idnits 2.17.00 (12 Aug 2021) /tmp/idnits45205/draft-ietf-ipsec-ikev2-14.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- ** It looks like you're using RFC 3978 boilerplate. You should update this to the boilerplate described in the IETF Trust License Policy document (see https://trustee.ietf.org/license-info), which is required now. -- Found old boilerplate from RFC 3978, Section 5.5 on line 4894. -- Found old boilerplate from RFC 3979, Section 5, paragraph 1 on line 4905. -- Found old boilerplate from RFC 3979, Section 5, paragraph 2 on line 4912. -- Found old boilerplate from RFC 3979, Section 5, paragraph 3 on line 4918. ** Found boilerplate matching RFC 3978, Section 5.4, paragraph 1 (on line 4886), which is fine, but *also* found old RFC 2026, Section 10.4C, paragraph 1 text on line 37. ** The document claims conformance with section 10 of RFC 2026, but uses some RFC 3978/3979 boilerplate. As RFC 3978/3979 replaces section 10 of RFC 2026, you should not claim conformance with it if you have changed to using RFC 3978/3979 boilerplate. ** The document seems to lack an RFC 3978 Section 5.1 IPR Disclosure Acknowledgement. ** This document has an original RFC 3978 Section 5.4 Copyright Line, instead of the newer IETF Trust Copyright according to RFC 4748. ** The document seems to lack an RFC 3978 Section 5.4 Reference to BCP 78 -- however, there's a paragraph with a matching beginning. Boilerplate error? ** This document has an original RFC 3978 Section 5.5 Disclaimer, instead of the newer disclaimer which includes the IETF Trust according to RFC 4748. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- ** The document seems to lack a 1id_guidelines paragraph about Internet-Drafts being working documents. == No 'Intended status' indicated for this document; assuming Proposed Standard == The page length should not exceed 58 lines per page, but there was 105 longer pages, the longest (page 2) being 60 lines == It seems as if not all pages are separated by form feeds - found 0 form feeds but 106 pages Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- == There are 2 instances of lines with non-RFC6890-compliant IPv4 addresses in the document. If these are example addresses, they should be changed. == There are 5 instances of lines with private range IPv4 addresses in the document. If these are generic example addresses, they should be changed to use any of the ranges defined in RFC 6890 (or successor): 192.0.2.x, 198.51.100.x or 203.0.113.x. -- The draft header indicates that this document obsoletes RFC2407, but the abstract doesn't seem to directly say this. It does mention RFC2407 though, so this could be OK. -- The draft header indicates that this document obsoletes RFC2408, but the abstract doesn't seem to directly say this. It does mention RFC2408 though, so this could be OK. -- The draft header indicates that this document obsoletes RFC2409, but the abstract doesn't seem to directly say this. It does mention RFC2409 though, so this could be OK. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the RFC 3978 Section 5.4 Copyright Line does not match the current year == Line 4486 has weird spacing: '... The equati...' == The document seems to lack the recommended RFC 2119 boilerplate, even if it appears to use RFC 2119 keywords. (The document does seem to have the reference to RFC 2119 which the ID-Checklist requires). -- The exact meaning of the all-uppercase expression 'NOT REQUIRED' is not defined in RFC 2119. If it is intended as a requirements expression, it should be rewritten using one of the combinations defined in RFC 2119; otherwise it should not be all-uppercase. == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'MUST not' in this paragraph: 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.). == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'MUST not' in this paragraph: 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. -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. If you have contacted all the original authors and they are all willing to grant the BCP78 rights to the IETF Trust, then this is fine, and you can ignore this comment. If not, you may need to add the pre-RFC5378 disclaimer. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (May 29, 2004) is 6566 days in the past. Is this intentional? -- Found something which looks like a code comment -- if you have code sections in the document, please surround them with '' and '' lines. Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Missing Reference: 'RFC2406' is mentioned on line 148, but not defined ** Obsolete undefined reference: RFC 2406 (Obsoleted by RFC 4303, RFC 4305) == Missing Reference: 'RFC2402' is mentioned on line 148, but not defined ** Obsolete undefined reference: RFC 2402 (Obsoleted by RFC 4302, RFC 4305) == Missing Reference: 'CERTREQ' is mentioned on line 1416, but not defined == Missing Reference: 'N' is mentioned on line 436, but not defined == Missing Reference: 'KEi' is mentioned on line 436, but not defined == Missing Reference: 'KEr' is mentioned on line 457, but not defined == Missing Reference: 'CP' is mentioned on line 534, but not defined -- Looks like a reference, but probably isn't: '0' on line 2756 -- Looks like a reference, but probably isn't: '1' on line 2757 == Missing Reference: '2401bis' is mentioned on line 3270, but not defined == Unused Reference: 'ESPCBC' is defined on line 4184, but no explicit reference was found in the text == Unused Reference: 'RFC3667' is defined on line 4208, but no explicit reference was found in the text == Unused Reference: 'RFC3668' is defined on line 4211, but no explicit reference was found in the text == Unused Reference: 'DES' is defined on line 4216, but no explicit reference was found in the text == Unused Reference: 'DH' is defined on line 4220, but no explicit reference was found in the text == Unused Reference: 'DSS' is defined on line 4227, but no explicit reference was found in the text == Unused Reference: 'HC98' is defined on line 4235, but no explicit reference was found in the text == Unused Reference: 'IDEA' is defined on line 4238, but no explicit reference was found in the text == Unused Reference: 'Ker01' is defined on line 4253, but no explicit reference was found in the text == Unused Reference: 'KBC96' is defined on line 4256, but no explicit reference was found in the text == Unused Reference: 'MD5' is defined on line 4263, but no explicit reference was found in the text == Unused Reference: 'MSST98' is defined on line 4266, but no explicit reference was found in the text == Unused Reference: 'PKCS1' is defined on line 4276, but no explicit reference was found in the text == Unused Reference: 'PK01' is defined on line 4279, but no explicit reference was found in the text == Unused Reference: 'Pip98' is defined on line 4283, but no explicit reference was found in the text == Unused Reference: 'RFC2474' is defined on line 4298, but no explicit reference was found in the text == Unused Reference: 'RFC2475' is defined on line 4303, but no explicit reference was found in the text == Unused Reference: 'RFC3715' is defined on line 4319, but no explicit reference was found in the text == Unused Reference: 'RSA' is defined on line 4323, but no explicit reference was found in the text == Unused Reference: 'SHA' is defined on line 4328, but no explicit reference was found in the text == Unused Reference: 'SKEME' is defined on line 4338, but no explicit reference was found in the text ** Obsolete normative reference: RFC 3513 (ref. 'ADDRIPV6') (Obsoleted by RFC 4291) ** Obsolete normative reference: RFC 2284 (ref. 'EAP') (Obsoleted by RFC 3748) == Outdated reference: draft-ietf-ipsec-udp-encaps has been published as RFC 3948 ** Obsolete normative reference: RFC 2401 (Obsoleted by RFC 4301) ** Obsolete normative reference: RFC 2434 (Obsoleted by RFC 5226) ** Obsolete normative reference: RFC 3280 (Obsoleted by RFC 5280) ** Obsolete normative reference: RFC 3667 (Obsoleted by RFC 3978) ** Obsolete normative reference: RFC 3668 (Obsoleted by RFC 3979) -- Obsolete informational reference (is this intentional?): RFC 2409 (ref. 'HC98') (Obsoleted by RFC 4306) -- Obsolete informational reference (is this intentional?): RFC 2251 (ref. 'LDAP') (Obsoleted by RFC 4510, RFC 4511, RFC 4512, RFC 4513) -- Obsolete informational reference (is this intentional?): RFC 2408 (ref. 'MSST98') (Obsoleted by RFC 4306) -- Obsolete informational reference (is this intentional?): RFC 2407 (ref. 'Pip98') (Obsoleted by RFC 4306) -- Obsolete informational reference (is this intentional?): RFC 2138 (ref. 'RADIUS') (Obsoleted by RFC 2865) -- Obsolete informational reference (is this intentional?): RFC 1750 (Obsoleted by RFC 4086) -- Duplicate reference: RFC2401, mentioned in 'RFC2401', was also mentioned in 'RFC2401bis'. -- Obsolete informational reference (is this intentional?): RFC 2401 (Obsoleted by RFC 4301) Summary: 17 errors (**), 0 flaws (~~), 40 warnings (==), 21 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 INTERNET-DRAFT Charlie Kaufman, Editor 2 draft-ietf-ipsec-ikev2-14.txt 3 Obsoletes: 2407, 2408, 2409 May 29, 2004 4 Expires: November 2004 6 Internet Key Exchange (IKEv2) Protocol 8 Status of this Memo 10 This document is an Internet-Draft and is subject to all provisions 11 of Section 10 of RFC2026. Internet-Drafts are working documents of 12 the Internet Engineering Task Force (IETF), its areas, and its 13 working groups. Note that other groups may also distribute working 14 documents as Internet-Drafts. 16 Internet-Drafts are draft documents valid for a maximum of six months 17 and may be updated, replaced, or obsoleted by other documents at any 18 time. It is inappropriate to use Internet-Drafts as reference 19 material or to cite them other than as "work in progress." 21 The list of current Internet-Drafts can be accessed at 22 http://www.ietf.org/1id-abstracts.html 24 The list of Internet-Draft Shadow Directories can be accessed at 25 http://www.ietf.org/shadow.html 27 This document is a submission by the IPSEC Working Group of the 28 Internet Engineering Task Force (IETF). Comments should be submitted 29 to the ipsec@lists.tislabs.com mailing list. 31 Distribution of this memo is unlimited. 33 This Internet-Draft expires in November 2004. 35 Copyright Notice 37 Copyright (C) The Internet Society (2004). All Rights Reserved. 39 Abstract 41 This document describes version 2 of the Internet Key Exchange (IKE) 42 protocol. IKE is a component of IPsec used for performing mutual 43 authentication and establishing and maintaining security 44 associations. 46 This version of the IKE specification combines the contents of what 47 were previously separate documents, including ISAKMP (RFC 2408), IKE 48 (RFC 2409), the Internet DOI (RFC 2407), NAT Traversal, Legacy 49 authentication, and remote address acquisition. 