diff options
Diffstat (limited to 'doc/standards/rfc5996.txt')
| -rw-r--r-- | doc/standards/rfc5996.txt | 7731 |
1 files changed, 7731 insertions, 0 deletions
diff --git a/doc/standards/rfc5996.txt b/doc/standards/rfc5996.txt new file mode 100644 index 000000000..cbefe6304 --- /dev/null +++ b/doc/standards/rfc5996.txt @@ -0,0 +1,7731 @@ + + + + + + +Internet Engineering Task Force (IETF) C. Kaufman +Request for Comments: 5996 Microsoft +Obsoletes: 4306, 4718 P. Hoffman +Category: Standards Track VPN Consortium +ISSN: 2070-1721 Y. Nir + Check Point + P. Eronen + Independent + September 2010 + + + Internet Key Exchange Protocol Version 2 (IKEv2) + +Abstract + + This document describes version 2 of the Internet Key Exchange (IKE) + protocol. IKE is a component of IPsec used for performing mutual + authentication and establishing and maintaining Security Associations + (SAs). This document replaces and updates RFC 4306, and includes all + of the clarifications from RFC 4718. + +Status of This Memo + + This is an Internet Standards Track document. + + This document is a product of the Internet Engineering Task Force + (IETF). It represents the consensus of the IETF community. It has + received public review and has been approved for publication by the + Internet Engineering Steering Group (IESG). Further information on + Internet Standards is available in Section 2 of RFC 5741. + + Information about the current status of this document, any errata, + and how to provide feedback on it may be obtained at + http://www.rfc-editor.org/info/rfc5996. + + + + + + + + + + + + + + + + + +Kaufman, et al. Standards Track [Page 1] + +RFC 5996 IKEv2bis September 2010 + + +Copyright Notice + + Copyright (c) 2010 IETF Trust and the persons identified as the + document authors. All rights reserved. + + This document is subject to BCP 78 and the IETF Trust's Legal + Provisions Relating to IETF Documents + (http://trustee.ietf.org/license-info) in effect on the date of + publication of this document. Please review these documents + carefully, as they describe your rights and restrictions with respect + to this document. Code Components extracted from this document must + include Simplified BSD License text as described in Section 4.e of + the Trust Legal Provisions and are provided without warranty as + described in the Simplified BSD License. + + This document may contain material from IETF Documents or IETF + Contributions published or made publicly available before November + 10, 2008. The person(s) controlling the copyright in some of this + material may not have granted the IETF Trust the right to allow + modifications of such material outside the IETF Standards Process. + Without obtaining an adequate license from the person(s) controlling + the copyright in such materials, this document may not be modified + outside the IETF Standards Process, and derivative works of it may + not be created outside the IETF Standards Process, except to format + it for publication as an RFC or to translate it into languages other + than English. + +Table of Contents + + 1. Introduction ....................................................5 + 1.1. Usage Scenarios ............................................6 + 1.1.1. Security Gateway to Security Gateway in + Tunnel Mode .........................................7 + 1.1.2. Endpoint-to-Endpoint Transport Mode .................7 + 1.1.3. Endpoint to Security Gateway in Tunnel Mode .........8 + 1.1.4. Other Scenarios .....................................9 + 1.2. The Initial Exchanges ......................................9 + 1.3. The CREATE_CHILD_SA Exchange ..............................13 + 1.3.1. Creating New Child SAs with the + CREATE_CHILD_SA Exchange ...........................14 + 1.3.2. Rekeying IKE SAs with the CREATE_CHILD_SA + Exchange ...........................................15 + 1.3.3. Rekeying Child SAs with the CREATE_CHILD_SA + Exchange ...........................................16 + 1.4. The INFORMATIONAL Exchange ................................17 + 1.4.1. Deleting an SA with INFORMATIONAL Exchanges ........17 + 1.5. Informational Messages outside of an IKE SA ...............18 + 1.6. Requirements Terminology ..................................19 + + + +Kaufman, et al. Standards Track [Page 2] + +RFC 5996 IKEv2bis September 2010 + + + 1.7. Significant Differences between RFC 4306 and This + Document ..................................................20 + 2. IKE Protocol Details and Variations ............................22 + 2.1. Use of Retransmission Timers ..............................23 + 2.2. Use of Sequence Numbers for Message ID ....................24 + 2.3. Window Size for Overlapping Requests ......................25 + 2.4. State Synchronization and Connection Timeouts .............26 + 2.5. Version Numbers and Forward Compatibility .................28 + 2.6. IKE SA SPIs and Cookies ...................................30 + 2.6.1. Interaction of COOKIE and INVALID_KE_PAYLOAD .......33 + 2.7. Cryptographic Algorithm Negotiation .......................34 + 2.8. Rekeying ..................................................34 + 2.8.1. Simultaneous Child SA Rekeying .....................36 + 2.8.2. Simultaneous IKE SA Rekeying .......................39 + 2.8.3. Rekeying the IKE SA versus Reauthentication ........40 + 2.9. Traffic Selector Negotiation ..............................40 + 2.9.1. Traffic Selectors Violating Own Policy .............43 + 2.10. Nonces ...................................................44 + 2.11. Address and Port Agility .................................44 + 2.12. Reuse of Diffie-Hellman Exponentials .....................44 + 2.13. Generating Keying Material ...............................45 + 2.14. Generating Keying Material for the IKE SA ................46 + 2.15. Authentication of the IKE SA .............................47 + 2.16. Extensible Authentication Protocol Methods ...............50 + 2.17. Generating Keying Material for Child SAs .................52 + 2.18. Rekeying IKE SAs Using a CREATE_CHILD_SA Exchange ........53 + 2.19. Requesting an Internal Address on a Remote Network .......53 + 2.20. Requesting the Peer's Version ............................55 + 2.21. Error Handling ...........................................56 + 2.21.1. Error Handling in IKE_SA_INIT .....................56 + 2.21.2. Error Handling in IKE_AUTH ........................57 + 2.21.3. Error Handling after IKE SA is Authenticated ......58 + 2.21.4. Error Handling Outside IKE SA .....................58 + 2.22. IPComp ...................................................59 + 2.23. NAT Traversal ............................................60 + 2.23.1. Transport Mode NAT Traversal ......................64 + 2.24. Explicit Congestion Notification (ECN) ...................68 + 2.25. Exchange Collisions ......................................68 + 2.25.1. Collisions while Rekeying or Closing Child SAs ....69 + 2.25.2. Collisions while Rekeying or Closing IKE SAs ......69 + 3. Header and Payload Formats .....................................69 + 3.1. The IKE Header ............................................70 + 3.2. Generic Payload Header ....................................73 + 3.3. Security Association Payload ..............................75 + 3.3.1. Proposal Substructure ..............................78 + 3.3.2. Transform Substructure .............................79 + 3.3.3. Valid Transform Types by Protocol ..................82 + 3.3.4. Mandatory Transform IDs ............................83 + + + +Kaufman, et al. Standards Track [Page 3] + +RFC 5996 IKEv2bis September 2010 + + + 3.3.5. Transform Attributes ...............................84 + 3.3.6. Attribute Negotiation ..............................86 + 3.4. Key Exchange Payload ......................................87 + 3.5. Identification Payloads ...................................87 + 3.6. Certificate Payload .......................................90 + 3.7. Certificate Request Payload ...............................93 + 3.8. Authentication Payload ....................................95 + 3.9. Nonce Payload .............................................96 + 3.10. Notify Payload ...........................................97 + 3.10.1. Notify Message Types ..............................98 + 3.11. Delete Payload ..........................................101 + 3.12. Vendor ID Payload .......................................102 + 3.13. Traffic Selector Payload ................................103 + 3.13.1. Traffic Selector .................................105 + 3.14. Encrypted Payload .......................................107 + 3.15. Configuration Payload ...................................109 + 3.15.1. Configuration Attributes .........................110 + 3.15.2. Meaning of INTERNAL_IP4_SUBNET and + INTERNAL_IP6_SUBNET ..............................113 + 3.15.3. Configuration Payloads for IPv6 ..................115 + 3.15.4. Address Assignment Failures ......................116 + 3.16. Extensible Authentication Protocol (EAP) Payload ........117 + 4. Conformance Requirements ......................................118 + 5. Security Considerations .......................................120 + 5.1. Traffic Selector Authorization ...........................123 + 6. IANA Considerations ...........................................124 + 7. Acknowledgements ..............................................125 + 8. References ....................................................126 + 8.1. Normative References .....................................126 + 8.2. Informative References ...................................127 + Appendix A. Summary of Changes from IKEv1 ........................132 + Appendix B. Diffie-Hellman Groups ................................133 + B.1. Group 1 - 768-bit MODP ....................................133 + B.2. Group 2 - 1024-bit MODP ...................................133 + Appendix C. Exchanges and Payloads ..............................134 + C.1. IKE_SA_INIT Exchange .....................................134 + C.2. IKE_AUTH Exchange without EAP .............................135 + C.3. IKE_AUTH Exchange with EAP ...............................136 + C.4. CREATE_CHILD_SA Exchange for Creating or Rekeying + Child SAs .................................................137 + C.5. CREATE_CHILD_SA Exchange for Rekeying the IKE SA ..........137 + C.6. INFORMATIONAL Exchange ....................................137 + + + + + + + + + +Kaufman, et al. Standards Track [Page 4] + +RFC 5996 IKEv2bis September 2010 + + +1. Introduction + + IP Security (IPsec) provides confidentiality, data integrity, access + control, and data source authentication to IP datagrams. These + services are provided by maintaining shared state between the source + and the sink of an IP datagram. This state defines, among other + things, the specific services provided to the datagram, which + cryptographic algorithms will be used to provide the services, and + the keys used as input to the cryptographic algorithms. + + Establishing this shared state in a manual fashion does not scale + well. Therefore, a protocol to establish this state dynamically is + needed. This document 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. IKEv2 was a change to the IKE protocol that was not backward + compatible. In contrast, the current document not only provides a + clarification of IKEv2, but makes minimum changes to the IKE + protocol. A list of the significant differences between RFC 4306 and + this document is given in Section 1.7. + + 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", and is sometimes called + a "request/response pair". The first exchange of messages + establishing an IKE SA are called the IKE_SA_INIT and IKE_AUTH + exchanges; subsequent IKE exchanges are called the 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 + + + +Kaufman, et al. Standards Track [Page 5] + +RFC 5996 IKEv2bis September 2010 + + + complete, and following that, any number of CREATE_CHILD_SA and + INFORMATIONAL exchanges may occur in any order. In some scenarios, + only a single Child SA is needed between the IPsec endpoints, and + therefore there would be no additional exchanges. Subsequent + exchanges MAY be used to establish additional Child SAs between the + same authenticated pair of endpoints and to perform housekeeping + functions. + + An 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 exchange of an IKE session, IKE_SA_INIT, negotiates + security parameters for the IKE SA, sends nonces, and sends Diffie- + Hellman values. + + The second exchange, 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 the Child SA). + + The types of subsequent exchanges are CREATE_CHILD_SA (which creates + a Child SA) and INFORMATIONAL (which deletes an SA, reports error + conditions, or does other housekeeping). Every request requires a + response. An INFORMATIONAL request with no payloads (other than the + empty Encrypted payload required by the syntax) is commonly used as a + check for liveness. These subsequent exchanges cannot be used until + the initial exchanges have completed. + + In the description that follows, we assume that no errors occur. + Modifications to the flow when errors occur are described in + Section 2.21. + +1.1. Usage Scenarios + + IKE is used to negotiate ESP or AH SAs in a number of different + scenarios, each with its own special requirements. + + + + + + + + + + + +Kaufman, et al. Standards Track [Page 6] + +RFC 5996 IKEv2bis September 2010 + + +1.1.1. Security Gateway to Security Gateway in Tunnel Mode + + +-+-+-+-+-+ +-+-+-+-+-+ + | | IPsec | | + Protected |Tunnel | tunnel |Tunnel | Protected + Subnet <-->|Endpoint |<---------->|Endpoint |<--> Subnet + | | | | + +-+-+-+-+-+ +-+-+-+-+-+ + + Figure 1: Security Gateway to Security Gateway Tunnel + + In this scenario, neither endpoint of the IP connection implements + IPsec, but network nodes between them protect traffic for part of the + way. Protection is transparent to the endpoints, and depends on + ordinary routing to send packets through the tunnel endpoints for + processing. Each endpoint would announce the set of addresses + "behind" it, and packets would be sent in tunnel mode where the inner + IP header would contain the IP addresses of the actual endpoints. + +1.1.2. Endpoint-to-Endpoint Transport 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. + + + + + + + +Kaufman, et al. Standards Track [Page 7] + +RFC 5996 IKEv2bis September 2010 + + + It is possible in this scenario that one or both of the protected + endpoints will be behind a network address translation (NAT) node, in + which case the tunneled packets will have to be UDP encapsulated so + that port numbers in the UDP headers can be used to identify + individual endpoints "behind" the NAT (see Section 2.23). + +1.1.3. Endpoint to Security Gateway in 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. 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 + + + + + +Kaufman, et al. Standards Track [Page 8] + +RFC 5996 IKEv2bis September 2010 + + + endpoint, and packets will have to be UDP encapsulated in order to be + routed properly. Interaction with NATs is covered in detail in + Section 2.23. + +1.1.4. Other Scenarios + + Other scenarios are possible, as are nested combinations of the + above. One notable example combines aspects of Sections 1.1.1 and + 1.1.3. A subnet may make all external accesses through a remote + security gateway using an IPsec tunnel, where the addresses on the + subnet are routed to the security gateway by the rest of the + Internet. An example would be someone's home network being virtually + on the Internet with static IP addresses even though connectivity is + provided by an ISP that assigns a single dynamically assigned IP + address to the user's security gateway (where the static IP addresses + and an IPsec relay are provided by a third party located elsewhere). + +1.2. The Initial Exchanges + + Communication using IKE always begins with IKE_SA_INIT and IKE_AUTH + exchanges (known in IKEv1 as Phase 1). These initial exchanges + normally consist of four messages, though in some scenarios that + number can grow. All communications using IKE consist of request/ + response pairs. We'll describe the base exchange first, followed by + variations. The first pair of messages (IKE_SA_INIT) negotiate + cryptographic algorithms, exchange nonces, and do a Diffie-Hellman + exchange [DH]. + + The second pair of messages (IKE_AUTH) authenticate the previous + messages, exchange identities and certificates, and establish the + first Child SA. Parts of these messages are encrypted and integrity + protected with keys established through the IKE_SA_INIT exchange, so + the identities are hidden from eavesdroppers and all fields in all + the messages are authenticated. See Section 2.14 for information on + how the encryption keys are generated. (A man-in-the-middle attacker + who cannot complete the IKE_AUTH exchange can nonetheless see the + identity of the initiator.) + + All messages following the initial exchange are cryptographically + protected using the cryptographic algorithms and keys negotiated in + 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 + 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. + + + +Kaufman, et al. Standards Track [Page 9] + +RFC 5996 IKEv2bis September 2010 + + + 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. + + In the following descriptions, the payloads contained in the message + are indicated by names as listed below. + + Notation Payload + ----------------------------------------- + AUTH Authentication + CERT Certificate + CERTREQ Certificate Request + CP Configuration + D Delete + EAP Extensible Authentication + HDR IKE header (not a payload) + IDi Identification - Initiator + IDr Identification - Responder + KE Key Exchange + Ni, Nr Nonce + N Notify + SA Security Association + SK Encrypted and Authenticated + 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]; this indicates that a Certificate Request payload + can optionally 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] + + + + + + +Kaufman, et al. Standards Track [Page 10] + +RFC 5996 IKEv2bis September 2010 + + + 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 + encryption and integrity protection are derived from SKEYSEED and are + known as SK_e (encryption) and SK_a (authentication, a.k.a. integrity + protection); see Sections 2.13 and 2.14 for details on the key + derivation. 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 Diffie-Hellman + 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 to which of + the responder's identities it wants to talk. 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 the fact that responder used an IDr different than the one + that was requested, the initiator can close the SA after noticing the + fact. + + The Traffic Selectors (TSi and TSr) are discussed in Section 2.9. + + 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. + + + + + +Kaufman, et al. Standards Track [Page 11] + +RFC 5996 IKEv2bis September 2010 + + + <-- 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. + + Both parties in the IKE_AUTH exchange MUST verify that all signatures + and Message Authentication Codes (MACs) are computed correctly. If + either side uses a shared secret for authentication, the names in the + ID payload MUST correspond to the key used to generate the AUTH + payload. + + Because 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. + + 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 Notify + message types 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. + + If the failure is related to creating the IKE SA (for example, an + AUTHENTICATION_FAILED Notify error message is returned), the IKE SA + is not created. Note that although the IKE_AUTH messages are + encrypted and integrity protected, if the peer receiving this Notify + error message has not yet authenticated the other end (or if the peer + fails to authenticate the other end for some reason), the information + needs to be treated with caution. More precisely, assuming that the + MAC verifies correctly, the sender of the error Notify message is + known to be the responder of the IKE_SA_INIT exchange, but the + sender's identity cannot be assured. + + + + + + +Kaufman, et al. Standards Track [Page 12] + +RFC 5996 IKEv2bis September 2010 + + + 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 + + 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. + + An SA is rekeyed by creating a new SA and then deleting the old one. + This section describes the first part of rekeying, the creation of + new SAs; Section 2.8 covers the mechanics of rekeying, including + moving traffic from old to new SAs and the deletion of the old SAs. + The two sections must be read together to understand the entire + process of rekeying. + + Either endpoint may initiate a CREATE_CHILD_SA exchange, so in this + section the term initiator refers to the endpoint initiating this + exchange. An implementation MAY refuse all CREATE_CHILD_SA requests + within an IKE SA. + + The CREATE_CHILD_SA request MAY optionally contain a KE payload for + an additional Diffie-Hellman exchange to enable stronger guarantees + of forward secrecy for the Child SA. The keying material for the + 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 Notify payload. There are two octets of data + associated with this notification: the accepted Diffie-Hellman 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 Notify payload. + + + + +Kaufman, et al. Standards Track [Page 13] + +RFC 5996 IKEv2bis September 2010 + + + 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. This + notification can also be used to reject IKE SA rekey. 