration option + allows a local administrator to decide whether the covert channel + provided by copying these bits outweighs the benefits of copying. + + o IPsec describes how to handle ECN or DS and provides the ability + to control propagation of changes in these fields between + unprotected and protected domains. In general, propagation from a + protected to an unprotected domain is a covert channel and thus + controls are provided to manage the bandwidth of this channel. + Propagation of ECN values in the other direction are controlled so + that only legitimate ECN changes (indicating occurrence of + congestion between the tunnel endpoints) are propagated. By + default, DS propagation from an unprotected domain to a protected + domain is not permitted. However, if the sender and receiver do + not share the same DS code space, and the receiver has no way of + learning how to map between the two spaces, then it may be + appropriate to deviate from the default. Specifically, an IPsec + implementation MAY be configurable in terms of how it processes + the outer DS field for tunnel mode for received packets. It may + be configured to either discard the outer DS value (the default) + OR to overwrite the inner DS field with the outer DS field. If + + + +Kent & Seo Standards Track [Page 56] + +RFC 4301 Security Architecture for IP December 2005 + + + offered, the discard vs. overwrite behavior MAY be configured on a + per-SA basis. This configuration option allows a local + administrator to decide whether the vulnerabilities created by + copying these bits outweigh the benefits of copying. See + [RFC2983] for further information on when each of these behaviors + may be useful, and also for the possible need for diffserv traffic + conditioning prior or subsequent to IPsec processing (including + tunnel decapsulation). + + o IPsec allows the IP version of the encapsulating header to be + different from that of the inner header. + + The tables in the following sub-sections show the handling for the + different header/option fields ("constructed" means that the value in + the outer field is constructed independently of the value in the + inner). + +5.1.2.1. IPv4: Header Construction for Tunnel Mode + + <-- How Outer Hdr Relates to Inner Hdr --> + Outer Hdr at Inner Hdr at + IPv4 Encapsulator Decapsulator + Header fields: -------------------- ------------ + version 4 (1) no change + header length constructed no change + DS Field copied from inner hdr (5) no change + ECN Field copied from inner hdr constructed (6) + total length constructed no change + ID constructed no change + flags (DF,MF) constructed, DF (4) no change + fragment offset constructed no change + TTL constructed (2) decrement (2) + protocol AH, ESP no change + checksum constructed constructed (2)(6) + src address constructed (3) no change + dest address constructed (3) no change + Options never copied no change + + Notes: + + (1) The IP version in the encapsulating header can be different + from the value in the inner header. + + (2) The TTL in the inner header is decremented by the encapsulator + prior to forwarding and by the decapsulator if it forwards the + packet. (The IPv4 checksum changes when the TTL changes.) + + + + + +Kent & Seo Standards Track [Page 57] + +RFC 4301 Security Architecture for IP December 2005 + + + Note: Decrementing the TTL value is a normal part of + forwarding a packet. Thus, a packet originating from the same + node as the encapsulator does not have its TTL decremented, + since the sending node is originating the packet rather than + forwarding it. This applies to BITS and native IPsec + implementations in hosts and routers. However, the IPsec + processing model includes an external forwarding capability. + TTL processing can be used to prevent looping of packets, + e.g., due to configuration errors, within the context of this + processing model. + + (3) Local and Remote addresses depend on the SA, which is used to + determine the Remote address, which in turn determines which + Local address (net interface) is used to forward the packet. + + Note: For multicast traffic, the destination address, or + source and destination addresses, may be required for + demuxing. In that case, it is important to ensure consistency + over the lifetime of the SA by ensuring that the source + address that appears in the encapsulating tunnel header is the + same as the one that was negotiated during the SA + establishment process. There is an exception to this general + rule, i.e., a mobile IPsec implementation will update its + source address as it moves. + + (4) Configuration determines whether to copy from the inner header + (IPv4 only), clear, or set the DF. + + (5) If the packet will immediately enter a domain for which the + DSCP value in the outer header is not appropriate, that value + MUST be mapped to an appropriate value for the domain + [NiBlBaBL98]. See RFC 2475 [BBCDWW98] for further + information. + + (6) If the ECN field in the inner header is set to ECT(0) or + ECT(1), where ECT is ECN-Capable Transport (ECT), and if the + ECN field in the outer header is set to Congestion Experienced + (CE), then set the ECN field in the inner header to CE; + otherwise, make no change to the ECN field in the inner + header. (The IPv4 checksum changes when the ECN changes.) + + Note: IPsec does not copy the options from the inner header into the + outer header, nor does IPsec construct the options in the outer + header. However, post-IPsec code MAY insert/construct options for + the outer header. + + + + + + +Kent & Seo Standards Track [Page 58] + +RFC 4301 Security Architecture for IP December 2005 + + +5.1.2.2. IPv6: Header Construction for Tunnel Mode + + <-- How Outer Hdr Relates Inner Hdr ---> + Outer Hdr at Inner Hdr at + IPv6 Encapsulator Decapsulator + Header fields: -------------------- ------------ + version 6 (1) no change + DS Field copied from inner hdr (5) no change (9) + ECN Field copied from inner hdr constructed (6) + flow label copied or configured (8) no change + payload length constructed no change + next header AH,ESP,routing hdr no change + hop limit constructed (2) decrement (2) + src address constructed (3) no change + dest address constructed (3) no change + Extension headers never copied (7) no change + + Notes: + + (1) - (6) See Section 5.1.2.1. + + (7) IPsec does not copy the extension headers from the inner + packet into outer headers, nor does IPsec construct extension + headers in the outer header. However, post-IPsec code MAY + insert/construct extension headers for the outer header. + + (8) See [RaCoCaDe04]. Copying is acceptable only for end systems, + not SGs. If an SG copied flow labels from the inner header to + the outer header, collisions might result. + + (9) An implementation MAY choose to provide a facility to pass the + DS value from the outer header to the inner header, on a per- + SA basis, for received tunnel mode packets. The motivation + for providing this feature is to accommodate situations in + which the DS code space at the receiver is different from that + of the sender and the receiver has no way of knowing how to + translate from the sender's space. There is a danger in + copying this value from the outer header to the inner header, + since it enables an attacker to modify the outer DSCP value in + a fashion that may adversely affect other traffic at the + receiver. Hence the default behavior for IPsec + implementations is NOT to permit such copying. + +5.2. Processing Inbound IP Traffic (unprotected-to-protected) + + Inbound processing is somewhat different from outbound processing, + because of the use of SPIs to map IPsec-protected traffic to SAs. + The inbound SPD cache (SPD-I) is applied only to bypassed or + + + +Kent & Seo Standards Track [Page 59] + +RFC 4301 Security Architecture for IP December 2005 + + + discarded traffic. If an arriving packet appears to be an IPsec + fragment from an unprotected interface, reassembly is performed prior + to IPsec processing. The intent for any SPD cache is that a packet + that fails to match any entry is then referred to the corresponding + SPD. Every SPD SHOULD have a nominal, final entry that catches + anything that is otherwise unmatched, and discards it. This ensures + that non-IPsec-protected traffic that arrives and does not match any + SPD-I entry will be discarded. + + Unprotected Interface + | + V + +-----+ IPsec protected + ------------------->|Demux|-------------------+ + | +-----+ | + | | | + | Not IPsec | | + | | | + | V | + | +-------+ +---------+ | + | |DISCARD|<---|SPD-I (*)| | + | +-------+ +---------+ | + | | | + | |-----+ | + | | | | + | | V | + | | +------+ | + | | | ICMP | | + | | +------+ | + | | V + +---------+ | +-----------+ + ....|SPD-O (*)|............|...................|PROCESS(**)|...IPsec + +---------+ | | (AH/ESP) | Boundary + ^ | +-----------+ + | | +---+ | + | BYPASS | +-->|IKE| | + | | | +---+ | + | V | V + | +----------+ +---------+ +----+ + |--------<------|Forwarding|<---------|SAD Check|-->|ICMP| + nested SAs +----------+ | (***) | +----+ + | +---------+ + V + Protected Interface + + Figure 3. Processing Model for Inbound Traffic + + + + + +Kent & Seo Standards Track [Page 60] + +RFC 4301 Security Architecture for IP December 2005 + + + (*) = The caches are shown here. If there is + a cache miss, then the SPD is checked. + There is no requirement that an + implementation buffer the packet if + there is a cache miss. + (**) = This processing includes using the + packet's SPI, etc., to look up the SA + in the SAD, which forms a cache of the + SPD for inbound packets (except for + cases noted in Sections 4.4.2 and 5). + See step 3a below. + (***) = This SAD check refers to step 4 below. + + Prior to performing AH or ESP processing, any IP fragments that + arrive via the unprotected interface are reassembled (by IP). Each + inbound IP datagram to which IPsec processing will be applied is + identified by the appearance of the AH or ESP values in the IP Next + Protocol field (or of AH or ESP as a next layer protocol in the IPv6 + context). + + IPsec MUST perform the following steps: + + 1. When a packet arrives, it may be tagged with the ID of the + interface (physical or virtual) via which it arrived, if + necessary, to support multiple SPDs and associated SPD-I caches. + (The interface ID is mapped to a corresponding SPD-ID.) + + 2. The packet is examined and demuxed into one of two categories: + - If the packet appears to be IPsec protected and it is addressed + to this device, an attempt is made to map it to an active SA + via the SAD. Note that the device may have multiple IP + addresses that may be used in the SAD lookup, e.g., in the case + of protocols such as SCTP. + - Traffic not addressed to this device, or addressed to this + device and not AH or ESP, is directed to SPD-I lookup. (This + implies that IKE traffic MUST have an explicit BYPASS entry in + the SPD.) If multiple SPDs are employed, the tag assigned to + the packet in step 1 is used to select the appropriate SPD-I + (and cache) to search. SPD-I lookup determines whether the + action is DISCARD or BYPASS. + + 3a. If the packet is addressed to the IPsec device and AH or ESP is + specified as the protocol, the packet is looked up in the SAD. + For unicast traffic, use only the SPI (or SPI plus protocol). + For multicast traffic, use the SPI plus the destination or SPI + plus destination and source addresses, as specified in Section + 4.1. In either case (unicast or multicast), if there is no match, + discard the traffic. This is an auditable event. The audit log + + + +Kent & Seo Standards Track [Page 61] + +RFC 4301 Security Architecture for IP December 2005 + + + entry for this event SHOULD include the current date/time, SPI, + source and destination of the packet, IPsec protocol, and any + other selector values of the packet that are available. If the + packet is found in the SAD, process it accordingly (see step 4). + + 3b. If the packet is not addressed to the device or is addressed to + this device and is not AH or ESP, look up the packet header in + the (appropriate) SPD-I cache. If there is a match and the + packet is to be discarded or bypassed, do so. If there is no + cache match, look up the packet in the corresponding SPD-I and + create a cache entry as appropriate. (No SAs are created in + response to receipt of a packet that requires IPsec protection; + only BYPASS or DISCARD cache entries can be created this way.) If + there is no match, discard the traffic. This is an auditable + event. The audit log entry for this event SHOULD include the + current date/time, SPI if available, IPsec protocol if available, + source and destination of the packet, and any other selector + values of the packet that are available. + + 3c. Processing of ICMP messages is assumed to take place on the + unprotected side of the IPsec boundary. Unprotected ICMP + messages are examined and local policy is applied to determine + whether to accept or reject these messages and, if accepted, what + action to take as a result. For example, if an ICMP unreachable + message is received, the implementation must decide whether to + act on it, reject it, or act on it with constraints. (See Section + 6.) + + 4. Apply AH or ESP processing as specified, using the SAD entry + selected in step 3a above. Then match the packet against the + inbound selectors identified by the SAD entry to verify that the + received packet is appropriate for the SA via which it was + received. + + 5. If an IPsec system receives an inbound packet on an SA and the + packet's header fields are not consistent with the selectors for + the SA, it MUST discard the packet. This is an auditable event. + The audit log entry for this event SHOULD include the current + date/time, SPI, IPsec protocol(s), source and destination of the + packet, any other selector values of the packet that are + available, and the selector values from the relevant SAD entry. + The system SHOULD also be capable of generating and sending an + IKE notification of INVALID_SELECTORS to the sender (IPsec peer), + indicating that the received packet was discarded because of + failure to pass selector checks. + + + + + + +Kent & Seo Standards Track [Page 62] + +RFC 4301 Security Architecture for IP December 2005 + + + To minimize the impact of a DoS attack, or a mis-configured peer, the + IPsec system SHOULD include a management control to allow an + administrator to configure the IPsec implementation to send or not + send this IKE notification, and if this facility is selected, to rate + limit the transmission of such notifications. + + After traffic is bypassed or processed through IPsec, it is handed to + the inbound forwarding function for disposition. This function may + cause the packet to be sent (outbound) across the IPsec boundary for + additional inbound IPsec processing, e.g., in support of nested SAs. + If so, then as with ALL outbound traffic that is to be bypassed, the + packet MUST be matched against an SPD-O entry. Ultimately, the + packet should be forwarded to the destination host or process for + disposition. + +6. ICMP Processing + + This section describes IPsec handling of ICMP traffic. There are two + categories of ICMP traffic: error messages (e.g., type = destination + unreachable) and non-error messages (e.g., type = echo). This + section applies exclusively to error messages. Disposition of + non-error, ICMP messages (that are not addressed to the IPsec + implementation itself) MUST be explicitly accounted for using SPD + entries. + + The discussion in this section applies to ICMPv6 as well as to + ICMPv4. Also, a mechanism SHOULD be provided to allow an + administrator to cause ICMP error messages (selected, all, or none) + to be logged as an aid to problem diagnosis. + +6.1. Processing ICMP Error Messages Directed to an IPsec Implementation + +6.1.1. ICMP Error Messages Received on the Unprotected Side of the + Boundary + + Figure 3 in Section 5.2 shows a distinct ICMP processing module on + the unprotected side of the IPsec boundary, for processing ICMP + messages (error or otherwise) that are addressed to the IPsec device + and that are not protected via AH or ESP. An ICMP message of this + sort is unauthenticated, and its processing may result in denial or + degradation of service. This suggests that, in general, it would be + desirable to ignore such messages. However, many ICMP messages will + be received by hosts or security gateways from unauthenticated + sources, e.g., routers in the public Internet. Ignoring these ICMP + messages can degrade service, e.g., because of a failure to process + PMTU message and redirection messages. Thus, there is also a + motivation for accepting and acting upon unauthenticated ICMP + messages. + + + +Kent & Seo Standards Track [Page 63] + +RFC 4301 Security Architecture for IP December 2005 + + + To accommodate both ends of this spectrum, a compliant IPsec + implementation MUST permit a local administrator to configure an + IPsec implementation to accept or reject unauthenticated ICMP + traffic. This control MUST be at the granularity of ICMP type and + MAY be at the granularity of ICMP type and code. Additionally, an + implementation SHOULD incorporate mechanisms and parameters for + dealing with such traffic. For example, there could be the ability + to establish a minimum PMTU for traffic (on a per destination basis), + to prevent receipt of an unauthenticated ICMP from setting the PMTU + to a trivial size. + + If an ICMP PMTU message passes the checks above and the system is + configured to accept it, then there are two possibilities. If the + implementation applies fragmentation on the ciphertext side of the + boundary, then the accepted PMTU information is passed to the + forwarding module (outside of the IPsec implementation), which uses + it to manage outbound packet fragmentation. If the implementation is + configured to effect plaintext side fragmentation, then the PMTU + information is passed to the plaintext side and processed as + described in Section 8.2. + +6.1.2. ICMP Error Messages Received on the Protected Side of the + Boundary + + These ICMP messages are not authenticated, but they do come from + sources on the protected side of the IPsec boundary. Thus, these + messages generally are viewed as more "trustworthy" than their + counterparts arriving from sources on the unprotected side of the + boundary. The major security concern here is that a compromised host + or router might emit erroneous ICMP error messages that could degrade + service for other devices "behind" the security gateway, or that + could even result in violations of confidentiality. For example, if + a bogus ICMP redirect were consumed by a security gateway, it could + cause the forwarding table on the protected side of the boundary to + be modified so as to deliver traffic to an inappropriate destination + "behind" the gateway. Thus, implementers MUST provide controls to + allow local administrators to constrain the processing of ICMP error + messages received on the protected side of the boundary, and directed + to the IPsec implementation. These controls are of the same type as + those employed on the unprotected side, described above in Section + 6.1.1. + +6.2. Processing Protected, Transit ICMP Error Messages + + When an ICMP error message is transmitted via an SA to a device + "behind" an IPsec implementation, both the payload and the header of + the ICMP message require checking from an access control perspective. + If one of these messages is forwarded to a host behind a security + + + +Kent & Seo Standards Track [Page 64] + +RFC 4301 Security Architecture for IP December 2005 + + + gateway, the receiving host IP implementation will make decisions + based on the payload, i.e., the header of the packet that purportedly + triggered the error response. Thus, an IPsec implementation MUST be + configurable to check that this payload header information is + consistent with the SA via which it arrives. (This means that the + payload header, with source and destination address and port fields + reversed, matches the traffic selectors for the SA.) If this sort of + check is not performed, then, for example, anyone with whom the + receiving IPsec system (A) has an active SA could send an ICMP + Destination Unreachable message that refers to any host/net with + which A is currently communicating, and thus effect a highly + efficient DoS attack regarding communication with other peers of A. + Normal IPsec receiver processing of traffic is not sufficient to + protect against such attacks. However, not all contexts may require + such checks, so it is also necessary to allow a local administrator + to configure an implementation to NOT perform such checks. + + To accommodate both policies, the following convention is adopted. + If an administrator wants to allow ICMP error messages to be carried + by an SA without inspection of the payload, then configure an SPD + entry that explicitly allows for carriage of such traffic. If an + administrator wants IPsec to check the payload of ICMP error messages + for consistency, then do not create any SPD entries that accommodate + carriage of such traffic based on the ICMP packet header. This + convention motivates the following processing description. + + IPsec senders and receivers MUST support the following processing for + ICMP error messages that are sent and received via SAs. + + If an SA exists that accommodates an outbound ICMP error message, + then the message is mapped to the SA and only the IP and ICMP headers + are checked upon receipt, just as would be the case for other + traffic. If no SA exists that matches the traffic selectors + associated with an ICMP error message, then the SPD is searched to + determine if such an SA can be created. If so, the SA is created and + the ICMP error message is transmitted via that SA. Upon receipt, + this message is subject to the usual traffic selector checks at the + receiver. This processing is exactly what would happen for traffic + in general, and thus does not represent any special processing for + ICMP error messages. + + If no SA exists that would carry the outbound ICMP message in + question, and if no SPD entry would allow carriage of this outbound + ICMP error message, then an IPsec implementation MUST map the message + to the SA that would carry the return traffic associated with the + packet that triggered the ICMP error message. This requires an IPsec + implementation to detect outbound ICMP error messages that map to no + extant SA or SPD entry, and treat them specially with regard to SA + + + +Kent & Seo Standards Track [Page 65] + +RFC 4301 Security Architecture for IP December 2005 + + + creation and lookup. The implementation extracts the header for the + packet that triggered the error (from the ICMP message payload), + reverses the source and destination IP address fields, extracts the + protocol field, and reverses the port fields (if accessible). It + then uses this extracted information to locate an appropriate, active + outbound SA, and transmits the error message via this SA. If no such + SA exists, no SA will be created, and this is an auditable event. + + If an IPsec implementation receives an inbound ICMP error message on + an SA, and the IP and ICMP headers of the message do not match the + traffic selectors for the SA, the receiver MUST process the received + message in a special fashion. Specifically, the receiver must + extract the header of the triggering packet from the ICMP payload, + and reverse fields as described above to determine if the packet is + consistent with the selectors for the SA via which the ICMP error + message was received. If the packet fails this check, the IPsec + implementation MUST NOT forwarded the ICMP message to the + destination. This is an auditable event. + +7. Handling Fragments (on the protected side of the IPsec boundary) + + Earlier sections of this document describe mechanisms for (a) + fragmenting an outbound packet after IPsec processing has been + applied and reassembling it at the receiver before IPsec processing + and (b) handling inbound fragments received from the unprotected side + of the IPsec boundary. This section describes how an implementation + should handle the processing of outbound plaintext fragments on the + protected side of the IPsec boundary. (See Appendix D, "Fragment + Handling Rationale".) In particular, it addresses: + + o mapping an outbound non-initial fragment to the right SA + (or finding the right SPD entry) + o verifying that a received non-initial fragment is + authorized for the SA via which it was received + o mapping outbound and inbound non-initial fragments to the + right SPD-O/SPD-I entry or the relevant cache entry, for + BYPASS/DISCARD traffic + + Note: In Section 4.1, transport mode SAs have been defined to not + carry fragments (IPv4 or IPv6). Note also that in Section 4.4.1, two + special values, ANY and OPAQUE, were defined for selectors and that + ANY includes OPAQUE. The term "non-trivial" is used to mean that the + selector has a value other than OPAQUE or ANY. + + Note: The term "non-initial fragment" is used here to indicate a + fragment that does not contain all the selector values that may be + needed for access control. As observed in Section 4.4.1, depending + on the Next Layer Protocol, in addition to Ports, the ICMP message + + + +Kent & Seo Standards Track [Page 66] + +RFC 4301 Security Architecture for IP December 2005 + + + type/code or Mobility Header type could be missing from non-initial + fragments. Also, for IPv6, even the first fragment might NOT contain + the Next Layer Protocol or Ports (or ICMP message type/code, or + Mobility Header type) depending on the kind and number of extension + headers present. If a non-initial fragment contains the Port (or + ICMP type and code or Mobility Header type) but not the Next Layer + Protocol, then unless there is an SPD entry for the relevant + Local/Remote addresses with ANY for Next Layer Protocol and Port (or + ICMP type and code or Mobility Header type), the fragment would not + contain all the selector information needed for access control. + + To address the above issues, three approaches have been defined: + + o Tunnel mode SAs that carry initial and non-initial fragments + (See Section 7.1.) + o Separate tunnel mode SAs for non-initial fragments (See + Section 7.2.) + o Stateful fragment checking (See Section 7.3.) + +7.1. Tunnel Mode SAs that Carry Initial and Non-Initial Fragments + + All implementations MUST support tunnel mode SAs that are configured + to pass traffic without regard to port field (or ICMP type/code or + Mobility Header type) values. If the SA will carry traffic for + specified protocols, the selector set for the SA MUST specify the + port fields (or ICMP type/code or Mobility Header type) as ANY. An + SA defined in this fashion will carry all traffic including initial + and non-initial fragments for the indicated Local/Remote addresses + and specified Next Layer protocol(s). If the SA will carry traffic + without regard to a specific protocol value (i.e., ANY is specified + as the (Next Layer) protocol selector value), then the port field + values are undefined and MUST be set to ANY as well. (As noted in + 4.4.1, ANY includes OPAQUE as well as all specific values.) + +7.2. Separate Tunnel Mode SAs for Non-Initial Fragments + + An implementation MAY support tunnel mode SAs that will carry only + non-initial fragments, separate from non-fragmented packets and + initial fragments. The OPAQUE value will be used to specify port (or + ICMP type/code or Mobility Header type) field selectors for an SA to + carry such fragments. Receivers MUST perform a minimum offset check + on IPv4 (non-initial) fragments to protect against overlapping + fragment attacks when SAs of this type are employed. Because such + checks cannot be performed on IPv6 non-initial fragments, users and + administrators are advised that carriage of such fragments may be + dangerous, and implementers may choose to NOT support such SAs for + IPv6 traffic. Also, an SA of this sort will carry all non-initial + fragments that match a specified Local/Remote address pair and + + + +Kent & Seo Standards Track [Page 67] + +RFC 4301 Security Architecture for IP December 2005 + + + protocol value, i.e., the fragments carried on this SA belong to + packets that if not fragmented, might have gone on separate SAs of + differing security. Therefore, users and administrators are advised + to protect such traffic using ESP (with integrity) and the + "strongest" integrity and encryption algorithms in use between both + peers. (Determination of the "strongest" algorithms requires + imposing an ordering of the available algorithms, a local + determination at the discretion of the initiator of the SA.) + + Specific port (or ICMP type/code or Mobility Header type) selector + values will be used to define SAs to carry initial fragments and + non-fragmented packets. This approach can be used if a user or + administrator wants to create one or more tunnel mode SAs between the + same Local/Remote addresses that discriminate based on port (or ICMP + type/code or Mobility Header type) fields. These SAs MUST have + non-trivial protocol selector values, otherwise approach #1 above + MUST be used. + + Note: In general, for the approach described in this section, one + needs only a single SA between two implementations to carry all + non-initial fragments. However, if one chooses to have multiple SAs + between the two implementations for QoS differentiation, then one + might also want multiple SAs to carry fragments-without-ports, one + for each supported QoS class. Since support for QoS via distinct SAs + is a local matter, not mandated by this document, the choice to have + multiple SAs to carry non-initial fragments should also be local. + +7.3. Stateful Fragment Checking + + An implementation MAY support some form of stateful fragment checking + for a tunnel mode SA with non-trivial port (or ICMP type/code or MH + type) field values (not ANY or OPAQUE). Implementations that will + transmit non-initial fragments on a tunnel mode SA that makes use of + non-trivial port (or ICMP type/code or MH type) selectors MUST notify + a peer via the IKE NOTIFY NON_FIRST_FRAGMENTS_ALSO payload. + + The peer MUST reject this proposal if it will not accept non-initial + fragments in this context. If an implementation does not + successfully negotiate transmission of non-initial fragments for such + an SA, it MUST NOT send such fragments over the SA. This standard + does not specify how peers will deal with such fragments, e.g., via + reassembly or other means, at either sender or receiver. However, a + receiver MUST discard non-initial fragments that arrive on an SA with + non-trivial port (or ICMP type/code or MH type) selector values + unless this feature has been negotiated. Also, the receiver MUST + discard non-initial fragments that do not comply with the security + policy applied to the overall packet. Discarding such packets is an + auditable event. Note that in network configurations where fragments + + + +Kent & Seo Standards Track [Page 68] + +RFC 4301 Security Architecture for IP December 2005 + + + of a packet might be sent or received via different security gateways + or BITW implementations, stateful strategies for tracking fragments + may fail. + +7.4. BYPASS/DISCARD Traffic + + All implementations MUST support DISCARDing of fragments using the + normal SPD packet classification mechanisms. All implementations + MUST support stateful fragment checking to accommodate BYPASS traffic + for which a non-trivial port range is specified. The concern is that + BYPASS of a cleartext, non-initial fragment arriving at an IPsec + implementation could undermine the security afforded IPsec-protected + traffic directed to the same destination. For example, consider an + IPsec implementation configured with an SPD entry that calls for + IPsec protection of traffic between a specific source/destination + address pair, and for a specific protocol and destination port, e.g., + TCP traffic on port 23 (Telnet). Assume that the implementation also + allows BYPASS of traffic from the same source/destination address + pair and protocol, but for a different destination port, e.g., port + 119 (NNTP). An attacker could send a non-initial fragment (with a + forged source address) that, if bypassed, could overlap with + IPsec-protected traffic from the same source and thus violate the + integrity of the IPsec-protected traffic. Requiring stateful + fragment checking for BYPASS entries with non-trivial port ranges + prevents attacks of this sort. As noted above, in network + configurations where fragments of a packet might be sent or received + via different security gateways or BITW implementations, stateful + strategies for tracking fragments may fail. + +8. Path MTU/DF Processing + + The application of AH or ESP to an outbound packet increases the size + of a packet and thus may cause a packet to exceed the PMTU for the SA + via which the packet will travel. An IPsec implementation also may + receive an unprotected ICMP PMTU message and, if it chooses to act + upon the message, the result will affect outbound traffic processing. + This section describes the processing required of an IPsec + implementation to deal with these two PMTU issues. + +8.1. DF Bit + + All IPsec implementations MUST support the option of copying the DF + bit from an outbound packet to the tunnel mode header that it emits, + when traffic is carried via a tunnel mode SA. This means that it + MUST be possible to configure the implementation's treatment of the + DF bit (set, clear, copy from inner header) for each SA. This + applies to SAs where both inner and outer headers are IPv4. + + + + +Kent & Seo Standards Track [Page 69] + +RFC 4301 Security Architecture for IP December 2005 + + +8.2. Path MTU (PMTU) Discovery + + This section discusses IPsec handling for unprotected Path MTU + Discovery messages. ICMP PMTU is used here to refer to an ICMP + message for: + + IPv4 (RFC 792 [Pos81b]): + - Type = 3 (Destination Unreachable) + - Code = 4 (Fragmentation needed and DF set) + - Next-Hop MTU in the low-order 16 bits of the + second word of the ICMP header (labeled "unused" + in RFC 792), with high-order 16 bits set to zero) + + IPv6 (RFC 2463 [CD98]): + - Type = 2 (Packet Too Big) + - Code = 0 (Fragmentation needed) + - Next-Hop MTU in the 32-bit MTU field of the ICMP6 + message + +8.2.1. Propagation of PMTU + + When an IPsec implementation receives an unauthenticated PMTU + message, and it is configured to process (vs. ignore) such messages, + it maps the message to the SA to which it corresponds. This mapping + is effected by extracting the header information from the payload of + the PMTU message and applying the procedure described in Section 5.2. + The PMTU determined by this message is used to update the SAD PMTU + field, taking into account the size of the AH or ESP header that will + be applied, any crypto synchronization data, and the overhead imposed + by an additional IP header, in the case of a tunnel mode SA. + + In a native host implementation, it is possible to maintain PMTU data + at the same granularity as for unprotected communication, so there is + no loss of functionality. Signaling of the PMTU information is + internal to the host. For all other IPsec implementation options, + the PMTU data must be propagated via a synthesized ICMP PMTU. In + these cases, the IPsec implementation SHOULD wait for outbound + traffic to be mapped to the SAD entry. When such traffic arrives, if + the traffic would exceed the updated PMTU value the traffic MUST be + handled as follows: + + Case 1: Original (cleartext) packet is IPv4 and has the DF + bit set. The implementation SHOULD discard the packet + and send a PMTU ICMP message. + + + + + + + +Kent & Seo Standards Track [Page 70] + +RFC 4301 Security Architecture for IP December 2005 + + + Case 2: Original (cleartext) packet is IPv4 and has the DF + bit clear. The implementation SHOULD fragment (before or + after encryption per its configuration) and then forward + the fragments. It SHOULD NOT send a PMTU ICMP message. + + Case 3: Original (cleartext) packet is IPv6. The implementation + SHOULD discard the packet and send a PMTU ICMP message. + +8.2.2. PMTU Aging + + In all IPsec implementations, the PMTU associated with an SA MUST be + "aged" and some mechanism is required to update the PMTU in a timely + manner, especially for discovering if the PMTU is smaller than + required by current network conditions. A given PMTU has to remain + in place long enough for a packet to get from the source of the SA to + the peer, and to propagate an ICMP error message if the current PMTU + is too big. + + Implementations SHOULD use the approach described in the Path MTU + Discovery document (RFC 1191 [MD90], Section 6.3), which suggests + periodically resetting the PMTU to the first-hop data-link MTU and + then letting the normal PMTU Discovery processes update the PMTU as + necessary. The period SHOULD be configurable. + +9. Auditing + + IPsec implementations are not required to support auditing. For the + most part, the granularity of auditing is a local matter. However, + several auditable events are identified in this document, and for + each of these events a minimum set of information that SHOULD be + included in an audit log is defined. Additional information also MAY + be included in the audit log for each of these events, and additional + events, not explicitly called out in this specification, also MAY + result in audit log entries. There is no requirement for the + receiver to transmit any message to the purported transmitter in + response to the detection of an auditable event, because of the + potential to induce denial of service via such action. + +10. Conformance Requirements + + All IPv4 IPsec implementations MUST comply with all requirements of + this document. All IPv6 implementations MUST comply with all + requirements of this document. + + + + + + + + +Kent & Seo Standards Track [Page 71] + +RFC 4301 Security Architecture for IP December 2005 + + +11. Security Considerations + + The focus of this document is security; hence security considerations + permeate this specification. + + IPsec imposes stringent constraints on bypass of IP header data in + both directions, across the IPsec barrier, especially when tunnel + mode SAs are employed. Some constraints are absolute, while others + are subject to local administrative controls, often on a per-SA + basis. For outbound traffic, these constraints are designed to limit + covert channel bandwidth. For inbound traffic, the constraints are + designed to prevent an adversary who has the ability to tamper with + one data stream (on the unprotected side of the IPsec barrier) from + adversely affecting other data streams (on the protected side of the + barrier). The discussion in Section 5 dealing with processing DSCP + values for tunnel mode SAs illustrates this concern. + + If an IPsec implementation is configured to pass ICMP error messages + over SAs based on the ICMP header values, without checking the header + information from the ICMP message payload, serious vulnerabilities + may arise. Consider a scenario in which several sites (A, B, and C) + are connected to one another via ESP-protected tunnels: A-B, A-C, and + B-C. Also assume that the traffic selectors for each tunnel specify + ANY for protocol and port fields and IP source/destination address + ranges that encompass the address range for the systems behind the + security gateways serving each site. This would allow a host at site + B to send an ICMP Destination Unreachable message to any host at site + A, that declares all hosts on the net at site C to be unreachable. + This is a very efficient DoS attack that could have been prevented if + the ICMP error messages were subjected to the checks that IPsec + provides, if the SPD is suitably configured, as described in Section + 6.2. + +12. IANA Considerations + + The IANA has assigned the value (3) for the asn1-modules registry and + has assigned the object identifier 1.3.6.1.5.8.3.1 for the SPD + module. See Appendix C, "ASN.1 for an SPD Entry". + +13. Differences from RFC 2401 + + This architecture document differs substantially from RFC 2401 + [RFC2401] in detail and in organization, but the fundamental notions + are unchanged. + + o The processing model has been revised to address new IPsec + scenarios, improve performance, and simplify implementation. This + includes a separation between forwarding (routing) and SPD + + + +Kent & Seo Standards Track [Page 72] + +RFC 4301 Security Architecture for IP December 2005 + + + selection, several SPD changes, and the addition of an outbound SPD + cache and an inbound SPD cache for bypassed or discarded traffic. + There is also a new database, the Peer Authorization Database + (PAD). This provides a link between an SA management protocol + (such as IKE) and the SPD. + + o There is no longer a requirement to support nested SAs or "SA + bundles". Instead this functionality can be achieved through SPD + and forwarding table configuration. An