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+
+Network Working Group C. Kaufman, Ed.
+Request for Comments: 4306 Microsoft
+Obsoletes: 2407, 2408, 2409 December 2005
+Category: Standards Track
+
+
+ Internet Key Exchange (IKEv2) Protocol
+
+Status of This Memo
+
+ This document specifies an Internet standards track protocol for the
+ Internet community, and requests discussion and suggestions for
+ improvements. Please refer to the current edition of the "Internet
+ Official Protocol Standards" (STD 1) for the standardization state
+ and status of this protocol. Distribution of this memo is unlimited.
+
+Copyright Notice
+
+ Copyright (C) The Internet Society (2005).
+
+Abstract
+
+ This document describes version 2 of the Internet Key Exchange (IKE)
+ protocol. IKE is a component of IPsec used for performing mutual
+ authentication and establishing and maintaining security associations
+ (SAs).
+
+ This version of the IKE specification combines the contents of what
+ were previously separate documents, including Internet Security
+ Association and Key Management Protocol (ISAKMP, RFC 2408), IKE (RFC
+ 2409), the Internet Domain of Interpretation (DOI, RFC 2407), Network
+ Address Translation (NAT) Traversal, Legacy authentication, and
+ remote address acquisition.
+
+ Version 2 of IKE does not interoperate with version 1, but it has
+ enough of the header format in common that both versions can
+ unambiguously run over the same UDP port.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Kaufman Standards Track [Page 1]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+Table of Contents
+
+ 1. Introduction ....................................................3
+ 1.1. Usage Scenarios ............................................5
+ 1.2. The Initial Exchanges ......................................7
+ 1.3. The CREATE_CHILD_SA Exchange ...............................9
+ 1.4. The INFORMATIONAL Exchange ................................11
+ 1.5. Informational Messages outside of an IKE_SA ...............12
+ 2. IKE Protocol Details and Variations ............................12
+ 2.1. Use of Retransmission Timers ..............................13
+ 2.2. Use of Sequence Numbers for Message ID ....................14
+ 2.3. Window Size for Overlapping Requests ......................14
+ 2.4. State Synchronization and Connection Timeouts .............15
+ 2.5. Version Numbers and Forward Compatibility .................17
+ 2.6. Cookies ...................................................18
+ 2.7. Cryptographic Algorithm Negotiation .......................21
+ 2.8. Rekeying ..................................................22
+ 2.9. Traffic Selector Negotiation ..............................24
+ 2.10. Nonces ...................................................26
+ 2.11. Address and Port Agility .................................26
+ 2.12. Reuse of Diffie-Hellman Exponentials .....................27
+ 2.13. Generating Keying Material ...............................27
+ 2.14. Generating Keying Material for the IKE_SA ................28
+ 2.15. Authentication of the IKE_SA .............................29
+ 2.16. Extensible Authentication Protocol Methods ...............31
+ 2.17. Generating Keying Material for CHILD_SAs .................33
+ 2.18. Rekeying IKE_SAs Using a CREATE_CHILD_SA exchange ........34
+ 2.19. Requesting an Internal Address on a Remote Network .......34
+ 2.20. Requesting the Peer's Version ............................35
+ 2.21. Error Handling ...........................................36
+ 2.22. IPComp ...................................................37
+ 2.23. NAT Traversal ............................................38
+ 2.24. Explicit Congestion Notification (ECN) ...................40
+ 3. Header and Payload Formats .....................................41
+ 3.1. The IKE Header ............................................41
+ 3.2. Generic Payload Header ....................................44
+ 3.3. Security Association Payload ..............................46
+ 3.4. Key Exchange Payload ......................................56
+ 3.5. Identification Payloads ...................................56
+ 3.6. Certificate Payload .......................................59
+ 3.7. Certificate Request Payload ...............................61
+ 3.8. Authentication Payload ....................................63
+ 3.9. Nonce Payload .............................................64
+ 3.10. Notify Payload ...........................................64
+ 3.11. Delete Payload ...........................................72
+ 3.12. Vendor ID Payload ........................................73
+ 3.13. Traffic Selector Payload .................................74
+ 3.14. Encrypted Payload ........................................77
+
+
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+ 3.15. Configuration Payload ....................................79
+ 3.16. Extensible Authentication Protocol (EAP) Payload .........84
+ 4. Conformance Requirements .......................................85
+ 5. Security Considerations ........................................88
+ 6. IANA Considerations ............................................90
+ 7. Acknowledgements ...............................................91
+ 8. References .....................................................91
+ 8.1. Normative References ......................................91
+ 8.2. Informative References ....................................92
+ Appendix A: Summary of Changes from IKEv1 .........................96
+ Appendix B: Diffie-Hellman Groups .................................97
+ B.1. Group 1 - 768 Bit MODP ....................................97
+ B.2. Group 2 - 1024 Bit MODP ...................................97
+
+1. Introduction
+
+ IP Security (IPsec) provides confidentiality, data integrity, access
+ control, and data source authentication to IP datagrams. These
+ services are provided by maintaining shared state between the source
+ and the sink of an IP datagram. This state defines, among other
+ things, the specific services provided to the datagram, which
+ cryptographic algorithms will be used to provide the services, and
+ the keys used as input to the cryptographic algorithms.
+
+ Establishing this shared state in a manual fashion does not scale
+ well. Therefore, a protocol to establish this state dynamically is
+ needed. This memo describes such a protocol -- the Internet Key
+ Exchange (IKE). This is version 2 of IKE. Version 1 of IKE was
+ defined in RFCs 2407, 2408, and 2409 [Pip98, MSST98, HC98]. This
+ single document is intended to replace all three of those RFCs.
+
+ Definitions of the primitive terms in this document (such as Security
+ Association or SA) can be found in [RFC4301].
+
+ Keywords "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT" and
+ "MAY" that appear in this document are to be interpreted as described
+ in [Bra97].
+
+ The term "Expert Review" is to be interpreted as defined in
+ [RFC2434].
+
+ IKE performs mutual authentication between two parties and
+ establishes an IKE security association (SA) that includes shared
+ secret information that can be used to efficiently establish SAs for
+ Encapsulating Security Payload (ESP) [RFC4303] and/or Authentication
+ Header (AH) [RFC4302] and a set of cryptographic algorithms to be
+ used by the SAs to protect the traffic that they carry. In this
+ document, the term "suite" or "cryptographic suite" refers to a
+
+
+
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+RFC 4306 IKEv2 December 2005
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+
+ complete set of algorithms used to protect an SA. An initiator
+ proposes one or more suites by listing supported algorithms that can
+ be combined into suites in a mix-and-match fashion. IKE can also
+ negotiate use of IP Compression (IPComp) [IPCOMP] in connection with
+ an ESP and/or AH SA. We call the IKE SA an "IKE_SA". The SAs for
+ ESP and/or AH that get set up through that IKE_SA we call
+ "CHILD_SAs".
+
+ All IKE communications consist of pairs of messages: a request and a
+ response. The pair is called an "exchange". We call the first
+ messages establishing an IKE_SA IKE_SA_INIT and IKE_AUTH exchanges
+ and subsequent IKE exchanges CREATE_CHILD_SA or INFORMATIONAL
+ exchanges. In the common case, there is a single IKE_SA_INIT
+ exchange and a single IKE_AUTH exchange (a total of four messages) to
+ establish the IKE_SA and the first CHILD_SA. In exceptional cases,
+ there may be more than one of each of these exchanges. In all cases,
+ all IKE_SA_INIT exchanges MUST complete before any other exchange
+ type, then all IKE_AUTH exchanges MUST complete, and following that
+ any number of CREATE_CHILD_SA and INFORMATIONAL exchanges may occur
+ in any order. In some scenarios, only a single CHILD_SA is needed
+ between the IPsec endpoints, and therefore there would be no
+ additional exchanges. Subsequent exchanges MAY be used to establish
+ additional CHILD_SAs between the same authenticated pair of endpoints
+ and to perform housekeeping functions.
+
+ IKE message flow always consists of a request followed by a response.
+ It is the responsibility of the requester to ensure reliability. If
+ the response is not received within a timeout interval, the requester
+ needs to retransmit the request (or abandon the connection).
+
+ The first request/response of an IKE session (IKE_SA_INIT) negotiates
+ security parameters for the IKE_SA, sends nonces, and sends Diffie-
+ Hellman values.
+
+ The second request/response (IKE_AUTH) transmits identities, proves
+ knowledge of the secrets corresponding to the two identities, and
+ sets up an SA for the first (and often only) AH and/or ESP CHILD_SA.
+
+ The types of subsequent exchanges are CREATE_CHILD_SA (which creates
+ a CHILD_SA) and INFORMATIONAL (which deletes an SA, reports error
+ conditions, or does other housekeeping). Every request requires a
+ response. An INFORMATIONAL request with no payloads (other than the
+ empty Encrypted payload required by the syntax) is commonly used as a
+ check for liveness. These subsequent exchanges cannot be used until
+ the initial exchanges have completed.
+
+
+
+
+
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+ In the description that follows, we assume that no errors occur.
+ Modifications to the flow should errors occur are described in
+ section 2.21.
+
+1.1. Usage Scenarios
+
+ IKE is expected to be used to negotiate ESP and/or AH SAs in a number
+ of different scenarios, each with its own special requirements.
+
+1.1.1. Security Gateway to Security Gateway Tunnel
+
+ +-+-+-+-+-+ +-+-+-+-+-+
+ ! ! IPsec ! !
+ Protected !Tunnel ! tunnel !Tunnel ! Protected
+ Subnet <-->!Endpoint !<---------->!Endpoint !<--> Subnet
+ ! ! ! !
+ +-+-+-+-+-+ +-+-+-+-+-+
+
+ Figure 1: Security Gateway to Security Gateway Tunnel
+
+ In this scenario, neither endpoint of the IP connection implements
+ IPsec, but network nodes between them protect traffic for part of the
+ way. Protection is transparent to the endpoints, and depends on
+ ordinary routing to send packets through the tunnel endpoints for
+ processing. Each endpoint would announce the set of addresses
+ "behind" it, and packets would be sent in tunnel mode where the inner
+ IP header would contain the IP addresses of the actual endpoints.
+
+1.1.2. Endpoint-to-Endpoint Transport
+
+ +-+-+-+-+-+ +-+-+-+-+-+
+ ! ! IPsec transport ! !
+ !Protected! or tunnel mode SA !Protected!
+ !Endpoint !<---------------------------------------->!Endpoint !
+ ! ! ! !
+ +-+-+-+-+-+ +-+-+-+-+-+
+
+ Figure 2: Endpoint to Endpoint
+
+ In this scenario, both endpoints of the IP connection implement
+ IPsec, as required of hosts in [RFC4301]. Transport mode will
+ commonly be used with no inner IP header. If there is an inner IP
+ header, the inner addresses will be the same as the outer addresses.
+ A single pair of addresses will be negotiated for packets to be
+ protected by this SA. These endpoints MAY implement application
+ layer access controls based on the IPsec authenticated identities of
+ the participants. This scenario enables the end-to-end security that
+ has been a guiding principle for the Internet since [RFC1958],
+
+
+
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+
+ [RFC2775], and a method of limiting the inherent problems with
+ complexity in networks noted by [RFC3439]. Although this scenario
+ may not be fully applicable to the IPv4 Internet, it has been
+ deployed successfully in specific scenarios within intranets using
+ IKEv1. It should be more broadly enabled during the transition to
+ IPv6 and with the adoption of IKEv2.
+
+ It is possible in this scenario that one or both of the protected
+ endpoints will be behind a network address translation (NAT) node, in
+ which case the tunneled packets will have to be UDP encapsulated so
+ that port numbers in the UDP headers can be used to identify
+ individual endpoints "behind" the NAT (see section 2.23).
+
+1.1.3. Endpoint to Security Gateway Tunnel
+
+ +-+-+-+-+-+ +-+-+-+-+-+
+ ! ! IPsec ! ! Protected
+ !Protected! tunnel !Tunnel ! Subnet
+ !Endpoint !<------------------------>!Endpoint !<--- and/or
+ ! ! ! ! Internet
+ +-+-+-+-+-+ +-+-+-+-+-+
+
+ Figure 3: Endpoint to Security Gateway Tunnel
+
+ In this scenario, a protected endpoint (typically a portable roaming
+ computer) connects back to its corporate network through an IPsec-
+ protected tunnel. It might use this tunnel only to access
+ information on the corporate network, or it might tunnel all of its
+ traffic back through the corporate network in order to take advantage
+ of protection provided by a corporate firewall against Internet-based
+ attacks. In either case, the protected endpoint will want an IP
+ address associated with the security gateway so that packets returned
+ to it will go to the security gateway and be tunneled back. This IP
+ address may be static or may be dynamically allocated by the security
+ gateway. In support of the latter case, IKEv2 includes a mechanism
+ for the initiator to request an IP address owned by the security
+ gateway for use for the duration of its SA.
+
+ In this scenario, packets will use tunnel mode. On each packet from
+ the protected endpoint, the outer IP header will contain the source
+ IP address associated with its current location (i.e., the address
+ that will get traffic routed to the endpoint directly), while the
+ inner IP header will contain the source IP address assigned by the
+ security gateway (i.e., the address that will get traffic routed to
+ the security gateway for forwarding to the endpoint). The outer
+ destination address will always be that of the security gateway,
+ while the inner destination address will be the ultimate destination
+ for the packet.
+
+
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+
+ In this scenario, it is possible that the protected endpoint will be
+ behind a NAT. In that case, the IP address as seen by the security
+ gateway will not be the same as the IP address sent by the protected
+ endpoint, and packets will have to be UDP encapsulated in order to be
+ routed properly.
+
+1.1.4. Other Scenarios
+
+ Other scenarios are possible, as are nested combinations of the
+ above. One notable example combines aspects of 1.1.1 and 1.1.3. A
+ subnet may make all external accesses through a remote security
+ gateway using an IPsec tunnel, where the addresses on the subnet are
+ routed to the security gateway by the rest of the Internet. An
+ example would be someone's home network being virtually on the
+ Internet with static IP addresses even though connectivity is
+ provided by an ISP that assigns a single dynamically assigned IP
+ address to the user's security gateway (where the static IP addresses
+ and an IPsec relay are provided by a third party located elsewhere).
+
+1.2. The Initial Exchanges
+
+ Communication using IKE always begins with IKE_SA_INIT and IKE_AUTH
+ exchanges (known in IKEv1 as Phase 1). These initial exchanges
+ normally consist of four messages, though in some scenarios that
+ number can grow. All communications using IKE consist of
+ request/response pairs. We'll describe the base exchange first,
+ followed by variations. The first pair of messages (IKE_SA_INIT)
+ negotiate cryptographic algorithms, exchange nonces, and do a
+ Diffie-Hellman exchange [DH].
+
+ The second pair of messages (IKE_AUTH) authenticate the previous
+ messages, exchange identities and certificates, and establish the
+ first CHILD_SA. Parts of these messages are encrypted and integrity
+ protected with keys established through the IKE_SA_INIT exchange, so
+ the identities are hidden from eavesdroppers and all fields in all
+ the messages are authenticated.
+
+ In the following descriptions, the payloads contained in the message
+ are indicated by names as listed below.
+
+ Notation Payload
+
+ AUTH Authentication
+ CERT Certificate
+ CERTREQ Certificate Request
+ CP Configuration
+ D Delete
+ E Encrypted
+
+
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+
+ EAP Extensible Authentication
+ HDR IKE Header
+ IDi Identification - Initiator
+ IDr Identification - Responder
+ KE Key Exchange
+ Ni, Nr Nonce
+ N Notify
+ SA Security Association
+ TSi Traffic Selector - Initiator
+ TSr Traffic Selector - Responder
+ V Vendor ID
+
+ The details of the contents of each payload are described in section
+ 3. Payloads that may optionally appear will be shown in brackets,
+ such as [CERTREQ], indicate that optionally a certificate request
+ payload can be included.
+
+ The initial exchanges are as follows:
+
+ Initiator Responder
+ ----------- -----------
+ HDR, SAi1, KEi, Ni -->
+
+ HDR contains the Security Parameter Indexes (SPIs), version numbers,
+ and flags of various sorts. The SAi1 payload states the
+ cryptographic algorithms the initiator supports for the IKE_SA. The
+ KE payload sends the initiator's Diffie-Hellman value. Ni is the
+ initiator's nonce.
+
+ <-- HDR, SAr1, KEr, Nr, [CERTREQ]
+
+ The responder chooses a cryptographic suite from the initiator's
+ offered choices and expresses that choice in the SAr1 payload,
+ completes the Diffie-Hellman exchange with the KEr payload, and sends
+ its nonce in the Nr payload.
+
+ At this point in the negotiation, each party can generate SKEYSEED,
+ from which all keys are derived for that IKE_SA. All but the headers
+ of all the messages that follow are encrypted and integrity
+ protected. The keys used for the encryption and integrity protection
+ are derived from SKEYSEED and are known as SK_e (encryption) and SK_a
+ (authentication, a.k.a. integrity protection). A separate SK_e and
+ SK_a is computed for each direction. In addition to the keys SK_e
+ and SK_a derived from the DH value for protection of the IKE_SA,
+ another quantity SK_d is derived and used for derivation of further
+ keying material for CHILD_SAs. The notation SK { ... } indicates
+ that these payloads are encrypted and integrity protected using that
+ direction's SK_e and SK_a.
+
+
+
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+
+ HDR, SK {IDi, [CERT,] [CERTREQ,] [IDr,]
+ AUTH, SAi2, TSi, TSr} -->
+
+ The initiator asserts its identity with the IDi payload, proves
+ knowledge of the secret corresponding to IDi and integrity protects
+ the contents of the first message using the AUTH payload (see section
+ 2.15). It might also send its certificate(s) in CERT payload(s) and
+ a list of its trust anchors in CERTREQ payload(s). If any CERT
+ payloads are included, the first certificate provided MUST contain
+ the public key used to verify the AUTH field. The optional payload
+ IDr enables the initiator to specify which of the responder's
+ identities it wants to talk to. This is useful when the machine on
+ which the responder is running is hosting multiple identities at the
+ same IP address. The initiator begins negotiation of a CHILD_SA
+ using the SAi2 payload. The final fields (starting with SAi2) are
+ described in the description of the CREATE_CHILD_SA exchange.
+
+ <-- HDR, SK {IDr, [CERT,] AUTH,
+ SAr2, TSi, TSr}
+
+ The responder asserts its identity with the IDr payload, optionally
+ sends one or more certificates (again with the certificate containing
+ the public key used to verify AUTH listed first), authenticates its
+ identity and protects the integrity of the second message with the
+ AUTH payload, and completes negotiation of a CHILD_SA with the
+ additional fields described below in the CREATE_CHILD_SA exchange.
+
+ The recipients of messages 3 and 4 MUST verify that all signatures
+ and MACs are computed correctly and that the names in the ID payloads
+ correspond to the keys used to generate the AUTH payload.
+
+1.3. The CREATE_CHILD_SA Exchange
+
+ This exchange consists of a single request/response pair, and was
+ referred to as a phase 2 exchange in IKEv1. It MAY be initiated by
+ either end of the IKE_SA after the initial exchanges are completed.
+
+ All messages following the initial exchange are cryptographically
+ protected using the cryptographic algorithms and keys negotiated in
+ the first two messages of the IKE exchange. These subsequent
+ messages use the syntax of the Encrypted Payload described in section
+ 3.14. All subsequent messages included an Encrypted Payload, even if
+ they are referred to in the text as "empty".
+
+ Either endpoint may initiate a CREATE_CHILD_SA exchange, so in this
+ section the term "initiator" refers to the endpoint initiating this
+ exchange.
+
+
+
+
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+
+ A CHILD_SA is created by sending a CREATE_CHILD_SA request. The
+ CREATE_CHILD_SA request MAY optionally contain a KE payload for an
+ additional Diffie-Hellman exchange to enable stronger guarantees of
+ forward secrecy for the CHILD_SA. The keying material for the
+ CHILD_SA is a function of SK_d established during the establishment
+ of the IKE_SA, the nonces exchanged during the CREATE_CHILD_SA
+ exchange, and the Diffie-Hellman value (if KE payloads are included
+ in the CREATE_CHILD_SA exchange).
+
+ In the CHILD_SA created as part of the initial exchange, a second KE
+ payload and nonce MUST NOT be sent. The nonces from the initial
+ exchange are used in computing the keys for the CHILD_SA.
+
+ The CREATE_CHILD_SA request contains:
+
+ Initiator Responder
+ ----------- -----------
+ HDR, SK {[N], SA, Ni, [KEi],
+ [TSi, TSr]} -->
+
+ The initiator sends SA offer(s) in the SA payload, a nonce in the Ni
+ payload, optionally a Diffie-Hellman value in the KEi payload, and
+ the proposed traffic selectors in the TSi and TSr payloads. If this
+ CREATE_CHILD_SA exchange is rekeying an existing SA other than the
+ IKE_SA, the leading N payload of type REKEY_SA MUST identify the SA
+ being rekeyed. If this CREATE_CHILD_SA exchange is not rekeying an
+ existing SA, the N payload MUST be omitted. If the SA offers include
+ different Diffie-Hellman groups, KEi MUST be an element of the group
+ the initiator expects the responder to accept. If it guesses wrong,
+ the CREATE_CHILD_SA exchange will fail, and it will have to retry
+ with a different KEi.
+
+ The message following the header is encrypted and the message
+ including the header is integrity protected using the cryptographic
+ algorithms negotiated for the IKE_SA.
+
+ The CREATE_CHILD_SA response contains:
+
+ <-- HDR, SK {SA, Nr, [KEr],
+ [TSi, TSr]}
+
+ The responder replies (using the same Message ID to respond) with the
+ accepted offer in an SA payload, and a Diffie-Hellman value in the
+ KEr payload if KEi was included in the request and the selected
+ cryptographic suite includes that group. If the responder chooses a
+ cryptographic suite with a different group, it MUST reject the
+ request. The initiator SHOULD repeat the request, but now with a KEi
+ payload from the group the responder selected.
+
+
+
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+ The traffic selectors for traffic to be sent on that SA are specified
+ in the TS payloads, which may be a subset of what the initiator of
+ the CHILD_SA proposed. Traffic selectors are omitted if this
+ CREATE_CHILD_SA request is being used to change the key of the
+ IKE_SA.
+
+1.4. The INFORMATIONAL Exchange
+
+ At various points during the operation of an IKE_SA, peers may desire
+ to convey control messages to each other regarding errors or
+ notifications of certain events. To accomplish this, IKE defines an
+ INFORMATIONAL exchange. INFORMATIONAL exchanges MUST ONLY occur
+ after the initial exchanges and are cryptographically protected with
+ the negotiated keys.
+
+ Control messages that pertain to an IKE_SA MUST be sent under that
+ IKE_SA. Control messages that pertain to CHILD_SAs MUST be sent
+ under the protection of the IKE_SA which generated them (or its
+ successor if the IKE_SA was replaced for the purpose of rekeying).
+
+ Messages in an INFORMATIONAL exchange contain zero or more
+ Notification, Delete, and Configuration payloads. The Recipient of
+ an INFORMATIONAL exchange request MUST send some response (else the
+ Sender will assume the message was lost in the network and will
+ retransmit it). That response MAY be a message with no payloads.
+ The request message in an INFORMATIONAL exchange MAY also contain no
+ payloads. This is the expected way an endpoint can ask the other
+ endpoint to verify that it is alive.
+
+ ESP and AH SAs always exist in pairs, with one SA in each direction.
+ When an SA is closed, both members of the pair MUST be closed. When
+ SAs are nested, as when data (and IP headers if in tunnel mode) are
+ encapsulated first with IPComp, then with ESP, and finally with AH
+ between the same pair of endpoints, all of the SAs MUST be deleted
+ together. Each endpoint MUST close its incoming SAs and allow the
+ other endpoint to close the other SA in each pair. To delete an SA,
+ an INFORMATIONAL exchange with one or more delete payloads is sent
+ listing the SPIs (as they would be expected in the headers of inbound
+ packets) of the SAs to be deleted. The recipient MUST close the
+ designated SAs. Normally, the reply in the INFORMATIONAL exchange
+ will contain delete payloads for the paired SAs going in the other
+ direction. There is one exception. If by chance both ends of a set
+ of SAs independently decide to close them, each may send a delete
+ payload and the two requests may cross in the network. If a node
+ receives a delete request for SAs for which it has already issued a
+ delete request, it MUST delete the outgoing SAs while processing the
+ request and the incoming SAs while processing the response. In that
+
+
+
+
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+
+ case, the responses MUST NOT include delete payloads for the deleted
+ SAs, since that would result in duplicate deletion and could in
+ theory delete the wrong SA.
+
+ A node SHOULD regard half-closed connections as anomalous and audit
+ their existence should they persist. Note that this specification
+ nowhere specifies time periods, so it is up to individual endpoints
+ to decide how long to wait. A node MAY refuse to accept incoming
+ data on half-closed connections but MUST NOT unilaterally close them
+ and reuse the SPIs. If connection state becomes sufficiently messed
+ up, a node MAY close the IKE_SA; doing so will implicitly close all
+ SAs negotiated under it. It can then rebuild the SAs it needs on a
+ clean base under a new IKE_SA.