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} + + 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. + + 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. + + + + + +Kaufman, et al. Standards Track [Page 14] + +RFC 5996 IKEv2bis September 2010 + + + 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. 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. + + The NON_FIRST_FRAGMENTS_ALSO notification is used for fragmentation + control. See [IPSECARCH] for a fuller explanation. 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. + + An IPCOMP_SUPPORTED notification, covered in Section 2.22, can also + be included in the exchange. + + A failed attempt to create a Child SA SHOULD NOT tear down the IKE + SA: there is no reason to lose the work done to set up the IKE SA. + See Section 2.21 for a list of error messages that might occur if + creating a Child SA fails. + +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 + payload MUST be included. A new initiator SPI is supplied in the SPI + field of the SA payload. Once a peer receives a request to rekey an + IKE SA or sends a request to rekey an IKE SA, it SHOULD NOT start any + new CREATE_CHILD_SA exchanges on the IKE SA that is being rekeyed. + + 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. + A new responder SPI is supplied in the SPI field of the SA payload. + + + +Kaufman, et al. Standards Track [Page 15] + +RFC 5996 IKEv2bis September 2010 + + + The new IKE SA has its message counters set to 0, regardless of what + they were in the earlier IKE SA. The first IKE requests from both + sides on the new IKE SA will have Message ID 0. The old IKE SA + retains its numbering, so any further requests (for example, to + delete the IKE SA) will have consecutive numbering. The new IKE SA + also has its window size reset to 1, and the initiator in this rekey + exchange is the new "original initiator" of the new IKE SA. + + Section 2.18 also covers IKE SA rekeying in detail. + +1.3.3. Rekeying Child SAs with the CREATE_CHILD_SA Exchange + + The CREATE_CHILD_SA request for rekeying a Child SA is: + + Initiator Responder + ------------------------------------------------------------------- + HDR, SK {N(REKEY_SA), 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 notifications described in Section 1.3.1 may also be sent in a + rekeying exchange. Usually, these will be the same notifications + that were used in the original exchange; for example, when rekeying a + transport mode SA, the USE_TRANSPORT_MODE notification will be used. + + 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. 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 message 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. Standards Track [Page 16] + +RFC 5996 IKEv2bis September 2010 + + + 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. Note that some informational messages, not + exchanges, can be sent outside the context of an IKE SA. Section + 2.21 also covers error messages in great detail. + + 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 that 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; otherwise, + the sender will assume the message was lost in the network and will + retransmit it. That response MAY be an empty message. 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 + + 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 + + + +Kaufman, et al. Standards Track [Page 17] + +RFC 5996 IKEv2bis September 2010 + + + sent listing the SPIs (as they would be expected in the headers of + inbound packets) of the SAs to be deleted. The recipient MUST close + the designated SAs. 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 the INFORMATIONAL exchange. + + Normally, the response 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. + + Similar to ESP and AH SAs, IKE SAs are also deleted by sending an + Informational exchange. Deleting an IKE SA implicitly closes any + remaining Child SAs negotiated under it. The response to a request + that deletes the IKE SA is an empty INFORMATIONAL response. + + 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 does not specify 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, as described above. It can then rebuild the SAs it needs on + a clean base under a new IKE SA. + +1.5. Informational Messages outside of an IKE SA + + There are some cases in which a node receives a packet that it cannot + process, but it may want to notify the sender about this situation. + + o If an ESP or AH packet arrives with an unrecognized SPI. This + might be due to the receiving node having recently crashed and + lost state, or because of some other system malfunction or attack. + + o If an encrypted IKE request packet arrives on port 500 or 4500 + with an unrecognized IKE SPI. This might be due to the receiving + node having recently crashed and lost state, or because of some + other system malfunction or attack. + + + + +Kaufman, et al. Standards Track [Page 18] + +RFC 5996 IKEv2bis September 2010 + + + o If an IKE request packet arrives with a higher major version + number than the implementation supports. + + In the first case, if the receiving node has an active IKE SA to the + IP address from whence the packet came, it MAY send an INVALID_SPI + notification of the wayward packet over that IKE SA in an + INFORMATIONAL exchange. The Notification Data contains the SPI of + the invalid packet. The recipient of this notification cannot tell + whether the SPI is for AH or ESP, but this is not important because + the SPIs are supposed to be different for the two. If no suitable + IKE SA exists, the node MAY send an informational message without + cryptographic protection to the source IP address, using the source + UDP port as the destination port if the packet was UDP (UDP- + encapsulated ESP or AH). In this case, it should only be used by the + recipient as a hint that something might be wrong (because it could + easily be forged). This message is not part of an INFORMATIONAL + exchange, and the receiving node MUST NOT respond to it because doing + so could cause a message loop. The message is constructed as + follows: 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, this being the exception to the rule in + Section 3.1 that prohibits zero IKE Initiator SPIs. The Initiator + flag is set to 1, the Response flag is set to 0, and the version + flags are set in the normal fashion; these flags are described in + Section 3.1. + + In the second and third cases, the message is always sent without + cryptographic protection (outside of an IKE SA), and includes either + an INVALID_IKE_SPI or an INVALID_MAJOR_VERSION notification (with no + notification data). The message 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 and Exchange Type are copied from the + request. The Response flag is set to 1, 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]. 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. + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this + document are to be interpreted as described in [MUSTSHOULD]. + + + + + + +Kaufman, et al. Standards Track [Page 19] + +RFC 5996 IKEv2bis September 2010 + + +1.7. Significant Differences between RFC 4306 and This Document + + This document contains clarifications and amplifications to IKEv2 + [IKEV2]. Many of the clarifications are based on [Clarif]. The + changes listed in that document were discussed in the IPsec Working + Group and, after the Working Group was disbanded, on the IPsec + mailing list. That document contains detailed explanations of areas + that were unclear in IKEv2, and is thus useful to implementers of + IKEv2. + + The protocol described in this document retains the same major + version number (2) and minor version number (0) as was used in RFC + 4306. That is, the version number is *not* changed from RFC 4306. + The small number of technical changes listed here are not expected to + affect RFC 4306 implementations that have already been deployed at + the time of publication of this document. + + This document makes the figures and references a bit more consistent + than they were in [IKEV2]. + + IKEv2 developers have noted that the SHOULD-level requirements in RFC + 4306 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 in RFC 4306. 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. + + 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 + + + + +Kaufman, et al. Standards Track [Page 20] + +RFC 5996 IKEv2bis September 2010 + + + ignore proposals that have configuration attribute type 5, the old + value for INTERNAL_ADDRESS_EXPIRY. This document also removed + INTERNAL_IP6_NBNS as a configuration attribute. + + This document removes the allowance for rejecting messages in which + the payloads were not in the "right" order; now implementations MUST + NOT reject them. This is due to the lack of clarity where the orders + for the payloads are described. + + The lists of items from RFC 4306 that ended up in the IANA registry + were trimmed to only include items that were actually defined in RFC + 4306. Also, many of those lists are now preceded with the very + important instruction to developers that they really should look at + the IANA registry at the time of development because new items have + been added since RFC 4306. + + This document adds clarification on when notifications are and are + not sent encrypted, depending on the state of the negotiation at the + time. + + This document discusses more about how to negotiate combined-mode + ciphers. + + In Section 1.3.2, "The KEi payload SHOULD be included" was changed to + be "The KEi payload MUST be included". This also led to changes in + Section 2.18. + + In Section 2.1, there is new material covering how the initiator's + SPI and/or IP is used to differentiate if this is a "half-open" IKE + SA or a new request. + + This document clarifies the use of the critical flag in Section 2.5. + + In Section 2.8, "Note that, when rekeying, the new Child SA MAY have + different Traffic Selectors and algorithms than the old one" was + changed to "Note that, when rekeying, the new Child SA SHOULD NOT + have different Traffic Selectors and algorithms than the old one". + + The new Section 2.8.2 covers simultaneous IKE SA rekeying. + + The new Section 2.9.2 covers Traffic Selectors in rekeying. + + This document adds the restriction in Section 2.13 that all + pseudorandom functions (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. + + + + + +Kaufman, et al. Standards Track [Page 21] + +RFC 5996 IKEv2bis September 2010 + + + Section 2.18 requires doing a Diffie-Hellman exchange when rekeying + the IKE_SA. In theory, RFC 4306 allowed a policy where the Diffie- + Hellman exchange was optional, but this was not useful (or + appropriate) when rekeying the IKE_SA. + + Section 2.21 has been greatly expanded to cover the different cases + where error responses are needed and the appropriate responses to + them. + + Section 2.23 clarified that, in NAT traversal, now both UDP- + encapsulated IPsec packets and non-UDP-encapsulated IPsec packets + need to be understood when receiving. + + Added Section 2.23.1 to describe NAT traversal when transport mode is + requested. + + Added Section 2.25 to explain how to act when there are timing + collisions when deleting and/or rekeying SAs, and two new error + notifications (TEMPORARY_FAILURE and CHILD_SA_NOT_FOUND) were + defined. + + In Section 3.6, "Implementations MUST support the HTTP method for + hash-and-URL lookup. The behavior of other URL methods is not + currently specified, and such methods SHOULD NOT be used in the + absence of a document specifying them" was added. + + In Section 3.15.3, a pointer to a new document that is related to + configuration of IPv6 addresses was added. + + Appendix C was expanded and clarified. + +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, digital + certificates), and IKEv2 itself does not have a mechanism for + + + +Kaufman, et al. Standards Track [Page 22] + +RFC 5996 IKEv2bis September 2010 + + + fragmenting large messages. IP defines a mechanism for fragmentation + of oversized UDP messages, but implementations vary in the maximum + message size supported. Furthermore, use of IP fragmentation opens + an implementation to denial-of-service (DoS) 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. 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. Implementations and configuration need to keep in + mind, however, that if the URL lookups are possible only after the + Child SA is established, recursion issues could prevent this + technique from working. + + 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. + +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 exchanges. 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 exchange, 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 causes 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). In order to allow saving memory, responders are + allowed to forget the response after a timeout of several minutes. + If the responder receives a retransmitted request for which it has + already forgotten the response, it MUST ignore the request (and not, + for example, attempt constructing a new response). + + + +Kaufman, et al. Standards Track [Page 23] + +RFC 5996 IKEv2bis September 2010 + + + IKE is a reliable protocol: the initiator MUST retransmit a request + until it either receives a corresponding response or deems the IKE SA + to have failed. In the latter case, the initiator discards all state + associated with the IKE SA and any Child SAs that were 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) do not have to be identical. + + 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 a retransmission belonging to an + existing "half-open" IKE SA (in which case the responder retransmits + the same response), or a new request (in which case the responder + creates a new IKE SA and sends a fresh response), or it 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. + + The retransmission policy for one-way messages is somewhat different + from that for regular messages. Because no acknowledgement is ever + sent, there is no reason to gratuitously retransmit one-way messages. + Given that all these messages are errors, it makes sense to send them + only once per "offending" packet, and only retransmit if further + offending packets are received. Still, it also makes sense to limit + retransmissions of such error messages. + +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. Retransmission of a message + MUST use the same Message ID as the original message. + + 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), and incremented for + each subsequent exchange. Thus, the first pair of IKE_AUTH messages + will have an ID of 1, the second (when EAP is used) will be 2, and so + on. The Message ID is reset to zero in the new IKE SA after the IKE + SA is rekeyed. + + + + +Kaufman, et al. Standards Track [Page 24] + +RFC 5996 IKEv2bis September 2010 + + + 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 a very different number + of requests, the Message IDs in the two directions can be very + different. There is no ambiguity in the messages, however, because + the Initiator and Response flags in the message header specify which + of the four messages a particular one is. + + Throughout this document, "initiator" refers to the party who + initiated the exchange being described. The "original initiator" + always refers to the party who initiated the exchange that 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 + + 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. + + After an IKE SA is set up, in order to maximize IKE throughput, an + IKE endpoint MAY issue multiple requests before getting a response to + any of them, up to the limit set by its peer's SET_WINDOW_SIZE. + These requests may pass one another over the network. An IKE + endpoint MUST be prepared to accept and process a request while it + + + +Kaufman, et al. Standards Track [Page 25] + +RFC 5996 IKEv2bis September 2010 + + + has a request outstanding in order to avoid a deadlock in this + situation. An IKE endpoint may also accept and process multiple + requests while it has a request outstanding. + + 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. + + 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, what + the responder should do when it receives a SET_WINDOW_SIZE + notification containing a smaller value than is currently in effect + is not defined. Thus, there is currently no way to reduce the window + size of an existing IKE SA; you can only increase it. When rekeying + an IKE SA, the new IKE SA starts with window size 1 until it is + explicitly increased by sending a new SET_WINDOW_SIZE notification. + + The INVALID_MESSAGE_ID notification is sent when an IKE Message ID + outside the supported window is received. This Notify message 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. + + + + + +Kaufman, et al. Standards Track [Page 26] + +RFC 5996 IKEv2bis September 2010 + + + 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). The INITIAL_CONTACT notification, if sent, MUST + be in the first IKE_AUTH request or response, not as a separate + exchange afterwards; receiving parties MAY ignore it in other + messages. + + Since IKE is designed to operate in spite of DoS attacks from the + network, an endpoint MUST NOT conclude that the other endpoint has + failed based on any routing information (e.g., ICMP messages) or IKE + messages that arrive without cryptographic protection (e.g., Notify + messages complaining about unknown SPIs). An endpoint MUST conclude + that the other endpoint has failed only when repeated attempts to + contact it have gone unanswered for a timeout period or when a + cryptographically protected INITIAL_CONTACT notification is received + on a different IKE SA to the same authenticated identity. An + endpoint should suspect that the other endpoint has failed based on + routing information and initiate a request to see whether the other + endpoint is alive. To check whether the other side is alive, IKE + specifies an empty INFORMATIONAL message 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 Notify messages MAY be + ignored. Implementations MUST limit the rate at which they take + actions based on unprotected messages. + + The number of retries and length 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, retransmission 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 + + + +Kaufman, et al. Standards Track [Page 27] + +RFC 5996 IKEv2bis September 2010 + + + 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 needs to stop sending over any SA if + some failure prevents it from receiving on all of the associated SAs. + If a system creates Child SAs that can fail independently from one + another without the associated IKE SA being able to send a delete + message, then the system MUST negotiate such Child SAs using separate + IKE SAs. + + There is a DoS attack on the initiator of an IKE SA that can be + avoided if the initiator takes the proper care. Since the first two + messages of an SA setup are not cryptographically protected, an + attacker could respond to the initiator's message before the genuine + responder and poison the connection setup attempt. To prevent this, + the initiator MAY be willing to accept multiple responses to its + first message, treat each as potentially legitimate, respond to it, + and then discard all the invalid half-open connections when it + receives a valid cryptographically protected response to any one of + its requests. Once a cryptographically valid response is received, + all subsequent responses should be ignored whether or not they are + cryptographically valid. + + Note that with these rules, there is no reason to negotiate and agree + upon an SA lifetime. If IKE presumes the partner is dead, based on + repeated lack of acknowledgement to an IKE message, then the IKE SA + and all Child SAs set up through that IKE SA are deleted. + + An IKE endpoint may at any time delete inactive Child SAs to recover + resources used to hold their state. If an IKE endpoint chooses to + delete Child SAs, it MUST send Delete payloads to the other end + notifying it of the deletion. It MAY similarly time out the IKE SA. + Closing the IKE SA implicitly closes all associated Child SAs. In + this case, an IKE endpoint SHOULD send a Delete payload indicating + that it has closed the IKE SA 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. 