51 Version 2 of IKE does not interoperate with version 1, but it has 52 enough of the header format in common that both versions can 53 unambiguously run over the same UDP port. 55 Table of Contents 57 1 Introduction...............................................3 58 1.1 Usage Scenarios..........................................5 59 1.2 The Initial Exchange.....................................7 60 1.3 The CREATE_CHILD_SA Exchange.............................9 61 1.4 The INFORMATIONAL Exchange..............................10 62 1.5 Informational Messages outside of an IKE_SA.............12 63 2 IKE Protocol Details and Variations.......................12 64 2.1 Use of Retransmission Timers............................12 65 2.2 Use of Sequence Numbers for Message ID..................13 66 2.3 Window Size for overlapping requests....................13 67 2.4 State Synchronization and Connection Timeouts...........14 68 2.5 Version Numbers and Forward Compatibility...............16 69 2.6 Cookies.................................................17 70 2.7 Cryptographic Algorithm Negotiation.....................19 71 2.8 Rekeying................................................20 72 2.9 Traffic Selector Negotiation............................23 73 2.10 Nonces.................................................25 74 2.11 Address and Port Agility...............................25 75 2.12 Reuse of Diffie-Hellman Exponentials...................25 76 2.13 Generating Keying Material.............................26 77 2.14 Generating Keying Material for the IKE_SA..............27 78 2.15 Authentication of the IKE_SA...........................28 79 2.16 Extended Authentication Protocol Methods...............29 80 2.17 Generating Keying Material for CHILD_SAs...............31 81 2.18 Rekeying IKE_SAs using a CREATE_CHILD_SA exchange......32 82 2.19 Requesting an internal address on a remote network.....32 83 2.20 Requesting a Peer's Version............................34 84 2.21 Error Handling.........................................34 85 2.22 IPComp.................................................35 86 2.23 NAT Traversal..........................................36 87 2.24 ECN (Explicit Congestion Notification).................39 88 3 Header and Payload Formats................................39 89 3.1 The IKE Header..........................................39 90 3.2 Generic Payload Header..................................42 91 3.3 Security Association Payload............................44 92 3.4 Key Exchange Payload....................................54 93 3.5 Identification Payloads.................................55 94 3.6 Certificate Payload.....................................57 95 3.7 Certificate Request Payload.............................59 96 3.8 Authentication Payload..................................61 97 3.9 Nonce Payload...........................................62 98 3.10 Notify Payload.........................................62 99 3.11 Delete Payload.........................................70 100 3.12 Vendor ID Payload......................................71 101 3.13 Traffic Selector Payload...............................72 102 3.14 Encrypted Payload......................................75 103 3.15 Configuration Payload..................................76 104 3.16 Extended Authentication Protocol (EAP) Payload.........81 105 4 Conformance Requirements..................................83 106 5 Security Considerations...................................85 107 6 IANA Considerations.......................................87 108 7 Acknowledgements..........................................88 109 8 References................................................88 110 8.1 Normative References....................................88 111 8.2 Informative References..................................89 112 Appendix A: Summary of Changes from IKEv1...................93 113 Appendix B: Diffie-Hellman Groups...........................95 114 Change History (To be removed from RFC).....................97 115 Editor's Address...........................................105 116 Full Copyright Statement...................................105 117 Intellectual Property Statement............................105 119 Requirements Terminology 121 Keywords "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT" and 122 "MAY" that appear in this document are to be interpreted as described 123 in [Bra97]. 125 The term "Expert Review" is to be interpreted as defined in 126 [RFC2434]. 128 1 Introduction 130 IP Security (IPsec) provides confidentiality, data integrity, access 131 control, and data source authentication to IP datagrams. These 132 services are provided by maintaining shared state between the source 133 and the sink of an IP datagram. This state defines, among other 134 things, the specific services provided to the datagram, which 135 cryptographic algorithms will be used to provide the services, and 136 the keys used as input to the cryptographic algorithms. 138 Establishing this shared state in a manual fashion does not scale 139 well. Therefore a protocol to establish this state dynamically is 140 needed. This memo describes such a protocol-- the Internet Key 141 Exchange (IKE). This is version 2 of IKE. Version 1 of IKE was 142 defined in RFCs 2407, 2408, and 2409. This single document is 143 intended to replace all three of those RFCs. 145 IKE performs mutual authentication between two parties and 146 establishes an IKE security association that includes shared secret 147 information that can be used to efficiently establish SAs for ESP 148 [RFC2406] and/or AH [RFC2402] and a set of cryptographic algorithms 149 to be used by the SAs to protect the traffic that they carry. In 150 this document, the term "suite" or "cryptographic suite" refers to a 151 complete set of algorithms used to protect an SA. An initiator 152 proposes one or more suites by listing supported algorithms that can 153 be combined into suites in a mix and match fashion. IKE can also 154 negotiate use of IPComp [IPCOMP] in connection with an ESP and/or AH 155 SA. We call the IKE SA an "IKE_SA". The SAs for ESP and/or AH that 156 get set up through that IKE_SA we call "CHILD_SA"s. 158 All IKE communications consist of pairs of messages: a request and a 159 response. The pair is called an "exchange". We call the first 160 messages establishing an IKE_SA IKE_SA_INIT and IKE_AUTH exchanges 161 and subsequent IKE exchanges CREATE_CHILD_SA or INFORMATIONAL 162 exchanges. In the common case, there is a single IKE_SA_INIT exchange 163 and a single IKE_AUTH exchange (a total of four messages) to 164 establish the IKE_SA and the first CHILD_SA. In exceptional cases, 165 there may be more than one of each of these exchanges. In all cases, 166 all IKE_SA_INIT exchanges MUST complete before any other exchange 167 type, then all IKE_AUTH exchanges MUST complete, and following that 168 any number of CREATE_CHILD_SA and INFORMATIONAL exchanges may occur 169 in any order. In some scenarios, only a single CHILD_SA is needed 170 between the IPsec endpoints and therefore there would be no 171 additional exchanges. Subsequent exchanges MAY be used to establish 172 additional CHILD_SAs between the same authenticated pair of endpoints 173 and to perform housekeeping functions. 175 IKE message flow always consists of a request followed by a response. 176 It is the responsibility of the requester to ensure reliability. If 177 the response is not received within a timeout interval, the requester 178 needs to retransmit the request (or abandon the connection). 180 The first request/response of an IKE session negotiates security 181 parameters for the IKE_SA, sends nonces, and sends Diffie-Hellman 182 values. We call the initial exchange IKE_SA_INIT (request and 183 response). 185 The second request/response, which we'll call IKE_AUTH transmits 186 identities, proves knowledge of the secrets corresponding to the two 187 identities, and sets up an SA for the first (and often only) AH 188 and/or ESP CHILD_SA. 190 The types of subsequent exchanges are CREATE_CHILD_SA (which creates 191 a CHILD_SA), and INFORMATIONAL (which deletes an SA, reports error 192 conditions, or does other housekeeping). Every request requires a 193 response. An INFORMATIONAL request with no payloads is commonly used 194 as a check for liveness. These subsequent exchanges cannot be used 195 until the initial exchanges have completed. 197 In the description that follows, we assume that no errors occur. 198 Modifications to the flow should errors occur are described in 199 section 2.21. 201 1.1 Usage Scenarios 203 IKE is expected to be used to negotiate ESP and/or AH SAs in a number 204 of different scenarios, each with its own special requirements. 206 1.1.1 Security Gateway to Security Gateway Tunnel 208 +-+-+-+-+-+ +-+-+-+-+-+ 209 ! ! IPsec ! ! 210 Protected !Tunnel ! Tunnel !Tunnel ! Protected 211 Subnet <-->!Endpoint !<---------->!Endpoint !<--> Subnet 212 ! ! ! ! 213 +-+-+-+-+-+ +-+-+-+-+-+ 215 Figure 1: Security Gateway to Security Gateway Tunnel 217 In this scenario, neither endpoint of the IP connection implements 218 IPsec, but network nodes between them protect traffic for part of the 219 way. Protection is transparent to the endpoints, and depends on 220 ordinary routing to send packets through the tunnel endpoints for 221 processing. Each endpoint would announce the set of addresses 222 "behind" it, and packets would be sent in Tunnel Mode where the inner 223 IP header would contain the IP addresses of the actual endpoints. 225 1.1.2 Endpoint to Endpoint Transport 227 +-+-+-+-+-+ +-+-+-+-+-+ 228 ! ! IPsec Transport ! ! 229 !Protected! or Tunnel Mode SA !Protected! 230 !Endpoint !<---------------------------------------->!Endpoint ! 231 ! ! ! ! 232 +-+-+-+-+-+ +-+-+-+-+-+ 234 Figure 2: Endpoint to Endpoint 236 In this scenario, both endpoints of the IP connection implement 237 IPsec, as required of hosts in [RFC2401bis]. Transport mode will 238 commonly be used with no inner IP header. If there is an inner IP 239 header, the inner addresses will be the same as the outer addresses. 240 A single pair of addresses will be negotiated for packets to be 241 protected by this SA. These endpoints MAY implement application layer 242 access controls based on the IPsec authenticated identities of the 243 participants. This scenario enables the end-to-end security that has 244 been a guiding principle for the Internet since [RFC1958], [RFC2775], 245 and a method of limiting the inherent problems with complexity in 246 networks noted by [RFC3439]. While this scenario may not be fully 247 applicable to the IPv4 Internet, it has been deployed successfully in 248 specific scenarios within intranets using IKEv1. It should be more 249 broadly enabled during the transition to IPv6 and with the adoption 250 of IKEv2. 252 It is possible in this scenario that one or both of the protected 253 endpoints will be behind a network address translation (NAT) node, in 254 which case the tunneled packets will have to be UDP encapsulated so 255 that port numbers in the UDP headers can be used to identify 256 individual endpoints "behind" the NAT (see section 2.23). 258 1.1.3 Endpoint to Security Gateway Transport 260 +-+-+-+-+-+ +-+-+-+-+-+ 261 ! ! IPsec ! ! Protected 262 !Protected! Tunnel !Tunnel ! Subnet 263 !Endpoint !<------------------------>!Endpoint !