+
+ The INFORMATIONAL exchange is defined as:
+
+ Initiator Responder
+ ----------- -----------
+ HDR, SK {[N,] [D,] [CP,] ...} -->
+ <-- HDR, SK {[N,] [D,] [CP], ...}
+
+ The processing of an INFORMATIONAL exchange is determined by its
+ component payloads.
+
+1.5. Informational Messages outside of an IKE_SA
+
+ If an encrypted IKE packet arrives on port 500 or 4500 with an
+ unrecognized SPI, it could be because the receiving node has recently
+ crashed and lost state or because of some other system malfunction or
+ attack. If the receiving node has an active IKE_SA to the IP address
+ from whence the packet came, it MAY send a notification of the
+ wayward packet over that IKE_SA in an INFORMATIONAL exchange. If it
+ does not have such an IKE_SA, it MAY send an Informational message
+ without cryptographic protection to the source IP address. Such a
+ message is not part of an informational exchange, and the receiving
+ node MUST NOT respond to it. Doing so could cause a message loop.
+
+2. IKE Protocol Details and Variations
+
+ IKE normally listens and sends on UDP port 500, though IKE messages
+ may also be received on UDP port 4500 with a slightly different
+ format (see section 2.23). Since UDP is a datagram (unreliable)
+ protocol, IKE includes in its definition recovery from transmission
+ errors, including packet loss, packet replay, and packet forgery.
+ IKE is designed to function so long as (1) at least one of a series
+ of retransmitted packets reaches its destination before timing out;
+ and (2) the channel is not so full of forged and replayed packets so
+
+
+
+
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+
+
+ as to exhaust the network or CPU capacities of either endpoint. Even
+ in the absence of those minimum performance requirements, IKE is
+ designed to fail cleanly (as though the network were broken).
+
+ Although IKEv2 messages are intended to be short, they contain
+ structures with no hard upper bound on size (in particular, X.509
+ certificates), and IKEv2 itself does not have a mechanism for
+ fragmenting large messages. IP defines a mechanism for fragmentation
+ of oversize UDP messages, but implementations vary in the maximum
+ message size supported. Furthermore, use of IP fragmentation opens
+ an implementation to denial of service attacks [KPS03]. Finally,
+ some NAT and/or firewall implementations may block IP fragments.
+
+ All IKEv2 implementations MUST be able to send, receive, and process
+ IKE messages that are up to 1280 bytes long, and they SHOULD be able
+ to send, receive, and process messages that are up to 3000 bytes
+ long. IKEv2 implementations SHOULD be aware of the maximum UDP
+ message size supported and MAY shorten messages by leaving out some
+ certificates or cryptographic suite proposals if that will keep
+ messages below the maximum. Use of the "Hash and URL" formats rather
+ than including certificates in exchanges where possible can avoid
+ most problems. Implementations and configuration should keep in
+ mind, however, that if the URL lookups are possible only after the
+ IPsec SA is established, recursion issues could prevent this
+ technique from working.
+
+2.1. Use of Retransmission Timers
+
+ All messages in IKE exist in pairs: a request and a response. The
+ setup of an IKE_SA normally consists of two request/response pairs.
+ Once the IKE_SA is set up, either end of the security association may
+ initiate requests at any time, and there can be many requests and
+ responses "in flight" at any given moment. But each message is
+ labeled as either a request or a response, and for each
+ request/response pair one end of the security association is the
+ initiator and the other is the responder.
+
+ For every pair of IKE messages, the initiator is responsible for
+ retransmission in the event of a timeout. The responder MUST never
+ retransmit a response unless it receives a retransmission of the
+ request. In that event, the responder MUST ignore the retransmitted
+ request except insofar as it triggers a retransmission of the
+ response. The initiator MUST remember each request until it receives
+ the corresponding response. The responder MUST remember each
+ response until it receives a request whose sequence number is larger
+ than the sequence number in the response plus its window size (see
+ section 2.3).
+
+
+
+
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+
+
+ IKE is a reliable protocol, in the sense that the initiator MUST
+ retransmit a request until either it receives a corresponding reply
+ OR it deems the IKE security association to have failed and it
+ discards all state associated with the IKE_SA and any CHILD_SAs
+ negotiated using that IKE_SA.
+
+2.2. Use of Sequence Numbers for Message ID
+
+ Every IKE message contains a Message ID as part of its fixed header.
+ This Message ID is used to match up requests and responses, and to
+ identify retransmissions of messages.
+
+ The Message ID is a 32-bit quantity, which is zero for the first IKE
+ request in each direction. The IKE_SA initial setup messages will
+ always be numbered 0 and 1. Each endpoint in the IKE Security
+ Association maintains two "current" Message IDs: the next one to be
+ used for a request it initiates and the next one it expects to see in
+ a request from the other end. These counters increment as requests
+ are generated and received. Responses always contain the same
+ message ID as the corresponding request. That means that after the
+ initial exchange, each integer n may appear as the message ID in four
+ distinct messages: the nth request from the original IKE initiator,
+ the corresponding response, the nth request from the original IKE
+ responder, and the corresponding response. If the two ends make very
+ different numbers of requests, the Message IDs in the two directions
+ can be very different. There is no ambiguity in the messages,
+ however, because the (I)nitiator and (R)esponse bits in the message
+ header specify which of the four messages a particular one is.
+
+ Note that Message IDs are cryptographically protected and provide
+ protection against message replays. In the unlikely event that
+ Message IDs grow too large to fit in 32 bits, the IKE_SA MUST be
+ closed. Rekeying an IKE_SA resets the sequence numbers.
+
+2.3. Window Size for Overlapping Requests
+
+ In order to maximize IKE throughput, an IKE endpoint MAY issue
+ multiple requests before getting a response to any of them if the
+ other endpoint has indicated its ability to handle such requests.
+ For simplicity, an IKE implementation MAY choose to process requests
+ strictly in order and/or wait for a response to one request before
+ issuing another. Certain rules must be followed to ensure
+ interoperability between implementations using different strategies.
+
+ After an IKE_SA is set up, either end can initiate one or more
+ requests. These requests may pass one another over the network. An
+ IKE endpoint MUST be prepared to accept and process a request while
+
+
+
+
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+
+
+ it has a request outstanding in order to avoid a deadlock in this
+ situation. An IKE endpoint SHOULD be prepared to accept and process
+ multiple requests while it has a request outstanding.
+
+ An IKE endpoint MUST wait for a response to each of its messages
+ before sending a subsequent message unless it has received a
+ SET_WINDOW_SIZE Notify message from its peer informing it that the
+ peer is prepared to maintain state for multiple outstanding messages
+ in order to allow greater throughput.
+
+ An IKE endpoint MUST NOT exceed the peer's stated window size for
+ transmitted IKE requests. In other words, if the responder stated
+ its window size is N, then when the initiator needs to make a request
+ X, it MUST wait until it has received responses to all requests up
+ through request X-N. An IKE endpoint MUST keep a copy of (or be able
+ to regenerate exactly) each request it has sent until it receives the
+ corresponding response. An IKE endpoint MUST keep a copy of (or be
+ able to regenerate exactly) the number of previous responses equal to
+ its declared window size in case its response was lost and the
+ initiator requests its retransmission by retransmitting the request.
+
+ An IKE endpoint supporting a window size greater than one SHOULD be
+ capable of processing incoming requests out of order to maximize
+ performance in the event of network failures or packet reordering.
+
+2.4. State Synchronization and Connection Timeouts
+
+ An IKE endpoint is allowed to forget all of its state associated with
+ an IKE_SA and the collection of corresponding CHILD_SAs at any time.
+ This is the anticipated behavior in the event of an endpoint crash
+ and restart. It is important when an endpoint either fails or
+ reinitializes its state that the other endpoint detect those
+ conditions and not continue to waste network bandwidth by sending
+ packets over discarded SAs and having them fall into a black hole.
+
+ Since IKE is designed to operate in spite of Denial of Service (DoS)
+ attacks from the network, an endpoint MUST NOT conclude that the
+ other endpoint has failed based on any routing information (e.g.,
+ ICMP messages) or IKE messages that arrive without cryptographic
+ protection (e.g., Notify messages complaining about unknown SPIs).
+ An endpoint MUST conclude that the other endpoint has failed only
+ when repeated attempts to contact it have gone unanswered for a
+ timeout period or when a cryptographically protected INITIAL_CONTACT
+ notification is received on a different IKE_SA to the same
+ authenticated identity. An endpoint SHOULD suspect that the other
+ endpoint has failed based on routing information and initiate a
+ request to see whether the other endpoint is alive. To check whether
+ the other side is alive, IKE specifies an empty INFORMATIONAL message
+
+
+
+Kaufman Standards Track [Page 15]
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+RFC 4306 IKEv2 December 2005
+
+
+ that (like all IKE requests) requires an acknowledgement (note that
+ within the context of an IKE_SA, an "empty" message consists of an
+ IKE header followed by an Encrypted payload that contains no
+ payloads). If a cryptographically protected message has been
+ received from the other side recently, unprotected notifications MAY
+ be ignored. Implementations MUST limit the rate at which they take
+ actions based on unprotected messages.
+
+ Numbers of retries and lengths of timeouts are not covered in this
+ specification because they do not affect interoperability. It is
+ suggested that messages be retransmitted at least a dozen times over
+ a period of at least several minutes before giving up on an SA, but
+ different environments may require different rules. To be a good
+ network citizen, retranmission times MUST increase exponentially to
+ avoid flooding the network and making an existing congestion
+ situation worse. If there has only been outgoing traffic on all of
+ the SAs associated with an IKE_SA, it is essential to confirm
+ liveness of the other endpoint to avoid black holes. If no
+ cryptographically protected messages have been received on an IKE_SA
+ or any of its CHILD_SAs recently, the system needs to perform a
+ liveness check in order to prevent sending messages to a dead peer.
+ Receipt of a fresh cryptographically protected message on an IKE_SA
+ or any of its CHILD_SAs ensures liveness of the IKE_SA and all of its
+ CHILD_SAs. Note that this places requirements on the failure modes
+ of an IKE endpoint. An implementation MUST NOT continue sending on
+ any SA if some failure prevents it from receiving on all of the
+ associated SAs. If CHILD_SAs can fail independently from one another
+ without the associated IKE_SA being able to send a delete message,
+ then they MUST be negotiated by separate IKE_SAs.
+
+ There is a Denial of Service attack on the initiator of an IKE_SA
+ that can be avoided if the initiator takes the proper care. Since
+ the first two messages of an SA setup are not cryptographically
+ protected, an attacker could respond to the initiator's message
+ before the genuine responder and poison the connection setup attempt.
+ To prevent this, the initiator MAY be willing to accept multiple
+ responses to its first message, treat each as potentially legitimate,
+ respond to it, and then discard all the invalid half-open connections
+ when it receives a valid cryptographically protected response to any
+ one of its requests. Once a cryptographically valid response is
+ received, all subsequent responses should be ignored whether or not
+ they are cryptographically valid.
+
+ Note that with these rules, there is no reason to negotiate and agree
+ upon an SA lifetime. If IKE presumes the partner is dead, based on
+ repeated lack of acknowledgement to an IKE message, then the IKE SA
+ and all CHILD_SAs set up through that IKE_SA are deleted.
+
+
+
+
+Kaufman Standards Track [Page 16]
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+RFC 4306 IKEv2 December 2005
+
+
+ An IKE endpoint may at any time delete inactive CHILD_SAs to recover
+ resources used to hold their state. If an IKE endpoint chooses to
+ delete CHILD_SAs, it MUST send Delete payloads to the other end
+ notifying it of the deletion. It MAY similarly time out the IKE_SA.
+ Closing the IKE_SA implicitly closes all associated CHILD_SAs. In
+ this case, an IKE endpoint SHOULD send a Delete payload indicating
+ that it has closed the IKE_SA.
+
+2.5. Version Numbers and Forward Compatibility
+
+ This document describes version 2.0 of IKE, meaning the major version
+ number is 2 and the minor version number is zero. It is likely that
+ some implementations will want to support both version 1.0 and
+ version 2.0, and in the future, other versions.
+
+ The major version number should be incremented only if the packet
+ formats or required actions have changed so dramatically that an
+ older version node would not be able to interoperate with a newer
+ version node if it simply ignored the fields it did not understand
+ and took the actions specified in the older specification. The minor
+ version number indicates new capabilities, and MUST be ignored by a
+ node with a smaller minor version number, but used for informational
+ purposes by the node with the larger minor version number. For
+ example, it might indicate the ability to process a newly defined
+ notification message. The node with the larger minor version number
+ would simply note that its correspondent would not be able to
+ understand that message and therefore would not send it.
+
+ If an endpoint receives a message with a higher major version number,
+ it MUST drop the message and SHOULD send an unauthenticated
+ notification message containing the highest version number it
+ supports. If an endpoint supports major version n, and major version
+ m, it MUST support all versions between n and m. If it receives a
+ message with a major version that it supports, it MUST respond with
+ that version number. In order to prevent two nodes from being
+ tricked into corresponding with a lower major version number than the
+ maximum that they both support, IKE has a flag that indicates that
+ the node is capable of speaking a higher major version number.
+
+ Thus, the major version number in the IKE header indicates the
+ version number of the message, not the highest version number that
+ the transmitter supports. If the initiator is capable of speaking
+ versions n, n+1, and n+2, and the responder is capable of speaking
+ versions n and n+1, then they will negotiate speaking n+1, where the
+ initiator will set the flag indicating its ability to speak a higher
+ version. If they mistakenly (perhaps through an active attacker
+
+
+
+
+
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+
+
+ sending error messages) negotiate to version n, then both will notice
+ that the other side can support a higher version number, and they
+ MUST break the connection and reconnect using version n+1.
+
+ Note that IKEv1 does not follow these rules, because there is no way
+ in v1 of noting that you are capable of speaking a higher version
+ number. So an active attacker can trick two v2-capable nodes into
+ speaking v1. When a v2-capable node negotiates down to v1, it SHOULD
+ note that fact in its logs.
+
+ Also for forward compatibility, all fields marked RESERVED MUST be
+ set to zero by a version 2.0 implementation and their content MUST be
+ ignored by a version 2.0 implementation ("Be conservative in what you
+ send and liberal in what you receive"). In this way, future versions
+ of the protocol can use those fields in a way that is guaranteed to
+ be ignored by implementations that do not understand them.
+ Similarly, payload types that are not defined are reserved for future
+ use; implementations of version 2.0 MUST skip over those payloads and
+ ignore their contents.
+
+ IKEv2 adds a "critical" flag to each payload header for further
+ flexibility for forward compatibility. If the critical flag is set
+ and the payload type is unrecognized, the message MUST be rejected
+ and the response to the IKE request containing that payload MUST
+ include a Notify payload UNSUPPORTED_CRITICAL_PAYLOAD, indicating an
+ unsupported critical payload was included. If the critical flag is
+ not set and the payload type is unsupported, that payload MUST be
+ ignored.
+
+ Although new payload types may be added in the future and may appear
+ interleaved with the fields defined in this specification,
+ implementations MUST send the payloads defined in this specification
+ in the order shown in the figures in section 2 and implementations
+ SHOULD reject as invalid a message with those payloads in any other
+ order.
+
+2.6. Cookies
+
+ The term "cookies" originates with Karn and Simpson [RFC2522] in
+ Photuris, an early proposal for key management with IPsec, and it has
+ persisted. The Internet Security Association and Key Management
+ Protocol (ISAKMP) [MSST98] fixed message header includes two eight-
+ octet fields titled "cookies", and that syntax is used by both IKEv1
+ and IKEv2 though in IKEv2 they are referred to as the IKE SPI and
+ there is a new separate field in a Notify payload holding the cookie.
+ The initial two eight-octet fields in the header are used as a
+ connection identifier at the beginning of IKE packets. Each endpoint
+
+
+
+
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+
+
+ chooses one of the two SPIs and SHOULD choose them so as to be unique
+ identifiers of an IKE_SA. An SPI value of zero is special and
+ indicates that the remote SPI value is not yet known by the sender.
+
+ Unlike ESP and AH where only the recipient's SPI appears in the
+ header of a message, in IKE the sender's SPI is also sent in every
+ message. Since the SPI chosen by the original initiator of the
+ IKE_SA is always sent first, an endpoint with multiple IKE_SAs open
+ that wants to find the appropriate IKE_SA using the SPI it assigned
+ must look at the I(nitiator) Flag bit in the header to determine
+ whether it assigned the first or the second eight octets.
+
+ In the first message of an initial IKE exchange, the initiator will
+ not know the responder's SPI value and will therefore set that field
+ to zero.
+
+ An expected attack against IKE is state and CPU exhaustion, where the
+ target is flooded with session initiation requests from forged IP
+ addresses. This attack can be made less effective if an
+ implementation of a responder uses minimal CPU and commits no state
+ to an SA until it knows the initiator can receive packets at the
+ address from which it claims to be sending them. To accomplish this,
+ a responder SHOULD -- when it detects a large number of half-open
+ IKE_SAs -- reject initial IKE messages unless they contain a Notify
+ payload of type COOKIE. It SHOULD instead send an unprotected IKE
+ message as a response and include COOKIE Notify payload with the
+ cookie data to be returned. Initiators who receive such responses
+ MUST retry the IKE_SA_INIT with a Notify payload of type COOKIE
+ containing the responder supplied cookie data as the first payload
+ and all other payloads unchanged. The initial exchange will then be
+ as follows:
+
+ Initiator Responder
+ ----------- -----------
+ HDR(A,0), SAi1, KEi, Ni -->
+
+ <-- HDR(A,0), N(COOKIE)
+
+ HDR(A,0), N(COOKIE), SAi1, KEi, Ni -->
+
+ <-- HDR(A,B), SAr1, KEr, Nr, [CERTREQ]
+
+ HDR(A,B), SK {IDi, [CERT,] [CERTREQ,] [IDr,]
+ AUTH, SAi2, TSi, TSr} -->
+
+ <-- HDR(A,B), SK {IDr, [CERT,] AUTH,
+ SAr2, TSi, TSr}
+
+
+
+
+Kaufman Standards Track [Page 19]
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+
+
+ The first two messages do not affect any initiator or responder state
+ except for communicating the cookie. In particular, the message
+ sequence numbers in the first four messages will all be zero and the
+ message sequence numbers in the last two messages will be one. 'A' is
+ the SPI assigned by the initiator, while 'B' is the SPI assigned by
+ the responder.
+
+ An IKE implementation SHOULD implement its responder cookie
+ generation in such a way as to not require any saved state to
+ recognize its valid cookie when the second IKE_SA_INIT message
+ arrives. The exact algorithms and syntax they use to generate
+ cookies do not affect interoperability and hence are not specified
+ here. The following is an example of how an endpoint could use
+ cookies to implement limited DOS protection.
+
+ A good way to do this is to set the responder cookie to be:
+
+ Cookie = <VersionIDofSecret> | Hash(Ni | IPi | SPIi | <secret>)
+
+ where <secret> is a randomly generated secret known only to the
+ responder and periodically changed and | indicates concatenation.
+ <VersionIDofSecret> should be changed whenever <secret> is
+ regenerated. The cookie can be recomputed when the IKE_SA_INIT
+ arrives the second time and compared to the cookie in the received
+ message. If it matches, the responder knows that the cookie was
+ generated since the last change to <secret> and that IPi must be the
+ same as the source address it saw the first time. Incorporating SPIi
+ into the calculation ensures that if multiple IKE_SAs are being set
+ up in parallel they will all get different cookies (assuming the
+ initiator chooses unique SPIi's). Incorporating Ni into the hash
+ ensures that an attacker who sees only message 2 can't successfully
+ forge a message 3.
+
+ If a new value for <secret> is chosen while there are connections in
+ the process of being initialized, an IKE_SA_INIT might be returned
+ with other than the current <VersionIDofSecret>. The responder in
+ that case MAY reject the message by sending another response with a
+ new cookie or it MAY keep the old value of <secret> around for a
+ short time and accept cookies computed from either one. The
+ responder SHOULD NOT accept cookies indefinitely after <secret> is
+ changed, since that would defeat part of the denial of service
+ protection. The responder SHOULD change the value of <secret>
+ frequently, especially if under attack.
+
+
+
+
+
+
+
+
+Kaufman Standards Track [Page 20]
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+RFC 4306 IKEv2 December 2005
+
+
+2.7. Cryptographic Algorithm Negotiation
+
+ The payload type known as "SA" indicates a proposal for a set of
+ choices of IPsec protocols (IKE, ESP, and/or AH) for the SA as well
+ as cryptographic algorithms associated with each protocol.
+
+ An SA payload consists of one or more proposals. Each proposal
+ includes one or more protocols (usually one). Each protocol contains
+ one or more transforms -- each specifying a cryptographic algorithm.
+ Each transform contains zero or more attributes (attributes are
+ needed only if the transform identifier does not completely specify
+ the cryptographic algorithm).
+
+ This hierarchical structure was designed to efficiently encode
+ proposals for cryptographic suites when the number of supported
+ suites is large because multiple values are acceptable for multiple
+ transforms. The responder MUST choose a single suite, which MAY be
+ any subset of the SA proposal following the rules below:
+
+ Each proposal contains one or more protocols. If a proposal is
+ accepted, the SA response MUST contain the same protocols in the
+ same order as the proposal. The responder MUST accept a single
+ proposal or reject them all and return an error. (Example: if a
+ single proposal contains ESP and AH and that proposal is accepted,
+ both ESP and AH MUST be accepted. If ESP and AH are included in
+ separate proposals, the responder MUST accept only one of them).
+
+ Each IPsec protocol proposal contains one or more transforms.
+ Each transform contains a transform type. The accepted
+ cryptographic suite MUST contain exactly one transform of each
+ type included in the proposal. For example: if an ESP proposal
+ includes transforms ENCR_3DES, ENCR_AES w/keysize 128, ENCR_AES
+ w/keysize 256, AUTH_HMAC_MD5, and AUTH_HMAC_SHA, the accepted
+ suite MUST contain one of the ENCR_ transforms and one of the
+ AUTH_ transforms. Thus, six combinations are acceptable.
+
+ Since the initiator sends its Diffie-Hellman value in the
+ IKE_SA_INIT, it must guess the Diffie-Hellman group that the
+ responder will select from its list of supported groups. If the
+ initiator guesses wrong, the responder will respond with a Notify
+ payload of type INVALID_KE_PAYLOAD indicating the selected group. In
+ this case, the initiator MUST retry the IKE_SA_INIT with the
+ corrected Diffie-Hellman group. The initiator MUST again propose its
+ full set of acceptable cryptographic suites because the rejection
+ message was unauthenticated and otherwise an active attacker could
+ trick the endpoints into negotiating a weaker suite than a stronger
+ one that they both prefer.
+
+
+
+
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+RFC 4306 IKEv2 December 2005
+
+
+2.8. Rekeying
+
+ IKE, ESP, and AH security associations use secret keys that SHOULD be
+ used only for a limited amount of time and to protect a limited
+ amount of data. This limits the lifetime of the entire security
+ association. When the lifetime of a security association expires,
+ the security association MUST NOT be used. If there is demand, new
+ security associations MAY be established. Reestablishment of
+ security associations to take the place of ones that expire is
+ referred to as "rekeying".
+
+ To allow for minimal IPsec implementations, the ability to rekey SAs
+ without restarting the entire IKE_SA is optional. An implementation
+ MAY refuse all CREATE_CHILD_SA requests within an IKE_SA. If an SA
+ has expired or is about to expire and rekeying attempts using the
+ mechanisms described here fail, an implementation MUST close the
+ IKE_SA and any associated CHILD_SAs and then MAY start new ones.
+ Implementations SHOULD support in-place rekeying of SAs, since doing
+ so offers better performance and is likely to reduce the number of
+ packets lost during the transition.
+
+ To rekey a CHILD_SA within an existing IKE_SA, create a new,
+ equivalent SA (see section 2.17 below), and when the new one is
+ established, delete the old one. To rekey an IKE_SA, establish a new
+ equivalent IKE_SA (see section 2.18 below) with the peer to whom the
+ old IKE_SA is shared using a CREATE_CHILD_SA within the existing
+ IKE_SA. An IKE_SA so created inherits all of the original IKE_SA's
+ CHILD_SAs. Use the new IKE_SA for all control messages needed to
+ maintain the CHILD_SAs created by the old IKE_SA, and delete the old
+ IKE_SA. The Delete payload to delete itself MUST be the last request
+ sent over an IKE_SA.
+
+ SAs SHOULD be rekeyed proactively, i.e., the new SA should be
+ established before the old one expires and becomes unusable. Enough
+ time should elapse between the time the new SA is established and the
+ old one becomes unusable so that traffic can be switched over to the
+ new SA.