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. + + + + + + +Kaufman, et al. Standards Track [Page 28] + +RFC 5996 IKEv2bis September 2010 + + + 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 + Notify message type. The node with the larger minor version number + would simply note that its correspondent would not be able to + understand that message and therefore would not send it. + + If an endpoint receives a message with a higher major version number, + it MUST drop the message and SHOULD send an unauthenticated Notify + 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 + 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. 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" [IP]). + 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 + + + +Kaufman, et al. Standards Track [Page 29] + +RFC 5996 IKEv2bis September 2010 + + + 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. 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 that 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. + + Although new payload types may be added in the future and may appear + interleaved with the fields defined in this specification, + implementations SHOULD send the payloads defined in this + specification in the order shown in the figures in Sections 1 and 2; + implementations MUST NOT reject as invalid a message with those + payloads in any other order. + +2.6. IKE SA SPIs and Cookies + + The initial two eight-octet fields in the header, called the "IKE + SPIs", 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: it 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 Initiator flag in the header to determine whether it + assigned the first or the second eight octets. + + + + + + +Kaufman, et al. Standards Track [Page 30] + +RFC 5996 IKEv2bis September 2010 + + + 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. 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 also in + the response message. However, if the responder sends a non-zero + responder SPI, the initiator should not reject the response for only + that reason. + + Two expected attacks against IKE are state and CPU exhaustion, where + the target is flooded with session initiation requests from forged IP + addresses. These attacks can be made less effective if 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. 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: + + 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. + + + + + +Kaufman, et al. Standards Track [Page 31] + +RFC 5996 IKEv2bis September 2010 + + + 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 used 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 in the hash + ensures that an attacker who sees only message 2 can't successfully + forge a message 3. Also, incorporating SPIi in the hash prevents an + attacker from fetching one cookie from the other end, and then + initiating many IKE_SA_INIT exchanges all with different initiator + SPIs (and perhaps port numbers) so that the responder thinks that + there are a lot of machines behind one NAT box that are all trying to + connect. + + If a new value for <secret> is chosen while there are connections in + the process of being initialized, an IKE_SA_INIT might be returned + with other than the current <VersionIDofSecret>. The responder in + that case MAY reject the message by sending another response with a + new cookie or it MAY keep the old value of <secret> around for a + short time and accept cookies computed from either one. The + responder should not accept cookies indefinitely after <secret> is + changed, since that would defeat part of the DoS protection. The + responder should change the value of <secret> frequently, especially + if under attack. + + 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, possibly using exponential back-off. An + + + +Kaufman, et al. Standards Track [Page 32] + +RFC 5996 IKEv2bis September 2010 + + + attacker can forge multiple cookie responses to the initiator's + IKE_SA_INIT message, and each of those forged cookie replies will + cause two packets to be sent: one packet from the initiator to the + responder (which will reject those cookies), and one response from + responder to initiator that includes the correct cookie. + + A note on terminology: 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 called "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. + +2.6.1. Interaction of COOKIE and INVALID_KE_PAYLOAD + + There are two common reasons why the initiator may have to retry the + IKE_SA_INIT exchange: the responder requests a cookie or wants a + different Diffie-Hellman group than was included in the KEi payload. + 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 round trip may be needed in some cases. An additional + round trip 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 KEi payloads in cookie calculation, it + will reject the request by sending a new cookie. + + If both peers support including the cookie in all retries, a slightly + shorter exchange can happen. + + 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. + + + + + +Kaufman, et al. Standards Track [Page 33] + +RFC 5996 IKEv2bis September 2010 + + +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. 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 ID does not completely specify the cryptographic + algorithm). + + This hierarchical structure was designed to efficiently encode + proposals for cryptographic suites when the number of supported + suites is large because multiple values are acceptable for multiple + transforms. The responder MUST choose a single suite, which may be + any subset of the SA proposal following the rules below. + + Each proposal contains one 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. 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. + + 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 algorithms 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"). + +2.8. Rekeying + + IKE, ESP, and AH Security Associations use secret keys that should be + used only for a limited amount of time and to protect a limited + amount of data. This limits the lifetime of the entire Security + Association. When the lifetime of a Security Association expires, + the Security Association MUST NOT be used. If there is demand, new + + + +Kaufman, et al. Standards Track [Page 34] + +RFC 5996 IKEv2bis September 2010 + + + Security Associations MAY be established. Reestablishment of + Security Associations to take the place of ones that expire is + referred to as "rekeying". + + To allow for minimal IPsec implementations, the ability to rekey SAs + without restarting the entire IKE SA is optional. An implementation + MAY refuse all CREATE_CHILD_SA requests within an IKE SA. If an SA + has expired or is about to expire and rekeying attempts using the + mechanisms described here fail, an implementation MUST close the IKE + SA and any associated Child SAs and then MAY start new ones. + Implementations may wish to support in-place rekeying of SAs, since + doing so offers better performance and is likely to reduce the number + of packets lost during the transition. + + To rekey a Child SA within an existing IKE SA, create a new, + equivalent SA (see Section 2.17 below), and when the new one is + established, delete the old one. Note that, when rekeying, the new + Child SA SHOULD NOT have different Traffic Selectors and algorithms + than 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. After the new equivalent IKE SA is created, the initiator + deletes the old IKE SA, and the Delete payload to delete itself MUST + be the last request sent over the old IKE SA. + + SAs should be rekeyed proactively, i.e., the new SA should be + established before the old one expires and becomes unusable. Enough + time should elapse between the time the new SA is established and the + old one becomes unusable so that traffic can be switched over to the + new SA. + + A difference between IKEv1 and IKEv2 is that in IKEv1 SA lifetimes + were negotiated. In IKEv2, each end of the SA is responsible for + enforcing its own lifetime policy on the SA and rekeying the SA when + necessary. If the two ends have different lifetime policies, the end + with the shorter lifetime will end up always being the one to request + the rekeying. If an SA has been inactive for a long time and if an + endpoint would not initiate the SA in the absence of traffic, the + endpoint MAY choose to close the SA instead of rekeying it when its + lifetime expires. It can also do so if there has been no traffic + since the last time the SA was rekeyed. + + + + + + +Kaufman, et al. Standards Track [Page 35] + +RFC 5996 IKEv2bis September 2010 + + + 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. + + There are timing windows -- particularly in the presence of lost + packets -- where endpoints may not agree on the state of an SA. The + responder to a CREATE_CHILD_SA MUST be prepared to accept messages on + an SA before sending its response to the creation request, so there + is no ambiguity for the initiator. The initiator MAY begin sending + on an SA as soon as it processes the response. The initiator, + however, cannot receive on a newly created SA until it receives and + processes the response to its CREATE_CHILD_SA request. How, then, is + the responder to know when it is OK to send on the newly created SA? + + From a technical correctness and interoperability perspective, the + responder MAY begin sending on an SA as soon as it sends its response + to the CREATE_CHILD_SA request. In some situations, however, this + could result in packets unnecessarily being dropped, so an + implementation MAY 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 other half of the SA pair, 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. 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 ESP message + on a newly created ESP 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 + + 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). + + + + +Kaufman, et al. Standards Track [Page 36] + +RFC 5996 IKEv2bis September 2010 + + + 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. "Lowest" means an + octet-by-octet 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 + node that initiated the surviving rekeyed SA should delete the + replaced SA after the new one is established. + + The following is an explanation on the impact this has on + implementations. Assume that hosts A and B have an existing Child 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 happening. + 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. + + + +Kaufman, et al. Standards Track [Page 37] + +RFC 5996 IKEv2bis September 2010 + + + 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. + + 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 + CHILD_SA_NOT_FOUND. + + <-- send resp1: N(CHILD_SA_NOT_FOUND) + recv resp1 <-- + + When A receives this error, it already knows there was simultaneous + rekeying, so it can ignore the error message. + + + + +Kaufman, et al. Standards Track [Page 38] + +RFC 5996 IKEv2bis September 2010 + + +2.8.2. Simultaneous IKE SA Rekeying + + Probably the most complex case occurs when both peers try to rekey + the IKE_SA at the same time. Basically, the text in Section 2.8 + applies to this case as well; however, it is important to ensure that + the Child SAs are inherited by the correct IKE_SA. + + The case where both endpoints notice the simultaneous rekeying works + the same way as with Child SAs. After the CREATE_CHILD_SA exchanges, + three IKE SAs exist between A and B: the old IKE SA and two new IKE + SAs. The new IKE SA containing the lowest nonce SHOULD be deleted by + the node that created it, and the other surviving new IKE SA MUST + inherit all the Child SAs. + + In addition to normal simultaneous rekeying cases, there is a special + case where one peer finishes its rekey before it even notices that + other peer is doing a rekey. If only one peer detects a simultaneous + rekey, redundant SAs are not created. In this case, when the peer + that did not notice the simultaneous rekey gets the request to rekey + the IKE SA that it has already successfully rekeyed, it SHOULD return + TEMPORARY_FAILURE because it is an IKE SA that it is currently trying + to close (whether or not it has already sent the delete notification + for the SA). If the peer that did notice the simultaneous rekey gets + the delete request from the other peer for the old IKE SA, it knows + that the other peer did not detect the simultaneous rekey, and the + first peer can forget its own rekey attempt. + + Host A Host B + ------------------------------------------------------------------- + send req1: + SA(..,SPIa1,..),Ni1,.. --> + <-- send req2: SA(..,SPIb1,..),Ni2,.. + --> recv req1 + <-- send resp1: SA(..,SPIb2,..),Nr2,.. + recv resp1 <-- + send req3: D() --> + --> recv req3 + + At this point, host B sees a request to close the IKE_SA. There's + not much more to do than to reply as usual. However, at this point + host B should stop retransmitting req2, since once host A receives + resp3, it will delete all the state associated with the old IKE_SA + and will not be able to reply to it. + + <-- send resp3: () + + The TEMPORARY_FAILURE notification was not included in RFC 4306, and + support of the TEMPORARY_FAILURE notification is not negotiated. + + + +Kaufman, et al. Standards Track [Page 39] + +RFC 5996 IKEv2bis September 2010 + + + Thus, older peers that implement RFC 4306 but not this document may + receive these notifications. In that case, they will treat it the + same as any other unknown error notification, and will stop the + exchange. Because the other peer has already rekeyed the exchange, + doing so does not have any ill effects. + +2.8.3. Rekeying the IKE SA versus Reauthentication + + Rekeying the IKE SA and reauthentication are different concepts in + IKEv2. Rekeying the IKE SA establishes new keys for the IKE SA and + resets the Message ID counters, but it does not authenticate the + parties again (no AUTH or EAP payloads are involved). + + 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. + 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 + 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 + + 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, although some implementations might + update their SPD in connection with the running of IKE (for an + example scenario, see Section 1.1.3). + + + + + +Kaufman, et al. Standards Track [Page 40] + +RFC 5996 IKEv2bis September 2010 + + + Traffic Selector (TS) payloads allow endpoints to communicate some of + the information from their SPD to their peers. These must be + communicated to IKE from the SPD (for example, the PF_KEY API [PFKEY] + uses the SADB_ACQUIRE message). 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) + 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 198.51.100.* 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 (198.51.100.0 - 198.51.100.255) 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. + + 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 + returned in the narrowed set. + + + + + + +Kaufman, et al. Standards Track [Page 41] + +RFC 5996 IKEv2bis September 2010 + + + 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 (198.51.100.43 - 198.51.100.43) and the source port and + IP protocol from the packet and the second containing (198.51.100.0 - + 198.51.100.255) 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: + + o If the responder's policy does not allow it to accept any part of + the proposed Traffic Selectors, it responds with a TS_UNACCEPTABLE + Notify message. + + 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 + (198.51.100.43 - 198.51.100.43) 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. 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. + + + +Kaufman, et al. Standards Track [Page 42] + +RFC 5996 IKEv2bis September 2010 + + + 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 didn't generate its + request based on the packet, but (for example) upon startup, there + would not be the very specific first Traffic Selectors helping the + responder to select the correct range. 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 SINGLE_PAIR_REQUIRED Notify message. + + 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 for only the + specific traffic it is trying to forward. + + 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 + + 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 198.51.100.66 is sent via host + B encrypted using AES, and traffic to all other hosts in + 198.51.100.0/24 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 (198.51.100.0-198.51.100.255), this will be accepted by + host B. Now, host B can also use this SA to send traffic from + 198.51.100.66, but those packets will be dropped by A since it + requires the use of AES for this traffic. Even if host A creates a + new SA only for 198.51.100.66 that uses AES, host B may freely + continue to use the first SA for the traffic. In this situation, + + + + +Kaufman, et al. Standards Track [Page 43] + +RFC 5996 IKEv2bis September 2010 + + + when proposing the SA, host A should have followed its own policy, + and included a TSr containing ((198.51.100.0- + 198.51.100.65),(198.51.100.67-198.51.100.255)) 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 + pseudorandom 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 pseudorandom function + (PRF). 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 over which it runs. 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 + + + + +Kaufman, et al. Standards Track [Page 44] + +RFC 5996 IKEv2bis September 2010 + + + 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. + + Because computing Diffie-Hellman exponentials is computationally + expensive, an endpoint may find it advantageous to reuse those + exponentials for multiple connection setups. There are several + reasonable strategies for doing this. An endpoint could choose a new + exponential only periodically though this could result in less-than- + perfect forward secrecy if some connection lasts for less than the + lifetime of the exponential. Or it could keep track of which + exponential was used for each connection and delete the information + associated with the exponential only when some corresponding + connection was closed. This would allow the exponential to be reused + without losing perfect forward secrecy at the cost of maintaining + more state. + + Whether and when to reuse Diffie-Hellman exponentials are private + decisions in the sense that they 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. See [REUSE] + for a security analysis of this practice and for additional security + considerations when reusing ephemeral Diffie-Hellman keys. + +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 pseudorandom function (PRF). + The PRF 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 definition 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. + + + +Kaufman, et al. Standards Track [Page 45] + +RFC 5996 IKEv2bis September 2010 + + + 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 PRFs accept keys of any length, but have a + preferred key size. The preferred key size MUST be 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, the PRF is + used iteratively. The term "prf+" describes a function that outputs + a pseudorandom stream based on the inputs to a pseudorandom function + called "prf". + + In the following, | indicates concatenation. prf+ is defined as: + + 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) + ... + + This continues until all the material needed to compute all required + keys has been output from prf+. 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 prf function is a single + octet. The prf+ function is not defined beyond 255 times the size of + the prf function 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 + + + +Kaufman, et al. Standards Track [Page 46] + +RFC 5996 IKEv2bis September 2010 + + + 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 MUST be the preferred key length of the PRF agreed upon. + + 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 backward-compatibility reasons, there are two PRFs that + are treated specially in this calculation. If the negotiated PRF is + AES-XCBC-PRF-128 [AESXCBCPRF128] or AES-CMAC-PRF-128 [AESCMACPRF128], + only the first 64 bits of Ni and the first 64 bits of Nr are used in + calculating SKEYSEED, but all the bits are used for input to the prf+ + function. + + 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 padded + shared secret as the key, as described later in this section) a block + of data. In these calculations, IDi' and IDr' are the entire ID + payloads excluding the fixed header. 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 the 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'). 