<--- and/or 264 ! ! ! ! Internet 265 +-+-+-+-+-+ +-+-+-+-+-+ 267 Figure 3: Endpoint to Security Gateway Tunnel 269 In this scenario, a protected endpoint (typically a portable roaming 270 computer) connects back to its corporate network through an IPsec 271 protected tunnel. It might use this tunnel only to access information 272 on the corporate network or it might tunnel all of its traffic back 273 through the corporate network in order to take advantage of 274 protection provided by a corporate firewall against Internet based 275 attacks. In either case, the protected endpoint will want an IP 276 address associated with the security gateway so that packets returned 277 to it will go to the security gateway and be tunneled back. This IP 278 address may be static or may be dynamically allocated by the security 279 gateway. In support of the latter case, IKEv2 includes a mechanism 280 for the initiator to request an IP address owned by the security 281 gateway for use for the duration of its SA. 283 In this scenario, packets will use tunnel mode. On each packet from 284 the protected endpoint, the outer IP header will contain the source 285 IP address associated with its current location (i.e., the address 286 that will get traffic routed to the endpoint directly) while the 287 inner IP header will contain the source IP address assigned by the 288 security gateway (i.e., the address that will get traffic routed to 289 the security gateway for forwarding to the endpoint). The outer 290 destination address will always be that of the security gateway, 291 while the inner destination address will be the ultimate destination 292 for the packet. 294 In this scenario, it is possible that the protected endpoint will be 295 behind a NAT. In that case, the IP address as seen by the security 296 gateway will not be the same as the IP address sent by the protected 297 endpoint, and packets will have to be UDP encapsulated in order to be 298 routed properly. 300 1.1.4 Other Scenarios 302 Other scenarios are possible, as are nested combinations of the 303 above. One notable example combines aspects of 1.1.1 and 1.1.3. A 304 subnet may make all external accesses through a remote security 305 gateway using an IPsec tunnel, where the addresses on the subnet are 306 routed to the security gateway by the rest of the Internet. An 307 example would be someone's home network being virtually on the 308 Internet with static IP addresses even though connectivity is 309 provided by an ISP that assigns a single dynamically assigned IP 310 address to the user's security gateway (where the static IP addresses 311 and an IPsec relay is provided by a third party located elsewhere). 313 1.2 The Initial Exchanges 315 Communication using IKE always begins with IKE_SA_INIT and IKE_AUTH 316 exchanges (known in IKEv1 as Phase 1). These initial exchanges 317 normally consist of four messages, though in some scenarios that 318 number can grow. All communications using IKE consist of 319 request/response pairs. We'll describe the base exchange first, 320 followed by variations. The first pair of messages (IKE_SA_INIT) 321 negotiate cryptographic algorithms, exchange nonces, and do a Diffie- 322 Hellman exchange. 324 The second pair of messages (IKE_AUTH) authenticate the previous 325 messages, exchange identities and certificates, and establish the 326 first CHILD_SA. Parts of these messages are encrypted and integrity 327 protected with keys established through the IKE_SA_INIT exchange, so 328 the identities are hidden from eavesdroppers and all fields in all 329 the messages are authenticated. 331 In the following description, the payloads contained in the message 332 are indicated by names such as SA. The details of the contents of 333 each payload are described later. Payloads which may optionally 334 appear will be shown in brackets, such as [CERTREQ], would indicate 335 that optionally a certificate request payload can be included. 337 To simplify the descriptions that follow by allowing the use of 338 gender specific personal pronouns, the initiator is assumed to be 339 named "Alice" and the responder "Bob". 341 The initial exchanges are as follows: 343 Initiator Responder 344 ----------- ----------- 345 HDR, SAi1, KEi, Ni --> 347 HDR contains the SPIs, version numbers, and flags of various sorts. 348 The SAi1 payload states the cryptographic algorithms the Initiator 349 supports for the IKE_SA. The KE payload sends the Initiator's 350 Diffie-Hellman value. Ni is the Initiator's nonce. 352 <-- HDR, SAr1, KEr, Nr, [CERTREQ] 354 The Responder chooses a cryptographic suite from the Initiator's 355 offered choices and expresses that choice in the SAr1 payload, 356 completes the Diffie-Hellman exchange with the KEr payload, and sends 357 its nonce in the Nr payload. 359 At this point in the negotiation each party can generate SKEYSEED, 360 from which all keys are derived for that IKE_SA. All but the headers 361 of all the messages that follow are encrypted and integrity 362 protected. The keys used for the encryption and integrity protection 363 are derived from SKEYSEED and are known as SK_e (encryption) and SK_a 364 (authentication, a.k.a. integrity protection). A separate SK_e and 365 SK_a is computed for each direction. In addition to the keys SK_e 366 and SK_a derived from the DH value for protection of the IKE_SA, 367 another quantity SK_d is derived and used for derivation of further 368 keying material for CHILD_SAs. The notation SK { ... } indicates 369 that these payloads are encrypted and integrity protected using that 370 direction's SK_e and SK_a. 372 HDR, SK {IDi, [CERT,] [CERTREQ,] [IDr,] 373 AUTH, SAi2, TSi, TSr} --> 375 The Initiator asserts her identity with the IDi payload, proves 376 knowledge of the secret corresponding to IDi and integrity protects 377 the contents of the first message using the AUTH payload (see section 378 2.15). She might also send her certificate(s) in CERT payload(s) and 379 a list of her trust anchors in CERTREQ payload(s). If any CERT 380 payloads are included, the first certificate provided MUST contain 381 the public key used to verify the AUTH field. The optional payload 382 IDr enables Alice to specify which of Bob's identities she wants to 383 talk to. This is useful when Bob is hosting multiple identities at 384 the same IP address. She begins negotiation of a CHILD_SA using the 385 SAi2 payload. The final fields (starting with SAi2) are described in 386 the description of the CREATE_CHILD_SA exchange. 388 <-- HDR, SK {IDr, [CERT,] AUTH, 389 SAr2, TSi, TSr} 391 The Responder asserts his identity with the IDr payload, optionally 392 sends one or more certificates (again with the certificate containing 393 the public key used to verify AUTH listed first), authenticates his 394 identity and protects the integrity of the second message with the 395 AUTH payload, and completes negotiation of a CHILD_SA with the 396 additional fields described below in the CREATE_CHILD_SA exchange. 398 The recipients of messages 3 and 4 MUST verify that all signatures 399 and MACs are computed correctly and that the names in the ID payloads 400 correspond to the keys used to generate the AUTH payload. 402 1.3 The CREATE_CHILD_SA Exchange 404 This exchange consists of a single request/response pair, and was 405 referred to as a phase 2 exchange in IKEv1. It MAY be initiated by 406 either end of the IKE_SA after the initial exchanges are completed. 408 All messages following the initial exchange are cryptographically 409 protected using the cryptographic algorithms and keys negotiated in 410 the first two messages of the IKE exchange. These subsequent 411 messages use the syntax of the Encrypted Payload described in section 412 3.14. 414 Either endpoint may initiate a CREATE_CHILD_SA exchange, so in this 415 section the term initiator refers to the endpoint initiating this 416 exchange. The term "Alice" will always refer to the initiator of the 417 outer IKE_SA. 419 A CHILD_SA is created by sending a CREATE_CHILD_SA request. The 420 CREATE_CHILD_SA request MAY optionally contain a KE payload for an 421 additional Diffie-Hellman exchange to enable stronger guarantees of 422 forward secrecy for the CHILD_SA. The keying material for the 423 CHILD_SA is a function of SK_d established during the establishment 424 of the IKE_SA, the nonces exchanged during the CREATE_CHILD_SA 425 exchange, and the Diffie-Hellman value (if KE payloads are included 426 in the CREATE_CHILD_SA exchange). 428 In the CHILD_SA created as part of the initial exchange, a second KE 429 payload and nonce MUST NOT be sent. The nonces from the initial 430 exchange are used in computing the keys for the CHILD_SA. 432 The CREATE_CHILD_SA request contains: 434 Initiator Responder 435 ----------- ----------- 436 HDR, SK {[N], SA, Ni, [KEi], 437 [TSi, TSr]} --> 439 The initiator sends SA offer(s) in the SA payload, a nonce in the Ni 440 payload, optionally a Diffie-Hellman value in the KEi payload, and 441 the proposed traffic selectors in the TSi and TSr payloads. If this 442 CREATE_CHILD_SA exchange is rekeying an existing SA other than the 443 IKE_SA, the leading N payload of type REKEY_SA MUST identify the SA 444 being rekeyed. If this CREATE_CHILD_SA exchange is not rekeying an 445 existing SA, the N payload MUST be omitted. If the SA offers include 446 different Diffie-Hellman groups, KEi MUST be an element of the group 447 the initiator expects the responder to accept. If it guesses wrong, 448 the CREATE_CHILD_SA exchange will fail and it will have to retry with 449 a different KEi. 451 The message following the header is encrypted and the message 452 including the header is integrity protected using the cryptographic 453 algorithms negotiated for the IKE_SA. 455 The CREATE_CHILD_SA response contains: 457 <-- HDR, SK {SA, Nr, [KEr], 458 [TSi, TSr]} 460 The responder replies (using the same Message ID to respond) with the 461 accepted offer in an SA payload, and a Diffie-Hellman value in the 462 KEr payload if KEi was included in the request and the selected 463 cryptographic suite includes that group. If the responder chooses a 464 cryptographic suite with a different group, it MUST reject the 465 request. The initiator SHOULD repeat the request, but now with a KEi 466 payload from the group the responder selected. 468 The traffic selectors for traffic to be sent on that SA are specified 469 in the TS payloads, which may be a subset of what the initiator of 470 the CHILD_SA proposed. Traffic selectors are omitted if this 471 CREATE_CHILD_SA request is being used to change the key of the 472 IKE_SA. 474 1.4 The INFORMATIONAL Exchange 476 At various points during the operation of an IKE_SA, peers may desire 477 to convey control messages to each other regarding errors or 478 notifications of certain events. To accomplish this IKE defines an 479 INFORMATIONAL exchange. INFORMATIONAL exchanges MAY ONLY occur after 480 the initial exchanges and are cryptographically protected with the 481 negotiated keys. 483 Control messages that pertain to an IKE_SA MUST be sent under that 484 IKE_SA. Control messages that pertain to CHILD_SAs MUST be sent under 485 the protection of the IKE_SA which generated them (or its successor 486 if the IKE_SA was replaced for the purpose of rekeying). 