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| author | Martin Willi <martin@strongswan.org> | 2008-12-05 09:41:20 +0000 |
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| committer | Martin Willi <martin@strongswan.org> | 2008-12-05 09:41:20 +0000 |
| commit | a6d7a6107cf18cc892381b4770bbd7119486c6ef (patch) | |
| tree | 340c3dfd7341778abb126175ba794b0ed223cc4a /doc | |
| parent | 876d5c63a31258a99afd5652deb5e4a2a13c3aea (diff) | |
| download | strongswan-a6d7a6107cf18cc892381b4770bbd7119486c6ef.tar.bz2 strongswan-a6d7a6107cf18cc892381b4770bbd7119486c6ef.tar.xz | |
added actual ikev2bis draft
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diff --git a/doc/standards/draft-ietf-ipsecme-ikev2bis-01.txt b/doc/standards/draft-ietf-ipsecme-ikev2bis-01.txt new file mode 100644 index 000000000..5751593f4 --- /dev/null +++ b/doc/standards/draft-ietf-ipsecme-ikev2bis-01.txt @@ -0,0 +1,7504 @@ + + + +Network Working Group C. Kaufman +Internet-Draft Microsoft +Obsoletes: 4306, 4718 P. Hoffman +(if approved) VPN Consortium +Intended status: Standards Track Y. Nir +Expires: May 3, 2009 Check Point + P. Eronen + Nokia + October 30, 2008 + + + Internet Key Exchange Protocol: IKEv2 + draft-ietf-ipsecme-ikev2bis-01 + +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 May 3, 2009. + +Copyright Notice + + Copyright (C) The IETF Trust (2008). + +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 + + + +Kaufman, et al. Expires May 3, 2009 [Page 1] + +Internet-Draft IKEv2bis October 2008 + + + (SAs). It replaces and updates RFC 4306, and includes all of the + clarifications from RFC 4718. + + +Table of Contents + + 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5 + 1.1. Usage Scenarios . . . . . . . . . . . . . . . . . . . . . 6 + 1.1.1. Security Gateway to Security Gateway Tunnel Mode . . 6 + 1.1.2. Endpoint-to-Endpoint Transport Mode . . . . . . . . . 7 + 1.1.3. Endpoint to Security Gateway Tunnel Mode . . . . . . 8 + 1.1.4. Other Scenarios . . . . . . . . . . . . . . . . . . . 8 + 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 . . . . . . . . . . . . . . . . . . . . . . 15 + 1.4. The INFORMATIONAL Exchange . . . . . . . . . . . . . . . 16 + 1.4.1. Deleting an SA with INFORMATIONAL Exchanges . . . . . 16 + 1.5. Informational Messages outside of an IKE SA . . . . . . . 17 + 1.6. Requirements Terminology . . . . . . . . . . . . . . . . 18 + 1.7. Differences Between RFC 4306 and This Document . . . . . 18 + 2. IKE Protocol Details and Variations . . . . . . . . . . . . . 20 + 2.1. Use of Retransmission Timers . . . . . . . . . . . . . . 21 + 2.2. Use of Sequence Numbers for Message ID . . . . . . . . . 22 + 2.3. Window Size for Overlapping Requests . . . . . . . . . . 22 + 2.4. State Synchronization and Connection Timeouts . . . . . . 24 + 2.5. Version Numbers and Forward Compatibility . . . . . . . . 26 + 2.6. IKE SA SPIs and Cookies . . . . . . . . . . . . . . . . . 28 + 2.6.1. Interaction of COOKIE and INVALID_KE_PAYLOAD . . . . 30 + 2.7. Cryptographic Algorithm Negotiation . . . . . . . . . . . 31 + 2.8. Rekeying . . . . . . . . . . . . . . . . . . . . . . . . 32 + 2.8.1. Simultaneous Child SA rekeying . . . . . . . . . . . 34 + 2.8.2. Rekeying the IKE SA Versus Reauthentication . . . . . 36 + 2.9. Traffic Selector Negotiation . . . . . . . . . . . . . . 37 + 2.9.1. Traffic Selectors Violating Own Policy . . . . . . . 40 + 2.10. Nonces . . . . . . . . . . . . . . . . . . . . . . . . . 40 + 2.11. Address and Port Agility . . . . . . . . . . . . . . . . 41 + 2.12. Reuse of Diffie-Hellman Exponentials . . . . . . . . . . 41 + 2.13. Generating Keying Material . . . . . . . . . . . . . . . 42 + 2.14. Generating Keying Material for the IKE SA . . . . . . . . 43 + 2.15. Authentication of the IKE SA . . . . . . . . . . . . . . 44 + 2.16. Extensible Authentication Protocol Methods . . . . . . . 46 + 2.17. Generating Keying Material for Child SAs . . . . . . . . 48 + 2.18. Rekeying IKE SAs Using a CREATE_CHILD_SA Exchange . . . . 49 + 2.19. Requesting an Internal Address on a Remote Network . . . 50 + + + +Kaufman, et al. Expires May 3, 2009 [Page 2] + +Internet-Draft IKEv2bis October 2008 + + + 2.19.1. Configuration Payloads . . . . . . . . . . . . . . . 51 + 2.20. Requesting the Peer's Version . . . . . . . . . . . . . . 53 + 2.21. Error Handling . . . . . . . . . . . . . . . . . . . . . 53 + 2.22. IPComp . . . . . . . . . . . . . . . . . . . . . . . . . 54 + 2.23. NAT Traversal . . . . . . . . . . . . . . . . . . . . . . 55 + 2.24. Explicit Congestion Notification (ECN) . . . . . . . . . 59 + 3. Header and Payload Formats . . . . . . . . . . . . . . . . . 59 + 3.1. The IKE Header . . . . . . . . . . . . . . . . . . . . . 59 + 3.2. Generic Payload Header . . . . . . . . . . . . . . . . . 62 + 3.3. Security Association Payload . . . . . . . . . . . . . . 64 + 3.3.1. Proposal Substructure . . . . . . . . . . . . . . . . 66 + 3.3.2. Transform Substructure . . . . . . . . . . . . . . . 68 + 3.3.3. Valid Transform Types by Protocol . . . . . . . . . . 71 + 3.3.4. Mandatory Transform IDs . . . . . . . . . . . . . . . 71 + 3.3.5. Transform Attributes . . . . . . . . . . . . . . . . 72 + 3.3.6. Attribute Negotiation . . . . . . . . . . . . . . . . 74 + 3.4. Key Exchange Payload . . . . . . . . . . . . . . . . . . 75 + 3.5. Identification Payloads . . . . . . . . . . . . . . . . . 75 + 3.6. Certificate Payload . . . . . . . . . . . . . . . . . . . 78 + 3.7. Certificate Request Payload . . . . . . . . . . . . . . . 80 + 3.8. Authentication Payload . . . . . . . . . . . . . . . . . 82 + 3.9. Nonce Payload . . . . . . . . . . . . . . . . . . . . . . 83 + 3.10. Notify Payload . . . . . . . . . . . . . . . . . . . . . 84 + 3.10.1. Notify Message Types . . . . . . . . . . . . . . . . 85 + 3.11. Delete Payload . . . . . . . . . . . . . . . . . . . . . 88 + 3.12. Vendor ID Payload . . . . . . . . . . . . . . . . . . . . 90 + 3.13. Traffic Selector Payload . . . . . . . . . . . . . . . . 91 + 3.13.1. Traffic Selector . . . . . . . . . . . . . . . . . . 92 + 3.14. Encrypted Payload . . . . . . . . . . . . . . . . . . . . 94 + 3.15. Configuration Payload . . . . . . . . . . . . . . . . . . 96 + 3.15.1. Configuration Attributes . . . . . . . . . . . . . . 97 + 3.15.2. Meaning of INTERNAL_IP4_SUBNET/INTERNAL_IP6_SUBNET . 100 + 3.15.3. Configuration payloads for IPv6 . . . . . . . . . . . 102 + 3.15.4. Address Assignment Failures . . . . . . . . . . . . . 103 + 3.16. Extensible Authentication Protocol (EAP) Payload . . . . 103 + 4. Conformance Requirements . . . . . . . . . . . . . . . . . . 105 + 5. Security Considerations . . . . . . . . . . . . . . . . . . . 107 + 5.1. Traffic selector authorization . . . . . . . . . . . . . 109 + 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 111 + 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 111 + 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 111 + 8.1. Normative References . . . . . . . . . . . . . . . . . . 111 + 8.2. Informative References . . . . . . . . . . . . . . . . . 113 + Appendix A. Summary of changes from IKEv1 . . . . . . . . . . . 117 + Appendix B. Diffie-Hellman Groups . . . . . . . . . . . . . . . 118 + B.1. Group 1 - 768 Bit MODP . . . . . . . . . . . . . . . . . 118 + B.2. Group 2 - 1024 Bit MODP . . . . . . . . . . . . . . . . . 118 + Appendix C. Exchanges and Payloads . . . . . . . . . . . . . . . 119 + + + +Kaufman, et al. Expires May 3, 2009 [Page 3] + +Internet-Draft IKEv2bis October 2008 + + + C.1. IKE_SA_INIT Exchange . . . . . . . . . . . . . . . . . . 119 + C.2. IKE_AUTH Exchange without EAP . . . . . . . . . . . . . . 120 + C.3. IKE_AUTH Exchange with EAP . . . . . . . . . . . . . . . 121 + C.4. CREATE_CHILD_SA Exchange for Creating or Rekeying + Child SAs . . . . . . . . . . . . . . . . . . . . . . . . 122 + C.5. CREATE_CHILD_SA Exchange for Rekeying the IKE SA . . . . 122 + C.6. INFORMATIONAL Exchange . . . . . . . . . . . . . . . . . 122 + Appendix D. Changes Between Internet Draft Versions . . . . . . 122 + D.1. Changes from IKEv2 to draft -00 . . . . . . . . . . . . . 123 + D.2. Changes from draft -00 to draft -01 . . . . . . . . . . . 123 + D.3. Changes from draft -00 to draft -01 . . . . . . . . . . . 125 + D.4. Changes from draft -01 to draft -02 . . . . . . . . . . . 126 + D.5. Changes from draft -02 to draft -03 . . . . . . . . . . . 127 + D.6. Changes from draft -03 to + draft-ietf-ipsecme-ikev2bis-00 . . . . . . . . . . . . . 128 + D.7. Changes from draft-ietf-ipsecme-ikev2bis-00 to + draft-ietf-ipsecme-ikev2bis-01 . . . . . . . . . . . . . 129 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 133 + Intellectual Property and Copyright Statements . . . . . . . . . 134 + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Kaufman, et al. Expires May 3, 2009 [Page 4] + +Internet-Draft IKEv2bis October 2008 + + +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 RFC 4306. }} + + 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 replaced all of those RFCs. + IKEv2 was defined in [IKEV2] (RFC 4306) and was clarified in [Clarif] + (RFC 4718). This document replaces and updates RFC 4306 and RFC + 4718. + + 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] 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) [IP-COMP] in connection with an ESP or AH SA. + The SAs for ESP 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 + + + +Kaufman, et al. Expires May 3, 2009 [Page 5] + +Internet-Draft IKEv2bis October 2008 + + + 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 or ESP Child SA + (unless there is failure setting up the AH or ESP Child SA, in which + case the IKE SA is still established without IPsec 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 or AH SAs in a number of + different scenarios, each with its own special requirements. + +1.1.1. Security Gateway to Security Gateway Tunnel Mode + + +-+-+-+-+-+ +-+-+-+-+-+ + | | IPsec | | + Protected |Tunnel | tunnel |Tunnel | Protected + Subnet <-->|Endpoint |<---------->|Endpoint |<--> Subnet + | | | | + +-+-+-+-+-+ +-+-+-+-+-+ + + Figure 1: Security Gateway to Security Gateway Tunnel + + + +Kaufman, et al. Expires May 3, 2009 [Page 6] + +Internet-Draft IKEv2bis October 2008 + + + 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 Mode + + +-+-+-+-+-+ +-+-+-+-+-+ + | | 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. 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 + 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). + + + + + + + + + + + + +Kaufman, et al. Expires May 3, 2009 [Page 7] + +Internet-Draft IKEv2bis October 2008 + + +1.1.3. Endpoint to Security Gateway Tunnel Mode + + +-+-+-+-+-+ +-+-+-+-+-+ + | | 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. + +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 + + + +Kaufman, et al. Expires May 3, 2009 [Page 8] + +Internet-Draft IKEv2bis October 2008 + + + 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. (See Section 2.14 for information on + how the encyrption keys are generated.) + + All messages following the initial exchange are cryptographically + protected using the cryptographic algorithms and keys negotiated in + the the IKE_SA_INIT exchange. These subsequent messages use the + syntax of the Encrypted Payload described in Section 3.14, encrypted + with keys that are derived as described in Section 2.14. All + subsequent messages include an Encrypted Payload, even if they are + referred to in the text as "empty". For the CREATE_CHILD_SA, + IKE_AUTH, or IKE_INFORMATIONAL exchanges, 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. + + In the following descriptions, the payloads contained in the message + are indicated by names as listed below. + + + + + + + + + + +Kaufman, et al. Expires May 3, 2009 [Page 9] + +Internet-Draft IKEv2bis October 2008 + + + 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. + + 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. The messages that + follow are encrypted and integrity protected in their entirety, with + the exception of the message headers. The keys used for the + + + +Kaufman, et al. Expires May 3, 2009 [Page 10] + +Internet-Draft IKEv2bis October 2008 + + + 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. If the IDr proposed by the + initiator is not acceptable to the responder, the responder might use + some other IDr to finish the exchange. If the initiator then does + not accept that fact that responder used different IDr than the one + that was requested, the initiator can close the SA after noticing the + fact. + + 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. + + + +Kaufman, et al. Expires May 3, 2009 [Page 11] + +Internet-Draft IKEv2bis October 2008 + + + {{ 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 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 payloads in the IKE_AUTH exchange + cannot contain Transform Type 4 (Diffie-Hellman Group) with any value + other than NONE. Implementations SHOULD omit the whole transform + substructure instead of sending value NONE. + +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, encrypted with keys that are derived as described in + Section 2.14. 