+
+ A difference between IKEv1 and IKEv2 is that in IKEv1 SA lifetimes
+ were negotiated. In IKEv2, each end of the SA is responsible for
+ enforcing its own lifetime policy on the SA and rekeying the SA when
+ necessary. If the two ends have different lifetime policies, the end
+ with the shorter lifetime will end up always being the one to request
+ the rekeying. If an SA bundle has been inactive for a long time and
+ if an endpoint would not initiate the SA in the absence of traffic,
+ the endpoint MAY choose to close the SA instead of rekeying it when
+ its lifetime expires. It SHOULD do so if there has been no traffic
+ since the last time the SA was rekeyed.
+
+
+
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+RFC 4306 IKEv2 December 2005
+
+
+ If the two ends have the same lifetime policies, it is possible that
+ both will initiate a rekeying at the same time (which will result in
+ redundant SAs). To reduce the probability of this happening, the
+ timing of rekeying requests SHOULD be jittered (delayed by a random
+ amount of time after the need for rekeying is noticed).
+
+ This form of rekeying may temporarily result in multiple similar SAs
+ between the same pairs of nodes. When there are two SAs eligible to
+ receive packets, a node MUST accept incoming packets through either
+ SA. If redundant SAs are created though such a collision, the SA
+ created with the lowest of the four nonces used in the two exchanges
+ SHOULD be closed by the endpoint that created it.
+
+ Note that IKEv2 deliberately allows parallel SAs with the same
+ traffic selectors between common endpoints. One of the purposes of
+ this is to support traffic quality of service (QoS) differences among
+ the SAs (see [RFC2474], [RFC2475], and section 4.1 of [RFC2983]).
+ Hence unlike IKEv1, the combination of the endpoints and the traffic
+ selectors may not uniquely identify an SA between those endpoints, so
+ the IKEv1 rekeying heuristic of deleting SAs on the basis of
+ duplicate traffic selectors SHOULD NOT be used.
+
+ The node that initiated the surviving rekeyed SA SHOULD delete the
+ replaced SA after the new one is established.
+
+ There are timing windows -- particularly in the presence of lost
+ packets -- where endpoints may not agree on the state of an SA. The
+ responder to a CREATE_CHILD_SA MUST be prepared to accept messages on
+ an SA before sending its response to the creation request, so there
+ is no ambiguity for the initiator. The initiator MAY begin sending
+ on an SA as soon as it processes the response. The initiator,
+ however, cannot receive on a newly created SA until it receives and
+ processes the response to its CREATE_CHILD_SA request. How, then, is
+ the responder to know when it is OK to send on the newly created SA?
+
+ From a technical correctness and interoperability perspective, the
+ responder MAY begin sending on an SA as soon as it sends its response
+ to the CREATE_CHILD_SA request. In some situations, however, this
+ could result in packets unnecessarily being dropped, so an
+ implementation MAY want to defer such sending.
+
+ The responder can be assured that the initiator is prepared to
+ receive messages on an SA if either (1) it has received a
+ cryptographically valid message on the new SA, or (2) the new SA
+ rekeys an existing SA and it receives an IKE request to close the
+ replaced SA. When rekeying an SA, the responder SHOULD continue to
+ send messages on the old SA until one of those events occurs. When
+ establishing a new SA, the responder MAY defer sending messages on a
+
+
+
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+RFC 4306 IKEv2 December 2005
+
+
+ new SA until either it receives one or a timeout has occurred. If an
+ initiator receives a message on an SA for which it has not received a
+ response to its CREATE_CHILD_SA request, it SHOULD interpret that as
+ a likely packet loss and retransmit the CREATE_CHILD_SA request. An
+ initiator MAY send a dummy message on a newly created SA if it has no
+ messages queued in order to assure the responder that the initiator
+ is ready to receive messages.
+
+2.9. Traffic Selector Negotiation
+
+ When an IP packet is received by an RFC4301-compliant IPsec subsystem
+ and matches a "protect" selector in its Security Policy Database
+ (SPD), the subsystem MUST protect that packet with IPsec. When no SA
+ exists yet, it is the task of IKE to create it. Maintenance of a
+ system's SPD is outside the scope of IKE (see [PFKEY] for an example
+ protocol), though some implementations might update their SPD in
+ connection with the running of IKE (for an example scenario, see
+ section 1.1.3).
+
+ Traffic Selector (TS) payloads allow endpoints to communicate some of
+ the information from their SPD to their peers. TS payloads specify
+ the selection criteria for packets that will be forwarded over the
+ newly set up SA. This can serve as a consistency check in some
+ scenarios to assure that the SPDs are consistent. In others, it
+ guides the dynamic update of the SPD.
+
+ Two TS payloads appear in each of the messages in the exchange that
+ creates a CHILD_SA pair. Each TS payload contains one or more
+ Traffic Selectors. Each Traffic Selector consists of an address
+ range (IPv4 or IPv6), a port range, and an IP protocol ID. In
+ support of the scenario described in section 1.1.3, an initiator may
+ request that the responder assign an IP address and tell the
+ initiator what it is.
+
+ IKEv2 allows the responder to choose a subset of the traffic proposed
+ by the initiator. This could happen when the configurations of the
+ two endpoints are being updated but only one end has received the new
+ information. Since the two endpoints may be configured by different
+ people, the incompatibility may persist for an extended period even
+ in the absence of errors. It also allows for intentionally different
+ configurations, as when one end is configured to tunnel all addresses
+ and depends on the other end to have the up-to-date list.
+
+ The first of the two TS payloads is known as TSi (Traffic Selector-
+ initiator). The second is known as TSr (Traffic Selector-responder).
+ TSi specifies the source address of traffic forwarded from (or the
+ destination address of traffic forwarded to) the initiator of the
+ CHILD_SA pair. TSr specifies the destination address of the traffic
+
+
+
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+RFC 4306 IKEv2 December 2005
+
+
+ forwarded to (or the source address of the traffic forwarded from)
+ the responder of the CHILD_SA pair. For example, if the original
+ initiator request the creation of a CHILD_SA pair, and wishes to
+ tunnel all traffic from subnet 192.0.1.* on the initiator's side to
+ subnet 192.0.2.* on the responder's side, the initiator would include
+ a single traffic selector in each TS payload. TSi would specify the
+ address range (192.0.1.0 - 192.0.1.255) and TSr would specify the
+ address range (192.0.2.0 - 192.0.2.255). Assuming that proposal was
+ acceptable to the responder, it would send identical TS payloads
+ back. (Note: The IP address range 192.0.2.* has been reserved for
+ use in examples in RFCs and similar documents. This document needed
+ two such ranges, and so also used 192.0.1.*. This should not be
+ confused with any actual address.)
+
+ The responder is allowed to narrow the choices by selecting a subset
+ of the traffic, for instance by eliminating or narrowing the range of
+ one or more members of the set of traffic selectors, provided the set
+ does not become the NULL set.
+
+ It is possible for the responder's policy to contain multiple smaller
+ ranges, all encompassed by the initiator's traffic selector, and with
+ the responder's policy being that each of those ranges should be sent
+ over a different SA. Continuing the example above, the responder
+ might have a policy of being willing to tunnel those addresses to and
+ from the initiator, but might require that each address pair be on a
+ separately negotiated CHILD_SA. If the initiator generated its
+ request in response to an incoming packet from 192.0.1.43 to
+ 192.0.2.123, there would be no way for the responder to determine
+ which pair of addresses should be included in this tunnel, and it
+ would have to make a guess or reject the request with a status of
+ SINGLE_PAIR_REQUIRED.
+
+ To enable the responder to choose the appropriate range in this case,
+ if the initiator has requested the SA due to a data packet, the
+ initiator SHOULD include as the first traffic selector in each of TSi
+ and TSr a very specific traffic selector including the addresses in
+ the packet triggering the request. In the example, the initiator
+ would include in TSi two traffic selectors: the first containing the
+ address range (192.0.1.43 - 192.0.1.43) and the source port and IP
+ protocol from the packet and the second containing (192.0.1.0 -
+ 192.0.1.255) with all ports and IP protocols. The initiator would
+ similarly include two traffic selectors in TSr.
+
+ If the responder's policy does not allow it to accept the entire set
+ of traffic selectors in the initiator's request, but does allow him
+ to accept the first selector of TSi and TSr, then the responder MUST
+ narrow the traffic selectors to a subset that includes the
+
+
+
+
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+
+
+ initiator's first choices. In this example, the responder might
+ respond with TSi being (192.0.1.43 - 192.0.1.43) with all ports and
+ IP protocols.
+
+ If the initiator creates the CHILD_SA pair not in response to an
+ arriving packet, but rather, say, upon startup, then there may be no
+ specific addresses the initiator prefers for the initial tunnel over
+ any other. In that case, the first values in TSi and TSr MAY be
+ ranges rather than specific values, and the responder chooses a
+ subset of the initiator's TSi and TSr that are acceptable. If more
+ than one subset is acceptable but their union is not, the responder
+ MUST accept some subset and MAY include a Notify payload of type
+ ADDITIONAL_TS_POSSIBLE to indicate that the initiator might want to
+ try again. This case will occur only when the initiator and
+ responder are configured differently from one another. If the
+ initiator and responder agree on the granularity of tunnels, the
+ initiator will never request a tunnel wider than the responder will
+ accept. Such misconfigurations SHOULD be recorded in error logs.
+
+2.10. Nonces
+
+ The IKE_SA_INIT messages each contain a nonce. These nonces are used
+ as inputs to cryptographic functions. The CREATE_CHILD_SA request
+ and the CREATE_CHILD_SA response also contain nonces. These nonces
+ are used to add freshness to the key derivation technique used to
+ obtain keys for CHILD_SA, and to ensure creation of strong pseudo-
+ random bits from the Diffie-Hellman key. Nonces used in IKEv2 MUST
+ be randomly chosen, MUST be at least 128 bits in size, and MUST be at
+ least half the key size of the negotiated prf. ("prf" refers to
+ "pseudo-random function", one of the cryptographic algorithms
+ negotiated in the IKE exchange.) If the same random number source is
+ used for both keys and nonces, care must be taken to ensure that the
+ latter use does not compromise the former.
+
+2.11. Address and Port Agility
+
+ IKE runs over UDP ports 500 and 4500, and implicitly sets up ESP and
+ AH associations for the same IP addresses it runs over. The IP
+ addresses and ports in the outer header are, however, not themselves
+ cryptographically protected, and IKE is designed to work even through
+ Network Address Translation (NAT) boxes. An implementation MUST
+ accept incoming requests even if the source port is not 500 or 4500,
+ and MUST respond to the address and port from which the request was
+ received. It MUST specify the address and port at which the request
+ was received as the source address and port in the response. IKE
+ functions identically over IPv4 or IPv6.
+
+
+
+
+
+Kaufman Standards Track [Page 26]
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+RFC 4306 IKEv2 December 2005
+
+
+2.12. Reuse of Diffie-Hellman Exponentials
+
+ IKE generates keying material using an ephemeral Diffie-Hellman
+ exchange in order to gain the property of "perfect forward secrecy".
+ This means that once a connection is closed and its corresponding
+ keys are forgotten, even someone who has recorded all of the data
+ from the connection and gets access to all of the long-term keys of
+ the two endpoints cannot reconstruct the keys used to protect the
+ conversation without doing a brute force search of the session key
+ space.
+
+ Achieving perfect forward secrecy requires that when a connection is
+ closed, each endpoint MUST forget not only the keys used by the
+ connection but also any information that could be used to recompute
+ those keys. In particular, it MUST forget the secrets used in the
+ Diffie-Hellman calculation and any state that may persist in the
+ state of a pseudo-random number generator that could be used to
+ recompute the Diffie-Hellman secrets.
+
+ Since the computing of Diffie-Hellman exponentials is computationally
+ expensive, an endpoint may find it advantageous to reuse those
+ exponentials for multiple connection setups. There are several
+ reasonable strategies for doing this. An endpoint could choose a new
+ exponential only periodically though this could result in less-than-
+ perfect forward secrecy if some connection lasts for less than the
+ lifetime of the exponential. Or it could keep track of which
+ exponential was used for each connection and delete the information
+ associated with the exponential only when some corresponding
+ connection was closed. This would allow the exponential to be reused
+ without losing perfect forward secrecy at the cost of maintaining
+ more state.
+
+ Decisions as to whether and when to reuse Diffie-Hellman exponentials
+ is a private decision in the sense that it will not affect
+ interoperability. An implementation that reuses exponentials MAY
+ choose to remember the exponential used by the other endpoint on past
+ exchanges and if one is reused to avoid the second half of the
+ calculation.
+
+2.13. Generating Keying Material
+
+ In the context of the IKE_SA, four cryptographic algorithms are
+ negotiated: an encryption algorithm, an integrity protection
+ algorithm, a Diffie-Hellman group, and a pseudo-random function
+ (prf). The pseudo-random function is used for the construction of
+ keying material for all of the cryptographic algorithms used in both
+ the IKE_SA and the CHILD_SAs.
+
+
+
+
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+RFC 4306 IKEv2 December 2005
+
+
+ We assume that each encryption algorithm and integrity protection
+ algorithm uses a fixed-size key and that any randomly chosen value of
+ that fixed size can serve as an appropriate key. For algorithms that
+ accept a variable length key, a fixed key size MUST be specified as
+ part of the cryptographic transform negotiated. For algorithms for
+ which not all values are valid keys (such as DES or 3DES with key
+ parity), the algorithm by which keys are derived from arbitrary
+ values MUST be specified by the cryptographic transform. For
+ integrity protection functions based on Hashed Message Authentication
+ Code (HMAC), the fixed key size is the size of the output of the
+ underlying hash function. When the prf function takes a variable
+ length key, variable length data, and produces a fixed-length output
+ (e.g., when using HMAC), the formulas in this document apply. When
+ the key for the prf function has fixed length, the data provided as a
+ key is truncated or padded with zeros as necessary unless exceptional
+ processing is explained following the formula.
+
+ Keying material will always be derived as the output of the
+ negotiated prf algorithm. Since the amount of keying material needed
+ may be greater than the size of the output of the prf algorithm, we
+ will use the prf iteratively. We will use the terminology prf+ to
+ describe the function that outputs a pseudo-random stream based on
+ the inputs to a prf as follows: (where | indicates concatenation)
+
+ prf+ (K,S) = T1 | T2 | T3 | T4 | ...
+
+ where:
+ T1 = prf (K, S | 0x01)
+ T2 = prf (K, T1 | S | 0x02)
+ T3 = prf (K, T2 | S | 0x03)
+ T4 = prf (K, T3 | S | 0x04)
+
+ continuing as needed to compute all required keys. The keys are
+ taken from the output string without regard to boundaries (e.g., if
+ the required keys are a 256-bit Advanced Encryption Standard (AES)
+ key and a 160-bit HMAC key, and the prf function generates 160 bits,
+ the AES key will come from T1 and the beginning of T2, while the HMAC
+ key will come from the rest of T2 and the beginning of T3).
+
+ The constant concatenated to the end of each string feeding the prf
+ is a single octet. prf+ in this document is not defined beyond 255
+ times the size of the prf output.
+
+2.14. Generating Keying Material for the IKE_SA
+
+ The shared keys are computed as follows. A quantity called SKEYSEED
+ is calculated from the nonces exchanged during the IKE_SA_INIT
+ exchange and the Diffie-Hellman shared secret established during that
+
+
+
+Kaufman Standards Track [Page 28]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ exchange. SKEYSEED is used to calculate seven other secrets: SK_d
+ used for deriving new keys for the CHILD_SAs established with this
+ IKE_SA; SK_ai and SK_ar used as a key to the integrity protection
+ algorithm for authenticating the component messages of subsequent
+ exchanges; SK_ei and SK_er used for encrypting (and of course
+ decrypting) all subsequent exchanges; and SK_pi and SK_pr, which are
+ used when generating an AUTH payload.
+
+ SKEYSEED and its derivatives are computed as follows:
+
+ SKEYSEED = prf(Ni | Nr, g^ir)
+
+ {SK_d | SK_ai | SK_ar | SK_ei | SK_er | SK_pi | SK_pr } = prf+
+ (SKEYSEED, Ni | Nr | SPIi | SPIr )
+
+ (indicating that the quantities SK_d, SK_ai, SK_ar, SK_ei, SK_er,
+ SK_pi, and SK_pr are taken in order from the generated bits of the
+ prf+). g^ir is the shared secret from the ephemeral Diffie-Hellman
+ exchange. g^ir is represented as a string of octets in big endian
+ order padded with zeros if necessary to make it the length of the
+ modulus. Ni and Nr are the nonces, stripped of any headers. If the
+ negotiated prf takes a fixed-length key and the lengths of Ni and Nr
+ do not add up to that length, half the bits must come from Ni and
+ half from Nr, taking the first bits of each.
+
+ The two directions of traffic flow use different keys. The keys used
+ to protect messages from the original initiator are SK_ai and SK_ei.
+ The keys used to protect messages in the other direction are SK_ar
+ and SK_er. Each algorithm takes a fixed number of bits of keying
+ material, which is specified as part of the algorithm. For integrity
+ algorithms based on a keyed hash, the key size is always equal to the
+ length of the output of the underlying hash function.
+
+2.15. Authentication of the IKE_SA
+
+ When not using extensible authentication (see section 2.16), the
+ peers are authenticated by having each sign (or MAC using a shared
+ secret as the key) a block of data. For the responder, the octets to
+ be signed start with the first octet of the first SPI in the header
+ of the second message and end with the last octet of the last payload
+ in the second message. Appended to this (for purposes of computing
+ the signature) are the initiator's nonce Ni (just the value, not the
+ payload containing it), and the value prf(SK_pr,IDr') where IDr' is
+ the responder's ID payload excluding the fixed header. Note that
+ neither the nonce Ni nor the value prf(SK_pr,IDr') are transmitted.
+ Similarly, the initiator signs the first message, starting with the
+ first octet of the first SPI in the header and ending with the last
+ octet of the last payload. Appended to this (for purposes of
+
+
+
+Kaufman Standards Track [Page 29]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ computing the signature) are the responder's nonce Nr, and the value
+ prf(SK_pi,IDi'). In the above calculation, IDi' and IDr' are the
+ entire ID payloads excluding the fixed header. It is critical to the
+ security of the exchange that each side sign the other side's nonce.
+
+ Note that all of the payloads are included under the signature,
+ including any payload types not defined in this document. If the
+ first message of the exchange is sent twice (the second time with a
+ responder cookie and/or a different Diffie-Hellman group), it is the
+ second version of the message that is signed.
+
+ Optionally, messages 3 and 4 MAY include a certificate, or
+ certificate chain providing evidence that the key used to compute a
+ digital signature belongs to the name in the ID payload. The
+ signature or MAC will be computed using algorithms dictated by the
+ type of key used by the signer, and specified by the Auth Method
+ field in the Authentication payload. There is no requirement that
+ the initiator and responder sign with the same cryptographic
+ algorithms. The choice of cryptographic algorithms depends on the
+ type of key each has. In particular, the initiator may be using a
+ shared key while the responder may have a public signature key and
+ certificate. It will commonly be the case (but it is not required)
+ that if a shared secret is used for authentication that the same key
+ is used in both directions. Note that it is a common but typically
+ insecure practice to have a shared key derived solely from a user-
+ chosen password without incorporating another source of randomness.
+
+ This is typically insecure because user-chosen passwords are unlikely
+ to have sufficient unpredictability to resist dictionary attacks and
+ these attacks are not prevented in this authentication method.
+ (Applications using password-based authentication for bootstrapping
+ and IKE_SA should use the authentication method in section 2.16,
+ which is designed to prevent off-line dictionary attacks.) The pre-
+ shared key SHOULD contain as much unpredictability as the strongest
+ key being negotiated. In the case of a pre-shared key, the AUTH
+ value is computed as:
+
+ AUTH = prf(prf(Shared Secret,"Key Pad for IKEv2"), <msg octets>)
+
+ where the string "Key Pad for IKEv2" is 17 ASCII characters without
+ null termination. The shared secret can be variable length. The pad
+ string is added so that if the shared secret is derived from a
+ password, the IKE implementation need not store the password in
+ cleartext, but rather can store the value prf(Shared Secret,"Key Pad
+ for IKEv2"), which could not be used as a password equivalent for
+ protocols other than IKEv2. As noted above, deriving the shared
+ secret from a password is not secure. This construction is used
+ because it is anticipated that people will do it anyway. The
+
+
+
+Kaufman Standards Track [Page 30]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ management interface by which the Shared Secret is provided MUST
+ accept ASCII strings of at least 64 octets and MUST NOT add a null
+ terminator before using them as shared secrets. It MUST also accept
+ a HEX encoding of the Shared Secret. The management interface MAY
+ accept other encodings if the algorithm for translating the encoding
+ to a binary string is specified. If the negotiated prf takes a
+ fixed-size key, the shared secret MUST be of that fixed size.
+
+2.16. Extensible Authentication Protocol Methods
+
+ In addition to authentication using public key signatures and shared
+ secrets, IKE supports authentication using methods defined in RFC
+ 3748 [EAP]. Typically, these methods are asymmetric (designed for a
+ user authenticating to a server), and they may not be mutual. For
+ this reason, these protocols are typically used to authenticate the
+ initiator to the responder and MUST be used in conjunction with a
+ public key signature based authentication of the responder to the
+ initiator. These methods are often associated with mechanisms
+ referred to as "Legacy Authentication" mechanisms.
+
+ While this memo references [EAP] with the intent that new methods can
+ be added in the future without updating this specification, some
+ simpler variations are documented here and in section 3.16. [EAP]
+ defines an authentication protocol requiring a variable number of
+ messages. Extensible Authentication is implemented in IKE as
+ additional IKE_AUTH exchanges that MUST be completed in order to
+ initialize the IKE_SA.
+
+ An initiator indicates a desire to use extensible authentication by
+ leaving out the AUTH payload from message 3. By including an IDi
+ payload but not an AUTH payload, the initiator has declared an
+ identity but has not proven it. If the responder is willing to use
+ an extensible authentication method, it will place an Extensible
+ Authentication Protocol (EAP) payload in message 4 and defer sending
+ SAr2, TSi, and TSr until initiator authentication is complete in a
+ subsequent IKE_AUTH exchange. In the case of a minimal extensible
+ authentication, the initial SA establishment will appear as follows:
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Kaufman Standards Track [Page 31]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ Initiator Responder
+ ----------- -----------
+ HDR, SAi1, KEi, Ni -->
+
+ <-- HDR, SAr1, KEr, Nr, [CERTREQ]
+
+ HDR, SK {IDi, [CERTREQ,] [IDr,]
+ SAi2, TSi, TSr} -->
+
+ <-- HDR, SK {IDr, [CERT,] AUTH,
+ EAP }
+
+ HDR, SK {EAP} -->
+
+ <-- HDR, SK {EAP (success)}
+
+ HDR, SK {AUTH} -->
+
+ <-- HDR, SK {AUTH, SAr2, TSi, TSr }
+
+ For EAP methods that create a shared key as a side effect of
+ authentication, that shared key MUST be used by both the initiator
+ and responder to generate AUTH payloads in messages 7 and 8 using the
+ syntax for shared secrets specified in section 2.15. The shared key
+ from EAP is the field from the EAP specification named MSK. The
+ shared key generated during an IKE exchange MUST NOT be used for any
+ other purpose.
+
+ EAP methods that do not establish a shared key SHOULD NOT be used, as
+ they are subject to a number of man-in-the-middle attacks [EAPMITM]
+ if these EAP methods are used in other protocols that do not use a
+ server-authenticated tunnel. Please see the Security Considerations
+ section for more details. If EAP methods that do not generate a
+ shared key are used, the AUTH payloads in messages 7 and 8 MUST be
+ generated using SK_pi and SK_pr, respectively.
+
+ The initiator of an IKE_SA using EAP SHOULD be capable of extending
+ the initial protocol exchange to at least ten IKE_AUTH exchanges in
+ the event the responder sends notification messages and/or retries
+ the authentication prompt. Once the protocol exchange defined by the
+ chosen EAP authentication method has successfully terminated, the
+ responder MUST send an EAP payload containing the Success message.
+ Similarly, if the authentication method has failed, the responder
+ MUST send an EAP payload containing the Failure message. The
+ responder MAY at any time terminate the IKE exchange by sending an
+ EAP payload containing the Failure message.
+
+
+
+
+
+Kaufman Standards Track [Page 32]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ Following such an extended exchange, the EAP AUTH payloads MUST be
+ included in the two messages following the one containing the EAP
+ Success message.
+
+2.17. Generating Keying Material for CHILD_SAs
+
+ A single CHILD_SA is created by the IKE_AUTH exchange, and additional
+ CHILD_SAs can optionally be created in CREATE_CHILD_SA exchanges.
+ Keying material for them is generated as follows:
+
+ KEYMAT = prf+(SK_d, Ni | Nr)
+
+ Where Ni and Nr are the nonces from the IKE_SA_INIT exchange if this
+ request is the first CHILD_SA created or the fresh Ni and Nr from the
+ CREATE_CHILD_SA exchange if this is a subsequent creation.
+
+ For CREATE_CHILD_SA exchanges including an optional Diffie-Hellman
+ exchange, the keying material is defined as:
+
+ KEYMAT = prf+(SK_d, g^ir (new) | Ni | Nr )
+
+ where g^ir (new) is the shared secret from the ephemeral Diffie-
+ Hellman exchange of this CREATE_CHILD_SA exchange (represented as an
+ octet string in big endian order padded with zeros in the high-order
+ bits if necessary to make it the length of the modulus).