example of a configuration + has been added in Appendix E. + + o SPD entries were redefined to provide more flexibility. Each SPD + entry now consists of 1 to N sets of selectors, where each selector + set contains one protocol and a "list of ranges" can now be + specified for the Local IP address, Remote IP address, and whatever + fields (if any) are associated with the Next Layer Protocol (Local + Port, Remote Port, ICMP message type and code, and Mobility Header + type). An individual value for a selector is represented via a + trivial range and ANY is represented via a range than spans all + values for the selector. An example of an ASN.1 description is + included in Appendix C. + + o TOS (IPv4) and Traffic Class (IPv6) have been replaced by DSCP and + ECN. The tunnel section has been updated to explain how to handle + DSCP and ECN bits. + + o For tunnel mode SAs, an SG, BITS, or BITW implementation is now + allowed to fragment packets before applying IPsec. This applies + only to IPv4. For IPv6 packets, only the originator is allowed to + fragment them. + + o When security is desired between two intermediate systems along a + path or between an intermediate system and an end system, transport + mode may now be used between security gateways and between a + security gateway and a host. + + o This document clarifies that for all traffic that crosses the IPsec + boundary, including IPsec management traffic, the SPD or associated + caches must be consulted. + + o This document defines how to handle the situation of a security + gateway with multiple subscribers requiring separate IPsec + contexts. + + o A definition of reserved SPIs has been added. + + + + + + +Kent & Seo Standards Track [Page 73] + +RFC 4301 Security Architecture for IP December 2005 + + + o Text has been added explaining why ALL IP packets must be checked + -- IPsec includes minimal firewall functionality to support access + control at the IP layer. + + o The tunnel section has been updated to clarify how to handle the IP + options field and IPv6 extension headers when constructing the + outer header. + + o SA mapping for inbound traffic has been updated to be consistent + with the changes made in AH and ESP for support of unicast and + multicast SAs. + + o Guidance has been added regarding how to handle the covert channel + created in tunnel mode by copying the DSCP value to outer header. + + o Support for AH in both IPv4 and IPv6 is no longer required. + + o PMTU handling has been updated. The appendix on + PMTU/DF/Fragmentation has been deleted. + + o Three approaches have been added for handling plaintext fragments + on the protected side of the IPsec boundary. Appendix D documents + the rationale behind them. + + o Added revised text describing how to derive selector values for SAs + (from the SPD entry or from the packet, etc.) + + o Added a new table describing the relationship between selector + values in an SPD entry, the PFP flag, and resulting selector values + in the corresponding SAD entry. + + o Added Appendix B to describe decorrelation. + + o Added text describing how to handle an outbound packet that must be + discarded. + + o Added text describing how to handle a DISCARDED inbound packet, + i.e., one that does not match the SA upon which it arrived. + + o IPv6 mobility header has been added as a possible Next Layer + Protocol. IPv6 Mobility Header message type has been added as a + selector. + + o ICMP message type and code have been added as selectors. + + o The selector "data sensitivity level" has been removed to simplify + things. + + + + +Kent & Seo Standards Track [Page 74] + +RFC 4301 Security Architecture for IP December 2005 + + + o Updated text describing handling ICMP error messages. The appendix + on "Categorization of ICMP Messages" has been deleted. + + o The text for the selector name has been updated and clarified. + + o The "Next Layer Protocol" has been further explained and a default + list of protocols to skip when looking for the Next Layer Protocol + has been added. + + o The text has been amended to say that this document assumes use of + IKEv2 or an SA management protocol with comparable features. + + o Text has been added clarifying the algorithm for mapping inbound + IPsec datagrams to SAs in the presence of multicast SAs. + + o The appendix "Sequence Space Window Code Example" has been removed. + + o With respect to IP addresses and ports, the terms "Local" and + "Remote" are used for policy rules (replacing source and + destination). "Local" refers to the entity being protected by an + IPsec implementation, i.e., the "source" address/port of outbound + packets or the "destination" address/port of inbound packets. + "Remote" refers to a peer entity or peer entities. The terms + "source" and "destination" are still used for packet header fields. + +14. Acknowledgements + + The authors would like to acknowledge the contributions of Ran + Atkinson, who played a critical role in initial IPsec activities, and + who authored the first series of IPsec standards: RFCs 1825-1827; and + Charlie Lynn, who made significant contributions to the second series + of IPsec standards (RFCs 2401, 2402, and 2406) and to the current + versions, especially with regard to IPv6 issues. The authors also + would like to thank the members of the IPsec and MSEC working groups + who have contributed to the development of this protocol + specification. + + + + + + + + + + + + + + + +Kent & Seo Standards Track [Page 75] + +RFC 4301 Security Architecture for IP December 2005 + + +Appendix A: Glossary + + This section provides definitions for several key terms that are + employed in this document. Other documents provide additional + definitions and background information relevant to this technology, + e.g., [Shi00], [VK83], and [HA94]. Included in this glossary are + generic security service and security mechanism terms, plus + IPsec-specific terms. + + Access Control + A security service that prevents unauthorized use of a resource, + including the prevention of use of a resource in an unauthorized + manner. In the IPsec context, the resource to which access is + being controlled is often: + + o for a host, computing cycles or data + o for a security gateway, a network behind the gateway + or bandwidth on that network. + + Anti-replay + See "Integrity" below. + + Authentication + Used informally to refer to the combination of two nominally + distinct security services, data origin authentication and + connectionless integrity. See the definitions below for each of + these services. + + Availability + When viewed as a security service, addresses the security concerns + engendered by attacks against networks that deny or degrade + service. For example, in the IPsec context, the use of + anti-replay mechanisms in AH and ESP support availability. + + Confidentiality + The security service that protects data from unauthorized + disclosure. The primary confidentiality concern in most instances + is unauthorized disclosure of application-level data, but + disclosure of the external characteristics of communication also + can be a concern in some circumstances. Traffic flow + confidentiality is the service that addresses this latter concern + by concealing source and destination addresses, message length, or + frequency of communication. In the IPsec context, using ESP in + tunnel mode, especially at a security gateway, can provide some + level of traffic flow confidentiality. (See also "Traffic + Analysis" below.) + + + + + +Kent & Seo Standards Track [Page 76] + +RFC 4301 Security Architecture for IP December 2005 + + + Data Origin Authentication + A security service that verifies the identity of the claimed + source of data. This service is usually bundled with + connectionless integrity service. + + Encryption + A security mechanism used to transform data from an intelligible + form (plaintext) into an unintelligible form (ciphertext), to + provide confidentiality. The inverse transformation process is + designated "decryption". Often the term "encryption" is used to + generically refer to both processes. + + Integrity + A security service that ensures that modifications to data are + detectable. Integrity comes in various flavors to match + application requirements. IPsec supports two forms of integrity: + connectionless and a form of partial sequence integrity. + Connectionless integrity is a service that detects modification of + an individual IP datagram, without regard to the ordering of the + datagram in a stream of traffic. The form of partial sequence + integrity offered in IPsec is referred to as anti-replay + integrity, and it detects arrival of duplicate IP datagrams + (within a constrained window). This is in contrast to + connection-oriented integrity, which imposes more stringent + sequencing requirements on traffic, e.g., to be able to detect + lost or re-ordered messages. Although authentication and + integrity services often are cited separately, in practice they + are intimately connected and almost always offered in tandem. + + Protected vs. Unprotected + "Protected" refers to the systems or interfaces that are inside + the IPsec protection boundary, and "unprotected" refers to the + systems or interfaces that are outside the IPsec protection + boundary. IPsec provides a boundary through which traffic passes. + There is an asymmetry to this barrier, which is reflected in the + processing model. Outbound data, if not discarded or bypassed, is + protected via the application of AH or ESP and the addition of the + corresponding headers. Inbound data, if not discarded or + bypassed, is processed via the removal of AH or ESP headers. In + this document, inbound traffic enters an IPsec implementation from + the "unprotected" interface. Outbound traffic enters the + implementation via the "protected" interface, or is internally + generated by the implementation on the "protected" side of the + boundary and directed toward the "unprotected" interface. An + IPsec implementation may support more than one interface on either + or both sides of the boundary. The protected interface may be + + + + + +Kent & Seo Standards Track [Page 77] + +RFC 4301 Security Architecture for IP December 2005 + + + internal, e.g., in a host implementation of IPsec. The protected + interface may link to a socket layer interface presented by the + OS. + + Security Association (SA) + A simplex (uni-directional) logical connection, created for + security purposes. All traffic traversing an SA is provided the + same security processing. In IPsec, an SA is an Internet-layer + abstraction implemented through the use of AH or ESP. State data + associated with an SA is represented in the SA Database (SAD). + + Security Gateway + An intermediate system that acts as the communications interface + between two networks. The set of hosts (and networks) on the + external side of the security gateway is termed unprotected (they + are generally at least less protected than those "behind" the SG), + while the networks and hosts on the internal side are viewed as + protected. The internal subnets and hosts served by a security + gateway are presumed to be trusted by virtue of sharing a common, + local, security administration. In the IPsec context, a security + gateway is a point at which AH and/or ESP is implemented in order + to serve a set of internal hosts, providing security services for + these hosts when they communicate with external hosts also + employing IPsec (either directly or via another security gateway). + + Security Parameters Index (SPI) + An arbitrary 32-bit value that is used by a receiver to identify + the SA to which an incoming packet should be bound. For a unicast + SA, the SPI can be used by itself to specify an SA, or it may be + used in conjunction with the IPsec protocol type. Additional IP + address information is used to identify multicast SAs. The SPI is + carried in AH and ESP protocols to enable the receiving system to + select the SA under which a received packet will be processed. An + SPI has only local significance, as defined by the creator of the + SA (usually the receiver of the packet carrying the SPI); thus an + SPI is generally viewed as an opaque bit string. However, the + creator of an SA may choose to interpret the bits in an SPI to + facilitate local processing. + + Traffic Analysis + The analysis of network traffic flow for the purpose of deducing + information that is useful to an adversary. Examples of such + information are frequency of transmission, the identities of the + conversing parties, sizes of packets, and flow identifiers + [Sch94]. + + + + + + +Kent & Seo Standards Track [Page 78] + +RFC 4301 Security Architecture for IP December 2005 + + +Appendix B: Decorrelation + + This appendix is based on work done for caching of policies in the IP + Security Policy Working Group by Luis Sanchez, Matt Condell, and John + Zao. + + Two SPD entries are correlated if there is a non-null intersection + between the values of corresponding selectors in each entry. Caching + correlated SPD entries can lead to incorrect policy enforcement. A + solution to this problem, which still allows for caching, is to + remove the ambiguities by decorrelating the entries. That is, the + SPD entries must be rewritten so that for every pair of entries there + exists a selector for which there is a null intersection between the + values in both of the entries. Once the entries are decorrelated, + there is no longer any ordering requirement on them, since only one + entry will match any lookup. The next section describes + decorrelation in more detail and presents an algorithm that may be + used to implement decorrelation. + +B.1. Decorrelation Algorithm + + The basic decorrelation algorithm takes each entry in a correlated + SPD and divides it into a set of entries using a tree structure. + The nodes of the tree are the selectors that may overlap between the + policies. At each node, the algorithm creates a branch for each of + the values of the selector. It also creates one branch for the + complement of the union of all selector values. Policies are then + formed by traversing the tree from the root to each leaf. The + policies at the leaves are compared to the set of already + decorrelated policy rules. Each policy at a leaf is either + completely overridden by a policy in the already decorrelated set and + is discarded or is decorrelated with all the policies in the + decorrelated set and is added to it. + + The basic algorithm does not guarantee an optimal set of decorrelated + entries. That is, the entries may be broken up into smaller sets + than is necessary, though they will still provide all the necessary + policy information. Some extensions to the basic algorithm are + described later to improve this and improve the performance of the + algorithm. + + C A set of ordered, correlated entries (a correlated SPD). + Ci The ith entry in C. + U The set of decorrelated entries being built from C. + Ui The ith entry in U. + Sik The kth selection for policy Ci. + Ai The action for policy Ci. + + + + +Kent & Seo Standards Track [Page 79] + +RFC 4301 Security Architecture for IP December 2005 + + + A policy (SPD entry) P may be expressed as a sequence of selector + values and an action (BYPASS, DISCARD, or PROTECT): + + Ci = Si1 x Si2 x ... x Sik -> Ai + + 1) Put C1 in set U as U1 + + For each policy Cj (j > 1) in C + + 2) If Cj is decorrelated with every entry in U, then add it to U. + + 3) If Cj is correlated with one or more entries in U, create a tree + rooted at the policy Cj that partitions Cj into a set of decorrelated + entries. The algorithm starts with a root node where no selectors + have yet been chosen. + + A) Choose a selector in Cj, Sjn, that has not yet been chosen when + traversing the tree from the root to this node. If there are no + selectors not yet used, continue to the next unfinished branch + until all branches have been completed. When the tree is + completed, go to step D. + + T is the set of entries in U that are correlated with the entry + at this node. + + The entry at this node is the entry formed by the selector + values of each of the branches between the root and this node. + Any selector values that are not yet represented by branches + assume the corresponding selector value in Cj, since the values + in Cj represent the maximum value for each selector. + + B) Add a branch to the tree for each value of the selector Sjn that + appears in any of the entries in T. (If the value is a superset + of the value of Sjn in Cj, then use the value in Cj, since that + value represents the universal set.) Also add a branch for the + complement of the union of all the values of the selector Sjn + in T. When taking the complement, remember that the universal + set is the value of Sjn in Cj. A branch need not be created + for the null set. + + C) Repeat A and B until the tree is completed. + + D) The entry to each leaf now represents an entry that is a subset + of Cj. The entries at the leaves completely partition Cj in + such a way that each entry is either completely overridden by + an entry in U, or is decorrelated with the entries in U. + + Add all the decorrelated entries at the leaves of the tree to U. + + + +Kent & Seo Standards Track [Page 80] + +RFC 4301 Security Architecture for IP December 2005 + + + 4) Get next Cj and go to 2. + + 5) When all entries in C have been processed, then U will contain an + decorrelated version of C. + + There are several optimizations that can be made to this algorithm. + A few of them are presented here. + + It is possible to optimize, or at least improve, the amount of + branching that occurs by carefully choosing the order of the + selectors used for the next branch. For example, if a selector Sjn + can be chosen so that all the values for that selector in T are equal + to or a superset of the value of Sjn in Cj, then only a single branch + needs to be created (since the complement will be null). + + Branches of the tree do not have to proceed with the entire + decorrelation algorithm. For example, if a node represents an entry + that is decorrelated with all the entries in U, then there is no + reason to continue decorrelating that branch. Also, if a branch is + completely overridden by an entry in U, then there is no reason to + continue decorrelating the branch. + + An additional optimization is to check to see if a branch is + overridden by one of the CORRELATED entries in set C that has already + been decorrelated. That is, if the branch is part of decorrelating + Cj, then check to see if it was overridden by an entry Cm, m < j. + This is a valid check, since all the entries Cm are already expressed + in U. + + Along with checking if an entry is already decorrelated in step 2, + check if Cj is overridden by any entry in U. If it is, skip it since + it is not relevant. An entry x is overridden by another entry y if + every selector in x is equal to or a subset of the corresponding + selector in entry y. + + + + + + + + + + + + + + + + + +Kent & Seo Standards Track [Page 81] + +RFC 4301 Security Architecture for IP December 2005 + + +Appendix C: ASN.1 for an SPD Entry + + This appendix is included as an additional way to describe SPD + entries, as defined in Section 4.4.1. It uses ASN.1 syntax that has + been successfully compiled. This syntax is merely illustrative and + need not be employed in an implementation to achieve compliance. The + SPD description in Section 4.4.1 is normative. + + SPDModule + + {iso(1) org (3) dod (6) internet (1) security (5) mechanisms (5) + ipsec (8) asn1-modules (3) spd-module (1) } + + DEFINITIONS IMPLICIT TAGS ::= + + BEGIN + + IMPORTS + RDNSequence FROM PKIX1Explicit88 + { iso(1) identified-organization(3) + dod(6) internet(1) security(5) mechanisms(5) pkix(7) + id-mod(0) id-pkix1-explicit(18) } ; + + -- An SPD is a list of policies in decreasing order of preference + SPD ::= SEQUENCE OF SPDEntry + + SPDEntry ::= CHOICE { + iPsecEntry IPsecEntry, -- PROTECT traffic + bypassOrDiscard [0] BypassOrDiscardEntry } -- DISCARD/BYPASS + + IPsecEntry ::= SEQUENCE { -- Each entry consists of + name NameSets OPTIONAL, + pFPs PacketFlags, -- Populate from packet flags + -- Applies to ALL of the corresponding + -- traffic selectors in the SelectorLists + condition SelectorLists, -- Policy "condition" + processing Processing -- Policy "action" + } + + BypassOrDiscardEntry ::= SEQUENCE { + bypass BOOLEAN, -- TRUE BYPASS, FALSE DISCARD + condition InOutBound } + + InOutBound ::= CHOICE { + outbound [0] SelectorLists, + inbound [1] SelectorLists, + bothways [2] BothWays } + + + + +Kent & Seo Standards Track [Page 82] + +RFC 4301 Security Architecture for IP December 2005 + + + BothWays ::= SEQUENCE { + inbound SelectorLists, + outbound SelectorLists } + + NameSets ::= SEQUENCE { + passed SET OF Names-R, -- Matched to IKE ID by + -- responder + local SET OF Names-I } -- Used internally by IKE + -- initiator + + Names-R ::= CHOICE { -- IKEv2 IDs + dName RDNSequence, -- ID_DER_ASN1_DN + fqdn FQDN, -- ID_FQDN + rfc822 [0] RFC822Name, -- ID_RFC822_ADDR + keyID OCTET STRING } -- KEY_ID + + Names-I ::= OCTET STRING -- Used internally by IKE + -- initiator + + FQDN ::= IA5String + + RFC822Name ::= IA5String + + PacketFlags ::= BIT STRING { + -- if set, take selector value from packet + -- establishing SA + -- else use value in SPD entry + localAddr (0), + remoteAddr (1), + protocol (2), + localPort (3), + remotePort (4) } + + SelectorLists ::= SET OF SelectorList + + SelectorList ::= SEQUENCE { + localAddr AddrList, + remoteAddr AddrList, + protocol ProtocolChoice } + + Processing ::= SEQUENCE { + extSeqNum BOOLEAN, -- TRUE 64 bit counter, FALSE 32 bit + seqOverflow BOOLEAN, -- TRUE rekey, FALSE terminate & audit + fragCheck BOOLEAN, -- TRUE stateful fragment checking, + -- FALSE no stateful fragment checking + lifetime SALifetime, + spi ManualSPI, + algorithms ProcessingAlgs, + + + +Kent & Seo Standards Track [Page 83] + +RFC 4301 Security Architecture for IP December 2005 + + + tunnel TunnelOptions OPTIONAL } -- if absent, use + -- transport mode + + SALifetime ::= SEQUENCE { + seconds [0] INTEGER OPTIONAL, + bytes [1] INTEGER OPTIONAL } + + ManualSPI ::= SEQUENCE { + spi INTEGER, + keys KeyIDs } + + KeyIDs ::= SEQUENCE OF OCTET STRING + + ProcessingAlgs ::= CHOICE { + ah [0] IntegrityAlgs, -- AH + esp [1] ESPAlgs} -- ESP + + ESPAlgs ::= CHOICE { + integrity [0] IntegrityAlgs, -- integrity only + confidentiality [1] ConfidentialityAlgs, -- confidentiality + -- only + both [2] IntegrityConfidentialityAlgs, + combined [3] CombinedModeAlgs } + + IntegrityConfidentialityAlgs ::= SEQUENCE { + integrity IntegrityAlgs, + confidentiality ConfidentialityAlgs } + + -- Integrity Algorithms, ordered by decreasing preference + IntegrityAlgs ::= SEQUENCE OF IntegrityAlg + + -- Confidentiality Algorithms, ordered by decreasing preference + ConfidentialityAlgs ::= SEQUENCE OF ConfidentialityAlg + + -- Integrity Algorithms + IntegrityAlg ::= SEQUENCE { + algorithm IntegrityAlgType, + parameters ANY -- DEFINED BY algorithm -- OPTIONAL } + + IntegrityAlgType ::= INTEGER { + none (0), + auth-HMAC-MD5-96 (1), + auth-HMAC-SHA1-96 (2), + auth-DES-MAC (3), + auth-KPDK-MD5 (4), + auth-AES-XCBC-96 (5) + -- tbd (6..65535) + } + + + +Kent & Seo Standards Track [Page 84] + +RFC 4301 Security Architecture for IP December 2005 + + + -- Confidentiality Algorithms + ConfidentialityAlg ::= SEQUENCE { + algorithm ConfidentialityAlgType, + parameters ANY -- DEFINED BY algorithm -- OPTIONAL } + + ConfidentialityAlgType ::= INTEGER { + encr-DES-IV64 (1), + encr-DES (2), + encr-3DES (3), + encr-RC5 (4), + encr-IDEA (5), + encr-CAST (6), + encr-BLOWFISH (7), + encr-3IDEA (8), + encr-DES-IV32 (9), + encr-RC4 (10), + encr-NULL (11), + encr-AES-CBC (12), + encr-AES-CTR (13) + -- tbd (14..65535) + } + + CombinedModeAlgs ::= SEQUENCE OF CombinedModeAlg + + CombinedModeAlg ::= SEQUENCE { + algorithm CombinedModeType, + parameters ANY -- DEFINED BY algorithm} -- defined outside + -- of this document for AES modes. + + CombinedModeType ::= INTEGER { + comb-AES-CCM (1), + comb-AES-GCM (2) + -- tbd (3..65535) + } + + TunnelOptions ::= SEQUENCE { + dscp DSCP, + ecn BOOLEAN, -- TRUE Copy CE to inner header + df DF, + addresses TunnelAddresses } + + TunnelAddresses ::= CHOICE { + ipv4 IPv4Pair, + ipv6 [0] IPv6Pair } + + IPv4Pair ::= SEQUENCE { + local OCTET STRING (SIZE(4)), + remote OCTET STRING (SIZE(4)) } + + + +Kent & Seo Standards Track [Page 85] + +RFC 4301 Security Architecture for IP December 2005 + + + IPv6Pair ::= SEQUENCE { + local OCTET STRING (SIZE(16)), + remote OCTET STRING (SIZE(16)) } + + DSCP ::= SEQUENCE { + copy BOOLEAN, -- TRUE copy from inner header + -- FALSE do not copy + mapping OCTET STRING OPTIONAL} -- points to table + -- if no copy + + DF ::= INTEGER { + clear (0), + set (1), + copy (2) } + + ProtocolChoice::= CHOICE { + anyProt AnyProtocol, -- for ANY protocol + noNext [0] NoNextLayerProtocol, -- has no next layer + -- items + oneNext [1] OneNextLayerProtocol, -- has one next layer + -- item + twoNext [2] TwoNextLayerProtocol, -- has two next layer + -- items + fragment FragmentNoNext } -- has no next layer + -- info + + AnyProtocol ::= SEQUENCE { + id INTEGER (0), -- ANY protocol + nextLayer AnyNextLayers } + + AnyNextLayers ::= SEQUENCE { -- with either + first AnyNextLayer, -- ANY next layer selector + second AnyNextLayer } -- ANY next layer selector + + NoNextLayerProtocol ::= INTEGER (2..254) + + FragmentNoNext ::= INTEGER (44) -- Fragment identifier + + OneNextLayerProtocol ::= SEQUENCE { + id INTEGER (1..254), -- ICMP, MH, ICMPv6 + nextLayer NextLayerChoice } -- ICMP Type*256+Code + -- MH Type*256 + + TwoNextLayerProtocol ::= SEQUENCE { + id INTEGER (2..254), -- Protocol + local NextLayerChoice, -- Local and + remote NextLayerChoice } -- Remote ports + + + + +Kent & Seo Standards Track [Page 86] + +RFC 4301 Security Architecture for IP December 2005 + + + NextLayerChoice ::= CHOICE { + any AnyNextLayer, + opaque [0] OpaqueNextLayer, + range [1] NextLayerRange } + + -- Representation of ANY in next layer field + AnyNextLayer ::= SEQUENCE { + start INTEGER (0), + end INTEGER (65535) } + + -- Representation of OPAQUE in next layer field. + -- Matches IKE convention + OpaqueNextLayer ::= SEQUENCE { + start INTEGER (65535), + end INTEGER (0) } + + -- Range for a next layer field + NextLayerRange ::= SEQUENCE { + start INTEGER (0..65535), + end INTEGER (0..65535) } + + -- List of IP addresses + AddrList ::= SEQUENCE { + v4List IPv4List OPTIONAL, + v6List [0] IPv6List OPTIONAL } + + -- IPv4 address representations + IPv4List ::= SEQUENCE OF IPv4Range + + IPv4Range ::= SEQUENCE { -- close, but not quite right ... + ipv4Start OCTET STRING (SIZE (4)), + ipv4End OCTET STRING (SIZE (4)) } + + -- IPv6 address representations + IPv6List ::= SEQUENCE OF IPv6Range + + IPv6Range ::= SEQUENCE { -- close, but not quite right ... + ipv6Start OCTET STRING (SIZE (16)), + ipv6End OCTET STRING (SIZE (16)) } + + END + + + + + + + + + + +Kent & Seo Standards Track [Page 87] + +RFC 4301 Security Architecture for IP December 2005 + + +Appendix D: Fragment Handling Rationale + + There are three issues that must be resolved regarding processing of + (plaintext) fragments in IPsec: + + - mapping a non-initial, outbound fragment to the right SA + (or finding the right SPD entry) + - verifying that a received, non-initial fragment is authorized + for the SA via which it is received + - mapping outbound and inbound non-initial fragments to the + right SPD/cache entry, for BYPASS/DISCARD traffic + + The first and third issues arise because we need a deterministic + algorithm for mapping traffic to SAs (and SPD/cache entries). All + three issues are important because we want to make sure that + non-initial fragments that cross the IPsec boundary do not cause the + access control policies in place at the receiver (or transmitter) to + be violated. + +D.1. Transport Mode and Fragments + + First, we note that transport mode SAs have been defined to not carry + fragments. This is a carryover from RFC 2401, where transport mode + SAs always terminated at endpoints. This is a fundamental + requirement because, in the worst case, an IPv4 fragment to which + IPsec was applied might then be fragmented (as a ciphertext packet), + en route to the destination. IP fragment reassembly procedures at + the IPsec receiver would not be able to distinguish between pre-IPsec + fragments and fragments created after IPsec processing. + + For IPv6, only the sender is allowed to fragment a packet. As for + IPv4, an IPsec implementation is allowed to fragment tunnel mode + packets after IPsec processing, because it is the sender relative to + the (outer) tunnel header. However, unlike IPv4, it would be + feasible to carry a plaintext fragment on a transport mode SA, + because the fragment header in IPv6 would appear after the AH or ESP + header, and thus would not cause confusion at the receiver with + respect to reassembly. Specifically, the receiver would not attempt + reassembly for the fragment until after IPsec processing. To keep + things simple, this specification prohibits carriage of fragments on + transport mode SAs for IPv6 traffic. + + When only end systems used transport mode SAs, the prohibition on + carriage of fragments was not a problem, since we assumed that the + end system could be configured to not offer a fragment to IPsec. For + a native host implementation, this seems reasonable, and, as someone + already noted, RFC 2401 warned that a BITS implementation might have + to reassemble fragments before performing an SA lookup. (It would + + + +Kent & Seo Standards Track [Page 88] + +RFC 4301 Security Architecture for IP December 2005 + + + then apply AH or ESP and could re-fragment the packet after IPsec + processing.) Because a BITS implementation is assumed to be able to + have access to all traffic emanating from its host, even if the host + has multiple interfaces, this was deemed a reasonable mandate. + + In this specification, it is acceptable to use transport mode in + cases where the IPsec implementation is not the ultimate destination, + e.g., between two SGs. In principle, this creates a new opportunity + for outbound, plaintext fragments to be mapped to a transport mode SA + for IPsec processing. However, in these new contexts in which a + transport mode SA is now approved for use, it seems likely that we + can continue to prohibit transmission of fragments, as seen by IPsec, + i.e., packets that have an "outer header" with a non-zero fragment + offset field. For example, in an IP overlay network, packets being + sent over transport mode SAs are IP-in-IP tunneled and thus have the + necessary inner header to accommodate fragmentation prior to IPsec + processing. When carried via a transport mode SA, IPsec would not + examine the inner IP header for such traffic, and thus would not + consider the packet to be a fragment. + +D.2. Tunnel Mode and Fragments + + For tunnel mode SAs, it has always been the case that outbound + fragments might arrive for processing at an IPsec implementation. + The need to accommodate fragmented outbound packets can pose a + problem because a non-initial fragment generally will not contain the + port fields associated with a next layer protocol such as TCP, UDP, + or SCTP. Thus, depending on the SPD configuration for a given IPsec + implementation, plaintext fragments might or might not pose a + problem. + + For example, if the SPD requires that all traffic between two address + ranges is offered IPsec protection (no BYPASS or DISCARD SPD entries + apply to this address range), then it should be easy to carry + non-initial fragments on the SA defined for this address range, since + the SPD entry implies an intent to carry ALL traffic between the + address ranges. But, if there are multiple SPD entries that could + match a fragment, and if these entries reference different subsets of + port fields (vs. ANY), then it is not possible to map an outbound + non-initial fragment to the right entry, unambiguously. (If we choose + to allow carriage of fragments on transport mode SAs for IPv6, the + problems arises in that context as well.) + + This problem largely, though not exclusively, motivated the + definition of OPAQUE as a selector value for port fields in RFC 2401. + The other motivation for OPAQUE is the observation that port fields + might not be accessible due to the prior application of IPsec. For + example, if a host applied IPsec to its traffic and that traffic + + + +Kent & Seo Standards Track [Page 89] + +RFC 4301 Security Architecture for IP December 2005 + + + arrived at an SG, these fields would be encrypted. The algorithm + specified for locating the "next layer protocol" described in RFC + 2401 also motivated use of OPAQUE to accommodate an encrypted next + layer protocol field in such circumstances. Nonetheless, the primary + use of the OPAQUE value was to match traffic selector fields in + packets that did not contain port fields (non-initial fragments), or + packets in which the port fields were already encrypted (as a result + of nested application of IPsec). RFC 2401 was ambiguous in + discussing the use of OPAQUE vs. ANY, suggesting in some places that + ANY might be an alternative to OPAQUE. + + We gain additional access control capability by defining both ANY and + OPAQUE values. OPAQUE can be defined to match only fields that are + not accessible. We could define ANY as the complement of OPAQUE, + i.e., it would match all values but only for accessible port fields. + We have therefore simplified the procedure employed to locate the + next layer protocol in this document, so that we treat ESP and AH as + next layer protocols. As a result, the notion of an encrypted next + layer protocol field has vanished, and there is also no need to worry + about encrypted port fields either. And accordingly, OPAQUE will be + applicable only to non-initial fragments. + + Since we have adopted the definitions above for ANY and OPAQUE, we + need to clarify how these values work when the specified protocol + does not have port fields, and when ANY is used for the protocol + selector. Accordingly, if a specific protocol value is used as a + selector, and if that protocol has no port fields, then the port + field selectors are to be ignored and ANY MUST be specified as the + value for the port fields. (In this context, ICMP TYPE and CODE + values are lumped together as a single port field (for IKEv2 + negotiation), as is the IPv6 Mobility Header TYPE value.) If the + protocol selector is ANY, then this should be treated as equivalent + to specifying a protocol for which no port fields are defined, and + thus the port selectors should be ignored, and MUST be set to ANY. + +D.3. The Problem of Non-Initial Fragments + + For an SG implementation, it is obvious that fragments might arrive + from end systems behind the SG. A BITW implementation also may + encounter fragments from a host or gateway behind it. (As noted + earlier, native host implementations and BITS implementations + probably can avoid the problems described below.) In the worst case, + fragments from a packet might arrive at distinct BITW or SG + instantiations and thus preclude reassembly as a solution option. + Hence, in RFC 2401 we adopted a general requirement that fragments + must be accommodated in tunnel mode for all implementations. However, + + + + + +Kent & Seo Standards Track [Page 90] + +RFC 4301 Security Architecture for IP December 2005 + + + RFC 2401 did not provide a perfect solution. The use of OPAQUE as a + selector value for port fields (a SHOULD in RFC 2401) allowed an SA + to carry non-initial fragments. + + Using the features defined in RFC 2401, if one defined an SA between + two IPsec (SG or BITW) implementations using the OPAQUE value for + both port fields, then all non-initial fragments matching the + source/destination (S/D) address and protocol values for the SA would + be mapped to that SA. Initial fragments would NOT map to this SA, if + we adopt a strict definition of OPAQUE. However, RFC 2401 did not + provide detailed guidance on this and thus it may not have been + apparent that use of this feature would essentially create a + "non-initial fragment only" SA. + + In the course of discussing the "fragment-only" SA approach, it was + noted that some subtle problems, problems not considered in RFC 2401, + would have to be avoided. For example, an SA of this sort must be + configured to offer the "highest quality" security services for any + traffic between the indicated S/D addresses (for the specified + protocol). This is necessary to ensure that any traffic captured by + the fragment-only SA is not offered degraded security relative to + what it would have been offered if the packet were not fragmented. A + possible problem here is that we may not be able to identify the + "highest quality" security services defined for use between two IPsec + implementation, since the choice of security protocols, options, and + algorithms is a lattice, not a totally ordered set. (We might safely + say that BYPASS < AH < ESP w/integrity, but it gets complicated if we + have multiple ESP encryption or integrity algorithm options.) So, one + has to impose a total ordering on these security parameters to make + this work, but this can be done locally. + + However, this conservative strategy has a possible performance + downside. If most traffic traversing an IPsec implementation for a + given S/D address pair (and specified protocol) is bypassed, then a + fragment-only SA for that address pair might cause a dramatic + increase in the volume of traffic afforded crypto processing. If the + crypto implementation cannot support high traffic rates, this could + cause problems. (An IPsec implementation that is capable of line rate + or near line rate crypto performance would not be adversely affected + by this SA configuration approach. Nonetheless, the performance + impact is a potential concern, specific to implementation + capabilities.) + + Another concern is that non-initial fragments sent over a dedicated + SA might be used to effect overlapping reassembly attacks, when + combined with an apparently acceptable initial fragment. (This sort + of attack assumes creation of bogus fragments and is not a side + effect of normal fragmentation.) This concern is easily addressed in + + + +Kent & Seo Standards Track [Page 91] + +RFC 4301 Security Architecture for IP December 2005 + + + IPv4, by checking the fragment offset value to ensure that no + non-initial fragments have a small enough offset to overlap port + fields that should be contained in the initial fragment. Recall that + the IPv4 MTU minimum is 576 bytes, and the max IP header length is 60 + bytes, so any ports should be present in the initial fragment. If we + require all non-initial fragments to have an offset of, say, 128 or + greater, just to be on the safe side, this should prevent successful + attacks of this sort. If the intent is only to protect against this + sort of reassembly attack, this check need be implemented only by a + receiver. + + IPv6 also has a fragment offset, carried in the fragmentation + extension header. However, IPv6 extension headers are variable in + length and there is no analogous max header length value that we can + use to check non-initial fragments, to reject ones that might be used + for an attack of the sort noted above. A receiver would need to + maintain state analogous to reassembly state, to provide equivalent + protection. So, only for IPv4 is it feasible to impose a fragment + offset check that would reject attacks designed to circumvent port + field checks by IPsec (or firewalls) when passing non-initial + fragments. + + Another possible concern is that in some topologies and SPD + configurations this approach might result in an access control + surprise. The notion is that if we create an SA to carry ALL + (non-initial) fragments, then that SA would carry some traffic that + might otherwise arrive as plaintext via a separate path, e.g., a path + monitored by a proxy firewall. But, this concern arises only if the + other path allows initial fragments to traverse it without requiring + reassembly, presumably a bad idea for a proxy firewall. Nonetheless, + this does represent a potential problem in some topologies and under + certain assumptions with respect to SPD and (other) firewall rule + sets, and administrators need to be warned of this possibility. + + A less serious concern is that non-initial fragments sent over a + non-initial fragment-only SA might represent a DoS opportunity, in + that they could be sent when no valid, initial fragment will ever + arrive. This might be used to attack hosts behind an SG or BITW + device. However, the incremental risk posed by this sort of attack, + which can be mounted only by hosts behind an SG or BITW device, seems + small. + + If we interpret the ANY selector value as encompassing OPAQUE, then a + single SA with ANY values for both port fields would be able to + accommodate all traffic matching the S/D address and protocol traffic + selectors, an alternative to using the OPAQUE value. But, using ANY + + + + + +Kent & Seo Standards Track [Page 92] + +RFC 