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. + + + + +Kaufman, et al. Expires May 3, 2009 [Page 12] + +Internet-Draft IKEv2bis October 2008 + + + 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). + + 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 selects a proposal using a + different Diffie-Hellman group (other than NONE), the responder MUST + reject the request and indicate its preferred Diffie-Hellman group in + the INVALID_KE_PAYLOAD Notification payload. {{ 3.10.1-17 }} There + are two octets of data associated with this notification: the + accepted D-H Group number in big endian order. 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. + + {{ 3.10.1-35 }} The responder sends a NO_ADDITIONAL_SAS notification + to indicate 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. + +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} + + + +Kaufman, et al. Expires May 3, 2009 [Page 13] + +Internet-Draft IKEv2bis October 2008 + + + 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. + + {{ 3.10.1-16391 }} The USE_TRANSPORT_MODE 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. + + {{ 3.10.1-16394 }} The ESP_TFC_PADDING_NOT_SUPPORTED notification + asserts that the sending endpoint will NOT accept packets that + contain Traffic Flow Confidentiality (TFC) padding over the Child SA + being negotiated. {{ Clarif-4.5 }} If neither endpoint accepts TFC + padding, this notification is included in both the request and the + response. If this notification is included in only one of the + messages, TFC padding can still be sent in the other direction. + + {{ 3.10.1-16395 }} The NON_FIRST_FRAGMENTS_ALSO notification is used + for fragmentation control. See [IPSECARCH] for a fuller explanation. + {{ Clarif-4.6 }} Both parties need to agree to sending non-first + fragments before either party does so. It 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 responder does + not want to send or receive non-first fragments, it only omits + NON_FIRST_FRAGMENTS_ALSO notification from its response, but does not + reject the whole Child SA creation. + +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. The KEi + + + +Kaufman, et al. Expires May 3, 2009 [Page 14] + +Internet-Draft IKEv2bis October 2008 + + + payload SHOULD be included. New initiator and responder SPIs are + supplied in the SPI fields of the SA 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, 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. + +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. + + {{ 3.10.1-16393 }} The REKEY_SA 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. {{ Clarif-5.4 }} The SA being rekeyed is + identified by the SPI field in the Notify payload; this is the SPI + the exchange initiator would expect in inbound ESP or AH packets. + There is no data associated with this Notify type. The Protocol ID + field of the REKEY_SA notification is set to match the protocol of + the SA we are rekeying, for example, 3 for ESP and 2 for AH. + + The CREATE_CHILD_SA response for rekeying a 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. + + + + +Kaufman, et al. Expires May 3, 2009 [Page 15] + +Internet-Draft IKEv2bis October 2008 + + + 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 rekeyed). + + 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. + + 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. + +1.4.1. Deleting an SA with INFORMATIONAL Exchanges + + {{ 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). 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 + + + +Kaufman, et al. Expires May 3, 2009 [Page 16] + +Internet-Draft IKEv2bis October 2008 + + + 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, one includes delete + payloads for the inbound half of each SA pair 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 + 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 ESP or AH 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. + +1.5. Informational Messages outside of an IKE SA + + If an encrypted IKE request 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. + + {{ 3.10.1-11 }} The INVALID_SPI notification 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 + + + +Kaufman, et al. Expires May 3, 2009 [Page 17] + +Internet-Draft IKEv2bis October 2008 + + + 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). + + {{ 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 is copied. The Response + bit is set to 1, and the version flags are set in the normal fashion. + + 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. The Initiator flag + is set, the Response bit is set to 0, and the version flags are set + in the normal fashion. + +1.6. Requirements Terminology + + 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. + + Keywords "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT" and + "MAY" that appear in this document are to be interpreted as described + in [MUSTSHOULD]. + +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 + + + +Kaufman, et al. Expires May 3, 2009 [Page 18] + +Internet-Draft IKEv2bis October 2008 + + + 4306. That is, the version number is *not* changed from RFC 4306. + + This document makes 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 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 3.10.1. This leads to + implementers not having all the needed information in the main body + of the document. Much of the material from those tables has been + moved into the associated parts of the main body of the document. + + 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 }}". Changes that come from moving + descriptive text out of the tables in Section 3.10.1 are marked with + that number and the message type that contained the text, such as "{{ + 3.10.1-16384 }}". + + This document removes discussion of nesting AH and ESP. This was a + mistake in RFC 4306 caused by the lag between finishing RFC 4306 and + RFC 4301. Basically, IKEv2 is based on RFC 4301, which does not + include "SA bundles" that were part of RFC 2401. 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. + + This document removes discussion of the INTERNAL_ADDRESS_EXPIRY + configuration attribute because its implementation was very + problematic. Implementations that conform to this document MUST + ignore proposals that have configuration attribute type 5, the old + value for INTERNAL_ADDRESS_EXPIRY. + + This document adds the restriction in Section 2.13 that all PRFs used + with IKEv2 MUST take variable-sized keys. This should not affect any + implementations because there were no standardized PRFs that have + fixed-size keys. + + A later version of this document may have all the {{ }} comments + + + +Kaufman, et al. Expires May 3, 2009 [Page 19] + +Internet-Draft IKEv2bis October 2008 + + + 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 octets long, and they SHOULD be able + to send, receive, and process messages that are up to 3000 octets + 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. + + {{ Clarif-7.5 }} The UDP payload of all packets containing IKE + messages sent on port 4500 MUST begin with the prefix of four zeros; + otherwise, the receiver won't know how to handle them. + + + + + + +Kaufman, et al. Expires May 3, 2009 [Page 20] + +Internet-Draft IKEv2bis October 2008 + + +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 or equal to 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. A retransmission from the initiator + MUST be bitwise identical to the original request. That is, + everything starting from the IKE Header (the IKE SA Initiator's SPI + onwards) must be bitwise identical; items before it (such as the IP + and UDP headers, and the zero non-ESP marker) do not have to be + identical. + + {{ Clarif-2.3 }} Retransmissions of the IKE_SA_INIT request require + some special handling. When a responder receives an IKE_SA_INIT + request, it has to determine whether the packet is 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 belongs to an existing IKE SA where the IKE_AUTH request has + been already received (in which case the responder ignores it). + + It is not sufficient to use the initiator's SPI and/or IP address to + differentiate between these three 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. + + + + +Kaufman, et al. Expires May 3, 2009 [Page 21] + +Internet-Draft IKEv2bis October 2008 + + +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 + IKE_SA_INIT messages (including retries of the message due to + responses such as COOKIE and INVALID_KE_PAYLOAD {{ Clarif-2.2 }}), + and incremented for each subsequent exchange. Rekeying an IKE SA + resets the sequence numbers. Thus, the first pair of IKE_AUTH + messages will have ID of 1, the second (when EAP is used) will be 2, + and so on. {{ Clarif-3.10 }} + + 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-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 "original responder" starts rekeying the IKE SA, that party + becomes the "original initiator" of the new IKE SA. + + 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 or rekeyed. + +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 + + + +Kaufman, et al. Expires May 3, 2009 [Page 22] + +Internet-Draft IKEv2bis October 2008 + + + 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. {{ Downgraded the SHOULD }} An IKE endpoint may also + accept and process multiple requests while it has a request + outstanding. + + {{ 3.10.1-16385 }} The SET_WINDOW_SIZE 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. The window size is always one until the initial + exchanges complete. + + 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 + + + +Kaufman, et al. Expires May 3, 2009 [Page 23] + +Internet-Draft IKEv2bis October 2008 + + + 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. + + {{ 3.10.1-9 }}The INVALID_MESSAGE_ID notification is 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. + +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. + + {{ 3.10.1-16384 }} The INITIAL_CONTACT 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; however, receiving parties need to deal with it + in other requests. + + 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 + + + +Kaufman, et al. Expires May 3, 2009 [Page 24] + +Internet-Draft IKEv2bis October 2008 + + + 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 + (fresh, i.e. not retransmitted) 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. + (This is sometimes called "dead peer detection" or "DPD", although it + is really detecting live peers, not dead ones.) 