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 + + + +Kaufman, et al. Standards Track [Page 47] + +RFC 5996 IKEv2bis September 2010 + + + 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'). It is critical to the security of the exchange + that each side sign the other side's nonce. + + 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 | RestOfInitIDPayload + RestOfInitIDPayload = IDType | RESERVED | InitIDData + MACedIDForI = prf(SK_pi, RestOfInitIDPayload) + + The responder's signed octets can be described as: + + ResponderSignedOctets = RealMessage2 | NonceIData | MACedIDForR + GenIKEHDR = [ four octets 0 if using port 4500 ] | RealIKEHDR + RealIKEHDR = SPIi | SPIr | . . . | Length + RealMessage2 = RealIKEHDR | RestOfMessage2 + NonceIPayload = PayloadHeader | NonceIData + ResponderIDPayload = PayloadHeader | RestOfRespIDPayload + 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, the same key is + used in both directions. + + + + + +Kaufman, et al. Standards Track [Page 48] + +RFC 5996 IKEv2bis September 2010 + + + Note that it is a common but typically insecure practice to have a + shared key derived solely from a user-chosen password without + incorporating another source of randomness. This is typically + insecure because user-chosen passwords are unlikely to have + sufficient unpredictability to resist dictionary attacks and these + attacks are not prevented in this authentication method. + (Applications using password-based authentication for bootstrapping + and IKE SA should use the authentication method in Section 2.16, + which is designed to prevent off-line dictionary attacks.) The pre- + shared key 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: + + For the initiator: + AUTH = prf( prf(Shared Secret, "Key Pad for IKEv2"), + <InitiatorSignedOctets>) + For the responder: + AUTH = prf( prf(Shared Secret, "Key Pad for IKEv2"), + <ResponderSignedOctets>) + + where the string "Key Pad for IKEv2" is 17 ASCII characters without + null termination. The shared secret can be variable length. The pad + string is added so that if the shared secret is derived from a + password, the IKE implementation need not store the password in + cleartext, but rather can store the value prf(Shared Secret,"Key Pad + for IKEv2"), which could not be used as a password equivalent for + protocols other than IKEv2. As noted above, deriving the shared + secret from a password is not secure. This construction is used + because it is anticipated that people will do it anyway. The + 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. + + There are two types of EAP authentication (described in + Section 2.16), and each type uses different values in the AUTH + computations shown above. If the EAP method is key-generating, + substitute master session key (MSK) for the shared secret in the + computation. For non-key-generating methods, substitute SK_pi and + SK_pr, respectively, for the shared secret in the two AUTH + computations. + + + + + + + + +Kaufman, et al. Standards Track [Page 49] + +RFC 5996 IKEv2bis September 2010 + + +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 document references [EAP] with the intent that new methods + can be added in the future without updating this specification, some + simpler variations are documented here. [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 EAP by leaving out the AUTH + payload from the first message in the IKE_AUTH exchange. (Note that + the AUTH payload is required for non-EAP authentication, and is thus + not marked as optional in the rest of this document.) 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 EAP method, it will place an Extensible Authentication Protocol + (EAP) payload in the response of the IKE_AUTH exchange and defer + sending SAr2, TSi, and TSr until initiator authentication is complete + in a subsequent IKE_AUTH exchange. In the case of a minimal EAP + method, the initial SA establishment will appear as follows: + + Initiator Responder + ------------------------------------------------------------------- + HDR, SAi1, KEi, Ni --> + <-- HDR, SAr1, KEr, Nr, [CERTREQ] + HDR, SK {IDi, [CERTREQ,] + [IDr,] SAi2, + TSi, TSr} --> + <-- HDR, SK {IDr, [CERT,] AUTH, + EAP } + HDR, SK {EAP} --> + <-- HDR, SK {EAP (success)} + HDR, SK {AUTH} --> + <-- HDR, SK {AUTH, SAr2, TSi, TSr } + + + + + + +Kaufman, et al. Standards Track [Page 50] + +RFC 5996 IKEv2bis September 2010 + + + 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. + + 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 + Success message. + + When the initiator authentication uses EAP, it is possible that the + contents of the IDi payload is used only for Authentication, + Authorization, and Accounting (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, if different from that in the + IDi payload, has to be sent from the AAA server to the IKEv2 + responder. + + + + +Kaufman, et al. Standards Track [Page 51] + +RFC 5996 IKEv2bis September 2010 + + +2.17. Generating Keying Material for Child SAs + + A single Child SA is created by the IKE_AUTH exchange, and additional + Child SAs can optionally be created in CREATE_CHILD_SA exchanges. + Keying material for them is generated as follows: + + KEYMAT = prf+(SK_d, Ni | Nr) + + Where Ni and Nr are the nonces from the IKE_SA_INIT exchange if this + request is the first Child SA created or the fresh Ni and Nr from the + CREATE_CHILD_SA exchange if this is a subsequent creation. + + For CREATE_CHILD_SA exchanges including an optional Diffie-Hellman + exchange, the keying material is defined as: + + KEYMAT = prf+(SK_d, g^ir (new) | Ni | Nr ) + + where g^ir (new) is the shared secret from the ephemeral Diffie- + Hellman exchange of this CREATE_CHILD_SA exchange (represented as an + octet string in big endian order padded with zeros in the high-order + bits if necessary to make it the length of the modulus). + + A single CHILD_SA negotiation may result in multiple Security + Associations. ESP and AH SAs exist in pairs (one in each direction), + so two SAs are created in a single Child SA negotiation for them. + Furthermore, Child SA negotiation may include some future IPsec + protocol(s) in addition to, or instead of, ESP or AH (for example, + ROHC_INTEG as described in [ROHCV2]). In any case, keying material + for each Child SA MUST be taken from the expanded KEYMAT using the + following rules: + + o All keys for SAs carrying data from the initiator to the responder + are taken before SAs going from the responder to the initiator. + + o If multiple IPsec protocols are negotiated, keying material for + each Child SA is taken in the order in which the protocol headers + will appear in the encapsulated packet. + + o If an IPsec protocol requires multiple keys, the order in which + they are taken from the SA's keying material needs to be described + in the protocol's specification. For ESP and AH, [IPSECARCH] + defines the order, namely: the encryption key (if any) MUST be + taken from the first bits and the integrity key (if any) MUST be + taken from the remaining bits. + + + + + + + +Kaufman, et al. Standards Track [Page 52] + +RFC 5996 IKEv2bis September 2010 + + + 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 Sections 1.3.2 and 2.8). 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. + + 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 to generate SKEYSEED. + + The main reason for 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 MUST + perform a new Diffie-Hellman exchange when rekeying the IKE SA. In + other words, an initiator MUST NOT propose the value "NONE" for the + Diffie-Hellman transform, and a responder MUST NOT accept such a + proposal. This means that a successful 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, using SPIi, SPIr, Ni, and Nr from the new + exchange, and using the new IKE SA's PRF. + +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 + + + +Kaufman, et al. Standards Track [Page 53] + +RFC 5996 IKEv2bis September 2010 + + + 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. Note, however, it is usual to + only assign one IP address during the IKE_AUTH exchange. That + address persists at least until the deletion of the IKE SA. + + 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 + (Bootstrap Protocol) 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. + + + + + + + + + + + + + + + + + + +Kaufman, et al. Standards Track [Page 54] + +RFC 5996 IKEv2bis September 2010 + + + 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: + + CP(CFG_REPLY)= + INTERNAL_ADDRESS(192.0.2.202) + INTERNAL_NETMASK(255.255.255.0) + INTERNAL_SUBNET(192.0.2.0/255.255.255.0) + TSi = (0, 0-65535,192.0.2.202-192.0.2.202) + TSr = (0, 0-65535,192.0.2.0-192.0.2.255) + + All returned values will be implementation dependent. As can be seen + in the above example, the IRAS MAY also send other attributes that + were not included in CP(CFG_REQUEST) and MAY ignore the non- + mandatory attributes that it does not support. + + The responder MUST NOT send a CFG_REPLY without having first received + a CP(CFG_REQUEST) from the initiator, because we do not want the IRAS + to perform an unnecessary configuration lookup if the IRAC cannot + process the REPLY. + + In the case where the IRAS's configuration requires that CP be used + for a given identity IDi, but IRAC has failed to send a + CP(CFG_REQUEST), IRAS MUST fail the request, and terminate the Child + SA creation with a FAILED_CP_REQUIRED error. The FAILED_CP_REQUIRED + is not fatal to the IKE SA; it simply causes the Child SA creation to + fail. The initiator can fix this by later starting a new + Configuration payload request. There is no associated data in the + FAILED_CP_REQUIRED error. + +2.20. Requesting the Peer's Version + + An IKE peer wishing to inquire about the other peer's IKE software + version information MAY use the method below. This is an example of + a configuration request within an INFORMATIONAL exchange, after the + IKE SA and first Child SA have been created. + + + + + + + +Kaufman, et al. Standards Track [Page 55] + +RFC 5996 IKEv2bis September 2010 + + + An IKE implementation MAY decline to give out version information + prior to authentication or even after authentication 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. + The general rule is that if a request is received that is badly + formatted, or unacceptable for reasons of policy (such as no matching + cryptographic algorithms), the response contains a Notify payload + indicating the error. The decision whether or not to send such a + response depends whether or not there is an authenticated IKE SA. + + If there is an error parsing or processing a response packet, the + general rule is to not send back any error message because responses + should not generate new requests (and a new request would be the only + way to send back an error message). Such errors in parsing or + processing response packets should still cause the recipient to clean + up the IKE state (for example, by sending a Delete for a bad SA). + + Only authentication failures (AUTHENTICATION_FAILED and EAP failure) + and malformed messages (INVALID_SYNTAX) lead to a deletion of the IKE + SA without requiring an explicit INFORMATIONAL exchange carrying a + Delete payload. Other error conditions MAY require such an exchange + if policy dictates that this is needed. If the exchange is + terminated with EAP Failure, an AUTHENTICATION_FAILED notification is + not sent. + +2.21.1. Error Handling in IKE_SA_INIT + + Errors that occur before a cryptographically protected IKE SA is + established need to be handled very carefully. There is a trade-off + between wanting to help the peer to diagnose a problem and thus + responding to the error and wanting to avoid being part of a DoS + attack based on forged messages. + + + +Kaufman, et al. Standards Track [Page 56] + +RFC 5996 IKEv2bis September 2010 + + + In an IKE_SA_INIT exchange, any error notification causes the + exchange to fail. Note that some error notifications such as COOKIE, + INVALID_KE_PAYLOAD or INVALID_MAJOR_VERSION may lead to a subsequent + successful exchange. Because all error notifications are completely + unauthenticated, the recipient should continue trying for some time + before giving up. The recipient should not immediately act based on + the error notification unless corrective actions are defined in this + specification, such as for COOKIE, INVALID_KE_PAYLOAD, and + INVALID_MAJOR_VERSION. + +2.21.2. Error Handling in IKE_AUTH + + All errors that occur in an IKE_AUTH exchange, causing the + authentication to fail for whatever reason (invalid shared secret, + invalid ID, untrusted certificate issuer, revoked or expired + certificate, etc.) SHOULD result in an AUTHENTICATION_FAILED + notification. If the error occurred on the responder, the + notification is returned in the protected response, and is usually + the only payload in that response. Although the IKE_AUTH messages + are encrypted and integrity protected, if the peer receiving this + notification has not authenticated the other end yet, that peer needs + to treat the information with caution. + + If the error occurs on the initiator, the notification MAY be + returned in a separate INFORMATIONAL exchange, usually with no other + payloads. This is an exception for the general rule of not starting + new exchanges based on errors in responses. + + Note, however, that request messages that contain an unsupported + critical payload, or where the whole message is malformed (rather + than just bad payload contents), MUST be rejected in their entirety, + and MUST only lead to an UNSUPPORTED_CRITICAL_PAYLOAD or + INVALID_SYNTAX Notification sent as a response. The receiver should + not verify the payloads related to authentication in this case. + + If authentication has succeeded in the IKE_AUTH exchange, the IKE SA + is established; however, establishing the Child SA or requesting + configuration information may still fail. This failure does not + automatically cause the IKE SA to be deleted. Specifically, a + responder may include all the payloads associated with authentication + (IDr, CERT, and AUTH) while sending error notifications for the + piggybacked exchanges (FAILED_CP_REQUIRED, NO_PROPOSAL_CHOSEN, and so + on), and the initiator MUST NOT fail the authentication because of + this. The initiator MAY, of course, for reasons of policy later + delete such an IKE SA. + + + + + + +Kaufman, et al. Standards Track [Page 57] + +RFC 5996 IKEv2bis September 2010 + + + In an IKE_AUTH exchange, or in the INFORMATIONAL exchange immediately + following it (in case an error happened when processing a response to + IKE_AUTH), the UNSUPPORTED_CRITICAL_PAYLOAD, INVALID_SYNTAX, and + AUTHENTICATION_FAILED notifications are the only ones to cause the + IKE SA to be deleted or not created, without a Delete payload. + Extension documents may define new error notifications with these + semantics, but MUST NOT use them unless the peer has been shown to + understand them, such as by using the Vendor ID payload. + +2.21.3. Error Handling after IKE SA is Authenticated + + After the IKE SA is authenticated, all requests having errors MUST + result in a response notifying about the error. + + In normal situations, there should not be cases where a valid + response from one peer results in an error situation in the other + peer, so there should not be any reason for a peer to send error + messages to the other end except as a response. Because sending such + error messages as an INFORMATIONAL exchange might lead to further + errors that could cause loops, such errors SHOULD NOT be sent. If + errors are seen that indicate that the peers do not have the same + state, it might be good to delete the IKE SA to clean up state and + start over. + + If a peer parsing a request notices that it is badly formatted (after + it has passed the message authentication code checks and window + checks) and it returns an INVALID_SYNTAX notification, then this + error notification is considered fatal in both peers, meaning that + the IKE SA is deleted without needing an explicit Delete payload. + +2.21.4. Error Handling Outside IKE SA + + A node needs to limit the rate at which it will send messages in + response to unprotected messages. + + If a node receives a message on UDP port 500 or 4500 outside the + context of an IKE SA known to it (and the message is not a request to + start an IKE SA), this may be the result of a recent crash of the + node. If the message is marked as a response, the node can audit the + suspicious event but MUST NOT respond. If the message is marked as a + request, the node can 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 where it came with the same IKE SPIs and the + Message ID copied. The response MUST NOT be cryptographically + protected and MUST contain an INVALID_IKE_SPI Notify payload. 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. + + + +Kaufman, et al. Standards Track [Page 58] + +RFC 5996 IKEv2bis September 2010 + + + A peer 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 that a genuine correspondent was + tricked into sending. A node should treat such a message (and also a + network message like ICMP destination unreachable) as a hint that + there might be problems with SAs to that IP address and should + initiate a liveness check for any such IKE SA. An implementation + SHOULD limit the frequency of such tests to avoid being tricked into + participating in a DoS attack. + + 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. + + A node receiving a suspicious message from an IP address (and port, + if NAT traversal is used) with which it has an IKE SA SHOULD send an + IKE Notify payload in an IKE INFORMATIONAL exchange over that SA. + 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. + +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 Notify message 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. + + The data associated with this Notify message includes a two-octet + IPComp CPI followed by a one-octet Transform ID optionally followed + by attributes whose length and format are defined by that Transform + ID. A message proposing an SA may contain multiple IPCOMP_SUPPORTED + notifications to indicate multiple supported algorithms. A message + accepting an SA may contain at most one. + + + +Kaufman, et al. Standards Track [Page 59] + +RFC 5996 IKEv2bis September 2010 + + + The Transform IDs are listed here. The values in the following table + are only current as of the publication date of RFC 4306. Other + values may have been added since then or will be added after the + publication of this document. Readers should refer to [IKEV2IANA] + for the latest values. + + Name Number Defined In + ------------------------------------- + IPCOMP_OUI 1 + IPCOMP_DEFLATE 2 RFC 2394 + IPCOMP_LZS 3 RFC 2395 + IPCOMP_LZJH 4 RFC 3051 + + 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 + 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 + + + +Kaufman, et al. Standards Track [Page 60] + +RFC 5996 IKEv2bis September 2010 + + + 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 UDP-encapsulated IPsec traffic but not + plain, unencapsulated 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 to and from 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. An IPsec + endpoint that discovers a NAT between it and its correspondent (as + described below) MUST send all subsequent traffic from port 4500, + which NATs should not treat specially (as they might with port 500). + + An initiator can use port 4500 for both IKE and ESP, regardless of + whether or not there is a NAT, even at the beginning of IKE. When + either side is using port 4500, sending ESP with UDP encapsulation is + not required, but understanding received UDP-encapsulated ESP packets + + + +Kaufman, et al. Standards Track [Page 61] + +RFC 5996 IKEv2bis September 2010 + + + is required. UDP encapsulation MUST NOT be done on port 500. If + Network Address Translation Traversal (NAT-T) is supported (that is, + if NAT_DETECTION_*_IP payloads were exchanged during IKE_SA_INIT), + all devices MUST be able to receive and process both UDP-encapsulated + ESP and non-UDP-encapsulated ESP packets at any time. Either side + can decide whether or not to use UDP encapsulation for ESP + irrespective of the choice made by the other side. However, if a NAT + is detected, both devices MUST use UDP encapsulation for ESP. + + 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 Both the 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 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 from 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 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 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 or recipient IP address + (respectively), address, and port, and if they don't match, it + SHOULD enable NAT traversal. In the case there is a mismatch of + the NAT_DETECTION_SOURCE_IP hash with all of the + NAT_DETECTION_SOURCE_IP payloads received, 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. + + + + +Kaufman, et al. Standards Track [Page 62] + +RFC 5996 IKEv2bis September 2010 + + + 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 a NAT (i.e., someone along + the route changed the source address of the original packet to + match the address of the NAT box). In this case, the system + receiving the payloads should allow dynamic updates of the other + systems' IP address, as described later. + + o The IKE initiator MUST check the NAT_DETECTION_SOURCE_IP or + NAT_DETECTION_DESTINATION_IP 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 transport mode NAT traversal, the + Traffic Selectors MUST contain exactly one IP address, which is + then used as the original IP address. This is covered in greater + detail in Section 2.23.1. + + 