+
+ A single CHILD_SA negotiation may result in multiple security
+ associations. ESP and AH SAs exist in pairs (one in each direction),
+ and four SAs could be created in a single CHILD_SA negotiation if a
+ combination of ESP and AH is being negotiated.
+
+ Keying material MUST be taken from the expanded KEYMAT in the
+ following order:
+
+ All keys for SAs carrying data from the initiator to the responder
+ are taken before SAs going in the reverse direction.
+
+ If multiple IPsec protocols are negotiated, keying material is
+ taken in the order in which the protocol headers will appear in
+ the encapsulated packet.
+
+ If a single protocol has both encryption and authentication keys,
+ the encryption key is taken from the first octets of KEYMAT and
+ the authentication key is taken from the next octets.
+
+ Each cryptographic algorithm takes a fixed number of bits of keying
+ material specified as part of the algorithm.
+
+
+
+
+Kaufman Standards Track [Page 33]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+2.18. Rekeying IKE_SAs Using a CREATE_CHILD_SA exchange
+
+ The CREATE_CHILD_SA exchange can be used to rekey an existing IKE_SA
+ (see section 2.8). New initiator and responder SPIs are supplied in
+ the SPI fields. The TS payloads are omitted when rekeying an IKE_SA.
+ SKEYSEED for the new IKE_SA is computed using SK_d from the existing
+ IKE_SA as follows:
+
+ SKEYSEED = prf(SK_d (old), [g^ir (new)] | Ni | Nr)
+
+ where g^ir (new) is the shared secret from the ephemeral Diffie-
+ Hellman exchange of this CREATE_CHILD_SA exchange (represented as an
+ octet string in big endian order padded with zeros if necessary to
+ make it the length of the modulus) and Ni and Nr are the two nonces
+ stripped of any headers.
+
+ The new IKE_SA MUST reset its message counters to 0.
+
+ SK_d, SK_ai, SK_ar, SK_ei, and SK_er are computed from SKEYSEED as
+ specified in section 2.14.
+
+2.19. Requesting an Internal Address on a Remote Network
+
+ Most commonly occurring in the endpoint-to-security-gateway scenario,
+ an endpoint may need an IP address in the network protected by the
+ security gateway and may need to have that address dynamically
+ assigned. A request for such a temporary address can be included in
+ any request to create a CHILD_SA (including the implicit request in
+ message 3) by including a CP payload.
+
+ This function provides address allocation to an IPsec Remote Access
+ Client (IRAC) trying to tunnel into a network protected by an IPsec
+ Remote Access Server (IRAS). Since the IKE_AUTH exchange creates an
+ IKE_SA and a CHILD_SA, the IRAC MUST request the IRAS-controlled
+ address (and optionally other information concerning the protected
+ network) in the IKE_AUTH exchange. The IRAS may procure an address
+ for the IRAC from any number of sources such as a DHCP/BOOTP server
+ or its own address pool.
+
+ Initiator Responder
+ ----------------------------- ---------------------------
+ HDR, SK {IDi, [CERT,] [CERTREQ,]
+ [IDr,] AUTH, CP(CFG_REQUEST),
+ SAi2, TSi, TSr} -->
+
+ <-- HDR, SK {IDr, [CERT,] AUTH,
+ CP(CFG_REPLY), SAr2,
+ TSi, TSr}
+
+
+
+Kaufman Standards Track [Page 34]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ In all cases, the CP payload MUST be inserted before the SA payload.
+ In variations of the protocol where there are multiple IKE_AUTH
+ exchanges, the CP payloads MUST be inserted in the messages
+ containing the SA payloads.
+
+ CP(CFG_REQUEST) MUST contain at least an INTERNAL_ADDRESS attribute
+ (either IPv4 or IPv6) but MAY contain any number of additional
+ attributes the initiator wants returned in the response.
+
+ For example, message from initiator to responder:
+ CP(CFG_REQUEST)=
+ INTERNAL_ADDRESS(0.0.0.0)
+ INTERNAL_NETMASK(0.0.0.0)
+ INTERNAL_DNS(0.0.0.0)
+ TSi = (0, 0-65535,0.0.0.0-255.255.255.255)
+ TSr = (0, 0-65535,0.0.0.0-255.255.255.255)
+
+ NOTE: Traffic Selectors contain (protocol, port range, address
+ range).
+
+ Message from responder to initiator:
+
+ CP(CFG_REPLY)=
+ INTERNAL_ADDRESS(192.0.2.202)
+ INTERNAL_NETMASK(255.255.255.0)
+ INTERNAL_SUBNET(192.0.2.0/255.255.255.0)
+ TSi = (0, 0-65535,192.0.2.202-192.0.2.202)
+ TSr = (0, 0-65535,192.0.2.0-192.0.2.255)
+
+ All returned values will be implementation dependent. As can be seen
+ in the above example, the IRAS MAY also send other attributes that
+ were not included in CP(CFG_REQUEST) and MAY ignore the non-mandatory
+ attributes that it does not support.
+
+ The responder MUST NOT send a CFG_REPLY without having first received
+ a CP(CFG_REQUEST) from the initiator, because we do not want the IRAS
+ to perform an unnecessary configuration lookup if the IRAC cannot
+ process the REPLY. In the case where the IRAS's configuration
+ requires that CP be used for a given identity IDi, but IRAC has
+ failed to send a CP(CFG_REQUEST), IRAS MUST fail the request, and
+ terminate the IKE exchange with a FAILED_CP_REQUIRED error.
+
+2.20. Requesting the Peer's Version
+
+ An IKE peer wishing to inquire about the other peer's IKE software
+ version information MAY use the method below. This is an example of
+ a configuration request within an INFORMATIONAL exchange, after the
+ IKE_SA and first CHILD_SA have been created.
+
+
+
+Kaufman Standards Track [Page 35]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ An IKE implementation MAY decline to give out version information
+ prior to authentication or even after authentication to prevent
+ trolling in case some implementation is known to have some security
+ weakness. In that case, it MUST either return an empty string or no
+ CP payload if CP is not supported.
+
+ Initiator Responder
+ ----------------------------- --------------------------
+ HDR, SK{CP(CFG_REQUEST)} -->
+ <-- HDR, SK{CP(CFG_REPLY)}
+
+ CP(CFG_REQUEST)=
+ APPLICATION_VERSION("")
+
+ CP(CFG_REPLY) APPLICATION_VERSION("foobar v1.3beta, (c) Foo Bar
+ Inc.")
+
+2.21. Error Handling
+
+ There are many kinds of errors that can occur during IKE processing.
+ If a request is received that is badly formatted or unacceptable for
+ reasons of policy (e.g., no matching cryptographic algorithms), the
+ response MUST contain a Notify payload indicating the error. If an
+ error occurs outside the context of an IKE request (e.g., the node is
+ getting ESP messages on a nonexistent SPI), the node SHOULD initiate
+ an INFORMATIONAL exchange with a Notify payload describing the
+ problem.
+
+ Errors that occur before a cryptographically protected IKE_SA is
+ established must be handled very carefully. There is a trade-off
+ between wanting to be helpful in diagnosing a problem and responding
+ to it and wanting to avoid being a dupe in a denial of service attack
+ based on forged messages.
+
+ If a node receives a message on UDP port 500 or 4500 outside the
+ context of an IKE_SA known to it (and not a request to start one), it
+ may be the result of a recent crash of the node. If the message is
+ marked as a response, the node MAY audit the suspicious event but
+ MUST NOT respond. If the message is marked as a request, the node
+ MAY audit the suspicious event and MAY send a response. If a
+ response is sent, the response MUST be sent to the IP address and
+ port from whence it came with the same IKE SPIs and the Message ID
+ copied. The response MUST NOT be cryptographically protected and
+ MUST contain a Notify payload indicating INVALID_IKE_SPI.
+
+ A node receiving such an unprotected Notify payload MUST NOT respond
+ and MUST NOT change the state of any existing SAs. The message might
+ be a forgery or might be a response the genuine correspondent was
+
+
+
+Kaufman Standards Track [Page 36]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ tricked into sending. A node SHOULD treat such a message (and also a
+ network message like ICMP destination unreachable) as a hint that
+ there might be problems with SAs to that IP address and SHOULD
+ initiate a liveness test for any such IKE_SA. An implementation
+ SHOULD limit the frequency of such tests to avoid being tricked into
+ participating in a denial of service attack.
+
+ A node receiving a suspicious message from an IP address with which
+ it has an IKE_SA MAY send an IKE Notify payload in an IKE
+ INFORMATIONAL exchange over that SA. The recipient MUST NOT change
+ the state of any SA's as a result but SHOULD audit the event to aid
+ in diagnosing malfunctions. A node MUST limit the rate at which it
+ will send messages in response to unprotected messages.
+
+2.22. IPComp
+
+ Use of IP compression [IPCOMP] can be negotiated as part of the setup
+ of a CHILD_SA. While IP compression involves an extra header in each
+ packet and a compression parameter index (CPI), the virtual
+ "compression association" has no life outside the ESP or AH SA that
+ contains it. Compression associations disappear when the
+ corresponding ESP or AH SA goes away. It is not explicitly mentioned
+ in any DELETE payload.
+
+ Negotiation of IP compression is separate from the negotiation of
+ cryptographic parameters associated with a CHILD_SA. A node
+ requesting a CHILD_SA MAY advertise its support for one or more
+ compression algorithms through one or more Notify payloads of type
+ IPCOMP_SUPPORTED. The response MAY indicate acceptance of a single
+ compression algorithm with a Notify payload of type IPCOMP_SUPPORTED.
+ These payloads MUST NOT occur in messages that do not contain SA
+ payloads.
+
+ Although there has been discussion of allowing multiple compression
+ algorithms to be accepted and to have different compression
+ algorithms available for the two directions of a CHILD_SA,
+ implementations of this specification MUST NOT accept an IPComp
+ algorithm that was not proposed, MUST NOT accept more than one, and
+ MUST NOT compress using an algorithm other than one proposed and
+ accepted in the setup of the CHILD_SA.
+
+ A side effect of separating the negotiation of IPComp from
+ cryptographic parameters is that it is not possible to propose
+ multiple cryptographic suites and propose IP compression with some of
+ them but not others.
+
+
+
+
+
+
+Kaufman Standards Track [Page 37]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+2.23. NAT Traversal
+
+ Network Address Translation (NAT) gateways are a controversial
+ subject. This section briefly describes what they are and how they
+ are likely to act on IKE traffic. Many people believe that NATs are
+ evil and that we should not design our protocols so as to make them
+ work better. IKEv2 does specify some unintuitive processing rules in
+ order that NATs are more likely to work.
+
+ NATs exist primarily because of the shortage of IPv4 addresses,
+ though there are other rationales. IP nodes that are "behind" a NAT
+ have IP addresses that are not globally unique, but rather are
+ assigned from some space that is unique within the network behind the
+ NAT but that are likely to be reused by nodes behind other NATs.
+ Generally, nodes behind NATs can communicate with other nodes behind
+ the same NAT and with nodes with globally unique addresses, but not
+ with nodes behind other NATs. There are exceptions to that rule.
+ When those nodes make connections to nodes on the real Internet, the
+ NAT gateway "translates" the IP source address to an address that
+ will be routed back to the gateway. Messages to the gateway from the
+ Internet have their destination addresses "translated" to the
+ internal address that will route the packet to the correct endnode.
+
+ NATs are designed to be "transparent" to endnodes. Neither software
+ on the node behind the NAT nor the node on the Internet requires
+ modification to communicate through the NAT. Achieving this
+ transparency is more difficult with some protocols than with others.
+ Protocols that include IP addresses of the endpoints within the
+ payloads of the packet will fail unless the NAT gateway understands
+ the protocol and modifies the internal references as well as those in
+ the headers. Such knowledge is inherently unreliable, is a network
+ layer violation, and often results in subtle problems.
+
+ Opening an IPsec connection through a NAT introduces special
+ problems. If the connection runs in transport mode, changing the IP
+ addresses on packets will cause the checksums to fail and the NAT
+ cannot correct the checksums because they are cryptographically
+ protected. Even in tunnel mode, there are routing problems because
+ transparently translating the addresses of AH and ESP packets
+ requires special logic in the NAT and that logic is heuristic and
+ unreliable in nature. For that reason, IKEv2 can negotiate UDP
+ encapsulation of IKE and ESP packets. This encoding is slightly less
+ efficient but is easier for NATs to process. In addition, firewalls
+ may be configured to pass IPsec traffic over UDP but not ESP/AH or
+ vice versa.
+
+
+
+
+
+
+Kaufman Standards Track [Page 38]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ It is a common practice of NATs to translate TCP and UDP port numbers
+ as well as addresses and use the port numbers of inbound packets to
+ decide which internal node should get a given packet. For this
+ reason, even though IKE packets MUST be sent from and to UDP port
+ 500, they MUST be accepted coming from any port and responses MUST be
+ sent to the port from whence they came. This is because the ports
+ may be modified as the packets pass through NATs. Similarly, IP
+ addresses of the IKE endpoints are generally not included in the IKE
+ payloads because the payloads are cryptographically protected and
+ could not be transparently modified by NATs.
+
+ Port 4500 is reserved for UDP-encapsulated ESP and IKE. When working
+ through a NAT, it is generally better to pass IKE packets over port
+ 4500 because some older NATs handle IKE traffic on port 500 cleverly
+ in an attempt to transparently establish IPsec connections between
+ endpoints that don't handle NAT traversal themselves. Such NATs may
+ interfere with the straightforward NAT traversal envisioned by this
+ document, so an IPsec endpoint that discovers a NAT between it and
+ its correspondent MUST send all subsequent traffic to and from port
+ 4500, which NATs should not treat specially (as they might with port
+ 500).
+
+ The specific requirements for supporting NAT traversal [RFC3715] are
+ listed below. Support for NAT traversal is optional. In this
+ section only, requirements listed as MUST apply only to
+ implementations supporting NAT traversal.
+
+ IKE MUST listen on port 4500 as well as port 500. IKE MUST
+ respond to the IP address and port from which packets arrived.
+
+ Both IKE initiator and responder MUST include in their IKE_SA_INIT
+ packets Notify payloads of type NAT_DETECTION_SOURCE_IP and
+ NAT_DETECTION_DESTINATION_IP. Those payloads can be used to
+ detect if there is NAT between the hosts, and which end is behind
+ the NAT. The location of the payloads in the IKE_SA_INIT packets
+ are just after the Ni and Nr payloads (before the optional CERTREQ
+ payload).
+
+ If none of the NAT_DETECTION_SOURCE_IP payload(s) received matches
+ the hash of the source IP and port found from the IP header of the
+ packet containing the payload, it means that the other end is
+ behind NAT (i.e., someone along the route changed the source
+ address of the original packet to match the address of the NAT
+ box). In this case, this end should allow dynamic update of the
+ other ends IP address, as described later.
+
+
+
+
+
+
+Kaufman Standards Track [Page 39]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ If the NAT_DETECTION_DESTINATION_IP payload received does not
+ match the hash of the destination IP and port found from the IP
+ header of the packet containing the payload, it means that this
+ end is behind a NAT. In this case, this end SHOULD start sending
+ keepalive packets as explained in [Hutt05].
+
+ The IKE initiator MUST check these payloads if present and if they
+ do not match the addresses in the outer packet MUST tunnel all
+ future IKE and ESP packets associated with this IKE_SA over UDP
+ port 4500.
+
+ To tunnel IKE packets over UDP port 4500, the IKE header has four
+ octets of zero prepended and the result immediately follows the
+ UDP header. To tunnel ESP packets over UDP port 4500, the ESP
+ header immediately follows the UDP header. Since the first four
+ bytes of the ESP header contain the SPI, and the SPI cannot
+ validly be zero, it is always possible to distinguish ESP and IKE
+ messages.
+
+ The original source and destination IP address required for the
+ transport mode TCP and UDP packet checksum fixup (see [Hutt05])
+ are obtained from the Traffic Selectors associated with the
+ exchange. In the case of NAT traversal, the Traffic Selectors
+ MUST contain exactly one IP address, which is then used as the
+ original IP address.
+
+ There are cases where a NAT box decides to remove mappings that
+ are still alive (for example, the keepalive interval is too long,
+ or the NAT box is rebooted). To recover in these cases, hosts
+ that are not behind a NAT SHOULD send all packets (including
+ retransmission packets) to the IP address and port from the last
+ valid authenticated packet from the other end (i.e., dynamically
+ update the address). A host behind a NAT SHOULD NOT do this
+ because it opens a DoS attack possibility. Any authenticated IKE
+ packet or any authenticated UDP-encapsulated ESP packet can be
+ used to detect that the IP address or the port has changed.
+
+ Note that similar but probably not identical actions will likely
+ be needed to make IKE work with Mobile IP, but such processing is
+ not addressed by this document.
+
+2.24. Explicit Congestion Notification (ECN)
+
+ When IPsec tunnels behave as originally specified in [RFC2401], ECN
+ usage is not appropriate for the outer IP headers because tunnel
+ decapsulation processing discards ECN congestion indications to the
+ detriment of the network. ECN support for IPsec tunnels for IKEv1-
+ based IPsec requires multiple operating modes and negotiation (see
+
+
+
+Kaufman Standards Track [Page 40]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ [RFC3168]). IKEv2 simplifies this situation by requiring that ECN be
+ usable in the outer IP headers of all tunnel-mode IPsec SAs created
+ by IKEv2. Specifically, tunnel encapsulators and decapsulators for
+ all tunnel-mode SAs created by IKEv2 MUST support the ECN full-
+ functionality option for tunnels specified in [RFC3168] and MUST
+ implement the tunnel encapsulation and decapsulation processing
+ specified in [RFC4301] to prevent discarding of ECN congestion
+ indications.
+
+3. Header and Payload Formats
+
+3.1. The IKE Header
+
+ IKE messages use UDP ports 500 and/or 4500, with one IKE message per
+ UDP datagram. Information from the beginning of the packet through
+ the UDP header is largely ignored except that the IP addresses and
+ UDP ports from the headers are reversed and used for return packets.
+ When sent on UDP port 500, IKE messages begin immediately following
+ the UDP header. When sent on UDP port 4500, IKE messages have
+ prepended four octets of zero. These four octets of zero are not
+ part of the IKE message and are not included in any of the length
+ fields or checksums defined by IKE. Each IKE message begins with the
+ IKE header, denoted HDR in this memo. Following the header are one
+ or more IKE payloads each identified by a "Next Payload" field in the
+ preceding payload. Payloads are processed in the order in which they
+ appear in an IKE message by invoking the appropriate processing
+ routine according to the "Next Payload" field in the IKE header and
+ subsequently according to the "Next Payload" field in the IKE payload
+ itself until a "Next Payload" field of zero indicates that no
+ payloads follow. If a payload of type "Encrypted" is found, that
+ payload is decrypted and its contents parsed as additional payloads.
+ An Encrypted payload MUST be the last payload in a packet and an
+ Encrypted payload MUST NOT contain another Encrypted payload.
+
+ The Recipient SPI in the header identifies an instance of an IKE
+ security association. It is therefore possible for a single instance
+ of IKE to multiplex distinct sessions with multiple peers.
+
+ All multi-octet fields representing integers are laid out in big
+ endian order (aka most significant byte first, or network byte
+ order).
+
+ The format of the IKE header is shown in Figure 4.
+
+
+
+
+
+
+
+
+Kaufman Standards Track [Page 41]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ 1 2 3
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! IKE_SA Initiator's SPI !
+ ! !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! IKE_SA Responder's SPI !
+ ! !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! Next Payload ! MjVer ! MnVer ! Exchange Type ! Flags !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! Message ID !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! Length !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+ Figure 4: IKE Header Format
+
+ o Initiator's SPI (8 octets) - A value chosen by the
+ initiator to identify a unique IKE security association. This
+ value MUST NOT be zero.
+
+ o Responder's SPI (8 octets) - A value chosen by the
+ responder to identify a unique IKE security association. This
+ value MUST be zero in the first message of an IKE Initial
+ Exchange (including repeats of that message including a
+ cookie) and MUST NOT be zero in any other message.
+
+ o Next Payload (1 octet) - Indicates the type of payload that
+ immediately follows the header. The format and value of each
+ payload are defined below.
+
+ o Major Version (4 bits) - Indicates the major version of the IKE
+ protocol in use. Implementations based on this version of IKE
+ MUST set the Major Version to 2. Implementations based on
+ previous versions of IKE and ISAKMP MUST set the Major Version
+ to 1. Implementations based on this version of IKE MUST reject
+ or ignore messages containing a version number greater than
+ 2.
+
+ o Minor Version (4 bits) - Indicates the minor version of the
+ IKE protocol in use. Implementations based on this version of
+ IKE MUST set the Minor Version to 0. They MUST ignore the
+ minor version number of received messages.
+
+ o Exchange Type (1 octet) - Indicates the type of exchange being
+ used. This constrains the payloads sent in each message and
+ orderings of messages in an exchange.
+
+
+
+Kaufman Standards Track [Page 42]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ Exchange Type Value
+
+ RESERVED 0-33
+ IKE_SA_INIT 34
+ IKE_AUTH 35
+ CREATE_CHILD_SA 36
+ INFORMATIONAL 37
+ RESERVED TO IANA 38-239
+ Reserved for private use 240-255
+
+ o Flags (1 octet) - Indicates specific options that are set
+ for the message. Presence of options are indicated by the
+ appropriate bit in the flags field being set. The bits are
+ defined LSB first, so bit 0 would be the least significant
+ bit of the Flags octet. In the description below, a bit
+ being 'set' means its value is '1', while 'cleared' means
+ its value is '0'.
+
+ -- X(reserved) (bits 0-2) - These bits MUST be cleared
+ when sending and MUST be ignored on receipt.
+
+ -- I(nitiator) (bit 3 of Flags) - This bit MUST be set in
+ messages sent by the original initiator of the IKE_SA
+ and MUST be cleared in messages sent by the original
+ responder. It is used by the recipient to determine
+ which eight octets of the SPI were generated by the
+ recipient.
+
+ -- V(ersion) (bit 4 of Flags) - This bit indicates that
+ the transmitter is capable of speaking a higher major
+ version number of the protocol than the one indicated
+ in the major version number field. Implementations of
+ IKEv2 must clear this bit when sending and MUST ignore
+ it in incoming messages.
+
+ -- R(esponse) (bit 5 of Flags) - This bit indicates that
+ this message is a response to a message containing
+ the same message ID. This bit MUST be cleared in all
+ request messages and MUST be set in all responses.
+ An IKE endpoint MUST NOT generate a response to a
+ message that is marked as being a response.
+
+ -- X(reserved) (bits 6-7 of Flags) - These bits MUST be
+ cleared when sending and MUST be ignored on receipt.
+
+
+
+
+
+
+
+Kaufman Standards Track [Page 43]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ o Message ID (4 octets) - Message identifier used to control
+ retransmission of lost packets and matching of requests and
+ responses. It is essential to the security of the protocol
+ because it is used to prevent message replay attacks.
+ See sections 2.1 and 2.2.
+
+ o Length (4 octets) - Length of total message (header + payloads)
+ in octets.
+
+3.2. Generic Payload Header
+
+ Each IKE payload defined in sections 3.3 through 3.16 begins with a
+ generic payload header, shown in Figure 5. Figures for each payload
+ below will include the generic payload header, but for brevity the
+ description of each field will be omitted.
+
+ 1 2 3
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! Next Payload !C! RESERVED ! Payload Length !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+ Figure 5: Generic Payload Header
+
+ The Generic Payload Header fields are defined as follows:
+
+ o Next Payload (1 octet) - Identifier for the payload type of the
+ next payload in the message. If the current payload is the last
+ in the message, then this field will be 0. This field provides a
+ "chaining" capability whereby additional payloads can be added to
+ a message by appending it to the end of the message and setting
+ the "Next Payload" field of the preceding payload to indicate the
+ new payload's type. An Encrypted payload, which must always be
+ the last payload of a message, is an exception. It contains data
+ structures in the format of additional payloads. In the header of
+ an Encrypted payload, the Next Payload field is set to the payload
+ type of the first contained payload (instead of 0).
+
+ Payload Type Values
+
+ Next Payload Type Notation Value
+
+ No Next Payload 0
+
+ RESERVED 1-32
+ Security Association SA 33
+ Key Exchange KE 34
+ Identification - Initiator IDi 35
+
+
+
+Kaufman Standards Track [Page 44]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ Identification - Responder IDr 36
+ Certificate CERT 37
+ Certificate Request CERTREQ 38
+ Authentication AUTH 39
+ Nonce Ni, Nr 40
+ Notify N 41
+ Delete D 42
+ Vendor ID V 43
+ Traffic Selector - Initiator TSi 44
+ Traffic Selector - Responder TSr 45
+ Encrypted E 46
+ Configuration CP 47
+ Extensible Authentication EAP 48
+ RESERVED TO IANA 49-127
+ PRIVATE USE 128-255
+
+ Payload type values 1-32 should not be used so that there is no
+ overlap with the code assignments for IKEv1. Payload type values
+ 49-127 are reserved to IANA for future assignment in IKEv2 (see
+ section 6). Payload type values 128-255 are for private use among
+ mutually consenting parties.