488 Messages in an INFORMATIONAL Exchange contain zero or more 489 Notification, Delete, and Configuration payloads. The Recipient of an 490 INFORMATIONAL Exchange request MUST send some response (else the 491 Sender will assume the message was lost in the network and will 492 retransmit it). That response MAY be a message with no payloads. The 493 request message in an INFORMATIONAL Exchange MAY also contain no 494 payloads. This is the expected way an endpoint can ask the other 495 endpoint to verify that it is alive. 497 ESP and AH SAs always exist in pairs, with one SA in each direction. 498 When an SA is closed, both members of the pair MUST be closed. When 499 SAs are nested, as when data (and IP headers if in tunnel mode) are 500 encapsulated first with IPComp, then with ESP, and finally with AH 501 between the same pair of endpoints, all of the SAs MUST be deleted 502 together. Each endpoint MUST close its incoming SAs and allow the 503 other endpoint to close the other SA in each pair. To delete an SA, 504 an INFORMATIONAL Exchange with one or more delete payloads is sent 505 listing the SPIs (as they would be expected in the headers of inbound 506 packets) of the SAs to be deleted. The recipient MUST close the 507 designated SAs. Normally, the reply in the INFORMATIONAL Exchange 508 will contain delete payloads for the paired SAs going in the other 509 direction. There is one exception. If by chance both ends of a set 510 of SAs independently decide to close them, each may send a delete 511 payload and the two requests may cross in the network. If a node 512 receives a delete request for SAs for which it has already issued a 513 delete request, it MUST delete the outgoing SAs while processing the 514 request and the incoming SAs while processing the response. In that 515 case, the responses MUST NOT include delete payloads for the deleted 516 SAs, since that would result in duplicate deletion and could in 517 theory delete the wrong SA. 519 A node SHOULD regard half closed connections as anomalous and audit 520 their existence should they persist. Note that this specification 521 nowhere specifies time periods, so it is up to individual endpoints 522 to decide how long to wait. A node MAY refuse to accept incoming data 523 on half closed connections but MUST NOT unilaterally close them and 524 reuse the SPIs. If connection state becomes sufficiently messed up, a 525 node MAY close the IKE_SA which will implicitly close all SAs 526 negotiated under it. It can then rebuild the SAs it needs on a clean 527 base under a new IKE_SA. 529 The INFORMATIONAL Exchange is defined as: 531 Initiator Responder 532 ----------- ----------- 533 HDR, SK {[N,] [D,] [CP,] ...} --> 534 <-- HDR, SK {[N,] [D,] [CP], ...} 536 The processing of an INFORMATIONAL Exchange is determined by its 537 component payloads. 539 1.5 Informational Messages outside of an IKE_SA 541 If a packet arrives with an unrecognized SPI, it could be because the 542 receiving node has recently crashed and lost state or because of some 543 other system malfunction or attack. If the receiving node has an 544 active IKE_SA to the IP address from whence the packet came, it MAY 545 send a notification of the wayward packet over that IKE_SA. If it 546 does not, it MAY send an Informational message without cryptographic 547 protection to the source IP address and port to alert it to a 548 possible problem. 550 2 IKE Protocol Details and Variations 552 IKE normally listens and sends on UDP port 500, though IKE messages 553 may also be received on UDP port 4500 with a slightly different 554 format (see section 2.23). Since UDP is a datagram (unreliable) 555 protocol, IKE includes in its definition recovery from transmission 556 errors, including packet loss, packet replay, and packet forgery. IKE 557 is designed to function so long as (1) at least one of a series of 558 retransmitted packets reaches its destination before timing out; and 559 (2) the channel is not so full of forged and replayed packets so as 560 to exhaust the network or CPU capacities of either endpoint. Even in 561 the absence of those minimum performance requirements, IKE is 562 designed to fail cleanly (as though the network were broken). 564 2.1 Use of Retransmission Timers 566 All messages in IKE exist in pairs: a request and a response. The 567 setup of an IKE_SA normally consists of two request/response pairs. 568 Once the IKE_SA is set up, either end of the security association may 569 initiate requests at any time, and there can be many requests and 570 responses "in flight" at any given moment. But each message is 571 labeled as either a request or a response and for each 572 request/response pair one end of the security association is the 573 Initiator and the other is the Responder. 575 For every pair of IKE messages, the Initiator is responsible for 576 retransmission in the event of a timeout. The Responder MUST never 577 retransmit a response unless it receives a retransmission of the 578 request. In that event, the Responder MUST ignore the retransmitted 579 request except insofar as it triggers a retransmission of the 580 response. The Initiator MUST remember each request until it receives 581 the corresponding response. The Responder MUST remember each response 582 until it receives a request whose sequence number is larger than the 583 sequence number in the response plus his window size (see section 584 2.3). 586 IKE is a reliable protocol, in the sense that the Initiator MUST 587 retransmit a request until either it receives a corresponding reply 588 OR it deems the IKE security association to have failed and it 589 discards all state associated with the IKE_SA and any CHILD_SAs 590 negotiated using that IKE_SA. 592 2.2 Use of Sequence Numbers for Message ID 594 Every IKE message contains a Message ID as part of its fixed header. 595 This Message ID is used to match up requests and responses, and to 596 identify retransmissions of messages. 598 The Message ID is a 32 bit quantity, which is zero for the first IKE 599 request in each direction. The IKE_SA initial setup messages will 600 always be numbered 0 and 1. Each endpoint in the IKE Security 601 Association maintains two "current" Message IDs: the next one to be 602 used for a request it initiates and the next one it expects to see in 603 a request from the other end. These counters increment as requests 604 are generated and received. Responses always contain the same message 605 ID as the corresponding request. That means that after the initial 606 exchange, each integer n may appear as the message ID in four 607 distinct messages: The nth request from the original IKE Initiator, 608 the corresponding response, the nth request from the original IKE 609 Responder, and the corresponding response. If the two ends make very 610 different numbers of requests, the Message IDs in the two directions 611 can be very different. There is no ambiguity in the messages, 612 however, because the (I)nitiator and (R)esponse bits in the message 613 header specify which of the four messages a particular one is. 615 Note that Message IDs are cryptographically protected and provide 616 protection against message replays. In the unlikely event that 617 Message IDs grow too large to fit in 32 bits, the IKE_SA MUST be 618 closed. Rekeying an IKE_SA resets the sequence numbers. 620 2.3 Window Size for overlapping requests 622 In order to maximize IKE throughput, an IKE endpoint MAY issue 623 multiple requests before getting a response to any of them if the 624 other endpoint has indicated its ability to handle such requests. For 625 simplicity, an IKE implementation MAY choose to process requests 626 strictly in order and/or wait for a response to one request before 627 issuing another. Certain rules must be followed to assure 628 interoperability between implementations using different strategies. 630 After an IKE_SA is set up, either end can initiate one or more 631 requests. These requests may pass one another over the network. An 632 IKE endpoint MUST be prepared to accept and process a request while 633 it has a request outstanding in order to avoid a deadlock in this 634 situation. An IKE endpoint SHOULD be prepared to accept and process 635 multiple requests while it has a request outstanding. 637 An IKE endpoint MUST wait for a response to each of its messages 638 before sending a subsequent message unless it has received a 639 SET_WINDOW_SIZE Notify message from its peer informing it that the 640 peer is prepared to maintain state for multiple outstanding messages 641 in order to allow greater throughput. 643 An IKE endpoint MUST NOT exceed the peer's stated window size for 644 transmitted IKE requests. In other words, if Bob stated his window 645 size is N, then when Alice needs to make a request X, she MUST wait 646 until she has received responses to all requests up through request 647 X-N. An IKE endpoint MUST keep a copy of (or be able to regenerate 648 exactly) each request it has sent until it receives the corresponding 649 response. An IKE endpoint MUST keep a copy of (or be able to 650 regenerate exactly) the number of previous responses equal to its 651 declared window size in case its response was lost and the Initiator 652 requests its retransmission by retransmitting the request. 654 An IKE endpoint supporting a window size greater than one SHOULD be 655 capable of processing incoming requests out of order to maximize 656 performance in the event of network failures or packet reordering. 658 2.4 State Synchronization and Connection Timeouts 660 An IKE endpoint is allowed to forget all of its state associated with 661 an IKE_SA and the collection of corresponding CHILD_SAs at any time. 662 This is the anticipated behavior in the event of an endpoint crash 663 and restart. It is important when an endpoint either fails or 664 reinitializes its state that the other endpoint detect those 665 conditions and not continue to waste network bandwidth by sending 666 packets over discarded SAs and having them fall into a black hole. 668 Since IKE is designed to operate in spite of Denial of Service (DoS) 669 attacks from the network, an endpoint MUST NOT conclude that the 670 other endpoint has failed based on any routing information (e.g., 671 ICMP messages) or IKE messages that arrive without cryptographic 672 protection (e.g., Notify messages complaining about unknown SPIs). An 673 endpoint MUST conclude that the other endpoint has failed only when 674 repeated attempts to contact it have gone unanswered for a timeout 675 period or when a cryptographically protected INITIAL_CONTACT 676 notification is received on a different IKE_SA to the same 677 authenticated identity. An endpoint SHOULD suspect that the other 678 endpoint has failed based on routing information and initiate a 679 request to see whether the other endpoint is alive. To check whether 680 the other side is alive, IKE specifies an empty INFORMATIONAL message 681 that (like all IKE requests) requires an acknowledgment. If a 682 cryptographically protected message has been received from the other 683 side recently, unprotected notifications MAY be ignored. 684 Implementations MUST limit the rate at which they take actions based 685 on unprotected messages. 