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). This will be apparent to a host if + it receives a packet whose integrity protection validates, but has + a different port, address, or both from the one that was + associated with the SA in the validated packet. When such a + validated packet is found, a host that does not support other + methods of recovery such as IKEv2 Mobility and Multihoming + (MOBIKE) [MOBIKE], and that is not behind a NAT, SHOULD send all + packets (including retransmission packets) to the IP address and + port in the validated packet, and SHOULD store this as the new + address and port combination for the SA (that is, they SHOULD + dynamically update the address). A host behind a NAT SHOULD NOT + do this type of dynamic address update if a validated packet has + + + +Kaufman, et al. Standards Track [Page 63] + +RFC 5996 IKEv2bis September 2010 + + + different port and/or address values because it opens a possible + DoS attack (such as allowing an attacker to break the connection + with a single packet). Also, dynamic address update should only + be done in response to a new packet; otherwise, an attacker can + revert the addresses with old replayed packets. Because of this, + dynamic updates can only be done safely if replay protection is + enabled. When IKEv2 is used with MOBIKE, dynamically updating the + addresses described above interferes with MOBIKE's way of + recovering from the same situation. See Section 3.8 of [MOBIKE] + for more information. + +2.23.1. Transport Mode NAT Traversal + + Transport mode used with NAT Traversal requires special handling of + the Traffic Selectors used in the IKEv2. The complete scenario looks + like: + + +------+ +------+ +------+ +------+ + |Client| IP1 | NAT | IPN1 IPN2 | NAT | IP2 |Server| + |node |<------>| A |<---------->| B |<------->| | + +------+ +------+ +------+ +------+ + + (Other scenarios are simplifications of this complex case, so this + discussion uses the complete scenario.) + + In this scenario, there are two address translating NATs: NAT A and + NAT B. NAT A is a dynamic NAT that maps the client's source address + IP1 to IPN1. NAT B is a static NAT configured so that connections + coming to IPN2 address are mapped to the gateway's address IP2, that + is, IPN2 destination address is mapped to IP2. This allows the + client to connect to a server by connecting to the IPN2. NAT B does + not necessarily need to be a static NAT, but the client needs to know + how to connect to the server, and it can only do that if it somehow + knows the outer address of the NAT B, that is, the IPN2 address. If + NAT B is a static NAT, then its address can be configured to the + client's configuration. Another option would be to find it using + some other protocol (like DNS), but that is outside of scope of + IKEv2. + + In this scenario, both the client and server are configured to use + transport mode for the traffic originating from the client node and + destined to the server. + + When the client starts creating the IKEv2 SA and Child SA for sending + traffic to the server, it may have a triggering packet with source IP + address of IP1, and a destination IP address of IPN2. Its Peer + Authorization Database (PAD) and SPD needs to have a configuration + matching those addresses (or wildcard entries covering them). + + + +Kaufman, et al. Standards Track [Page 64] + +RFC 5996 IKEv2bis September 2010 + + + Because this is transport mode, it uses exactly same addresses as the + Traffic Selectors and outer IP address of the IKE packets. For + transport mode, it MUST use exactly one IP address in the TSi and TSr + payloads. It can have multiple Traffic Selectors if it has, for + example, multiple port ranges that it wants to negotiate, but all TSi + entries must use the IP1-IP1 range as the IP addresses, and all TSr + entries must have the IPN2-IPN2 range as IP addresses. The first + Traffic Selector of TSi and TSr SHOULD have very specific Traffic + Selectors including protocol and port numbers, such as from the + packet triggering the request. + + NAT A will then replace the source address of the IKE packet from IP1 + to IPN1, and NAT B will replace the destination address of the IKE + packet from IPN2 to IP2, so when the packet arrives to the server it + will still have the exactly same Traffic Selectors that were sent by + the client, but the IP address of the IKE packet has been replaced by + IPN1 and IP2. + + When the server receives this packet, it normally looks in the Peer + Authorization Database (PAD) described in RFC 4301 [IPSECARCH] based + on the ID and then searches the SPD based on the Traffic Selectors. + Because IP1 does not really mean anything to the server (it is the + address client has behind the NAT), it is useless to do a lookup + based on that if transport mode is used. On the other hand, the + server cannot know whether transport mode is allowed by its policy + before it finds the matching SPD entry. + + In this case, the server should first check that the initiator + requested transport mode, and then do address substitution on the + Traffic Selectors. It needs to first store the old Traffic Selector + IP addresses to be used later for the incremental checksum fixup (the + IP address in the TSi can be stored as the original source address + and the IP address in the TSr can be stored as the original + destination address). After that, if the other end was detected as + being behind a NAT, the server replaces the IP address in TSi + payloads with the IP address obtained from the source address of the + IKE packet received (that is, it replaces IP1 in TSi with IPN1). If + the server's end was detected to be behind NAT, it replaces the IP + address in the TSr payloads with the IP address obtained from the + destination address of the IKE packet received (that is, it replaces + IPN2 in TSr with IP2). + + After this address substitution, both the Traffic Selectors and the + IKE UDP source/destination addresses look the same, and the server + does SPD lookup based on those new Traffic Selectors. If an entry is + found and it allows transport mode, then that entry is used. If an + entry is found but it does not allow transport mode, then the server + MAY undo the address substitution and redo the SPD lookup using the + + + +Kaufman, et al. Standards Track [Page 65] + +RFC 5996 IKEv2bis September 2010 + + + original Traffic Selectors. If the second lookup succeeds, the + server will create an SA in tunnel mode using real Traffic Selectors + sent by the other end. + + This address substitution in transport mode is needed because the SPD + is looked up using the addresses that will be seen by the local host. + This also will make sure the Security Association Database (SAD) + entries for the tunnel exit checks and return packets is added using + the addresses as seen by the local operating system stack. + + The most common case is that the server's SPD will contain wildcard + entries matching any addresses, but this also allows making different + SPD entries, for example, for different known NATs' outer addresses. + + After the SPD lookup, the server will do Traffic Selector narrowing + based on the SPD entry it found. It will again use the already + substituted Traffic Selectors, and it will thus send back Traffic + Selectors having IPN1 and IP2 as their IP addresses; it can still + narrow down the protocol number or port ranges used by the Traffic + Selectors. The SAD entry created for the Child SA will have the + addresses as seen by the server, namely IPN1 and IP2. + + When the client receives the server's response to the Child SA, it + will do similar processing. If the transport mode SA was created, + the client can store the original returned Traffic Selectors as + original source and destination addresses. It will replace the IP + addresses in the Traffic Selectors with the ones from the IP header + of the IKE packet: it will replace IPN1 with IP1 and IP2 with IPN2. + Then, it will use those Traffic Selectors when verifying the SA + against sent Traffic Selectors, and when installing the SAD entry. + + A summary of the rules for NAT traversal in transport mode is: + + For the client proposing transport mode: + + - The TSi entries MUST have exactly one IP address, and that MUST + match the source address of the IKE SA. + + - The TSr entries MUST have exactly one IP address, and that MUST + match the destination address of the IKE SA. + + - The first TSi and TSr Traffic Selectors SHOULD have very specific + Traffic Selectors including protocol and port numbers, such as + from the packet triggering the request. + + - There MAY be multiple TSi and TSr entries. + + + + + +Kaufman, et al. Standards Track [Page 66] + +RFC 5996 IKEv2bis September 2010 + + + - If transport mode for the SA was selected (that is, if the server + included USE_TRANSPORT_MODE notification in its response): + + - Store the original Traffic Selectors as the received source and + destination address. + + - If the server is behind a NAT, substitute the IP address in the + TSr entries with the remote address of the IKE SA. + + - If the client is behind a NAT, substitute the IP address in the + TSi entries with the local address of the IKE SA. + + - Do address substitution before using those Traffic Selectors + for anything other than storing original content of them. + This includes verification that Traffic Selectors were narrowed + correctly by the other end, creation of the SAD entry, and so on. + + For the responder, when transport mode is proposed by client: + + - Store the original Traffic Selector IP addresses as received source + and destination address, in case undo address + substitution is needed, to use as the "real source and destination + address" specified by [UDPENCAPS], and for TCP/UDP checksum fixup. + + - If the client is behind a NAT, substitute the IP address in the + TSi entries with the remote address of the IKE SA. + + - If the server is behind a NAT, substitute the IP address in the + TSr entries with the local address of the IKE SA. + + - Do PAD and SPD lookup using the ID and substituted Traffic + Selectors. + + - If no SPD entry was found, or if found SPD entry does not + allow transport mode, undo the Traffic Selector substitutions. + Do PAD and SPD lookup again using the ID and original Traffic + Selectors, but also searching for tunnel mode SPD entry (that + is, fall back to tunnel mode). + + - However, if a transport mode SPD entry was found, do normal + traffic selection narrowing based on the substituted Traffic + Selectors and SPD entry. Use the resulting Traffic Selectors when + creating SAD entries, and when sending Traffic Selectors back to + the client. + + + + + + + +Kaufman, et al. Standards Track [Page 67] + +RFC 5996 IKEv2bis September 2010 + + +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 Child 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. + +2.25. Exchange Collisions + + Because IKEv2 exchanges can be initiated by either peer, it is + possible that two exchanges affecting the same SA partly overlap. + This can lead to a situation where the SA state information is + temporarily not synchronized, and a peer can receive a request that + it cannot process in a normal fashion. + + Obviously, using a window size greater than 1 leads to more complex + situations, especially if requests are processed out of order. This + section concentrates on problems that can arise even with a window + size of 1, and recommends solutions. + + A TEMPORARY_FAILURE notification SHOULD be sent when a peer receives + a request that cannot be completed due to a temporary condition such + as a rekeying operation. When a peer receives a TEMPORARY_FAILURE + notification, it MUST NOT immediately retry the operation; it MUST + wait so that the sender may complete whatever operation caused the + temporary condition. The recipient MAY retry the request one or more + times over a period of several minutes. If a peer continues to + receive TEMPORARY_FAILURE on the same IKE SA after several minutes, + it SHOULD conclude that the state information is out of sync and + close the IKE SA. + + A CHILD_SA_NOT_FOUND notification SHOULD be sent when a peer receives + a request to rekey a Child SA that does not exist. The SA that the + initiator attempted to rekey is indicated by the SPI field in the + Notify payload, which is copied from the SPI field in the REKEY_SA + notification. A peer that receives a CHILD_SA_NOT_FOUND notification + SHOULD silently delete the Child SA (if it still exists) and send a + request to create a new Child SA from scratch (if the Child SA does + not yet exist). + + + +Kaufman, et al. Standards Track [Page 68] + +RFC 5996 IKEv2bis September 2010 + + +2.25.1. Collisions while Rekeying or Closing Child SAs + + If a peer receives a request to rekey a Child SA that it is currently + trying to close, it SHOULD reply with TEMPORARY_FAILURE. If a peer + receives a request to rekey a Child SA that it is currently rekeying, + it SHOULD reply as usual, and SHOULD prepare to close redundant SAs + later based on the nonces (see Section 2.8.1). If a peer receives a + request to rekey a Child SA that does not exist, it SHOULD reply with + CHILD_SA_NOT_FOUND. + + If a peer receives a request to close a Child SA that it is currently + trying to close, it SHOULD reply without a Delete payload (see + Section 1.4.1). If a peer receives a request to close a Child SA + that it is currently rekeying, it SHOULD reply as usual, with a + Delete payload. If a peer receives a request to close a Child SA + that does not exist, it SHOULD reply without a Delete payload. + + If a peer receives a request to rekey the IKE SA, and it is currently + creating, rekeying, or closing a Child SA of that IKE SA, it SHOULD + reply with TEMPORARY_FAILURE. + +2.25.2. Collisions while Rekeying or Closing IKE SAs + + If a peer receives a request to rekey an IKE SA that it is currently + rekeying, it SHOULD reply as usual, and SHOULD prepare to close + redundant SAs and move inherited Child SAs later based on the nonces + (see Section 2.8.2). If a peer receives a request to rekey an IKE SA + that it is currently trying to close, it SHOULD reply with + TEMPORARY_FAILURE. + + If a peer receives a request to close an IKE SA that it is currently + rekeying, it SHOULD reply as usual, and forget about its own rekeying + request. If a peer receives a request to close an IKE SA that it is + currently trying to close, it SHOULD reply as usual, and forget about + its own close request. + + If a peer receives a request to create or rekey a Child SA when it is + currently rekeying the IKE SA, it SHOULD reply with + TEMPORARY_FAILURE. If a peer receives a request to delete a Child SA + when it is currently rekeying the IKE SA, it SHOULD reply as usual, + with a Delete payload. + +3. Header and Payload Formats + + In the tables in this section, some cryptographic primitives and + configuration 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 + + + +Kaufman, et al. Standards Track [Page 69] + +RFC 5996 IKEv2bis September 2010 + + + 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 zeros 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 document. Following the header are + one or more IKE payloads each identified by a "Next Payload" field in + the preceding payload. Payloads are identified in the order in which + they appear in an IKE message by looking in the "Next Payload" field + in the IKE header, and subsequently according to the "Next Payload" + field in the IKE payload itself until a "Next Payload" field of zero + indicates that no payloads follow. If a payload of type "Encrypted" + is found, that payload is decrypted and its contents parsed as + additional payloads. An Encrypted payload MUST be the last payload + in a packet and an Encrypted payload MUST NOT contain another + Encrypted payload. + + The responder's 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, including + multiple sessions per peer. + + All multi-octet fields representing integers are laid out in big + endian order (also known as "most significant byte first", or + "network byte order"). + + + + + + + + + + + + + + + + +Kaufman, et al. Standards Track [Page 70] + +RFC 5996 IKEv2bis September 2010 + + + 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). + + o Next Payload (1 octet) - Indicates the type of payload that + immediately follows the header. The format and value of each + payload are defined below. + + o Major Version (4 bits) - Indicates the major version of the IKE + protocol in use. Implementations based on this version of IKE + MUST set the major version to 2. Implementations based on + previous versions of IKE and ISAKMP MUST set the major version to + 1. Implementations based on this version of IKE MUST reject or + ignore messages containing a version number greater than 2 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. + + + + + +Kaufman, et al. Standards Track [Page 71] + +RFC 5996 IKEv2bis September 2010 + + + o Exchange Type (1 octet) - Indicates the type of exchange being + used. This constrains the payloads sent in each message in an + exchange. The values in the following table are only current as + of the publication date of RFC 4306. Other values may have been + added since then or will be added after the publication of this + document. Readers should refer to [IKEV2IANA] for the latest + values. + + Exchange Type Value + ---------------------------------- + IKE_SA_INIT 34 + IKE_AUTH 35 + CREATE_CHILD_SA 36 + INFORMATIONAL 37 + + 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 as follows: + + +-+-+-+-+-+-+-+-+ + |X|X|R|V|I|X|X|X| + +-+-+-+-+-+-+-+-+ + + In the description below, a bit being 'set' means its value is '1', + while 'cleared' means its value is '0'. 'X' bits MUST be cleared + when sending and MUST be ignored on receipt. + + * R (Response) - 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 (with one exception; + see Section 2.21.2). + + * V (Version) - 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. + + * I (Initiator) - 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. + + + + + +Kaufman, et al. Standards Track [Page 72] + +RFC 5996 IKEv2bis September 2010 + + + o Message ID (4 octets, unsigned integer) - Message identifier used + to control retransmission of lost packets and matching of requests + and responses. It is essential to the security of the protocol + because it is used to prevent message replay attacks. See + Sections 2.1 and 2.2. + + o Length (4 octets, unsigned integer) - Length of the total message + (header + payloads) in octets. + +3.2. Generic Payload Header + + Each IKE payload defined in Sections 3.3 through 3.16 begins with a + generic payload header, shown in Figure 5. Figures for each payload + below will include the generic payload header, but for brevity, the + description of each field will be omitted. + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Next Payload |C| RESERVED | Payload Length | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 5: Generic Payload Header + + The Generic Payload Header fields are defined as follows: + + o Next Payload (1 octet) - Identifier for the payload type of the + next payload in the message. If the current payload is the last + in the message, then this field will be 0. This field provides a + "chaining" capability whereby additional payloads can be added to + a message by appending each one 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); + conversely, the Next Payload field of the last contained payload + is set to zero). The payload type values are listed here. The + values in the following table are only current as of the + publication date of RFC 4306. Other values may have been added + since then or will be added after the publication of this + document. Readers should refer to [IKEV2IANA] for the latest + values. + + + + + + + +Kaufman, et al. Standards Track [Page 73] + +RFC 5996 IKEv2bis September 2010 + + + Next Payload Type Notation Value + -------------------------------------------------- + No Next Payload 0 + 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 and Authenticated SK 46 + Configuration CP 47 + Extensible Authentication EAP 48 + + (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. See Section 2.5 for more + information on this bit. + + o RESERVED (7 bits) - MUST be sent as zero; MUST be ignored on + receipt. + + o Payload Length (2 octets, unsigned integer) - Length in octets of + the current payload, including the generic payload header. + + + + + +Kaufman, et al. Standards Track [Page 74] + +RFC 5996 IKEv2bis September 2010 + + + 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 document, 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 have changed from + ISAKMP and IKEv1 is to make the encodings more compact in common + cases. + + The Proposal structure contains within it a Proposal Num 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 Num 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 + MUST either offer no integrity algorithm or a single integrity + algorithm of "none", with no integrity algorithm being the + RECOMMENDED method. 