+
+ o Critical (1 bit) - MUST be set to zero if the sender wants the
+ recipient to skip this payload if it does not understand the
+ payload type code in the Next Payload field of the previous
+ payload. MUST be set to one if the sender wants the recipient to
+ reject this entire message if it does not understand the payload
+ type. MUST be ignored by the recipient if the recipient
+ understands the payload type code. MUST be set to zero for
+ payload types defined in this document. Note that the critical
+ bit applies to the current payload rather than the "next" payload
+ whose type code appears in the first octet. The reasoning behind
+ not setting the critical bit for payloads defined in this document
+ is that all implementations MUST understand all payload types
+ defined in this document and therefore must ignore the Critical
+ bit's value. Skipped payloads are expected to have valid Next
+ Payload and Payload Length fields.
+
+ o RESERVED (7 bits) - MUST be sent as zero; MUST be ignored on
+ receipt.
+
+ o Payload Length (2 octets) - Length in octets of the current
+ payload, including the generic payload header.
+
+
+
+
+
+
+
+
+Kaufman Standards Track [Page 45]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+3.3. Security Association Payload
+
+ The Security Association Payload, denoted SA in this memo, is used to
+ negotiate attributes of a security association. Assembly of Security
+ Association Payloads requires great peace of mind. An SA payload MAY
+ contain multiple proposals. If there is more than one, they MUST be
+ ordered from most preferred to least preferred. Each proposal may
+ contain multiple IPsec protocols (where a protocol is IKE, ESP, or
+ AH), each protocol MAY contain multiple transforms, and each
+ transform MAY contain multiple attributes. When parsing an SA, an
+ implementation MUST check that the total Payload Length is consistent
+ with the payload's internal lengths and counts. Proposals,
+ Transforms, and Attributes each have their own variable length
+ encodings. They are nested such that the Payload Length of an SA
+ includes the combined contents of the SA, Proposal, Transform, and
+ Attribute information. The length of a Proposal includes the lengths
+ of all Transforms and Attributes it contains. The length of a
+ Transform includes the lengths of all Attributes it contains.
+
+ The syntax of Security Associations, Proposals, Transforms, and
+ Attributes is based on ISAKMP; however, the semantics are somewhat
+ different. The reason for the complexity and the hierarchy is to
+ allow for multiple possible combinations of algorithms to be encoded
+ in a single SA. Sometimes there is a choice of multiple algorithms,
+ whereas other times there is a combination of algorithms. For
+ example, an initiator might want to propose using (AH w/MD5 and ESP
+ w/3DES) OR (ESP w/MD5 and 3DES).
+
+ One of the reasons the semantics of the SA payload has changed from
+ ISAKMP and IKEv1 is to make the encodings more compact in common
+ cases.
+
+ The Proposal structure contains within it a Proposal # and an IPsec
+ protocol ID. Each structure MUST have the same Proposal # as the
+ previous one or be one (1) greater. The first Proposal MUST have a
+ Proposal # of one (1). If two successive structures have the same
+ Proposal number, it means that the proposal consists of the first
+ structure AND the second. So a proposal of AH AND ESP would have two
+ proposal structures, one for AH and one for ESP and both would have
+ Proposal #1. A proposal of AH OR ESP would have two proposal
+ structures, one for AH with Proposal #1 and one for ESP with Proposal
+ #2.
+
+ Each Proposal/Protocol structure is followed by one or more transform
+ structures. The number of different transforms is generally
+ determined by the Protocol. AH generally has a single transform: an
+ integrity check algorithm. ESP generally has two: an encryption
+ algorithm and an integrity check algorithm. IKE generally has four
+
+
+
+Kaufman Standards Track [Page 46]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ transforms: a Diffie-Hellman group, an integrity check algorithm, a
+ prf algorithm, and an encryption algorithm. If an algorithm that
+ combines encryption and integrity protection is proposed, it MUST be
+ proposed as an encryption algorithm and an integrity protection
+ algorithm MUST NOT be proposed. For each Protocol, the set of
+ permissible transforms is assigned transform ID numbers, which appear
+ in the header of each transform.
+
+ If there are multiple transforms with the same Transform Type, the
+ proposal is an OR of those transforms. If there are multiple
+ Transforms with different Transform Types, the proposal is an AND of
+ the different groups. For example, to propose ESP with (3DES or
+ IDEA) and (HMAC_MD5 or HMAC_SHA), the ESP proposal would contain two
+ Transform Type 1 candidates (one for 3DES and one for IDEA) and two
+ Transform Type 2 candidates (one for HMAC_MD5 and one for HMAC_SHA).
+ This effectively proposes four combinations of algorithms. If the
+ initiator wanted to propose only a subset of those, for example (3DES
+ and HMAC_MD5) or (IDEA and HMAC_SHA), there is no way to encode that
+ as multiple transforms within a single Proposal. Instead, the
+ initiator would have to construct two different Proposals, each with
+ two transforms.
+
+ A given transform MAY have one or more Attributes. Attributes are
+ necessary when the transform can be used in more than one way, as
+ when an encryption algorithm has a variable key size. The transform
+ would specify the algorithm and the attribute would specify the key
+ size. Most transforms do not have attributes. A transform MUST NOT
+ have multiple attributes of the same type. To propose alternate
+ values for an attribute (for example, multiple key sizes for the AES
+ encryption algorithm), and implementation MUST include multiple
+ Transforms with the same Transform Type each with a single Attribute.
+
+ Note that the semantics of Transforms and Attributes are quite
+ different from those in IKEv1. In IKEv1, a single Transform carried
+ multiple algorithms for a protocol with one carried in the Transform
+ and the others carried in the Attributes.
+
+ 1 2 3
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! Next Payload !C! RESERVED ! Payload Length !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! !
+ ~ <Proposals> ~
+ ! !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+ Figure 6: Security Association Payload
+
+
+
+Kaufman Standards Track [Page 47]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ o Proposals (variable) - One or more proposal substructures.
+
+ The payload type for the Security Association Payload is thirty
+ three (33).
+
+3.3.1. Proposal Substructure
+
+ 1 2 3
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! 0 (last) or 2 ! RESERVED ! Proposal Length !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! Proposal # ! Protocol ID ! SPI Size !# of Transforms!
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ~ SPI (variable) ~
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! !
+ ~ <Transforms> ~
+ ! !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+ Figure 7: Proposal Substructure
+
+ o 0 (last) or 2 (more) (1 octet) - Specifies whether this is the
+ last Proposal Substructure in the SA. This syntax is inherited
+ from ISAKMP, but is unnecessary because the last Proposal could
+ be identified from the length of the SA. The value (2)
+ corresponds to a Payload Type of Proposal in IKEv1, and the
+ first 4 octets of the Proposal structure are designed to look
+ somewhat like the header of a Payload.
+
+ o RESERVED (1 octet) - MUST be sent as zero; MUST be ignored on
+ receipt.
+
+ o Proposal Length (2 octets) - Length of this proposal, including
+ all transforms and attributes that follow.
+
+ o Proposal # (1 octet) - When a proposal is made, the first
+ proposal in an SA payload MUST be #1, and subsequent proposals
+ MUST either be the same as the previous proposal (indicating an
+ AND of the two proposals) or one more than the previous
+ proposal (indicating an OR of the two proposals). When a
+ proposal is accepted, all of the proposal numbers in the SA
+ payload MUST be the same and MUST match the number on the
+ proposal sent that was accepted.
+
+
+
+
+
+
+Kaufman Standards Track [Page 48]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ o Protocol ID (1 octet) - Specifies the IPsec protocol identifier
+ for the current negotiation. The defined values are:
+
+ Protocol Protocol ID
+ RESERVED 0
+ IKE 1
+ AH 2
+ ESP 3
+ RESERVED TO IANA 4-200
+ PRIVATE USE 201-255
+
+ o SPI Size (1 octet) - For an initial IKE_SA negotiation, this
+ field MUST be zero; the SPI is obtained from the outer header.
+ During subsequent negotiations, it is equal to the size, in
+ octets, of the SPI of the corresponding protocol (8 for IKE, 4
+ for ESP and AH).
+
+ o # of Transforms (1 octet) - Specifies the number of transforms
+ in this proposal.
+
+ o SPI (variable) - The sending entity's SPI. Even if the SPI Size
+ is not a multiple of 4 octets, there is no padding applied to
+ the payload. When the SPI Size field is zero, this field is
+ not present in the Security Association payload.
+
+ o Transforms (variable) - One or more transform substructures.
+
+3.3.2. Transform Substructure
+
+ 1 2 3
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! 0 (last) or 3 ! RESERVED ! Transform Length !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ !Transform Type ! RESERVED ! Transform ID !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! !
+ ~ Transform Attributes ~
+ ! !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+ Figure 8: Transform Substructure
+
+ o 0 (last) or 3 (more) (1 octet) - Specifies whether this is the
+ last Transform Substructure in the Proposal. This syntax is
+ inherited from ISAKMP, but is unnecessary because the last
+ Proposal could be identified from the length of the SA. The
+
+
+
+
+Kaufman Standards Track [Page 49]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ value (3) corresponds to a Payload Type of Transform in IKEv1,
+ and the first 4 octets of the Transform structure are designed
+ to look somewhat like the header of a Payload.
+
+ o RESERVED - MUST be sent as zero; MUST be ignored on receipt.
+
+ o Transform Length - The length (in octets) of the Transform
+ Substructure including Header and Attributes.
+
+ o Transform Type (1 octet) - The type of transform being
+ specified in this transform. Different protocols support
+ different transform types. For some protocols, some of the
+ transforms may be optional. If a transform is optional and the
+ initiator wishes to propose that the transform be omitted, no
+ transform of the given type is included in the proposal. If
+ the initiator wishes to make use of the transform optional to
+ the responder, it includes a transform substructure with
+ transform ID = 0 as one of the options.
+
+ o Transform ID (2 octets) - The specific instance of the
+ transform type being proposed.
+
+ Transform Type Values
+
+ Transform Used In
+ Type
+ RESERVED 0
+ Encryption Algorithm (ENCR) 1 (IKE and ESP)
+ Pseudo-random Function (PRF) 2 (IKE)
+ Integrity Algorithm (INTEG) 3 (IKE, AH, optional in ESP)
+ Diffie-Hellman Group (D-H) 4 (IKE, optional in AH & ESP)
+ Extended Sequence Numbers (ESN) 5 (AH and ESP)
+ RESERVED TO IANA 6-240
+ PRIVATE USE 241-255
+
+ For Transform Type 1 (Encryption Algorithm), defined Transform IDs
+ are:
+
+ Name Number Defined In
+ RESERVED 0
+ ENCR_DES_IV64 1 (RFC1827)
+ ENCR_DES 2 (RFC2405), [DES]
+ ENCR_3DES 3 (RFC2451)
+ ENCR_RC5 4 (RFC2451)
+ ENCR_IDEA 5 (RFC2451), [IDEA]
+ ENCR_CAST 6 (RFC2451)
+ ENCR_BLOWFISH 7 (RFC2451)
+ ENCR_3IDEA 8 (RFC2451)
+
+
+
+Kaufman Standards Track [Page 50]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ ENCR_DES_IV32 9
+ RESERVED 10
+ ENCR_NULL 11 (RFC2410)
+ ENCR_AES_CBC 12 (RFC3602)
+ ENCR_AES_CTR 13 (RFC3664)
+
+ values 14-1023 are reserved to IANA. Values 1024-65535 are
+ for private use among mutually consenting parties.
+
+ For Transform Type 2 (Pseudo-random Function), defined Transform IDs
+ are:
+
+ Name Number Defined In
+ RESERVED 0
+ PRF_HMAC_MD5 1 (RFC2104), [MD5]
+ PRF_HMAC_SHA1 2 (RFC2104), [SHA]
+ PRF_HMAC_TIGER 3 (RFC2104)
+ PRF_AES128_XCBC 4 (RFC3664)
+
+ values 5-1023 are reserved to IANA. Values 1024-65535 are for
+ private use among mutually consenting parties.
+
+ For Transform Type 3 (Integrity Algorithm), defined Transform IDs
+ are:
+
+ Name Number Defined In
+ NONE 0
+ AUTH_HMAC_MD5_96 1 (RFC2403)
+ AUTH_HMAC_SHA1_96 2 (RFC2404)
+ AUTH_DES_MAC 3
+ AUTH_KPDK_MD5 4 (RFC1826)
+ AUTH_AES_XCBC_96 5 (RFC3566)
+
+ values 6-1023 are reserved to IANA. Values 1024-65535 are for
+ private use among mutually consenting parties.
+
+ For Transform Type 4 (Diffie-Hellman Group), defined Transform IDs
+ are:
+
+ Name Number
+ NONE 0
+ Defined in Appendix B 1 - 2
+ RESERVED 3 - 4
+ Defined in [ADDGROUP] 5
+ RESERVED TO IANA 6 - 13
+ Defined in [ADDGROUP] 14 - 18
+ RESERVED TO IANA 19 - 1023
+ PRIVATE USE 1024-65535
+
+
+
+Kaufman Standards Track [Page 51]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ For Transform Type 5 (Extended Sequence Numbers), defined Transform
+ IDs are:
+
+ Name Number
+ No Extended Sequence Numbers 0
+ Extended Sequence Numbers 1
+ RESERVED 2 - 65535
+
+3.3.3. Valid Transform Types by Protocol
+
+ The number and type of transforms that accompany an SA payload are
+ dependent on the protocol in the SA itself. An SA payload proposing
+ the establishment of an SA has the following mandatory and optional
+ transform types. A compliant implementation MUST understand all
+ mandatory and optional types for each protocol it supports (though it
+ need not accept proposals with unacceptable suites). A proposal MAY
+ omit the optional types if the only value for them it will accept is
+ NONE.
+
+ Protocol Mandatory Types Optional Types
+ IKE ENCR, PRF, INTEG, D-H
+ ESP ENCR, ESN INTEG, D-H
+ AH INTEG, ESN D-H
+
+3.3.4. Mandatory Transform IDs
+
+ The specification of suites that MUST and SHOULD be supported for
+ interoperability has been removed from this document because they are
+ likely to change more rapidly than this document evolves.
+
+ An important lesson learned from IKEv1 is that no system should only
+ implement the mandatory algorithms and expect them to be the best
+ choice for all customers. For example, at the time that this
+ document was written, many IKEv1 implementers were starting to
+ migrate to AES in Cipher Block Chaining (CBC) mode for Virtual
+ Private Network (VPN) applications. Many IPsec systems based on
+ IKEv2 will implement AES, additional Diffie-Hellman groups, and
+ additional hash algorithms, and some IPsec customers already require
+ these algorithms in addition to the ones listed above.
+
+ It is likely that IANA will add additional transforms in the future,
+ and some users may want to use private suites, especially for IKE
+ where implementations should be capable of supporting different
+ parameters, up to certain size limits. In support of this goal, all
+ implementations of IKEv2 SHOULD include a management facility that
+ allows specification (by a user or system administrator) of Diffie-
+ Hellman (DH) parameters (the generator, modulus, and exponent lengths
+ and values) for new DH groups. Implementations SHOULD provide a
+
+
+
+Kaufman Standards Track [Page 52]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ management interface via which these parameters and the associated
+ transform IDs may be entered (by a user or system administrator), to
+ enable negotiating such groups.
+
+ All implementations of IKEv2 MUST include a management facility that
+ enables a user or system administrator to specify the suites that are
+ acceptable for use with IKE. Upon receipt of a payload with a set of
+ transform IDs, the implementation MUST compare the transmitted
+ transform IDs against those locally configured via the management
+ controls, to verify that the proposed suite is acceptable based on
+ local policy. The implementation MUST reject SA proposals that are
+ not authorized by these IKE suite controls. Note that cryptographic
+ suites that MUST be implemented need not be configured as acceptable
+ to local policy.
+
+3.3.5. Transform Attributes
+
+ Each transform in a Security Association payload may include
+ attributes that modify or complete the specification of the
+ transform. These attributes are type/value pairs and are defined
+ below. For example, if an encryption algorithm has a variable-length
+ key, the key length to be used may be specified as an attribute.
+ Attributes can have a value with a fixed two octet length or a
+ variable-length value. For the latter, the attribute is encoded as
+ type/length/value.
+
+ 1 2 3
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ !A! Attribute Type ! AF=0 Attribute Length !
+ !F! ! AF=1 Attribute Value !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! AF=0 Attribute Value !
+ ! AF=1 Not Transmitted !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+ Figure 9: Data Attributes
+
+ o Attribute Type (2 octets) - Unique identifier for each type of
+ attribute (see below).
+
+ The most significant bit of this field is the Attribute Format
+ bit (AF). It indicates whether the data attributes follow the
+ Type/Length/Value (TLV) format or a shortened Type/Value (TV)
+ format. If the AF bit is zero (0), then the Data Attributes
+ are of the Type/Length/Value (TLV) form. If the AF bit is a
+ one (1), then the Data Attributes are of the Type/Value form.
+
+
+
+
+Kaufman Standards Track [Page 53]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ o Attribute Length (2 octets) - Length in octets of the Attribute
+ Value. When the AF bit is a one (1), the Attribute Value is
+ only 2 octets and the Attribute Length field is not present.
+
+ o Attribute Value (variable length) - Value of the Attribute
+ associated with the Attribute Type. If the AF bit is a zero
+ (0), this field has a variable length defined by the Attribute
+ Length field. If the AF bit is a one (1), the Attribute Value
+ has a length of 2 octets.
+
+ Note that only a single attribute type (Key Length) is defined, and
+ it is fixed length. The variable-length encoding specification is
+ included only for future extensions. The only algorithms defined in
+ this document that accept attributes are the AES-based encryption,
+ integrity, and pseudo-random functions, which require a single
+ attribute specifying key width.
+
+ Attributes described as basic MUST NOT be encoded using the
+ variable-length encoding. Variable-length attributes MUST NOT be
+ encoded as basic even if their value can fit into two octets. NOTE:
+ This is a change from IKEv1, where increased flexibility may have
+ simplified the composer of messages but certainly complicated the
+ parser.
+
+ Attribute Type Value Attribute Format
+ --------------------------------------------------------------
+ RESERVED 0-13 Key Length (in bits)
+ 14 TV RESERVED 15-17
+ RESERVED TO IANA 18-16383 PRIVATE USE
+ 16384-32767
+
+ Values 0-13 and 15-17 were used in a similar context in IKEv1 and
+ should not be assigned except to matching values. Values 18-16383
+ are reserved to IANA. Values 16384-32767 are for private use among
+ mutually consenting parties.
+
+ - Key Length
+
+ When using an Encryption Algorithm that has a variable-length key,
+ this attribute specifies the key length in bits (MUST use network
+ byte order). This attribute MUST NOT be used when the specified
+ Encryption Algorithm uses a fixed-length key.
+
+
+
+
+
+
+
+
+
+Kaufman Standards Track [Page 54]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+3.3.6. Attribute Negotiation
+
+ During security association negotiation, initiators present offers to
+ responders. Responders MUST select a single complete set of
+ parameters from the offers (or reject all offers if none are
+ acceptable). If there are multiple proposals, the responder MUST
+ choose a single proposal number and return all of the Proposal
+ substructures with that Proposal number. If there are multiple
+ Transforms with the same type, the responder MUST choose a single
+ one. Any attributes of a selected transform MUST be returned
+ unmodified. The initiator of an exchange MUST check that the
+ accepted offer is consistent with one of its proposals, and if not
+ that response MUST be rejected.
+
+ Negotiating Diffie-Hellman groups presents some special challenges.
+ SA offers include proposed attributes and a Diffie-Hellman public
+ number (KE) in the same message. If in the initial exchange the
+ initiator offers to use one of several Diffie-Hellman groups, it
+ SHOULD pick the one the responder is most likely to accept and
+ include a KE corresponding to that group. If the guess turns out to
+ be wrong, the responder will indicate the correct group in the
+ response and the initiator SHOULD pick an element of that group for
+ its KE value when retrying the first message. It SHOULD, however,
+ continue to propose its full supported set of groups in order to
+ prevent a man-in-the-middle downgrade attack.
+
+ Implementation Note:
+
+ Certain negotiable attributes can have ranges or could have
+ multiple acceptable values. These include the key length of a
+ variable key length symmetric cipher. To further interoperability
+ and to support upgrading endpoints independently, implementers of
+ this protocol SHOULD accept values that they deem to supply
+ greater security. For instance, if a peer is configured to accept
+ a variable-length cipher with a key length of X bits and is
+ offered that cipher with a larger key length, the implementation
+ SHOULD accept the offer if it supports use of the longer key.
+
+ Support of this capability allows an implementation to express a
+ concept of "at least" a certain level of security -- "a key length of
+ _at least_ X bits for cipher Y".
+
+
+
+
+
+
+
+
+
+
+Kaufman Standards Track [Page 55]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+3.4. Key Exchange Payload
+
+ The Key Exchange Payload, denoted KE in this memo, is used to
+ exchange Diffie-Hellman public numbers as part of a Diffie-Hellman
+ key exchange. The Key Exchange Payload consists of the IKE generic
+ payload header followed by the Diffie-Hellman public value itself.
+
+ 1 2 3
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! Next Payload !C! RESERVED ! Payload Length !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! DH Group # ! RESERVED !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! !
+ ~ Key Exchange Data ~
+ ! !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+ Figure 10: Key Exchange Payload Format
+
+ A key exchange payload is constructed by copying one's Diffie-Hellman
+ public value into the "Key Exchange Data" portion of the payload.
+ The length of the Diffie-Hellman public value MUST be equal to the
+ length of the prime modulus over which the exponentiation was
+ performed, prepending zero bits to the value if necessary.
+
+ The DH Group # identifies the Diffie-Hellman group in which the Key
+ Exchange Data was computed (see section 3.3.2). If the selected
+ proposal uses a different Diffie-Hellman group, the message MUST be
+ rejected with a Notify payload of type INVALID_KE_PAYLOAD.
+
+ The payload type for the Key Exchange payload is thirty four (34).
+
+3.5. Identification Payloads
+
+ The Identification Payloads, denoted IDi and IDr in this memo, allow
+ peers to assert an identity to one another. This identity may be
+ used for policy lookup, but does not necessarily have to match
+ anything in the CERT payload; both fields may be used by an
+ implementation to perform access control decisions.
+
+ NOTE: In IKEv1, two ID payloads were used in each direction to hold
+ Traffic Selector (TS) information for data passing over the SA. In
+ IKEv2, this information is carried in TS payloads (see section 3.13).
+
+
+
+
+
+
+Kaufman Standards Track [Page 56]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ The Identification Payload consists of the IKE generic payload header
+ followed by identification fields as follows:
+
+ 1 2 3
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! Next Payload !C! RESERVED ! Payload Length !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! ID Type ! RESERVED |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! !
+ ~ Identification Data ~
+ ! !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+ Figure 11: Identification Payload Format
+
+ o ID Type (1 octet) - Specifies the type of Identification being
+ used.
+
+ o RESERVED - MUST be sent as zero; MUST be ignored on receipt.
+
+ o Identification Data (variable length) - Value, as indicated by the
+ Identification Type. The length of the Identification Data is
+ computed from the size in the ID payload header.
+
+ The payload types for the Identification Payload are thirty five (35)
+ for IDi and thirty six (36) for IDr.
+
+ The following table lists the assigned values for the Identification
+ Type field, followed by a description of the Identification Data
+ which follows:
+
+ ID Type Value
+ ------- -----
+ RESERVED 0
+
+ ID_IPV4_ADDR 1
+
+ A single four (4) octet IPv4 address.
+
+ ID_FQDN 2
+
+ A fully-qualified domain name string. An example of a
+ ID_FQDN is, "example.com". The string MUST not contain any
+ terminators (e.g., NULL, CR, etc.).
+
+
+
+
+
+Kaufman Standards Track [Page 57]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ ID_RFC822_ADDR 3
+
+ A fully-qualified RFC822 email address string, An example of
+ a ID_RFC822_ADDR is, "jsmith@example.com". The string MUST
+ not contain any terminators.
+
+ Reserved to IANA 4
+
+ ID_IPV6_ADDR 5
+
+ A single sixteen (16) octet IPv6 address.
+
+ Reserved to IANA 6 - 8
+
+ ID_DER_ASN1_DN 9
+
+ The binary Distinguished Encoding Rules (DER) encoding of an
+ ASN.1 X.500 Distinguished Name [X.501].
+
+ ID_DER_ASN1_GN 10
+
+ The binary DER encoding of an ASN.1 X.500 GeneralName
+ [X.509].
+
+ ID_KEY_ID 11
+
+ An opaque octet stream which may be used to pass vendor-
+ specific information necessary to do certain proprietary
+ types of identification.