4301 Security Architecture for IP December 2005 + + + here precludes multiple, distinct SAs between the same IPsec + implementations for the same address pairs and protocol. So, it is + not an exactly equivalent alternative. + + Fundamentally, fragment handling problems arise only when more than + one SA is defined with the same S/D address and protocol selector + values, but with different port field selector values. + +D.4. BYPASS/DISCARD Traffic + + We also have to address the non-initial fragment processing issue for + BYPASS/DISCARD entries, independent of SA processing. This is + largely a local matter for two reasons: + + 1) We have no means for coordinating SPD entries for such + traffic between IPsec implementations since IKE is not + invoked. + 2) Many of these entries refer to traffic that is NOT + directed to or received from a location that is using + IPsec. So there is no peer IPsec implementation with + which to coordinate via any means. + + However, this document should provide guidance here, consistent with + our goal of offering a well-defined, access control function for all + traffic, relative to the IPsec boundary. To that end, this document + says that implementations MUST support fragment reassembly for + BYPASS/DISCARD traffic when port fields are specified. An + implementation also MUST permit a user or administrator to accept + such traffic or reject such traffic using the SPD conventions + described in Section 4.4.1. The concern is that BYPASS of a + cleartext, non-initial fragment arriving at an IPsec implementation + could undermine the security afforded IPsec-protected traffic + directed to the same destination. For example, consider an IPsec + implementation configured with an SPD entry that calls for + IPsec-protection of traffic between a specific source/destination + address pair, and for a specific protocol and destination port, e.g., + TCP traffic on port 23 (Telnet). Assume that the implementation also + allows BYPASS of traffic from the same source/destination address + pair and protocol, but for a different destination port, e.g., port + 119 (NNTP). An attacker could send a non-initial fragment (with a + forged source address) that, if bypassed, could overlap with + IPsec-protected traffic from the same source and thus violate the + integrity of the IPsec-protected traffic. Requiring stateful + fragment checking for BYPASS entries with non-trivial port ranges + prevents attacks of this sort. + + + + + + +Kent & Seo Standards Track [Page 93] + +RFC 4301 Security Architecture for IP December 2005 + + +D.5. Just say no to ports? + + It has been suggested that we could avoid the problems described + above by not allowing port field selectors to be used in tunnel mode. + But the discussion above shows this to be an unnecessarily stringent + approach, i.e., since no problems arise for the native OS and BITS + implementations. Moreover, some WG members have described scenarios + where use of tunnel mode SAs with (non-trivial) port field selectors + is appropriate. So the challenge is defining a strategy that can + deal with this problem in BITW and SG contexts. Also note that + BYPASS/DISCARD entries in the SPD that make use of ports pose the + same problems, irrespective of tunnel vs. transport mode notions. + + Some folks have suggested that a firewall behind an SG or BITW should + be left to enforce port-level access controls and the effects of + fragmentation. However, this seems to be an incongruous suggestion + in that elsewhere in IPsec (e.g., in IKE payloads) we are concerned + about firewalls that always discard fragments. If many firewalls + don't pass fragments in general, why should we expect them to deal + with fragments in this case? So, this analysis rejects the suggestion + of disallowing use of port field selectors with tunnel mode SAs. + +D.6. Other Suggested Solutions + + One suggestion is to reassemble fragments at the sending IPsec + implementation, and thus avoid the problem entirely. This approach + is invisible to a receiver and thus could be adopted as a purely + local implementation option. + + A more sophisticated version of this suggestion calls for + establishing and maintaining minimal state from each initial fragment + encountered, to allow non-initial fragments to be matched to the + right SAs or SPD/cache entries. This implies an extension to the + current processing model (and the old one). The IPsec implementation + would intercept all fragments; capture Source/Destination IP + addresses, protocol, packet ID, and port fields from initial + fragments; and then use this data to map non-initial fragments to SAs + that require port fields. If this approach is employed, the receiver + needs to employ an equivalent scheme, as it too must verify that + received fragments are consistent with SA selector values. A + non-initial fragment that arrives prior to an initial fragment could + be cached or discarded, awaiting arrival of the corresponding initial + fragment. + + A downside of both approaches noted above is that they will not + always work. When a BITW device or SG is configured in a topology + that might allow some fragments for a packet to be processed at + different SGs or BITW devices, then there is no guarantee that all + + + +Kent & Seo Standards Track [Page 94] + +RFC 4301 Security Architecture for IP December 2005 + + + fragments will ever arrive at the same IPsec device. This approach + also raises possible processing problems. If the sender caches + non-initial fragments until the corresponding initial fragment + arrives, buffering problems might arise, especially at high speeds. + If the non-initial fragments are discarded rather than cached, there + is no guarantee that traffic will ever pass, e.g., retransmission + will result in different packet IDs that cannot be matched with prior + transmissions. In any case, housekeeping procedures will be needed + to decide when to delete the fragment state data, adding some + complexity to the system. Nonetheless, this is a viable solution in + some topologies, and these are likely to be common topologies. + + The Working Group rejected an earlier version of the convention of + creating an SA to carry only non-initial fragments, something that + was supported implicitly under the RFC 2401 model via use of OPAQUE + port fields, but never clearly articulated in RFC 2401. The + (rejected) text called for each non-initial fragment to be treated as + protocol 44 (the IPv6 fragment header protocol ID) by the sender and + receiver. This approach has the potential to make IPv4 and IPv6 + fragment handling more uniform, but it does not fundamentally change + the problem, nor does it address the issue of fragment handling for + BYPASS/DISCARD traffic. Given the fragment overlap attack problem + that IPv6 poses, it does not seem that it is worth the effort to + adopt this strategy. + +D.7. Consistency + + Earlier, the WG agreed to allow an IPsec BITS, BITW, or SG to perform + fragmentation prior to IPsec processing. If this fragmentation is + performed after SA lookup at the sender, there is no "mapping to the + right SA" problem. But, the receiver still needs to be able to + verify that the non-initial fragments are consistent with the SA via + which they are received. Since the initial fragment might be lost en + route, the receiver encounters all of the potential problems noted + above. Thus, if we are to be consistent in our decisions, we need to + say how a receiver will deal with the non-initial fragments that + arrive. + +D.8. Conclusions + + There is no simple, uniform way to handle fragments in all contexts. + Different approaches work better in different contexts. Thus, this + document offers 3 choices -- one MUST and two MAYs. At some point in + the future, if the community gains experience with the two MAYs, they + may become SHOULDs or MUSTs or other approaches may be proposed. + + + + + + +Kent & Seo Standards Track [Page 95] + +RFC 4301 Security Architecture for IP December 2005 + + +Appendix E: Example of Supporting Nested SAs via SPD and Forwarding + Table Entries + + This appendix provides an example of how to configure the SPD and + forwarding tables to support a nested pair of SAs, consistent with + the new processing model. For simplicity, this example assumes just + one SPD-I. + + The goal in this example is to support a transport mode SA from A to + C, carried over a tunnel mode SA from A to B. For example, A might + be a laptop connected to the public Internet, B might be a firewall + that protects a corporate network, and C might be a server on the + corporate network that demands end-to-end authentication of A's + traffic. + + +---+ +---+ +---+ + | A |=====| B | | C | + | |------------| | + | |=====| | | | + +---+ +---+ +---+ + + A's SPD contains entries of the form: + + Next Layer + Rule Local Remote Protocol Action + ---- ----- ------ ---------- ----------------------- + 1 C A ESP BYPASS + 2 A C ICMP,ESP PROTECT(ESP,tunnel,integr+conf) + 3 A C ANY PROTECT(ESP,transport,integr-only) + 4 A B ICMP,IKE BYPASS + + A's unprotected-side forwarding table is set so that outbound packets + destined for C are looped back to the protected side. A's + protected-side forwarding table is set so that inbound ESP packets + are looped back to the unprotected side. A's forwarding tables + contain entries of the form: + + Unprotected-side forwarding table + + Rule Local Remote Protocol Action + ---- ----- ------ -------- --------------------------- + 1 A C ANY loop back to protected side + 2 A B ANY forward to B + + + + + + + + +Kent & Seo Standards Track [Page 96] + +RFC 4301 Security Architecture for IP December 2005 + + + Protected-side forwarding table + + Rule Local Remote Protocol Action + ---- ----- ------ -------- ----------------------------- + 1 A C ESP loop back to unprotected side + + An outbound TCP packet from A to C would match SPD rule 3 and have + transport mode ESP applied to it. The unprotected-side forwarding + table would then loop back the packet. The packet is compared + against SPD-I (see Figure 2), matches SPD rule 1, and so it is + BYPASSed. The packet is treated as an outbound packet and compared + against the SPD for a third time. This time it matches SPD rule 2, + so ESP is applied in tunnel mode. This time the forwarding table + doesn't loop back the packet, because the outer destination address + is B, so the packet goes out onto the wire. + + An inbound TCP packet from C to A is wrapped in two ESP headers; the + outer header (ESP in tunnel mode) shows B as the source, whereas the + inner header (ESP transport mode) shows C as the source. Upon + arrival at A, the packet would be mapped to an SA based on the SPI, + have the outer header removed, and be decrypted and + integrity-checked. Then it would be matched against the SAD + selectors for this SA, which would specify C as the source and A as + the destination, derived from SPD rule 2. The protected-side + forwarding function would then send it back to the unprotected side + based on the addresses and the next layer protocol (ESP), indicative + of nesting. It is compared against SPD-O (see Figure 3) and found to + match SPD rule 1, so it is BYPASSed. The packet is mapped to an SA + based on the SPI, integrity-checked, and compared against the SAD + selectors derived from SPD rule 3. The forwarding function then + passes it up to the next layer, because it isn't an ESP packet. + + + + + + + + + + + + + + + + + + + + +Kent & Seo Standards Track [Page 97] + +RFC 4301 Security Architecture for IP December 2005 + + +References + +Normative References + + [BBCDWW98] Blake, S., Black, D., Carlson, M., Davies, E., Wang, + Z., and W. Weiss, "An Architecture for Differentiated + Service", RFC 2475, December 1998. + + [Bra97] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Level", BCP 14, RFC 2119, March 1997. + + [CD98] Conta, A. and S. Deering, "Internet Control Message + Protocol (ICMPv6) for the Internet Protocol Version 6 + (IPv6) Specification", RFC 2463, December 1998. + + [DH98] Deering, S., and R. Hinden, "Internet Protocol, + Version 6 (IPv6) Specification", RFC 2460, December + 1998. + + [Eas05] 3rd Eastlake, D., "Cryptographic Algorithm + Implementation Requirements For Encapsulating Security + Payload (ESP) and Authentication Header (AH)", RFC + 4305, December 2005. + + [HarCar98] Harkins, D. and D. Carrel, "The Internet Key Exchange + (IKE)", RFC 2409, November 1998. + + [Kau05] Kaufman, C., Ed., "The Internet Key Exchange (IKEv2) + Protocol", RFC 4306, December 2005. + + [Ken05a] Kent, S., "IP Encapsulating Security Payload (ESP)", + RFC 4303, December 2005. + + [Ken05b] Kent, S., "IP Authentication Header", RFC 4302, + December 2005. + + [MD90] Mogul, J. and S. Deering, "Path MTU discovery", RFC + 1191, November 1990. + + [Mobip] Johnson, D., Perkins, C., and J. Arkko, "Mobility + Support in IPv6", RFC 3775, June 2004. + + [Pos81a] Postel, J., "Internet Protocol", STD 5, RFC 791, + September 1981. + + [Pos81b] Postel, J., "Internet Control Message Protocol", RFC + 792, September 1981. + + + + +Kent & Seo Standards Track [Page 98] + +RFC 4301 Security Architecture for IP December 2005 + + + [Sch05] Schiller, J., "Cryptographic Algorithms for use in the + Internet Key Exchange Version 2 (IKEv2)", RFC 4307, + December 2005. + + [WaKiHo97] Wahl, M., Kille, S., and T. Howes, "Lightweight + Directory Access Protocol (v3): UTF-8 String + Representation of Distinguished Names", RFC 2253, + December 1997. + +Informative References + + [CoSa04] Condell, M., and L. Sanchez, "On the Deterministic + Enforcement of Un-ordered Security Policies", BBN + Technical Memo 1346, March 2004. + + [FaLiHaMeTr00] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. + Traina, "Generic Routing Encapsulation (GRE)", RFC + 2784, March 2000. + + [Gro02] Grossman, D., "New Terminology and Clarifications for + Diffserv", RFC 3260, April 2002. + [HC03] Holbrook, H. and B. Cain, "Source Specific Multicast + for IP", Work in Progress, November 3, 2002. + + [HA94] Haller, N. and R. Atkinson, "On Internet + Authentication", RFC 1704, October 1994. + + [NiBlBaBL98] Nichols, K., Blake, S., Baker, F., and D. Black, + "Definition of the Differentiated Services Field (DS + Field) in the IPv4 and IPv6 Headers", RFC 2474, + December 1998. + + [Per96] Perkins, C., "IP Encapsulation within IP", RFC 2003, + October 1996. + + [RaFlBl01] Ramakrishnan, K., Floyd, S., and D. Black, "The + Addition of Explicit Congestion Notification (ECN) to + IP", RFC 3168, September 2001. + + [RFC2401] Kent, S. and R. Atkinson, "Security Architecture for + the Internet Protocol", RFC 2401, November 1998. + + [RFC2983] Black, D., "Differentiated Services and Tunnels", RFC + 2983, October 2000. + + [RFC3547] Baugher, M., Weis, B., Hardjono, T., and H. Harney, + "The Group Domain of Interpretation", RFC 3547, July + 2003. + + + +Kent & Seo Standards Track [Page 99] + +RFC 4301 Security Architecture for IP December 2005 + + + [RFC3740] Hardjono, T. and B. Weis, "The Multicast Group + Security Architecture", RFC 3740, March 2004. + + [RaCoCaDe04] Rajahalme, J., Conta, A., Carpenter, B., and S. + Deering, "IPv6 Flow Label Specification", RFC 3697, + March 2004. + + [Sch94] Schneier, B., Applied Cryptography, Section 8.6, John + Wiley & Sons, New York, NY, 1994. + + [Shi00] Shirey, R., "Internet Security Glossary", RFC 2828, + May 2000. + + [SMPT01] Shacham, A., Monsour, B., Pereira, R., and M. Thomas, + "IP Payload Compression Protocol (IPComp)", RFC 3173, + September 2001. + + [ToEgWa04] Touch, J., Eggert, L., and Y. Wang, "Use of IPsec + Transport Mode for Dynamic Routing", RFC 3884, + September 2004. + + [VK83] V.L. Voydock & S.T. Kent, "Security Mechanisms in + High-level Networks", ACM Computing Surveys, Vol. 15, + No. 2, June 1983. + +Authors' Addresses + + Stephen Kent + BBN Technologies + 10 Moulton Street + Cambridge, MA 02138 + USA + + Phone: +1 (617) 873-3988 + EMail: kent@bbn.com + + + Karen Seo + BBN Technologies + 10 Moulton Street + Cambridge, MA 02138 + USA + + Phone: +1 (617) 873-3152 + EMail: kseo@bbn.com + + + + + + +Kent & Seo Standards Track [Page 100] + +RFC 4301 Security Architecture for IP December 2005 + + +Full Copyright Statement + + Copyright (C) The Internet Society (2005). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET + ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, + INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE + INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at ietf- + ipr@ietf.org. + +Acknowledgement + + Funding for the RFC Editor function is currently provided by the + Internet Society. + + + + + + + +Kent & Seo Standards Track [Page 101] + diff --git a/src/charon/doc/standards/rfc4306.txt b/src/charon/doc/standards/rfc4306.txt new file mode 100644 index 000000000..fad6cea0e --- /dev/null +++ b/src/charon/doc/standards/rfc4306.txt @@ -0,0 +1,5547 @@ + + + + + + +Network Working Group C. Kaufman, Ed. +Request for Comments: 4306 Microsoft +Obsoletes: 2407, 2408, 2409 December 2005 +Category: Standards Track + + + Internet Key Exchange (IKEv2) Protocol + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (C) The Internet Society (2005). + +Abstract + + This document describes version 2 of the Internet Key Exchange (IKE) + protocol. IKE is a component of IPsec used for performing mutual + authentication and establishing and maintaining security associations + (SAs). + + This version of the IKE specification combines the contents of what + were previously separate documents, including Internet Security + Association and Key Management Protocol (ISAKMP, RFC 2408), IKE (RFC + 2409), the Internet Domain of Interpretation (DOI, RFC 2407), Network + Address Translation (NAT) Traversal, Legacy authentication, and + remote address acquisition. + + Version 2 of IKE does not interoperate with version 1, but it has + enough of the header format in common that both versions can + unambiguously run over the same UDP port. + + + + + + + + + + + + + + +Kaufman Standards Track [Page 1] + +RFC 4306 IKEv2 December 2005 + + +Table of Contents + + 1. Introduction ....................................................3 + 1.1. Usage Scenarios ............................................5 + 1.2. The Initial Exchanges ......................................7 + 1.3. The CREATE_CHILD_SA Exchange ...............................9 + 1.4. The INFORMATIONAL Exchange ................................11 + 1.5. Informational Messages outside of an IKE_SA ...............12 + 2. IKE Protocol Details and Variations ............................12 + 2.1. Use of Retransmission Timers ..............................13 + 2.2. Use of Sequence Numbers for Message ID ....................14 + 2.3. Window Size for Overlapping Requests ......................14 + 2.4. State Synchronization and Connection Timeouts .............15 + 2.5. Version Numbers and Forward Compatibility .................17 + 2.6. Cookies ...................................................18 + 2.7. Cryptographic Algorithm Negotiation .......................21 + 2.8. Rekeying ..................................................22 + 2.9. Traffic Selector Negotiation ..............................24 + 2.10. Nonces ...................................................26 + 2.11. Address and Port Agility .................................26 + 2.12. Reuse of Diffie-Hellman Exponentials .....................27 + 2.13. Generating Keying Material ...............................27 + 2.14. Generating Keying Material for the IKE_SA ................28 + 2.15. Authentication of the IKE_SA .............................29 + 2.16. Extensible Authentication Protocol Methods ...............31 + 2.17. Generating Keying Material for CHILD_SAs .................33 + 2.18. Rekeying IKE_SAs Using a CREATE_CHILD_SA exchange ........34 + 2.19. Requesting an Internal Address on a Remote Network .......34 + 2.20. Requesting the Peer's Version ............................35 + 2.21. Error Handling ...........................................36 + 2.22. IPComp ...................................................37 + 2.23. NAT Traversal ............................................38 + 2.24. Explicit Congestion Notification (ECN) ...................40 + 3. Header and Payload Formats .....................................41 + 3.1. The IKE Header ............................................41 + 3.2. Generic Payload Header ....................................44 + 3.3. Security Association Payload ..............................46 + 3.4. Key Exchange Payload ......................................56 + 3.5. Identification Payloads ...................................56 + 3.6. Certificate Payload .......................................59 + 3.7. Certificate Request Payload ...............................61 + 3.8. Authentication Payload ....................................63 + 3.9. Nonce Payload .............................................64 + 3.10. Notify Payload ...........................................64 + 3.11. Delete Payload ...........................................72 + 3.12. Vendor ID Payload ........................................73 + 3.13. Traffic Selector Payload .................................74 + 3.14. Encrypted Payload ........................................77 + + + +Kaufman Standards Track [Page 2] + +RFC 4306 IKEv2 December 2005 + + + 3.15. Configuration Payload ....................................79 + 3.16. Extensible Authentication Protocol (EAP) Payload .........84 + 4. Conformance Requirements .......................................85 + 5. Security Considerations ........................................88 + 6. IANA Considerations ............................................90 + 7. Acknowledgements ...............................................91 + 8. References .....................................................91 + 8.1. Normative References ......................................91 + 8.2. Informative References ....................................92 + Appendix A: Summary of Changes from IKEv1 .........................96 + Appendix B: Diffie-Hellman Groups .................................97 + B.1. Group 1 - 768 Bit MODP ....................................97 + B.2. Group 2 - 1024 Bit MODP ...................................97 + +1. Introduction + + IP Security (IPsec) provides confidentiality, data integrity, access + control, and data source authentication to IP datagrams. These + services are provided by maintaining shared state between the source + and the sink of an IP datagram. This state defines, among other + things, the specific services provided to the datagram, which + cryptographic algorithms will be used to provide the services, and + the keys used as input to the cryptographic algorithms. + + Establishing this shared state in a manual fashion does not scale + well. Therefore, a protocol to establish this state dynamically is + needed. This memo describes such a protocol -- the Internet Key + Exchange (IKE). This is version 2 of IKE. Version 1 of IKE was + defined in RFCs 2407, 2408, and 2409 [Pip98, MSST98, HC98]. This + single document is intended to replace all three of those RFCs. + + Definitions of the primitive terms in this document (such as Security + Association or SA) can be found in [RFC4301]. + + Keywords "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT" and + "MAY" that appear in this document are to be interpreted as described + in [Bra97]. + + The term "Expert Review" is to be interpreted as defined in + [RFC2434]. + + IKE performs mutual authentication between two parties and + establishes an IKE security association (SA) that includes shared + secret information that can be used to efficiently establish SAs for + Encapsulating Security Payload (ESP) [RFC4303] and/or Authentication + Header (AH) [RFC4302] and a set of cryptographic algorithms to be + used by the SAs to protect the traffic that they carry. In this + document, the term "suite" or "cryptographic suite" refers to a + + + +Kaufman Standards Track [Page 3] + +RFC 4306 IKEv2 December 2005 + + + complete set of algorithms used to protect an SA. An initiator + proposes one or more suites by listing supported algorithms that can + be combined into suites in a mix-and-match fashion. IKE can also + negotiate use of IP Compression (IPComp) [IPCOMP] in connection with + an ESP and/or AH SA. We call the IKE SA an "IKE_SA". The SAs for + ESP and/or AH that get set up through that IKE_SA we call + "CHILD_SAs". + + All IKE communications consist of pairs of messages: a request and a + response. The pair is called an "exchange". We call the first + messages establishing an IKE_SA IKE_SA_INIT and IKE_AUTH exchanges + and subsequent IKE exchanges CREATE_CHILD_SA or INFORMATIONAL + exchanges. In the common case, there is a single IKE_SA_INIT + exchange and a single IKE_AUTH exchange (a total of four messages) to + establish the IKE_SA and the first CHILD_SA. In exceptional cases, + there may be more than one of each of these exchanges. In all cases, + all IKE_SA_INIT exchanges MUST complete before any other exchange + type, then all IKE_AUTH exchanges MUST complete, and following that + any number of CREATE_CHILD_SA and INFORMATIONAL exchanges may occur + in any order. In some scenarios, only a single CHILD_SA is needed + between the IPsec endpoints, and therefore there would be no + additional exchanges. Subsequent exchanges MAY be used to establish + additional CHILD_SAs between the same authenticated pair of endpoints + and to perform housekeeping functions. + + IKE message flow always consists of a request followed by a response. + It is the responsibility of the requester to ensure reliability. If + the response is not received within a timeout interval, the requester + needs to retransmit the request (or abandon the connection). + + The first request/response of an IKE session (IKE_SA_INIT) negotiates + security parameters for the IKE_SA, sends nonces, and sends Diffie- + Hellman values. + + The second request/response (IKE_AUTH) transmits identities, proves + knowledge of the secrets corresponding to the two identities, and + sets up an SA for the first (and often only) AH and/or ESP CHILD_SA. + + The types of subsequent exchanges are CREATE_CHILD_SA (which creates + a CHILD_SA) and INFORMATIONAL (which deletes an SA, reports error + conditions, or does other housekeeping). Every request requires a + response. An INFORMATIONAL request with no payloads (other than the + empty Encrypted payload required by the syntax) is commonly used as a + check for liveness. These subsequent exchanges cannot be used until + the initial exchanges have completed. + + + + + + +Kaufman Standards Track [Page 4] + +RFC 4306 IKEv2 December 2005 + + + In the description that follows, we assume that no errors occur. + Modifications to the flow should errors occur are described in + section 2.21. + +1.1. Usage Scenarios + + IKE is expected to be used to negotiate ESP and/or AH SAs in a number + of different scenarios, each with its own special requirements. + +1.1.1. Security Gateway to Security Gateway Tunnel + + +-+-+-+-+-+ +-+-+-+-+-+ + ! ! IPsec ! ! + Protected !Tunnel ! tunnel !Tunnel ! Protected + Subnet <-->!Endpoint !<---------->!Endpoint !<--> Subnet + ! ! ! ! + +-+-+-+-+-+ +-+-+-+-+-+ + + Figure 1: Security Gateway to Security Gateway Tunnel + + In this scenario, neither endpoint of the IP connection implements + IPsec, but network nodes between them protect traffic for part of the + way. Protection is transparent to the endpoints, and depends on + ordinary routing to send packets through the tunnel endpoints for + processing. Each endpoint would announce the set of addresses + "behind" it, and packets would be sent in tunnel mode where the inner + IP header would contain the IP addresses of the actual endpoints. + +1.1.2. Endpoint-to-Endpoint Transport + + +-+-+-+-+-+ +-+-+-+-+-+ + ! ! IPsec transport ! ! + !Protected! or tunnel mode SA !Protected! + !Endpoint !<---------------------------------------->!Endpoint ! + ! ! ! ! + +-+-+-+-+-+ +-+-+-+-+-+ + + Figure 2: Endpoint to Endpoint + + In this scenario, both endpoints of the IP connection implement + IPsec, as required of hosts in [RFC4301]. Transport mode will + commonly be used with no inner IP header. If there is an inner IP + header, the inner addresses will be the same as the outer addresses. + A single pair of addresses will be negotiated for packets to be + protected by this SA. These endpoints MAY implement application + layer access controls based on the IPsec authenticated identities of + the participants. This scenario enables the end-to-end security that + has been a guiding principle for the Internet since [RFC1958], + + + +Kaufman Standards Track [Page 5] + +RFC 4306 IKEv2 December 2005 + + + [RFC2775], and a method of limiting the inherent problems with + complexity in networks noted by [RFC3439]. Although this scenario + may not be fully applicable to the IPv4 Internet, it has been + deployed successfully in specific scenarios within intranets using + IKEv1. It should be more broadly enabled during the transition to + IPv6 and with the adoption of IKEv2. + + It is possible in this scenario that one or both of the protected + endpoints will be behind a network address translation (NAT) node, in + which case the tunneled packets will have to be UDP encapsulated so + that port numbers in the UDP headers can be used to identify + individual endpoints "behind" the NAT (see section 2.23). + +1.1.3. Endpoint to Security Gateway Tunnel + + +-+-+-+-+-+ +-+-+-+-+-+ + ! ! IPsec ! ! Protected + !Protected! tunnel !Tunnel ! Subnet + !Endpoint !<------------------------>!Endpoint !<--- and/or + ! ! ! ! Internet + +-+-+-+-+-+ +-+-+-+-+-+ + + Figure 3: Endpoint to Security Gateway Tunnel + + In this scenario, a protected endpoint (typically a portable roaming + computer) connects back to its corporate network through an IPsec- + protected tunnel. It might use this tunnel only to access + information on the corporate network, or it might tunnel all of its + traffic back through the corporate network in order to take advantage + of protection provided by a corporate firewall against Internet-based + attacks. In either case, the protected endpoint will want an IP + address associated with the security gateway so that packets returned + to it will go to the security gateway and be tunneled back. This IP + address may be static or may be dynamically allocated by the security + gateway. In support of the latter case, IKEv2 includes a mechanism + for the initiator to request an IP address owned by the security + gateway for use for the duration of its SA. + + In this scenario, packets will use tunnel mode. On each packet from + the protected endpoint, the outer IP header will contain the source + IP address associated with its current location (i.e., the address + that will get traffic routed to the endpoint directly), while the + inner IP header will contain the source IP address assigned by the + security gateway (i.e., the address that will get traffic routed to + the security gateway for forwarding to the endpoint). The outer + destination address will always be that of the security gateway, + while the inner destination address will be the ultimate destination + for the packet. + + + +Kaufman Standards Track [Page 6] + +RFC 4306 IKEv2 December 2005 + + + In this scenario, it is possible that the protected endpoint will be + behind a NAT. In that case, the IP address as seen by the security + gateway will not be the same as the IP address sent by the protected + endpoint, and packets will have to be UDP encapsulated in order to be + routed properly. + +1.1.4. Other Scenarios + + Other scenarios are possible, as are nested combinations of the + above. One notable example combines aspects of 1.1.1 and 1.1.3. A + subnet may make all external accesses through a remote security + gateway using an IPsec tunnel, where the addresses on the subnet are + routed to the security gateway by the rest of the Internet. An + example would be someone's home network being virtually on the + Internet with static IP addresses even though connectivity is + provided by an ISP that assigns a single dynamically assigned IP + address to the user's security gateway (where the static IP addresses + and an IPsec relay are provided by a third party located elsewhere). + +1.2. The Initial Exchanges + + Communication using IKE always begins with IKE_SA_INIT and IKE_AUTH + exchanges (known in IKEv1 as Phase 1). These initial exchanges + normally consist of four messages, though in some scenarios that + number can grow. All communications using IKE consist of + request/response pairs. We'll describe the base exchange first, + followed by variations. The first pair of messages (IKE_SA_INIT) + negotiate cryptographic algorithms, exchange nonces, and do a + Diffie-Hellman exchange [DH]. + + The second pair of messages (IKE_AUTH) authenticate the previous + messages, exchange identities and certificates, and establish the + first CHILD_SA. Parts of these messages are encrypted and integrity + protected with keys established through the IKE_SA_INIT exchange, so + the identities are hidden from eavesdroppers and all fields in all + the messages are authenticated. + + In the following descriptions, the payloads contained in the message + are indicated by names as listed below. + + Notation Payload + + AUTH Authentication + CERT Certificate + CERTREQ Certificate Request + CP Configuration + D Delete + E Encrypted + + + +Kaufman Standards Track [Page 7] + +RFC 4306 IKEv2 December 2005 + + + EAP Extensible Authentication + HDR IKE Header + IDi Identification - Initiator + IDr Identification - Responder + KE Key Exchange + Ni, Nr Nonce + N Notify + SA Security Association + TSi Traffic Selector - Initiator + TSr Traffic Selector - Responder + V Vendor ID + + The details of the contents of each payload are described in section + 3. Payloads that may optionally appear will be shown in brackets, + such as [CERTREQ], indicate that optionally a certificate request + payload can be included. + + The initial exchanges are as follows: + + Initiator Responder + ----------- ----------- + HDR, SAi1, KEi, Ni --> + + HDR contains the Security Parameter Indexes (SPIs), version numbers, + and flags of various sorts. The SAi1 payload states the + cryptographic algorithms the initiator supports for the IKE_SA. The + KE payload sends the initiator's Diffie-Hellman value. Ni is the + initiator's nonce. + + <-- HDR, SAr1, KEr, Nr, [CERTREQ] + + The responder chooses a cryptographic suite from the initiator's + offered choices and expresses that choice in the SAr1 payload, + completes the Diffie-Hellman exchange with the KEr payload, and sends + its nonce in the Nr payload. + + At this point in the negotiation, each party can generate SKEYSEED, + from which all keys are derived for that IKE_SA. All but the headers + of all the messages that follow are encrypted and integrity + protected. The keys used for the encryption and integrity protection + are derived from SKEYSEED and are known as SK_e (encryption) and SK_a + (authentication, a.k.a. integrity protection). A separate SK_e and + SK_a is computed for each direction. In addition to the keys SK_e + and SK_a derived from the DH value for protection of the IKE_SA, + another quantity SK_d is derived and used for derivation of further + keying material for CHILD_SAs. The notation SK { ... } indicates + that these payloads are encrypted and integrity protected using that + direction's SK_e and SK_a. + + + +Kaufman Standards Track [Page 8] + +RFC 4306 IKEv2 December 2005 + + + HDR, SK {IDi, [CERT,] [CERTREQ,] [IDr,] + AUTH, SAi2, TSi, TSr} --> + + The initiator asserts its identity with the IDi payload, proves + knowledge of the secret corresponding to IDi and integrity protects + the contents of the first message using the AUTH payload (see section + 2.15). It might also send its certificate(s) in CERT payload(s) and + a list of its trust anchors in CERTREQ payload(s). If any CERT + payloads are included, the first certificate provided MUST contain + the public key used to verify the AUTH field. The optional payload + IDr enables the initiator to specify which of the responder's + identities it wants to talk to. This is useful when the machine on + which the responder is running is hosting multiple identities at the + same IP address. The initiator begins negotiation of a CHILD_SA + using the SAi2 payload. The final fields (starting with SAi2) are + described in the description of the CREATE_CHILD_SA exchange. + + <-- HDR, SK {IDr, [CERT,] AUTH, + SAr2, TSi, TSr} + + The responder asserts its identity with the IDr payload, optionally + sends one or more certificates (again with the certificate containing + the public key used to verify AUTH listed first), authenticates its + identity and protects the integrity of the second message with the + AUTH payload, and completes negotiation of a CHILD_SA with the + additional fields described below in the CREATE_CHILD_SA exchange. + + The recipients of messages 3 and 4 MUST verify that all signatures + and MACs are computed correctly and that the names in the ID payloads + correspond to the keys used to generate the AUTH payload. + +1.3. The CREATE_CHILD_SA Exchange + + This exchange consists of a single request/response pair, and was + referred to as a phase 2 exchange in IKEv1. It MAY be initiated by + either end of the IKE_SA after the initial exchanges are completed. + + All messages following the initial exchange are cryptographically + protected using the cryptographic algorithms and keys negotiated in + the first two messages of the IKE exchange. These subsequent + messages use the syntax of the Encrypted Payload described in section + 3.14. All subsequent messages included an Encrypted Payload, even if + they are referred to in the text as "empty". + + Either endpoint may initiate a CREATE_CHILD_SA exchange, so in this + section the term "initiator" refers to the endpoint initiating this + exchange. + + + + +Kaufman Standards Track [Page 9] + +RFC 4306 IKEv2 December 2005 + + + A CHILD_SA is created by sending a CREATE_CHILD_SA request. The + CREATE_CHILD_SA request MAY optionally contain a KE payload for an + additional Diffie-Hellman exchange to enable stronger guarantees of + forward secrecy for the CHILD_SA. The keying material for the + CHILD_SA is a function of SK_d established during the establishment + of the IKE_SA, the nonces exchanged during the CREATE_CHILD_SA + exchange, and the Diffie-Hellman value (if KE payloads are included + in the CREATE_CHILD_SA exchange). + + In the CHILD_SA created as part of the initial exchange, a second KE + payload and nonce MUST NOT be sent. The nonces from the initial + exchange are used in computing the keys for the CHILD_SA. + + The CREATE_CHILD_SA request contains: + + Initiator Responder + ----------- ----------- + HDR, SK {[N], SA, Ni, [KEi], + [TSi, TSr]} --> + + The initiator sends SA offer(s) in the SA payload, a nonce in the Ni + payload, optionally a Diffie-Hellman value in the KEi payload, and + the proposed traffic selectors in the TSi and TSr payloads. If this + CREATE_CHILD_SA exchange is rekeying an existing SA other than the + IKE_SA, the leading N payload of type REKEY_SA MUST identify the SA + being rekeyed. If this CREATE_CHILD_SA exchange is not rekeying an + existing SA, the N payload MUST be omitted. If the SA offers include + different Diffie-Hellman groups, KEi MUST be an element of the group + the initiator expects the responder to accept. If it guesses wrong, + the CREATE_CHILD_SA exchange will fail, and it will have to retry + with a different KEi. + + The message following the header is encrypted and the message + including the header is integrity protected using the cryptographic + algorithms negotiated for the IKE_SA. + + The CREATE_CHILD_SA response contains: + + <-- HDR, SK {SA, Nr, [KEr], + [TSi, TSr]} + + The responder replies (using the same Message ID to respond) with the + accepted offer in an SA payload, and a Diffie-Hellman value in the + KEr payload if KEi was included in the request and the selected + cryptographic suite includes that group. If the responder chooses a + cryptographic suite with a different group, it MUST reject the + request. The initiator SHOULD repeat the request, but now with a KEi + payload from the group the responder selected. + + + +Kaufman Standards Track [Page 10] + +RFC 4306 IKEv2 December 2005 + + + The traffic selectors for traffic to be sent on that SA are specified + in the TS payloads, which may be a subset of what the initiator of + the CHILD_SA proposed. Traffic selectors are omitted if this + CREATE_CHILD_SA request is being used to change the key of the + IKE_SA. + +1.4. The INFORMATIONAL Exchange + + At various points during the operation of an IKE_SA, peers may desire + to convey control messages to each other regarding errors or + notifications of certain events. To accomplish this, IKE defines an + INFORMATIONAL exchange. INFORMATIONAL exchanges MUST ONLY occur + after the initial exchanges and are cryptographically protected with + the negotiated keys. + + Control messages that pertain to an IKE_SA MUST be sent under that + IKE_SA. Control messages that pertain to CHILD_SAs MUST be sent + under the protection of the IKE_SA which generated them (or its + successor if the IKE_SA was replaced for the purpose of rekeying). + + Messages in an INFORMATIONAL exchange contain zero or more + Notification, Delete, and Configuration payloads. The Recipient of + an INFORMATIONAL exchange request MUST send some response (else the + Sender will assume the message was lost in the network and will + retransmit it). That response MAY be a message with no payloads. + The request message in an INFORMATIONAL exchange MAY also contain no + payloads. This is the expected way an endpoint can ask the other + endpoint to verify that it is alive. + + ESP and AH SAs always exist in pairs, with one SA in each direction. + When an SA is closed, both members of the pair MUST be closed. When + SAs are nested, as when data (and IP headers if in tunnel mode) are + encapsulated first with IPComp, then with ESP, and finally with AH + between the same pair of endpoints, all of the SAs MUST be deleted + together. Each endpoint MUST close its incoming SAs and allow the + other endpoint to close the other SA in each pair. To delete an SA, + an INFORMATIONAL exchange with one or more delete payloads is sent + listing the SPIs (as they would be expected in the headers of inbound + packets) of the SAs to be deleted. The recipient MUST close the + designated SAs. Normally, the reply in the INFORMATIONAL exchange + will contain delete payloads for the paired SAs going in the other + direction. There is one exception. If by chance both ends of a set + of SAs independently decide to close them, each may send a delete + payload and the two requests may cross in the network. If a node + receives a delete request for SAs for which it has already issued a + delete request, it MUST delete the outgoing SAs while processing the + request and the incoming SAs while processing the response. In that + + + + +Kaufman Standards Track [Page 11] + +RFC 4306 IKEv2 December 2005 + + + case, the responses MUST NOT include delete payloads for the deleted + SAs, since that would result in duplicate deletion and could in + theory delete the wrong SA. + + A node SHOULD regard half-closed connections as anomalous and audit + their existence should they persist. Note that this specification + nowhere specifies time periods, so it is up to individual endpoints + to decide how long to wait. A node MAY refuse to accept incoming + data on half-closed connections but MUST NOT unilaterally close them + and reuse the SPIs. If connection state becomes sufficiently messed + up, a node MAY close the IKE_SA; doing so will implicitly close all + SAs negotiated under it. It can then rebuild the SAs it needs on a + clean base under a new IKE_SA. + + The INFORMATIONAL exchange is defined as: + + Initiator Responder + ----------- ----------- + HDR, SK {[N,] [D,] [CP,] ...