687 Numbers of retries and lengths of timeouts are not covered in this 688 specification because they do not affect interoperability. It is 689 suggested that messages be retransmitted at least a dozen times over 690 a period of at least several minutes before giving up on an SA, but 691 different environments may require different rules. If there has only 692 been outgoing traffic on all of the SAs associated with an IKE_SA, it 693 is essential to confirm liveness of the other endpoint to avoid black 694 holes. If no cryptographically protected messages have been received 695 on an IKE_SA or any of its CHILD_SAs recently, the system needs to 696 perform a liveness check in order to prevent sending messages to a 697 dead peer. Receipt of a fresh cryptographically protected message on 698 an IKE_SA or any of its CHILD_SAs assures liveness of the IKE_SA and 699 all of its CHILD_SAs. Note that this places requirements on the 700 failure modes of an IKE endpoint. An implementation MUST NOT continue 701 sending on any SA if some failure prevents it from receiving on all 702 of the associated SAs. If CHILD_SAs can fail independently from one 703 another without the associated IKE_SA being able to send a delete 704 message, then they MUST be negotiated by separate IKE_SAs. 706 There is a Denial of Service attack on the Initiator of an IKE_SA 707 that can be avoided if the Initiator takes the proper care. Since the 708 first two messages of an SA setup are not cryptographically 709 protected, an attacker could respond to the Initiator's message 710 before the genuine Responder and poison the connection setup attempt. 711 To prevent this, the Initiator MAY be willing to accept multiple 712 responses to its first message, treat each as potentially legitimate, 713 respond to it, and then discard all the invalid half open connections 714 when she receives a valid cryptographically protected response to any 715 one of her requests. Once a cryptographically valid response is 716 received, all subsequent responses should be ignored whether or not 717 they are cryptographically valid. 719 Note that with these rules, there is no reason to negotiate and agree 720 upon an SA lifetime. If IKE presumes the partner is dead, based on 721 repeated lack of acknowledgment to an IKE message, then the IKE SA 722 and all CHILD_SAs set up through that IKE_SA are deleted. 724 An IKE endpoint may at any time delete inactive CHILD_SAs to recover 725 resources used to hold their state. If an IKE endpoint chooses to do 726 so, it MUST send Delete payloads to the other end notifying it of the 727 deletion. It MAY similarly time out the IKE_SA. Closing the IKE_SA 728 implicitly closes all associated CHILD_SAs. In this case, an IKE 729 endpoint SHOULD send a Delete payload indicating that it has closed 730 the IKE_SA. 732 2.5 Version Numbers and Forward Compatibility 734 This document describes version 2.0 of IKE, meaning the major version 735 number is 2 and the minor version number is zero. It is likely that 736 some implementations will want to support both version 1.0 and 737 version 2.0, and in the future, other versions. 739 The major version number should only be incremented if the packet 740 formats or required actions have changed so dramatically that an 741 older version node would not be able to interoperate with a newer 742 version node if it simply ignored the fields it did not understand 743 and took the actions specified in the older specification. The minor 744 version number indicates new capabilities, and MUST be ignored by a 745 node with a smaller minor version number, but used for informational 746 purposes by the node with the larger minor version number. For 747 example, it might indicate the ability to process a newly defined 748 notification message. The node with the larger minor version number 749 would simply note that its correspondent would not be able to 750 understand that message and therefore would not send it. 752 If an endpoint receives a message with a higher major version number, 753 it MUST drop the message and SHOULD send an unauthenticated 754 notification message containing the highest version number it 755 supports. If an endpoint supports major version n, and major version 756 m, it MUST support all versions between n and m. If it receives a 757 message with a major version that it supports, it MUST respond with 758 that version number. In order to prevent two nodes from being tricked 759 into corresponding with a lower major version number than the maximum 760 that they both support, IKE has a flag that indicates that the node 761 is capable of speaking a higher major version number. 763 Thus the major version number in the IKE header indicates the version 764 number of the message, not the highest version number that the 765 transmitter supports. If Alice is capable of speaking versions n, 766 n+1, and n+2, and Bob is capable of speaking versions n and n+1, then 767 they will negotiate speaking n+1, where Alice will set the flag 768 indicating ability to speak a higher version. If they mistakenly 769 (perhaps through an active attacker sending error messages) negotiate 770 to version n, then both will notice that the other side can support a 771 higher version number, and they MUST break the connection and 772 reconnect using version n+1. 774 Note that IKEv1 does not follow these rules, because there is no way 775 in v1 of noting that you are capable of speaking a higher version 776 number. So an active attacker can trick two v2-capable nodes into 777 speaking v1. When a v2-capable node negotiates down to v1, it SHOULD 778 note that fact in its logs. 780 Also for forward compatibility, all fields marked RESERVED MUST be 781 set to zero by a version 2.0 implementation and their content MUST be 782 ignored by a version 2.0 implementation ("Be conservative in what you 783 send and liberal in what you receive"). In this way, future versions 784 of the protocol can use those fields in a way that is guaranteed to 785 be ignored by implementations that do not understand them. 786 Similarly, payload types that are not defined are reserved for future 787 use and implementations of version 2.0 MUST skip over those payloads 788 and ignore their contents. 790 IKEv2 adds a "critical" flag to each payload header for further 791 flexibility for forward compatibility. If the critical flag is set 792 and the payload type is unrecognized, the message MUST be rejected 793 and the response to the IKE request containing that payload MUST 794 include a Notify payload UNSUPPORTED_CRITICAL_PAYLOAD, indicating an 795 unsupported critical payload was included. If the critical flag is 796 not set and the payload type is unsupported, that payload MUST be 797 ignored. 799 While new payload types may be added in the future and may appear 800 interleaved with the fields defined in this specification, 801 implementations MUST send the payloads defined in this specification 802 in the order shown in the figures in section 2 and implementations 803 SHOULD reject as invalid a message with those payloads in any other 804 order. 806 2.6 Cookies 808 The term "cookies" originates with Karn and Simpson [RFC2522] in 809 Photuris, an early proposal for key management with IPsec, and it has 810 persisted. The ISAKMP fixed message header includes two eight octet 811 fields titled "cookies", and that syntax is used by both IKEv1 and 812 IKEv2 though in IKEv2 they are referred to as the IKE SPI and there 813 is a new separate field in a Notify payload holding the cookie. The 814 initial two eight octet fields in the header are used as a connection 815 identifier at the beginning of IKE packets. Each endpoint chooses one 816 of the two SPIs and SHOULD choose them so as to be unique identifiers 817 of an IKE_SA. An SPI value of zero is special and indicates that the 818 remote SPI value is not yet known by the sender. 820 Unlike ESP and AH where only the recipient's SPI appears in the 821 header of a message, in IKE the sender's SPI is also sent in every 822 message. Since the SPI chosen by the original initiator of the IKE_SA 823 is always sent first, an endpoint with multiple IKE_SAs open that 824 wants to find the appropriate IKE_SA using the SPI it assigned must 825 look at the I(nitiator) Flag bit in the header to determine whether 826 it assigned the first or the second eight octets. 828 In the first message of an initial IKE exchange, the initiator will 829 not know the responder's SPI value and will therefore set that field 830 to zero. 832 An expected attack against IKE is state and CPU exhaustion, where the 833 target is flooded with session initiation requests from forged IP 834 addresses. This attack can be made less effective if an 835 implementation of a responder uses minimal CPU and commits no state 836 to an SA until it knows the initiator can receive packets at the 837 address from which he claims to be sending them. To accomplish this, 838 a responder SHOULD - when it detects a large number of half-open 839 IKE_SAs - reject initial IKE messages unless they contain a Notify 840 payload of type COOKIE. It SHOULD instead send an unprotected IKE 841 message as a response and include COOKIE Notify payload with the 842 cookie data to be returned. Initiators who receive such responses 843 MUST retry the IKE_SA_INIT with a Notify payload of type COOKIE 844 containing the responder supplied cookie data as the first payload 845 and all other payloads unchanged. The initial exchange will then be 846 as follows: 848 Initiator Responder 849 ----------- ----------- 850 HDR(A,0), SAi1, KEi, Ni --> 852 <-- HDR(A,0), N(COOKIE) 854 HDR(A,0), N(COOKIE), SAi1, KEi, Ni --> 856 <-- HDR(A,B), SAr1, KEr, Nr, [CERTREQ] 858 HDR(A,B), SK {IDi, [CERT,] [CERTREQ,] [IDr,] 859 AUTH, SAi2, TSi, TSr} --> 861 <-- HDR(A,B), SK {IDr, [CERT,] AUTH, 862 SAr2, TSi, TSr} 864 The first two messages do not affect any initiator or responder state 865 except for communicating the cookie. In particular, the message 866 sequence numbers in the first four messages will all be zero and the 867 message sequence numbers in the last two messages will be one. 'A' is 868 the SPI assigned by the initiator, while 'B' is the SPI assigned by 869 the responder. 871 An IKE implementation SHOULD implement its responder cookie 872 generation in such a way as to not require any saved state to 873 recognize its valid cookie when the second IKE_SA_INIT message 874 arrives. The exact algorithms and syntax they use to generate 875 cookies does not affect interoperability and hence is not specified 876 here. The following is an example of how an endpoint could use 877 cookies to implement limited DOS protection. 879 A good way to do this is to set the responder cookie to be: 881 Cookie = | Hash(Ni | IPi | SPIi | ) 883 where is a randomly generated secret known only to the 884 responder and periodically changed and | indicates concatenation. 885 should be changed whenever is 886 regenerated. The cookie can be recomputed when the IKE_SA_INIT 887 arrives the second time and compared to the cookie in the received 888 message. If it matches, the responder knows that SPIr was generated 889 since the last change to and that IPi must be the same as 890 the source address it saw the first time. Incorporating SPIi into the 891 calculation assures that if multiple IKE_SAs are being set up in 892 parallel they will all get different cookies (assuming the initiator 893 chooses unique SPIi's). Incorporating Ni into the hash assures that 894 an attacker who sees only message 2 can't successfully forge a 895 message 3. 