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 + + + +Kaufman, et al. Standards Track [Page 75] + +RFC 5996 IKEv2bis September 2010 + + + the normal ciphers with the integrity algorithms. For example, one + such proposal would have two proposal structures. Proposal 1 is ESP + with AES-128, AES-192, and AES-256 bits in Cipher Block Chaining + (CBC) mode, with either HMAC-SHA1-96 or XCBC-96 as the integrity + algorithm; Proposal 2 is AES-128 or AES-256 in GCM mode with an + 8-octet Integrity Check Value (ICV). Both proposals allow but do not + require the use of ESNs (Extended Sequence Numbers). This can be + illustrated as: + + SA Payload + | + +--- Proposal #1 ( Proto ID = ESP(3), SPI size = 4, + | | 7 transforms, SPI = 0x052357bb ) + | | + | +-- Transform ENCR ( Name = ENCR_AES_CBC ) + | | +-- Attribute ( Key Length = 128 ) + | | + | +-- Transform ENCR ( Name = ENCR_AES_CBC ) + | | +-- Attribute ( Key Length = 192 ) + | | + | +-- Transform ENCR ( Name = ENCR_AES_CBC ) + | | +-- Attribute ( Key Length = 256 ) + | | + | +-- Transform INTEG ( Name = AUTH_HMAC_SHA1_96 ) + | +-- Transform INTEG ( Name = AUTH_AES_XCBC_96 ) + | +-- Transform ESN ( Name = ESNs ) + | +-- Transform ESN ( Name = No ESNs ) + | + +--- Proposal #2 ( Proto ID = ESP(3), SPI size = 4, + | 4 transforms, SPI = 0x35a1d6f2 ) + | + +-- Transform ENCR ( Name = AES-GCM with a 8 octet ICV ) + | +-- Attribute ( Key Length = 128 ) + | + +-- Transform ENCR ( Name = AES-GCM with a 8 octet ICV ) + | +-- Attribute ( Key Length = 256 ) + | + +-- Transform ESN ( Name = ESNs ) + +-- Transform ESN ( Name = No ESNs ) + + 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 (ESNs) 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, + + + + +Kaufman, et al. Standards Track [Page 76] + +RFC 5996 IKEv2bis September 2010 + + + and an encryption algorithm. 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), an implementation MUST include multiple + transforms with the same Transform Type each with a single Attribute. + + Note that the semantics of Transforms and Attributes are quite + different from those in IKEv1. In IKEv1, a single Transform carried + multiple algorithms for a protocol with one carried in the Transform + and the others carried in the Attributes. + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Next Payload |C| RESERVED | Payload Length | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + ~ <Proposals> ~ + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 6: Security Association Payload + + o Proposals (variable) - One or more proposal substructures. + + + + + +Kaufman, et al. Standards Track [Page 77] + +RFC 5996 IKEv2bis September 2010 + + + 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 Num | Protocol ID | SPI Size |Num 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, unsigned integer) - Length of this + proposal, including all transforms and attributes that follow. + + o Proposal Num (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 values in the following table + are only current as of the publication date of RFC 4306. Other + values may have been added since then or will be added after the + publication of this document. Readers should refer to [IKEV2IANA] + for the latest values. + + + +Kaufman, et al. Standards Track [Page 78] + +RFC 5996 IKEv2bis September 2010 + + + Protocol Protocol ID + ----------------------------------- + IKE 1 + AH 2 + ESP 3 + + 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 Num Transforms (1 octet) - Specifies the number of transforms in + this proposal. + + o SPI (variable) - The sending entity's SPI. Even if the SPI Size + is not a multiple of 4 octets, there is no padding applied to the + payload. When the SPI Size field is zero, this field is not + present in the Security Association payload. + + o Transforms (variable) - One or more transform substructures. + +3.3.2. Transform Substructure + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | 0 (last) or 3 | RESERVED | Transform Length | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + |Transform Type | RESERVED | Transform ID | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + ~ Transform Attributes ~ + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 8: Transform Substructure + + o 0 (last) or 3 (more) (1 octet) - Specifies whether this is the + last Transform Substructure in the Proposal. This syntax is + inherited from ISAKMP, but is unnecessary because the last + 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. + + + + +Kaufman, et al. Standards Track [Page 79] + +RFC 5996 IKEv2bis September 2010 + + + 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 listed below. The values in the + following table are only current as of the publication date of RFC + 4306. Other values may have been added since then or will be added + after the publication of this document. Readers should refer to + [IKEV2IANA] for the latest values. + + Description Trans. Used In + Type + ------------------------------------------------------------------ + Encryption Algorithm (ENCR) 1 IKE and ESP + Pseudorandom 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 + + (*) 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), the Transform IDs are + listed below. The values in the following table are only current as + of the publication date of RFC 4306. Other values may have been + added since then or will be added after the publication of this + document. Readers should refer to [IKEV2IANA] for the latest values. + + + + + + + + + +Kaufman, et al. Standards Track [Page 80] + +RFC 5996 IKEv2bis September 2010 + + + Name Number Defined In + --------------------------------------------------- + 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) + ENCR_NULL 11 (RFC2410) + ENCR_AES_CBC 12 (RFC3602) + ENCR_AES_CTR 13 (RFC3686) + + For Transform Type 2 (Pseudorandom Function), the Transform IDs are + listed below. The values in the following table are only current as + of the publication date of RFC 4306. Other values may have been + added since then or will be added after the publication of this + document. Readers should refer to [IKEV2IANA] for the latest values. + + Name Number Defined In + ------------------------------------------------------ + PRF_HMAC_MD5 1 (RFC2104), [MD5] + PRF_HMAC_SHA1 2 (RFC2104), [SHA] + PRF_HMAC_TIGER 3 (UNSPECIFIED) + + For Transform Type 3 (Integrity Algorithm), defined Transform IDs are + listed below. The values in the following table are only current as + of the publication date of RFC 4306. Other values may have been + added since then or will be added after the publication of this + document. Readers should refer to [IKEV2IANA] for the latest values. + + 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) + + For Transform Type 4 (Diffie-Hellman group), defined Transform IDs + are listed below. The values in the following table are only current + as of the publication date of RFC 4306. Other values may have been + added since then or will be added after the publication of this + document. Readers should refer to [IKEV2IANA] for the latest values. + + + + +Kaufman, et al. Standards Track [Page 81] + +RFC 5996 IKEv2bis September 2010 + + + Name Number Defined In + ---------------------------------------- + NONE 0 + 768-bit MODP 1 Appendix B + 1024-bit MODP 2 Appendix B + 1536-bit MODP 5 [ADDGROUP] + 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] + + Although ESP and AH do not directly include a Diffie-Hellman + exchange, a Diffie-Hellman group MAY be negotiated for the Child SA. + This allows the peers to employ Diffie-Hellman in the CREATE_CHILD_SA + exchange, providing perfect forward secrecy for the generated Child + SA keys. + + For Transform Type 5 (Extended Sequence Numbers), defined Transform + IDs are listed below. The values in the following table are only + current as of the publication date of RFC 4306. Other values may + have been added since then or will be added after the publication of + this document. Readers should refer to [IKEV2IANA] for the latest + values. + + Name Number + -------------------------------------------- + No Extended Sequence Numbers 0 + Extended Sequence Numbers 1 + + 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 + + + + + +Kaufman, et al. Standards Track [Page 82] + +RFC 5996 IKEv2bis September 2010 + + + 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. At the + time of publication of this document, [RFC4307] specifies these + suites, but note that it might be updated in the future, and other + RFCs might specify different sets of suites. + + 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. + + 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 parameters (the generator, modulus, and exponent lengths and + values) for new Diffie-Hellman 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 + + + +Kaufman, et al. Standards Track [Page 83] + +RFC 5996 IKEv2bis September 2010 + + + 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 + + o Attribute Format (AF) (1 bit) - Indicates whether the data + attribute follows 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. + + 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 + + + +Kaufman, et al. Standards Track [Page 84] + +RFC 5996 IKEv2bis September 2010 + + + be encoded using the variable-length encoding unless that length + exceeds two bytes. 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. + + The values in the following table are only current as of the + publication date of RFC 4306. Other values may have been added since + then or will be added after the publication of this document. + Readers should refer to [IKEV2IANA] for the latest values. + + Attribute Type Value Attribute Format + ------------------------------------------------------------ + Key Length (in bits) 14 TV + + 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: + + o The Key Length attribute MUST NOT be used with transforms that use + a fixed-length key. For example, this includes ENCR_DES, + ENCR_IDEA, and all the Type 2 (Pseudorandom 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 + proposals not containing it MUST be rejected). For example, this + includes 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. For example, + these transforms include 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. + + + + + + +Kaufman, et al. Standards Track [Page 85] + +RFC 5996 IKEv2bis September 2010 + + + Support for 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 the next section), an initiator willing to + accept multiple key lengths has to include multiple transforms with + the same Transform Type, each with a 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 + MUST terminate the exchange. + + 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 it does not + understand, or one 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 + 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 responder selects a + proposal using a different Diffie-Hellman group (other than NONE), + 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. If one of the proposals offered is for the + Diffie-Hellman group of NONE, and the responder selects that Diffie- + Hellman group, then it MUST ignore the initiator's KE payload and + omit the KE payload from the response. + + + + + +Kaufman, et al. Standards Track [Page 86] + +RFC 5996 IKEv2bis September 2010 + + +3.4. Key Exchange Payload + + The Key Exchange payload, denoted KE in this document, 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 | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Diffie-Hellman Group Num | 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 for modular + exponentiation group (MODP) groups 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 Diffie-Hellman Group Num identifies the Diffie-Hellman group in + which the Key Exchange Data was computed (see Section 3.3.2). This + Diffie-Hellman Group Num MUST match a Diffie-Hellman group specified + in a proposal in the SA payload that is sent in the same message, and + SHOULD match the Diffie-Hellman group in the first group in the first + proposal, if such exists. If none of the proposals in that SA + payload specifies a Diffie-Hellman group, the KE payload MUST NOT be + present. 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. See also Sections 1.2 and 2.7. + + 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 document, + allow peers to assert an identity to one another. This identity may + be used for policy lookup, but does not necessarily have to match + anything in the CERT payload; both fields may be used by an + implementation to perform access control decisions. When using the + + + +Kaufman, et al. Standards Track [Page 87] + +RFC 5996 IKEv2bis September 2010 + + + 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 are 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 Peer Authorization Database (PAD) as described in RFC 4301 + [IPSECARCH] describes the use of the ID payload in IKEv2 and provides + a formal model for the binding of identity to policy in addition to + providing services that deal more specifically with the details of + policy enforcement. The PAD is intended to provide a link between + the SPD and the IKE Security Association management. See Section + 4.4.3 of RFC 4301 for more details. + + The Identification payload consists of the IKE generic payload header + followed by identification fields as follows: + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Next Payload |C| RESERVED | Payload Length | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | ID Type | RESERVED | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + ~ Identification Data ~ + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 11: Identification Payload Format + + o ID Type (1 octet) - Specifies the type of Identification being + used. + + o RESERVED - MUST be sent as zero; MUST be ignored on receipt. + + o Identification Data (variable length) - Value, as indicated by the + Identification Type. The length of the Identification Data is + computed from the size in the ID payload header. + + The payload types for the Identification payload are thirty-five (35) + for IDi and thirty-six (36) for IDr. + + + + + +Kaufman, et al. Standards Track [Page 88] + +RFC 5996 IKEv2bis September 2010 + + + The following table lists the assigned semantics for the + Identification Type field. The values in the following table are + only current as of the publication date of RFC 4306. Other values + may have been added since then or will be added after the publication + of this document. Readers should refer to [IKEV2IANA] for the latest + values. + + ID Type Value + ------------------------------------------------------------------- + ID_IPV4_ADDR 1 + A single four (4) octet IPv4 address. + + ID_FQDN 2 + A fully-qualified domain name string. An example of an 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 RFC 822 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. + + ID_IPV6_ADDR 5 + A single sixteen (16) octet IPv6 address. + + ID_DER_ASN1_DN 9 + The binary Distinguished Encoding Rules (DER) encoding of an + ASN.1 X.500 Distinguished Name [PKIX]. + + ID_DER_ASN1_GN 10 + The binary DER encoding of an ASN.1 X.509 GeneralName [PKIX]. + + ID_KEY_ID 11 + An opaque octet stream that may be used to pass vendor- + specific information necessary to do certain proprietary + types of identification. + + Two implementations will interoperate only if each can generate a + type of ID acceptable to the other. To assure maximum + interoperability, implementations MUST be configurable to send at + least one of ID_IPV4_ADDR, ID_FQDN, ID_RFC822_ADDR, or ID_KEY_ID, and + MUST be configurable to accept all of these four types. + Implementations SHOULD be capable of generating and accepting all of + these types. IPv6-capable implementations MUST additionally be + + + +Kaufman, et al. Standards Track [Page 89] + +RFC 5996 IKEv2bis September 2010 + + + configurable to accept ID_IPV6_ADDR. IPv6-only implementations MAY + be configurable to send only ID_IPV6_ADDR instead of ID_IPV4_ADDR for + IP addresses. + + 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 document, 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. The Hash and + URL formats of the Certificate payloads should be used in case 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. The values in the following table are + only current as of the publication date of RFC 4306. Other values + + + +Kaufman, et al. Standards Track [Page 90] + +RFC 5996 IKEv2bis September 2010 + + + may have been added since then or will be added after the + publication of this document. Readers should refer to [IKEV2IANA] + for the latest values. + + Certificate Encoding Value + ---------------------------------------------------- + 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 + + 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" contains a DER-encoded X.509 + certificate whose public key is used to validate the sender's AUTH + payload. Note that with this encoding, if a chain of certificates + needs to be sent, multiple CERT payloads are used, only the first + of which holds the public key used to validate the sender's AUTH + payload. + + o "Certificate Revocation List" contains a DER-encoded X.509 + certificate revocation list. + + o "Raw RSA Key" contains a PKCS #1 encoded RSA key, that is, a DER- + encoded RSAPublicKey structure (see [RSA] and [PKCS1]). + + o Hash and URL encodings 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 + + + + +Kaufman, et al. Standards Track [Page 91] + +RFC 5996 IKEv2bis September 2010 + + + cached and makes IKE less subject to DoS attacks that become + easier to mount when IKE messages are large enough to require IP + fragmentation [DOSUDPPROT]. + + The "Hash and URL of a bundle" type uses the following ASN.1 + definition for the 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 + Hash and URL format (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. + + Implementations MUST support the HTTP [HTTP] method for hash-and-URL + lookup. The behavior of other URL methods [URLS] is not currently + specified, and such methods SHOULD NOT be used in the absence of a + document specifying them. + + + + + + + + +Kaufman, et al. Standards Track [Page 92] + +RFC 5996 IKEv2bis September 2010 + + +3.7. Certificate Request Payload + + The Certificate Request payload, denoted CERTREQ in this document, + 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. + + The Certificate Request payload is defined as follows: + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Next Payload |C| RESERVED | Payload Length | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Cert Encoding | | + +-+-+-+-+-+-+-+-+ | + ~ Certification Authority ~ + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 13: Certificate Request Payload Format + + o Certificate Encoding (1 octet) - Contains an encoding of the type + or format of certificate requested. Values are listed in + Section 3.6. + + o Certification Authority (variable length) - Contains an encoding + of an acceptable certification authority for the type of + certificate requested. + + The payload type for the Certificate Request payload is thirty-eight + (38). + + The Certificate Encoding field has the same values as those defined + in Section 3.6. The Certification Authority field contains an + indicator of trusted authorities for this certificate type. The + Certification Authority value is a concatenated list of SHA-1 hashes + of the public keys of trusted Certification Authorities (CAs). Each + is encoded as the SHA-1 hash of the Subject Public Key Info element + (see section 4.1.2.7 of [PKIX]) from each Trust Anchor certificate. + The 20-octet hashes are concatenated and included with no other + formatting. + + The contents of the "Certification Authority" field are defined only + for X.509 certificates, which are types 4, 12, and 13. Other values + SHOULD NOT be used until Standards-Track specifications that specify + their use are published. + + + + +Kaufman, et al. Standards Track [Page 93] + +RFC 5996 IKEv2bis September 2010 + + + Note that the term "Certificate Request" is somewhat misleading, in + that values other than certificates are defined in a "Certificate" + payload and requests for those values can be present in a Certificate + Request payload. The syntax of the Certificate Request payload in + such cases is not defined in this document. + + The Certificate Request payload is processed by inspecting the "Cert + Encoding" field to determine whether the processor has any + certificates of this type. If so, the "Certification Authority" + field is inspected to determine if the processor has any certificates + that can be validated up to one of the specified certification + authorities. This can be a chain of certificates. + + If an end-entity certificate exists that satisfies the criteria + specified in the CERTREQ, a certificate or certificate chain SHOULD + be sent back to the certificate requestor if the recipient of the + CERTREQ: + + o is configured to use certificate authentication, + + o is allowed to send a CERT payload, + + o has matching CA trust policy governing the current negotiation, + and + + o has at least one time-wise and usage-appropriate end-entity + certificate chaining to a CA provided in the CERTREQ. + + Certificate revocation checking must be considered during the + chaining process used to select a certificate. Note that even if two + peers are configured to use two different CAs, cross-certification + relationships should be supported by appropriate selection logic. + + The intent is not to prevent communication through the strict + adherence of selection of a certificate based on CERTREQ, when an + alternate certificate could be selected by the sender that would + still enable the recipient to successfully validate and trust it + through trust conveyed by cross-certification, CRLs, or other out-of- + band configured means. Thus, the processing of a CERTREQ should be + seen as a suggestion for a certificate to select, not a mandated one. + If no certificates exist, then the CERTREQ is ignored. This is not + an error condition of the protocol. There may be cases where there + is a preferred CA sent in the CERTREQ, but an alternate might be + acceptable (perhaps after prompting a human operator). + + + + + + + +Kaufman, et al. Standards Track [Page 94] + +RFC 5996 IKEv2bis September 2010 + + + 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 document, contains + data used for authentication purposes. The syntax of the + Authentication data varies according to the Auth Method as specified + below. + + The Authentication payload is defined as follows: + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Next Payload |C| RESERVED | Payload Length | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Auth Method | RESERVED | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + ~ Authentication Data ~ + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 14: Authentication Payload Format + + o Auth Method (1 octet) - Specifies the method of authentication + used. The types of signatures are listed here. The values in the + following table are only current as of the publication date of RFC + 4306. Other values may have been added since then or will be + added after the publication of this document. Readers should + refer to [IKEV2IANA] for the latest values. + + Mechanism Value + ----------------------------------------------------------------- + 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] + (implementers should note that IKEv1 used a different method for + RSA signatures). 