} --> + <-- HDR, SK {[N,] [D,] [CP], ...} + + The processing of an INFORMATIONAL exchange is determined by its + component payloads. + +1.5. Informational Messages outside of an IKE_SA + + If an encrypted IKE packet arrives on port 500 or 4500 with an + unrecognized SPI, it could be because the receiving node has recently + crashed and lost state or because of some other system malfunction or + attack. If the receiving node has an active IKE_SA to the IP address + from whence the packet came, it MAY send a notification of the + wayward packet over that IKE_SA in an INFORMATIONAL exchange. If it + does not have such an IKE_SA, it MAY send an Informational message + without cryptographic protection to the source IP address. Such a + message is not part of an informational exchange, and the receiving + node MUST NOT respond to it. Doing so could cause a message loop. + +2. IKE Protocol Details and Variations + + IKE normally listens and sends on UDP port 500, though IKE messages + may also be received on UDP port 4500 with a slightly different + format (see section 2.23). Since UDP is a datagram (unreliable) + protocol, IKE includes in its definition recovery from transmission + errors, including packet loss, packet replay, and packet forgery. + IKE is designed to function so long as (1) at least one of a series + of retransmitted packets reaches its destination before timing out; + and (2) the channel is not so full of forged and replayed packets so + + + + +Kaufman Standards Track [Page 12] + +RFC 4306 IKEv2 December 2005 + + + as to exhaust the network or CPU capacities of either endpoint. Even + in the absence of those minimum performance requirements, IKE is + designed to fail cleanly (as though the network were broken). + + Although IKEv2 messages are intended to be short, they contain + structures with no hard upper bound on size (in particular, X.509 + certificates), and IKEv2 itself does not have a mechanism for + fragmenting large messages. IP defines a mechanism for fragmentation + of oversize UDP messages, but implementations vary in the maximum + message size supported. Furthermore, use of IP fragmentation opens + an implementation to denial of service attacks [KPS03]. Finally, + some NAT and/or firewall implementations may block IP fragments. + + All IKEv2 implementations MUST be able to send, receive, and process + IKE messages that are up to 1280 bytes long, and they SHOULD be able + to send, receive, and process messages that are up to 3000 bytes + long. IKEv2 implementations SHOULD be aware of the maximum UDP + message size supported and MAY shorten messages by leaving out some + certificates or cryptographic suite proposals if that will keep + messages below the maximum. Use of the "Hash and URL" formats rather + than including certificates in exchanges where possible can avoid + most problems. Implementations and configuration should keep in + mind, however, that if the URL lookups are possible only after the + IPsec SA is established, recursion issues could prevent this + technique from working. + +2.1. Use of Retransmission Timers + + All messages in IKE exist in pairs: a request and a response. The + setup of an IKE_SA normally consists of two request/response pairs. + Once the IKE_SA is set up, either end of the security association may + initiate requests at any time, and there can be many requests and + responses "in flight" at any given moment. But each message is + labeled as either a request or a response, and for each + request/response pair one end of the security association is the + initiator and the other is the responder. + + For every pair of IKE messages, the initiator is responsible for + retransmission in the event of a timeout. The responder MUST never + retransmit a response unless it receives a retransmission of the + request. In that event, the responder MUST ignore the retransmitted + request except insofar as it triggers a retransmission of the + response. The initiator MUST remember each request until it receives + the corresponding response. The responder MUST remember each + response until it receives a request whose sequence number is larger + than the sequence number in the response plus its window size (see + section 2.3). + + + + +Kaufman Standards Track [Page 13] + +RFC 4306 IKEv2 December 2005 + + + IKE is a reliable protocol, in the sense that the initiator MUST + retransmit a request until either it receives a corresponding reply + OR it deems the IKE security association to have failed and it + discards all state associated with the IKE_SA and any CHILD_SAs + negotiated using that IKE_SA. + +2.2. Use of Sequence Numbers for Message ID + + Every IKE message contains a Message ID as part of its fixed header. + This Message ID is used to match up requests and responses, and to + identify retransmissions of messages. + + The Message ID is a 32-bit quantity, which is zero for the first IKE + request in each direction. The IKE_SA initial setup messages will + always be numbered 0 and 1. Each endpoint in the IKE Security + Association maintains two "current" Message IDs: the next one to be + used for a request it initiates and the next one it expects to see in + a request from the other end. These counters increment as requests + are generated and received. Responses always contain the same + message ID as the corresponding request. That means that after the + initial exchange, each integer n may appear as the message ID in four + distinct messages: the nth request from the original IKE initiator, + the corresponding response, the nth request from the original IKE + responder, and the corresponding response. If the two ends make very + different numbers of requests, the Message IDs in the two directions + can be very different. There is no ambiguity in the messages, + however, because the (I)nitiator and (R)esponse bits in the message + header specify which of the four messages a particular one is. + + Note that Message IDs are cryptographically protected and provide + protection against message replays. In the unlikely event that + Message IDs grow too large to fit in 32 bits, the IKE_SA MUST be + closed. Rekeying an IKE_SA resets the sequence numbers. + +2.3. Window Size for Overlapping Requests + + In order to maximize IKE throughput, an IKE endpoint MAY issue + multiple requests before getting a response to any of them if the + other endpoint has indicated its ability to handle such requests. + For simplicity, an IKE implementation MAY choose to process requests + strictly in order and/or wait for a response to one request before + issuing another. Certain rules must be followed to ensure + interoperability between implementations using different strategies. + + After an IKE_SA is set up, either end can initiate one or more + requests. These requests may pass one another over the network. An + IKE endpoint MUST be prepared to accept and process a request while + + + + +Kaufman Standards Track [Page 14] + +RFC 4306 IKEv2 December 2005 + + + it has a request outstanding in order to avoid a deadlock in this + situation. An IKE endpoint SHOULD be prepared to accept and process + multiple requests while it has a request outstanding. + + An IKE endpoint MUST wait for a response to each of its messages + before sending a subsequent message unless it has received a + SET_WINDOW_SIZE Notify message from its peer informing it that the + peer is prepared to maintain state for multiple outstanding messages + in order to allow greater throughput. + + An IKE endpoint MUST NOT exceed the peer's stated window size for + transmitted IKE requests. In other words, if the responder stated + its window size is N, then when the initiator needs to make a request + X, it MUST wait until it has received responses to all requests up + through request X-N. An IKE endpoint MUST keep a copy of (or be able + to regenerate exactly) each request it has sent until it receives the + corresponding response. An IKE endpoint MUST keep a copy of (or be + able to regenerate exactly) the number of previous responses equal to + its declared window size in case its response was lost and the + initiator requests its retransmission by retransmitting the request. + + An IKE endpoint supporting a window size greater than one SHOULD be + capable of processing incoming requests out of order to maximize + performance in the event of network failures or packet reordering. + +2.4. State Synchronization and Connection Timeouts + + An IKE endpoint is allowed to forget all of its state associated with + an IKE_SA and the collection of corresponding CHILD_SAs at any time. + This is the anticipated behavior in the event of an endpoint crash + and restart. It is important when an endpoint either fails or + reinitializes its state that the other endpoint detect those + conditions and not continue to waste network bandwidth by sending + packets over discarded SAs and having them fall into a black hole. + + Since IKE is designed to operate in spite of Denial of Service (DoS) + attacks from the network, an endpoint MUST NOT conclude that the + other endpoint has failed based on any routing information (e.g., + ICMP messages) or IKE messages that arrive without cryptographic + protection (e.g., Notify messages complaining about unknown SPIs). + An endpoint MUST conclude that the other endpoint has failed only + when repeated attempts to contact it have gone unanswered for a + timeout period or when a cryptographically protected INITIAL_CONTACT + notification is received on a different IKE_SA to the same + authenticated identity. An endpoint SHOULD suspect that the other + endpoint has failed based on routing information and initiate a + request to see whether the other endpoint is alive. To check whether + the other side is alive, IKE specifies an empty INFORMATIONAL message + + + +Kaufman Standards Track [Page 15] + +RFC 4306 IKEv2 December 2005 + + + that (like all IKE requests) requires an acknowledgement (note that + within the context of an IKE_SA, an "empty" message consists of an + IKE header followed by an Encrypted payload that contains no + payloads). If a cryptographically protected message has been + received from the other side recently, unprotected notifications MAY + be ignored. Implementations MUST limit the rate at which they take + actions based on unprotected messages. + + Numbers of retries and lengths of timeouts are not covered in this + specification because they do not affect interoperability. It is + suggested that messages be retransmitted at least a dozen times over + a period of at least several minutes before giving up on an SA, but + different environments may require different rules. To be a good + network citizen, retranmission times MUST increase exponentially to + avoid flooding the network and making an existing congestion + situation worse. If there has only been outgoing traffic on all of + the SAs associated with an IKE_SA, it is essential to confirm + liveness of the other endpoint to avoid black holes. If no + cryptographically protected messages have been received on an IKE_SA + or any of its CHILD_SAs recently, the system needs to perform a + liveness check in order to prevent sending messages to a dead peer. + Receipt of a fresh cryptographically protected message on an IKE_SA + or any of its CHILD_SAs ensures liveness of the IKE_SA and all of its + CHILD_SAs. Note that this places requirements on the failure modes + of an IKE endpoint. An implementation MUST NOT continue sending on + any SA if some failure prevents it from receiving on all of the + associated SAs. If CHILD_SAs can fail independently from one another + without the associated IKE_SA being able to send a delete message, + then they MUST be negotiated by separate IKE_SAs. + + There is a Denial of Service attack on the initiator of an IKE_SA + that can be avoided if the initiator takes the proper care. Since + the first two messages of an SA setup are not cryptographically + protected, an attacker could respond to the initiator's message + before the genuine responder and poison the connection setup attempt. + To prevent this, the initiator MAY be willing to accept multiple + responses to its first message, treat each as potentially legitimate, + respond to it, and then discard all the invalid half-open connections + when it receives a valid cryptographically protected response to any + one of its requests. Once a cryptographically valid response is + received, all subsequent responses should be ignored whether or not + they are cryptographically valid. + + Note that with these rules, there is no reason to negotiate and agree + upon an SA lifetime. If IKE presumes the partner is dead, based on + repeated lack of acknowledgement to an IKE message, then the IKE SA + and all CHILD_SAs set up through that IKE_SA are deleted. + + + + +Kaufman Standards Track [Page 16] + +RFC 4306 IKEv2 December 2005 + + + An IKE endpoint may at any time delete inactive CHILD_SAs to recover + resources used to hold their state. If an IKE endpoint chooses to + delete CHILD_SAs, it MUST send Delete payloads to the other end + notifying it of the deletion. It MAY similarly time out the IKE_SA. + Closing the IKE_SA implicitly closes all associated CHILD_SAs. In + this case, an IKE endpoint SHOULD send a Delete payload indicating + that it has closed the IKE_SA. + +2.5. Version Numbers and Forward Compatibility + + This document describes version 2.0 of IKE, meaning the major version + number is 2 and the minor version number is zero. It is likely that + some implementations will want to support both version 1.0 and + version 2.0, and in the future, other versions. + + The major version number should be incremented only if the packet + formats or required actions have changed so dramatically that an + older version node would not be able to interoperate with a newer + version node if it simply ignored the fields it did not understand + and took the actions specified in the older specification. The minor + version number indicates new capabilities, and MUST be ignored by a + node with a smaller minor version number, but used for informational + purposes by the node with the larger minor version number. For + example, it might indicate the ability to process a newly defined + notification message. The node with the larger minor version number + would simply note that its correspondent would not be able to + understand that message and therefore would not send it. + + If an endpoint receives a message with a higher major version number, + it MUST drop the message and SHOULD send an unauthenticated + notification message containing the highest version number it + supports. If an endpoint supports major version n, and major version + m, it MUST support all versions between n and m. If it receives a + message with a major version that it supports, it MUST respond with + that version number. In order to prevent two nodes from being + tricked into corresponding with a lower major version number than the + maximum that they both support, IKE has a flag that indicates that + the node is capable of speaking a higher major version number. + + Thus, the major version number in the IKE header indicates the + version number of the message, not the highest version number that + the transmitter supports. If the initiator is capable of speaking + versions n, n+1, and n+2, and the responder is capable of speaking + versions n and n+1, then they will negotiate speaking n+1, where the + initiator will set the flag indicating its ability to speak a higher + version. If they mistakenly (perhaps through an active attacker + + + + + +Kaufman Standards Track [Page 17] + +RFC 4306 IKEv2 December 2005 + + + sending error messages) negotiate to version n, then both will notice + that the other side can support a higher version number, and they + MUST break the connection and reconnect using version n+1. + + Note that IKEv1 does not follow these rules, because there is no way + in v1 of noting that you are capable of speaking a higher version + number. So an active attacker can trick two v2-capable nodes into + speaking v1. When a v2-capable node negotiates down to v1, it SHOULD + note that fact in its logs. + + Also for forward compatibility, all fields marked RESERVED MUST be + set to zero by a version 2.0 implementation and their content MUST be + ignored by a version 2.0 implementation ("Be conservative in what you + send and liberal in what you receive"). In this way, future versions + of the protocol can use those fields in a way that is guaranteed to + be ignored by implementations that do not understand them. + Similarly, payload types that are not defined are reserved for future + use; implementations of version 2.0 MUST skip over those payloads and + ignore their contents. + + IKEv2 adds a "critical" flag to each payload header for further + flexibility for forward compatibility. If the critical flag is set + and the payload type is unrecognized, the message MUST be rejected + and the response to the IKE request containing that payload MUST + include a Notify payload UNSUPPORTED_CRITICAL_PAYLOAD, indicating an + unsupported critical payload was included. If the critical flag is + not set and the payload type is unsupported, that payload MUST be + ignored. + + Although new payload types may be added in the future and may appear + interleaved with the fields defined in this specification, + implementations MUST send the payloads defined in this specification + in the order shown in the figures in section 2 and implementations + SHOULD reject as invalid a message with those payloads in any other + order. + +2.6. Cookies + + The term "cookies" originates with Karn and Simpson [RFC2522] in + Photuris, an early proposal for key management with IPsec, and it has + persisted. The Internet Security Association and Key Management + Protocol (ISAKMP) [MSST98] fixed message header includes two eight- + octet fields titled "cookies", and that syntax is used by both IKEv1 + and IKEv2 though in IKEv2 they are referred to as the IKE SPI and + there is a new separate field in a Notify payload holding the cookie. + The initial two eight-octet fields in the header are used as a + connection identifier at the beginning of IKE packets. Each endpoint + + + + +Kaufman Standards Track [Page 18] + +RFC 4306 IKEv2 December 2005 + + + chooses one of the two SPIs and SHOULD choose them so as to be unique + identifiers of an IKE_SA. An SPI value of zero is special and + indicates that the remote SPI value is not yet known by the sender. + + Unlike ESP and AH where only the recipient's SPI appears in the + header of a message, in IKE the sender's SPI is also sent in every + message. Since the SPI chosen by the original initiator of the + IKE_SA is always sent first, an endpoint with multiple IKE_SAs open + that wants to find the appropriate IKE_SA using the SPI it assigned + must look at the I(nitiator) Flag bit in the header to determine + whether it assigned the first or the second eight octets. + + In the first message of an initial IKE exchange, the initiator will + not know the responder's SPI value and will therefore set that field + to zero. + + An expected attack against IKE is state and CPU exhaustion, where the + target is flooded with session initiation requests from forged IP + addresses. This attack can be made less effective if an + implementation of a responder uses minimal CPU and commits no state + to an SA until it knows the initiator can receive packets at the + address from which it claims to be sending them. To accomplish this, + a responder SHOULD -- when it detects a large number of half-open + IKE_SAs -- reject initial IKE messages unless they contain a Notify + payload of type COOKIE. It SHOULD instead send an unprotected IKE + message as a response and include COOKIE Notify payload with the + cookie data to be returned. Initiators who receive such responses + MUST retry the IKE_SA_INIT with a Notify payload of type COOKIE + containing the responder supplied cookie data as the first payload + and all other payloads unchanged. The initial exchange will then be + as follows: + + Initiator Responder + ----------- ----------- + HDR(A,0), SAi1, KEi, Ni --> + + <-- HDR(A,0), N(COOKIE) + + HDR(A,0), N(COOKIE), SAi1, KEi, Ni --> + + <-- HDR(A,B), SAr1, KEr, Nr, [CERTREQ] + + HDR(A,B), SK {IDi, [CERT,] [CERTREQ,] [IDr,] + AUTH, SAi2, TSi, TSr} --> + + <-- HDR(A,B), SK {IDr, [CERT,] AUTH, + SAr2, TSi, TSr} + + + + +Kaufman Standards Track [Page 19] + +RFC 4306 IKEv2 December 2005 + + + The first two messages do not affect any initiator or responder state + except for communicating the cookie. In particular, the message + sequence numbers in the first four messages will all be zero and the + message sequence numbers in the last two messages will be one. 'A' is + the SPI assigned by the initiator, while 'B' is the SPI assigned by + the responder. + + An IKE implementation SHOULD implement its responder cookie + generation in such a way as to not require any saved state to + recognize its valid cookie when the second IKE_SA_INIT message + arrives. The exact algorithms and syntax they use to generate + cookies do not affect interoperability and hence are not specified + here. The following is an example of how an endpoint could use + cookies to implement limited DOS protection. + + A good way to do this is to set the responder cookie to be: + + Cookie = <VersionIDofSecret> | Hash(Ni | IPi | SPIi | <secret>) + + where <secret> is a randomly generated secret known only to the + responder and periodically changed and | indicates concatenation. + <VersionIDofSecret> should be changed whenever <secret> is + regenerated. The cookie can be recomputed when the IKE_SA_INIT + arrives the second time and compared to the cookie in the received + message. If it matches, the responder knows that the cookie was + generated since the last change to <secret> and that IPi must be the + same as the source address it saw the first time. Incorporating SPIi + into the calculation ensures that if multiple IKE_SAs are being set + up in parallel they will all get different cookies (assuming the + initiator chooses unique SPIi's). Incorporating Ni into the hash + ensures that an attacker who sees only message 2 can't successfully + forge a message 3. + + If a new value for <secret> is chosen while there are connections in + the process of being initialized, an IKE_SA_INIT might be returned + with other than the current <VersionIDofSecret>. The responder in + that case MAY reject the message by sending another response with a + new cookie or it MAY keep the old value of <secret> around for a + short time and accept cookies computed from either one. The + responder SHOULD NOT accept cookies indefinitely after <secret> is + changed, since that would defeat part of the denial of service + protection. The responder SHOULD change the value of <secret> + frequently, especially if under attack. + + + + + + + + +Kaufman Standards Track [Page 20] + +RFC 4306 IKEv2 December 2005 + + +2.7. Cryptographic Algorithm Negotiation + + The payload type known as "SA" indicates a proposal for a set of + choices of IPsec protocols (IKE, ESP, and/or AH) for the SA as well + as cryptographic algorithms associated with each protocol. + + An SA payload consists of one or more proposals. Each proposal + includes one or more protocols (usually one). Each protocol contains + one or more transforms -- each specifying a cryptographic algorithm. + Each transform contains zero or more attributes (attributes are + needed only if the transform identifier does not completely specify + the cryptographic algorithm). + + This hierarchical structure was designed to efficiently encode + proposals for cryptographic suites when the number of supported + suites is large because multiple values are acceptable for multiple + transforms. The responder MUST choose a single suite, which MAY be + any subset of the SA proposal following the rules below: + + Each proposal contains one or more protocols. If a proposal is + accepted, the SA response MUST contain the same protocols in the + same order as the proposal. The responder MUST accept a single + proposal or reject them all and return an error. (Example: if a + single proposal contains ESP and AH and that proposal is accepted, + both ESP and AH MUST be accepted. If ESP and AH are included in + separate proposals, the responder MUST accept only one of them). + + Each IPsec protocol proposal contains one or more transforms. + Each transform contains a transform type. The accepted + cryptographic suite MUST contain exactly one transform of each + type included in the proposal. For example: if an ESP proposal + includes transforms ENCR_3DES, ENCR_AES w/keysize 128, ENCR_AES + w/keysize 256, AUTH_HMAC_MD5, and AUTH_HMAC_SHA, the accepted + suite MUST contain one of the ENCR_ transforms and one of the + AUTH_ transforms. Thus, six combinations are acceptable. + + Since the initiator sends its Diffie-Hellman value in the + IKE_SA_INIT, it must guess the Diffie-Hellman group that the + responder will select from its list of supported groups. If the + initiator guesses wrong, the responder will respond with a Notify + payload of type INVALID_KE_PAYLOAD indicating the selected group. In + this case, the initiator MUST retry the IKE_SA_INIT with the + corrected Diffie-Hellman group. The initiator MUST again propose its + full set of acceptable cryptographic suites because the rejection + message was unauthenticated and otherwise an active attacker could + trick the endpoints into negotiating a weaker suite than a stronger + one that they both prefer. + + + + +Kaufman Standards Track [Page 21] + +RFC 4306 IKEv2 December 2005 + + +2.8. Rekeying + + IKE, ESP, and AH security associations use secret keys that SHOULD be + used only for a limited amount of time and to protect a limited + amount of data. This limits the lifetime of the entire security + association. When the lifetime of a security association expires, + the security association MUST NOT be used. If there is demand, new + security associations MAY be established. Reestablishment of + security associations to take the place of ones that expire is + referred to as "rekeying". + + To allow for minimal IPsec implementations, the ability to rekey SAs + without restarting the entire IKE_SA is optional. An implementation + MAY refuse all CREATE_CHILD_SA requests within an IKE_SA. If an SA + has expired or is about to expire and rekeying attempts using the + mechanisms described here fail, an implementation MUST close the + IKE_SA and any associated CHILD_SAs and then MAY start new ones. + Implementations SHOULD support in-place rekeying of SAs, since doing + so offers better performance and is likely to reduce the number of + packets lost during the transition. + + To rekey a CHILD_SA within an existing IKE_SA, create a new, + equivalent SA (see section 2.17 below), and when the new one is + established, delete the old one. To rekey an IKE_SA, establish a new + equivalent IKE_SA (see section 2.18 below) with the peer to whom the + old IKE_SA is shared using a CREATE_CHILD_SA within the existing + IKE_SA. An IKE_SA so created inherits all of the original IKE_SA's + CHILD_SAs. Use the new IKE_SA for all control messages needed to + maintain the CHILD_SAs created by the old IKE_SA, and delete the old + IKE_SA. The Delete payload to delete itself MUST be the last request + sent over an IKE_SA. + + SAs SHOULD be rekeyed proactively, i.e., the new SA should be + established before the old one expires and becomes unusable. Enough + time should elapse between the time the new SA is established and the + old one becomes unusable so that traffic can be switched over to the + new SA. + + A difference between IKEv1 and IKEv2 is that in IKEv1 SA lifetimes + were negotiated. In IKEv2, each end of the SA is responsible for + enforcing its own lifetime policy on the SA and rekeying the SA when + necessary. If the two ends have different lifetime policies, the end + with the shorter lifetime will end up always being the one to request + the rekeying. If an SA bundle has been inactive for a long time and + if an endpoint would not initiate the SA in the absence of traffic, + the endpoint MAY choose to close the SA instead of rekeying it when + its lifetime expires. It SHOULD do so if there has been no traffic + since the last time the SA was rekeyed. + + + +Kaufman Standards Track [Page 22] + +RFC 4306 IKEv2 December 2005 + + + If the two ends have the same lifetime policies, it is possible that + both will initiate a rekeying at the same time (which will result in + redundant SAs). To reduce the probability of this happening, the + timing of rekeying requests SHOULD be jittered (delayed by a random + amount of time after the need for rekeying is noticed). + + This form of rekeying may temporarily result in multiple similar SAs + between the same pairs of nodes. When there are two SAs eligible to + receive packets, a node MUST accept incoming packets through either + SA. If redundant SAs are created though such a collision, the SA + created with the lowest of the four nonces used in the two exchanges + SHOULD be closed by the endpoint that created it. + + Note that IKEv2 deliberately allows parallel SAs with the same + traffic selectors between common endpoints. One of the purposes of + this is to support traffic quality of service (QoS) differences among + the SAs (see [RFC2474], [RFC2475], and section 4.1 of [RFC2983]). + Hence unlike IKEv1, the combination of the endpoints and the traffic + selectors may not uniquely identify an SA between those endpoints, so + the IKEv1 rekeying heuristic of deleting SAs on the basis of + duplicate traffic selectors SHOULD NOT be used. + + The node that initiated the surviving rekeyed SA SHOULD delete the + replaced SA after the new one is established. + + There are timing windows -- particularly in the presence of lost + packets -- where endpoints may not agree on the state of an SA. The + responder to a CREATE_CHILD_SA MUST be prepared to accept messages on + an SA before sending its response to the creation request, so there + is no ambiguity for the initiator. The initiator MAY begin sending + on an SA as soon as it processes the response. The initiator, + however, cannot receive on a newly created SA until it receives and + processes the response to its CREATE_CHILD_SA request. How, then, is + the responder to know when it is OK to send on the newly created SA? + + From a technical correctness and interoperability perspective, the + responder MAY begin sending on an SA as soon as it sends its response + to the CREATE_CHILD_SA request. In some situations, however, this + could result in packets unnecessarily being dropped, so an + implementation MAY want to defer such sending. + + The responder can be assured that the initiator is prepared to + receive messages on an SA if either (1) it has received a + cryptographically valid message on the new SA, or (2) the new SA + rekeys an existing SA and it receives an IKE request to close the + replaced SA. When rekeying an SA, the responder SHOULD continue to + send messages on the old SA until one of those events occurs. When + establishing a new SA, the responder MAY defer sending messages on a + + + +Kaufman Standards Track [Page 23] + +RFC 4306 IKEv2 December 2005 + + + new SA until either it receives one or a timeout has occurred. If an + initiator receives a message on an SA for which it has not received a + response to its CREATE_CHILD_SA request, it SHOULD interpret that as + a likely packet loss and retransmit the CREATE_CHILD_SA request. An + initiator MAY send a dummy message on a newly created SA if it has no + messages queued in order to assure the responder that the initiator + is ready to receive messages. + +2.9. Traffic Selector Negotiation + + When an IP packet is received by an RFC4301-compliant IPsec subsystem + and matches a "protect" selector in its Security Policy Database + (SPD), the subsystem MUST protect that packet with IPsec. When no SA + exists yet, it is the task of IKE to create it. Maintenance of a + system's SPD is outside the scope of IKE (see [PFKEY] for an example + protocol), though some implementations might update their SPD in + connection with the running of IKE (for an example scenario, see + section 1.1.3). + + Traffic Selector (TS) payloads allow endpoints to communicate some of + the information from their SPD to their peers. TS payloads specify + the selection criteria for packets that will be forwarded over the + newly set up SA. This can serve as a consistency check in some + scenarios to assure that the SPDs are consistent. In others, it + guides the dynamic update of the SPD. + + Two TS payloads appear in each of the messages in the exchange that + creates a CHILD_SA pair. Each TS payload contains one or more + Traffic Selectors. Each Traffic Selector consists of an address + range (IPv4 or IPv6), a port range, and an IP protocol ID. In + support of the scenario described in section 1.1.3, an initiator may + request that the responder assign an IP address and tell the + initiator what it is. + + IKEv2 allows the responder to choose a subset of the traffic proposed + by the initiator. This could happen when the configurations of the + two endpoints are being updated but only one end has received the new + information. Since the two endpoints may be configured by different + people, the incompatibility may persist for an extended period even + in the absence of errors. It also allows for intentionally different + configurations, as when one end is configured to tunnel all addresses + and depends on the other end to have the up-to-date list. + + The first of the two TS payloads is known as TSi (Traffic Selector- + initiator). The second is known as TSr (Traffic Selector-responder). + TSi specifies the source address of traffic forwarded from (or the + destination address of traffic forwarded to) the initiator of the + CHILD_SA pair. TSr specifies the destination address of the traffic + + + +Kaufman Standards Track [Page 24] + +RFC 4306 IKEv2 December 2005 + + + forwarded to (or the source address of the traffic forwarded from) + the responder of the CHILD_SA pair. For example, if the original + initiator request the creation of a CHILD_SA pair, and wishes to + tunnel all traffic from subnet 192.0.1.* on the initiator's side to + subnet 192.0.2.* on the responder's side, the initiator would include + a single traffic selector in each TS payload. TSi would specify the + address range (192.0.1.0 - 192.0.1.255) and TSr would specify the + address range (192.0.2.0 - 192.0.2.255). Assuming that proposal was + acceptable to the responder, it would send identical TS payloads + back. (Note: The IP address range 192.0.2.* has been reserved for + use in examples in RFCs and similar documents. This document needed + two such ranges, and so also used 192.0.1.