897 If a new value for is chosen while there are connections in 898 the process of being initialized, an IKE_SA_INIT might be returned 899 with other than the current . The responder in 900 that case MAY reject the message by sending another response with a 901 new cookie or it MAY keep the old value of around for a 902 short time and accept cookies computed from either one. The 903 responder SHOULD NOT accept cookies indefinitely after is 904 changed, since that would defeat part of the denial of service 905 protection. The responder SHOULD change the value of 906 frequently, especially if under attack. 908 2.7 Cryptographic Algorithm Negotiation 910 The payload type known as "SA" indicates a proposal for a set of 911 choices of IPsec protocols (IKE, ESP, and/or AH) for the SA as well 912 as cryptographic algorithms associated with each protocol. 914 An SA consists of one or more proposals. Each proposal includes one 915 or more protocols (usually one). Each protocol contains one or more 916 transforms - each specifying a cryptographic algorithm. Each 917 transform contains zero or more attributes (attributes are only 918 needed if the transform identifier does not completely specify the 919 cryptographic algorithm). 921 This hierarchical structure was designed to efficiently encode 922 proposals for cryptographic suites when the number of supported 923 suites is large because multiple values are acceptable for multiple 924 transforms. The responder MUST choose a single suite, which MAY be 925 any subset of the SA proposal following the rules below: 927 Each proposal contains one or more protocols. If a proposal is 928 accepted, the SA response MUST contain the same protocols in the 929 same order as the proposal. The responder MUST accept a single 930 proposal or reject them all and return an error. (Example: if a 931 single proposal contains ESP and AH and that proposal is accepted, 932 both ESP and AH MUST be accepted. If ESP and AH are included in 933 separate proposals, the responder MUST accept only one of them). 935 Each IPsec protocol proposal contains one or more transforms. Each 936 transform contains a transform type. The accepted cryptographic 937 suite MUST contain exactly one transform of each type included in 938 the proposal. For example: if an ESP proposal includes transforms 939 ENCR_3DES, ENCR_AES w/keysize 128, ENCR_AES w/keysize 256, 940 AUTH_HMAC_MD5, and AUTH_HMAC_SHA, the accepted suite MUST contain 941 one of the ENCR_ transforms and one of the AUTH_ transforms. Thus 942 six combinations are acceptable. 944 Since Alice sends her Diffie-Hellman value in the IKE_SA_INIT, she 945 must guess at the Diffie-Hellman group that Bob will select from her 946 list of supported groups. If she guesses wrong, Bob will respond 947 with a Notify payload of type INVALID_KE_PAYLOAD indicating the 948 selected group. In this case, Alice MUST retry the IKE_SA_INIT with 949 the corrected Diffie-Hellman group. Alice MUST again propose her full 950 set of acceptable cryptographic suites because the rejection message 951 was unauthenticated and otherwise an active attacker could trick 952 Alice and Bob into negotiating a weaker suite than a stronger one 953 that they both prefer. 955 2.8 Rekeying 957 IKE, ESP, and AH security associations use secret keys which SHOULD 958 only be used for a limited amount of time and to protect a limited 959 amount of data. This limits the lifetime of the entire security 960 association. When the lifetime of a security association expires the 961 security association MUST NOT be used. If there is demand, new 962 security associations MAY be established. Reestablishment of 963 security associations to take the place of ones which expire is 964 referred to as "rekeying". 966 To allow for minimal IPsec implementations, the ability to rekey SAs 967 without restarting the entire IKE_SA is optional. An implementation 968 MAY refuse all CREATE_CHILD_SA requests within an IKE_SA. If an SA 969 has expired or is about to expire and rekeying attempts using the 970 mechanisms described here fail, an implementation MUST close the 971 IKE_SA and any associated CHILD_SAs and then MAY start new ones. 972 Implementations SHOULD support in place rekeying of SAs, since doing 973 so offers better performance and is likely to reduce the number of 974 packets lost during the transition. 976 To rekey a CHILD_SA within an existing IKE_SA, create a new, 977 equivalent SA (see section 2.17 below), and when the new one is 978 established, delete the old one. To rekey an IKE_SA, establish a new 979 equivalent IKE_SA (see section 2.18 below) with the peer to whom the 980 old IKE_SA is shared using a CREATE_CHILD_SA within the existing 981 IKE_SA. An IKE_SA so created inherits all of the original IKE_SA's 982 CHILD_SAs. Use the new IKE_SA for all control messages needed to 983 maintain the CHILD_SAs created by the old IKE_SA, and delete the old 984 IKE_SA. The Delete payload to delete itself MUST be the last request 985 sent over an IKE_SA. 987 SAs SHOULD be rekeyed proactively, i.e., the new SA should be 988 established before the old one expires and becomes unusable. Enough 989 time should elapse between the time the new SA is established and the 990 old one becomes unusable so that traffic can be switched over to the 991 new SA. 993 A difference between IKEv1 and IKEv2 is that in IKEv1 SA lifetimes 994 were negotiated. In IKEv2, each end of the SA is responsible for 995 enforcing its own lifetime policy on the SA and rekeying the SA when 996 necessary. If the two ends have different lifetime policies, the end 997 with the shorter lifetime will end up always being the one to request 998 the rekeying. If an SA bundle has been inactive for a long time and 999 if an endpoint would not initiate the SA in the absence of traffic, 1000 the endpoint MAY choose to close the SA instead of rekeying it when 1001 its lifetime expires. It SHOULD do so if there has been no traffic 1002 since the last time the SA was rekeyed. 1004 If the two ends have the same lifetime policies, it is possible that 1005 both will initiate a rekeying at the same time (which will result in 1006 redundant SAs). To reduce the probability of this happening, the 1007 timing of rekeying requests SHOULD be jittered (delayed by a random 1008 amount of time after the need for rekeying is noticed). 1010 This form of rekeying may temporarily result in multiple similar SAs 1011 between the same pairs of nodes. When there are two SAs eligible to 1012 receive packets, a node MUST accept incoming packets through either 1013 SA. If redundant SAs are created though such a collision, the SA 1014 created with the lowest of the four nonces used in the two exchanges 1015 SHOULD be closed by the endpoint that created it. 1017 Note that IKEv2 deliberately allows parallel SAs with the same 1018 traffic selectors between common endpoints. One of the purposes of 1019 this is to support traffic QoS differences among the SAs (see section 1020 4.1 of [RFC2983]). Hence unlike IKEv1, the combination of the 1021 endpoints and the traffic selectors may not uniquely identify an SA 1022 between those endpoints, so the IKEv1 rekeying heuristic of deleting 1023 SAs on the basis of duplicate traffic selectors SHOULD NOT be used. 1025 The node that initiated the surviving rekeyed SA SHOULD delete the 1026 replaced SA after the new one is established. 1028 There are timing windows - particularly in the presence of lost 1029 packets - where endpoints may not agree on the state of an SA. The 1030 responder to a CREATE_CHILD_SA MUST be prepared to accept messages on 1031 an SA before sending its response to the creation request, so there 1032 is no ambiguity for the initiator. The initiator MAY begin sending on 1033 an SA as soon as it processes the response. The initiator, however, 1034 cannot receive on a newly created SA until it receives and processes 1035 the response to its CREATE_CHILD_SA request. How, then, is the 1036 responder to know when it is OK to send on the newly created SA? 1038 From a technical correctness and interoperability perspective, the 1039 responder MAY begin sending on an SA as soon as it sends its response 1040 to the CREATE_CHILD_SA request. In some situations, however, this 1041 could result in packets unnecessarily being dropped, so an 1042 implementation MAY want to defer such sending. 1044 The responder can be assured that the initiator is prepared to 1045 receive messages on an SA if either (1) it has received a 1046 cryptographically valid message on the new SA, or (2) the new SA 1047 rekeys an existing SA and it receives an IKE request to close the 1048 replaced SA. When rekeying an SA, the responder SHOULD continue to 1049 send requests on the old SA until it one of those events occurs. When 1050 establishing a new SA, the responder MAY defer sending messages on a 1051 new SA until either it receives one or a timeout has occurred. If an 1052 initiator receives a message on an SA for which it has not received a 1053 response to its CREATE_CHILD_SA request, it SHOULD interpret that as 1054 a likely packet loss and retransmit the CREATE_CHILD_SA request. An 1055 initiator MAY send a dummy message on a newly created SA if it has no 1056 messages queued in order to assure the responder that the initiator 1057 is ready to receive messages. 1059 2.9 Traffic Selector Negotiation 1061 When an IP packet is received by an RFC2401 compliant IPsec subsystem 1062 and matches a "protect" selector in its SPD, the subsystem MUST 1063 protect that packet with IPsec. When no SA exists yet it is the task 1064 of IKE to create it. Maintenance of a system's SPD is outside the 1065 scope of IKE (see [PFKEY] for an example protocol), though some 1066 implementations might update their SPD in connection with the running 1067 of IKE (for an example scenario, see section 1.1.3). 1069 Traffic Selector (TS) payloads allow endpoints to communicate some of 1070 the information from their SPD to their peers. TS payloads specify 1071 the selection criteria for packets that will be forwarded over the 1072 newly set up SA. This can serve as a consistency check in some 1073 scenarios to assure that the SPDs are consistent. In others, it 1074 guides the dynamic update of the SPD. 1076 Two TS payloads appear in each of the messages in the exchange that 1077 creates a CHILD_SA pair. Each TS payload contains one or more Traffic 1078 Selectors. Each Traffic Selector consists of an address range (IPv4 1079 or IPv6), a port range, and an IP protocol ID. In support of the 1080 scenario described in section 1.1.3, an initiator may request that 1081 the responder assign an IP address and tell the initiator what it is. 1083 IKEv2 allows the responder to choose a subset of the traffic proposed 1084 by the initiator. This could happen when the configuration of the 1085 two endpoints are being updated but only one end has received the new 1086 information. Since the two endpoints may be configured by different 1087 people, the incompatibility may persist for an extended period even 1088 in the absence of errors. It also allows for intentionally different 1089 configurations, as when one end is configured to tunnel all addresses 1090 and depends on the other end to have the up to date list. 1092 The first of the two TS payloads is known as TSi (Traffic Selector- 1093 initiator). The second is known as TSr (Traffic Selector-responder). 