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. Implementations can use the + certificates received from a given peer as a hint for selecting a + mutually understood hash function for the AUTH payload signature. + + + +Kaufman, et al. Standards Track [Page 95] + +RFC 5996 IKEv2bis September 2010 + + + Note, however, that the hash algorithm used in the AUTH payload + signature doesn't have to be the same as any hash algorithm(s) + used in the certificate(s). + + 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. + + DSS Digital Signature 3 + Computed as specified in Section 2.15 using a DSS private key + (see [DSS]) over a SHA-1 hash. + + 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 as Ni and Nr in this document for the + initiator's and responder's nonce, respectively, contains random data + used to guarantee liveness during an exchange and protect against + replay attacks. + + The Nonce payload is defined as follows: + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Next Payload |C| RESERVED | Payload Length | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + ~ Nonce Data ~ + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 15: Nonce Payload Format + + o Nonce Data (variable length) - Contains the random data generated + by the transmitting entity. + + The payload type for the Nonce payload is forty (40). + + The size of the Nonce Data MUST be between 16 and 256 octets, + inclusive. Nonce values MUST NOT be reused. + + + + + + +Kaufman, et al. Standards Track [Page 96] + +RFC 5996 IKEv2bis September 2010 + + +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: + 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 in the SPI field, this field indicates the + type of that SA. For notifications concerning Child SAs, this + field MUST contain either (2) to indicate AH or (3) to indicate + ESP. 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. + + 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. + + + + +Kaufman, et al. Standards Track [Page 97] + +RFC 5996 IKEv2bis September 2010 + + + o Notification Data (variable length) - Status 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 + managing an SA database wishes to communicate with a peer process. + + The table below lists the Notification messages and their + corresponding values. The number of different error statuses was + greatly reduced from IKEv1 both for simplification and to avoid + giving configuration information to probers. + + Types in the range 0 - 16383 are intended for reporting errors. An + implementation receiving a Notify payload with one of these types + that it does not recognize in a response MUST assume that the + corresponding request has failed entirely. Unrecognized error types + in a request and status types in a request or response MUST be + ignored, 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. + + More information on error handling can be found in Section 2.21. + + The values in the following table are only current as of the + publication date of RFC 4306, plus two error types added in this + document. Other values may have been added since then or will be + added after the publication of this document. Readers should refer + to [IKEV2IANA] for the latest values. + + NOTIFY messages: error types Value + ------------------------------------------------------------------- + UNSUPPORTED_CRITICAL_PAYLOAD 1 + See Section 2.5. + + INVALID_IKE_SPI 4 + See Section 2.21. + + INVALID_MAJOR_VERSION 5 + See Section 2.5. + + + + +Kaufman, et al. Standards Track [Page 98] + +RFC 5996 IKEv2bis September 2010 + + + 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 DoS + attack using forged messages, this status may only be + returned for and in an encrypted packet if the Message ID and + cryptographic checksum were valid. To avoid leaking information + to someone probing a node, this status MUST be sent in response + to any error not covered by one of the other status types. + To aid debugging, more detailed error information should be + written to a console or log. + + INVALID_MESSAGE_ID 9 + See Section 2.3. + + INVALID_SPI 11 + See Section 1.5. + + NO_PROPOSAL_CHOSEN 14 + None of the proposed crypto suites was acceptable. This can be + sent in any case where the offered proposals (including but not + limited to SA payload values, USE_TRANSPORT_MODE notify, + IPCOMP_SUPPORTED notify) are not acceptable for the responder. + This can also be used as "generic" Child SA error when Child SA + cannot be created for some other reason. See also Section 2.7. + + INVALID_KE_PAYLOAD 17 + See Sections 1.2 and 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. See also + Section 2.21.2. + + 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. + + + +Kaufman, et al. Standards Track [Page 99] + +RFC 5996 IKEv2bis September 2010 + + + 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 Child SA. + + TEMPORARY_FAILURE 43 + See section 2.25. + + CHILD_SA_NOT_FOUND 44 + See section 2.25. + + + + 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. + + + + +Kaufman, et al. Standards Track [Page 100] + +RFC 5996 IKEv2bis September 2010 + + + ESP_TFC_PADDING_NOT_SUPPORTED 16394 + See Section 1.3.1. + + NON_FIRST_FRAGMENTS_ALSO 16395 + See Section 1.3.1. + +3.11. Delete Payload + + The Delete payload, denoted D in this document, contains a protocol- + specific Security Association identifier that the sender has removed + from its Security Association database and is, therefore, no longer + valid. Figure 17 shows the format of the Delete payload. It is + possible to send multiple SPIs in a Delete payload; however, each SPI + MUST be for the same protocol. Mixing of protocol identifiers MUST + NOT be performed in the Delete payload. It is permitted, however, to + include multiple Delete payloads in a single INFORMATIONAL exchange + where each Delete payload lists SPIs for a different protocol. + + Deletion of the IKE SA is indicated by a protocol ID of 1 (IKE) but + no SPIs. Deletion of a Child SA, such as ESP or AH, will contain the + IPsec protocol ID of that protocol (2 for AH, 3 for ESP), and the SPI + is the SPI the sending endpoint would expect in inbound ESP or AH + 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 | Num 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. + + + + + +Kaufman, et al. Standards Track [Page 101] + +RFC 5996 IKEv2bis September 2010 + + + o Num of SPIs (2 octets, unsigned integer) - 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 Num of SPIs fields. + + The payload type for the Delete payload is forty-two (42). + +3.12. Vendor ID Payload + + The Vendor ID payload, denoted V in this document, 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 document, such as + private payloads, private exchanges, private notifications, etc. + Unfamiliar Vendor IDs MUST be ignored. + + Writers of documents who wish to extend this protocol MUST define a + Vendor ID payload to announce the ability to implement the extension + in the document. It is expected that documents 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: + + + + + + + + + + + +Kaufman, et al. Standards Track [Page 102] + +RFC 5996 IKEv2bis September 2010 + + + 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 information. + If you want to show off, you might include the latitude and + longitude and time where you were when you chose the ID and some + random input. A message digest of a long unique string is + preferable to the long unique string itself. + + The payload type for the Vendor ID payload is forty-three (43). + +3.13. Traffic Selector Payload + + The Traffic Selector payload, denoted TS in this document, allows + peers to identify packet flows for processing by IPsec security + services. The Traffic Selector payload consists of the IKE generic + payload header followed by individual Traffic Selectors as follows: + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Next Payload |C| RESERVED | Payload Length | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Number of TSs | RESERVED | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + ~ <Traffic Selectors> ~ + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 19: Traffic Selectors Payload Format + + o Number of TSs (1 octet) - Number of Traffic Selectors being + provided. + + + + + +Kaufman, et al. Standards Track [Page 103] + +RFC 5996 IKEv2bis September 2010 + + + 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. + + There is no requirement that TSi and TSr contain the same number of + individual Traffic Selectors. Thus, they are interpreted as follows: + a packet matches a given TSi/TSr if it matches at least one of the + individual selectors in TSi, and at least one of the individual + selectors in TSr. + + For instance, the following Traffic Selectors: + + TSi = ((17, 100, 198.51.100.66-198.51.100.66), + (17, 200, 198.51.100.66-198.51.100.66)) + 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 198.51.100.66 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. + + + + + + + + + + + + + + + + + +Kaufman, et al. Standards Track [Page 104] + +RFC 5996 IKEv2bis September 2010 + + +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 (such as UDP, TCP, and ICMP). A value of zero means + that the protocol ID is not relevant to this Traffic Selector -- + the SA can carry all protocols. + + o Selector Length - Specifies the length of this Traffic Selector + substructure including the header. + + o Start Port (2 octets, unsigned integer) - 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. ICMP and + ICMPv6 Type and Code values, as well as Mobile IP version 6 + (MIPv6) mobility header (MH) Type values, are represented in this + field as specified in Section 4.4.1.1 of [IPSECARCH]. ICMP Type + and Code values are treated as a single 16-bit integer port + number, with Type in the most significant eight bits and Code in + the least significant eight bits. MIPv6 MH Type values are + treated as a single 16-bit integer port number, with Type in the + most significant eight bits and the least significant eight bits + set to zero. + + + + +Kaufman, et al. Standards Track [Page 105] + +RFC 5996 IKEv2bis September 2010 + + + o End Port (2 octets, unsigned integer) - 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. ICMP and + ICMPv6 Type and Code values, as well as MIPv6 MH Type values, are + represented in this field as specified in Section 4.4.1.1 of + [IPSECARCH]. ICMP Type and Code values are treated as a single + 16-bit integer port number, with Type in the most significant + eight bits and Code in the least significant eight bits. MIPv6 MH + Type values are treated as a single 16-bit integer port number, + with Type in the most significant eight bits and the least + significant eight bits set to zero. + + 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. + + The Traffic Selector types 7 and 8 can also refer to ICMP or ICMPv6 + type and code fields, as well as MH Type fields for the IPv6 mobility + header [MIPV6]. Note, however, that neither ICMP nor MIPv6 packets + have separate source and destination fields. The method for + specifying the Traffic Selectors for ICMP and MIPv6 is shown by + example in Section 4.4.1.3 of [IPSECARCH]. + + The following table lists values for the Traffic Selector Type field + and the corresponding Address Selector Data. The values in the + following table are only current as of the publication date of RFC + 4306. Other values may have been added since then or will be added + after the publication of this document. Readers should refer to + [IKEV2IANA] for the latest values. + + TS Type Value + ------------------------------------------------------------------- + TS_IPV4_ADDR_RANGE 7 + + + + + + + + +Kaufman, et al. Standards Track [Page 106] + +RFC 5996 IKEv2bis September 2010 + + + 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. + +3.14. Encrypted Payload + + The Encrypted payload, denoted SK{...} in this document, 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. This payload is also called the + "Encrypted and Authenticated" payload. + + The algorithms for encryption and integrity protection are negotiated + during IKE SA setup, and the keys are computed as specified in + Sections 2.14 and 2.18. + + 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. + + When an authenticated encryption algorithm is used to protect the IKE + SA, the construction of the Encrypted payload is different than what + is described here. See [AEAD] for more information on authenticated + encryption algorithms and their use in ESP. + + The payload type for an Encrypted payload is forty-six (46). The + Encrypted payload consists of the IKE generic payload header followed + by individual fields as follows: + + + + + +Kaufman, et al. Standards Track [Page 107] + +RFC 5996 IKEv2bis September 2010 + + + 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, + initialization vector (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. 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. For modes + other than CBC, the IV format and processing is specified in the + document specifying the encryption algorithm and mode. + + o IKE payloads are as specified earlier in this section. This field + is encrypted with the negotiated cipher. + + o Padding MAY contain any value chosen by the sender, and MUST have + a length that makes the combination of the payloads, the Padding, + and the Pad Length to be a multiple of the encryption block size. + This field is encrypted with the negotiated cipher. + + + +Kaufman, et al. Standards Track [Page 108] + +RFC 5996 IKEv2bis September 2010 + + + 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. The values in the following table are + only current as of the publication date of RFC 4306. Other values + may have been added since then or will be added after the + publication of this document. Readers should refer to [IKEV2IANA] + for the latest values. + + + + + + +Kaufman, et al. Standards Track [Page 109] + +RFC 5996 IKEv2bis September 2010 + + + CFG Type Value + -------------------------- + CFG_REQUEST 1 + CFG_REPLY 2 + CFG_SET 3 + CFG_ACK 4 + + o RESERVED (3 octets) - MUST be sent as zero; MUST be ignored on + receipt. + + o Configuration Attributes (variable length) - These are type length + value (TLV) structures 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, unsigned integer) - Length in octets of value. + + o Value (0 or more octets) - The variable-length value of this + Configuration Attribute. The following lists the attribute types. + + The values in the following table are only current as of the + publication date of RFC 4306 (except INTERNAL_ADDRESS_EXPIRY and + INTERNAL_IP6_NBNS which were removed by this document). Other values + may have been added since then or will be added after the publication + of this document. Readers should refer to [IKEV2IANA] for the latest + values. + + + + + +Kaufman, et al. Standards Track [Page 110] + +RFC 5996 IKEv2bis September 2010 + + + Attribute Type Value Multi-Valued Length + ------------------------------------------------------------ + INTERNAL_IP4_ADDRESS 1 YES* 0 or 4 octets + INTERNAL_IP4_NETMASK 2 NO 0 or 4 octets + INTERNAL_IP4_DNS 3 YES 0 or 4 octets + INTERNAL_IP4_NBNS 4 YES 0 or 4 octets + INTERNAL_IP4_DHCP 6 YES 0 or 4 octets + APPLICATION_VERSION 7 NO 0 or more + INTERNAL_IP6_ADDRESS 8 YES* 0 or 17 octets + INTERNAL_IP6_DNS 10 YES 0 or 16 octets + INTERNAL_IP6_DHCP 12 YES 0 or 16 octets + INTERNAL_IP4_SUBNET 13 YES 0 or 8 octets + SUPPORTED_ATTRIBUTES 14 NO Multiple of 2 + INTERNAL_IP6_SUBNET 15 YES 17 octets + + * These attributes may be multi-valued on return only if + multiple values were requested. + + o INTERNAL_IP4_ADDRESS, INTERNAL_IP6_ADDRESS - An address on the + internal network, sometimes called a red node address or private + address, and it MAY be a private address on the Internet. 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 as long as this IKE SA (or its rekeyed + successors) requesting the address is valid. 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 response messages (e.g., + 255.255.255.0), and it MUST be used only with an + INTERNAL_IP4_ADDRESS attribute. INTERNAL_IP4_NETMASK in a + CFG_REPLY means roughly the same thing as INTERNAL_IP4_SUBNET + containing the same information ("send traffic to these addresses + through me"), but also implies a link boundary. For instance, the + client could use its own address and the netmask to calculate the + broadcast address of the link. An empty INTERNAL_IP4_NETMASK + attribute can be included in a CFG_REQUEST to request this + + + + + +Kaufman, et al. Standards Track [Page 111] + +RFC 5996 IKEv2bis September 2010 + + + 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_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. + + 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. + + + + + + + +Kaufman, et al. Standards Track [Page 112] + +RFC 5996 IKEv2bis September 2010 + + + Note that no recommendations are made in this document as to how an + implementation actually figures out what information to send in a + response. That is, we do not recommend any specific method of an + IRAS determining which DNS server should be returned to a requesting + IRAC. + + The CFG_REQUEST and CFG_REPLY pair 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. Unrecognized or unsupported attributes + MUST be ignored in both requests and responses. + + The CFG_SET and CFG_ACK pair 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 implementation of this + specification MAY ignore CFG_SET payloads. + +3.15.2. Meaning of INTERNAL_IP4_SUBNET and INTERNAL_IP6_SUBNET + + 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 Child SAs whose Traffic + Selectors cover the address in question, new SAs need to be created. + + + + + + + + + + +Kaufman, et al. Standards Track [Page 113] + +RFC 5996 IKEv2bis September 2010 + + + For instance, if there are two subnets, 198.51.100.0/26 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(198.51.100.234) + INTERNAL_IP4_SUBNET(198.51.100.0/255.255.255.192) + INTERNAL_IP4_SUBNET(192.0.2.0/255.255.255.0) + TSi = (0, 0-65535, 198.51.100.234-198.51.100.234) + TSr = ((0, 0-65535, 198.51.100.0-198.51.100.63), + (0, 0-65535, 192.0.2.0-192.0.2.255)) + + In these cases, the INTERNAL_IP4_SUBNET does not really carry any + useful information. + + A different possible response would have been this: + + CP(CFG_REPLY) = + INTERNAL_IP4_ADDRESS(198.51.100.234) + INTERNAL_IP4_SUBNET(198.51.100.0/255.255.255.192) + INTERNAL_IP4_SUBNET(192.0.2.0/255.255.255.0) + TSi = (0, 0-65535, 198.51.100.234-198.51.100.234) + TSr = (0, 0-65535, 0.0.0.0-255.255.255.255) + + That response 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(198.51.100.234) + INTERNAL_IP4_SUBNET(198.51.100.0/255.255.255.192) + INTERNAL_IP4_SUBNET(192.0.2.0/255.255.255.0) + TSi = (0, 0-65535, 198.51.100.234-198.51.100.234) + TSr = (0, 0-65535, 198.51.100.0-198.51.100.63) + + + +Kaufman, et al. Standards Track [Page 114] + +RFC 5996 IKEv2bis September 2010 + + + 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 response might be: + + CP(CFG_REPLY) = + INTERNAL_IP4_ADDRESS(198.51.100.234) + INTERNAL_IP4_SUBNET(198.51.100.0/255.255.255.192) + INTERNAL_IP4_SUBNET(192.0.2.0/255.255.255.0) + TSi = (0, 0-65535, 198.51.100.234-198.51.100.234) + TSr = (0, 0-65535, 192.0.2.155-192.0.2.155) + + Because the meaning of INTERNAL_IP4_SUBNET/INTERNAL_IP6_SUBNET in + CFG_REQUESTs is unclear, they cannot be used reliably in + CFG_REQUESTs. + +3.15.3. Configuration Payloads for IPv6 + + 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. + Note that there is an additional document that discusses IPv6 + configuration in IKEv2, [IPV6CONFIG]. At the present time, it is an + experimental document, but there is a hope that with more + implementation experience, it will gain the same standards treatment + as this document. + + 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) + + + + + + + + +Kaufman, et al. Standards Track [Page 115] + +RFC 5996 IKEv2bis September 2010 + + + 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 [ADDRIPV6]. In particular, they do not + necessarily have link-local addresses, and this may complicate the + use of protocols that assume them, such as [MLDV2]. + +3.15.4. Address Assignment Failures + + 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. 