*. This should not be + confused with any actual address.) + + The responder is allowed to narrow the choices by selecting a subset + of the traffic, for instance by eliminating or narrowing the range of + one or more members of the set of traffic selectors, provided the set + does not become the NULL set. + + It is possible for the responder's policy to contain multiple smaller + ranges, all encompassed by the initiator's traffic selector, and with + the responder's policy being that each of those ranges should be sent + over a different SA. Continuing the example above, the responder + might have a policy of being willing to tunnel those addresses to and + from the initiator, but might require that each address pair be on a + separately negotiated CHILD_SA. If the initiator generated its + request in response to an incoming packet from 192.0.1.43 to + 192.0.2.123, there would be no way for the responder to determine + which pair of addresses should be included in this tunnel, and it + would have to make a guess or reject the request with a status of + SINGLE_PAIR_REQUIRED. + + To enable the responder to choose the appropriate range in this case, + if the initiator has requested the SA due to a data packet, the + initiator SHOULD include as the first traffic selector in each of TSi + and TSr a very specific traffic selector including the addresses in + the packet triggering the request. In the example, the initiator + would include in TSi two traffic selectors: the first containing the + address range (192.0.1.43 - 192.0.1.43) and the source port and IP + protocol from the packet and the second containing (192.0.1.0 - + 192.0.1.255) with all ports and IP protocols. The initiator would + similarly include two traffic selectors in TSr. + + If the responder's policy does not allow it to accept the entire set + of traffic selectors in the initiator's request, but does allow him + to accept the first selector of TSi and TSr, then the responder MUST + narrow the traffic selectors to a subset that includes the + + + + +Kaufman Standards Track [Page 25] + +RFC 4306 IKEv2 December 2005 + + + initiator's first choices. In this example, the responder might + respond with TSi being (192.0.1.43 - 192.0.1.43) with all ports and + IP protocols. + + If the initiator creates the CHILD_SA pair not in response to an + arriving packet, but rather, say, upon startup, then there may be no + specific addresses the initiator prefers for the initial tunnel over + any other. In that case, the first values in TSi and TSr MAY be + ranges rather than specific values, and the responder chooses a + subset of the initiator's TSi and TSr that are acceptable. If more + than one subset is acceptable but their union is not, the responder + MUST accept some subset and MAY include a Notify payload of type + ADDITIONAL_TS_POSSIBLE to indicate that the initiator might want to + try again. This case will occur only when the initiator and + responder are configured differently from one another. If the + initiator and responder agree on the granularity of tunnels, the + initiator will never request a tunnel wider than the responder will + accept. Such misconfigurations SHOULD be recorded in error logs. + +2.10. Nonces + + The IKE_SA_INIT messages each contain a nonce. These nonces are used + as inputs to cryptographic functions. The CREATE_CHILD_SA request + and the CREATE_CHILD_SA response also contain nonces. These nonces + are used to add freshness to the key derivation technique used to + obtain keys for CHILD_SA, and to ensure creation of strong pseudo- + random bits from the Diffie-Hellman key. Nonces used in IKEv2 MUST + be randomly chosen, MUST be at least 128 bits in size, and MUST be at + least half the key size of the negotiated prf. ("prf" refers to + "pseudo-random function", one of the cryptographic algorithms + negotiated in the IKE exchange.) If the same random number source is + used for both keys and nonces, care must be taken to ensure that the + latter use does not compromise the former. + +2.11. Address and Port Agility + + IKE runs over UDP ports 500 and 4500, and implicitly sets up ESP and + AH associations for the same IP addresses it runs over. The IP + addresses and ports in the outer header are, however, not themselves + cryptographically protected, and IKE is designed to work even through + Network Address Translation (NAT) boxes. An implementation MUST + accept incoming requests even if the source port is not 500 or 4500, + and MUST respond to the address and port from which the request was + received. It MUST specify the address and port at which the request + was received as the source address and port in the response. IKE + functions identically over IPv4 or IPv6. + + + + + +Kaufman Standards Track [Page 26] + +RFC 4306 IKEv2 December 2005 + + +2.12. Reuse of Diffie-Hellman Exponentials + + IKE generates keying material using an ephemeral Diffie-Hellman + exchange in order to gain the property of "perfect forward secrecy". + This means that once a connection is closed and its corresponding + keys are forgotten, even someone who has recorded all of the data + from the connection and gets access to all of the long-term keys of + the two endpoints cannot reconstruct the keys used to protect the + conversation without doing a brute force search of the session key + space. + + Achieving perfect forward secrecy requires that when a connection is + closed, each endpoint MUST forget not only the keys used by the + connection but also any information that could be used to recompute + those keys. In particular, it MUST forget the secrets used in the + Diffie-Hellman calculation and any state that may persist in the + state of a pseudo-random number generator that could be used to + recompute the Diffie-Hellman secrets. + + Since the computing of Diffie-Hellman exponentials is computationally + expensive, an endpoint may find it advantageous to reuse those + exponentials for multiple connection setups. There are several + reasonable strategies for doing this. An endpoint could choose a new + exponential only periodically though this could result in less-than- + perfect forward secrecy if some connection lasts for less than the + lifetime of the exponential. Or it could keep track of which + exponential was used for each connection and delete the information + associated with the exponential only when some corresponding + connection was closed. This would allow the exponential to be reused + without losing perfect forward secrecy at the cost of maintaining + more state. + + Decisions as to whether and when to reuse Diffie-Hellman exponentials + is a private decision in the sense that it will not affect + interoperability. An implementation that reuses exponentials MAY + choose to remember the exponential used by the other endpoint on past + exchanges and if one is reused to avoid the second half of the + calculation. + +2.13. Generating Keying Material + + In the context of the IKE_SA, four cryptographic algorithms are + negotiated: an encryption algorithm, an integrity protection + algorithm, a Diffie-Hellman group, and a pseudo-random function + (prf). The pseudo-random function is used for the construction of + keying material for all of the cryptographic algorithms used in both + the IKE_SA and the CHILD_SAs. + + + + +Kaufman Standards Track [Page 27] + +RFC 4306 IKEv2 December 2005 + + + We assume that each encryption algorithm and integrity protection + algorithm uses a fixed-size key and that any randomly chosen value of + that fixed size can serve as an appropriate key. For algorithms that + accept a variable length key, a fixed key size MUST be specified as + part of the cryptographic transform negotiated. For algorithms for + which not all values are valid keys (such as DES or 3DES with key + parity), the algorithm by which keys are derived from arbitrary + values MUST be specified by the cryptographic transform. For + integrity protection functions based on Hashed Message Authentication + Code (HMAC), the fixed key size is the size of the output of the + underlying hash function. When the prf function takes a variable + length key, variable length data, and produces a fixed-length output + (e.g., when using HMAC), the formulas in this document apply. When + the key for the prf function has fixed length, the data provided as a + key is truncated or padded with zeros as necessary unless exceptional + processing is explained following the formula. + + Keying material will always be derived as the output of the + negotiated prf algorithm. Since the amount of keying material needed + may be greater than the size of the output of the prf algorithm, we + will use the prf iteratively. We will use the terminology prf+ to + describe the function that outputs a pseudo-random stream based on + the inputs to a prf as follows: (where | indicates concatenation) + + prf+ (K,S) = T1 | T2 | T3 | T4 | ... + + where: + T1 = prf (K, S | 0x01) + T2 = prf (K, T1 | S | 0x02) + T3 = prf (K, T2 | S | 0x03) + T4 = prf (K, T3 | S | 0x04) + + continuing as needed to compute all required keys. The keys are + taken from the output string without regard to boundaries (e.g., if + the required keys are a 256-bit Advanced Encryption Standard (AES) + key and a 160-bit HMAC key, and the prf function generates 160 bits, + the AES key will come from T1 and the beginning of T2, while the HMAC + key will come from the rest of T2 and the beginning of T3). + + The constant concatenated to the end of each string feeding the prf + is a single octet. prf+ in this document is not defined beyond 255 + times the size of the prf output. + +2.14. Generating Keying Material for the IKE_SA + + The shared keys are computed as follows. A quantity called SKEYSEED + is calculated from the nonces exchanged during the IKE_SA_INIT + exchange and the Diffie-Hellman shared secret established during that + + + +Kaufman Standards Track [Page 28] + +RFC 4306 IKEv2 December 2005 + + + exchange. SKEYSEED is used to calculate seven other secrets: SK_d + used for deriving new keys for the CHILD_SAs established with this + IKE_SA; SK_ai and SK_ar used as a key to the integrity protection + algorithm for authenticating the component messages of subsequent + exchanges; SK_ei and SK_er used for encrypting (and of course + decrypting) all subsequent exchanges; and SK_pi and SK_pr, which are + used when generating an AUTH payload. + + SKEYSEED and its derivatives are computed as follows: + + SKEYSEED = prf(Ni | Nr, g^ir) + + {SK_d | SK_ai | SK_ar | SK_ei | SK_er | SK_pi | SK_pr } = prf+ + (SKEYSEED, Ni | Nr | SPIi | SPIr ) + + (indicating that the quantities SK_d, SK_ai, SK_ar, SK_ei, SK_er, + SK_pi, and SK_pr are taken in order from the generated bits of the + prf+). g^ir is the shared secret from the ephemeral Diffie-Hellman + exchange. g^ir is represented as a string of octets in big endian + order padded with zeros if necessary to make it the length of the + modulus. Ni and Nr are the nonces, stripped of any headers. If the + negotiated prf takes a fixed-length key and the lengths of Ni and Nr + do not add up to that length, half the bits must come from Ni and + half from Nr, taking the first bits of each. + + The two directions of traffic flow use different keys. The keys used + to protect messages from the original initiator are SK_ai and SK_ei. + The keys used to protect messages in the other direction are SK_ar + and SK_er. Each algorithm takes a fixed number of bits of keying + material, which is specified as part of the algorithm. For integrity + algorithms based on a keyed hash, the key size is always equal to the + length of the output of the underlying hash function. + +2.15. Authentication of the IKE_SA + + When not using extensible authentication (see section 2.16), the + peers are authenticated by having each sign (or MAC using a shared + secret as the key) a block of data. For the responder, the octets to + be signed start with the first octet of the first SPI in the header + of the second message and end with the last octet of the last payload + in the second message. Appended to this (for purposes of computing + the signature) are the initiator's nonce Ni (just the value, not the + payload containing it), and the value prf(SK_pr,IDr') where IDr' is + the responder's ID payload excluding the fixed header. Note that + neither the nonce Ni nor the value prf(SK_pr,IDr') are transmitted. + Similarly, the initiator signs the first message, starting with the + first octet of the first SPI in the header and ending with the last + octet of the last payload. Appended to this (for purposes of + + + +Kaufman Standards Track [Page 29] + +RFC 4306 IKEv2 December 2005 + + + computing the signature) are the responder's nonce Nr, and the value + prf(SK_pi,IDi'). In the above calculation, IDi' and IDr' are the + entire ID payloads excluding the fixed header. It is critical to the + security of the exchange that each side sign the other side's nonce. + + Note that all of the payloads are included under the signature, + including any payload types not defined in this document. If the + first message of the exchange is sent twice (the second time with a + responder cookie and/or a different Diffie-Hellman group), it is the + second version of the message that is signed. + + Optionally, messages 3 and 4 MAY include a certificate, or + certificate chain providing evidence that the key used to compute a + digital signature belongs to the name in the ID payload. The + signature or MAC will be computed using algorithms dictated by the + type of key used by the signer, and specified by the Auth Method + field in the Authentication payload. There is no requirement that + the initiator and responder sign with the same cryptographic + algorithms. The choice of cryptographic algorithms depends on the + type of key each has. In particular, the initiator may be using a + shared key while the responder may have a public signature key and + certificate. It will commonly be the case (but it is not required) + that if a shared secret is used for authentication that the same key + is used in both directions. Note that it is a common but typically + insecure practice to have a shared key derived solely from a user- + chosen password without incorporating another source of randomness. + + This is typically insecure because user-chosen passwords are unlikely + to have sufficient unpredictability to resist dictionary attacks and + these attacks are not prevented in this authentication method. + (Applications using password-based authentication for bootstrapping + and IKE_SA should use the authentication method in section 2.16, + which is designed to prevent off-line dictionary attacks.) The pre- + shared key SHOULD contain as much unpredictability as the strongest + key being negotiated. In the case of a pre-shared key, the AUTH + value is computed as: + + AUTH = prf(prf(Shared Secret,"Key Pad for IKEv2"), <msg octets>) + + where the string "Key Pad for IKEv2" is 17 ASCII characters without + null termination. The shared secret can be variable length. The pad + string is added so that if the shared secret is derived from a + password, the IKE implementation need not store the password in + cleartext, but rather can store the value prf(Shared Secret,"Key Pad + for IKEv2"), which could not be used as a password equivalent for + protocols other than IKEv2. As noted above, deriving the shared + secret from a password is not secure. This construction is used + because it is anticipated that people will do it anyway. The + + + +Kaufman Standards Track [Page 30] + +RFC 4306 IKEv2 December 2005 + + + management interface by which the Shared Secret is provided MUST + accept ASCII strings of at least 64 octets and MUST NOT add a null + terminator before using them as shared secrets. It MUST also accept + a HEX encoding of the Shared Secret. The management interface MAY + accept other encodings if the algorithm for translating the encoding + to a binary string is specified. If the negotiated prf takes a + fixed-size key, the shared secret MUST be of that fixed size. + +2.16. Extensible Authentication Protocol Methods + + In addition to authentication using public key signatures and shared + secrets, IKE supports authentication using methods defined in RFC + 3748 [EAP]. Typically, these methods are asymmetric (designed for a + user authenticating to a server), and they may not be mutual. For + this reason, these protocols are typically used to authenticate the + initiator to the responder and MUST be used in conjunction with a + public key signature based authentication of the responder to the + initiator. These methods are often associated with mechanisms + referred to as "Legacy Authentication" mechanisms. + + While this memo references [EAP] with the intent that new methods can + be added in the future without updating this specification, some + simpler variations are documented here and in section 3.16. [EAP] + defines an authentication protocol requiring a variable number of + messages. Extensible Authentication is implemented in IKE as + additional IKE_AUTH exchanges that MUST be completed in order to + initialize the IKE_SA. + + An initiator indicates a desire to use extensible authentication by + leaving out the AUTH payload from message 3. By including an IDi + payload but not an AUTH payload, the initiator has declared an + identity but has not proven it. If the responder is willing to use + an extensible authentication method, it will place an Extensible + Authentication Protocol (EAP) payload in message 4 and defer sending + SAr2, TSi, and TSr until initiator authentication is complete in a + subsequent IKE_AUTH exchange. In the case of a minimal extensible + authentication, the initial SA establishment will appear as follows: + + + + + + + + + + + + + + +Kaufman Standards Track [Page 31] + +RFC 4306 IKEv2 December 2005 + + + Initiator Responder + ----------- ----------- + HDR, SAi1, KEi, Ni --> + + <-- HDR, SAr1, KEr, Nr, [CERTREQ] + + HDR, SK {IDi, [CERTREQ,] [IDr,] + SAi2, TSi, TSr} --> + + <-- HDR, SK {IDr, [CERT,] AUTH, + EAP } + + HDR, SK {EAP} --> + + <-- HDR, SK {EAP (success)} + + HDR, SK {AUTH} --> + + <-- HDR, SK {AUTH, SAr2, TSi, TSr } + + For EAP methods that create a shared key as a side effect of + authentication, that shared key MUST be used by both the initiator + and responder to generate AUTH payloads in messages 7 and 8 using the + syntax for shared secrets specified in section 2.15. The shared key + from EAP is the field from the EAP specification named MSK. The + shared key generated during an IKE exchange MUST NOT be used for any + other purpose. + + EAP methods that do not establish a shared key SHOULD NOT be used, as + they are subject to a number of man-in-the-middle attacks [EAPMITM] + if these EAP methods are used in other protocols that do not use a + server-authenticated tunnel. Please see the Security Considerations + section for more details. If EAP methods that do not generate a + shared key are used, the AUTH payloads in messages 7 and 8 MUST be + generated using SK_pi and SK_pr, respectively. + + The initiator of an IKE_SA using EAP SHOULD be capable of extending + the initial protocol exchange to at least ten IKE_AUTH exchanges in + the event the responder sends notification messages and/or retries + the authentication prompt. Once the protocol exchange defined by the + chosen EAP authentication method has successfully terminated, the + responder MUST send an EAP payload containing the Success message. + Similarly, if the authentication method has failed, the responder + MUST send an EAP payload containing the Failure message. The + responder MAY at any time terminate the IKE exchange by sending an + EAP payload containing the Failure message. + + + + + +Kaufman Standards Track [Page 32] + +RFC 4306 IKEv2 December 2005 + + + Following such an extended exchange, the EAP AUTH payloads MUST be + included in the two messages following the one containing the EAP + Success message. + +2.17. Generating Keying Material for CHILD_SAs + + A single CHILD_SA is created by the IKE_AUTH exchange, and additional + CHILD_SAs can optionally be created in CREATE_CHILD_SA exchanges. + Keying material for them is generated as follows: + + KEYMAT = prf+(SK_d, Ni | Nr) + + Where Ni and Nr are the nonces from the IKE_SA_INIT exchange if this + request is the first CHILD_SA created or the fresh Ni and Nr from the + CREATE_CHILD_SA exchange if this is a subsequent creation. + + For CREATE_CHILD_SA exchanges including an optional Diffie-Hellman + exchange, the keying material is defined as: + + KEYMAT = prf+(SK_d, g^ir (new) | Ni | Nr ) + + where g^ir (new) is the shared secret from the ephemeral Diffie- + Hellman exchange of this CREATE_CHILD_SA exchange (represented as an + octet string in big endian order padded with zeros in the high-order + bits if necessary to make it the length of the modulus). + + A single CHILD_SA negotiation may result in multiple security + associations. ESP and AH SAs exist in pairs (one in each direction), + and four SAs could be created in a single CHILD_SA negotiation if a + combination of ESP and AH is being negotiated. + + Keying material MUST be taken from the expanded KEYMAT in the + following order: + + All keys for SAs carrying data from the initiator to the responder + are taken before SAs going in the reverse direction. + + If multiple IPsec protocols are negotiated, keying material is + taken in the order in which the protocol headers will appear in + the encapsulated packet. + + If a single protocol has both encryption and authentication keys, + the encryption key is taken from the first octets of KEYMAT and + the authentication key is taken from the next octets. + + Each cryptographic algorithm takes a fixed number of bits of keying + material specified as part of the algorithm. + + + + +Kaufman Standards Track [Page 33] + +RFC 4306 IKEv2 December 2005 + + +2.18. Rekeying IKE_SAs Using a CREATE_CHILD_SA exchange + + The CREATE_CHILD_SA exchange can be used to rekey an existing IKE_SA + (see section 2.8). New initiator and responder SPIs are supplied in + the SPI fields. The TS payloads are omitted when rekeying an IKE_SA. + SKEYSEED for the new IKE_SA is computed using SK_d from the existing + IKE_SA as follows: + + SKEYSEED = prf(SK_d (old), [g^ir (new)] | Ni | Nr) + + where g^ir (new) is the shared secret from the ephemeral Diffie- + Hellman exchange of this CREATE_CHILD_SA exchange (represented as an + octet string in big endian order padded with zeros if necessary to + make it the length of the modulus) and Ni and Nr are the two nonces + stripped of any headers. + + The new IKE_SA MUST reset its message counters to 0. + + SK_d, SK_ai, SK_ar, SK_ei, and SK_er are computed from SKEYSEED as + specified in section 2.14. + +2.19. Requesting an Internal Address on a Remote Network + + Most commonly occurring in the endpoint-to-security-gateway scenario, + an endpoint may need an IP address in the network protected by the + security gateway and may need to have that address dynamically + assigned. A request for such a temporary address can be included in + any request to create a CHILD_SA (including the implicit request in + message 3) by including a CP payload. + + This function provides address allocation to an IPsec Remote Access + Client (IRAC) trying to tunnel into a network protected by an IPsec + Remote Access Server (IRAS). Since the IKE_AUTH exchange creates an + IKE_SA and a CHILD_SA, the IRAC MUST request the IRAS-controlled + address (and optionally other information concerning the protected + network) in the IKE_AUTH exchange. The IRAS may procure an address + for the IRAC from any number of sources such as a DHCP/BOOTP server + or its own address pool. + + Initiator Responder + ----------------------------- --------------------------- + HDR, SK {IDi, [CERT,] [CERTREQ,] + [IDr,] AUTH, CP(CFG_REQUEST), + SAi2, TSi, TSr} --> + + <-- HDR, SK {IDr, [CERT,] AUTH, + CP(CFG_REPLY), SAr2, + TSi, TSr} + + + +Kaufman Standards Track [Page 34] + +RFC 4306 IKEv2 December 2005 + + + In all cases, the CP payload MUST be inserted before the SA payload. + In variations of the protocol where there are multiple IKE_AUTH + exchanges, the CP payloads MUST be inserted in the messages + containing the SA payloads. + + CP(CFG_REQUEST) MUST contain at least an INTERNAL_ADDRESS attribute + (either IPv4 or IPv6) but MAY contain any number of additional + attributes the initiator wants returned in the response. + + For example, message from initiator to responder: + CP(CFG_REQUEST)= + INTERNAL_ADDRESS(0.0.0.0) + INTERNAL_NETMASK(0.0.0.0) + INTERNAL_DNS(0.0.0.0) + TSi = (0, 0-65535,0.0.0.0-255.255.255.255) + TSr = (0, 0-65535,0.0.0.0-255.255.255.255) + + NOTE: Traffic Selectors contain (protocol, port range, address + range). + + Message from responder to initiator: + + CP(CFG_REPLY)= + INTERNAL_ADDRESS(192.0.2.202) + INTERNAL_NETMASK(255.255.255.0) + INTERNAL_SUBNET(192.0.2.0/255.255.255.0) + TSi = (0, 0-65535,192.0.2.202-192.0.2.202) + TSr = (0, 0-65535,192.0.2.0-192.0.2.255) + + All returned values will be implementation dependent. As can be seen + in the above example, the IRAS MAY also send other attributes that + were not included in CP(CFG_REQUEST) and MAY ignore the non-mandatory + attributes that it does not support. + + The responder MUST NOT send a CFG_REPLY without having first received + a CP(CFG_REQUEST) from the initiator, because we do not want the IRAS + to perform an unnecessary configuration lookup if the IRAC cannot + process the REPLY. In the case where the IRAS's configuration + requires that CP be used for a given identity IDi, but IRAC has + failed to send a CP(CFG_REQUEST), IRAS MUST fail the request, and + terminate the IKE exchange with a FAILED_CP_REQUIRED error. + +2.20. Requesting the Peer's Version + + An IKE peer wishing to inquire about the other peer's IKE software + version information MAY use the method below. This is an example of + a configuration request within an INFORMATIONAL exchange, after the + IKE_SA and first CHILD_SA have been created. + + + +Kaufman Standards Track [Page 35] + +RFC 4306 IKEv2 December 2005 + + + An IKE implementation MAY decline to give out version information + prior to authentication or even after authentication to prevent + trolling in case some implementation is known to have some security + weakness. In that case, it MUST either return an empty string or no + CP payload if CP is not supported. + + Initiator Responder + ----------------------------- -------------------------- + HDR, SK{CP(CFG_REQUEST)} --> + <-- HDR, SK{CP(CFG_REPLY)} + + CP(CFG_REQUEST)= + APPLICATION_VERSION("") + + CP(CFG_REPLY) APPLICATION_VERSION("foobar v1.3beta, (c) Foo Bar + Inc.") + +2.21. Error Handling + + There are many kinds of errors that can occur during IKE processing. + If a request is received that is badly formatted or unacceptable for + reasons of policy (e.g., no matching cryptographic algorithms), the + response MUST contain a Notify payload indicating the error. If an + error occurs outside the context of an IKE request (e.g., the node is + getting ESP messages on a nonexistent SPI), the node SHOULD initiate + an INFORMATIONAL exchange with a Notify payload describing the + problem. + + Errors that occur before a cryptographically protected IKE_SA is + established must be handled very carefully. There is a trade-off + between wanting to be helpful in diagnosing a problem and responding + to it and wanting to avoid being a dupe in a denial of service attack + based on forged messages. + + If a node receives a message on UDP port 500 or 4500 outside the + context of an IKE_SA known to it (and not a request to start one), it + may be the result of a recent crash of the node. If the message is + marked as a response, the node MAY audit the suspicious event but + MUST NOT respond. If the message is marked as a request, the node + MAY audit the suspicious event and MAY send a response. If a + response is sent, the response MUST be sent to the IP address and + port from whence it came with the same IKE SPIs and the Message ID + copied. The response MUST NOT be cryptographically protected and + MUST contain a Notify payload indicating INVALID_IKE_SPI. + + A node receiving such an unprotected Notify payload MUST NOT respond + and MUST NOT change the state of any existing SAs. The message might + be a forgery or might be a response the genuine correspondent was + + + +Kaufman Standards Track [Page 36] + +RFC 4306 IKEv2 December 2005 + + + tricked into sending. A node SHOULD treat such a message (and also a + network message like ICMP destination unreachable) as a hint that + there might be problems with SAs to that IP address and SHOULD + initiate a liveness test for any such IKE_SA. An implementation + SHOULD limit the frequency of such tests to avoid being tricked into + participating in a denial of service attack. + + A node receiving a suspicious message from an IP address with which + it has an IKE_SA MAY send an IKE Notify payload in an IKE + INFORMATIONAL exchange over that SA. The recipient MUST NOT change + the state of any SA's as a result but SHOULD audit the event to aid + in diagnosing malfunctions. A node MUST limit the rate at which it + will send messages in response to unprotected messages. + +2.22. IPComp + + Use of IP compression [IPCOMP] can be negotiated as part of the setup + of a CHILD_SA. While IP compression involves an extra header in each + packet and a compression parameter index (CPI), the virtual + "compression association" has no life outside the ESP or AH SA that + contains it. Compression associations disappear when the + corresponding ESP or AH SA goes away. It is not explicitly mentioned + in any DELETE payload. + + Negotiation of IP compression is separate from the negotiation of + cryptographic parameters associated with a CHILD_SA. A node + requesting a CHILD_SA MAY advertise its support for one or more + compression algorithms through one or more Notify payloads of type + IPCOMP_SUPPORTED. The response MAY indicate acceptance of a single + compression algorithm with a Notify payload of type IPCOMP_SUPPORTED. + These payloads MUST NOT occur in messages that do not contain SA + payloads. + + Although there has been discussion of allowing multiple compression + algorithms to be accepted and to have different compression + algorithms available for the two directions of a CHILD_SA, + implementations of this specification MUST NOT accept an IPComp + algorithm that was not proposed, MUST NOT accept more than one, and + MUST NOT compress using an algorithm other than one proposed and + accepted in the setup of the CHILD_SA. + + A side effect of separating the negotiation of IPComp from + cryptographic parameters is that it is not possible to propose + multiple cryptographic suites and propose IP compression with some of + them but not others. + + + + + + +Kaufman Standards Track [Page 37] + +RFC 4306 IKEv2 December 2005 + + +2.23. NAT Traversal + + Network Address Translation (NAT) gateways are a controversial + subject. This section briefly describes what they are and how they + are likely to act on IKE traffic. Many people believe that NATs are + evil and that we should not design our protocols so as to make them + work better. IKEv2 does specify some unintuitive processing rules in + order that NATs are more likely to work. + + NATs exist primarily because of the shortage of IPv4 addresses, + though there are other rationales. IP nodes that are "behind" a NAT + have IP addresses that are not globally unique, but rather are + assigned from some space that is unique within the network behind the + NAT but that are likely to be reused by nodes behind other NATs. + Generally, nodes behind NATs can communicate with other nodes behind + the same NAT and with nodes with globally unique addresses, but not + with nodes behind other NATs. There are exceptions to that rule. + When those nodes make connections to nodes on the real Internet, the + NAT gateway "translates" the IP source address to an address that + will be routed back to the gateway. Messages to the gateway from the + Internet have their destination addresses "translated" to the + internal address that will route the packet to the correct endnode. + + NATs are designed to be "transparent" to endnodes. Neither software + on the node behind the NAT nor the node on the Internet requires + modification to communicate through the NAT. Achieving this + transparency is more difficult with some protocols than with others. + Protocols that include IP addresses of the endpoints within the + payloads of the packet will fail unless the NAT gateway understands + the protocol and modifies the internal references as well as those in + the headers. Such knowledge is inherently unreliable, is a network + layer violation, and often results in subtle problems. + + Opening an IPsec connection through a NAT introduces special + problems. If the connection runs in transport mode, changing the IP + addresses on packets will cause the checksums to fail and the NAT + cannot correct the checksums because they are cryptographically + protected. Even in tunnel mode, there are routing problems because + transparently translating the addresses of AH and ESP packets + requires special logic in the NAT and that logic is heuristic and + unreliable in nature. For that reason, IKEv2 can negotiate UDP + encapsulation of IKE and ESP packets. This encoding is slightly less + efficient but is easier for NATs to process. In addition, firewalls + may be configured to pass IPsec traffic over UDP but not ESP/AH or + vice versa. + + + + + + +Kaufman Standards Track [Page 38] + +RFC 4306 IKEv2 December 2005 + + + It is a common practice of NATs to translate TCP and UDP port numbers + as well as addresses and use the port numbers of inbound packets to + decide which internal node should get a given packet. For this + reason, even though IKE packets MUST be sent from and to UDP port + 500, they MUST be accepted coming from any port and responses MUST be + sent to the port from whence they came. This is because the ports + may be modified as the packets pass through NATs. Similarly, IP + addresses of the IKE endpoints are generally not included in the IKE + payloads because the payloads are cryptographically protected and + could not be transparently modified by NATs. + + Port 4500 is reserved for UDP-encapsulated ESP and IKE. When working + through a NAT, it is generally better to pass IKE packets over port + 4500 because some older NATs handle IKE traffic on port 500 cleverly + in an attempt to transparently establish IPsec connections between + endpoints that don't handle NAT traversal themselves. Such NATs may + interfere with the straightforward NAT traversal envisioned by this + document, so an IPsec endpoint that discovers a NAT between it and + its correspondent MUST send all subsequent traffic to and from port + 4500, which NATs should not treat specially (as they might with port + 500). + + The specific requirements for supporting NAT traversal [RFC3715] are + listed below. Support for NAT traversal is optional. In this + section only, requirements listed as MUST apply only to + implementations supporting NAT traversal. + + IKE MUST listen on port 4500 as well as port 500. IKE MUST + respond to the IP address and port from which packets arrived. + + Both IKE initiator and responder MUST include in their IKE_SA_INIT + packets Notify payloads of type NAT_DETECTION_SOURCE_IP and + NAT_DETECTION_DESTINATION_IP. Those payloads can be used to + detect if there is NAT between the hosts, and which end is behind + the NAT. The location of the payloads in the IKE_SA_INIT packets + are just after the Ni and Nr payloads (before the optional CERTREQ + payload). + + If none of the NAT_DETECTION_SOURCE_IP payload(s) received matches + the hash of the source IP and port found from the IP header of the + packet containing the payload, it means that the other end is + behind NAT (i.e., someone along the route changed the source + address of the original packet to match the address of the NAT + box). In this case, this end should allow dynamic update of the + other ends IP address, as described later. + + + + + + +Kaufman Standards Track [Page 39] + +RFC 4306 IKEv2 December 2005 + + + If the NAT_DETECTION_DESTINATION_IP payload received does not + match the hash of the destination IP and port found from the IP + header of the packet containing the payload, it means that this + end is behind a NAT. In this case, this end SHOULD start sending + keepalive packets as explained in [Hutt05]. + + The IKE initiator MUST check these payloads if present and if they + do not match the addresses in the outer packet MUST tunnel all + future IKE and ESP packets associated with this IKE_SA over UDP + port 4500. + + To tunnel IKE packets over UDP port 4500, the IKE header has four + octets of zero prepended and the result immediately follows the + UDP header. To tunnel ESP packets over UDP port 4500, the ESP + header immediately follows the UDP header. Since the first four + bytes of the ESP header contain the SPI, and the SPI cannot + validly be zero, it is always possible to distinguish ESP and IKE + messages. + + The original source and destination IP address required for the + transport mode TCP and UDP packet checksum fixup (see [Hutt05]) + are obtained from the Traffic Selectors associated with the + exchange. In the case of NAT traversal, the Traffic Selectors + MUST contain exactly one IP address, which is then used as the + original IP address. + + There are cases where a NAT box decides to remove mappings that + are still alive (for example, the keepalive interval is too long, + or the NAT box is rebooted). To recover in these cases, hosts + that are not behind a NAT SHOULD send all packets (including + retransmission packets) to the IP address and port from the last + valid authenticated packet from the other end (i.e., dynamically + update the address). A host behind a NAT SHOULD NOT do this + because it opens a DoS attack possibility. Any authenticated IKE + packet or any authenticated UDP-encapsulated ESP packet can be + used to detect that the IP address or the port has changed. + + Note that similar but probably not identical actions will likely + be needed to make IKE work with Mobile IP, but such processing is + not addressed by this document. + +2.24. Explicit Congestion Notification (ECN) + + When IPsec tunnels behave as originally specified in [RFC2401], ECN + usage is not appropriate for the outer IP headers because tunnel + decapsulation processing discards ECN congestion indications to the + detriment of the network. ECN support for IPsec tunnels for IKEv1- + based IPsec requires multiple operating modes and negotiation (see + + + +Kaufman Standards Track [Page 40] + +RFC 4306 IKEv2 December 2005 + + + [RFC3168]). IKEv2 simplifies this situation by requiring that ECN be + usable in the outer IP headers of all tunnel-mode IPsec SAs created + by IKEv2. Specifically, tunnel encapsulators and decapsulators for + all tunnel-mode SAs created by IKEv2 MUST support the ECN full- + functionality option for tunnels specified in [RFC3168] and MUST + implement the tunnel encapsulation and decapsulation processing + specified in [RFC4301] to prevent discarding of ECN congestion + indications. + +3. Header and Payload Formats + +3.1. The IKE Header + + IKE messages use UDP ports 500 and/or 4500, with one IKE message per + UDP datagram. Information from the beginning of the packet through + the UDP header is largely ignored except that the IP addresses and + UDP ports from the headers are reversed and used for return packets. + When sent on UDP port 500, IKE messages begin immediately following + the UDP header. When sent on UDP port 4500, IKE messages have + prepended four octets of zero. These four octets of zero are not + part of the IKE message and are not included in any of the length + fields or checksums defined by IKE. Each IKE message begins with the + IKE header, denoted HDR in this memo. Following the header are one + or more IKE payloads each identified by a "Next Payload" field in the + preceding payload. Payloads are processed in the order in which they + appear in an IKE message by invoking the appropriate processing + routine according to the "Next Payload" field in the IKE header and + subsequently according to the "Next Payload" field in the IKE payload + itself until a "Next Payload" field of zero indicates that no + payloads follow. If a payload of type "Encrypted" is found, that + payload is decrypted and its contents parsed as additional payloads. + An Encrypted payload MUST be the last payload in a packet and an + Encrypted payload MUST NOT contain another Encrypted payload. + + The Recipient SPI in the header identifies an instance of an IKE + security association. It is therefore possible for a single instance + of IKE to multiplex distinct sessions with multiple peers. + + All multi-octet fields representing integers are laid out in big + endian order (aka most significant byte first, or network byte + order). + + The format of the IKE header is shown in Figure 4. + + + + + + + + +Kaufman Standards Track [Page 41] + +RFC 4306 IKEv2 December 2005 + + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! IKE_SA Initiator's SPI ! + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! IKE_SA Responder's SPI ! + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload ! MjVer ! MnVer ! Exchange Type ! Flags ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Message ID ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 4: IKE Header Format + + o Initiator's SPI (8 octets) - A value chosen by the + initiator to identify a unique IKE security association. This + value MUST NOT be zero. + + o Responder's SPI (8 octets) - A value chosen by the + responder to identify a unique IKE security association. This + value MUST be zero in the first message of an IKE Initial + Exchange (including repeats of that message including a + cookie) and MUST NOT be zero in any other message. + + o Next Payload (1 octet) - Indicates the type of payload that + immediately follows the header. The format and value of each + payload are defined below. + + o Major Version (4 bits) - Indicates the major version of the IKE + protocol in use. Implementations based on this version of IKE + MUST set the Major Version to 2. Implementations based on + previous versions of IKE and ISAKMP MUST set the Major Version + to 1. Implementations based on this version of IKE MUST reject + or ignore messages containing a version number greater than + 2. + + o Minor Version (4 bits) - Indicates the minor version of the + IKE protocol in use. Implementations based on this version of + IKE MUST set the Minor Version to 0. They MUST ignore the + minor version number of received messages. + + o Exchange Type (1 octet) - Indicates the type of exchange being + used. This constrains the payloads sent in each message and + orderings of messages in an exchange. + + + +Kaufman Standards Track [Page 42] + +RFC 4306 IKEv2 December 2005 + + + Exchange Type Value + + RESERVED 0-33 + IKE_SA_INIT 34 + IKE_AUTH 35 + CREATE_CHILD_SA 36 + INFORMATIONAL 37 + RESERVED TO IANA 38-239 + Reserved for private use 240-255 + + o Flags (1 octet) - Indicates specific options that are set + for the message. Presence of options are indicated by the + appropriate bit in the flags field being set. The bits are + defined LSB first, so bit 0 would be the least significant + bit of the Flags octet. In the description below, a bit + being 'set' means its value is '1', while 'cleared' means + its value is '0'. + + -- X(reserved) (bits 0-2) - These bits MUST be cleared + when sending and MUST be ignored on receipt. + + -- I(nitiator) (bit 3 of Flags) - This bit MUST be set in + messages sent by the original initiator of the IKE_SA + and MUST be cleared in messages sent by the original + responder. It is used by the recipient to determine + which eight octets of the SPI were generated by the + recipient. + + -- V(ersion) (bit 4 of Flags) - This bit indicates that + the transmitter is capable of speaking a higher major + version number of the protocol than the one indicated + in the major version number field. Implementations of + IKEv2 must clear this bit when sending and MUST ignore + it in incoming messages. + + -- R(esponse) (bit 5 of Flags) - This bit indicates that + this message is a response to a message containing + the same message ID. This bit MUST be cleared in all + request messages and MUST be set in all responses. + An IKE endpoint MUST NOT generate a response to a + message that is marked as being a response. + + -- X(reserved) (bits 6-7 of Flags) - These bits MUST be + cleared when sending and MUST be ignored on receipt. + + + + + + + +Kaufman Standards Track [Page 