1094 TSi specifies the source address of traffic forwarded from (or the 1095 destination address of traffic forwarded to) the initiator of the 1096 CHILD_SA pair. TSr specifies the destination address of the traffic 1097 forwarded from (or the source address of the traffic forwarded to) 1098 the responder of the CHILD_SA pair. For example, if Alice initiates 1099 the creation of the CHILD_SA pair from Alice to Bob, and wishes to 1100 tunnel all traffic from subnet 10.2.16.* on Alice's side to subnet 1101 10.16.*.* on Bob's side, Alice would include a single traffic 1102 selector in each TS payload. TSi would specify the address range 1103 (10.2.16.0 - 10.2.16.255) and TSr would specify the address range 1104 (10.16.0.0 - 10.16.255.255). Assuming that proposal was acceptable to 1105 Bob, he would send identical TS payloads back. 1107 The Responder is allowed to narrow the choices by selecting a subset 1108 of the traffic, for instance by eliminating or narrowing the range of 1109 one or more members of the set of traffic selectors, provided the set 1110 does not become the NULL set. 1112 It is possible for the Responder's policy to contain multiple smaller 1113 ranges, all encompassed by the Initiator's traffic selector, and with 1114 the Responder's policy being that each of those ranges should be sent 1115 over a different SA. Continuing the example above, Bob might have a 1116 policy of being willing to tunnel those addresses to and from Alice, 1117 but might require that each address pair be on a separately 1118 negotiated CHILD_SA. If Alice generated her request in response to an 1119 incoming packet from 10.2.16.43 to 10.16.2.123, there would be no way 1120 for Bob to determine which pair of addresses should be included in 1121 this tunnel, and he would have to make his best guess or reject the 1122 request with a status of SINGLE_PAIR_REQUIRED. 1124 To enable Bob to choose the appropriate range in this case, if Alice 1125 has initiated the SA due to a data packet, Alice SHOULD include as 1126 the first traffic selector in each of TSi and TSr a very specific 1127 traffic selector including the addresses in the packet triggering the 1128 request. In the example, Alice would include in TSi two traffic 1129 selectors: the first containing the address range (10.2.16.43 - 1130 10.2.16.43) and the source port and IP protocol from the packet and 1131 the second containing (10.2.16.0 - 10.2.16.255) with all ports and IP 1132 protocols. She would similarly include two traffic selectors in TSr. 1134 If Bob's policy does not allow him to accept the entire set of 1135 traffic selectors in Alice's request, but does allow him to accept 1136 the first selector of TSi and TSr, then Bob MUST narrow the traffic 1137 selectors to a subset that includes Alice's first choices. In this 1138 example, Bob might respond with TSi being (10.2.16.43 - 10.2.16.43) 1139 with all ports and IP protocols. 1141 If Alice creates the CHILD_SA pair not in response to an arriving 1142 packet, but rather - say - upon startup, then there may be no 1143 specific addresses Alice prefers for the initial tunnel over any 1144 other. In that case, the first values in TSi and TSr MAY be ranges 1145 rather than specific values, and Bob chooses a subset of Alice's TSi 1146 and TSr that are acceptable to him. If more than one subset is 1147 acceptable but their union is not, Bob MUST accept some subset and 1148 MAY include a Notify payload of type ADDITIONAL_TS_POSSIBLE to 1149 indicate that Alice might want to try again. This case will only 1150 occur when Alice and Bob are configured differently from one another. 1152 If Alice and Bob agree on the granularity of tunnels, she will never 1153 request a tunnel wider than Bob will accept. 1155 2.10 Nonces 1157 The IKE_SA_INIT messages each contain a nonce. These nonces are used 1158 as inputs to cryptographic functions. The CREATE_CHILD_SA request 1159 and the CREATE_CHILD_SA response also contain nonces. These nonces 1160 are used to add freshness to the key derivation technique used to 1161 obtain keys for CHILD_SA, and to ensure creation of strong 1162 pseudorandom bits from the Diffie-Hellman key. Nonces used in IKEv2 1163 MUST be randomly chosen, MUST be at least 128 bits in size, and MUST 1164 be at least half the key size of the negotiated prf. ("prf" refers to 1165 "pseudo-random function", one of the cryptographic algorithms 1166 negotiated in the IKE exchange). If the same random number source is 1167 used for both keys and nonces, care must be taken to ensure that the 1168 latter use does not compromise the former. 1170 2.11 Address and Port Agility 1172 IKE runs over UDP ports 500 and 4500, and implicitly sets up ESP and 1173 AH associations for the same IP addresses it runs over. The IP 1174 addresses and ports in the outer header are, however, not themselves 1175 cryptographically protected, and IKE is designed to work even through 1176 Network Address Translation (NAT) boxes. An implementation MUST 1177 accept incoming requests even if the source port is not 500 or 4500, 1178 and MUST respond to the address and port from which the request was 1179 received. It MUST specify the address and port at which the request 1180 was received as the source address and port in the response. IKE 1181 functions identically over IPv4 or IPv6. 1183 2.12 Reuse of Diffie-Hellman Exponentials 1185 IKE generates keying material using an ephemeral Diffie-Hellman 1186 exchange in order to gain the property of "perfect forward secrecy". 1187 This means that once a connection is closed and its corresponding 1188 keys are forgotten, even someone who has recorded all of the data 1189 from the connection and gets access to all of the long-term keys of 1190 the two endpoints cannot reconstruct the keys used to protect the 1191 conversation without doing a brute force search of the session key 1192 space. 1194 Achieving perfect forward secrecy requires that when a connection is 1195 closed, each endpoint MUST forget not only the keys used by the 1196 connection but any information that could be used to recompute those 1197 keys. In particular, it MUST forget the secrets used in the Diffie- 1198 Hellman calculation and any state that may persist in the state of a 1199 pseudo-random number generator that could be used to recompute the 1200 Diffie-Hellman secrets. 1202 Since the computing of Diffie-Hellman exponentials is computationally 1203 expensive, an endpoint may find it advantageous to reuse those 1204 exponentials for multiple connection setups. There are several 1205 reasonable strategies for doing this. An endpoint could choose a new 1206 exponential only periodically though this could result in less-than- 1207 perfect forward secrecy if some connection lasts for less than the 1208 lifetime of the exponential. Or it could keep track of which 1209 exponential was used for each connection and delete the information 1210 associated with the exponential only when some corresponding 1211 connection was closed. This would allow the exponential to be reused 1212 without losing perfect forward secrecy at the cost of maintaining 1213 more state. 1215 Decisions as to whether and when to reuse Diffie-Hellman exponentials 1216 is a private decision in the sense that it will not affect 1217 interoperability. An implementation that reuses exponentials MAY 1218 choose to remember the exponential used by the other endpoint on past 1219 exchanges and if one is reused to avoid the second half of the 1220 calculation. 1222 2.13 Generating Keying Material 1224 In the context of the IKE_SA, four cryptographic algorithms are 1225 negotiated: an encryption algorithm, an integrity protection 1226 algorithm, a Diffie-Hellman group, and a pseudo-random function 1227 (prf). The pseudo-random function is used for the construction of 1228 keying material for all of the cryptographic algorithms used in both 1229 the IKE_SA and the CHILD_SAs. 1231 We assume that each encryption algorithm and integrity protection 1232 algorithm uses a fixed size key, and that any randomly chosen value 1233 of that fixed size can serve as an appropriate key. For algorithms 1234 that accept a variable length key, a fixed key size MUST be specified 1235 as part of the cryptographic transform negotiated. For algorithms 1236 for which not all values are valid keys (such as DES or 3DES with key 1237 parity), they algorithm by which keys are derived from arbitrary 1238 values MUST be specified by the cryptographic transform. For 1239 integrity protection functions based on HMAC, the fixed key size is 1240 the size of the output of the underlying hash function. When the prf 1241 function takes a variable length key, variable length data, and 1242 produces a fixed length output (e.g., when using HMAC), the formulas 1243 in this document apply. When the key for the prf function has fixed 1244 length, the data provided as a key is truncated or padded with zeros 1245 as necessary unless exceptional processing is explained following the 1246 formula. 1248 Keying material will always be derived as the output of the 1249 negotiated prf algorithm. Since the amount of keying material needed 1250 may be greater than the size of the output of the prf algorithm, we 1251 will use the prf iteratively. We will use the terminology prf+ to 1252 describe the function that outputs a pseudo-random stream based on 1253 the inputs to a prf as follows: (where | indicates concatenation) 1255 prf+ (K,S) = T1 | T2 | T3 | T4 | ... 1257 where: 1258 T1 = prf (K, S | 0x01) 1259 T2 = prf (K, T1 | S | 0x02) 1260 T3 = prf (K, T2 | S | 0x03) 1261 T4 = prf (K, T3 | S | 0x04) 1263 continuing as needed to compute all required keys. The keys are taken 1264 from the output string without regard to boundaries (e.g., if the 1265 required keys are a 256 bit AES key and a 160 bit HMAC key, and the 1266 prf function generates 160 bits, the AES key will come from T1 and 1267 the beginning of T2, while the HMAC key will come from the rest of T2 1268 and the beginning of T3). 1270 The constant concatenated to the end of each string feeding the prf 1271 is a single octet. prf+ in this document is not defined beyond 255 1272 times the size of the prf output. 1274 2.14 Generating Keying Material for the IKE_SA 1276 The shared keys are computed as follows. A quantity called SKEYSEED 1277 is calculated from the nonces exchanged during the IKE_SA_INIT 1278 exchange and the Diffie-Hellman shared secret established during that 1279 exchange. SKEYSEED is used to calculate seven other secrets: SK_d 1280 used for deriving new keys for the CHILD_SAs established with this 1281 IKE_SA; SK_ai and SK_ar used as a key to the integrity protection 1282 algorithm for authenticating the component messages of subsequent 1283 exchanges; SK_ei and SK_er used for encrypting (and of course 1284 decrypting) all subsequent exchanges; and SK_pi and SK_pr which are 1285 used when generating an AUTH payload. 