+
+ Reserved to IANA 12-200
+
+ Reserved for private use 201-255
+
+ Two implementations will interoperate only if each can generate a
+ type of ID acceptable to the other. To assure maximum
+ interoperability, implementations MUST be configurable to send at
+ least one of ID_IPV4_ADDR, ID_FQDN, ID_RFC822_ADDR, or ID_KEY_ID, and
+ MUST be configurable to accept all of these types. Implementations
+ SHOULD be capable of generating and accepting all of these types.
+ IPv6-capable implementations MUST additionally be configurable to
+ accept ID_IPV6_ADDR. IPv6-only implementations MAY be configurable
+ to send only ID_IPV6_ADDR.
+
+
+
+
+
+
+
+
+Kaufman Standards Track [Page 58]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+3.6. Certificate Payload
+
+ The Certificate Payload, denoted CERT in this memo, provides a means
+ to transport certificates or other authentication-related information
+ via IKE. Certificate payloads SHOULD be included in an exchange if
+ certificates are available to the sender unless the peer has
+ indicated an ability to retrieve this information from elsewhere
+ using an HTTP_CERT_LOOKUP_SUPPORTED Notify payload. Note that the
+ term "Certificate Payload" is somewhat misleading, because not all
+ authentication mechanisms use certificates and data other than
+ certificates may be passed in this payload.
+
+ The Certificate Payload is defined as follows:
+
+ 1 2 3
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! Next Payload !C! RESERVED ! Payload Length !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! Cert Encoding ! !
+ +-+-+-+-+-+-+-+-+ !
+ ~ Certificate Data ~
+ ! !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+ Figure 12: Certificate Payload Format
+
+ o Certificate Encoding (1 octet) - This field indicates the type
+ of certificate or certificate-related information contained in
+ the Certificate Data field.
+
+ Certificate Encoding Value
+ -------------------- -----
+ RESERVED 0
+ PKCS #7 wrapped X.509 certificate 1
+ PGP Certificate 2
+ DNS Signed Key 3
+ X.509 Certificate - Signature 4
+ Kerberos Token 6
+ Certificate Revocation List (CRL) 7
+ Authority Revocation List (ARL) 8
+ SPKI Certificate 9
+ X.509 Certificate - Attribute 10
+ Raw RSA Key 11
+ Hash and URL of X.509 certificate 12
+ Hash and URL of X.509 bundle 13
+ RESERVED to IANA 14 - 200
+ PRIVATE USE 201 - 255
+
+
+
+Kaufman Standards Track [Page 59]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ o Certificate Data (variable length) - Actual encoding of
+ certificate data. The type of certificate is indicated by the
+ Certificate Encoding field.
+
+ The payload type for the Certificate Payload is thirty seven (37).
+
+ Specific syntax is for some of the certificate type codes above is
+ not defined in this document. The types whose syntax is defined in
+ this document are:
+
+ X.509 Certificate - Signature (4) contains a DER encoded X.509
+ certificate whose public key is used to validate the sender's AUTH
+ payload.
+
+ Certificate Revocation List (7) contains a DER encoded X.509
+ certificate revocation list.
+
+ Raw RSA Key (11) contains a PKCS #1 encoded RSA key (see [RSA] and
+ [PKCS1]).
+
+ Hash and URL encodings (12-13) allow IKE messages to remain short
+ by replacing long data structures with a 20 octet SHA-1 hash (see
+ [SHA]) of the replaced value followed by a variable-length URL
+ that resolves to the DER encoded data structure itself. This
+ improves efficiency when the endpoints have certificate data
+ cached and makes IKE less subject to denial of service attacks
+ that become easier to mount when IKE messages are large enough to
+ require IP fragmentation [KPS03].
+
+ Use the following ASN.1 definition for an X.509 bundle:
+
+ CertBundle
+ { iso(1) identified-organization(3) dod(6) internet(1)
+ security(5) mechanisms(5) pkix(7) id-mod(0)
+ id-mod-cert-bundle(34) }
+
+ DEFINITIONS EXPLICIT TAGS ::=
+ BEGIN
+
+ IMPORTS
+ Certificate, CertificateList
+ FROM PKIX1Explicit88
+ { iso(1) identified-organization(3) dod(6)
+ internet(1) security(5) mechanisms(5) pkix(7)
+ id-mod(0) id-pkix1-explicit(18) } ;
+
+
+
+
+
+
+Kaufman Standards Track [Page 60]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ CertificateOrCRL ::= CHOICE {
+ cert [0] Certificate,
+ crl [1] CertificateList }
+
+ CertificateBundle ::= SEQUENCE OF CertificateOrCRL
+
+ END
+
+ Implementations MUST be capable of being configured to send and
+ accept up to four X.509 certificates in support of authentication,
+ and also MUST be capable of being configured to send and accept the
+ first two Hash and URL formats (with HTTP URLs). Implementations
+ SHOULD be capable of being configured to send and accept Raw RSA
+ keys. If multiple certificates are sent, the first certificate MUST
+ contain the public key used to sign the AUTH payload. The other
+ certificates may be sent in any order.
+
+3.7. Certificate Request Payload
+
+ The Certificate Request Payload, denoted CERTREQ in this memo,
+ provides a means to request preferred certificates via IKE and can
+ appear in the IKE_INIT_SA response and/or the IKE_AUTH request.
+ Certificate Request payloads MAY be included in an exchange when the
+ sender needs to get the certificate of the receiver. If multiple CAs
+ are trusted and the cert encoding does not allow a list, then
+ multiple Certificate Request payloads SHOULD be transmitted.
+
+ The Certificate Request Payload is defined as follows:
+
+ 1 2 3
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! Next Payload !C! RESERVED ! Payload Length !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! Cert Encoding ! !
+ +-+-+-+-+-+-+-+-+ !
+ ~ Certification Authority ~
+ ! !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+ Figure 13: Certificate Request Payload Format
+
+ o Certificate Encoding (1 octet) - Contains an encoding of the type
+ or format of certificate requested. Values are listed in section
+ 3.6.
+
+
+
+
+
+
+Kaufman Standards Track [Page 61]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ o Certification Authority (variable length) - Contains an encoding
+ of an acceptable certification authority for the type of
+ certificate requested.
+
+ The payload type for the Certificate Request Payload is thirty eight
+ (38).
+
+ The Certificate Encoding field has the same values as those defined
+ in section 3.6. The Certification Authority field contains an
+ indicator of trusted authorities for this certificate type. The
+ Certification Authority value is a concatenated list of SHA-1 hashes
+ of the public keys of trusted Certification Authorities (CAs). Each
+ is encoded as the SHA-1 hash of the Subject Public Key Info element
+ (see section 4.1.2.7 of [RFC3280]) from each Trust Anchor
+ certificate. The twenty-octet hashes are concatenated and included
+ with no other formatting.
+
+ Note that the term "Certificate Request" is somewhat misleading, in
+ that values other than certificates are defined in a "Certificate"
+ payload and requests for those values can be present in a Certificate
+ Request Payload. The syntax of the Certificate Request payload in
+ such cases is not defined in this document.
+
+ The Certificate Request Payload is processed by inspecting the "Cert
+ Encoding" field to determine whether the processor has any
+ certificates of this type. If so, the "Certification Authority"
+ field is inspected to determine if the processor has any certificates
+ that can be validated up to one of the specified certification
+ authorities. This can be a chain of certificates.
+
+ If an end-entity certificate exists that satisfies the criteria
+ specified in the CERTREQ, a certificate or certificate chain SHOULD
+ be sent back to the certificate requestor if the recipient of the
+ CERTREQ:
+
+ - is configured to use certificate authentication,
+
+ - is allowed to send a CERT payload,
+
+ - has matching CA trust policy governing the current negotiation, and
+
+ - has at least one time-wise and usage appropriate end-entity
+ certificate chaining to a CA provided in the CERTREQ.
+
+ Certificate revocation checking must be considered during the
+ chaining process used to select a certificate. Note that even if two
+ peers are configured to use two different CAs, cross-certification
+ relationships should be supported by appropriate selection logic.
+
+
+
+Kaufman Standards Track [Page 62]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ The intent is not to prevent communication through the strict
+ adherence of selection of a certificate based on CERTREQ, when an
+ alternate certificate could be selected by the sender that would
+ still enable the recipient to successfully validate and trust it
+ through trust conveyed by cross-certification, CRLs, or other out-
+ of-band configured means. Thus, the processing of a CERTREQ should
+ be seen as a suggestion for a certificate to select, not a mandated
+ one. If no certificates exist, then the CERTREQ is ignored. This is
+ not an error condition of the protocol. There may be cases where
+ there is a preferred CA sent in the CERTREQ, but an alternate might
+ be acceptable (perhaps after prompting a human operator).
+
+3.8. Authentication Payload
+
+ The Authentication Payload, denoted AUTH in this memo, contains data
+ used for authentication purposes. The syntax of the Authentication
+ data varies according to the Auth Method as specified below.
+
+ The Authentication Payload is defined as follows:
+
+ 1 2 3
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! Next Payload !C! RESERVED ! Payload Length !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! Auth Method ! RESERVED !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! !
+ ~ Authentication Data ~
+ ! !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+ Figure 14: Authentication Payload Format
+
+ o Auth Method (1 octet) - Specifies the method of authentication
+ used. Values defined are:
+
+ RSA Digital Signature (1) - Computed as specified in section
+ 2.15 using an RSA private key over a PKCS#1 padded hash (see
+ [RSA] and [PKCS1]).
+
+ Shared Key Message Integrity Code (2) - Computed as specified in
+ section 2.15 using the shared key associated with the identity
+ in the ID payload and the negotiated prf function
+
+ DSS Digital Signature (3) - Computed as specified in section
+ 2.15 using a DSS private key (see [DSS]) over a SHA-1 hash.
+
+
+
+
+Kaufman Standards Track [Page 63]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ The values 0 and 4-200 are reserved to IANA. The values 201-255
+ are available for private use.
+
+ o Authentication Data (variable length) - see section 2.15.
+
+ The payload type for the Authentication Payload is thirty nine (39).
+
+3.9. Nonce Payload
+
+ The Nonce Payload, denoted Ni and Nr in this memo for the initiator's
+ and responder's nonce respectively, contains random data used to
+ guarantee liveness during an exchange and protect against replay
+ attacks.
+
+ The Nonce Payload is defined as follows:
+
+ 1 2 3
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! Next Payload !C! RESERVED ! Payload Length !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! !
+ ~ Nonce Data ~
+ ! !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+ Figure 15: Nonce Payload Format
+
+ o Nonce Data (variable length) - Contains the random data generated
+ by the transmitting entity.
+
+ The payload type for the Nonce Payload is forty (40).
+
+ The size of a Nonce MUST be between 16 and 256 octets inclusive.
+ Nonce values MUST NOT be reused.
+
+3.10. Notify Payload
+
+ The Notify Payload, denoted N in this document, is used to transmit
+ informational data, such as error conditions and state transitions,
+ to an IKE peer. A Notify Payload may appear in a response message
+ (usually specifying why a request was rejected), in an INFORMATIONAL
+ Exchange (to report an error not in an IKE request), or in any other
+ message to indicate sender capabilities or to modify the meaning of
+ the request.
+
+
+
+
+
+
+Kaufman Standards Track [Page 64]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ The Notify Payload is defined as follows:
+
+ 1 2 3
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! Next Payload !C! RESERVED ! Payload Length !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! Protocol ID ! SPI Size ! Notify Message Type !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! !
+ ~ Security Parameter Index (SPI) ~
+ ! !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! !
+ ~ Notification Data ~
+ ! !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+ Figure 16: Notify Payload Format
+
+ o Protocol ID (1 octet) - If this notification concerns an existing
+ SA, this field indicates the type of that SA. For IKE_SA
+ notifications, this field MUST be one (1). For notifications
+ concerning IPsec SAs this field MUST contain either (2) to
+ indicate AH or (3) to indicate ESP. For notifications that do not
+ relate to an existing SA, this field MUST be sent as zero and MUST
+ be ignored on receipt. All other values for this field are
+ reserved to IANA for future assignment.
+
+ o SPI Size (1 octet) - Length in octets of the SPI as defined by the
+ IPsec protocol ID or zero if no SPI is applicable. For a
+ notification concerning the IKE_SA, the SPI Size MUST be zero.
+
+ o Notify Message Type (2 octets) - Specifies the type of
+ notification message.
+
+ o SPI (variable length) - Security Parameter Index.
+
+ o Notification Data (variable length) - Informational or error data
+ transmitted in addition to the Notify Message Type. Values for
+ this field are type specific (see below).
+
+ The payload type for the Notify Payload is forty one (41).
+
+
+
+
+
+
+
+
+Kaufman Standards Track [Page 65]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+3.10.1. Notify Message Types
+
+ Notification information can be error messages specifying why an SA
+ could not be established. It can also be status data that a process
+ managing an SA database wishes to communicate with a peer process.
+ The table below lists the Notification messages and their
+ corresponding values. The number of different error statuses was
+ greatly reduced from IKEv1 both for simplification and to avoid
+ giving configuration information to probers.
+
+ Types in the range 0 - 16383 are intended for reporting errors. An
+ implementation receiving a Notify payload with one of these types
+ that it does not recognize in a response MUST assume that the
+ corresponding request has failed entirely. Unrecognized error types
+ in a request and status types in a request or response MUST be
+ ignored except that they SHOULD be logged.
+
+ Notify payloads with status types MAY be added to any message and
+ MUST be ignored if not recognized. They are intended to indicate
+ capabilities, and as part of SA negotiation are used to negotiate
+ non-cryptographic parameters.
+
+ NOTIFY MESSAGES - ERROR TYPES Value
+ ----------------------------- -----
+ RESERVED 0
+
+ UNSUPPORTED_CRITICAL_PAYLOAD 1
+
+ Sent if the payload has the "critical" bit set and the
+ payload type is not recognized. Notification Data contains
+ the one-octet payload type.
+
+ INVALID_IKE_SPI 4
+
+ Indicates an IKE message was received with an unrecognized
+ destination SPI. This usually indicates that the recipient
+ has rebooted and forgotten the existence of an IKE_SA.
+
+ INVALID_MAJOR_VERSION 5
+
+ Indicates the recipient cannot handle the version of IKE
+ specified in the header. The closest version number that
+ the recipient can support will be in the reply header.
+
+ INVALID_SYNTAX 7
+
+ Indicates the IKE message that was received was invalid
+ because some type, length, or value was out of range or
+
+
+
+Kaufman Standards Track [Page 66]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ because the request was rejected for policy reasons. To
+ avoid a denial of service attack using forged messages, this
+ status may only be returned for and in an encrypted packet
+ if the message ID and cryptographic checksum were valid. To
+ avoid leaking information to someone probing a node, this
+ status MUST be sent in response to any error not covered by
+ one of the other status types. To aid debugging, more
+ detailed error information SHOULD be written to a console or
+ log.
+
+ INVALID_MESSAGE_ID 9
+
+ Sent when an IKE message ID outside the supported window is
+ received. This Notify MUST NOT be sent in a response; the
+ invalid request MUST NOT be acknowledged. Instead, inform
+ the other side by initiating an INFORMATIONAL exchange with
+ Notification data containing the four octet invalid message
+ ID. Sending this notification is optional, and
+ notifications of this type MUST be rate limited.
+
+ INVALID_SPI 11
+
+ MAY be sent in an IKE INFORMATIONAL exchange when a node
+ receives an ESP or AH packet with an invalid SPI. The
+ Notification Data contains the SPI of the invalid packet.
+ This usually indicates a node has rebooted and forgotten an
+ SA. If this Informational Message is sent outside the
+ context of an IKE_SA, it should be used by the recipient
+ only as a "hint" that something might be wrong (because it
+ could easily be forged).
+
+ NO_PROPOSAL_CHOSEN 14
+
+ None of the proposed crypto suites was acceptable.
+
+ INVALID_KE_PAYLOAD 17
+
+ The D-H Group # field in the KE payload is not the group #
+ selected by the responder for this exchange. There are two
+ octets of data associated with this notification: the
+ accepted D-H Group # in big endian order.
+
+ AUTHENTICATION_FAILED 24
+
+ Sent in the response to an IKE_AUTH message when for some
+ reason the authentication failed. There is no associated
+ data.
+
+
+
+
+Kaufman Standards Track [Page 67]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ SINGLE_PAIR_REQUIRED 34
+
+ This error indicates that a CREATE_CHILD_SA request is
+ unacceptable because its sender is only willing to accept
+ traffic selectors specifying a single pair of addresses. The
+ requestor is expected to respond by requesting an SA for only
+ the specific traffic it is trying to forward.
+
+ NO_ADDITIONAL_SAS 35
+
+ This error indicates that a CREATE_CHILD_SA request is
+ unacceptable because the responder is unwilling to accept any
+ more CHILD_SAs on this IKE_SA. Some minimal implementations may
+ only accept a single CHILD_SA setup in the context of an initial
+ IKE exchange and reject any subsequent attempts to add more.
+
+ INTERNAL_ADDRESS_FAILURE 36
+
+ Indicates an error assigning an internal address (i.e.,
+ INTERNAL_IP4_ADDRESS or INTERNAL_IP6_ADDRESS) during the
+ processing of a Configuration Payload by a responder. If this
+ error is generated within an IKE_AUTH exchange, no CHILD_SA will
+ be created.
+
+ FAILED_CP_REQUIRED 37
+
+ Sent by responder in the case where CP(CFG_REQUEST) was expected
+ but not received, and so is a conflict with locally configured
+ policy. There is no associated data.
+
+ TS_UNACCEPTABLE 38
+
+ Indicates that none of the addresses/protocols/ports in the
+ supplied traffic selectors is acceptable.
+
+ INVALID_SELECTORS 39
+
+ MAY be sent in an IKE INFORMATIONAL exchange when a node
+ receives an ESP or AH packet whose selectors do not match
+ those of the SA on which it was delivered (and that caused
+ the packet to be dropped). The Notification Data contains
+ the start of the offending packet (as in ICMP messages) and
+ the SPI field of the notification is set to match the SPI of
+ the IPsec SA.
+
+ RESERVED TO IANA - Error types 40 - 8191
+
+ Private Use - Errors 8192 - 16383
+
+
+
+Kaufman Standards Track [Page 68]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ NOTIFY MESSAGES - STATUS TYPES Value
+ ------------------------------ -----
+
+ INITIAL_CONTACT 16384
+
+ This notification asserts that this IKE_SA is the only
+ IKE_SA currently active between the authenticated
+ identities. It MAY be sent when an IKE_SA is established
+ after a crash, and the recipient MAY use this information to
+ delete any other IKE_SAs it has to the same authenticated
+ identity without waiting for a timeout. This notification
+ MUST NOT be sent by an entity that may be replicated (e.g.,
+ a roaming user's credentials where the user is allowed to
+ connect to the corporate firewall from two remote systems at
+ the same time).
+
+ SET_WINDOW_SIZE 16385
+
+ This notification asserts that the sending endpoint is
+ capable of keeping state for multiple outstanding exchanges,
+ permitting the recipient to send multiple requests before
+ getting a response to the first. The data associated with a
+ SET_WINDOW_SIZE notification MUST be 4 octets long and
+ contain the big endian representation of the number of
+ messages the sender promises to keep. Window size is always
+ one until the initial exchanges complete.
+
+ ADDITIONAL_TS_POSSIBLE 16386
+
+ This notification asserts that the sending endpoint narrowed
+ the proposed traffic selectors but that other traffic
+ selectors would also have been acceptable, though only in a
+ separate SA (see section 2.9). There is no data associated
+ with this Notify type. It may be sent only as an additional
+ payload in a message including accepted TSs.
+
+ IPCOMP_SUPPORTED 16387
+
+ This notification may be included only in a message
+ containing an SA payload negotiating a CHILD_SA and
+ indicates a willingness by its sender to use IPComp on this
+ SA. The data associated with this notification includes a
+ two-octet IPComp CPI followed by a one-octet transform ID
+ optionally followed by attributes whose length and format
+ are defined by that transform ID. A message proposing an SA
+ may contain multiple IPCOMP_SUPPORTED notifications to
+ indicate multiple supported algorithms. A message accepting
+ an SA may contain at most one.
+
+
+
+Kaufman Standards Track [Page 69]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ The transform IDs currently defined are:
+
+ NAME NUMBER DEFINED IN
+ ----------- ------ -----------
+ RESERVED 0
+ IPCOMP_OUI 1
+ IPCOMP_DEFLATE 2 RFC 2394
+ IPCOMP_LZS 3 RFC 2395
+ IPCOMP_LZJH 4 RFC 3051
+
+ values 5-240 are reserved to IANA. Values 241-255 are
+ for private use among mutually consenting parties.
+
+ NAT_DETECTION_SOURCE_IP 16388
+
+ This notification is used by its recipient to determine
+ whether the source is behind a NAT box. The data associated
+ with this notification is a SHA-1 digest of the SPIs (in the
+ order they appear in the header), IP address, and port on
+ which this packet was sent. There MAY be multiple Notify
+ payloads of this type in a message if the sender does not
+ know which of several network attachments will be used to
+ send the packet. The recipient of this notification MAY
+ compare the supplied value to a SHA-1 hash of the SPIs,
+ source IP address, and port, and if they don't match it
+ SHOULD enable NAT traversal (see section 2.23).
+ Alternately, it MAY reject the connection attempt if NAT
+ traversal is not supported.
+
+ NAT_DETECTION_DESTINATION_IP 16389
+
+ This notification is used by its recipient to determine
+ whether it is behind a NAT box. The data associated with
+ this notification is a SHA-1 digest of the SPIs (in the
+ order they appear in the header), IP address, and port to
+ which this packet was sent. The recipient of this
+ notification MAY compare the supplied value to a hash of the
+ SPIs, destination IP address, and port, and if they don't
+ match it SHOULD invoke NAT traversal (see section 2.23). If
+ they don't match, it means that this end is behind a NAT and
+ this end SHOULD start sending keepalive packets as defined
+ in [Hutt05]. Alternately, it MAY reject the connection
+ attempt if NAT traversal is not supported.
+
+
+
+
+
+
+
+
+Kaufman Standards Track [Page 70]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ COOKIE 16390
+
+ This notification MAY be included in an IKE_SA_INIT
+ response. It indicates that the request should be retried
+ with a copy of this notification as the first payload. This
+ notification MUST be included in an IKE_SA_INIT request
+ retry if a COOKIE notification was included in the initial
+ response. The data associated with this notification MUST
+ be between 1 and 64 octets in length (inclusive).
+
+ USE_TRANSPORT_MODE 16391
+
+ This notification MAY be included in a request message that
+ also includes an SA payload requesting a CHILD_SA. It
+ requests that the CHILD_SA use transport mode rather than
+ tunnel mode for the SA created. If the request is accepted,
+ the response MUST also include a notification of type
+ USE_TRANSPORT_MODE. If the responder declines the request,
+ the CHILD_SA will be established in tunnel mode. If this is
+ unacceptable to the initiator, the initiator MUST delete the
+ SA. Note: Except when using this option to negotiate
+ transport mode, all CHILD_SAs will use tunnel mode.
+
+ Note: The ECN decapsulation modifications specified in
+ [RFC4301] MUST be performed for every tunnel mode SA created
+ by IKEv2.
+
+ HTTP_CERT_LOOKUP_SUPPORTED 16392
+
+ This notification MAY be included in any message that can
+ include a CERTREQ payload and indicates that the sender is
+ capable of looking up certificates based on an HTTP-based
+ URL (and hence presumably would prefer to receive
+ certificate specifications in that format).
+
+ REKEY_SA 16393
+
+ This notification MUST be included in a CREATE_CHILD_SA
+ exchange if the purpose of the exchange is to replace an
+ existing ESP or AH SA. The SPI field identifies the SA
+ being rekeyed. There is no data.
+
+ ESP_TFC_PADDING_NOT_SUPPORTED 16394
+
+ This notification asserts that the sending endpoint will NOT
+ accept packets that contain Flow Confidentiality (TFC)
+ padding.
+
+
+
+
+Kaufman Standards Track [Page 71]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ NON_FIRST_FRAGMENTS_ALSO 16395
+
+ Used for fragmentation control. See [RFC4301] for
+ explanation.
+
+ RESERVED TO IANA - STATUS TYPES 16396 - 40959
+
+ Private Use - STATUS TYPES 40960 - 65535
+
+3.11. Delete Payload
+
+ The Delete Payload, denoted D in this memo, contains a protocol-
+ specific security association identifier that the sender has removed
+ from its security association database and is, therefore, no longer
+ valid. Figure 17 shows the format of the Delete Payload. It is
+ possible to send multiple SPIs in a Delete payload; however, each SPI
+ MUST be for the same protocol. Mixing of protocol identifiers MUST
+ NOT be performed in a Delete payload. It is permitted, however, to
+ include multiple Delete payloads in a single INFORMATIONAL exchange
+ where each Delete payload lists SPIs for a different protocol.
+
+ Deletion of the IKE_SA is indicated by a protocol ID of 1 (IKE) but
+ no SPIs. Deletion of a CHILD_SA, such as ESP or AH, will contain the
+ IPsec protocol ID of that protocol (2 for AH, 3 for ESP), and the SPI
+ is the SPI the sending endpoint would expect in inbound ESP or AH
+ packets.