43] + +RFC 4306 IKEv2 December 2005 + + + o Message ID (4 octets) - Message identifier used to control + retransmission of lost packets and matching of requests and + responses. It is essential to the security of the protocol + because it is used to prevent message replay attacks. + See sections 2.1 and 2.2. + + o Length (4 octets) - Length of total message (header + payloads) + in octets. + +3.2. Generic Payload Header + + Each IKE payload defined in sections 3.3 through 3.16 begins with a + generic payload header, shown in Figure 5. Figures for each payload + below will include the generic payload header, but for brevity the + description of each field will be omitted. + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 5: Generic Payload Header + + The Generic Payload Header fields are defined as follows: + + o Next Payload (1 octet) - Identifier for the payload type of the + next payload in the message. If the current payload is the last + in the message, then this field will be 0. This field provides a + "chaining" capability whereby additional payloads can be added to + a message by appending it to the end of the message and setting + the "Next Payload" field of the preceding payload to indicate the + new payload's type. An Encrypted payload, which must always be + the last payload of a message, is an exception. It contains data + structures in the format of additional payloads. In the header of + an Encrypted payload, the Next Payload field is set to the payload + type of the first contained payload (instead of 0). + + Payload Type Values + + Next Payload Type Notation Value + + No Next Payload 0 + + RESERVED 1-32 + Security Association SA 33 + Key Exchange KE 34 + Identification - Initiator IDi 35 + + + +Kaufman Standards Track [Page 44] + +RFC 4306 IKEv2 December 2005 + + + Identification - Responder IDr 36 + Certificate CERT 37 + Certificate Request CERTREQ 38 + Authentication AUTH 39 + Nonce Ni, Nr 40 + Notify N 41 + Delete D 42 + Vendor ID V 43 + Traffic Selector - Initiator TSi 44 + Traffic Selector - Responder TSr 45 + Encrypted E 46 + Configuration CP 47 + Extensible Authentication EAP 48 + RESERVED TO IANA 49-127 + PRIVATE USE 128-255 + + Payload type values 1-32 should not be used so that there is no + overlap with the code assignments for IKEv1. Payload type values + 49-127 are reserved to IANA for future assignment in IKEv2 (see + section 6). Payload type values 128-255 are for private use among + mutually consenting parties. + + o Critical (1 bit) - MUST be set to zero if the sender wants the + recipient to skip this payload if it does not understand the + payload type code in the Next Payload field of the previous + payload. MUST be set to one if the sender wants the recipient to + reject this entire message if it does not understand the payload + type. MUST be ignored by the recipient if the recipient + understands the payload type code. MUST be set to zero for + payload types defined in this document. Note that the critical + bit applies to the current payload rather than the "next" payload + whose type code appears in the first octet. The reasoning behind + not setting the critical bit for payloads defined in this document + is that all implementations MUST understand all payload types + defined in this document and therefore must ignore the Critical + bit's value. Skipped payloads are expected to have valid Next + Payload and Payload Length fields. + + o RESERVED (7 bits) - MUST be sent as zero; MUST be ignored on + receipt. + + o Payload Length (2 octets) - Length in octets of the current + payload, including the generic payload header. + + + + + + + + +Kaufman Standards Track [Page 45] + +RFC 4306 IKEv2 December 2005 + + +3.3. Security Association Payload + + The Security Association Payload, denoted SA in this memo, is used to + negotiate attributes of a security association. Assembly of Security + Association Payloads requires great peace of mind. An SA payload MAY + contain multiple proposals. If there is more than one, they MUST be + ordered from most preferred to least preferred. Each proposal may + contain multiple IPsec protocols (where a protocol is IKE, ESP, or + AH), each protocol MAY contain multiple transforms, and each + transform MAY contain multiple attributes. When parsing an SA, an + implementation MUST check that the total Payload Length is consistent + with the payload's internal lengths and counts. Proposals, + Transforms, and Attributes each have their own variable length + encodings. They are nested such that the Payload Length of an SA + includes the combined contents of the SA, Proposal, Transform, and + Attribute information. The length of a Proposal includes the lengths + of all Transforms and Attributes it contains. The length of a + Transform includes the lengths of all Attributes it contains. + + The syntax of Security Associations, Proposals, Transforms, and + Attributes is based on ISAKMP; however, the semantics are somewhat + different. The reason for the complexity and the hierarchy is to + allow for multiple possible combinations of algorithms to be encoded + in a single SA. Sometimes there is a choice of multiple algorithms, + whereas other times there is a combination of algorithms. For + example, an initiator might want to propose using (AH w/MD5 and ESP + w/3DES) OR (ESP w/MD5 and 3DES). + + One of the reasons the semantics of the SA payload has changed from + ISAKMP and IKEv1 is to make the encodings more compact in common + cases. + + The Proposal structure contains within it a Proposal # and an IPsec + protocol ID. Each structure MUST have the same Proposal # as the + previous one or be one (1) greater. The first Proposal MUST have a + Proposal # of one (1). If two successive structures have the same + Proposal number, it means that the proposal consists of the first + structure AND the second. So a proposal of AH AND ESP would have two + proposal structures, one for AH and one for ESP and both would have + Proposal #1. A proposal of AH OR ESP would have two proposal + structures, one for AH with Proposal #1 and one for ESP with Proposal + #2. + + Each Proposal/Protocol structure is followed by one or more transform + structures. The number of different transforms is generally + determined by the Protocol. AH generally has a single transform: an + integrity check algorithm. ESP generally has two: an encryption + algorithm and an integrity check algorithm. IKE generally has four + + + +Kaufman Standards Track [Page 46] + +RFC 4306 IKEv2 December 2005 + + + transforms: a Diffie-Hellman group, an integrity check algorithm, a + prf algorithm, and an encryption algorithm. If an algorithm that + combines encryption and integrity protection is proposed, it MUST be + proposed as an encryption algorithm and an integrity protection + algorithm MUST NOT be proposed. For each Protocol, the set of + permissible transforms is assigned transform ID numbers, which appear + in the header of each transform. + + If there are multiple transforms with the same Transform Type, the + proposal is an OR of those transforms. If there are multiple + Transforms with different Transform Types, the proposal is an AND of + the different groups. For example, to propose ESP with (3DES or + IDEA) and (HMAC_MD5 or HMAC_SHA), the ESP proposal would contain two + Transform Type 1 candidates (one for 3DES and one for IDEA) and two + Transform Type 2 candidates (one for HMAC_MD5 and one for HMAC_SHA). + This effectively proposes four combinations of algorithms. If the + initiator wanted to propose only a subset of those, for example (3DES + and HMAC_MD5) or (IDEA and HMAC_SHA), there is no way to encode that + as multiple transforms within a single Proposal. Instead, the + initiator would have to construct two different Proposals, each with + two transforms. + + A given transform MAY have one or more Attributes. Attributes are + necessary when the transform can be used in more than one way, as + when an encryption algorithm has a variable key size. The transform + would specify the algorithm and the attribute would specify the key + size. Most transforms do not have attributes. A transform MUST NOT + have multiple attributes of the same type. To propose alternate + values for an attribute (for example, multiple key sizes for the AES + encryption algorithm), and implementation MUST include multiple + Transforms with the same Transform Type each with a single Attribute. + + Note that the semantics of Transforms and Attributes are quite + different from those in IKEv1. In IKEv1, a single Transform carried + multiple algorithms for a protocol with one carried in the Transform + and the others carried in the Attributes. + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ <Proposals> ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 6: Security Association Payload + + + +Kaufman Standards Track [Page 47] + +RFC 4306 IKEv2 December 2005 + + + o Proposals (variable) - One or more proposal substructures. + + The payload type for the Security Association Payload is thirty + three (33). + +3.3.1. Proposal Substructure + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! 0 (last) or 2 ! RESERVED ! Proposal Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Proposal # ! Protocol ID ! SPI Size !# of Transforms! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ~ SPI (variable) ~ + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ <Transforms> ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 7: Proposal Substructure + + o 0 (last) or 2 (more) (1 octet) - Specifies whether this is the + last Proposal Substructure in the SA. This syntax is inherited + from ISAKMP, but is unnecessary because the last Proposal could + be identified from the length of the SA. The value (2) + corresponds to a Payload Type of Proposal in IKEv1, and the + first 4 octets of the Proposal structure are designed to look + somewhat like the header of a Payload. + + o RESERVED (1 octet) - MUST be sent as zero; MUST be ignored on + receipt. + + o Proposal Length (2 octets) - Length of this proposal, including + all transforms and attributes that follow. + + o Proposal # (1 octet) - When a proposal is made, the first + proposal in an SA payload MUST be #1, and subsequent proposals + MUST either be the same as the previous proposal (indicating an + AND of the two proposals) or one more than the previous + proposal (indicating an OR of the two proposals). When a + proposal is accepted, all of the proposal numbers in the SA + payload MUST be the same and MUST match the number on the + proposal sent that was accepted. + + + + + + +Kaufman Standards Track [Page 48] + +RFC 4306 IKEv2 December 2005 + + + o Protocol ID (1 octet) - Specifies the IPsec protocol identifier + for the current negotiation. The defined values are: + + Protocol Protocol ID + RESERVED 0 + IKE 1 + AH 2 + ESP 3 + RESERVED TO IANA 4-200 + PRIVATE USE 201-255 + + o SPI Size (1 octet) - For an initial IKE_SA negotiation, this + field MUST be zero; the SPI is obtained from the outer header. + During subsequent negotiations, it is equal to the size, in + octets, of the SPI of the corresponding protocol (8 for IKE, 4 + for ESP and AH). + + o # of Transforms (1 octet) - Specifies the number of transforms + in this proposal. + + o SPI (variable) - The sending entity's SPI. Even if the SPI Size + is not a multiple of 4 octets, there is no padding applied to + the payload. When the SPI Size field is zero, this field is + not present in the Security Association payload. + + o Transforms (variable) - One or more transform substructures. + +3.3.2. Transform Substructure + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! 0 (last) or 3 ! RESERVED ! Transform Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + !Transform Type ! RESERVED ! Transform ID ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ Transform Attributes ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 8: Transform Substructure + + o 0 (last) or 3 (more) (1 octet) - Specifies whether this is the + last Transform Substructure in the Proposal. This syntax is + inherited from ISAKMP, but is unnecessary because the last + Proposal could be identified from the length of the SA. The + + + + +Kaufman Standards Track [Page 49] + +RFC 4306 IKEv2 December 2005 + + + value (3) corresponds to a Payload Type of Transform in IKEv1, + and the first 4 octets of the Transform structure are designed + to look somewhat like the header of a Payload. + + o RESERVED - MUST be sent as zero; MUST be ignored on receipt. + + o Transform Length - The length (in octets) of the Transform + Substructure including Header and Attributes. + + o Transform Type (1 octet) - The type of transform being + specified in this transform. Different protocols support + different transform types. For some protocols, some of the + transforms may be optional. If a transform is optional and the + initiator wishes to propose that the transform be omitted, no + transform of the given type is included in the proposal. If + the initiator wishes to make use of the transform optional to + the responder, it includes a transform substructure with + transform ID = 0 as one of the options. + + o Transform ID (2 octets) - The specific instance of the + transform type being proposed. + + Transform Type Values + + Transform Used In + Type + RESERVED 0 + Encryption Algorithm (ENCR) 1 (IKE and ESP) + Pseudo-random Function (PRF) 2 (IKE) + Integrity Algorithm (INTEG) 3 (IKE, AH, optional in ESP) + Diffie-Hellman Group (D-H) 4 (IKE, optional in AH & ESP) + Extended Sequence Numbers (ESN) 5 (AH and ESP) + RESERVED TO IANA 6-240 + PRIVATE USE 241-255 + + For Transform Type 1 (Encryption Algorithm), defined Transform IDs + are: + + Name Number Defined In + RESERVED 0 + ENCR_DES_IV64 1 (RFC1827) + ENCR_DES 2 (RFC2405), [DES] + ENCR_3DES 3 (RFC2451) + ENCR_RC5 4 (RFC2451) + ENCR_IDEA 5 (RFC2451), [IDEA] + ENCR_CAST 6 (RFC2451) + ENCR_BLOWFISH 7 (RFC2451) + ENCR_3IDEA 8 (RFC2451) + + + +Kaufman Standards Track [Page 50] + +RFC 4306 IKEv2 December 2005 + + + ENCR_DES_IV32 9 + RESERVED 10 + ENCR_NULL 11 (RFC2410) + ENCR_AES_CBC 12 (RFC3602) + ENCR_AES_CTR 13 (RFC3664) + + values 14-1023 are reserved to IANA. Values 1024-65535 are + for private use among mutually consenting parties. + + For Transform Type 2 (Pseudo-random Function), defined Transform IDs + are: + + Name Number Defined In + RESERVED 0 + PRF_HMAC_MD5 1 (RFC2104), [MD5] + PRF_HMAC_SHA1 2 (RFC2104), [SHA] + PRF_HMAC_TIGER 3 (RFC2104) + PRF_AES128_XCBC 4 (RFC3664) + + values 5-1023 are reserved to IANA. Values 1024-65535 are for + private use among mutually consenting parties. + + For Transform Type 3 (Integrity Algorithm), defined Transform IDs + are: + + Name Number Defined In + NONE 0 + AUTH_HMAC_MD5_96 1 (RFC2403) + AUTH_HMAC_SHA1_96 2 (RFC2404) + AUTH_DES_MAC 3 + AUTH_KPDK_MD5 4 (RFC1826) + AUTH_AES_XCBC_96 5 (RFC3566) + + values 6-1023 are reserved to IANA. Values 1024-65535 are for + private use among mutually consenting parties. + + For Transform Type 4 (Diffie-Hellman Group), defined Transform IDs + are: + + Name Number + NONE 0 + Defined in Appendix B 1 - 2 + RESERVED 3 - 4 + Defined in [ADDGROUP] 5 + RESERVED TO IANA 6 - 13 + Defined in [ADDGROUP] 14 - 18 + RESERVED TO IANA 19 - 1023 + PRIVATE USE 1024-65535 + + + +Kaufman Standards Track [Page 51] + +RFC 4306 IKEv2 December 2005 + + + For Transform Type 5 (Extended Sequence Numbers), defined Transform + IDs are: + + Name Number + No Extended Sequence Numbers 0 + Extended Sequence Numbers 1 + RESERVED 2 - 65535 + +3.3.3. Valid Transform Types by Protocol + + The number and type of transforms that accompany an SA payload are + dependent on the protocol in the SA itself. An SA payload proposing + the establishment of an SA has the following mandatory and optional + transform types. A compliant implementation MUST understand all + mandatory and optional types for each protocol it supports (though it + need not accept proposals with unacceptable suites). A proposal MAY + omit the optional types if the only value for them it will accept is + NONE. + + Protocol Mandatory Types Optional Types + IKE ENCR, PRF, INTEG, D-H + ESP ENCR, ESN INTEG, D-H + AH INTEG, ESN D-H + +3.3.4. Mandatory Transform IDs + + The specification of suites that MUST and SHOULD be supported for + interoperability has been removed from this document because they are + likely to change more rapidly than this document evolves. + + An important lesson learned from IKEv1 is that no system should only + implement the mandatory algorithms and expect them to be the best + choice for all customers. For example, at the time that this + document was written, many IKEv1 implementers were starting to + migrate to AES in Cipher Block Chaining (CBC) mode for Virtual + Private Network (VPN) applications. Many IPsec systems based on + IKEv2 will implement AES, additional Diffie-Hellman groups, and + additional hash algorithms, and some IPsec customers already require + these algorithms in addition to the ones listed above. + + It is likely that IANA will add additional transforms in the future, + and some users may want to use private suites, especially for IKE + where implementations should be capable of supporting different + parameters, up to certain size limits. In support of this goal, all + implementations of IKEv2 SHOULD include a management facility that + allows specification (by a user or system administrator) of Diffie- + Hellman (DH) parameters (the generator, modulus, and exponent lengths + and values) for new DH groups. Implementations SHOULD provide a + + + +Kaufman Standards Track [Page 52] + +RFC 4306 IKEv2 December 2005 + + + management interface via which these parameters and the associated + transform IDs may be entered (by a user or system administrator), to + enable negotiating such groups. + + All implementations of IKEv2 MUST include a management facility that + enables a user or system administrator to specify the suites that are + acceptable for use with IKE. Upon receipt of a payload with a set of + transform IDs, the implementation MUST compare the transmitted + transform IDs against those locally configured via the management + controls, to verify that the proposed suite is acceptable based on + local policy. The implementation MUST reject SA proposals that are + not authorized by these IKE suite controls. Note that cryptographic + suites that MUST be implemented need not be configured as acceptable + to local policy. + +3.3.5. Transform Attributes + + Each transform in a Security Association payload may include + attributes that modify or complete the specification of the + transform. These attributes are type/value pairs and are defined + below. For example, if an encryption algorithm has a variable-length + key, the key length to be used may be specified as an attribute. + Attributes can have a value with a fixed two octet length or a + variable-length value. For the latter, the attribute is encoded as + type/length/value. + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + !A! Attribute Type ! AF=0 Attribute Length ! + !F! ! AF=1 Attribute Value ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! AF=0 Attribute Value ! + ! AF=1 Not Transmitted ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 9: Data Attributes + + o Attribute Type (2 octets) - Unique identifier for each type of + attribute (see below). + + The most significant bit of this field is the Attribute Format + bit (AF). It indicates whether the data attributes follow the + Type/Length/Value (TLV) format or a shortened Type/Value (TV) + format. If the AF bit is zero (0), then the Data Attributes + are of the Type/Length/Value (TLV) form. If the AF bit is a + one (1), then the Data Attributes are of the Type/Value form. + + + + +Kaufman Standards Track [Page 53] + +RFC 4306 IKEv2 December 2005 + + + o Attribute Length (2 octets) - Length in octets of the Attribute + Value. When the AF bit is a one (1), the Attribute Value is + only 2 octets and the Attribute Length field is not present. + + o Attribute Value (variable length) - Value of the Attribute + associated with the Attribute Type. If the AF bit is a zero + (0), this field has a variable length defined by the Attribute + Length field. If the AF bit is a one (1), the Attribute Value + has a length of 2 octets. + + Note that only a single attribute type (Key Length) is defined, and + it is fixed length. The variable-length encoding specification is + included only for future extensions. The only algorithms defined in + this document that accept attributes are the AES-based encryption, + integrity, and pseudo-random functions, which require a single + attribute specifying key width. + + Attributes described as basic MUST NOT be encoded using the + variable-length encoding. Variable-length attributes MUST NOT be + encoded as basic even if their value can fit into two octets. NOTE: + This is a change from IKEv1, where increased flexibility may have + simplified the composer of messages but certainly complicated the + parser. + + Attribute Type Value Attribute Format + -------------------------------------------------------------- + RESERVED 0-13 Key Length (in bits) + 14 TV RESERVED 15-17 + RESERVED TO IANA 18-16383 PRIVATE USE + 16384-32767 + + Values 0-13 and 15-17 were used in a similar context in IKEv1 and + should not be assigned except to matching values. Values 18-16383 + are reserved to IANA. Values 16384-32767 are for private use among + mutually consenting parties. + + - Key Length + + When using an Encryption Algorithm that has a variable-length key, + this attribute specifies the key length in bits (MUST use network + byte order). This attribute MUST NOT be used when the specified + Encryption Algorithm uses a fixed-length key. + + + + + + + + + +Kaufman Standards Track [Page 54] + +RFC 4306 IKEv2 December 2005 + + +3.3.6. Attribute Negotiation + + During security association negotiation, initiators present offers to + responders. Responders MUST select a single complete set of + parameters from the offers (or reject all offers if none are + acceptable). If there are multiple proposals, the responder MUST + choose a single proposal number and return all of the Proposal + substructures with that Proposal number. If there are multiple + Transforms with the same type, the responder MUST choose a single + one. Any attributes of a selected transform MUST be returned + unmodified. The initiator of an exchange MUST check that the + accepted offer is consistent with one of its proposals, and if not + that response MUST be rejected. + + Negotiating Diffie-Hellman groups presents some special challenges. + SA offers include proposed attributes and a Diffie-Hellman public + number (KE) in the same message. If in the initial exchange the + initiator offers to use one of several Diffie-Hellman groups, it + SHOULD pick the one the responder is most likely to accept and + include a KE corresponding to that group. If the guess turns out to + be wrong, the responder will indicate the correct group in the + response and the initiator SHOULD pick an element of that group for + its KE value when retrying the first message. It SHOULD, however, + continue to propose its full supported set of groups in order to + prevent a man-in-the-middle downgrade attack. + + Implementation Note: + + Certain negotiable attributes can have ranges or could have + multiple acceptable values. These include the key length of a + variable key length symmetric cipher. To further interoperability + and to support upgrading endpoints independently, implementers of + this protocol SHOULD accept values that they deem to supply + greater security. For instance, if a peer is configured to accept + a variable-length cipher with a key length of X bits and is + offered that cipher with a larger key length, the implementation + SHOULD accept the offer if it supports use of the longer key. + + Support of this capability allows an implementation to express a + concept of "at least" a certain level of security -- "a key length of + _at least_ X bits for cipher Y". + + + + + + + + + + +Kaufman Standards Track [Page 55] + +RFC 4306 IKEv2 December 2005 + + +3.4. Key Exchange Payload + + The Key Exchange Payload, denoted KE in this memo, is used to + exchange Diffie-Hellman public numbers as part of a Diffie-Hellman + key exchange. The Key Exchange Payload consists of the IKE generic + payload header followed by the Diffie-Hellman public value itself. + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! DH Group # ! RESERVED ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ Key Exchange Data ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 10: Key Exchange Payload Format + + A key exchange payload is constructed by copying one's Diffie-Hellman + public value into the "Key Exchange Data" portion of the payload. + The length of the Diffie-Hellman public value MUST be equal to the + length of the prime modulus over which the exponentiation was + performed, prepending zero bits to the value if necessary. + + The DH Group # identifies the Diffie-Hellman group in which the Key + Exchange Data was computed (see section 3.3.2). If the selected + proposal uses a different Diffie-Hellman group, the message MUST be + rejected with a Notify payload of type INVALID_KE_PAYLOAD. + + The payload type for the Key Exchange payload is thirty four (34). + +3.5. Identification Payloads + + The Identification Payloads, denoted IDi and IDr in this memo, allow + peers to assert an identity to one another. This identity may be + used for policy lookup, but does not necessarily have to match + anything in the CERT payload; both fields may be used by an + implementation to perform access control decisions. + + NOTE: In IKEv1, two ID payloads were used in each direction to hold + Traffic Selector (TS) information for data passing over the SA. In + IKEv2, this information is carried in TS payloads (see section 3.13). + + + + + + +Kaufman Standards Track [Page 56] + +RFC 4306 IKEv2 December 2005 + + + The Identification Payload consists of the IKE generic payload header + followed by identification fields as follows: + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ID Type ! RESERVED | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ Identification Data ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 11: Identification Payload Format + + o ID Type (1 octet) - Specifies the type of Identification being + used. + + o RESERVED - MUST be sent as zero; MUST be ignored on receipt. + + o Identification Data (variable length) - Value, as indicated by the + Identification Type. The length of the Identification Data is + computed from the size in the ID payload header. + + The payload types for the Identification Payload are thirty five (35) + for IDi and thirty six (36) for IDr. + + The following table lists the assigned values for the Identification + Type field, followed by a description of the Identification Data + which follows: + + ID Type Value + ------- ----- + RESERVED 0 + + ID_IPV4_ADDR 1 + + A single four (4) octet IPv4 address. + + ID_FQDN 2 + + A fully-qualified domain name string. An example of a + ID_FQDN is, "example.com". The string MUST not contain any + terminators (e.g., NULL, CR, etc.). + + + + + +Kaufman Standards Track [Page 57] + +RFC 4306 IKEv2 December 2005 + + + ID_RFC822_ADDR 3 + + A fully-qualified RFC822 email address string, An example of + a ID_RFC822_ADDR is, "jsmith@example.com". The string MUST + not contain any terminators. + + Reserved to IANA 4 + + ID_IPV6_ADDR 5 + + A single sixteen (16) octet IPv6 address. + + Reserved to IANA 6 - 8 + + ID_DER_ASN1_DN 9 + + The binary Distinguished Encoding Rules (DER) encoding of an + ASN.1 X.500 Distinguished Name [X.501]. + + ID_DER_ASN1_GN 10 + + The binary DER encoding of an ASN.1 X.500 GeneralName + [X.509]. + + ID_KEY_ID 11 + + An opaque octet stream which may be used to pass vendor- + specific information necessary to do certain proprietary + types of identification. + + Reserved to IANA 12-200 + + Reserved for private use 201-255 + + Two implementations will interoperate only if each can generate a + type of ID acceptable to the other. To assure maximum + interoperability, implementations MUST be configurable to send at + least one of ID_IPV4_ADDR, ID_FQDN, ID_RFC822_ADDR, or ID_KEY_ID, and + MUST be configurable to accept all of these types. Implementations + SHOULD be capable of generating and accepting all of these types. + IPv6-capable implementations MUST additionally be configurable to + accept ID_IPV6_ADDR. IPv6-only implementations MAY be configurable + to send only ID_IPV6_ADDR. + + + + + + + + +Kaufman Standards Track [Page 58] + +RFC 4306 IKEv2 December 2005 + + +3.6. Certificate Payload + + The Certificate Payload, denoted CERT in this memo, provides a means + to transport certificates or other authentication-related information + via IKE. Certificate payloads SHOULD be included in an exchange if + certificates are available to the sender unless the peer has + indicated an ability to retrieve this information from elsewhere + using an HTTP_CERT_LOOKUP_SUPPORTED Notify payload. Note that the + term "Certificate Payload" is somewhat misleading, because not all + authentication mechanisms use certificates and data other than + certificates may be passed in this payload. + + The Certificate Payload is defined as follows: + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Cert Encoding ! ! + +-+-+-+-+-+-+-+-+ ! + ~ Certificate Data ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 12: Certificate Payload Format + + o Certificate Encoding (1 octet) - This field indicates the type + of certificate or certificate-related information contained in + the Certificate Data field. + + Certificate Encoding Value + -------------------- ----- + RESERVED 0 + PKCS #7 wrapped X.509 certificate 1 + PGP Certificate 2 + DNS Signed Key 3 + X.509 Certificate - Signature 4 + Kerberos Token 6 + Certificate Revocation List (CRL) 7 + Authority Revocation List (ARL) 8 + SPKI Certificate 9 + X.509 Certificate - Attribute 10 + Raw RSA Key 11 + Hash and URL of X.509 certificate 12 + Hash and URL of X.509 bundle 13 + RESERVED to IANA 14 - 200 + PRIVATE USE 201 - 255 + + + +Kaufman Standards Track [Page 59] + +RFC 4306 IKEv2 December 2005 + + + o Certificate Data (variable length) - Actual encoding of + certificate data. The type of certificate is indicated by the + Certificate Encoding field. + + The payload type for the Certificate Payload is thirty seven (37). + + Specific syntax is for some of the certificate type codes above is + not defined in this document. The types whose syntax is defined in + this document are: + + X.509 Certificate - Signature (4) contains a DER encoded X.509 + certificate whose public key is used to validate the sender's AUTH + payload. + + Certificate Revocation List (7) contains a DER encoded X.509 + certificate revocation list. + + Raw RSA Key (11) contains a PKCS #1 encoded RSA key (see [RSA] and + [PKCS1]). + + Hash and URL encodings (12-13) allow IKE messages to remain short + by replacing long data structures with a 20 octet SHA-1 hash (see + [SHA]) of the replaced value followed by a variable-length URL + that resolves to the DER encoded data structure itself. This + improves efficiency when the endpoints have certificate data + cached and makes IKE less subject to denial of service attacks + that become easier to mount when IKE messages are large enough to + require IP fragmentation [KPS03]. + + Use the following ASN.1 definition for an X.509 bundle: + + CertBundle + { iso(1) identified-organization(3) dod(6) internet(1) + security(5) mechanisms(5) pkix(7) id-mod(0) + id-mod-cert-bundle(34) } + + DEFINITIONS EXPLICIT TAGS ::= + BEGIN + + IMPORTS + Certificate, CertificateList + FROM PKIX1Explicit88 + { iso(1) identified-organization(3) dod(6) + internet(1) security(5) mechanisms(5) pkix(7) + id-mod(0) id-pkix1-explicit(18) } ; + + + + + + +Kaufman Standards Track [Page 60] + +RFC 4306 IKEv2 December 2005 + + + CertificateOrCRL ::= CHOICE { + cert [0] Certificate, + crl [1] CertificateList } + + CertificateBundle ::= SEQUENCE OF CertificateOrCRL + + END + + Implementations MUST be capable of being configured to send and + accept up to four X.509 certificates in support of authentication, + and also MUST be capable of being configured to send and accept the + first two Hash and URL formats (with HTTP URLs). Implementations + SHOULD be capable of being configured to send and accept Raw RSA + keys. If multiple certificates are sent, the first certificate MUST + contain the public key used to sign the AUTH payload. The other + certificates may be sent in any order. + +3.7. Certificate Request Payload + + The Certificate Request Payload, denoted CERTREQ in this memo, + provides a means to request preferred certificates via IKE and can + appear in the IKE_INIT_SA response and/or the IKE_AUTH request. + Certificate Request payloads MAY be included in an exchange when the + sender needs to get the certificate of the receiver. If multiple CAs + are trusted and the cert encoding does not allow a list, then + multiple Certificate Request payloads SHOULD be transmitted. + + The Certificate Request Payload is defined as follows: + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Cert Encoding ! ! + +-+-+-+-+-+-+-+-+ ! + ~ Certification Authority ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 13: Certificate Request Payload Format + + o Certificate Encoding (1 octet) - Contains an encoding of the type + or format of certificate requested. Values are listed in section + 3.6. + + + + + + +Kaufman Standards Track [Page 61] + +RFC 4306 IKEv2 December 2005 + + + o Certification Authority (variable length) - Contains an encoding + of an acceptable certification authority for the type of + certificate requested. + + The payload type for the Certificate Request Payload is thirty eight + (38). + + The Certificate Encoding field has the same values as those defined + in section 3.6. The Certification Authority field contains an + indicator of trusted authorities for this certificate type. The + Certification Authority value is a concatenated list of SHA-1 hashes + of the public keys of trusted Certification Authorities (CAs). Each + is encoded as the SHA-1 hash of the Subject Public Key Info element + (see section 4.1.2.7 of [RFC3280]) from each Trust Anchor + certificate. The twenty-octet hashes are concatenated and included + with no other formatting. + + Note that the term "Certificate Request" is somewhat misleading, in + that values other than certificates are defined in a "Certificate" + payload and requests for those values can be present in a Certificate + Request Payload. The syntax of the Certificate Request payload in + such cases is not defined in this document. + + The Certificate Request Payload is processed by inspecting the "Cert + Encoding" field to determine whether the processor has any + certificates of this type. If so, the "Certification Authority" + field is inspected to determine if the processor has any certificates + that can be validated up to one of the specified certification + authorities. This can be a chain of certificates. + + If an end-entity certificate exists that satisfies the criteria + specified in the CERTREQ, a certificate or certificate chain SHOULD + be sent back to the certificate requestor if the recipient of the + CERTREQ: + + - is configured to use certificate authentication, + + - is allowed to send a CERT payload, + + - has matching CA trust policy governing the current negotiation, and + + - has at least one time-wise and usage appropriate end-entity + certificate chaining to a CA provided in the CERTREQ. + + Certificate revocation checking must be considered during the + chaining process used to select a certificate. Note that even if two + peers are configured to use two different CAs, cross-certification + relationships should be supported by appropriate selection logic. + + + +Kaufman Standards Track [Page 62] + +RFC 4306 IKEv2 December 2005 + + + The intent is not to prevent communication through the strict + adherence of selection of a certificate based on CERTREQ, when an + alternate certificate could be selected by the sender that would + still enable the recipient to successfully validate and trust it + through trust conveyed by cross-certification, CRLs, or other out- + of-band configured means. Thus, the processing of a CERTREQ should + be seen as a suggestion for a certificate to select, not a mandated + one. If no certificates exist, then the CERTREQ is ignored. This is + not an error condition of the protocol. There may be cases where + there is a preferred CA sent in the CERTREQ, but an alternate might + be acceptable (perhaps after prompting a human operator). + +3.8. Authentication Payload + + The Authentication Payload, denoted AUTH in this memo, contains data + used for authentication purposes. The syntax of the Authentication + data varies according to the Auth Method as specified below. + + The Authentication Payload is defined as follows: + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Auth Method ! RESERVED ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ Authentication Data ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 14: Authentication Payload Format + + o Auth Method (1 octet) - Specifies the method of authentication + used. Values defined are: + + RSA Digital Signature (1) - Computed as specified in section + 2.15 using an RSA private key over a PKCS#1 padded hash (see + [RSA] and [PKCS1]). + + Shared Key Message Integrity Code (2) - Computed as specified in + section 2.15 using the shared key associated with the identity + in the ID payload and the negotiated prf function + + DSS Digital Signature (3) - Computed as specified in section + 2.15 using a DSS private key (see [DSS]) over a SHA-1 hash. + + + + +Kaufman Standards Track [Page 63] + +RFC 4306 IKEv2 December 2005 + + + The values 0 and 4-200 are reserved to IANA. The values 201-255 + are available for private use. + + o Authentication Data (variable length) - see section 2.15. + + The payload type for the Authentication Payload is thirty nine (39). + +3.9. Nonce Payload + + The Nonce Payload, denoted Ni and Nr in this memo for the initiator's + and responder's nonce respectively, contains random data used to + guarantee liveness during an exchange and protect against replay + attacks. + + The Nonce Payload is defined as follows: + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ Nonce Data ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 15: Nonce Payload Format + + o Nonce Data (variable length) - Contains the random data generated + by the transmitting entity. + + The payload type for the Nonce Payload is forty (40). + + The size of a Nonce MUST be between 16 and 256 octets inclusive. + Nonce values MUST NOT be reused. + +3.10. Notify Payload + + The Notify Payload, denoted N in this document, is used to transmit + informational data, such as error conditions and state transitions, + to an IKE peer. A Notify Payload may appear in a response message + (usually specifying why a request was rejected), in an INFORMATIONAL + Exchange (to report an error not in an IKE request), or in any other + message to indicate sender capabilities or to modify the meaning of + the request. + + + + + + +Kaufman Standards Track [Page 64] + +RFC 4306 IKEv2 December 2005 + + + The Notify Payload is defined as follows: + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Protocol ID ! SPI Size ! Notify Message Type ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ Security Parameter Index (SPI) ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ Notification Data ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 16: Notify Payload Format + + o Protocol ID (1 octet) - If this notification concerns an existing + SA, this field indicates the type of that SA. For IKE_SA + notifications, this field MUST be one (1). For notifications + concerning IPsec SAs this field MUST contain either (2) to + indicate AH or (3) to indicate ESP. For notifications that do not + relate to an existing SA, this field MUST be sent as zero and MUST + be ignored on receipt. All other values for this field are + reserved to IANA for future assignment. + + o SPI Size (1 octet) - Length in octets of the SPI as defined by the + IPsec protocol ID or zero if no SPI is applicable. For a + notification concerning the IKE_SA, the SPI Size MUST be zero. + + o Notify Message Type (2 octets) - Specifies the type of + notification message. + + o SPI (variable length) - Security Parameter Index. + + o Notification Data (variable length) - Informational or error data + transmitted in addition to the Notify Message Type. Values for + this field are type specific (see below). + + The payload type for the Notify Payload is forty one (41). + + + + + + + + +Kaufman Standards Track [Page 65] + +RFC 4306 IKEv2 December 2005 + + +3.10.1. Notify Message Types + + Notification information can be error messages specifying why an SA + could not be established. It can also be status data that a process + managing an SA database wishes to communicate with a peer process. + The table below lists the Notification messages and their + corresponding values. The number of different error