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 + + + +Kaufman, et al. Expires May 3, 2009 [Page 25] + +Internet-Draft IKEv2bis October 2008 + + + 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 replacement for + [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. + + {{ 3.10.1-5 }} If an endpoint receives a message with a higher major + version number, it MUST drop the message and SHOULD send an + unauthenticated notification message of type INVALID_MAJOR_VERSION + containing the highest (closest) 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 + + + +Kaufman, et al. Expires May 3, 2009 [Page 26] + +Internet-Draft IKEv2bis October 2008 + + + 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 a 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, and their + content MUST be ignored by an implementation running version 2.0 ("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. {{ 3.10.1-1 }} In that + Notify payload, the notification data contains the one-octet payload + type. If the critical flag is not set and the payload type is + unsupported, that payload MUST be ignored. Payloads sent in IKE + response messages MUST NOT have the critical flag set. Note that the + critical flag applies only to the payload type, not the contents. If + the payload type is recognized, but the payload contains something + which is not (such as an unknown transform inside an SA payload, or + an unknown Notify Message Type inside a Notify payload), the critical + flag is ignored. + + {{ Demoted the SHOULD in the second clause }}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; implementations are explicitly allowed to + reject as invalid a message with those payloads in any other order. + + + + +Kaufman, et al. Expires May 3, 2009 [Page 27] + +Internet-Draft IKEv2bis October 2008 + + +2.6. IKE SA SPIs and 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, although 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 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. + + Incoming IKE packets are mapped to an IKE SA only using the packet's + SPI, not using (for example) the source IP address of the packet. + + 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. + + When a responder detects a large number of half-open IKE SAs, it + SHOULD reply to IKE_SA_INIT requests with a response containing the + COOKIE notification. {{ 3.10.1-16390 }} The data associated with this + notification MUST be between 1 and 64 octets in length (inclusive), + and its generation is described later in this section. If the + IKE_SA_INIT response includes the COOKIE notification, the initiator + MUST then retry the IKE_SA_INIT request, and include the COOKIE + notification containing the received data as the first payload, and + all other payloads unchanged. The initial exchange will then be as + follows: + + + + +Kaufman, et al. Expires May 3, 2009 [Page 28] + +Internet-Draft IKEv2bis October 2008 + + + 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. + + {{ Demoted the SHOULD }} An IKE implementation can 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 + + + +Kaufman, et al. Expires May 3, 2009 [Page 29] + +Internet-Draft IKEv2bis October 2008 + + + 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. The initiator should limit the number of + cookie exchanges it tries before giving up. An attacker can forge + multiple cookie responses to the initiator's IKE_SA_INIT message, and + each of those forged cookie reply will trigger two packets: one + packet from the initiator to the responder (which will reject those + cookies), and one reply from responder to initiator that includes the + correct 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 + calculation, it will reject the request by sending a new cookie. + + + +Kaufman, et al. Expires May 3, 2009 [Page 30] + +Internet-Draft IKEv2bis October 2008 + + + 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 + + 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, or AH) for the SA as well as + cryptographic algorithms associated with each protocol. + + An SA payload consists of one or more proposals. {{ Clarif-7.13 }} + Each proposal includes one protocol. 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: + + {{ Clarif-7.13 }} Each proposal contains one protocol. If a proposal + is accepted, the SA response MUST contain the same protocol. The + responder MUST accept a single proposal or reject them all and return + an error. {{ 3.10.1-14 }} The error is given in a notification of + type NO_PROPOSAL_CHOSEN. + + 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. + + + +Kaufman, et al. Expires May 3, 2009 [Page 31] + +Internet-Draft IKEv2bis October 2008 + + + If an initiator proposes both normal ciphers with integrity + protection as well as combined-mode ciphers, then two proposals are + needed. One of the proposals includes the normal ciphers with the + integrity algoritms for them, and the other proposal includes all the + combined mode ciphers without the integrity algorithms (because + combined mode ciphers are not allowed to have any integrity algorithm + other than "none"). + + 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. + + {{ Clarif-2.1 }} When the IKE_SA_INIT exchange does not result in the + creation of an IKE SA due to INVALID_KE_PAYLOAD, NO_PROPOSAL_CHOSEN, + or COOKIE (see Section 2.6), the responder's SPI will be zero. + However, if the responder sends a non-zero responder SPI, the + initiator should not reject the response for only that reason. + +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, + + + +Kaufman, et al. Expires May 3, 2009 [Page 32] + +Internet-Draft IKEv2bis October 2008 + + + 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, and the new IKE SA is used for all control messages needed to + maintain those Child SAs. The old IKE SA is then deleted, and the + Delete payload to delete itself MUST be the last request sent over + the old IKE SA. Note that, when rekeying, the new Child SA MAY have + different traffic selectors and algorithms than the old one. + + {{ 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 + 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 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 + + + +Kaufman, et al. Expires May 3, 2009 [Page 33] + +Internet-Draft IKEv2bis October 2008 + + + 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 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 + 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. + +2.8.1. 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 + + + +Kaufman, et al. Expires May 3, 2009 [Page 34] + +Internet-Draft IKEv2bis October 2008 + + + 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 <-- + + 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 resp3: 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 May 3, 2009 [Page 35] + +Internet-Draft IKEv2bis October 2008 + + + 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 May 3, 2009 [Page 36] + +Internet-Draft IKEv2bis October 2008 + + + 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 are extensions + that add this functionality such as [REAUTH]. + +2.9. Traffic Selector Negotiation + + {{ Clarif-7.2 }} When an RFC4301-compliant IPsec subsystem receives + an IP packet that 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, although it only applies to IKEv1), 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. + + 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) + + + +Kaufman, et al. Expires May 3, 2009 [Page 37] + +Internet-Draft IKEv2bis October 2008 + + + the responder of the Child SA pair. For example, if the original + initiator requests 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.) + + 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. + + When the responder chooses a subset of the traffic proposed by the + initiator, it narrows the traffic selectors to some subset of the + initiator's proposal (provided the set does not become the null set). + If the type of traffic selector proposed is unknown, the responder + ignores that traffic selector, so that the unknown type is not be + returned in the narrowed set. + + 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 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 can be ranges rather than + specific values. + + The responder performs the narrowing as follows: {{ Clarif-4.10 }} + + + + + +Kaufman, et al. Expires May 3, 2009 [Page 38] + +Internet-Draft IKEv2bis October 2008 + + + o If the responder's policy does not allow it to accept any part of + the proposed traffic selectors, it responds with TS_UNACCEPTABLE. + + o If the responder's policy allows the entire set of traffic covered + by TSi and TSr, no narrowing is necessary, and the responder can + return the same TSi and TSr values. + + o If the responder's policy allows it 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 above, the responder might respond with TSi being + (192.0.1.43 - 192.0.1.43) with all ports and IP protocols. + + o If the responder's policy does not allow it to accept the first + selector of TSi and TSr, the responder narrows to an acceptable + subset of TSi and TSr. + + When narrowing is done, there may be several subsets that are + acceptable but their union is not. In this case, the responder + arbitrarily chooses one of them, and MAY include an + ADDITIONAL_TS_POSSIBLE notification in the response. {{ 3.10.1-16386 + }} The ADDITIONAL_TS_POSSIBLE notification asserts that the responder + narrowed the proposed traffic selectors but that other traffic + selectors would also have been acceptable, though only in a separate + SA. There is no data associated with this Notify type. 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. + + 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. + + {{ 3.10.1-34 }} The SINGLE_PAIR_REQUIRED 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 + + + +Kaufman, et al. Expires May 3, 2009 [Page 39] + +Internet-Draft IKEv2bis October 2008 + + + for only the specific traffic it is trying to forward. + + {{ Clarif-4.11 }} Few implementations will have policies that require + separate SAs for each address pair. Because of this, if only some + parts of the TSi and TSr proposed by the initiator are acceptable to + the responder, responders SHOULD narrow the selectors to an + acceptable subset rather than use SINGLE_PAIR_REQUIRED. + +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. If you use decorrelated + policies from [IPSECARCH], this kind of policy violations cannot + happen. + + 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 (192.0.1.0-192.0.1.255), 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'. + +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- + + + +Kaufman, et al. Expires May 3, 2009 [Page 40] + +Internet-Draft IKEv2bis October 2008 + + + 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. + + 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 + + + +Kaufman, et al. Expires May 3, 2009 [Page 41] + +Internet-Draft IKEv2bis October 2008 + + + 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 (see Section 3.3.5 for + the defintion of the Key Length transform attribute). 