+
+ The Delete Payload is defined as follows:
+
+ 1 2 3
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! Next Payload !C! RESERVED ! Payload Length !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! Protocol ID ! SPI Size ! # of SPIs !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! !
+ ~ Security Parameter Index(es) (SPI) ~
+ ! !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+ Figure 17: Delete Payload Format
+
+ o Protocol ID (1 octet) - Must be 1 for an IKE_SA, 2 for AH, or 3
+ for ESP.
+
+
+
+
+
+
+Kaufman Standards Track [Page 72]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ o SPI Size (1 octet) - Length in octets of the SPI as defined by the
+ protocol ID. It MUST be zero for IKE (SPI is in message header)
+ or four for AH and ESP.
+
+ o # of SPIs (2 octets) - The number of SPIs contained in the Delete
+ payload. The size of each SPI is defined by the SPI Size field.
+
+ o Security Parameter Index(es) (variable length) - Identifies the
+ specific security association(s) to delete. The length of this
+ field is determined by the SPI Size and # of SPIs fields.
+
+ The payload type for the Delete Payload is forty two (42).
+
+3.12. Vendor ID Payload
+
+ The Vendor ID Payload, denoted V in this memo, contains a vendor
+ defined constant. The constant is used by vendors to identify and
+ recognize remote instances of their implementations. This mechanism
+ allows a vendor to experiment with new features while maintaining
+ backward compatibility.
+
+ A Vendor ID payload MAY announce that the sender is capable to
+ accepting certain extensions to the protocol, or it MAY simply
+ identify the implementation as an aid in debugging. A Vendor ID
+ payload MUST NOT change the interpretation of any information defined
+ in this specification (i.e., the critical bit MUST be set to 0).
+ Multiple Vendor ID payloads MAY be sent. An implementation is NOT
+ REQUIRED to send any Vendor ID payload at all.
+
+ A Vendor ID payload may be sent as part of any message. Reception of
+ a familiar Vendor ID payload allows an implementation to make use of
+ Private USE numbers described throughout this memo -- private
+ payloads, private exchanges, private notifications, etc. Unfamiliar
+ Vendor IDs MUST be ignored.
+
+ Writers of Internet-Drafts who wish to extend this protocol MUST
+ define a Vendor ID payload to announce the ability to implement the
+ extension in the Internet-Draft. It is expected that Internet-Drafts
+ that gain acceptance and are standardized will be given "magic
+ numbers" out of the Future Use range by IANA, and the requirement to
+ use a Vendor ID will go away.
+
+
+
+
+
+
+
+
+
+
+Kaufman Standards Track [Page 73]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ The Vendor ID Payload fields are defined as follows:
+
+ 1 2 3
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! Next Payload !C! RESERVED ! Payload Length !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! !
+ ~ Vendor ID (VID) ~
+ ! !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+ Figure 18: Vendor ID Payload Format
+
+ o Vendor ID (variable length) - It is the responsibility of the
+ person choosing the Vendor ID to assure its uniqueness in spite of
+ the absence of any central registry for IDs. Good practice is to
+ include a company name, a person name, or some such. If you want
+ to show off, you might include the latitude and longitude and time
+ where you were when you chose the ID and some random input. A
+ message digest of a long unique string is preferable to the long
+ unique string itself.
+
+ The payload type for the Vendor ID Payload is forty three (43).
+
+3.13. Traffic Selector Payload
+
+ The Traffic Selector Payload, denoted TS in this memo, allows peers
+ to identify packet flows for processing by IPsec security services.
+ The Traffic Selector Payload consists of the IKE generic payload
+ header followed by individual traffic selectors as follows:
+
+ 1 2 3
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! Next Payload !C! RESERVED ! Payload Length !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! Number of TSs ! RESERVED !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! !
+ ~ <Traffic Selectors> ~
+ ! !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+ Figure 19: Traffic Selectors Payload Format
+
+ o Number of TSs (1 octet) - Number of traffic selectors being
+ provided.
+
+
+
+Kaufman Standards Track [Page 74]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ o RESERVED - This field MUST be sent as zero and MUST be ignored on
+ receipt.
+
+ o Traffic Selectors (variable length) - One or more individual
+ traffic selectors.
+
+ The length of the Traffic Selector payload includes the TS header and
+ all the traffic selectors.
+
+ The payload type for the Traffic Selector payload is forty four (44)
+ for addresses at the initiator's end of the SA and forty five (45)
+ for addresses at the responder's end.
+
+3.13.1. Traffic Selector
+
+ 1 2 3
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! TS Type !IP Protocol ID*| Selector Length |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ | Start Port* | End Port* |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! !
+ ~ Starting Address* ~
+ ! !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! !
+ ~ Ending Address* ~
+ ! !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+ Figure 20: Traffic Selector
+
+ * Note: All fields other than TS Type and Selector Length depend on
+ the TS Type. The fields shown are for TS Types 7 and 8, the only two
+ values currently defined.
+
+ o TS Type (one octet) - Specifies the type of traffic selector.
+
+ o IP protocol ID (1 octet) - Value specifying an associated IP
+ protocol ID (e.g., UDP/TCP/ICMP). A value of zero means that the
+ protocol ID is not relevant to this traffic selector -- the SA can
+ carry all protocols.
+
+ o Selector Length - Specifies the length of this Traffic Selector
+ Substructure including the header.
+
+
+
+
+
+Kaufman Standards Track [Page 75]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ o Start Port (2 octets) - Value specifying the smallest port number
+ allowed by this Traffic Selector. For protocols for which port is
+ undefined, or if all ports are allowed, this field MUST be zero.
+ For the ICMP protocol, the two one-octet fields Type and Code are
+ treated as a single 16-bit integer (with Type in the most
+ significant eight bits and Code in the least significant eight
+ bits) port number for the purposes of filtering based on this
+ field.
+
+ o End Port (2 octets) - Value specifying the largest port number
+ allowed by this Traffic Selector. For protocols for which port is
+ undefined, or if all ports are allowed, this field MUST be 65535.
+ For the ICMP protocol, the two one-octet fields Type and Code are
+ treated as a single 16-bit integer (with Type in the most
+ significant eight bits and Code in the least significant eight
+ bits) port number for the purposed of filtering based on this
+ field.
+
+ o Starting Address - The smallest address included in this Traffic
+ Selector (length determined by TS type).
+
+ o Ending Address - The largest address included in this Traffic
+ Selector (length determined by TS type).
+
+ Systems that are complying with [RFC4301] that wish to indicate "ANY"
+ ports MUST set the start port to 0 and the end port to 65535; note
+ that according to [RFC4301], "ANY" includes "OPAQUE". Systems
+ working with [RFC4301] that wish to indicate "OPAQUE" ports, but not
+ "ANY" ports, MUST set the start port to 65535 and the end port to 0.
+
+ The following table lists the assigned values for the Traffic
+ Selector Type field and the corresponding Address Selector Data.
+
+ TS Type Value
+ ------- -----
+ RESERVED 0-6
+
+ TS_IPV4_ADDR_RANGE 7
+
+ A range of IPv4 addresses, represented by two four-octet
+ values. The first value is the beginning IPv4 address
+ (inclusive) and the second value is the ending IPv4 address
+ (inclusive). All addresses falling between the two
+ specified addresses are considered to be within the list.
+
+
+
+
+
+
+
+Kaufman Standards Track [Page 76]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ TS_IPV6_ADDR_RANGE 8
+
+ A range of IPv6 addresses, represented by two sixteen-octet
+ values. The first value is the beginning IPv6 address
+ (inclusive) and the second value is the ending IPv6 address
+ (inclusive). All addresses falling between the two
+ specified addresses are considered to be within the list.
+
+ RESERVED TO IANA 9-240
+ PRIVATE USE 241-255
+
+3.14. Encrypted Payload
+
+ The Encrypted Payload, denoted SK{...} or E in this memo, contains
+ other payloads in encrypted form. The Encrypted Payload, if present
+ in a message, MUST be the last payload in the message. Often, it is
+ the only payload in the message.
+
+ The algorithms for encryption and integrity protection are negotiated
+ during IKE_SA setup, and the keys are computed as specified in
+ sections 2.14 and 2.18.
+
+ The encryption and integrity protection algorithms are modeled after
+ the ESP algorithms described in RFCs 2104 [KBC96], 4303 [RFC4303],
+ and 2451 [ESPCBC]. This document completely specifies the
+ cryptographic processing of IKE data, but those documents should be
+ consulted for design rationale. We require a block cipher with a
+ fixed block size and an integrity check algorithm that computes a
+ fixed-length checksum over a variable size message.
+
+ The payload type for an Encrypted payload is forty six (46). The
+ Encrypted Payload consists of the IKE generic payload header followed
+ by individual fields as follows:
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Kaufman Standards Track [Page 77]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ 1 2 3
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! Next Payload !C! RESERVED ! Payload Length !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! Initialization Vector !
+ ! (length is block size for encryption algorithm) !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ~ Encrypted IKE Payloads ~
+ + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! ! Padding (0-255 octets) !
+ +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
+ ! ! Pad Length !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ~ Integrity Checksum Data ~
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+ Figure 21: Encrypted Payload Format
+
+ o Next Payload - The payload type of the first embedded payload.
+ Note that this is an exception in the standard header format,
+ since the Encrypted payload is the last payload in the message and
+ therefore the Next Payload field would normally be zero. But
+ because the content of this payload is embedded payloads and there
+ was no natural place to put the type of the first one, that type
+ is placed here.
+
+ o Payload Length - Includes the lengths of the header, IV, Encrypted
+ IKE Payloads, Padding, Pad Length, and Integrity Checksum Data.
+
+ o Initialization Vector - A randomly chosen value whose length is
+ equal to the block length of the underlying encryption algorithm.
+ Recipients MUST accept any value. Senders SHOULD either pick this
+ value pseudo-randomly and independently for each message or use
+ the final ciphertext block of the previous message sent. Senders
+ MUST NOT use the same value for each message, use a sequence of
+ values with low hamming distance (e.g., a sequence number), or use
+ ciphertext from a received message.
+
+ o IKE Payloads are as specified earlier in this section. This field
+ is encrypted with the negotiated cipher.
+
+ o Padding MAY contain any value chosen by the sender, and MUST have
+ a length that makes the combination of the Payloads, the Padding,
+ and the Pad Length to be a multiple of the encryption block size.
+ This field is encrypted with the negotiated cipher.
+
+
+
+
+
+Kaufman Standards Track [Page 78]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ o Pad Length is the length of the Padding field. The sender SHOULD
+ set the Pad Length to the minimum value that makes the combination
+ of the Payloads, the Padding, and the Pad Length a multiple of the
+ block size, but the recipient MUST accept any length that results
+ in proper alignment. This field is encrypted with the negotiated
+ cipher.
+
+ o Integrity Checksum Data is the cryptographic checksum of the
+ entire message starting with the Fixed IKE Header through the Pad
+ Length. The checksum MUST be computed over the encrypted message.
+ Its length is determined by the integrity algorithm negotiated.
+
+3.15. Configuration Payload
+
+ The Configuration payload, denoted CP in this document, is used to
+ exchange configuration information between IKE peers. The exchange
+ is for an IRAC to request an internal IP address from an IRAS and to
+ exchange other information of the sort that one would acquire with
+ Dynamic Host Configuration Protocol (DHCP) if the IRAC were directly
+ connected to a LAN.
+
+ Configuration payloads are of type CFG_REQUEST/CFG_REPLY or
+ CFG_SET/CFG_ACK (see CFG Type in the payload description below).
+ CFG_REQUEST and CFG_SET payloads may optionally be added to any IKE
+ request. The IKE response MUST include either a corresponding
+ CFG_REPLY or CFG_ACK or a Notify payload with an error type
+ indicating why the request could not be honored. An exception is
+ that a minimal implementation MAY ignore all CFG_REQUEST and CFG_SET
+ payloads, so a response message without a corresponding CFG_REPLY or
+ CFG_ACK MUST be accepted as an indication that the request was not
+ supported.
+
+ "CFG_REQUEST/CFG_REPLY" allows an IKE endpoint to request information
+ from its peer. If an attribute in the CFG_REQUEST Configuration
+ Payload is not zero-length, it is taken as a suggestion for that
+ attribute. The CFG_REPLY Configuration Payload MAY return that
+ value, or a new one. It MAY also add new attributes and not include
+ some requested ones. Requestors MUST ignore returned attributes that
+ they do not recognize.
+
+ Some attributes MAY be multi-valued, in which case multiple attribute
+ values of the same type are sent and/or returned. Generally, all
+ values of an attribute are returned when the attribute is requested.
+ For some attributes (in this version of the specification only
+ internal addresses), multiple requests indicates a request that
+ multiple values be assigned. For these attributes, the number of
+ values returned SHOULD NOT exceed the number requested.
+
+
+
+
+Kaufman Standards Track [Page 79]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ If the data type requested in a CFG_REQUEST is not recognized or not
+ supported, the responder MUST NOT return an error type but rather
+ MUST either send a CFG_REPLY that MAY be empty or a reply not
+ containing a CFG_REPLY payload at all. Error returns are reserved
+ for cases where the request is recognized but cannot be performed as
+ requested or the request is badly formatted.
+
+ "CFG_SET/CFG_ACK" allows an IKE endpoint to push configuration data
+ to its peer. In this case, the CFG_SET Configuration Payload
+ contains attributes the initiator wants its peer to alter. The
+ responder MUST return a Configuration Payload if it accepted any of
+ the configuration data and it MUST contain the attributes that the
+ responder accepted with zero-length data. Those attributes that it
+ did not accept MUST NOT be in the CFG_ACK Configuration Payload. If
+ no attributes were accepted, the responder MUST return either an
+ empty CFG_ACK payload or a response message without a CFG_ACK
+ payload. There are currently no defined uses for the CFG_SET/CFG_ACK
+ exchange, though they may be used in connection with extensions based
+ on Vendor IDs. An minimal implementation of this specification MAY
+ ignore CFG_SET payloads.
+
+ Extensions via the CP payload SHOULD NOT be used for general purpose
+ management. Its main intent is to provide a bootstrap mechanism to
+ exchange information within IPsec from IRAS to IRAC. While it MAY be
+ useful to use such a method to exchange information between some
+ Security Gateways (SGW) or small networks, existing management
+ protocols such as DHCP [DHCP], RADIUS [RADIUS], SNMP, or LDAP [LDAP]
+ should be preferred for enterprise management as well as subsequent
+ information exchanges.
+
+ The Configuration Payload is defined as follows:
+
+ 1 2 3
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! Next Payload !C! RESERVED ! Payload Length !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! CFG Type ! RESERVED !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! !
+ ~ Configuration Attributes ~
+ ! !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+ Figure 22: Configuration Payload Format
+
+ The payload type for the Configuration Payload is forty seven (47).
+
+
+
+
+Kaufman Standards Track [Page 80]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ o CFG Type (1 octet) - The type of exchange represented by the
+ Configuration Attributes.
+
+ CFG Type Value
+ =========== =====
+ RESERVED 0
+ CFG_REQUEST 1
+ CFG_REPLY 2
+ CFG_SET 3
+ CFG_ACK 4
+
+ values 5-127 are reserved to IANA. Values 128-255 are for private
+ use among mutually consenting parties.
+
+ o RESERVED (3 octets) - MUST be sent as zero; MUST be ignored on
+ receipt.
+
+ o Configuration Attributes (variable length) - These are type length
+ values specific to the Configuration Payload and are defined
+ below. There may be zero or more Configuration Attributes in this
+ payload.
+
+3.15.1. Configuration Attributes
+
+ 1 2 3
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ !R| Attribute Type ! Length |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ | |
+ ~ Value ~
+ | |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+ Figure 23: Configuration Attribute Format
+
+ o Reserved (1 bit) - This bit MUST be set to zero and MUST be
+ ignored on receipt.
+
+ o Attribute Type (15 bits) - A unique identifier for each of the
+ Configuration Attribute Types.
+
+ o Length (2 octets) - Length in octets of Value.
+
+ o Value (0 or more octets) - The variable-length value of this
+ Configuration Attribute.
+
+
+
+
+
+Kaufman Standards Track [Page 81]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ The following attribute types have been defined:
+
+ Multi-
+ Attribute Type Value Valued Length
+ ======================= ===== ====== ==================
+ RESERVED 0
+ INTERNAL_IP4_ADDRESS 1 YES* 0 or 4 octets
+ INTERNAL_IP4_NETMASK 2 NO 0 or 4 octets
+ INTERNAL_IP4_DNS 3 YES 0 or 4 octets
+ INTERNAL_IP4_NBNS 4 YES 0 or 4 octets
+ INTERNAL_ADDRESS_EXPIRY 5 NO 0 or 4 octets
+ INTERNAL_IP4_DHCP 6 YES 0 or 4 octets
+ APPLICATION_VERSION 7 NO 0 or more
+ INTERNAL_IP6_ADDRESS 8 YES* 0 or 17 octets
+ RESERVED 9
+ INTERNAL_IP6_DNS 10 YES 0 or 16 octets
+ INTERNAL_IP6_NBNS 11 YES 0 or 16 octets
+ INTERNAL_IP6_DHCP 12 YES 0 or 16 octets
+ INTERNAL_IP4_SUBNET 13 YES 0 or 8 octets
+ SUPPORTED_ATTRIBUTES 14 NO Multiple of 2
+ INTERNAL_IP6_SUBNET 15 YES 17 octets
+
+ * These attributes may be multi-valued on return only if multiple
+ values were requested.
+
+ Types 16-16383 are reserved to IANA. Values 16384-32767 are for
+ private use among mutually consenting parties.
+
+ o INTERNAL_IP4_ADDRESS, INTERNAL_IP6_ADDRESS - An address on the
+ internal network, sometimes called a red node address or
+ private address and MAY be a private address on the Internet.
+ In a request message, the address specified is a requested
+ address (or zero if no specific address is requested). If a
+ specific address is requested, it likely indicates that a
+ previous connection existed with this address and the requestor
+ would like to reuse that address. With IPv6, a requestor MAY
+ supply the low-order address bytes it wants to use. Multiple
+ internal addresses MAY be requested by requesting multiple
+ internal address attributes. The responder MAY only send up to
+ the number of addresses requested. The INTERNAL_IP6_ADDRESS is
+ made up of two fields: the first is a sixteen-octet IPv6
+ address and the second is a one-octet prefix-length as defined
+ in [ADDRIPV6].
+
+ The requested address is valid until the expiry time defined
+ with the INTERNAL_ADDRESS EXPIRY attribute or there are no
+ IKE_SAs between the peers.
+
+
+
+
+Kaufman Standards Track [Page 82]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ o INTERNAL_IP4_NETMASK - The internal network's netmask. Only
+ one netmask is allowed in the request and reply messages (e.g.,
+ 255.255.255.0), and it MUST be used only with an
+ INTERNAL_IP4_ADDRESS attribute.
+
+ o INTERNAL_IP4_DNS, INTERNAL_IP6_DNS - Specifies an address of a
+ DNS server within the network. Multiple DNS servers MAY be
+ requested. The responder MAY respond with zero or more DNS
+ server attributes.
+
+ o INTERNAL_IP4_NBNS, INTERNAL_IP6_NBNS - Specifies an address of
+ a NetBios Name Server (WINS) within the network. Multiple NBNS
+ servers MAY be requested. The responder MAY respond with zero
+ or more NBNS server attributes.
+
+ o INTERNAL_ADDRESS_EXPIRY - Specifies the number of seconds that
+ the host can use the internal IP address. The host MUST renew
+ the IP address before this expiry time. Only one of these
+ attributes MAY be present in the reply.
+
+ o INTERNAL_IP4_DHCP, INTERNAL_IP6_DHCP - Instructs the host to
+ send any internal DHCP requests to the address contained within
+ the attribute. Multiple DHCP servers MAY be requested. The
+ responder MAY respond with zero or more DHCP server attributes.
+
+ o APPLICATION_VERSION - The version or application information of
+ the IPsec host. This is a string of printable ASCII characters
+ that is NOT null terminated.
+
+ o INTERNAL_IP4_SUBNET - The protected sub-networks that this
+ edge-device protects. This attribute is made up of two fields:
+ the first is an IP address and the second is a netmask.
+ Multiple sub-networks MAY be requested. The responder MAY
+ respond with zero or more sub-network attributes.
+
+ o SUPPORTED_ATTRIBUTES - When used within a Request, this
+ attribute MUST be zero-length and specifies a query to the
+ responder to reply back with all of the attributes that it
+ supports. The response contains an attribute that contains a
+ set of attribute identifiers each in 2 octets. The length
+ divided by 2 (octets) would state the number of supported
+ attributes contained in the response.
+
+
+
+
+
+
+
+
+
+Kaufman Standards Track [Page 83]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ o INTERNAL_IP6_SUBNET - The protected sub-networks that this
+ edge-device protects. This attribute is made up of two fields:
+ the first is a sixteen-octet IPv6 address and the second is a
+ one-octet prefix-length as defined in [ADDRIPV6]. Multiple
+ sub-networks MAY be requested. The responder MAY respond with
+ zero or more sub-network attributes.
+
+ Note that no recommendations are made in this document as to how
+ an implementation actually figures out what information to send in
+ a reply. That is, we do not recommend any specific method of an
+ IRAS determining which DNS server should be returned to a
+ requesting IRAC.
+
+3.16. Extensible Authentication Protocol (EAP) Payload
+
+ The Extensible Authentication Protocol Payload, denoted EAP in this
+ memo, allows IKE_SAs to be authenticated using the protocol defined
+ in RFC 3748 [EAP] and subsequent extensions to that protocol. The
+ full set of acceptable values for the payload is defined elsewhere,
+ but a short summary of RFC 3748 is included here to make this
+ document stand alone in the common cases.
+
+ 1 2 3
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! Next Payload !C! RESERVED ! Payload Length !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! !
+ ~ EAP Message ~
+ ! !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+ Figure 24: EAP Payload Format
+
+ The payload type for an EAP Payload is forty eight (48).
+
+ 1 2 3
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! Code ! Identifier ! Length !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ ! Type ! Type_Data...
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
+
+ Figure 25: EAP Message Format
+
+ o Code (1 octet) indicates whether this message is a Request (1),
+ Response (2), Success (3), or Failure (4).
+
+
+
+Kaufman Standards Track [Page 84]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ o Identifier (1 octet) is used in PPP to distinguish replayed
+ messages from repeated ones. Since in IKE, EAP runs over a
+ reliable protocol, it serves no function here. In a response
+ message, this octet MUST be set to match the identifier in the
+ corresponding request. In other messages, this field MAY be set
+ to any value.
+
+ o Length (2 octets) is the length of the EAP message and MUST be
+ four less than the Payload Length of the encapsulating payload.
+
+ o Type (1 octet) is present only if the Code field is Request (1) or
+ Response (2). For other codes, the EAP message length MUST be
+ four octets and the Type and Type_Data fields MUST NOT be present.
+ In a Request (1) message, Type indicates the data being requested.
+ In a Response (2) message, Type MUST either be Nak or match the
+ type of the data requested. The following types are defined in
+ RFC 3748:
+
+ 1 Identity
+ 2 Notification
+ 3 Nak (Response Only)
+ 4 MD5-Challenge
+ 5 One-Time Password (OTP)
+ 6 Generic Token Card
+
+ o Type_Data (Variable Length) varies with the Type of Request and
+ the associated Response. For the documentation of the EAP
+ methods, see [EAP].
+
+ Note that since IKE passes an indication of initiator identity in
+ message 3 of the protocol, the responder SHOULD NOT send EAP Identity
+ requests. The initiator SHOULD, however, respond to such requests if
+ it receives them.
+
+4. Conformance Requirements
+
+ In order to assure that all implementations of IKEv2 can
+ interoperate, there are "MUST support" requirements in addition to
+ those listed elsewhere. Of course, IKEv2 is a security protocol, and
+ one of its major functions is to allow only authorized parties to
+ successfully complete establishment of SAs. So a particular
+ implementation may be configured with any of a number of restrictions
+ concerning algorithms and trusted authorities that will prevent
+ universal interoperability.
+
+
+
+
+
+
+
+Kaufman Standards Track [Page 85]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ IKEv2 is designed to permit minimal implementations that can
+ interoperate with all compliant implementations. There are a series
+ of optional features that can easily be ignored by a particular
+ implementation if it does not support that feature. Those features
+ include:
+
+ Ability to negotiate SAs through a NAT and tunnel the resulting
+ ESP SA over UDP.
+
+ Ability to request (and respond to a request for) a temporary IP
+ address on the remote end of a tunnel.
+
+ Ability to support various types of legacy authentication.
+
+ Ability to support window sizes greater than one.
+
+ Ability to establish multiple ESP and/or AH SAs within a single
+ IKE_SA.
+
+ Ability to rekey SAs.
+
+ To assure interoperability, all implementations MUST be capable of
+ parsing all payload types (if only to skip over them) and to ignore
+ payload types that it does not support unless the critical bit is set
+ in the payload header. If the critical bit is set in an unsupported
+ payload header, all implementations MUST reject the messages
+ containing those payloads.