statuses was + greatly reduced from IKEv1 both for simplification and to avoid + giving configuration information to probers. + + Types in the range 0 - 16383 are intended for reporting errors. An + implementation receiving a Notify payload with one of these types + that it does not recognize in a response MUST assume that the + corresponding request has failed entirely. Unrecognized error types + in a request and status types in a request or response MUST be + ignored except that they SHOULD be logged. + + Notify payloads with status types MAY be added to any message and + MUST be ignored if not recognized. They are intended to indicate + capabilities, and as part of SA negotiation are used to negotiate + non-cryptographic parameters. + + NOTIFY MESSAGES - ERROR TYPES Value + ----------------------------- ----- + RESERVED 0 + + UNSUPPORTED_CRITICAL_PAYLOAD 1 + + Sent if the payload has the "critical" bit set and the + payload type is not recognized. Notification Data contains + the one-octet payload type. + + INVALID_IKE_SPI 4 + + Indicates an IKE message was received with an unrecognized + destination SPI. This usually indicates that the recipient + has rebooted and forgotten the existence of an IKE_SA. + + INVALID_MAJOR_VERSION 5 + + Indicates the recipient cannot handle the version of IKE + specified in the header. The closest version number that + the recipient can support will be in the reply header. + + INVALID_SYNTAX 7 + + Indicates the IKE message that was received was invalid + because some type, length, or value was out of range or + + + +Kaufman Standards Track [Page 66] + +RFC 4306 IKEv2 December 2005 + + + because the request was rejected for policy reasons. To + avoid a denial of service attack using forged messages, this + status may only be returned for and in an encrypted packet + if the message ID and cryptographic checksum were valid. To + avoid leaking information to someone probing a node, this + status MUST be sent in response to any error not covered by + one of the other status types. To aid debugging, more + detailed error information SHOULD be written to a console or + log. + + INVALID_MESSAGE_ID 9 + + Sent when an IKE message ID outside the supported window is + received. This Notify MUST NOT be sent in a response; the + invalid request MUST NOT be acknowledged. Instead, inform + the other side by initiating an INFORMATIONAL exchange with + Notification data containing the four octet invalid message + ID. Sending this notification is optional, and + notifications of this type MUST be rate limited. + + INVALID_SPI 11 + + MAY be sent in an IKE INFORMATIONAL exchange when a node + receives an ESP or AH packet with an invalid SPI. The + Notification Data contains the SPI of the invalid packet. + This usually indicates a node has rebooted and forgotten an + SA. If this Informational Message is sent outside the + context of an IKE_SA, it should be used by the recipient + only as a "hint" that something might be wrong (because it + could easily be forged). + + NO_PROPOSAL_CHOSEN 14 + + None of the proposed crypto suites was acceptable. + + INVALID_KE_PAYLOAD 17 + + The D-H Group # field in the KE payload is not the group # + selected by the responder for this exchange. There are two + octets of data associated with this notification: the + accepted D-H Group # in big endian order. + + AUTHENTICATION_FAILED 24 + + Sent in the response to an IKE_AUTH message when for some + reason the authentication failed. There is no associated + data. + + + + +Kaufman Standards Track [Page 67] + +RFC 4306 IKEv2 December 2005 + + + SINGLE_PAIR_REQUIRED 34 + + This error indicates that a CREATE_CHILD_SA request is + unacceptable because its sender is only willing to accept + traffic selectors specifying a single pair of addresses. The + requestor is expected to respond by requesting an SA for only + the specific traffic it is trying to forward. + + NO_ADDITIONAL_SAS 35 + + This error indicates that a CREATE_CHILD_SA request is + unacceptable because the responder is unwilling to accept any + more CHILD_SAs on this IKE_SA. Some minimal implementations may + only accept a single CHILD_SA setup in the context of an initial + IKE exchange and reject any subsequent attempts to add more. + + INTERNAL_ADDRESS_FAILURE 36 + + Indicates an error assigning an internal address (i.e., + INTERNAL_IP4_ADDRESS or INTERNAL_IP6_ADDRESS) during the + processing of a Configuration Payload by a responder. If this + error is generated within an IKE_AUTH exchange, no CHILD_SA will + be created. + + FAILED_CP_REQUIRED 37 + + Sent by responder in the case where CP(CFG_REQUEST) was expected + but not received, and so is a conflict with locally configured + policy. There is no associated data. + + TS_UNACCEPTABLE 38 + + Indicates that none of the addresses/protocols/ports in the + supplied traffic selectors is acceptable. + + INVALID_SELECTORS 39 + + MAY be sent in an IKE INFORMATIONAL exchange when a node + receives an ESP or AH packet whose selectors do not match + those of the SA on which it was delivered (and that caused + the packet to be dropped). The Notification Data contains + the start of the offending packet (as in ICMP messages) and + the SPI field of the notification is set to match the SPI of + the IPsec SA. + + RESERVED TO IANA - Error types 40 - 8191 + + Private Use - Errors 8192 - 16383 + + + +Kaufman Standards Track [Page 68] + +RFC 4306 IKEv2 December 2005 + + + NOTIFY MESSAGES - STATUS TYPES Value + ------------------------------ ----- + + INITIAL_CONTACT 16384 + + This notification asserts that this IKE_SA is the only + IKE_SA currently active between the authenticated + identities. It MAY be sent when an IKE_SA is established + after a crash, and the recipient MAY use this information to + delete any other IKE_SAs it has to the same authenticated + identity without waiting for a timeout. This notification + MUST NOT be sent by an entity that may be replicated (e.g., + a roaming user's credentials where the user is allowed to + connect to the corporate firewall from two remote systems at + the same time). + + SET_WINDOW_SIZE 16385 + + This notification asserts that the sending endpoint is + capable of keeping state for multiple outstanding exchanges, + permitting the recipient to send multiple requests before + getting a response to the first. The data associated with a + SET_WINDOW_SIZE notification MUST be 4 octets long and + contain the big endian representation of the number of + messages the sender promises to keep. Window size is always + one until the initial exchanges complete. + + ADDITIONAL_TS_POSSIBLE 16386 + + This notification asserts that the sending endpoint narrowed + the proposed traffic selectors but that other traffic + selectors would also have been acceptable, though only in a + separate SA (see section 2.9). There is no data associated + with this Notify type. It may be sent only as an additional + payload in a message including accepted TSs. + + IPCOMP_SUPPORTED 16387 + + This notification may be included only in a message + containing an SA payload negotiating a CHILD_SA and + indicates a willingness by its sender to use IPComp on this + SA. The data associated with this notification includes a + two-octet IPComp CPI followed by a one-octet transform ID + optionally followed by attributes whose length and format + are defined by that transform ID. A message proposing an SA + may contain multiple IPCOMP_SUPPORTED notifications to + indicate multiple supported algorithms. A message accepting + an SA may contain at most one. + + + +Kaufman Standards Track [Page 69] + +RFC 4306 IKEv2 December 2005 + + + The transform IDs currently defined are: + + NAME NUMBER DEFINED IN + ----------- ------ ----------- + RESERVED 0 + IPCOMP_OUI 1 + IPCOMP_DEFLATE 2 RFC 2394 + IPCOMP_LZS 3 RFC 2395 + IPCOMP_LZJH 4 RFC 3051 + + values 5-240 are reserved to IANA. Values 241-255 are + for private use among mutually consenting parties. + + NAT_DETECTION_SOURCE_IP 16388 + + This notification is used by its recipient to determine + whether the source is behind a NAT box. The data associated + with this notification is a SHA-1 digest of the SPIs (in the + order they appear in the header), IP address, and port on + which this packet was sent. There MAY be multiple Notify + payloads of this type in a message if the sender does not + know which of several network attachments will be used to + send the packet. The recipient of this notification MAY + compare the supplied value to a SHA-1 hash of the SPIs, + source IP address, and port, and if they don't match it + SHOULD enable NAT traversal (see section 2.23). + Alternately, it MAY reject the connection attempt if NAT + traversal is not supported. + + NAT_DETECTION_DESTINATION_IP 16389 + + This notification is used by its recipient to determine + whether it is behind a NAT box. The data associated with + this notification is a SHA-1 digest of the SPIs (in the + order they appear in the header), IP address, and port to + which this packet was sent. The recipient of this + notification MAY compare the supplied value to a hash of the + SPIs, destination IP address, and port, and if they don't + match it SHOULD invoke NAT traversal (see section 2.23). If + they don't match, it means that this end is behind a NAT and + this end SHOULD start sending keepalive packets as defined + in [Hutt05]. Alternately, it MAY reject the connection + attempt if NAT traversal is not supported. + + + + + + + + +Kaufman Standards Track [Page 70] + +RFC 4306 IKEv2 December 2005 + + + COOKIE 16390 + + This notification MAY be included in an IKE_SA_INIT + response. It indicates that the request should be retried + with a copy of this notification as the first payload. This + notification MUST be included in an IKE_SA_INIT request + retry if a COOKIE notification was included in the initial + response. The data associated with this notification MUST + be between 1 and 64 octets in length (inclusive). + + USE_TRANSPORT_MODE 16391 + + This notification MAY be included in a request message that + also includes an SA payload requesting a CHILD_SA. It + requests that the CHILD_SA use transport mode rather than + tunnel mode for the SA created. If the request is accepted, + the response MUST also include a notification of type + USE_TRANSPORT_MODE. If the responder declines the request, + the CHILD_SA will be established in tunnel mode. If this is + unacceptable to the initiator, the initiator MUST delete the + SA. Note: Except when using this option to negotiate + transport mode, all CHILD_SAs will use tunnel mode. + + Note: The ECN decapsulation modifications specified in + [RFC4301] MUST be performed for every tunnel mode SA created + by IKEv2. + + HTTP_CERT_LOOKUP_SUPPORTED 16392 + + This notification MAY be included in any message that can + include a CERTREQ payload and indicates that the sender is + capable of looking up certificates based on an HTTP-based + URL (and hence presumably would prefer to receive + certificate specifications in that format). + + REKEY_SA 16393 + + This notification MUST be included in a CREATE_CHILD_SA + exchange if the purpose of the exchange is to replace an + existing ESP or AH SA. The SPI field identifies the SA + being rekeyed. There is no data. + + ESP_TFC_PADDING_NOT_SUPPORTED 16394 + + This notification asserts that the sending endpoint will NOT + accept packets that contain Flow Confidentiality (TFC) + padding. + + + + +Kaufman Standards Track [Page 71] + +RFC 4306 IKEv2 December 2005 + + + NON_FIRST_FRAGMENTS_ALSO 16395 + + Used for fragmentation control. See [RFC4301] for + explanation. + + RESERVED TO IANA - STATUS TYPES 16396 - 40959 + + Private Use - STATUS TYPES 40960 - 65535 + +3.11. Delete Payload + + The Delete Payload, denoted D in this memo, contains a protocol- + specific security association identifier that the sender has removed + from its security association database and is, therefore, no longer + valid. Figure 17 shows the format of the Delete Payload. It is + possible to send multiple SPIs in a Delete payload; however, each SPI + MUST be for the same protocol. Mixing of protocol identifiers MUST + NOT be performed in a Delete payload. It is permitted, however, to + include multiple Delete payloads in a single INFORMATIONAL exchange + where each Delete payload lists SPIs for a different protocol. + + Deletion of the IKE_SA is indicated by a protocol ID of 1 (IKE) but + no SPIs. Deletion of a CHILD_SA, such as ESP or AH, will contain the + IPsec protocol ID of that protocol (2 for AH, 3 for ESP), and the SPI + is the SPI the sending endpoint would expect in inbound ESP or AH + packets. + + The Delete Payload is defined as follows: + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Protocol ID ! SPI Size ! # of SPIs ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ Security Parameter Index(es) (SPI) ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 17: Delete Payload Format + + o Protocol ID (1 octet) - Must be 1 for an IKE_SA, 2 for AH, or 3 + for ESP. + + + + + + +Kaufman Standards Track [Page 72] + +RFC 4306 IKEv2 December 2005 + + + o SPI Size (1 octet) - Length in octets of the SPI as defined by the + protocol ID. It MUST be zero for IKE (SPI is in message header) + or four for AH and ESP. + + o # of SPIs (2 octets) - The number of SPIs contained in the Delete + payload. The size of each SPI is defined by the SPI Size field. + + o Security Parameter Index(es) (variable length) - Identifies the + specific security association(s) to delete. The length of this + field is determined by the SPI Size and # of SPIs fields. + + The payload type for the Delete Payload is forty two (42). + +3.12. Vendor ID Payload + + The Vendor ID Payload, denoted V in this memo, contains a vendor + defined constant. The constant is used by vendors to identify and + recognize remote instances of their implementations. This mechanism + allows a vendor to experiment with new features while maintaining + backward compatibility. + + A Vendor ID payload MAY announce that the sender is capable to + accepting certain extensions to the protocol, or it MAY simply + identify the implementation as an aid in debugging. A Vendor ID + payload MUST NOT change the interpretation of any information defined + in this specification (i.e., the critical bit MUST be set to 0). + Multiple Vendor ID payloads MAY be sent. An implementation is NOT + REQUIRED to send any Vendor ID payload at all. + + A Vendor ID payload may be sent as part of any message. Reception of + a familiar Vendor ID payload allows an implementation to make use of + Private USE numbers described throughout this memo -- private + payloads, private exchanges, private notifications, etc. Unfamiliar + Vendor IDs MUST be ignored. + + Writers of Internet-Drafts who wish to extend this protocol MUST + define a Vendor ID payload to announce the ability to implement the + extension in the Internet-Draft. It is expected that Internet-Drafts + that gain acceptance and are standardized will be given "magic + numbers" out of the Future Use range by IANA, and the requirement to + use a Vendor ID will go away. + + + + + + + + + + +Kaufman Standards Track [Page 73] + +RFC 4306 IKEv2 December 2005 + + + The Vendor ID Payload fields are defined as follows: + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ Vendor ID (VID) ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 18: Vendor ID Payload Format + + o Vendor ID (variable length) - It is the responsibility of the + person choosing the Vendor ID to assure its uniqueness in spite of + the absence of any central registry for IDs. Good practice is to + include a company name, a person name, or some such. If you want + to show off, you might include the latitude and longitude and time + where you were when you chose the ID and some random input. A + message digest of a long unique string is preferable to the long + unique string itself. + + The payload type for the Vendor ID Payload is forty three (43). + +3.13. Traffic Selector Payload + + The Traffic Selector Payload, denoted TS in this memo, allows peers + to identify packet flows for processing by IPsec security services. + The Traffic Selector Payload consists of the IKE generic payload + header followed by individual traffic selectors as follows: + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Number of TSs ! RESERVED ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ <Traffic Selectors> ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 19: Traffic Selectors Payload Format + + o Number of TSs (1 octet) - Number of traffic selectors being + provided. + + + +Kaufman Standards Track [Page 74] + +RFC 4306 IKEv2 December 2005 + + + o RESERVED - This field MUST be sent as zero and MUST be ignored on + receipt. + + o Traffic Selectors (variable length) - One or more individual + traffic selectors. + + The length of the Traffic Selector payload includes the TS header and + all the traffic selectors. + + The payload type for the Traffic Selector payload is forty four (44) + for addresses at the initiator's end of the SA and forty five (45) + for addresses at the responder's end. + +3.13.1. Traffic Selector + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! TS Type !IP Protocol ID*| Selector Length | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Start Port* | End Port* | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ Starting Address* ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ Ending Address* ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 20: Traffic Selector + + * Note: All fields other than TS Type and Selector Length depend on + the TS Type. The fields shown are for TS Types 7 and 8, the only two + values currently defined. + + o TS Type (one octet) - Specifies the type of traffic selector. + + o IP protocol ID (1 octet) - Value specifying an associated IP + protocol ID (e.g., UDP/TCP/ICMP). A value of zero means that the + protocol ID is not relevant to this traffic selector -- the SA can + carry all protocols. + + o Selector Length - Specifies the length of this Traffic Selector + Substructure including the header. + + + + + +Kaufman Standards Track [Page 75] + +RFC 4306 IKEv2 December 2005 + + + o Start Port (2 octets) - Value specifying the smallest port number + allowed by this Traffic Selector. For protocols for which port is + undefined, or if all ports are allowed, this field MUST be zero. + For the ICMP protocol, the two one-octet fields Type and Code are + treated as a single 16-bit integer (with Type in the most + significant eight bits and Code in the least significant eight + bits) port number for the purposes of filtering based on this + field. + + o End Port (2 octets) - Value specifying the largest port number + allowed by this Traffic Selector. For protocols for which port is + undefined, or if all ports are allowed, this field MUST be 65535. + For the ICMP protocol, the two one-octet fields Type and Code are + treated as a single 16-bit integer (with Type in the most + significant eight bits and Code in the least significant eight + bits) port number for the purposed of filtering based on this + field. + + o Starting Address - The smallest address included in this Traffic + Selector (length determined by TS type). + + o Ending Address - The largest address included in this Traffic + Selector (length determined by TS type). + + Systems that are complying with [RFC4301] that wish to indicate "ANY" + ports MUST set the start port to 0 and the end port to 65535; note + that according to [RFC4301], "ANY" includes "OPAQUE". Systems + working with [RFC4301] that wish to indicate "OPAQUE" ports, but not + "ANY" ports, MUST set the start port to 65535 and the end port to 0. + + The following table lists the assigned values for the Traffic + Selector Type field and the corresponding Address Selector Data. + + TS Type Value + ------- ----- + RESERVED 0-6 + + TS_IPV4_ADDR_RANGE 7 + + A range of IPv4 addresses, represented by two four-octet + values. The first value is the beginning IPv4 address + (inclusive) and the second value is the ending IPv4 address + (inclusive). All addresses falling between the two + specified addresses are considered to be within the list. + + + + + + + +Kaufman Standards Track [Page 76] + +RFC 4306 IKEv2 December 2005 + + + TS_IPV6_ADDR_RANGE 8 + + A range of IPv6 addresses, represented by two sixteen-octet + values. The first value is the beginning IPv6 address + (inclusive) and the second value is the ending IPv6 address + (inclusive). All addresses falling between the two + specified addresses are considered to be within the list. + + RESERVED TO IANA 9-240 + PRIVATE USE 241-255 + +3.14. Encrypted Payload + + The Encrypted Payload, denoted SK{...} or E in this memo, contains + other payloads in encrypted form. The Encrypted Payload, if present + in a message, MUST be the last payload in the message. Often, it is + the only payload in the message. + + The algorithms for encryption and integrity protection are negotiated + during IKE_SA setup, and the keys are computed as specified in + sections 2.14 and 2.18. + + The encryption and integrity protection algorithms are modeled after + the ESP algorithms described in RFCs 2104 [KBC96], 4303 [RFC4303], + and 2451 [ESPCBC]. This document completely specifies the + cryptographic processing of IKE data, but those documents should be + consulted for design rationale. We require a block cipher with a + fixed block size and an integrity check algorithm that computes a + fixed-length checksum over a variable size message. + + The payload type for an Encrypted payload is forty six (46). The + Encrypted Payload consists of the IKE generic payload header followed + by individual fields as follows: + + + + + + + + + + + + + + + + + + +Kaufman Standards Track [Page 77] + +RFC 4306 IKEv2 December 2005 + + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Initialization Vector ! + ! (length is block size for encryption algorithm) ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ~ Encrypted IKE Payloads ~ + + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! Padding (0-255 octets) ! + +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+ + ! ! Pad Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ~ Integrity Checksum Data ~ + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 21: Encrypted Payload Format + + o Next Payload - The payload type of the first embedded payload. + Note that this is an exception in the standard header format, + since the Encrypted payload is the last payload in the message and + therefore the Next Payload field would normally be zero. But + because the content of this payload is embedded payloads and there + was no natural place to put the type of the first one, that type + is placed here. + + o Payload Length - Includes the lengths of the header, IV, Encrypted + IKE Payloads, Padding, Pad Length, and Integrity Checksum Data. + + o Initialization Vector - A randomly chosen value whose length is + equal to the block length of the underlying encryption algorithm. + Recipients MUST accept any value. Senders SHOULD either pick this + value pseudo-randomly and independently for each message or use + the final ciphertext block of the previous message sent. Senders + MUST NOT use the same value for each message, use a sequence of + values with low hamming distance (e.g., a sequence number), or use + ciphertext from a received message. + + o IKE Payloads are as specified earlier in this section. This field + is encrypted with the negotiated cipher. + + o Padding MAY contain any value chosen by the sender, and MUST have + a length that makes the combination of the Payloads, the Padding, + and the Pad Length to be a multiple of the encryption block size. + This field is encrypted with the negotiated cipher. + + + + + +Kaufman Standards Track [Page 78] + +RFC 4306 IKEv2 December 2005 + + + o Pad Length is the length of the Padding field. The sender SHOULD + set the Pad Length to the minimum value that makes the combination + of the Payloads, the Padding, and the Pad Length a multiple of the + block size, but the recipient MUST accept any length that results + in proper alignment. This field is encrypted with the negotiated + cipher. + + o Integrity Checksum Data is the cryptographic checksum of the + entire message starting with the Fixed IKE Header through the Pad + Length. The checksum MUST be computed over the encrypted message. + Its length is determined by the integrity algorithm negotiated. + +3.15. Configuration Payload + + The Configuration payload, denoted CP in this document, is used to + exchange configuration information between IKE peers. The exchange + is for an IRAC to request an internal IP address from an IRAS and to + exchange other information of the sort that one would acquire with + Dynamic Host Configuration Protocol (DHCP) if the IRAC were directly + connected to a LAN. + + Configuration payloads are of type CFG_REQUEST/CFG_REPLY or + CFG_SET/CFG_ACK (see CFG Type in the payload description below). + CFG_REQUEST and CFG_SET payloads may optionally be added to any IKE + request. The IKE response MUST include either a corresponding + CFG_REPLY or CFG_ACK or a Notify payload with an error type + indicating why the request could not be honored. An exception is + that a minimal implementation MAY ignore all CFG_REQUEST and CFG_SET + payloads, so a response message without a corresponding CFG_REPLY or + CFG_ACK MUST be accepted as an indication that the request was not + supported. + + "CFG_REQUEST/CFG_REPLY" allows an IKE endpoint to request information + from its peer. If an attribute in the CFG_REQUEST Configuration + Payload is not zero-length, it is taken as a suggestion for that + attribute. The CFG_REPLY Configuration Payload MAY return that + value, or a new one. It MAY also add new attributes and not include + some requested ones. Requestors MUST ignore returned attributes that + they do not recognize. + + Some attributes MAY be multi-valued, in which case multiple attribute + values of the same type are sent and/or returned. Generally, all + values of an attribute are returned when the attribute is requested. + For some attributes (in this version of the specification only + internal addresses), multiple requests indicates a request that + multiple values be assigned. For these attributes, the number of + values returned SHOULD NOT exceed the number requested. + + + + +Kaufman Standards Track [Page 79] + +RFC 4306 IKEv2 December 2005 + + + If the data type requested in a CFG_REQUEST is not recognized or not + supported, the responder MUST NOT return an error type but rather + MUST either send a CFG_REPLY that MAY be empty or a reply not + containing a CFG_REPLY payload at all. Error returns are reserved + for cases where the request is recognized but cannot be performed as + requested or the request is badly formatted. + + "CFG_SET/CFG_ACK" allows an IKE endpoint to push configuration data + to its peer. In this case, the CFG_SET Configuration Payload + contains attributes the initiator wants its peer to alter. The + responder MUST return a Configuration Payload if it accepted any of + the configuration data and it MUST contain the attributes that the + responder accepted with zero-length data. Those attributes that it + did not accept MUST NOT be in the CFG_ACK Configuration Payload. If + no attributes were accepted, the responder MUST return either an + empty CFG_ACK payload or a response message without a CFG_ACK + payload. There are currently no defined uses for the CFG_SET/CFG_ACK + exchange, though they may be used in connection with extensions based + on Vendor IDs. An minimal implementation of this specification MAY + ignore CFG_SET payloads. + + Extensions via the CP payload SHOULD NOT be used for general purpose + management. Its main intent is to provide a bootstrap mechanism to + exchange information within IPsec from IRAS to IRAC. While it MAY be + useful to use such a method to exchange information between some + Security Gateways (SGW) or small networks, existing management + protocols such as DHCP [DHCP], RADIUS [RADIUS], SNMP, or LDAP [LDAP] + should be preferred for enterprise management as well as subsequent + information exchanges. + + The Configuration Payload is defined as follows: + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! CFG Type ! RESERVED ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ Configuration Attributes ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 22: Configuration Payload Format + + The payload type for the Configuration Payload is forty seven (47). + + + + +Kaufman Standards Track [Page 80] + +RFC 4306 IKEv2 December 2005 + + + o CFG Type (1 octet) - The type of exchange represented by the + Configuration Attributes. + + CFG Type Value + =========== ===== + RESERVED 0 + CFG_REQUEST 1 + CFG_REPLY 2 + CFG_SET 3 + CFG_ACK 4 + + values 5-127 are reserved to IANA. Values 128-255 are for private + use among mutually consenting parties. + + o RESERVED (3 octets) - MUST be sent as zero; MUST be ignored on + receipt. + + o Configuration Attributes (variable length) - These are type length + values specific to the Configuration Payload and are defined + below. There may be zero or more Configuration Attributes in this + payload. + +3.15.1. Configuration Attributes + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + !R| Attribute Type ! Length | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + ~ Value ~ + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 23: Configuration Attribute Format + + o Reserved (1 bit) - This bit MUST be set to zero and MUST be + ignored on receipt. + + o Attribute Type (15 bits) - A unique identifier for each of the + Configuration Attribute Types. + + o Length (2 octets) - Length in octets of Value. + + o Value (0 or more octets) - The variable-length value of this + Configuration Attribute. + + + + + +Kaufman Standards Track [Page 81] + +RFC 4306 IKEv2 December 2005 + + + The following attribute types have been defined: + + Multi- + Attribute Type Value Valued Length + ======================= ===== ====== ================== + RESERVED 0 + INTERNAL_IP4_ADDRESS 1 YES* 0 or 4 octets + INTERNAL_IP4_NETMASK 2 NO 0 or 4 octets + INTERNAL_IP4_DNS 3 YES 0 or 4 octets + INTERNAL_IP4_NBNS 4 YES 0 or 4 octets + INTERNAL_ADDRESS_EXPIRY 5 NO 0 or 4 octets + INTERNAL_IP4_DHCP 6 YES 0 or 4 octets + APPLICATION_VERSION 7 NO 0 or more + INTERNAL_IP6_ADDRESS 8 YES* 0 or 17 octets + RESERVED 9 + INTERNAL_IP6_DNS 10 YES 0 or 16 octets + INTERNAL_IP6_NBNS 11 YES 0 or 16 octets + INTERNAL_IP6_DHCP 12 YES 0 or 16 octets + INTERNAL_IP4_SUBNET 13 YES 0 or 8 octets + SUPPORTED_ATTRIBUTES 14 NO Multiple of 2 + INTERNAL_IP6_SUBNET 15 YES 17 octets + + * These attributes may be multi-valued on return only if multiple + values were requested. + + Types 16-16383 are reserved to IANA. Values 16384-32767 are for + private use among mutually consenting parties. + + o INTERNAL_IP4_ADDRESS, INTERNAL_IP6_ADDRESS - An address on the + internal network, sometimes called a red node address or + private address and MAY be a private address on the Internet. + In a request message, the address specified is a requested + address (or zero if no specific address is requested). If a + specific address is requested, it likely indicates that a + previous connection existed with this address and the requestor + would like to reuse that address. With IPv6, a requestor MAY + supply the low-order address bytes it wants to use. Multiple + internal addresses MAY be requested by requesting multiple + internal address attributes. The responder MAY only send up to + the number of addresses requested. The INTERNAL_IP6_ADDRESS is + made up of two fields: the first is a sixteen-octet IPv6 + address and the second is a one-octet prefix-length as defined + in [ADDRIPV6]. + + The requested address is valid until the expiry time defined + with the INTERNAL_ADDRESS EXPIRY attribute or there are no + IKE_SAs between the peers. + + + + +Kaufman Standards Track [Page 82] + +RFC 4306 IKEv2 December 2005 + + + o INTERNAL_IP4_NETMASK - The internal network's netmask. Only + one netmask is allowed in the request and reply messages (e.g., + 255.255.255.0), and it MUST be used only with an + INTERNAL_IP4_ADDRESS attribute. + + o INTERNAL_IP4_DNS, INTERNAL_IP6_DNS - Specifies an address of a + DNS server within the network. Multiple DNS servers MAY be + requested. The responder MAY respond with zero or more DNS + server attributes. + + o INTERNAL_IP4_NBNS, INTERNAL_IP6_NBNS - Specifies an address of + a NetBios Name Server (WINS) within the network. Multiple NBNS + servers MAY be requested. The responder MAY respond with zero + or more NBNS server attributes. + + o INTERNAL_ADDRESS_EXPIRY - Specifies the number of seconds that + the host can use the internal IP address. The host MUST renew + the IP address before this expiry time. Only one of these + attributes MAY be present in the reply. + + o INTERNAL_IP4_DHCP, INTERNAL_IP6_DHCP - Instructs the host to + send any internal DHCP requests to the address contained within + the attribute. Multiple DHCP servers MAY be requested. The + responder MAY respond with zero or more DHCP server attributes. + + o APPLICATION_VERSION - The version or application information of + the IPsec host. This is a string of printable ASCII characters + that is NOT null terminated. + + o INTERNAL_IP4_SUBNET - The protected sub-networks that this + edge-device protects. This attribute is made up of two fields: + the first is an IP address and the second is a netmask. + Multiple sub-networks MAY be requested. The responder MAY + respond with zero or more sub-network attributes. + + o SUPPORTED_ATTRIBUTES - When used within a Request, this + attribute MUST be zero-length and specifies a query to the + responder to reply back with all of the attributes that it + supports. The response contains an attribute that contains a + set of attribute identifiers each in 2 octets. The length + divided by 2 (octets) would state the number of supported + attributes contained in the response. + + + + + + + + + +Kaufman Standards Track [Page 83] + +RFC 4306 IKEv2 December 2005 + + + o INTERNAL_IP6_SUBNET - The protected sub-networks that this + edge-device protects. This attribute is made up of two fields: + the first is a sixteen-octet IPv6 address and the second is a + one-octet prefix-length as defined in [ADDRIPV6]. Multiple + sub-networks MAY be requested. The responder MAY respond with + zero or more sub-network attributes. + + Note that no recommendations are made in this document as to how + an implementation actually figures out what information to send in + a reply. That is, we do not recommend any specific method of an + IRAS determining which DNS server should be returned to a + requesting IRAC. + +3.16. Extensible Authentication Protocol (EAP) Payload + + The Extensible Authentication Protocol Payload, denoted EAP in this + memo, allows IKE_SAs to be authenticated using the protocol defined + in RFC 3748 [EAP] and subsequent extensions to that protocol. The + full set of acceptable values for the payload is defined elsewhere, + but a short summary of RFC 3748 is included here to make this + document stand alone in the common cases. + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! ! + ~ EAP Message ~ + ! ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 24: EAP Payload Format + + The payload type for an EAP Payload is forty eight (48). + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Code ! Identifier ! Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Type ! Type_Data... + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- + + Figure 25: EAP Message Format + + o Code (1 octet) indicates whether this message is a Request (1), + Response (2), Success (3), or Failure (4). + + + +Kaufman Standards Track [Page 84] + +RFC 4306 IKEv2 December 2005 + + + o Identifier (1 octet) is used in PPP to distinguish replayed + messages from repeated ones. Since in IKE, EAP runs over a + reliable protocol, it serves no function here. In a response + message, this octet MUST be set to match the identifier in the + corresponding request. In other messages, this field MAY be set + to any value. + + o Length (2 octets) is the length of the EAP message and MUST be + four less than the Payload Length of the encapsulating payload. + + o Type (1 octet) is present only if the Code field is Request (1) or + Response (2). For other codes, the EAP message length MUST be + four octets and the Type and Type_Data fields MUST NOT be present. + In a Request (1) message, Type indicates the data being requested. + In a Response (2) message, Type MUST either be Nak or match the + type of the data requested. The following types are defined in + RFC 3748: + + 1 Identity + 2 Notification + 3 Nak (Response Only) + 4 MD5-Challenge + 5 One-Time Password (OTP) + 6 Generic Token Card + + o Type_Data (Variable Length) varies with the Type of Request and + the associated Response. For the documentation of the EAP + methods, see [EAP]. + + Note that since IKE passes an indication of initiator identity in + message 3 of the protocol, the responder SHOULD NOT send EAP Identity + requests. The initiator SHOULD, however, respond to such requests if + it receives them. + +4. Conformance Requirements + + In order to assure that all implementations of IKEv2 can + interoperate, there are "MUST support" requirements in addition to + those listed elsewhere. Of course, IKEv2 is a security protocol, and + one of its major functions is to allow only authorized parties to + successfully complete establishment of SAs. So a particular + implementation may be configured with any of a number of restrictions + concerning algorithms and trusted authorities that will prevent + universal interoperability. + + + + + + + +Kaufman Standards Track [Page 85] + +RFC 4306 IKEv2 December 2005 + + + IKEv2 is designed to permit minimal implementations that can + interoperate with all compliant implementations. There are a series + of optional features that can easily be ignored by a particular + implementation if it does not support that feature. Those features + include: + + Ability to negotiate SAs through a NAT and tunnel the resulting + ESP SA over UDP. + + Ability to request (and respond to a request for) a temporary IP + address on the remote end of a tunnel. + + Ability to support various types of legacy authentication. + + Ability to support window sizes greater than one. + + Ability to establish multiple ESP and/or AH SAs within a single + IKE_SA. + + Ability to rekey SAs. + + To assure interoperability, all implementations MUST be capable of + parsing all payload types (if only to skip over them) and to ignore + payload types that it does not support unless the critical bit is set + in the payload header. If the critical bit is set in an unsupported + payload header, all implementations MUST reject the messages + containing those payloads. + + Every implementation MUST be capable of doing four-message + IKE_SA_INIT and IKE_AUTH exchanges establishing two SAs (one for IKE, + one for ESP and/or AH). Implementations MAY be initiate-only or + respond-only if appropriate for their platform. Every implementation + MUST be capable of responding to an INFORMATIONAL exchange, but a + minimal implementation MAY respond to any INFORMATIONAL message with + an empty INFORMATIONAL reply (note that within the context of an + IKE_SA, an "empty" message consists of an IKE header followed by an + Encrypted payload with no payloads contained in it). A minimal + implementation MAY support the CREATE_CHILD_SA exchange only in so + far as to recognize requests and reject them with a Notify payload of + type NO_ADDITIONAL_SAS. A minimal implementation need not be able to + initiate CREATE_CHILD_SA or INFORMATIONAL exchanges. When an SA + expires (based on locally configured values of either lifetime or + octets passed), and implementation MAY either try to renew it with a + CREATE_CHILD_SA exchange or it MAY delete (close) the old SA and + create a new one. If the responder rejects the CREATE_CHILD_SA + request with a NO_ADDITIONAL_SAS notification, the implementation + MUST be capable of instead closing the old SA and creating a new one. + + + + +Kaufman Standards Track [Page 86] + +RFC 4306 IKEv2 December 2005 + + + Implementations are not required to support requesting temporary IP + addresses or responding to such requests. If an implementation does + support issuing such requests, it MUST include a CP payload in + message 3 containing at least a field of type INTERNAL_IP4_ADDRESS or + INTERNAL_IP6_ADDRESS. All other fields are optional. If an + implementation supports responding to such requests, it MUST parse + the CP payload of type CFG_REQUEST in message 3 and recognize a field + of type INTERNAL_IP4_ADDRESS or INTERNAL_IP6_ADDRESS. If it supports + leasing an address of the appropriate type, it MUST return a CP + payload of type CFG_REPLY containing an address of the requested + type. The responder SHOULD include all of the other related + attributes if it has them. + + A minimal IPv4 responder implementation will ignore the contents of + the CP payload except to determine that it includes an + INTERNAL_IP4_ADDRESS attribute and will respond with the address and + other related attributes regardless of whether the initiator + requested them. + + A minimal IPv4 initiator will generate a CP payload containing only + an INTERNAL_IP4_ADDRESS attribute and will parse the response + ignoring attributes it does not know how to use. The only attribute + it MUST be able to process is INTERNAL_ADDRESS_EXPIRY, which it must + use to bound the lifetime of the SA unless it successfully renews the + lease before it expires. Minimal initiators need not be able to + request lease renewals and minimal responders need not respond to + them. + + For an implementation to be called conforming to this specification, + it MUST be possible to configure it to accept the following: + + PKIX Certificates containing and signed by RSA keys of size 1024 or + 2048 bits, where the ID passed is any of ID_KEY_ID, ID_FQDN, + ID_RFC822_ADDR, or ID_DER_ASN1_DN. + + Shared key authentication where the ID passes is any of ID_KEY_ID, + ID_FQDN, or ID_RFC822_ADDR. + + Authentication where the responder is authenticated using PKIX + Certificates and the initiator is authenticated using shared key + authentication. + + + + + + + + + + +Kaufman Standards Track [Page 87] + +RFC 4306 IKEv2 December 2005 + + +5. Security Considerations + + While this protocol is designed to minimize disclosure of + configuration information to unauthenticated peers, some such + disclosure is unavoidable. One peer or the other must identify + itself first and prove its identity first. To avoid probing, the + initiator of an exchange is required to identify itself first, and + usually is required to authenticate itself first. The initiator can, + however, learn that the responder supports IKE and what cryptographic + protocols it supports. The responder (or someone impersonating the + responder) can probe the initiator not only for its identity, but + using CERTREQ payloads may be able to determine what certificates the + initiator is willing to use. + + Use of EAP authentication changes the probing possibilities somewhat. + When EAP authentication is used, the responder proves its identity + before the initiator does, so an initiator that knew the name of a + valid initiator could probe the responder for both its name and + certificates. + + Repeated rekeying using CREATE_CHILD_SA without additional Diffie- + Hellman exchanges leaves all SAs vulnerable to cryptanalysis of a + single key or overrun of either endpoint. Implementers should take + note of this fact and set a limit on CREATE_CHILD_SA exchanges + between exponentiations. This memo does not prescribe such a limit. + + The strength of a key derived from a Diffie-Hellman exchange using + any of the groups defined here depends on the inherent strength of + the group, the size of the exponent used, and the entropy provided by + the random number generator used. Due to these inputs, it is + difficult to determine the strength of a key for any of the defined + groups. Diffie-Hellman group number two, when used with a strong + random number generator and an exponent no less than 200 bits, is + common for use with 3DES. Group five provides greater security than + group two. Group one is for historic purposes only and does not + provide sufficient strength except for use with DES, which is also + for historic use only. Implementations should make note of these + estimates when establishing policy and negotiating security + parameters. + + Note that these limitations are on the Diffie-Hellman groups + themselves. There is nothing in IKE that prohibits using stronger + groups nor is there anything that will dilute the strength obtained + from stronger groups (limited by the strength of the other algorithms + negotiated including the prf function). In fact, the extensible + framework of IKE encourages the definition of more groups; use of + elliptical curve groups may greatly increase strength using much + smaller numbers. + + + +Kaufman Standards Track [Page 88] + +RFC 4306 IKEv2 December 2005 + + + It is assumed that all Diffie-Hellman exponents are erased from + memory after use. In particular, these exponents MUST NOT be derived + from long-lived secrets like the seed to a pseudo-random generator + that is not erased after use. + + The strength of all keys is limited by the size of the output of the + negotiated prf function. For this reason, a prf function whose + output is less than 128 bits (e.g., 3DES-CBC) MUST NOT be used with + this protocol. + + The security of this protocol is critically dependent on the + randomness of the randomly chosen parameters. These should be + generated by a strong random or properly seeded pseudo-random source + (see [RFC4086]). Implementers should take care to ensure that use of + random numbers for both keys and nonces is engineered in a fashion + that does not undermine the security of the keys. + + For information on the rationale of many of the cryptographic design + choices in this protocol, see [SIGMA] and [SKEME]. Though the + security of negotiated CHILD_SAs does not depend on the strength of + the encryption and integrity protection negotiated in the IKE_SA, + implementations MUST NOT negotiate NONE as the IKE integrity + protection algorithm or ENCR_NULL as the IKE encryption algorithm. + + When using pre-shared keys, a critical consideration is how to assure + the randomness of these secrets. The strongest practice is to ensure + that any pre-shared key contain as much randomness as the strongest + key being negotiated. Deriving a shared secret from a password, + name, or other low-entropy source is not secure. These sources are + subject to dictionary and social engineering attacks, among others. + + The NAT_DETECTION_*_IP notifications contain a hash of the addresses + and ports in an attempt to hide internal IP addresses behind a NAT. + Since the IPv4 address space is only 32 bits, and it is usually very + sparse, it would be possible for an attacker to find out the internal + address used behind the NAT box by trying all possible IP addresses + and trying to find the matching hash. The port numbers are normally + fixed to 500, and the SPIs can be extracted from the packet. This + reduces the number of hash calculations to 2^32. With an educated + guess of the use of private address space, the number of hash + calculations is much smaller. Designers should therefore not assume + that use of IKE will not leak internal address information. + + When using an EAP authentication method that does not generate a + shared key for protecting a subsequent AUTH payload, certain man-in- + the-middle and server impersonation attacks are possible [EAPMITM]. + These vulnerabilities occur when EAP is also used in protocols that + are not protected with a secure tunnel. Since EAP is a general- + + + +Kaufman Standards Track [Page 89] + +RFC 4306 IKEv2 December 2005 + + + purpose authentication protocol, which is often used to provide + single-signon facilities, a deployed IPsec solution that relies on an + EAP authentication method that does not generate a shared key (also + known as a non-key-generating EAP method) can become compromised due + to the deployment of an entirely unrelated application that also + happens to use the same non-key-generating EAP method, but in an + unprotected fashion. Note that this vulnerability is not limited to + just EAP, but can occur in other scenarios where an authentication + infrastructure is reused. For example, if the EAP mechanism used by + IKEv2 utilizes a token authenticator, a man-in-the-middle attacker + could impersonate the web server, intercept the token authentication + exchange, and use it to initiate an IKEv2 connection. For this + reason, use of non-key-generating EAP methods SHOULD be avoided where + possible. Where they are used, it is extremely important that all + usages of these EAP methods SHOULD utilize a protected tunnel, where + the initiator validates the responder's certificate before initiating + the EAP exchange. Implementers SHOULD describe the vulnerabilities + of using non-key-generating EAP methods in the documentation of their + implementations so that the administrators deploying IPsec solutions + are aware of these dangers. + + An implementation using EAP MUST also use a public-key-based + authentication of the server to the client before the EAP exchange + begins, even if the EAP method offers mutual authentication. This + avoids having additional IKEv2 protocol variations and protects the + EAP data from active attackers. + + If the messages of IKEv2 are long enough that IP-level fragmentation + is necessary, it is possible that attackers could prevent the + exchange from completing by exhausting the reassembly buffers. The + chances of this can be minimized by using the Hash and URL encodings + instead of sending certificates (see section 3.6). Additional + mitigations are discussed in [KPS03]. + +6. IANA Considerations + + This document defines a number of new field types and values where + future assignments will be managed by the IANA. + + The following registries have been created by the IANA: + + IKEv2 Exchange Types (section 3.1) + IKEv2 Payload Types (section 3.2) + IKEv2 Transform Types (section 3.3.2) + IKEv2 Transform Attribute Types (section 3.3.2) + IKEv2 Encryption Transform IDs (section 3.3.2) + IKEv2 Pseudo-random Function Transform IDs (section 3.3.2) + IKEv2 Integrity Algorithm Transform IDs (section 3.3.2) + + + +Kaufman Standards Track [Page 90] + +RFC 4306 IKEv2 December 2005 + + + IKEv2 Diffie-Hellman Transform IDs (section 3.3.2) + IKEv2 Identification Payload ID Types (section 3.5) + IKEv2 Certificate Encodings (section 3.6) + IKEv2 Authentication Method (section 3.8) + IKEv2 Notify Message Types (section 3.10.1) + IKEv2 Notification IPCOMP Transform IDs (section 3.10.1) + IKEv2 Security Protocol Identifiers (section 3.3.1) + IKEv2 Traffic Selector Types (section 3.13.1) + IKEv2 Configuration Payload CFG Types (section 3.15) + IKEv2 Configuration Payload Attribute Types (section 3.15.1) + + Note: When creating a new Transform Type, a new registry for it must + be created. + + Changes and additions to any of those registries are by expert + review. + +7. Acknowledgements + + This document is a collaborative effort of the entire IPsec WG. If + there were no limit to the number of authors that could appear on an + RFC, the following, in alphabetical order, would have been listed: + Bill Aiello, Stephane Beaulieu, Steve Bellovin, Sara Bitan, Matt + Blaze, Ran Canetti, Darren Dukes, Dan Harkins, Paul Hoffman, John + Ioannidis, Charlie Kaufman, Steve Kent, Angelos Keromytis, Tero + Kivinen, Hugo Krawczyk, Andrew Krywaniuk, Radia Perlman, Omer + Reingold, and Michael Richardson. Many other people contributed to + the design. It is an evolution of IKEv1, ISAKMP, and the IPsec DOI, + each of which has its own list of authors. Hugh Daniel suggested the + feature of having the initiator, in message 3, specify a name for the + responder, and gave the feature the cute name "You Tarzan, Me Jane". + David Faucher and Valery Smyzlov helped refine the design of the + traffic selector negotiation. + +8. References + +8.1. Normative References + + [ADDGROUP] Kivinen, T. and M. Kojo, "More Modular Exponential (MODP) + Diffie-Hellman groups for Internet Key Exchange (IKE)", + RFC 3526, May 2003. + + [ADDRIPV6] Hinden, R. and S. Deering, "Internet Protocol Version 6 + (IPv6) Addressing Architecture", RFC 3513, April 2003. + + [Bra97] Bradner, S., "Key Words for use in RFCs to indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + + + +Kaufman Standards Track [Page 91] + +RFC 4306 IKEv2 December 2005 + + + [EAP] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. + Levkowetz, "Extensible Authentication Protocol (EAP)", RFC + 3748, June 2004. + + [ESPCBC] Pereira, R. and R. Adams, "The ESP CBC-Mode Cipher + Algorithms", RFC 2451, November 1998. + + [Hutt05] Huttunen, A., Swander, B., Volpe, V., DiBurro, L., and M. + Stenberg, "UDP Encapsulation of IPsec ESP Packets", RFC + 3948, January 2005. + + [RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an + IANA Considerations Section in RFCs", BCP 26, RFC 2434, + October 1998. + + [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition + of Explicit Congestion Notification (ECN) to IP", RFC + 3168, September 2001. + + [RFC3280] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet + X.509 Public Key Infrastructure Certificate and + Certificate Revocation List (CRL) Profile", RFC 3280, + April 2002. + + [RFC4301] Kent, S. and K. Seo, "Security Architecture for the + Internet Protocol", RFC 4301, December 2005. + +8.2. Informative References + + [DES] ANSI X3.106, "American National Standard for Information + Systems-Data Link Encryption", American National Standards + Institute, 1983. + + [DH] Diffie, W., and Hellman M., "New Directions in + Cryptography", IEEE Transactions on Information Theory, V. + IT-22, n. 6, June 1977. + + [DHCP] Droms, R., "Dynamic Host Configuration Protocol", RFC + 2131, March 1997. + + [DSS] NIST, "Digital Signature Standard", FIPS 186, National + Institute of Standards and Technology, U.S. Department of + Commerce, May, 1994. + + [EAPMITM] Asokan, N., Nierni, V., and Nyberg, K., "Man-in-the-Middle + in Tunneled Authentication Protocols", + http://eprint.iacr.org/2002/163, November 2002. + + + + +Kaufman Standards Track [Page 92] + +RFC 4306 IKEv2 December 2005 + + + [HC98] Harkins, D. and D. Carrel, "The Internet Key Exchange + (IKE)", RFC 2409, November 1998. + + [IDEA] Lai, X., "On the Design and Security of Block Ciphers," + ETH Series in Information Processing, v. 1, Konstanz: + Hartung-Gorre Verlag, 1992. + + [IPCOMP] Shacham, A., Monsour, B., Pereira, R., and M. Thomas, "IP + Payload Compression Protocol (IPComp)", RFC 3173, + September 2001. + + [KPS03] Kaufman, C., Perlman, R., and Sommerfeld, B., "DoS + protection for UDP-based protocols", ACM Conference on + Computer and Communications Security, October 2003. + + [KBC96] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- + Hashing for Message Authentication", RFC 2104, February + 1997. + + [LDAP] Wahl, M., Howes, T., and S Kille, "Lightweight Directory + Access Protocol (v3)", RFC 2251, December 1997. + + [MD5] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, + April 1992. + + [MSST98] Maughan, D., Schertler, M., Schneider, M., and J. Turner, + "Internet Security Association and Key Management Protocol + (ISAKMP)", RFC 2408, November 1998. + + [Orm96] Orman, H., "The OAKLEY Key Determination Protocol", RFC + 2412, November 1998. + + [PFKEY] McDonald, D., Metz, C., and B. Phan, "PF_KEY Key + Management API, Version 2", RFC 2367, July 1998. + + [PKCS1] Jonsson, J. and B. Kaliski, "Public-Key Cryptography + Standards (PKCS) #1: RSA Cryptography Specifications + Version 2.1", RFC 3447, February 2003. + + [PK01] Perlman, R., and Kaufman, C., "Analysis of the IPsec key + exchange Standard", WET-ICE Security Conference, MIT,2001, + http://sec.femto.org/wetice-2001/papers/radia-paper.pdf. + + [Pip98] Piper, D., "The Internet IP Security Domain Of + Interpretation for ISAKMP", RFC 2407, November 1998. + + + + + + +Kaufman Standards Track [Page 93] + +RFC 4306 IKEv2 December 2005 + + + [RADIUS] Rigney, C., Willens, S., Rubens, A., and W. Simpson, + "Remote Authentication Dial In User Service (RADIUS)", RFC + 2865, June 2000. + + [RFC4086] Eastlake, D., 3rd, Schiller, J., and S. Crocker, + "Randomness Requirements for Security", BCP 106, RFC 4086, + June 2005. + + [RFC1958] Carpenter, B., "Architectural Principles of the Internet", + RFC 1958, June 1996. + + [RFC2401] Kent, S. and R. Atkinson, "Security Architecture for the + Internet Protocol", RFC 2401, November 1998. + + [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, + "Definition of the Differentiated Services Field (DS + Field) in the IPv4 and IPv6 Headers", RFC 2474, December + 1998. + + [RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z., + and W. Weiss, "An Architecture for Differentiated + Service", RFC 2475, December 1998. + + [RFC2522] Karn, P. and W. Simpson, "Photuris: Session-Key Management + Protocol", RFC 2522, March 1999. + + [RFC2775] Carpenter, B., "Internet Transparency", RFC 2775, February + 2000. + + [RFC2983] Black, D., "Differentiated Services and Tunnels", RFC + 2983, October 2000. + + [RFC3439] Bush, R. and D. Meyer, "Some Internet Architectural + Guidelines and Philosophy", RFC 3439, December 2002. + + [RFC3715] Aboba, B. and W. Dixon, "IPsec-Network Address Translation + (NAT) Compatibility Requirements", RFC 3715, March 2004. + + [RFC4302] Kent, S., "IP Authentication Header", RFC 4302, December + 2005. + + [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC + 4303, December 2005. + + [RSA] Rivest, R., Shamir, A., and Adleman, L., "A Method for + Obtaining Digital Signatures and Public-Key + Cryptosystems", Communications of the ACM, v. 21, n. 2, + February 1978. + + + +Kaufman Standards Track [Page 94] + +RFC 4306 IKEv2 December 2005 + + + [SHA] NIST, "Secure Hash Standard", FIPS 180-1, National + Institute of Standards and Technology, U.S. Department of + Commerce, May 1994. + + [SIGMA] Krawczyk, H., "SIGMA: the `SIGn-and-MAc' Approach to + Authenticated Diffie-Hellman and its Use in the IKE + Protocols", in Advances in Cryptography - CRYPTO 2003 + Proceedings, LNCS 2729, Springer, 2003. Available at: + http://www.informatik.uni-trier.de/~ley/db/conf/ + crypto/crypto2003.html. + + [SKEME] Krawczyk, H., "SKEME: A Versatile Secure Key Exchange + Mechanism for Internet", from IEEE Proceedings of the 1996 + Symposium on Network and Distributed Systems Security. + + [X.501] ITU-T Recommendation X.501: Information Technology - Open + Systems Interconnection - The Directory: Models, 1993. + + [X.509] ITU-T Recommendation X.509 (1997 E): Information + Technology - Open Systems Interconnection - The Directory: + Authentication Framework, June 1997. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Kaufman Standards Track [Page 95] + +RFC 4306 IKEv2 December 2005 + + +Appendix A: Summary of changes from IKEv1 + + The goals of this revision to IKE are: + + 1) To define the entire IKE protocol in a single document, replacing + RFCs 2407, 2408, and 2409 and incorporating subsequent changes to + support NAT Traversal, Extensible Authentication, and Remote Address + acquisition; + + 2) To simplify IKE by replacing the eight different initial exchanges + with a single four-message exchange (with changes in authentication + mechanisms affecting only a single AUTH payload rather than + restructuring the entire exchange) see [PK01]; + + 3) To remove the Domain of Interpretation (DOI), Situation (SIT), and + Labeled Domain Identifier fields, and the Commit and Authentication + only bits; + + 4) To decrease IKE's latency in the common case by making the initial + exchange be 2 round trips (4 messages), and allowing the ability to + piggyback setup of a CHILD_SA on that exchange; + + 5) To replace the cryptographic syntax for protecting the IKE + messages themselves with one based closely on ESP to simplify + implementation and security analysis; + + 6) To reduce the number of possible error states by making the + protocol reliable (all messages are acknowledged) and sequenced. + This allows shortening CREATE_CHILD_SA exchanges from 3 messages to + 2; + + 7) To increase robustness by allowing the responder to not do + significant processing until it receives a message proving that the + initiator can receive messages at its claimed IP address, and not + commit any state to an exchange until the initiator can be + cryptographically authenticated; + + 8) To fix cryptographic weaknesses such as the problem with + symmetries in hashes used for authentication documented by Tero + Kivinen; + + 9) To specify Traffic Selectors in their own payloads type rather + than overloading ID payloads, and making more flexible the Traffic + Selectors that may be specified; + + 10) To specify required behavior under certain error conditions or + when data that is not understood is received, to make it easier to + make future revisions that do not break backward compatibility; + + + +Kaufman Standards Track [Page 96] + +RFC 4306 IKEv2 December 2005 + + + 11) To simplify and clarify how shared state is maintained in the + presence of network failures and Denial of Service attacks; and + + 12) To maintain existing syntax and magic numbers to the extent + possible to make it likely that implementations of IKEv1 can be + enhanced to support IKEv2 with minimum effort. + +Appendix B: Diffie-Hellman Groups + + There are two Diffie-Hellman groups defined here for use in IKE. + These groups were generated by Richard Schroeppel at the University + of Arizona. Properties of these primes are described in [Orm96]. + + The strength supplied by group one may not be sufficient for the + mandatory-to-implement encryption algorithm and is here for historic + reasons. + + Additional Diffie-Hellman groups have been defined in [ADDGROUP]. + +B.1. Group 1 - 768 Bit MODP + + This group is assigned id 1 (one). + + The prime is: 2^768 - 2 ^704 - 1 + 2^64 * { [2^638 pi] + 149686 } Its + hexadecimal value is: + + FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1 29024E08 + 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD EF9519B3 CD3A431B + 302B0A6D F25F1437 4FE1356D 6D51C245 E485B576 625E7EC6 F44C42E9 + A63A3620 FFFFFFFF FFFFFFFF + + The generator is 2. + +B.2. Group 2 - 1024 Bit MODP + + This group is assigned id 2 (two). + + The prime is 2^1024 - 2^960 - 1 + 2^64 * { [2^894 pi] + 129093 }. + Its hexadecimal value is: + + FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1 29024E08 + 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD EF9519B3 CD3A431B + 302B0A6D F25F1437 4FE1356D 6D51C245 E485B576 625E7EC6 F44C42E9 + A637ED6B 0BFF5CB6 F406B7ED EE386BFB 5A899FA5 AE9F2411 7C4B1FE6 + 49286651 ECE65381 FFFFFFFF FFFFFFFF + + The generator is 2. + + + + +Kaufman Standards Track [Page 97] + +RFC 4306 IKEv2 December 2005 + + +Editor's Address + + Charlie Kaufman + Microsoft Corporation + 1 Microsoft Way + Redmond, WA 98052 + + Phone: 1-425-707-3335 + EMail: charliek@microsoft.com + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Kaufman Standards Track [Page 98] + +RFC 4306 IKEv2 December 2005 + + +Full Copyright Statement + + Copyright (C) The Internet Society (2005). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET + ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, + INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE + INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at ietf- + ipr@ietf.org. + +Acknowledgement + + Funding for the RFC Editor function is currently provided by the + Internet Society. + + + + + + + +Kaufman Standards Track [Page 99] + diff --git a/src/charon/doc/standards/rfc4307.txt b/src/charon/doc/standards/rfc4307.txt new file mode 100644 index 000000000..5617a2551 --- /dev/null +++ b/src/charon/doc/standards/rfc4307.txt @@ -0,0 +1,339 @@ + + + + + + +Network Working Group J. Schiller +Request for Comments: 4307 Massachusetts Institute of Technology +Category: Standards Track December 2005 + + + Cryptographic Algorithms for Use in the + Internet Key Exchange Version 2 (IKEv2) + +Status of This Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (C) The Internet Society (2005). + +Abstract + + The IPsec series of protocols makes use of various cryptographic + algorithms in order to provide security services. The Internet Key + Exchange (IKE (RFC 2409) and IKEv2) provide a mechanism to negotiate + which algorithms should be used in any given association. However, + to ensure interoperability between disparate implementations, it is + necessary to specify a set of mandatory-to-implement algorithms to + ensure that there is at least one algorithm that all implementations + will have available. This document defines the current set of + algorithms that are mandatory to implement as part of IKEv2, as well + as algorithms that should be implemented because they may be promoted + to mandatory at some future time. + +1. Introduction + + The Internet Key Exchange protocol provides for the negotiation of + cryptographic algorithms between both endpoints of a cryptographic + + association. Different implementations of IPsec and IKE may provide + different algorithms. However, the IETF desires that all + implementations should have some way to interoperate. In particular, + this requires that IKE define a set of mandatory-to-implement + algorithms because IKE itself uses such algorithms as part of its own + negotiations. This requires that some set of algorithms be specified + as "mandatory-to-implement" for IKE. + + + + + +Schiller Standards Track [Page 1] + +RFC 4307 IKEv2 Cryptographic Algorithms December 2005 + + + The nature of cryptography is that new algorithms surface + continuously and existing algorithms are continuously attacked. An + algorithm believed to be strong today may be demonstrated to be weak + tomorrow. Given this, the choice of mandatory-to-implement algorithm + should be conservative so as to minimize the likelihood of it being + compromised quickly. Thought should also be given to performance + considerations as many uses of IPsec will be in environments where + performance is a concern. + + Finally, we need to recognize that the mandatory-to-implement + algorithm(s) may need to change over time to adapt to the changing + world. For this reason, the selection of mandatory-to-implement + algorithms was removed from the main IKEv2 specification and placed + in this document. As the choice of algorithm changes, only this + document should need to be updated. + + Ideally, the mandatory-to-implement algorithm of tomorrow should + already be available in most implementations of IPsec by the time it + is made mandatory. To facilitate this, we will attempt to identify + those algorithms (that are known today) in this document. There is + no guarantee that the algorithms we believe today may be mandatory in + the future will in fact become so. All algorithms known today are + subject to cryptographic attack and may be broken in the future. + +2. Requirements Terminology + + Keywords "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT", and + "MAY" that appear in this document are to be interpreted as described + in [RFC2119]. + + We define some additional terms here: + + SHOULD+ This term means the same as SHOULD. However, it is likely + that an algorithm marked as SHOULD+ will be promoted at + some future time to be a MUST. + + SHOULD- This term means the same as SHOULD. However, an algorithm + marked as SHOULD- may be deprecated to a MAY in a future + version of this document. + + MUST- This term means the same as MUST. However, we expect at + some point that this algorithm will no longer be a MUST in + a future document. Although its status will be determined + at a later time, it is reasonable to expect that if a + future revision of a document alters the status of a MUST- + algorithm, it will remain at least a SHOULD or a SHOULD-. + + + + + +Schiller Standards Track [Page 2] + +RFC 4307 IKEv2 Cryptographic Algorithms December 2005 + + +3. Algorithm Selection + +3.1. IKEv2 Algorithm Selection + +3.1.1. Encrypted Payload Algorithms + + The IKEv2 Encrypted Payload requires both a confidentiality algorithm + and an integrity algorithm. For confidentiality, implementations + MUST- implement 3DES-CBC and SHOULD+ implement AES-128-CBC. For + integrity, HMAC-SHA1 MUST be implemented. + +3.1.2. Diffie-Hellman Groups + + There are several Modular Exponential (MODP) groups that are defined + for use in IKEv2. They are defined in both the [IKEv2] base document + and in the MODP extensions document. They are identified by group + number. Any groups not listed here are considered as "MAY be + implemented". + + Group Number Bit Length Status Defined + 2 1024 MODP Group MUST- [RFC2409] + 14 2048 MODP Group SHOULD+ [RFC3526] + +3.1.3. IKEv2 Transform Type 1 Algorithms + + IKEv2 defines several possible algorithms for Transfer Type 1 + (encryption). These are defined below with their implementation + status. + + Name Number Defined In Status + RESERVED 0 + ENCR_3DES 3 [RFC2451] MUST- + ENCR_NULL 11 [RFC2410] MAY + ENCR_AES_CBC 12 [AES-CBC] SHOULD+ + ENCR_AES_CTR 13 [AES-CTR] SHOULD + +3.1.4. IKEv2 Transform Type 2 Algorithms + + Transfer Type 2 Algorithms are pseudo-random functions used to + generate random values when needed. + + Name Number Defined In Status + RESERVED 0 + PRF_HMAC_MD5 1 [RFC2104] MAY + PRF_HMAC_SHA1 2 [RFC2104] MUST + PRF_AES128_CBC 4 [AESPRF] SHOULD+ + + + + + +Schiller Standards Track [Page 3] + +RFC 4307 IKEv2 Cryptographic Algorithms December 2005 + + +3.1.5. IKEv2 Transform Type 3 Algorithms + + Transfer Type 3 Algorithms are Integrity algorithms used to protect + data against tampering. + + Name Number Defined In Status + NONE 0 + AUTH_HMAC_MD5_96 1 [RFC2403] MAY + AUTH_HMAC_SHA1_96 2 [RFC2404] MUST + AUTH_AES_XCBC_96 5 [AES-MAC] SHOULD+ + +4. Security Considerations + + The security of cryptographic-based systems depends on both the + strength of the cryptographic algorithms chosen and the strength of + the keys used with those algorithms. The security also depends on + the engineering of the protocol used by the system to ensure that + there are no non-cryptographic ways to bypass the security of the + overall system. + + This document concerns itself with the selection of cryptographic + algorithms for the use of IKEv2, specifically with the selection of + "mandatory-to-implement" algorithms. The algorithms identified in + this document as "MUST implement" or "SHOULD implement" are not known + to be broken at the current time, and cryptographic research so far + leads us to believe that they will likely remain secure into the + foreseeable future. However, this isn't necessarily forever. We + would therefore expect that new revisions of this document will be + issued from time to time that reflect the current best practice in + this area. + +5. Normative References + + [RFC2409] Harkins, D. and D. Carrel, "The Internet Key Exchange + (IKE)", RFC 2409, November 1998. + + [IKEv2] Kaufman, C., Ed., "Internet Key Exchange (IKEv2) + Protocol", RFC 4306, December 2005. + + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [RFC3526] Kivinen, T. and M. Kojo, "More Modular Exponential + (MODP) Diffie-Hellman groups for Internet Key Exchange + (IKE)", RFC 3526, May 2003. + + [RFC2451] Pereira, R. and R. Adams, "The ESP CBC-Mode Cipher + Algorithms", RFC 2451, November 1998. + + + +Schiller Standards Track [Page 4] + +RFC 4307 IKEv2 Cryptographic Algorithms December 2005 + + + [RFC2410] Glenn, R. and S. Kent, "The NULL Encryption Algorithm + and Its Use With IPsec", RFC 2410, November 1998. + + [AES-CBC] Frankel, S., Glenn, R., and S. Kelly, "The AES-CBC + Cipher Algorithm and Its Use with IPsec", RFC 3602, + September 2003. + + [AES-CTR] Housley, R., "Using Advanced Encryption Standard (AES) + Counter Mode With IPsec Encapsulating Security Payload + (ESP)", RFC 3686, January 2004. + + [RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: + Keyed-Hashing for Message Authentication", RFC 2104, + February 1997. + + [AESPRF] Hoffman, P., "The AES-XCBC-PRF-128 Algorithm for the + Internet Key Exchange Protocol (IKE)", RFC 3664, January + 2004. + + [RFC2403] Madson, C. and R. Glenn, "The Use of HMAC-MD5-96 within + ESP and AH", RFC 2403, November 1998. + + [RFC2404] Madson, C. and R. Glenn, "The Use of HMAC-SHA-1-96 + within ESP and AH", RFC 2404, November 1998. + + [AES-MAC] Frankel, S. and H. Herbert, "The AES-XCBC-MAC-96 + Algorithm and Its Use With IPsec", RFC 3566, September + 2003. + +Author's Address + + Jeffrey I. Schiller + Massachusetts Institute of Technology + Room W92-190 + 77 Massachusetts Avenue + Cambridge, MA 02139-4307 + USA + + Phone: +1 (617) 253-0161 + EMail: jis@mit.edu + + + + + + + + + + + +Schiller Standards Track [Page 5] + +RFC 4307 IKEv2 Cryptographic Algorithms December 2005 + + +Full Copyright Statement + + Copyright (C) The Internet Society (2005). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET + ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, + INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE + INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at ietf- + ipr@ietf.org. + +Acknowledgement + + Funding for the RFC Editor function is currently provided by the + Internet Society. + + + + + + + +Schiller Standards Track [Page 6] + diff --git a/src/charon/doc/standards/rfc4478.txt b/src/charon/doc/standards/rfc4478.txt new file mode 100644 index 000000000..45bf32536 --- /dev/null +++ b/src/charon/doc/standards/rfc4478.txt @@ -0,0 +1,283 @@ + + + + + + +Network Working Group Y. Nir +Request for Comments: 4478 Check Point +Category: Experimental April 2006 + + + Repeated Authentication in Internet Key Exchange (IKEv2) Protocol + +Status of This Memo + + This memo defines an Experimental Protocol for the Internet + community. It does not specify an Internet standard of any kind. + Discussion and suggestions for improvement are requested. + Distribution of this memo is unlimited. + +Copyright Notice + + Copyright (C) The Internet Society (2006). + +Abstract + + This document extends the Internet Key Exchange (IKEv2) Protocol + document [IKEv2]. With some IPsec peers, particularly in the remote + access scenario, it is desirable to repeat the mutual authentication + periodically. The purpose of this is to limit the time that security + associations (SAs) can be used by a third party who has gained + control of the IPsec peer. This document describes a mechanism to + perform this function. + +1. Introduction + + In several cases, such as the remote access scenario, policy dictates + that the mutual authentication needs to be repeated periodically. + Repeated authentication can usually be achieved by simply repeating + the Initial exchange by whichever side has a stricter policy. + + However, in the remote access scenario it is usually up to a human + user to supply the authentication credentials, and often Extensible + Authentication Protocol (EAP) is used for authentication, which makes + it unreasonable or impossible for the remote access gateway to + initiate the IKEv2 exchange. + + This document describes a new notification that the original + Responder can send to the original Initiator with the number of + seconds before the authentication needs to be repeated. The + Initiator SHOULD repeat the Initial exchange before that time is + expired. If the Initiator fails to do so, the Responder may close + all Security Associations. + + + + +Nir Experimental [Page 1] + +RFC 4478 Repeated Authentication in IKEv2 April 2006 + + + Repeated authentication is not the same as IKE SA rekeying, and need + not be tied to it. The key words "MUST", "MUST NOT", "SHOULD", + "SHOULD NOT", and "MAY" in this document are to be interpreted as + described in [RFC2119]. + +2. Authentication Lifetime + + The Responder in an IKEv2 negotiation MAY be configured to limit the + time that an IKE SA and the associated IPsec SAs may be used before + the peer is required to repeat the authentication, through a new + Initial Exchange. + + The Responder MUST send this information to the Initiator in an + AUTH_LIFETIME notification either in the last message of an IKE_AUTH + exchange, or in an INFORMATIONAL request, which may be sent at any + time. + + When sent as part of the IKE SA setup, the AUTH_LIFETIME notification + is used as follows: + + Initiator Responder + ------------------------------- ----------------------------- + HDR, SAi1, KEi, Ni --> + <-- HDR, SAr1, KEr, Nr, [CERTREQ] + HDR, SK {IDi, [CERT,] [CERTREQ,] + [IDr,] AUTH, SAi2, TSi, TSr} --> + <-- HDR, SK {IDr, [CERT,] AUTH, + SAr2, TSi, TSr, + N(AUTH_LIFETIME)} + + The separate Informational exchange is formed as follows: + + <-- HDR, SK {N(AUTH_LIFETIME)} + HDR SK {} --> + + The AUTH_LIFETIME notification is described in Section 3. + + The original Responder that sends the AUTH_LIFETIME notification + SHOULD send a DELETE notification soon after the end of the lifetime + period, unless the IKE SA is deleted before the lifetime period + elapses. If the IKE SA is rekeyed, then the time limit applies to + the new SA. + + An Initiator that received an AUTH_LIFETIME notification SHOULD + repeat the Initial exchange within the time indicated in the + notification. The time is measured from the time that the original + Initiator receives the notification. + + + + +Nir Experimental [Page 2] + +RFC 4478 Repeated Authentication in IKEv2 April 2006 + + + A special case is where the notification is sent in an Informational + exchange, and the lifetime is zero. In that case, the original + responder SHOULD allow a reasonable time for the repeated + authentication to occur. + + The AUTH_LIFETIME notification MUST be protected and MAY be sent by + the original Responder at any time. If the policy changes, the + original Responder MAY send it again in a new Informational. + + The new Initial exchange is not altered. The initiator SHOULD delete + the old IKE SA within a reasonable time of the new Auth exchange. + +3. AUTH_LIFETIME Notification + + The AUTH_LIFETIME message is a notification payload formatted as + follows: + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Next Payload !C! RESERVED ! Payload Length ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Protocol ID ! SPI Size ! Notify Message Type ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + ! Lifetime ! + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + o Payload Length is 12. + o Protocol ID (1 octet) MUST be 0. + o SPI size is 0 (SPI is in message header). + o Notify Message type is 16403 by IANA. + o Lifetime is the amount of time (in seconds) left before the + peer should repeat the Initial exchange. A zero value + signifies that the Initial exchange should begin immediately. + It is usually not reasonable to set this value to less than 300 + (5 minutes) since that is too cumbersome for a user. + It is also usually not reasonable to set this value to more + than 86400 (1 day) as that would negate the security benefit of + repeating the authentication. + +4. Interoperability with Non-Supporting IKEv2 Implementations + + IKEv2 implementations that do not support the AUTH_LIFETIME + notification will ignore it and will not repeat the authentication. + In that case the original Responder will send a Delete notification + for the IKE SA in an Informational exchange. Such implementations + may be configured manually to repeat the authentication periodically. + + + + +Nir Experimental [Page 3] + +RFC 4478 Repeated Authentication in IKEv2 April 2006 + + + Non-supporting Responders are not a problem because they will simply + not send these notifications. In that case, there is no requirement + that the original Initiator re-authenticate. + +5. Security Considerations + + The AUTH_LIFETIME notification sent by the Responder does not + override any security policy on the Initiator. In particular, the + Initiator may have a different policy regarding re-authentication, + requiring more frequent re-authentication. Such an Initiator can + repeat the authentication earlier then is required by the + notification. + + An Initiator MAY set reasonable limits on the amount of time in the + AUTH_LIFETIME notification. For example, an authentication lifetime + of less than 300 seconds from SA initiation may be considered + unreasonable. + +6. IANA Considerations + + The IANA has assigned a notification payload type for the + AUTH_LIFETIME notifications from the IKEv2 Notify Message Types + registry. + +7. Normative References + + [IKEv2] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", RFC + 4306, December 2005. + + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + +Author's Address + + Yoav Nir + Check Point Software Technologies + + EMail: ynir@checkpoint.com + + + + + + + + + + + + + +Nir Experimental [Page 4] + +RFC 4478 Repeated Authentication in IKEv2 April 2006 + + +Full Copyright Statement + + Copyright (C) The Internet Society (2006). + + This document is subject to the rights, licenses and restrictions + contained in BCP 78, and except as set forth therein, the authors + retain all their rights. + + This document and the information contained herein are provided on an + "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS + OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET + ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, + INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE + INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. Information + on the procedures with respect to rights in RFC documents can be + found in BCP 78 and BCP 79. + + Copies of IPR disclosures made to the IETF Secretariat and any + assurances of licenses to be made available, or the result of an + attempt made to obtain a general license or permission for the use of + such proprietary rights by implementers or users of this + specification can be obtained from the IETF on-line IPR repository at + http://www.ietf.org/ipr. + + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at + ietf-ipr@ietf.org. + +Acknowledgement + + Funding for the RFC Editor function is provided by the IETF + Administrative Support Activity (IASA). + + + + + + + +Nir Experimental [Page 5] + |