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. + + It is assumed that pseudo-random functions (PRFs) accept keys of any + length, but have a preferred key size. The preferred key size is + used as the length of SK_d, SK_pi, and SK_pr (see Section 2.14). For + PRFs based on the HMAC construction, the preferred key size is equal + to the length of the output of the underlying hash function. Other + types of PRFs MUST specify their preferred key size. + + 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) + + + + +Kaufman, et al. Expires May 3, 2009 [Page 42] + +Internet-Draft IKEv2bis October 2008 + + + 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. The lengths of SK_d, SK_pi, + and SK_pr are the preferred key length of the agreed-to PRF. + + 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. For + historical backwards-compatibility reasons, there are two PRFs that + are treated specially in this calculation. If the negotiated PRF is + + + +Kaufman, et al. Expires May 3, 2009 [Page 43] + +Internet-Draft IKEv2bis October 2008 + + + AES-XCBC-PRF-128 [RFC4434] or AES-CMAC-PRF-128 [RFC4615], only the + first 64 bits of Ni and the first 64 bits of Nr are used in the + calculation. + + 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. + +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 (IKE_SA_INIT response) 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 (IKE_SA_INIT request), 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) + + The responder's signed octets can be described as: + + + + + + + +Kaufman, et al. Expires May 3, 2009 [Page 44] + +Internet-Draft IKEv2bis October 2008 + + + 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 | RespIDData + 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 multiple times (such as with a + responder cookie and/or a different Diffie-Hellman group), it is the + latest 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 + password, the IKE implementation need not store the password in + + + +Kaufman, et al. Expires May 3, 2009 [Page 45] + +Internet-Draft IKEv2bis October 2008 + + + 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. + +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, et al. Expires May 3, 2009 [Page 46] + +Internet-Draft IKEv2bis October 2008 + + + 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. This + 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 + 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 + + + +Kaufman, et al. Expires May 3, 2009 [Page 47] + +Internet-Draft IKEv2bis October 2008 + + + 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. + +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). + + For ESP and AH, a single Child SA negotiation results in two security + associations (one in each direction). Keying material MUST be taken + from the expanded KEYMAT in the following order: + + o The encryption key (if any) for the SA carrying data from the + initiator to the responder. + + o The authentication key (if any) for the SA carrying data from the + initiator to the responder. + + o The encryption key (if any) for the SA carrying data from the + responder to the initiator. + + + + + +Kaufman, et al. Expires May 3, 2009 [Page 48] + +Internet-Draft IKEv2bis October 2008 + + + o The authentication key (if any) for the SA carrying data from the + responder to the initiator. + + Each cryptographic algorithm takes a fixed number of bits of keying + material specified as part of the algorithm, or negotiated in SA + payloads (see Section 2.13 for description of key lengths, and + Section 3.3.5 for the definition of the Key Length transform + attribute). + +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. + + {{ Clarif-5.12}} The main 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. Therefore, implementations SHOULD + perform a new Diffie-Hellman exchange when rekeying the IKE SA. In + other words, an initiator SHOULD NOT propose the value "NONE" for the + D-H transform, and a responder SHOULD NOT accept such a proposal. + This means that a succesful exchange rekeying the IKE SA always + includes the KEi/KEr payloads. + + 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. + + + + + + + +Kaufman, et al. Expires May 3, 2009 [Page 49] + +Internet-Draft IKEv2bis October 2008 + + +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). + + Message from responder to initiator: + + + +Kaufman, et al. Expires May 3, 2009 [Page 50] + +Internet-Draft IKEv2bis October 2008 + + + 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. + + {{ 3.10.1-37 }} The FAILED_CP_REQUIRED notification is 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. + + 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. The + FAILED_CP_REQUIRED is not fatal to the IKE SA; it simply causes the + Child SA creation fail. The initiator can fix this by later starting + a new configuration payload request. + +2.19.1. Configuration Payloads + + Editor's note: some of this sub-section is redundant and will go away + in the next version of the document. + + 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 + can be performed as agreed for this SA. + + 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 + + + +Kaufman, et al. Expires May 3, 2009 [Page 51] + +Internet-Draft IKEv2bis October 2008 + + + 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 + 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 + + + +Kaufman, et al. Expires May 3, 2009 [Page 52] + +Internet-Draft IKEv2bis October 2008 + + + well as subsequent information exchanges. + +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.") + +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 + + + +Kaufman, et al. Expires May 3, 2009 [Page 53] + +Internet-Draft IKEv2bis October 2008 + + + 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. {{ 3.10.1-4 + }} The INVALID_IKE_SPI notification 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. + + 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. + +2.22. IPComp + + Use of IP compression [IP-COMP] 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. 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 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. + + + +Kaufman, et al. Expires May 3, 2009 [Page 54] + +Internet-Draft IKEv2bis October 2008 + + + {{ 3.10.1-16387 }}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 + + 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. + + In some cases, Robust Header Compression (ROHC) may be more + appropriate than IP Compression. [ROHCV2] defines the use of ROHC + with IKEv2 and IPsec. + +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 + + + +Kaufman, et al. Expires May 3, 2009 [Page 55] + +Internet-Draft IKEv2bis October 2008 + + + 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 will use 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 + or 4500, 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. {{ Clarif-7.6 + }} An IPsec endpoint that discovers a NAT between it and its + correspondent MUST send all subsequent traffic from port 4500, which + + + +Kaufman, et al. Expires May 3, 2009 [Page 56] + +Internet-Draft IKEv2bis October 2008 + + + 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 + is just after the Ni and Nr payloads (before the optional CERTREQ + payload). + + o {{ 3.10.1-16388 }} The data associated with the + NAT_DETECTION_SOURCE_IP 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 + NAT_DETECTION_SOURCE_IP payloads in a message if the sender does + not know which of several network attachments will be used to send + the packet. + + o {{ 3.10.1-16389 }} The data associated with the + NAT_DETECTION_DESTINATION_IP 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. + + o {{ 3.10.1-16388 }} {{ 3.10.1-16389 }} The recipient of either the + NAT_DETECTION_SOURCE_IP or NAT_DETECTION_DESTINATION_IP + 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. In the case of a mismatching + NAT_DETECTION_SOURCE_IP hash, the recipient MAY reject the + connection attempt if NAT traversal is not supported. In the case + of a mismatching NAT_DETECTION_DESTINATION_IP hash, it means that + the system receiving the NAT_DETECTION_DESTINATION_IP payload is + behind a NAT and that system SHOULD start sending keepalive + packets as defined in [UDPENCAPS]; alternately, it MAY reject the + connection attempt if NAT traversal is not supported. + + o If none of the NAT_DETECTION_SOURCE_IP payload(s) received matches + the expected value of the source IP and port found from the IP + header of the packet containing the payload, it means that the + system sending those payloads is behind NAT (i.e., someone along + + + +Kaufman, et al. Expires May 3, 2009 [Page 57] + +Internet-Draft IKEv2bis October 2008 + + + the route changed the source address of the original packet to + match the address of the NAT box). In this case, the system + receiving the payloads should allow dynamic update of the other + systems' 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 the + system receiving the NAT_DETECTION_DESTINATION_IP payload is + behind a NAT. In this case, that system 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 + octets of the ESP header contain the SPI, and the SPI cannot + validly be zero, it is always possible to distinguish ESP and IKE + messages. + + o Implementations MUST process received UDP-encapsulated ESP packets + even when no NAT was detected. + + 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. + + + + + + +Kaufman, et al. Expires May 3, 2009 [Page 58] + +Internet-Draft IKEv2bis October 2008 + + +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 + + In the tables in this section, some cryptographic primitives and + configuation attributes are marked as "UNSPECIFIED". These are items + for which there are no known specifications and therefore + interoperability is currently impossible. A future specification may + describe their use, but until such specification is made, + implementations SHOULD NOT attempt to use items marked as + "UNSPECIFIED" in implementations that are meant to be interoperable. + +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 + + + +Kaufman, et al. Expires May 3, 2009 [Page 59] + +Internet-Draft IKEv2bis October 2008 + + + 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 (also known as "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. + + 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 + + + +Kaufman, et al. Expires May 3, 2009 [Page 60] + +Internet-Draft IKEv2bis October 2008 + + + 1. Implementations based on this version of IKE MUST reject or + ignore messages containing a version number greater than 2 with an + INVALID_MAJOR_VERSION notification message as described in Section + 2.5. + + 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 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 + PRIVATE USE 240-255 + + o Flags (1 octet) - Indicates specific options that are set for the + message. Presence of options is 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. This bit changes to reflect + who initiated the last rekey of the IKE SA. + + * 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. + + + + + +Kaufman, et al. Expires May 3, 2009 [Page 61] + +Internet-Draft IKEv2bis October 2008 + + + * 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 + "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: + + + + +Kaufman, et al. Expires May 3, 2009 [Page 62] + +Internet-Draft IKEv2bis October 2008 + + + 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 + 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, et al. Expires May 3, 2009 [Page 63] + +Internet-Draft IKEv2bis October 2008 + + + {{ Clarif-7.10 }} Many payloads contain fields marked as "RESERVED". + Some payloads in IKEv2 (and historically in IKEv1) are not aligned to + 4-octet boundaries. + +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 + contains a single IPsec protocol (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 ESP with either + (3DES and HMAC_MD5) or (AES and HMAC_SHA1). + + 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 a proposal number one (1) + greater than the previous structure. The first Proposal in the + initiator's SA payload MUST have a Proposal # of one (1). One reason + to use multiple proposals is to propose both standard crypto ciphers + and combined-mode ciphers. Combined-mode ciphers include both + integrity and encryption in a single encryption algorithm, and are + not allowed to be offered with a separate integrity algorithm other + than "none". If an initiator wants to propose both combined-mode + ciphers and normal ciphers, it must include two proposals: one will + have all the combined-mode ciphers, and the other will have all the + normal ciphers with the integrity algorithms. For example, one such + + + +Kaufman, et al. Expires May 3, 2009 [Page 64] + +Internet-Draft IKEv2bis October 2008 + + + proposal would have