+
+ Every implementation MUST be capable of doing four-message
+ IKE_SA_INIT and IKE_AUTH exchanges establishing two SAs (one for IKE,
+ one for ESP and/or AH). Implementations MAY be initiate-only or
+ respond-only if appropriate for their platform. Every implementation
+ MUST be capable of responding to an INFORMATIONAL exchange, but a
+ minimal implementation MAY respond to any INFORMATIONAL message with
+ an empty INFORMATIONAL reply (note that within the context of an
+ IKE_SA, an "empty" message consists of an IKE header followed by an
+ Encrypted payload with no payloads contained in it). A minimal
+ implementation MAY support the CREATE_CHILD_SA exchange only in so
+ far as to recognize requests and reject them with a Notify payload of
+ type NO_ADDITIONAL_SAS. A minimal implementation need not be able to
+ initiate CREATE_CHILD_SA or INFORMATIONAL exchanges. When an SA
+ expires (based on locally configured values of either lifetime or
+ octets passed), and implementation MAY either try to renew it with a
+ CREATE_CHILD_SA exchange or it MAY delete (close) the old SA and
+ create a new one. If the responder rejects the CREATE_CHILD_SA
+ request with a NO_ADDITIONAL_SAS notification, the implementation
+ MUST be capable of instead closing the old SA and creating a new one.
+
+
+
+
+Kaufman Standards Track [Page 86]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ Implementations are not required to support requesting temporary IP
+ addresses or responding to such requests. If an implementation does
+ support issuing such requests, it MUST include a CP payload in
+ message 3 containing at least a field of type INTERNAL_IP4_ADDRESS or
+ INTERNAL_IP6_ADDRESS. All other fields are optional. If an
+ implementation supports responding to such requests, it MUST parse
+ the CP payload of type CFG_REQUEST in message 3 and recognize a field
+ of type INTERNAL_IP4_ADDRESS or INTERNAL_IP6_ADDRESS. If it supports
+ leasing an address of the appropriate type, it MUST return a CP
+ payload of type CFG_REPLY containing an address of the requested
+ type. The responder SHOULD include all of the other related
+ attributes if it has them.
+
+ A minimal IPv4 responder implementation will ignore the contents of
+ the CP payload except to determine that it includes an
+ INTERNAL_IP4_ADDRESS attribute and will respond with the address and
+ other related attributes regardless of whether the initiator
+ requested them.
+
+ A minimal IPv4 initiator will generate a CP payload containing only
+ an INTERNAL_IP4_ADDRESS attribute and will parse the response
+ ignoring attributes it does not know how to use. The only attribute
+ it MUST be able to process is INTERNAL_ADDRESS_EXPIRY, which it must
+ use to bound the lifetime of the SA unless it successfully renews the
+ lease before it expires. Minimal initiators need not be able to
+ request lease renewals and minimal responders need not respond to
+ them.
+
+ For an implementation to be called conforming to this specification,
+ it MUST be possible to configure it to accept the following:
+
+ PKIX Certificates containing and signed by RSA keys of size 1024 or
+ 2048 bits, where the ID passed is any of ID_KEY_ID, ID_FQDN,
+ ID_RFC822_ADDR, or ID_DER_ASN1_DN.
+
+ Shared key authentication where the ID passes is any of ID_KEY_ID,
+ ID_FQDN, or ID_RFC822_ADDR.
+
+ Authentication where the responder is authenticated using PKIX
+ Certificates and the initiator is authenticated using shared key
+ authentication.
+
+
+
+
+
+
+
+
+
+
+Kaufman Standards Track [Page 87]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+5. Security Considerations
+
+ While this protocol is designed to minimize disclosure of
+ configuration information to unauthenticated peers, some such
+ disclosure is unavoidable. One peer or the other must identify
+ itself first and prove its identity first. To avoid probing, the
+ initiator of an exchange is required to identify itself first, and
+ usually is required to authenticate itself first. The initiator can,
+ however, learn that the responder supports IKE and what cryptographic
+ protocols it supports. The responder (or someone impersonating the
+ responder) can probe the initiator not only for its identity, but
+ using CERTREQ payloads may be able to determine what certificates the
+ initiator is willing to use.
+
+ Use of EAP authentication changes the probing possibilities somewhat.
+ When EAP authentication is used, the responder proves its identity
+ before the initiator does, so an initiator that knew the name of a
+ valid initiator could probe the responder for both its name and
+ certificates.
+
+ Repeated rekeying using CREATE_CHILD_SA without additional Diffie-
+ Hellman exchanges leaves all SAs vulnerable to cryptanalysis of a
+ single key or overrun of either endpoint. Implementers should take
+ note of this fact and set a limit on CREATE_CHILD_SA exchanges
+ between exponentiations. This memo does not prescribe such a limit.
+
+ The strength of a key derived from a Diffie-Hellman exchange using
+ any of the groups defined here depends on the inherent strength of
+ the group, the size of the exponent used, and the entropy provided by
+ the random number generator used. Due to these inputs, it is
+ difficult to determine the strength of a key for any of the defined
+ groups. Diffie-Hellman group number two, when used with a strong
+ random number generator and an exponent no less than 200 bits, is
+ common for use with 3DES. Group five provides greater security than
+ group two. Group one is for historic purposes only and does not
+ provide sufficient strength except for use with DES, which is also
+ for historic use only. Implementations should make note of these
+ estimates when establishing policy and negotiating security
+ parameters.
+
+ Note that these limitations are on the Diffie-Hellman groups
+ themselves. There is nothing in IKE that prohibits using stronger
+ groups nor is there anything that will dilute the strength obtained
+ from stronger groups (limited by the strength of the other algorithms
+ negotiated including the prf function). In fact, the extensible
+ framework of IKE encourages the definition of more groups; use of
+ elliptical curve groups may greatly increase strength using much
+ smaller numbers.
+
+
+
+Kaufman Standards Track [Page 88]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ It is assumed that all Diffie-Hellman exponents are erased from
+ memory after use. In particular, these exponents MUST NOT be derived
+ from long-lived secrets like the seed to a pseudo-random generator
+ that is not erased after use.
+
+ The strength of all keys is limited by the size of the output of the
+ negotiated prf function. For this reason, a prf function whose
+ output is less than 128 bits (e.g., 3DES-CBC) MUST NOT be used with
+ this protocol.
+
+ The security of this protocol is critically dependent on the
+ randomness of the randomly chosen parameters. These should be
+ generated by a strong random or properly seeded pseudo-random source
+ (see [RFC4086]). Implementers should take care to ensure that use of
+ random numbers for both keys and nonces is engineered in a fashion
+ that does not undermine the security of the keys.
+
+ For information on the rationale of many of the cryptographic design
+ choices in this protocol, see [SIGMA] and [SKEME]. Though the
+ security of negotiated CHILD_SAs does not depend on the strength of
+ the encryption and integrity protection negotiated in the IKE_SA,
+ implementations MUST NOT negotiate NONE as the IKE integrity
+ protection algorithm or ENCR_NULL as the IKE encryption algorithm.
+
+ When using pre-shared keys, a critical consideration is how to assure
+ the randomness of these secrets. The strongest practice is to ensure
+ that any pre-shared key contain as much randomness as the strongest
+ key being negotiated. Deriving a shared secret from a password,
+ name, or other low-entropy source is not secure. These sources are
+ subject to dictionary and social engineering attacks, among others.
+
+ The NAT_DETECTION_*_IP notifications contain a hash of the addresses
+ and ports in an attempt to hide internal IP addresses behind a NAT.
+ Since the IPv4 address space is only 32 bits, and it is usually very
+ sparse, it would be possible for an attacker to find out the internal
+ address used behind the NAT box by trying all possible IP addresses
+ and trying to find the matching hash. The port numbers are normally
+ fixed to 500, and the SPIs can be extracted from the packet. This
+ reduces the number of hash calculations to 2^32. With an educated
+ guess of the use of private address space, the number of hash
+ calculations is much smaller. Designers should therefore not assume
+ that use of IKE will not leak internal address information.
+
+ When using an EAP authentication method that does not generate a
+ shared key for protecting a subsequent AUTH payload, certain man-in-
+ the-middle and server impersonation attacks are possible [EAPMITM].
+ These vulnerabilities occur when EAP is also used in protocols that
+ are not protected with a secure tunnel. Since EAP is a general-
+
+
+
+Kaufman Standards Track [Page 89]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ purpose authentication protocol, which is often used to provide
+ single-signon facilities, a deployed IPsec solution that relies on an
+ EAP authentication method that does not generate a shared key (also
+ known as a non-key-generating EAP method) can become compromised due
+ to the deployment of an entirely unrelated application that also
+ happens to use the same non-key-generating EAP method, but in an
+ unprotected fashion. Note that this vulnerability is not limited to
+ just EAP, but can occur in other scenarios where an authentication
+ infrastructure is reused. For example, if the EAP mechanism used by
+ IKEv2 utilizes a token authenticator, a man-in-the-middle attacker
+ could impersonate the web server, intercept the token authentication
+ exchange, and use it to initiate an IKEv2 connection. For this
+ reason, use of non-key-generating EAP methods SHOULD be avoided where
+ possible. Where they are used, it is extremely important that all
+ usages of these EAP methods SHOULD utilize a protected tunnel, where
+ the initiator validates the responder's certificate before initiating
+ the EAP exchange. Implementers SHOULD describe the vulnerabilities
+ of using non-key-generating EAP methods in the documentation of their
+ implementations so that the administrators deploying IPsec solutions
+ are aware of these dangers.
+
+ An implementation using EAP MUST also use a public-key-based
+ authentication of the server to the client before the EAP exchange
+ begins, even if the EAP method offers mutual authentication. This
+ avoids having additional IKEv2 protocol variations and protects the
+ EAP data from active attackers.
+
+ If the messages of IKEv2 are long enough that IP-level fragmentation
+ is necessary, it is possible that attackers could prevent the
+ exchange from completing by exhausting the reassembly buffers. The
+ chances of this can be minimized by using the Hash and URL encodings
+ instead of sending certificates (see section 3.6). Additional
+ mitigations are discussed in [KPS03].
+
+6. IANA Considerations
+
+ This document defines a number of new field types and values where
+ future assignments will be managed by the IANA.
+
+ The following registries have been created by the IANA:
+
+ IKEv2 Exchange Types (section 3.1)
+ IKEv2 Payload Types (section 3.2)
+ IKEv2 Transform Types (section 3.3.2)
+ IKEv2 Transform Attribute Types (section 3.3.2)
+ IKEv2 Encryption Transform IDs (section 3.3.2)
+ IKEv2 Pseudo-random Function Transform IDs (section 3.3.2)
+ IKEv2 Integrity Algorithm Transform IDs (section 3.3.2)
+
+
+
+Kaufman Standards Track [Page 90]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ IKEv2 Diffie-Hellman Transform IDs (section 3.3.2)
+ IKEv2 Identification Payload ID Types (section 3.5)
+ IKEv2 Certificate Encodings (section 3.6)
+ IKEv2 Authentication Method (section 3.8)
+ IKEv2 Notify Message Types (section 3.10.1)
+ IKEv2 Notification IPCOMP Transform IDs (section 3.10.1)
+ IKEv2 Security Protocol Identifiers (section 3.3.1)
+ IKEv2 Traffic Selector Types (section 3.13.1)
+ IKEv2 Configuration Payload CFG Types (section 3.15)
+ IKEv2 Configuration Payload Attribute Types (section 3.15.1)
+
+ Note: When creating a new Transform Type, a new registry for it must
+ be created.
+
+ Changes and additions to any of those registries are by expert
+ review.
+
+7. Acknowledgements
+
+ This document is a collaborative effort of the entire IPsec WG. If
+ there were no limit to the number of authors that could appear on an
+ RFC, the following, in alphabetical order, would have been listed:
+ Bill Aiello, Stephane Beaulieu, Steve Bellovin, Sara Bitan, Matt
+ Blaze, Ran Canetti, Darren Dukes, Dan Harkins, Paul Hoffman, John
+ Ioannidis, Charlie Kaufman, Steve Kent, Angelos Keromytis, Tero
+ Kivinen, Hugo Krawczyk, Andrew Krywaniuk, Radia Perlman, Omer
+ Reingold, and Michael Richardson. Many other people contributed to
+ the design. It is an evolution of IKEv1, ISAKMP, and the IPsec DOI,
+ each of which has its own list of authors. Hugh Daniel suggested the
+ feature of having the initiator, in message 3, specify a name for the
+ responder, and gave the feature the cute name "You Tarzan, Me Jane".
+ David Faucher and Valery Smyzlov helped refine the design of the
+ traffic selector negotiation.
+
+8. References
+
+8.1. Normative References
+
+ [ADDGROUP] Kivinen, T. and M. Kojo, "More Modular Exponential (MODP)
+ Diffie-Hellman groups for Internet Key Exchange (IKE)",
+ RFC 3526, May 2003.
+
+ [ADDRIPV6] Hinden, R. and S. Deering, "Internet Protocol Version 6
+ (IPv6) Addressing Architecture", RFC 3513, April 2003.
+
+ [Bra97] Bradner, S., "Key Words for use in RFCs to indicate
+ Requirement Levels", BCP 14, RFC 2119, March 1997.
+
+
+
+
+Kaufman Standards Track [Page 91]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ [EAP] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
+ Levkowetz, "Extensible Authentication Protocol (EAP)", RFC
+ 3748, June 2004.
+
+ [ESPCBC] Pereira, R. and R. Adams, "The ESP CBC-Mode Cipher
+ Algorithms", RFC 2451, November 1998.
+
+ [Hutt05] Huttunen, A., Swander, B., Volpe, V., DiBurro, L., and M.
+ Stenberg, "UDP Encapsulation of IPsec ESP Packets", RFC
+ 3948, January 2005.
+
+ [RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
+ IANA Considerations Section in RFCs", BCP 26, RFC 2434,
+ October 1998.
+
+ [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
+ of Explicit Congestion Notification (ECN) to IP", RFC
+ 3168, September 2001.
+
+ [RFC3280] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet
+ X.509 Public Key Infrastructure Certificate and
+ Certificate Revocation List (CRL) Profile", RFC 3280,
+ April 2002.
+
+ [RFC4301] Kent, S. and K. Seo, "Security Architecture for the
+ Internet Protocol", RFC 4301, December 2005.
+
+8.2. Informative References
+
+ [DES] ANSI X3.106, "American National Standard for Information
+ Systems-Data Link Encryption", American National Standards
+ Institute, 1983.
+
+ [DH] Diffie, W., and Hellman M., "New Directions in
+ Cryptography", IEEE Transactions on Information Theory, V.
+ IT-22, n. 6, June 1977.
+
+ [DHCP] Droms, R., "Dynamic Host Configuration Protocol", RFC
+ 2131, March 1997.
+
+ [DSS] NIST, "Digital Signature Standard", FIPS 186, National
+ Institute of Standards and Technology, U.S. Department of
+ Commerce, May, 1994.
+
+ [EAPMITM] Asokan, N., Nierni, V., and Nyberg, K., "Man-in-the-Middle
+ in Tunneled Authentication Protocols",
+ http://eprint.iacr.org/2002/163, November 2002.
+
+
+
+
+Kaufman Standards Track [Page 92]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ [HC98] Harkins, D. and D. Carrel, "The Internet Key Exchange
+ (IKE)", RFC 2409, November 1998.
+
+ [IDEA] Lai, X., "On the Design and Security of Block Ciphers,"
+ ETH Series in Information Processing, v. 1, Konstanz:
+ Hartung-Gorre Verlag, 1992.
+
+ [IPCOMP] Shacham, A., Monsour, B., Pereira, R., and M. Thomas, "IP
+ Payload Compression Protocol (IPComp)", RFC 3173,
+ September 2001.
+
+ [KPS03] Kaufman, C., Perlman, R., and Sommerfeld, B., "DoS
+ protection for UDP-based protocols", ACM Conference on
+ Computer and Communications Security, October 2003.
+
+ [KBC96] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
+ Hashing for Message Authentication", RFC 2104, February
+ 1997.
+
+ [LDAP] Wahl, M., Howes, T., and S Kille, "Lightweight Directory
+ Access Protocol (v3)", RFC 2251, December 1997.
+
+ [MD5] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
+ April 1992.
+
+ [MSST98] Maughan, D., Schertler, M., Schneider, M., and J. Turner,
+ "Internet Security Association and Key Management Protocol
+ (ISAKMP)", RFC 2408, November 1998.
+
+ [Orm96] Orman, H., "The OAKLEY Key Determination Protocol", RFC
+ 2412, November 1998.
+
+ [PFKEY] McDonald, D., Metz, C., and B. Phan, "PF_KEY Key
+ Management API, Version 2", RFC 2367, July 1998.
+
+ [PKCS1] Jonsson, J. and B. Kaliski, "Public-Key Cryptography
+ Standards (PKCS) #1: RSA Cryptography Specifications
+ Version 2.1", RFC 3447, February 2003.
+
+ [PK01] Perlman, R., and Kaufman, C., "Analysis of the IPsec key
+ exchange Standard", WET-ICE Security Conference, MIT,2001,
+ http://sec.femto.org/wetice-2001/papers/radia-paper.pdf.
+
+ [Pip98] Piper, D., "The Internet IP Security Domain Of
+ Interpretation for ISAKMP", RFC 2407, November 1998.
+
+
+
+
+
+
+Kaufman Standards Track [Page 93]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ [RADIUS] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
+ "Remote Authentication Dial In User Service (RADIUS)", RFC
+ 2865, June 2000.
+
+ [RFC4086] Eastlake, D., 3rd, Schiller, J., and S. Crocker,
+ "Randomness Requirements for Security", BCP 106, RFC 4086,
+ June 2005.
+
+ [RFC1958] Carpenter, B., "Architectural Principles of the Internet",
+ RFC 1958, June 1996.
+
+ [RFC2401] Kent, S. and R. Atkinson, "Security Architecture for the
+ Internet Protocol", RFC 2401, November 1998.
+
+ [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
+ "Definition of the Differentiated Services Field (DS
+ Field) in the IPv4 and IPv6 Headers", RFC 2474, December
+ 1998.
+
+ [RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
+ and W. Weiss, "An Architecture for Differentiated
+ Service", RFC 2475, December 1998.
+
+ [RFC2522] Karn, P. and W. Simpson, "Photuris: Session-Key Management
+ Protocol", RFC 2522, March 1999.
+
+ [RFC2775] Carpenter, B., "Internet Transparency", RFC 2775, February
+ 2000.
+
+ [RFC2983] Black, D., "Differentiated Services and Tunnels", RFC
+ 2983, October 2000.
+
+ [RFC3439] Bush, R. and D. Meyer, "Some Internet Architectural
+ Guidelines and Philosophy", RFC 3439, December 2002.
+
+ [RFC3715] Aboba, B. and W. Dixon, "IPsec-Network Address Translation
+ (NAT) Compatibility Requirements", RFC 3715, March 2004.
+
+ [RFC4302] Kent, S., "IP Authentication Header", RFC 4302, December
+ 2005.
+
+ [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC
+ 4303, December 2005.
+
+ [RSA] Rivest, R., Shamir, A., and Adleman, L., "A Method for
+ Obtaining Digital Signatures and Public-Key
+ Cryptosystems", Communications of the ACM, v. 21, n. 2,
+ February 1978.
+
+
+
+Kaufman Standards Track [Page 94]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ [SHA] NIST, "Secure Hash Standard", FIPS 180-1, National
+ Institute of Standards and Technology, U.S. Department of
+ Commerce, May 1994.
+
+ [SIGMA] Krawczyk, H., "SIGMA: the `SIGn-and-MAc' Approach to
+ Authenticated Diffie-Hellman and its Use in the IKE
+ Protocols", in Advances in Cryptography - CRYPTO 2003
+ Proceedings, LNCS 2729, Springer, 2003. Available at:
+ http://www.informatik.uni-trier.de/~ley/db/conf/
+ crypto/crypto2003.html.
+
+ [SKEME] Krawczyk, H., "SKEME: A Versatile Secure Key Exchange
+ Mechanism for Internet", from IEEE Proceedings of the 1996
+ Symposium on Network and Distributed Systems Security.
+
+ [X.501] ITU-T Recommendation X.501: Information Technology - Open
+ Systems Interconnection - The Directory: Models, 1993.
+
+ [X.509] ITU-T Recommendation X.509 (1997 E): Information
+ Technology - Open Systems Interconnection - The Directory:
+ Authentication Framework, June 1997.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Kaufman Standards Track [Page 95]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+Appendix A: Summary of changes from IKEv1
+
+ The goals of this revision to IKE are:
+
+ 1) To define the entire IKE protocol in a single document, replacing
+ RFCs 2407, 2408, and 2409 and incorporating subsequent changes to
+ support NAT Traversal, Extensible Authentication, and Remote Address
+ acquisition;
+
+ 2) To simplify IKE by replacing the eight different initial exchanges
+ with a single four-message exchange (with changes in authentication
+ mechanisms affecting only a single AUTH payload rather than
+ restructuring the entire exchange) see [PK01];
+
+ 3) To remove the Domain of Interpretation (DOI), Situation (SIT), and
+ Labeled Domain Identifier fields, and the Commit and Authentication
+ only bits;
+
+ 4) To decrease IKE's latency in the common case by making the initial
+ exchange be 2 round trips (4 messages), and allowing the ability to
+ piggyback setup of a CHILD_SA on that exchange;
+
+ 5) To replace the cryptographic syntax for protecting the IKE
+ messages themselves with one based closely on ESP to simplify
+ implementation and security analysis;
+
+ 6) To reduce the number of possible error states by making the
+ protocol reliable (all messages are acknowledged) and sequenced.
+ This allows shortening CREATE_CHILD_SA exchanges from 3 messages to
+ 2;
+
+ 7) To increase robustness by allowing the responder to not do
+ significant processing until it receives a message proving that the
+ initiator can receive messages at its claimed IP address, and not
+ commit any state to an exchange until the initiator can be
+ cryptographically authenticated;
+
+ 8) To fix cryptographic weaknesses such as the problem with
+ symmetries in hashes used for authentication documented by Tero
+ Kivinen;
+
+ 9) To specify Traffic Selectors in their own payloads type rather
+ than overloading ID payloads, and making more flexible the Traffic
+ Selectors that may be specified;
+
+ 10) To specify required behavior under certain error conditions or
+ when data that is not understood is received, to make it easier to
+ make future revisions that do not break backward compatibility;
+
+
+
+Kaufman Standards Track [Page 96]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+ 11) To simplify and clarify how shared state is maintained in the
+ presence of network failures and Denial of Service attacks; and
+
+ 12) To maintain existing syntax and magic numbers to the extent
+ possible to make it likely that implementations of IKEv1 can be
+ enhanced to support IKEv2 with minimum effort.
+
+Appendix B: Diffie-Hellman Groups
+
+ There are two Diffie-Hellman groups defined here for use in IKE.
+ These groups were generated by Richard Schroeppel at the University
+ of Arizona. Properties of these primes are described in [Orm96].
+
+ The strength supplied by group one may not be sufficient for the
+ mandatory-to-implement encryption algorithm and is here for historic
+ reasons.
+
+ Additional Diffie-Hellman groups have been defined in [ADDGROUP].
+
+B.1. Group 1 - 768 Bit MODP
+
+ This group is assigned id 1 (one).
+
+ The prime is: 2^768 - 2 ^704 - 1 + 2^64 * { [2^638 pi] + 149686 } Its
+ hexadecimal value is:
+
+ FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1 29024E08
+ 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD EF9519B3 CD3A431B
+ 302B0A6D F25F1437 4FE1356D 6D51C245 E485B576 625E7EC6 F44C42E9
+ A63A3620 FFFFFFFF FFFFFFFF
+
+ The generator is 2.
+
+B.2. Group 2 - 1024 Bit MODP
+
+ This group is assigned id 2 (two).
+
+ The prime is 2^1024 - 2^960 - 1 + 2^64 * { [2^894 pi] + 129093 }.
+ Its hexadecimal value is:
+
+ FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1 29024E08
+ 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD EF9519B3 CD3A431B
+ 302B0A6D F25F1437 4FE1356D 6D51C245 E485B576 625E7EC6 F44C42E9
+ A637ED6B 0BFF5CB6 F406B7ED EE386BFB 5A899FA5 AE9F2411 7C4B1FE6
+ 49286651 ECE65381 FFFFFFFF FFFFFFFF
+
+ The generator is 2.
+
+
+
+
+Kaufman Standards Track [Page 97]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+Editor's Address
+
+ Charlie Kaufman
+ Microsoft Corporation
+ 1 Microsoft Way
+ Redmond, WA 98052
+
+ Phone: 1-425-707-3335
+ EMail: charliek@microsoft.com
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Kaufman Standards Track [Page 98]
+\f
+RFC 4306 IKEv2 December 2005
+
+
+Full Copyright Statement
+
+ Copyright (C) The Internet Society (2005).
+
+ This document is subject to the rights, licenses and restrictions
+ contained in BCP 78, and except as set forth therein, the authors
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+Kaufman Standards Track [Page 99]
+\f
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