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. + + + + + +Kaufman, et al. Standards Track [Page 116] + +RFC 5996 IKEv2bis September 2010 + + + 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. + + If the initiator does not receive the IP address(es) required by its + policy, it MAY keep the IKE SA up and retry the Configuration payload + as separate INFORMATIONAL exchange after suitable timeout, or it MAY + tear down the IKE SA by sending a Delete payload inside a separate + INFORMATIONAL exchange and later retry IKE SA from the beginning + after some timeout. Such a timeout should not be too short + (especially if the IKE SA is started from the beginning) because + these error situations may not be able to be fixed quickly; the + timeout should likely be several minutes. For example, an address + shortage problem on the responder will probably only be fixed when + more entries are returned to the address pool when other clients + disconnect or when responder is reconfigured with larger address + pool. + +3.16. Extensible Authentication Protocol (EAP) Payload + + The Extensible Authentication Protocol payload, denoted EAP in this + document, allows IKE SAs to be authenticated using the protocol + defined in RFC 3748 [EAP] and subsequent extensions to that protocol. + When using EAP, an appropriate EAP method needs to be selected. Many + of these methods have been defined, specifying the protocol's use + with various authentication mechanisms. EAP method types are listed + in [EAP-IANA]. A short summary of the EAP format is included here + for clarity. + + 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Next Payload |C| RESERVED | Payload Length | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + ~ EAP Message ~ + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + Figure 24: EAP Payload Format + + The payload type for an EAP payload is forty-eight (48). + + + + + + + + +Kaufman, et al. Standards Track [Page 117] + +RFC 5996 IKEv2bis September 2010 + + + 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. + + o Length (2 octets, unsigned integer) 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. Note that since IKE passes an + indication of initiator identity in the first message in the + IKE_AUTH exchange, the responder SHOULD NOT send EAP Identity + requests (type 1). The initiator MAY, however, respond to such + requests if it receives them. + + o Type_Data (Variable Length) varies with the Type of Request and + the associated Response. For the documentation of the EAP + methods, see [EAP]. + + Note that since IKE passes an indication of initiator identity in the + first message in the IKE_AUTH exchange, the responder should not send + EAP Identity requests. The initiator may, however, respond to such + requests if it receives them. + +4. Conformance Requirements + + In order to assure that all implementations of IKEv2 can + interoperate, there are "MUST support" requirements in addition to + those listed elsewhere. Of course, IKEv2 is a security protocol, and + + + +Kaufman, et al. Standards Track [Page 118] + +RFC 5996 IKEv2bis September 2010 + + + 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. The following are + features that can be omitted in a minimal implementation: + + 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 EAP-based 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 + implementation MAY respond to any request in the INFORMATIONAL + exchange with an empty response (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 + + + +Kaufman, et al. Standards Track [Page 119] + +RFC 5996 IKEv2bis September 2010 + + + 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 and its policy requires using temporary + IP addresses, it MUST include a CP payload in the first message in + the IKE_AUTH exchange 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 the first message + in the IKE_AUTH exchange and recognize a field of type + INTERNAL_IP4_ADDRESS or INTERNAL_IP6_ADDRESS. If it supports leasing + an address of the appropriate type, it MUST return a CP payload of + type CFG_REPLY containing an address of the requested type. The + responder may include any other related attributes. + + For an implementation to be called conforming to this specification, + it MUST be possible to configure it to accept the following: + + o Public Key Infrastructure using X.509 (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. + + 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. + + + + +Kaufman, et al. Standards Track [Page 120] + +RFC 5996 IKEv2bis September 2010 + + + 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. Implementers should take note of this fact and set a + limit on CREATE_CHILD_SA exchanges between exponentiations. This + document does not prescribe such a limit. + + The strength of a key derived from a Diffie-Hellman exchange using + any of the groups defined here depends on the inherent strength of + the group, the size of the exponent used, and the entropy provided by + the random number generator used. Due to these inputs, it is + difficult to determine the strength of a key for any of the defined + groups. Diffie-Hellman group number two, when used with a strong + random number generator and an exponent no less than 200 bits, is + common for use with 3DES. Group five provides greater security than + group two. Group one is for historic purposes only and does not + provide sufficient strength except for use with DES, which is also + for historic use only. Implementations should make note of these + estimates when establishing policy and negotiating security + parameters. + + Note that these limitations are on the Diffie-Hellman groups + themselves. There is nothing in IKE that prohibits using stronger + groups nor is there anything that will dilute the strength obtained + from stronger groups (limited by the strength of the other algorithms + negotiated including the PRF). In fact, the extensible framework of + IKE encourages the definition of more groups; use of elliptic 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 IKE_SA_INIT and IKE_AUTH exchanges happen before the initiator + has been authenticated. As a result, an implementation of this + protocol needs to be completely robust when deployed on any insecure + network. Implementation vulnerabilities, particularly DoS attacks, + can be exploited by unauthenticated peers. This issue is + particularly worrisome because of the unlimited number of messages in + EAP-based authentication. + + The strength of all keys is limited by the size of the output of the + negotiated PRF. For this reason, a PRF whose output is less than 128 + bits (e.g., 3DES-CBC) MUST NOT be used with this protocol. + + + +Kaufman, et al. Standards Track [Page 121] + +RFC 5996 IKEv2bis September 2010 + + + 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 pseudorandom 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 + 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 + + + +Kaufman, et al. Standards Track [Page 122] + +RFC 5996 IKEv2bis September 2010 + + + 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. Implementers should describe the + vulnerabilities of using non-key-generating EAP methods in the + documentation of their implementations so that the administrators + deploying IPsec solutions are aware of these dangers. + + An implementation using EAP MUST also use a public-key-based + authentication of the server to the client before the EAP + 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]. + + Admission control is critical to the security of the protocol. For + example, trust anchors used for identifying IKE peers should probably + be different than those used for other forms of trust, such as those + used to identify public web servers. Moreover, although IKE provides + a great deal of leeway in defining the security policy for a trusted + peer's identity, credentials, and the correlation between them, + having such security policy defined explicitly is essential to a + secure implementation. + +5.1. Traffic Selector Authorization + + IKEv2 relies on information in the Peer Authorization Database (PAD) + when determining what kind of Child SAs a peer is allowed to create. + This process is described in Section 4.4.3 of [IPSECARCH]. When a + peer requests the creation of an Child SA with some Traffic + Selectors, the PAD must contain "Child SA Authorization Data" linking + the identity authenticated by IKEv2 and the addresses permitted for + Traffic Selectors. + + For example, the PAD might be configured so that authenticated + identity "sgw23.example.com" is allowed to create Child SAs for + 192.0.2.0/24, meaning this security gateway is a valid + "representative" for these addresses. Host-to-host IPsec requires + + + + +Kaufman, et al. Standards Track [Page 123] + +RFC 5996 IKEv2bis September 2010 + + + similar entries, linking, for example, "fooserver4.example.com" with + 198.51.100.66/32, meaning this identity is 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 Child SAs with address 198.51.100.66, and + prevents fooserver4 from creating Child 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 Child SAs + with that address in the Traffic Selectors. For example, even if + sgw23 would be able to spoof its IP address as 198.51.100.66, it + could not create Child 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 Child 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 Child + SAs with any Traffic Selectors. This is not an appropriate or secure + configuration in most circumstances. See [H2HIPSEC] for an extensive + discussion about this issue, and the limitations of host-to-host + IPsec in general. + +6. IANA Considerations + + [IKEV2] defined many field types and values. IANA has already + registered those types and values in [IKEV2IANA], so they are not + listed here again. + + + +Kaufman, et al. Standards Track [Page 124] + +RFC 5996 IKEv2bis September 2010 + + + Two items have been removed from the IKEv2 Configuration Payload + Attribute Types table: INTERNAL_IP6_NBNS and INTERNAL_ADDRESS_EXPIRY. + + Two new additions to the IKEv2 parameters "NOTIFY MESSAGES - ERROR + TYPES" registry are defined here that were not defined in [IKEV2]: + + 43 TEMPORARY_FAILURE + 44 CHILD_SA_NOT_FOUND + + IANA has changed the existing IKEv2 Payload Types table from: + + 46 Encrypted E [IKEV2] + + to + + 46 Encrypted and Authenticated SK [This document] + + IANA has updated all references to RFC 4306 to point to this + document. + +7. Acknowledgements + + Many individuals in the IPsecME Working Group were very helpful in + contributing ideas and text for this document, 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 Smyslov helped refine the design of the + Traffic Selector negotiation. + + + + + + + + + +Kaufman, et al. Standards Track [Page 125] + +RFC 5996 IKEv2bis September 2010 + + +8. References + +8.1. Normative References + + [ADDGROUP] Kivinen, T. and M. Kojo, "More Modular Exponential (MODP) + Diffie-Hellman groups for Internet Key Exchange (IKE)", + RFC 3526, May 2003. + + [ADDRIPV6] Hinden, R. and S. Deering, "IP Version 6 Addressing + Architecture", RFC 4291, February 2006. + + [AEAD] Black, D. and D. McGrew, "Using Authenticated Encryption + Algorithms with the Encrypted Payload of the Internet Key + Exchange version 2 (IKEv2) Protocol", RFC 5282, + August 2008. + + [AESCMACPRF128] + 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. + + [AESXCBCPRF128] + Hoffman, P., "The AES-XCBC-PRF-128 Algorithm for the + Internet Key Exchange Protocol (IKE)", RFC 4434, + 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. + + [HTTP] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., + Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext + Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. + + [IKEV2IANA] + "Internet Key Exchange Version 2 (IKEv2) Parameters", + <http://www.iana.org>. + + + + + +Kaufman, et al. Standards Track [Page 126] + +RFC 5996 IKEv2bis September 2010 + + + [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] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., + Housley, R., and W. Polk, "Internet X.509 Public Key + Infrastructure Certificate and Certificate Revocation List + (CRL) Profile", RFC 5280, May 2008. + + [RFC4307] Schiller, J., "Cryptographic Algorithms for Use in the + Internet Key Exchange Version 2 (IKEv2)", RFC 4307, + December 2005. + + [UDPENCAPS] + Huttunen, A., Swander, B., Volpe, V., DiBurro, L., and M. + Stenberg, "UDP Encapsulation of IPsec ESP Packets", + RFC 3948, January 2005. + + [URLS] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform + Resource Identifier (URI): Generic Syntax", STD 66, + RFC 3986, January 2005. + +8.2. Informative References + + [AH] Kent, S., "IP Authentication Header", RFC 4302, + December 2005. + + [ARCHGUIDEPHIL] + Bush, R. and D. Meyer, "Some Internet Architectural + Guidelines and Philosophy", RFC 3439, December 2002. + + [ARCHPRINC] + Carpenter, B., "Architectural Principles of the Internet", + RFC 1958, June 1996. + + [Clarif] Eronen, P. and P. Hoffman, "IKEv2 Clarifications and + Implementation Guidelines", RFC 4718, October 2006. + + + + + + +Kaufman, et al. Standards Track [Page 127] + +RFC 5996 IKEv2bis September 2010 + + + [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. + + [DIFFSERVARCH] + Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z., + and W. Weiss, "An Architecture for Differentiated + Services", RFC 2475, December 1998. + + [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 + 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. + + [EAP-IANA] "Extensible Authentication Protocol (EAP) Registry: Method + Types", <http://www.iana.org>. + + [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. + + + + +Kaufman, et al. Standards Track [Page 128] + +RFC 5996 IKEv2bis September 2010 + + + [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] Klensin, J., "Internationalized Domain Names for + Applications (IDNA): Definitions and Document Framework", + RFC 5890, August 2010. + + [IKEV1] Harkins, D. and D. Carrel, "The Internet Key Exchange + (IKE)", RFC 2409, November 1998. + + [IKEV2] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", + RFC 4306, December 2005. + + [IP] Postel, J., "Internet Protocol", STD 5, RFC 791, + September 1981. + + [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. + + [IPV6CONFIG] + Eronen, P., Laganier, J., and C. Madson, "IPv6 + Configuration in Internet Key Exchange Protocol Version 2 + (IKEv2)", RFC 5739, February 2010. + + [ISAKMP] Maughan, D., Schneider, M., and M. Schertler, "Internet + Security Association and Key Management Protocol + (ISAKMP)", RFC 2408, November 1998. + + + + +Kaufman, et al. Standards Track [Page 129] + +RFC 5996 IKEv2bis September 2010 + + + [MAILFORMAT] + Resnick, P., Ed., "Internet Message Format", RFC 5322, + October 2008. + + [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. + + [MOBIKE] Eronen, P., "IKEv2 Mobility and Multihoming Protocol + (MOBIKE)", RFC 4555, June 2006. + + [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., Arkko, J., and P. Eronen, "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 + Management API, Version 2", RFC 2367, July 1998. + + [PHOTURIS] Karn, P. and W. Simpson, "Photuris: Session-Key Management + Protocol", RFC 2522, March 1999. + + [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. + + [REUSE] Menezes, A. and B. Ustaoglu, "On Reusing Ephemeral Keys In + Diffie-Hellman Key Agreement Protocols", December 2008, + <http://www.cacr.math.uwaterloo.ca/techreports/2008/ + cacr2008-24.pdf>. + + + + + +Kaufman, et al. Standards Track [Page 130] + +RFC 5996 IKEv2bis September 2010 + + + [ROHCV2] Ertekin, E., Christou, C., Jasani, R., Kivinen, T., and C. + Bormann, "IKEv2 Extensions to Support Robust Header + Compression over IPsec", RFC 5857, May 2010. + + [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. + + + + + + + + + + + + + + + + + + + + + + + + +Kaufman, et al. Standards Track [Page 131] + +RFC 5996 IKEv2bis September 2010 + + +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); + + 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 + backward compatibility; + + + +Kaufman, et al. Standards Track [Page 132] + +RFC 5996 IKEv2bis September 2010 + + + 11. To simplify and clarify how shared state is maintained in the + presence of network failures and DoS 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 1 may not be sufficient for typical + uses and is here for historic reasons. + + Additional Diffie-Hellman groups have been defined in [ADDGROUP]. + +B.1. Group 1 - 768-bit MODP + + This group is assigned ID 1 (one). + + The prime is: 2^768 - 2 ^704 - 1 + 2^64 * { [2^638 pi] + 149686 } + Its hexadecimal value is: + + FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1 + 29024E08 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD + EF9519B3 CD3A431B 302B0A6D F25F1437 4FE1356D 6D51C245 + E485B576 625E7EC6 F44C42E9 A63A3620 FFFFFFFF FFFFFFFF + + The generator is 2. + +B.2. Group 2 - 1024-bit MODP + + This group is assigned ID 2 (two). + + The prime is 2^1024 - 2^960 - 1 + 2^64 * { [2^894 pi] + 129093 }. + Its hexadecimal value is: + + FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1 + 29024E08 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD + EF9519B3 CD3A431B 302B0A6D F25F1437 4FE1356D 6D51C245 + E485B576 625E7EC6 F44C42E9 A637ED6B 0BFF5CB6 F406B7ED + EE386BFB 5A899FA5 AE9F2411 7C4B1FE6 49286651 ECE65381 + FFFFFFFF FFFFFFFF + + The generator is 2. + + + + +Kaufman, et al. Standards Track [Page 133] + +RFC 5996 IKEv2bis September 2010 + + +Appendix C. Exchanges and Payloads + + This appendix contains a short summary of the IKEv2 exchanges, and + what payloads can appear in which message. This appendix is purely + informative; if it disagrees with the body of this document, 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+][N+] + + normal response <-- SA, KE, Nr, + (no cookie) [N(NAT_DETECTION_SOURCE_IP), + N(NAT_DETECTION_DESTINATION_IP)], + [[N(HTTP_CERT_LOOKUP_SUPPORTED)], CERTREQ+], + [V+][N+] + + cookie response <-- N(COOKIE), + [V+][N+] + + different Diffie- <-- N(INVALID_KE_PAYLOAD), + Hellman group [V+][N+] + wanted + + + + + + + + + + + + + + + + + + + + + +Kaufman, et al. Standards Track [Page 134] + +RFC 5996 IKEv2bis September 2010 + + +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+][N+] + + 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+][N+] + + error in Child SA <-- IDr, [CERT+], + creation AUTH, + N(error), + [V+][N+] + + + + + + + + + + + + + + + + + + + + + +Kaufman, et al. Standards Track [Page 135] + +RFC 5996 IKEv2bis September 2010 + + +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+][N+] + + first response <-- IDr, [CERT+], AUTH, + EAP, + [V+][N+] + + / --> 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+][N+] + + + + + + + + + + + + + + + + + + +Kaufman, et al. Standards Track [Page 136] + +RFC 5996 IKEv2bis September 2010 + + +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+][N+] + + 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+][N+] + + error case <-- N(error) + + different Diffie- <-- N(INVALID_KE_PAYLOAD), + Hellman group [V+][N+] + wanted + +C.5. CREATE_CHILD_SA Exchange for Rekeying the IKE SA + + request --> SA, Ni, KEi + [V+][N+] + + response <-- SA, Nr, KEr + [V+][N+] + +C.6. INFORMATIONAL Exchange + + request --> [N+], + [D+], + [CP(CFG_REQUEST)] + + response <-- [N+], + [D+], + [CP(CFG_REPLY)] + + + + + + + + +Kaufman, et al. Standards Track [Page 137] + +RFC 5996 IKEv2bis September 2010 + + +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 + Independent + + EMail: pe@iki.fi + + + + + + + + + + + + + + + + +Kaufman, et al. Standards Track [Page 138] + |