two proposal structures: ESP with ENCR_AES-CCM_8, + ENCR_AES-CCM_12, and ENCR_AES-CCM_16 as Proposal #1, and ESP with + ENCR_AES_CBC, ENCR_3DES, AUTH_AES_XCBC_96, and AUTH_HMAC_SHA1_96 as + 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 two transforms: + Extended Sequence Numbers (ESN) and an integrity check algorithm. + ESP generally has three: ESN, 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 AES- + CBC) and (HMAC_MD5 or HMAC_SHA), the ESP proposal would contain two + Transform Type 1 candidates (one for 3DES and one for AEC-CBC) and + two Transform Type 3 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 May 3, 2009 [Page 65] + +Internet-Draft IKEv2bis October 2008 + + + 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 May 3, 2009 [Page 66] + +Internet-Draft IKEv2bis October 2008 + + + o Proposal # (1 octet) - When a proposal is made, the first proposal + in an SA payload MUST be #1, and subsequent proposals MUST be one + more than the previous proposal (indicating an OR of the two + proposals). When a proposal is accepted, the proposal number in + the SA payload 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 May 3, 2009 [Page 67] + +Internet-Draft IKEv2bis October 2008 + + +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 + transform could be identified from the length of the proposal. + 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 transform type values are: + + + + + + + + +Kaufman, et al. Expires May 3, 2009 [Page 68] + +Internet-Draft IKEv2bis October 2008 + + + 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 + + (*) Negotiating an integrity algorithm is mandatory for the + Encrypted payload format specified in this document. For example, + [AEAD] specifies additional formats based on authenticated + encryption, in which a separate integrity algorithm is not + negotiated. + + For Transform Type 1 (Encryption Algorithm), defined Transform IDs + are: + + Name Number Defined In + --------------------------------------------------- + RESERVED 0 + ENCR_DES_IV64 1 (UNSPECIFIED) + 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 (UNSPECIFIED) + ENCR_DES_IV32 9 (UNSPECIFIED) + RESERVED 10 + ENCR_NULL 11 (RFC2410) + ENCR_AES_CBC 12 (RFC3602) + ENCR_AES_CTR 13 (RFC3686) + RESERVED TO IANA 14-1023 + PRIVATE USE 1024-65535 + + For Transform Type 2 (Pseudo-random Function), defined Transform IDs + are: + + + + + + + + + +Kaufman, et al. Expires May 3, 2009 [Page 69] + +Internet-Draft IKEv2bis October 2008 + + + 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 (RFC4434) + RESERVED TO IANA 5-1023 + PRIVATE USE 1024-65535 + + 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 (UNSPECIFIED) + AUTH_KPDK_MD5 4 (UNSPECIFIED) + 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 Defined in + ---------------------------------------- + NONE 0 + 768 Bit MODP 1 Appendix B + 1024 Bit MODP 2 Appendix B + RESERVED TO IANA 3-4 + 1536-bit MODP 5 [ADDGROUP] + RESERVED TO IANA 6-13 + 2048-bit MODP 14 [ADDGROUP] + 3072-bit MODP 15 [ADDGROUP] + 4096-bit MODP 16 [ADDGROUP] + 6144-bit MODP 17 [ADDGROUP] + 8192-bit MODP 18 [ADDGROUP] + RESERVED TO IANA 19-1023 + PRIVATE USE 1024-65535 + + For Transform Type 5 (Extended Sequence Numbers), defined Transform + IDs are: + + + + + + +Kaufman, et al. Expires May 3, 2009 [Page 70] + +Internet-Draft IKEv2bis October 2008 + + + Name Number + -------------------------------------------- + No Extended Sequence Numbers 0 + Extended Sequence Numbers 1 + RESERVED 2 - 65535 + + {{ Clarif-4.4 }} Note that an initiator who supports ESNs will + usually include two ESN transforms, with values "0" and "1", in its + proposals. A proposal containing a single ESN transform with value + "1" means that using normal (non-extended) sequence numbers is not + acceptable. + + Numerous additional transform types have been defined since the + publication of RFC 4306. Please refer to the IANA IKEv2 registry for + details. + +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 + + (*) Negotiating an integrity algorithm is mandatory for the + Encrypted payload format specified in this document. For example, + [AEAD] specifies additional formats based on authenticated + encryption, in which a separate integrity algorithm is not + negotiated. + +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. + + + +Kaufman, et al. Expires May 3, 2009 [Page 71] + +Internet-Draft IKEv2bis October 2008 + + + 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. + +3.3.5. Transform Attributes + + Each transform in a Security Association payload may include + attributes that modify or complete the specification of the + transform. The set of valid attributes depends on the transform. + Currently, only a single attribute type is defined: the Key Length + attribute is used by certain encryption transforms with variable- + length keys (see below for details). + + The attributes are type/value pairs and are defined below. + 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 + + + +Kaufman, et al. Expires May 3, 2009 [Page 72] + +Internet-Draft IKEv2bis October 2008 + + + o Attribute Format (AF) (1 bit) - Indicates whether the data + attribute follow the Type/Length/Value (TLV) format or a shortened + Type/Value (TV) format. If the AF bit is zero (0), then the + attribute uses TLV format; if the AF bit is one (1), the TV format + (with two-byte value) is used. + + o Attribute Type (15 bits) - Unique identifier for each type of + attribute (see below). + + 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 the only currently defined attribute type (Key Length) is + fixed length; the variable-length encoding specification is included + only for future extensions. Attributes described as fixed length + MUST NOT be encoded using the variable-length encoding. Variable- + length attributes MUST NOT be encoded as fixed-length 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. + + The Key Length attribute specifies the key length in bits (MUST use + network byte order) for certain transforms as follows: {{ Clarif-7.11 + }} + + o The Key Length attribute MUST NOT be used with transforms that use + a fixed length key. This includes, e.g., ENCR_DES, ENCR_IDEA, and + all the Type 2 (Pseudo-random function) and Type 3 (Integrity + Algorithm) transforms specified in this document. It is + recommended that future Type 2 or 3 transforms do not use this + attribute. + + o Some transforms specify that the Key Length attribute MUST be + always included (omitting the attribute is not allowed, and + + + +Kaufman, et al. Expires May 3, 2009 [Page 73] + +Internet-Draft IKEv2bis October 2008 + + + proposals not containing it MUST be rejected). This includes, + e.g., ENCR_AES_CBC and ENCR_AES_CTR. + + o Some transforms allow variable-length keys, but also specify a + default key length if the attribute is not included. These + transforms include, e.g., ENCR_RC5 and ENCR_BLOWFISH. + + Implementation note: 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 a responder to express a concept of + "at least" a certain level of security -- "a key length of _at least_ + X bits for cipher Y". However, as the attribute is always returned + unchanged (see Section 3.3.6), an initiator willing to accept + multiple key lengths has to include multiple transforms with the same + Transform Type, each with different Key Length attribute. + +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. If the selected proposal has 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. + + If the responder receives a proposal that contains a Transform Type + it does not understand, or a proposal that is missing a mandatory + Transform Type, it MUST consider this proposal unacceptable; however, + other proposals in the same SA payload are processed as usual. + Similarly, if the responder receives a transform that contains a + Transform Attribute it does not understand, it MUST consider this + transform unacceptable; other transforms with the same Transform Type + are processed as usual. This allows new Transform Types and + Transform Attributes to be defined in the future. + + 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 + + + +Kaufman, et al. Expires May 3, 2009 [Page 74] + +Internet-Draft IKEv2bis October 2008 + + + 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. + +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 (other than NONE), 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 + + + +Kaufman, et al. Expires May 3, 2009 [Page 75] + +Internet-Draft IKEv2bis October 2008 + + + 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. + + The following table lists the assigned values for the Identification + Type field: + + + + + + + +Kaufman, et al. Expires May 3, 2009 [Page 76] + +Internet-Draft IKEv2bis October 2008 + + + 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.). All characters in the ID_FQDN are ASCII; + for an "internationalized domain name", the syntax is as defined + in [IDNA], for example "xn--tmonesimerkki-bfbb.example.net". + + 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. Because of [EAI], implementations would + be wise to treat this field as UTF-8 encoded text, not as + pure ASCII. + + 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 + + + +Kaufman, et al. Expires May 3, 2009 [Page 77] + +Internet-Draft IKEv2bis October 2008 + + + 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. + + {{ 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 May 3, 2009 [Page 78] + +Internet-Draft IKEv2bis October 2008 + + + Certificate Encoding Value + ---------------------------------------------------- + RESERVED 0 + PKCS #7 wrapped X.509 certificate 1 UNSPECIFIED + PGP Certificate 2 UNSPECIFIED + DNS Signed Key 3 UNSPECIFIED + X.509 Certificate - Signature 4 + Kerberos Token 6 UNSPECIFIED + Certificate Revocation List (CRL) 7 + Authority Revocation List (ARL) 8 UNSPECIFIED + SPKI Certificate 9 UNSPECIFIED + X.509 Certificate - Attribute 10 UNSPECIFIED + 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 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 May 3, 2009 [Page 79] + +Internet-Draft IKEv2bis October 2008 + + + 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 + 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 certificate encoding does not allow a list, then + multiple Certificate Request payloads would need to be transmitted. + + The Certificate Request Payload is defined as follows: + + + + + + +Kaufman, et al. Expires May 3, 2009 [Page 80] + +Internet-Draft IKEv2bis October 2008 + + + 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, + 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" + + + +Kaufman, et al. Expires May 3, 2009 [Page 81] + +Internet-Draft IKEv2bis October 2008 + + + 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). + + {{ 3.10.1-16392 }} The HTTP_CERT_LOOKUP_SUPPORTED 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). + +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. + + + + +Kaufman, et al. Expires May 3, 2009 [Page 82] + +Internet-Draft IKEv2bis October 2008 + + + 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 with RSASSA-PKCS1-v1_5 + signature scheme specified in [PKCS1] (implementors should note + that IKEv1 used a different method for RSA signatures) {{ + Clarif-3.3 }}. {{ 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. + + * 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. + + 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 + + + +Kaufman, et al. Expires May 3, 2009 [Page 83] + +Internet-Draft IKEv2bis October 2008 + + + 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 May 3, 2009 [Page 84] + +Internet-Draft IKEv2bis October 2008 + + + 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 whose SPI is given the SPI field, this field indicates the type + of that SA. For notifications concerning IPsec SAs this field + MUST contain either (2) to indicate AH or (3) to indicate ESP. {{ + Clarif-7.8 }} Of the notifications defined in this document, the + SPI is included only with INVALID_SELECTORS and REKEY_SA. If the + SPI field is empty, 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 and + the field must be empty. + + 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 May 3, 2009 [Page 85] + +Internet-Draft IKEv2bis October 2008 + + + 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 + See Section 2.5. + + INVALID_IKE_SPI 4 + See Section 2.21. + + INVALID_MAJOR_VERSION 5 + See Section 2.5. + + 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 + information should be written to a console or log. + + INVALID_MESSAGE_ID 9 + See Section 2.3. + + INVALID_SPI 11 + + + +Kaufman, et al. Expires May 3, 2009 [Page 86] + +Internet-Draft IKEv2bis October 2008 + + + See Section 1.5. + + NO_PROPOSAL_CHOSEN 14 + See Section 2.7. + + INVALID_KE_PAYLOAD 17 + See Section 1.3. + + 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 + See Section 2.9. + + NO_ADDITIONAL_SAS 35 + See Section 1.3. + + INTERNAL_ADDRESS_FAILURE 36 + See Section 3.15.4. + + FAILED_CP_REQUIRED 37 + See Section 2.19. + + TS_UNACCEPTABLE 38 + See Section 2.9. + + 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 + + + + + + + + + + + + + +Kaufman, et al. Expires May 3, 2009 [Page 87] + +Internet-Draft IKEv2bis October 2008 + + + NOTIFY messages: status types Value + ------------------------------------------------------------------- + + INITIAL_CONTACT 16384 + See Section 2.4. + + SET_WINDOW_SIZE 16385 + See Section 2.3. + + ADDITIONAL_TS_POSSIBLE 16386 + See Section 2.9. + + IPCOMP_SUPPORTED 16387 + See Section 2.22. + + NAT_DETECTION_SOURCE_IP 16388 + See Section 2.23. + + NAT_DETECTION_DESTINATION_IP 16389 + See Section 2.23. + + COOKIE 16390 + See Section 2.6. + + USE_TRANSPORT_MODE 16391 + See Section 1.3.1. + + HTTP_CERT_LOOKUP_SUPPORTED 16392 + See Section 3.6. + + REKEY_SA 16393 + See Section 1.3.3. + + ESP_TFC_PADDING_NOT_SUPPORTED 16394 + See Section 1.3.1. + + NON_FIRST_FRAGMENTS_ALSO 16395 + See Section 1.3.1. + + 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 + + + +Kaufman, et al. Expires May 3, 2009 [Page 88] + +Internet-Draft IKEv2bis October 2008 + + + 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 + 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). + + + + + + + +Kaufman, et al. Expires May 3, 2009 [Page 89] + +Internet-Draft IKEv2bis October 2008 + + +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 of + 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. + + 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 + + + +Kaufman, et al. Expires May 3, 2009 [Page 90] + +Internet-Draft IKEv2bis October 2008 + + + 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. + + 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. + + + +Kaufman, et al. Expires May 3, 2009 [Page 91] + +Internet-Draft IKEv2bis October 2008 + + + 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 + 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. + + + + + +Kaufman, et al. Expires May 3, 2009 [Page 92] + +Internet-Draft IKEv2bis October 2008 + + + 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 (including protocol 0), 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 (including protocol 0), 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. + + + +Kaufman, et al. Expires May 3, 2009 [Page 93] + +Internet-Draft IKEv2bis October 2008 + + + 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. + + 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. + + This document specifies the cryptographic processing of Encrypted + payloads using a block cipher in CBC mode and an integrity check + algorithm that computes a fixed-length checksum over a variable size + message. The design is 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. Future + documents may specify the processing of Encrypted payloads for other + types of transforms, such as counter mode encryption and + authenticated encryption algorithms. Peers MUST NOT negotiate + transforms for which no such specification exists. + + + +Kaufman, et al. Expires May 3, 2009 [Page 94] + +Internet-Draft IKEv2bis October 2008 + + + 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: + + 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 - For CBC mode ciphers, the length of the + initialization vector (IV) is equal to the block length of the + underlying encryption algorithm. Senders MUST select a new + unpredictable IV for every message; recipients MUST accept any + value. For other modes than CBC, the IV format and processing is + specified in the document specifying the encryption algorithm and + mode. The reader is encouraged to consult [MODES] for advice on + IV generation. In particular, using the final ciphertext block of + the previous message is not considered unpredictable. + + o IKE Payloads are as specified earlier in this section. This field + is encrypted with the negotiated cipher. + + + + + +Kaufman, et al. Expires May 3, 2009 [Page 95] + +Internet-Draft IKEv2bis October 2008 + + + 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. + + 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. + + 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). + + o CFG Type (1 octet) - The type of exchange represented by the + Configuration Attributes. + + + + + +Kaufman, et al. Expires May 3, 2009 [Page 96] + +Internet-Draft IKEv2bis October 2008 + + + 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 May 3, 2009 [Page 97] + +Internet-Draft IKEv2bis October 2008 + + + 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 + RESERVED 5 + 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 octets 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 there are no IKE + SAs between the peers. This is described in more detail in + Section 3.15.3. + + 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. {{ Clarif-6.4 }} + INTERNAL_IP4_NETMASK in a CFG_REPLY means roughly the same thing + + + +Kaufman, et al. Expires May 3, 2009 [Page 98] + +Internet-Draft IKEv2bis October 2008 + + + 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 - 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_IP6_NBNS - {{ Clarif-6.6 }} NetBIOS is not defined for + IPv6; therefore, INTERNAL_IP6_NBNS is also unspecified and is only + retained for compatibility with RFC 4306. + + 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. This is discussed in + more detail in Section 3.15.2. + + 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, et al. Expires May 3, 2009 [Page 99] + +Internet-Draft IKEv2bis October 2008 + + + 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. This is discussed in more detail in Section + 3.15.2. + + 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): + + 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)) + + + + +Kaufman, et al. Expires May 3, 2009 [Page 100] + +Internet-Draft IKEv2bis October 2008 + + + 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: + + 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) + + + + +Kaufman, et al. Expires May 3, 2009 [Page 101] + +Internet-Draft IKEv2bis October 2008 + + + 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. + + 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]. + + + + +Kaufman, et al. Expires May 3, 2009 [Page 102] + +Internet-Draft IKEv2bis October 2008 + + +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 during the processing of a Configuration + Payload, it responds with an INTERNAL_ADDRESS_FAILURE notification. + The IKE SA is still created even if the initial Child SA cannot be + created because of this failure. {{ 3.10.1-36 }} If this error is + generated within an IKE_AUTH exchange, no Child SA will be created. + 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. + + 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 ~ + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + + + +Kaufman, et al. Expires May 3, 2009 [Page 103] + +Internet-Draft IKEv2bis October 2008 + + + 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: + + 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 + + + +Kaufman, et al. Expires May 3, 2009 [Page 104] + +Internet-Draft IKEv2bis October 2008 + + + 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 or AH SAs within a single IKE + SA. + + 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 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 + + + +Kaufman, et al. Expires May 3, 2009 [Page 105] + +Internet-Draft IKEv2bis October 2008 + + + 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. + + 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. + + 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 passed is any of ID_KEY_ID, + ID_FQDN, or ID_RFC822_ADDR. + + + +Kaufman, et al. Expires May 3, 2009 [Page 106] + +Internet-Draft IKEv2bis October 2008 + + + 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. + + 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 + + + +Kaufman, et al. Expires May 3, 2009 [Page 107] + +Internet-Draft IKEv2bis October 2008 + + + 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. + + 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 + 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 + + + +Kaufman, et al. Expires May 3, 2009 [Page 108] + +Internet-Draft IKEv2bis October 2008 + + + 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 authentication. {{ 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 strong authentication of + the server to the client before the EAP authentication 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 [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 + + + +Kaufman, et al. Expires May 3, 2009 [Page 109] + +Internet-Draft IKEv2bis October 2008 + + + 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. + + 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. + + + + +Kaufman, et al. Expires May 3, 2009 [Page 110] + +Internet-Draft IKEv2bis October 2008 + + +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. However, + IANA should update all references to RFC 4306 to point to this + document. + + +7. Acknowledgements + + 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. + + This paragraph lists references that appear only in figures. The + section is only here to keep the 'xml2rfc' program happy, and needs + to be removed when the document is published. The RFC Editor will + remove it before publication. [AEAD] [EAI] [DES] [IDEA] [MD5] + [X.501] [X.509] + + +8. References + +8.1. Normative References + + [ADDGROUP] + Kivinen, T. and M. Kojo, "More Modular Exponential (MODP) + + + +Kaufman, et al. Expires May 3, 2009 [Page 111] + +Internet-Draft IKEv2bis October 2008 + + + 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 4291, February 2006. + + [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. + + [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. + + [PKCS1] Jonsson, J. and B. Kaliski, "Public-Key Cryptography + Standards (PKCS) #1: RSA Cryptography Specifications + Version 2.1", RFC 3447, February 2003. + + [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. + + [RFC4434] Hoffman, P., "The AES-XCBC-PRF-128 Algorithm for the + Internet Key Exchange Protocol (IKE)", RFC 4434, + February 2006. + + [RFC4615] Song, J., Poovendran, R., Lee, J., and T. Iwata, "The + Advanced Encryption Standard-Cipher-based Message + Authentication Code-Pseudo-Random Function-128 (AES-CMAC- + PRF-128) Algorithm for the Internet Key Exchange Protocol + (IKE)", RFC 4615, August 2006. + + [UDPENCAPS] + Huttunen, A., Swander, B., Volpe, V., DiBurro, L., and M. + Stenberg, "UDP Encapsulation of IPsec ESP Packets", + + + +Kaufman, et al. Expires May 3, 2009 [Page 112] + +Internet-Draft IKEv2bis October 2008 + + + RFC 3948, January 2005. + +8.2. Informative References + + [AEAD] McGrew, D., "An Interface and Algorithms for Authenticated + Encryption", RFC 5116, January 2008. + + [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. + + [Clarif] Eronen, P. and P. Hoffman, "IKEv2 Clarifications and + Implementation Guidelines", RFC 4718, October 2006. + + [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. + + [DOI] Piper, D., "The Internet IP Security Domain of + + + +Kaufman, et al. Expires May 3, 2009 [Page 113] + +Internet-Draft IKEv2bis October 2008 + + + 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", + Draft FIPS 186-3, June 2008. + + [EAI] Abel, Y., "Internationalized Email Headers", RFC 5335, + September 2008. + + [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. + + [IDNA] Faltstrom, P., Hoffman, P., and A. Costello, + "Internationalizing Domain Names in Applications (IDNA)", + RFC 3490, March 2003. + + [IKEV1] Harkins, D. and D. Carrel, "The Internet Key Exchange + (IKE)", RFC 2409, November 1998. + + [IKEV2] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", + + + +Kaufman, et al. Expires May 3, 2009 [Page 114] + +Internet-Draft IKEv2bis October 2008 + + + RFC 4306, December 2005. + + [IP-COMP] 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 4291, February 2006. + + [ISAKMP] Maughan, D., Schneider, M., and M. Schertler, "Internet + Security Association and Key Management Protocol + (ISAKMP)", RFC 2408, November 1998. + + [LDAP] Sermersheim, J., "Lightweight Directory Access Protocol + (v3)", RFC 4511, June 2006. + + [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. + + [MODES] National Institute of Standards and Technology, U.S. + Department of Commerce, "Recommendation for Block Cipher + Modes of Operation", SP 800-38A, 2001. + + [NAI] Aboba, B., Beadles, M., Eronen, P., and J. Arkko, "The + Network Access Identifier", RFC 4282, December 2005. + + [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 + + + +Kaufman, et al. Expires May 3, 2009 [Page 115] + +Internet-Draft IKEv2bis October 2008 + + + Management API, Version 2", RFC 2367, July 1998. + + [PHOTURIS] + Karn, P. and W. Simpson, "Photuris: Session-Key Management + Protocol", RFC 2522, March 1999. + + [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 Internet Key Exchange + (IKEv2) Protocol", RFC 4478, April 2006. + + [ROHCV2] Ertekin, et. al., E., "IKEv2 Extensions to Support Robust + Header Compression over IPsec (ROHCoIPsec)", + draft-ietf-rohc-ikev2-extensions-hcoipsec (work in + progress), October 2008. + + [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 180-3, October 2008. + + [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", + + + +Kaufman, et al. Expires May 3, 2009 [Page 116] + +Internet-Draft IKEv2bis October 2008 + + + 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: + + 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; + + 8. To fix cryptographic weaknesses such as the problem with + symmetries in hashes used for authentication documented by Tero + Kivinen; + + + + + +Kaufman, et al. Expires May 3, 2009 [Page 117] + +Internet-Draft IKEv2bis October 2008 + + + 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; + + 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 May 3, 2009 [Page 118] + +Internet-Draft IKEv2bis October 2008 + + + 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+] + + cookie response <-- N(COOKIE), + [V+] + + different D-H <-- N(INVALID_KE_PAYLOAD), + group wanted [V+] + + + + + + + +Kaufman, et al. Expires May 3, 2009 [Page 119] + +Internet-Draft IKEv2bis October 2008 + + +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+] + + error in Child SA <-- IDr, [CERT+], + creation AUTH, + N(error), + [V+] + + + + + + + + + + + + + + + + + + + + + +Kaufman, et al. Expires May 3, 2009 [Page 120] + +Internet-Draft IKEv2bis October 2008 + + +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 May 3, 2009 [Page 121] + +Internet-Draft IKEv2bis October 2008 + + +C.4. CREATE_CHILD_SA Exchange for Creating or Rekeying Child SAs + + request --> [N(REKEY_SA)], + [CP(CFG_REQUEST)], + [N(IPCOMP_SUPPORTED)+], + [N(USE_TRANSPORT_MODE)], + [N(ESP_TFC_PADDING_NOT_SUPPORTED)], + [N(NON_FIRST_FRAGMENTS_ALSO)], + SA, Ni, [KEi], TSi, TSr + [V+] + + normal <-- [CP(CFG_REPLY)], + 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)] + [V+] + + error case <-- N(error) + + different D-H <-- N(INVALID_KE_PAYLOAD), + group wanted [V+] + +C.5. CREATE_CHILD_SA Exchange for Rekeying the IKE SA + + request --> SA, Ni, [KEi] + [V+] + + response <-- SA, Nr, [KEr] + [V+] + +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, but should + be left intact until then so that reviewers can follow what has + + + +Kaufman, et al. Expires May 3, 2009 [Page 122] + +Internet-Draft IKEv2bis October 2008 + + + changed. + +D.1. Changes from IKEv2 to draft -00 + + There were a zillion additions from RFC 4718. 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 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. + +D.2. Changes from draft -00 to draft -01 + + The most significant technical change was to make KE optional but + strongly recommended in Section 1.3.2. + + Updated all references to the IKEv2 Clarifications document to RFC + 4718. + + Moved a lot of the protocol description out of the long tables in + Section 3.10.1 into the body of the document. These are noted with + "{{ 3.10.1-nnnn }}", where "nnnn" is the notification type number. + + Made some table changes based on suggestions from Alfred Hoenes. + + Changed "byte" to "octet" in many places. + + Removed discussion of ESP+AH bundles in many places, and added a + paragraph about it in Section 1.7. + + Removed the discussion of INTERNAL_ADDRESS_EXPIRY in many places, and + added a paragraph about it in Section 1.7. + + Moved Clarif-7.10 from Section 1.2 to Section 3.2. + + In the figure in Section 1.3.2, made KEi optional, and added text + saying "The KEi payload SHOULD be included." + + In the figure in Section 1.3.2, maked KEr optional, and removed text + + + +Kaufman, et al. Expires May 3, 2009 [Page 123] + +Internet-Draft IKEv2bis October 2008 + + + saying "KEi and KEr are required for rekeying an IKE SA." + + In Section 1.4, clarified that the half-closed connections being + discussed are AH and ESP. + + Rearranged the end of Section 1.7, and added the new notation for + moving text out of 3.10.1. + + Clarified the wording in the second paragraph of Section 2.2. This + allowd the removal of the fourth paragraph, which previously had + Clarif-2.2 in it. + + In section 2.5, removed "or later" from "version 2.0". + + Added the question for implementers about payload order at the end of + Section 2.5. + + Corrected Section 2.7 based on Clarif-7-13 to say that you can't do + ESP and AH at one time. + + In Section 2.8, clarified the wording about how to replace an IKE SA. + + Clarified the text in the last many paragraphs in Section 2.9. Also + moved some text from near the beginning of 2.9 to the beginning of + 2.9.1. + + Removed some redundant text in Section 2.9 concerning creating a + Child SA pair not in response to an arriving packet. + + Added the following to the end of the first paragraph of Section + 2.14: "The lengths of SK_d, SK_pi, and SK_pr are the key length of + the agreed-to PRF." + + Added the restriction in Section 2.15 that all PRFs used with IKEv2 + MUST take variable-sized keys. + + In Section 2.17, removed "If multiple IPsec protocols are negotiated, + keying material is taken in the order in which the protocol headers + will appear in the encapsulated packet" because multiple IPsec + protocols cannot be negotiated at one time. + + Added the material from Clarif-5.12 to Section 2.18. + + Changed "hash of" to "expected value of" in Section 2.23. + + In the bulleted list in Section 2.23, replaced "this end" with a + clearer description of which system is being discussed. + + + + +Kaufman, et al. Expires May 3, 2009 [Page 124] + +Internet-Draft IKEv2bis October 2008 + + + Added the paragraph at the beginning of Section 3 about + interoperability and UNSPECIFIED values ("In the tables in this + section..."). + + Fixed Section 3.3 to not include proposal that include both AH and + ESP. Ditto for the "Proposal #" bullet in Section 3.3.1. + + In the description of ID_FQDN in Section 3.5, added "All characters + in the ID_FQDN are ASCII; this follows that for an "internationalized + domain name" as defined in [IDNA]." + + In Section 3.8, shortened and clarified the description of "RSA + Digital Signature". + + In Section 3.10, shortened and clarified the description of "Protocol + ID". + + In Section 3.15, "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" is shortened to just "The requested + address is valid until there are no IKE SAs between the peers." + + In Section 3.15.1, changed "INTERNAL_IP6_NBNS" to unspecified. + + Made [ADDRIPV6] an informative reference instead of a normative + reference and updated it. + + Made [PKCS1] a normative reference instead of an informative + reference and changed the pointer to RFC 3447. + +D.3. Changes from draft -00 to draft -01 + + In Section 1.5, added "request" to first sentence to make it "If an + encrypted IKE request packet arrives on port 500 or 4500 with an + unrecognized SPI...". + + In Section 3.3, fifth paragraph, upped the number of transforms for + AH and ESP by one each to account for ESN, which is now mandatory. + + In Section 2.1, added "or equal to" in "The responder MUST remember + each response until it receives a request whose sequence number is + larger than or equal to the sequence number in the response plus its + window size." + + In Section 2.18, removed " 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." because it is no longer relevant. + + + + +Kaufman, et al. Expires May 3, 2009 [Page 125] + +Internet-Draft IKEv2bis October 2008 + + +D.4. Changes from draft -01 to draft -02 + + Many grammatical fixes. + + In Section 1.2, reworded Clarif-4.3 to be clearer. + + In Section 1.3.3, reworded 3.10.1-16393 and Clarif-5.4 to remove + redundant text. + + In Section 2.13, replaced text about variable length keys with + clearer explanation and requirement on non-HMAC PRFs. Also added + "preferred" to Section 2.14 for the key length, and removed redundant + text. + + In Section 2.14, removed the "half and half" description and replaced + it with exceptions for RFC4434 and RFC4615. + + Removed the now-redundant "All PRFs used with IKEv2 MUST take + variable-sized keys" from Section 2.15. + + In Section 2.15, added "(IKE_SA_INIT response)" after "of the second + message" and "(IKE_SA_INIT request)" after "the first message". + + In Section 2.17, simplified because there are no more bundles. "A + single Child SA negotiation may result in multiple security + associations. ESP and AH SAs exist in pairs (one in each + direction)." becomes "For ESP and AH, a single Child SA negotiation + results in two security associations (one in each direction)." + + In section 3.3, made the example of combinations of algorithms and + the contents of the first proposal clearer. + + Added Clarif-4.4 to the end of Section 3.3.2. + + Reordered Section 3.3.5 and added Clarif-7.11. + + Clarified Section 3.3.6 about choosing a single proposal. Also added + second paragraph about transforms not understood, and clarified third + paragraph about picking D-H groups. + + Moved 3.10.1-16392 from Section 3.6 to 3.7. + + In Section 3.10, clarified 3.10.1-16394. + + Updated Section 6 to indicate that there is nothing new for IANA in + this spec. Also removed the definition of "Expert Review" from + Section 1.6 for the same reason. + + + + +Kaufman, et al. Expires May 3, 2009 [Page 126] + +Internet-Draft IKEv2bis October 2008 + + + In Appendix A, removed "and not commit any state to an exchange until + the initiator can be cryptographically authenticated" because that + was only true in an earlier version of IKEv2. + +D.5. Changes from draft -02 to draft -03 + + In Section 1.3, changed "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." to "If the responder selects a proposal using + a different Diffie-Hellman group (other than NONE), the responder + MUST reject the request and indicate its preferred Diffie-Hellman + group in the INVALID_KE_PAYLOAD Notification payload. + + In Section 2.3, added the last two paragraphs covering why you + initiator's SPI and/or IP to differentiate if this is a "half-open" + IKE SA or a new request. Also removed similar text from Section 2.2. + + In Section 2.5, added "Payloads sent in IKE response messages MUST + NOT have the critical flag set. Note that the critical flag applies + only to the payload type, not the contents. If the payload type is + recognized, but the payload contains something which is not (such as + an unknown transform inside an SA payload, or an unknown Notify + Message Type inside a Notify payload), the critical flag is ignored." + + In Section 2.6, moved the text about {{ 3.10.1-16390 }} later in the + section. Also reworded the text to make it clearer what the COOKIE + is for. + + Moved text from {{ Clarif-2.1 }} from Section 2.6 to Section 2.7. + + In Section 2.13, added "(see Section 3.3.5 for the defintion of the + Key Length transform attribute)". + + In Section 2.17, change the description of the keying material from + the list with two bullets to a clearer list. + + In Section 2.23, added "Implementations MUST process received UDP- + encapsulated ESP packets even when no NAT was detected." + + In Section 3.3, changed "Each proposal may contain a" to "Each + proposal contains a". + + Added the asterisks to the transform type table in Section 3.3.2 and + the types table in 3.3.3 to foreshadow future developments. + + In Section 3.3.2, changed the following algorithms to (UNSPECIFIED) + because the RFCs listed didn't really specify how to implement them + + + +Kaufman, et al. Expires May 3, 2009 [Page 127] + +Internet-Draft IKEv2bis October 2008 + + + in an interoperable fashion: + + Encryption Algorithms + ENCR_DES_IV64 1 (RFC1827) + ENCR_3IDEA 8 (RFC2451) + ENCR_DES_IV32 9 + Pseudo-random Functions + PRF_HMAC_TIGER 3 (RFC2104) + Integrity Algorithms + AUTH_DES_MAC 3 + AUTH_KPDK_MD5 4 (RFC1826) + + In Section 3.4, added "(other than NONE)" to the second-to-last + paragraph. + + Rewrote the third paragraph of Section 3.14 to talk about other + modes, and to clarify which encryption and integrity protection we + are talking about. + + Changed the "Initialization Vector" bullet in Section 3.14 to specify + better what is needed for the IV. Upgraded the SHOULDs to MUSTs. + Also added the reference for [MODES]. + + In Section 5, in the second-to-last paragraph, changed "a public-key- + based" to "strong" to match the wording in Section 2.16. + +D.6. Changes from draft -03 to draft-ietf-ipsecme-ikev2bis-00 + + Changed the document's filename to draft-ietf-ipsecme-ikev2bis-00. + Added Yoav Nir as a co-author. + + In many places in the document, changed "and/or" to "or" when talking + about combinations of ESP and AH SAs. For example, in the intro, it + said "can be used to efficiently establish SAs for Encapsulating + Security Payload (ESP) and/or Authentication Header (AH)". This is + changed to "or" to indicate that you can only establish one type of + SA at a time. + + In Section 1, clarified that RFC 4306 already replaced IKEv1, and + that this document replaces RFC 4306. Also fixed Section 2.5 for + similar issue. Also updated the Abstract to cover this. + + In Section 2.15, in the responder's signed octets, changed: + + RestOfRespIDPayload = IDType | RESERVED | InitIDData + to + RestOfRespIDPayload = IDType | RESERVED | RespIDData + + + + +Kaufman, et al. Expires May 3, 2009 [Page 128] + +Internet-Draft IKEv2bis October 2008 + + + In 2.16, changed "strong" back to "public key signature based" to + make it the same as 4306. + + In section 3.10, added "and the field must be empty" to make it clear + that a zero-length SPI is really empty. + +D.7. Changes from draft-ietf-ipsecme-ikev2bis-00 to + draft-ietf-ipsecme-ikev2bis-01 + + Throughout, changed "IKE_SA" to "IKE SA", and changed "CHILD_SA" to + "Child SA" (except left "CREATE_CHILD_SA" alone). + + Added the middle sentence in the Abstract to say what IKE actually + does. + + Added in section 1 "(unless there is failure setting up the AH or ESP + Child SA, in which case the IKE SA is still established without IPsec + SA)". + + Clarified the titles of 1.1.1, 1.1.2, and 1.1.3. + + In 1.1.2, changed "If there is an inner IP header, the inner + addresses will be the same as the outer addresses." because we are + talking about transport mode here. + + Added reference to section 2.14 to setion 1.2 and 1.3. + + In 1.2, clarified what is and isn't encrypted in a message. + + Added the following to 1.2: "If the IDr proposed by the initiator is + not acceptable to the responder, the responder might use some other + IDr to finish the exchange. If the initiator then does not accept + that fact that responder used different IDr than the one that was + requested, the initiator can close the SA after noticing the fact." + + Moved the paragraph beginning "All messages following..." from 1.3 up + to 1.2, and reworded it to apply to all the cases it covers. + + At the end of section 1.3.1, clarified that the responder is the one + who controls whether non-first-fragments will be sent, and reworded + the paragraph. + + In section 1.3.3, added "The Protocol ID field of the REKEY_SA + notification is set to match the protocol of the SA we are rekeying, + for example, 3 for ESP and 2 for AH." [Issue #10] + + In 1.3.2, added "of the SA payload" to "New initiator and responder + SPIs are supplied in the SPI fields." + + + +Kaufman, et al. Expires May 3, 2009 [Page 129] + +Internet-Draft IKEv2bis October 2008 + + + In 1.3.3, fixed the art. + + <-- HDR, SK {SA, Nr, [KEr], + Si, TSr} + becomes + <-- HDR, SK {SA, Nr, [KEr], + TSi, TSr} + + + In 1.4 and 2.18, changed "replaced for the purpose of rekeying" to + "rekeyed". + + Split out the SA deletion material from section 1.4 into its own + subsection, 1.4.1. + + Clarified which bits are set at the end of Section 1.5. + + In 1.7, added "That is, the version number is *not* changed from RFC + 4306.". + + In 2.1, added wording about retransmissions needing to be identical. + + In 2.2, added "or rekeyed" to "In the unlikely event that Message IDs + grow too large to fit in 32 bits, the IKE SA MUST be closed" + + In 2.2, moved the sentence "Rekeying an IKE SA resets the sequence + numbers." up higher so it would be more likely to be seen. [Issue + #15] + + Moved the definition of "original initiator" from 2.8 into 2.2 + because that is where it is first used. + + In 2.4, added "fresh (i.e., not retransmitted)" to "If a + cryptographically protected message has been received from the other + side recently". Also added the sentence saying that liveness checks + are sometimes call dead peer detection. + + Removed the question to implementers about payload order in 2.5. + + Changed the title of 2.6 to "IKE SA SPIs and Cookies". Also, in the + paragraph that describes how to implement the responder, changed the + lower-case "should" to "can" to emphasize that this is a choice. + + Added the second paragraph in 2.6 to make it clear that the SPI is + used for mapping. + + In section 2.6, upgraded "needs to choose them so as to be unique + identifiers of an IKE_SA" to a MUST. + + + +Kaufman, et al. Expires May 3, 2009 [Page 130] + +Internet-Draft IKEv2bis October 2008 + + + Added sentences at the end of 2.6 eplaining wny the initiator should + limit the number of responses it sends out. + + In 2.6.1, added the example of the shorter exchange; this is copied + from RFC 4718 but was dropped in early drafts of this document. + + Added the paragraph to 2.7 that describes needing two proposals if + you are having both normal ciphers and combined-mode ciphers. [Issue + #20]. + + In section 2.8, added "Note that, when rekeying, the new Child SA MAY + have different traffic selectors and algorithms than the old one." + + Added a note in 2.9 that PFKEY applies only to IKEv1. Also added + that unknown traffic selector types are not returned in narrowed + responses. + + Added note in the first paragraph of Setion 2.9.1 about decorrelated + policies preventing the problem mentioned. + + In 2.12, removed "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." + + In 2.15, noted that the retry could happen multiple times for + different reasons. + + In section 2.16, changed "This shared key generated during an IKE + exchange" to "This key". + + At the end of 2.19, added statement that FAILED_CP_REQUIRED is not + fatal to the IKE SA. + + Added the reference to ROHCV2 to the end of 2.22. + + In 2.23, changed "can negotiate" to "will use". for UDP + encapsulation. Added "or 4500" to "...MUST be sent from and to UDP + port 500". Also removed the text about why not to do NAT-traversal + over port 500 because we later say you can't do that anyway. [Issue + #27] Also removed the last paragraph, which obliquely pointed to + MOBIKE. More will be added later on MOBIKE. + + In 3.1, removed "and orderings of messages" from "Exchange type". + [Issue #29] + + In 3.1, added "This bit changes to reflect who initiated the last + rekey of the IKE SA." to the description of the Initiator bit. + + + +Kaufman, et al. Expires May 3, 2009 [Page 131] + +Internet-Draft IKEv2bis October 2008 + + + In 3.3, added a long example of why you might use a Proposal + structure because of combined-mode algorithms. [Issue #42] + + In 3.3.2, changed "is unnecessary because the last Proposal could be + identified from the length of the SA" to "is unnecessary because the + last transform could be identified from the length of the proposal." + + Added reference to AEAD to 3.3.2 and 3.3.3. + + Added the reference to RFC 2104 back for PRF_HMAC_TIGER in 3.3.2. + [Issue #33] + + Added note at the bottom of 3.3.2 to see the IANA registry. + + In 3.3.4, removed all the "this could happen in the future" stuff + because it already happened. + + Added a reference to email address internationalization to 3.5, + making the address binary (not ASCII). + + In the table in 3.6, made "Authority Revocation List (ARL) 8" and + "X.509 Certificate - Attribute 10" unspecified. + + In 3.7, changed the last sentence of the first paragraph to eliminate + the non-protocol SHOULD. + + In 3.13.1, added "(including protocol 0)" for the start port and end + port. + + In 3.14, updated the discussion of initialization modes to reflect + that it is only about CBC, and that other specs have to specify their + own IVs. + + In 3.15.1, added a pointer to 3.15.3. In the entries for + INTERNAL_IP4_SUBNET and INTERNAL_IP6_SUBNET, added a pointer to + 3.15.2. + + In 3.15.4, added "The IKE SA is still created even if the initial + Child SA cannot be created because of this failure." + + Changed "EAP exchange" to "EAP authentication" in 5. + + Removed "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." from section 5 because it is not possible in + most implementations to do so. + + Updated a bunch of reference to their newer versions. + + + +Kaufman, et al. Expires May 3, 2009 [Page 132] + +Internet-Draft IKEv2bis October 2008 + + + Added "[V+]" to the end of the exchanges in C.4 and C.5. + + Added two more response templates to Appendix C.1. Added another + response template in Appendix C.2. Added two more responses in + Appendix C.4. + + +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 + + + Yoav Nir + Check Point Software Technologies Ltd. + 5 Hasolelim St. + Tel Aviv 67897 + Israel + + Email: ynir@checkpoint.com + + + Pasi Eronen + Nokia Research Center + P.O. Box 407 + FIN-00045 Nokia Group + Finland + + Email: pasi.eronen@nokia.com + + + + + + +Kaufman, et al. Expires May 3, 2009 [Page 133] + +Internet-Draft IKEv2bis October 2008 + + +Full Copyright Statement + + Copyright (C) The IETF Trust (2008). + + 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, THE IETF TRUST 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. 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