1287 SKEYSEED and its derivatives are computed as follows: 1289 SKEYSEED = prf(Ni | Nr, g^ir) 1291 {SK_d | SK_ai | SK_ar | SK_ei | SK_er | SK_pi | SK_pr } 1292 = prf+ (SKEYSEED, Ni | Nr | SPIi | SPIr ) 1294 (indicating that the quantities SK_d, SK_ai, SK_ar, SK_ei, SK_er, 1295 SK_pi, and SK_pr are taken in order from the generated bits of the 1296 prf+). g^ir is the shared secret from the ephemeral Diffie-Hellman 1297 exchange. g^ir is represented as a string of octets in big endian 1298 order padded with zeros if necessary to make it the length of the 1299 modulus. Ni and Nr are the nonces, stripped of any headers. If the 1300 negotiated prf takes a fixed length key and the lengths of Ni and Nr 1301 do not add up to that length, half the bits must come from Ni and 1302 half from Nr, taking the first bits of each. 1304 The two directions of traffic flow use different keys. The keys used 1305 to protect messages from the original initiator are SK_ai and SK_ei. 1306 The keys used to protect messages in the other direction are SK_ar 1307 and SK_er. Each algorithm takes a fixed number of bits of keying 1308 material, which is specified as part of the algorithm. For integrity 1309 algorithms based on a keyed hash, the key size is always equal to the 1310 length of the output of the underlying hash function. 1312 2.15 Authentication of the IKE_SA 1314 When not using extended authentication (see section 2.16), the peers 1315 are authenticated by having each sign (or MAC using a shared secret 1316 as the key) a block of data. For the responder, the octets to be 1317 signed start with the first octet of the first SPI in the header of 1318 the second message and end with the last octet of the last payload in 1319 the second message. Appended to this (for purposes of computing the 1320 signature) are the initiator's nonce Ni (just the value, not the 1321 payload containing it), and the value prf(SK_pr,IDr') where IDr' is 1322 the responder's ID payload excluding the fixed header. Note that 1323 neither the nonce Ni nor the value prf(SK_pr,IDr') are transmitted. 1324 Similarly, the initiator signs the first message, starting with the 1325 first octet of the first SPI in the header and ending with the last 1326 octet of the last payload. Appended to this (for purposes of 1327 computing the signature) are the responder's nonce Nr, and the value 1328 prf(SK_pi,IDi'). In the above calculation, IDi' and IDr' are the 1329 entire ID payloads excluding the fixed header. It is critical to the 1330 security of the exchange that each side sign the other side's nonce. 1332 Note that all of the payloads are included under the signature, 1333 including any payload types not defined in this document. If the 1334 first message of the exchange is sent twice (the second time with a 1335 responder cookie and/or a different Diffie-Hellman group), it is the 1336 second version of the message that is signed. 1338 Optionally, messages 3 and 4 MAY include a certificate, or 1339 certificate chain providing evidence that the key used to compute a 1340 digital signature belongs to the name in the ID payload. The 1341 signature or MAC will be computed using algorithms dictated by the 1342 type of key used by the signer, and specified by the Auth Method 1343 field in the Authentication payload. There is no requirement that 1344 the Initiator and Responder sign with the same cryptographic 1345 algorithms. The choice of cryptographic algorithms depends on the 1346 type of key each has. In particular, the initiator may be using a 1347 shared key while the responder may have a public signature key and 1348 certificate. It will commonly be the case (but it is not required) 1349 that if a shared secret is used for authentication that the same key 1350 is used in both directions. Note that it is a common but typically 1351 insecure practice to have a shared key derived solely from a user 1352 chosen password without incorporating another source of randomness. 1353 This is typically insecure because user chosen passwords are unlikely 1354 to have sufficient unpredictability to resist dictionary attacks and 1355 these attacks are not prevented in this authentication method. 1356 (Applications using password-based authentication for bootstrapping 1357 and IKE_SA should use the authentication method in section 2.16, 1358 which is designed to prevent off-line dictionary attacks). The pre- 1359 shared key SHOULD contain as much unpredictability as the strongest 1360 key being negotiated. In the case of a pre-shared key, the AUTH 1361 value is computed as: 1363 AUTH = prf(prf(Shared Secret,"Key Pad for IKEv2"), ) 1366 where the string "Key Pad for IKEv2" is 17 ASCII characters without 1367 null termination. The shared secret can be variable length. The pad 1368 string is added so that if the shared secret is derived from a 1369 password, the IKE implementation need not store the password in 1370 cleartext, but rather can store the value prf(Shared Secret,"Key Pad 1371 for IKEv2"), which could not be used as a password equivalent for 1372 protocols other than IKEv2. As noted above, deriving the shared 1373 secret from a password is not secure. This construction is used 1374 because it is anticipated that people will do it anyway. The 1375 management interface by which the Shared Secret is provided MUST 1376 accept ASCII strings of at least 64 octets and MUST NOT add a null 1377 terminator before using them as shared secrets. The management 1378 interface MAY accept other forms, like hex encoding. If the 1379 negotiated prf takes a fixed size key, the shared secret MUST be of 1380 that fixed size. 1382 2.16 Extended Authentication Protocol Methods 1384 In addition to authentication using public key signatures and shared 1385 secrets, IKE supports authentication using methods defined in RFC 1386 2284 [EAP]. Typically, these methods are asymmetric (designed for a 1387 user authenticating to a server), and they may not be mutual. For 1388 this reason, these protocols are typically used to authenticate the 1389 initiator to the responder and MUST be used in conjunction with a 1390 public key signature based authentication of the responder to the 1391 initiator. These methods are often associated with mechanisms 1392 referred to as "Legacy Authentication" mechanisms. 1394 While this memo references [EAP] with the intent that new methods can 1395 be added in the future without updating this specification, the 1396 protocols expected to be used most commonly are documented here and 1397 in section 3.16. [EAP] defines an authentication protocol requiring 1398 a variable number of messages. Extended Authentication is implemented 1399 in IKE as additional IKE_AUTH exchanges that MUST be completed in 1400 order to initialize the IKE_SA. 1402 An initiator indicates a desire to use extended authentication by 1403 leaving out the AUTH payload from message 3. By including an IDi 1404 payload but not an AUTH payload, the initiator has declared an 1405 identity but has not proven it. If the responder is willing to use an 1406 extended authentication method, it will place an EAP payload in 1407 message 4 and defer sending SAr2, TSi, and TSr until initiator 1408 authentication is complete in a subsequent IKE_AUTH exchange. In the 1409 case of a minimal extended authentication, the initial SA 1410 establishment will appear as follows: 1412 Initiator Responder 1413 ----------- ----------- 1414 HDR, SAi1, KEi, Ni --> 1416 <-- HDR, SAr1, KEr, Nr, [CERTREQ] 1418 HDR, SK {IDi, [CERTREQ,] [IDr,] 1419 SAi2, TSi, TSr} --> 1421 <-- HDR, SK {IDr, [CERT,] AUTH, 1422 EAP } 1424 HDR, SK {EAP} --> 1426 <-- HDR, SK {EAP (success)} 1428 HDR, SK {AUTH} --> 1430 <-- HDR, SK {AUTH, SAr2, TSi, TSr } 1432 For EAP methods that create a shared key as a side effect of 1433 authentication, that shared key MUST be used by both the Initiator 1434 and Responder to generate AUTH payloads in messages 5 and 6 using the 1435 syntax for shared secrets specified in section 2.15. The shared key 1436 from EAP is the field from the EAP specification named MSK. The 1437 shared key generated during an IKE exchange MUST NOT be used for any 1438 other purpose. 1440 EAP methods that do not establish a shared key SHOULD NOT be used, as 1441 they are subject to a number of man-in-the-middle attacks [EAPMITM] 1442 if these EAP methods are used in other protocols that do not use a 1443 server-authenticated tunnel. Please see the Security Considerations 1444 section for more details. If EAP methods that do not generate a 1445 shared key are used, the AUTH payloads in messages 7 and 8 MUST be 1446 generated using SK_pi and SK_pr respectively. 1448 The Initiator of an IKE_SA using EAP SHOULD be capable of extending 1449 the initial protocol exchange to at least ten IKE_AUTH exchanges in 1450 the event the Responder sends notification messages and/or retries 1451 the authentication prompt. The protocol terminates when the Responder 1452 sends the Initiator an EAP payload containing either a success or 1453 failure type. In such an extended exchange, the EAP AUTH payloads 1454 MUST be included in the two messages following the one containing the 1455 EAP (success) message. 1457 2.17 Generating Keying Material for CHILD_SAs 1459 CHILD_SAs are created either by being piggybacked on the IKE_AUTH 1460 exchange, or in a CREATE_CHILD_SA exchange. Keying material for them 1461 is generated as follows: 1463 KEYMAT = prf+(SK_d, Ni | Nr) 1465 Where Ni and Nr are the Nonces from the IKE_SA_INIT exchange if this 1466 request is the first CHILD_SA created or the fresh Ni and Nr from the 1467 CREATE_CHILD_SA exchange if this is a subsequent creation. 1469 For CREATE_CHILD_SA exchanges with PFS the keying material is defined 1470 as: 1472 KEYMAT = prf+(SK_d, g^ir (new) | Ni | Nr ) 1474 where g^ir (new) is the shared secret from the ephemeral Diffie- 1475 Hellman exchange of this CREATE_CHILD_SA exchange (represented as an 1476 octet string in big endian order padded with zeros in the high order 1477 bits if necessary to make it the length of the modulus). 1479 A single CHILD_SA negotiation may result in multiple security 1480 associations. ESP and AH SAs exist in pairs (one in each direction), 1481 and four SAs could be created in a single CHILD_SA negotiation if a 1482 combination of ESP and AH is being negotiated. 1484 Keying material MUST be taken from the expanded KEYMAT in the 1485 following order: 1487 All keys for SAs carrying data from the initiator to the responder 1488 are taken before SAs going in the reverse direction. 1490 If multiple IPsec protocols are negotiated, keying material is 1491 taken in the order in which the protocol headers will appear in 1492 the encapsulated packet. 1494 If a single protocol has both encryption and authentication keys, 1495 the encryption key is taken from the first octets of KEYMAT and 1496 the authentication key is taken from the next octets. 1498 Each cryptographic algorithm takes a fixed number of bits of keying 1499 material specified as part of the algorithm. 1501 2.18 Rekeying IKE_SAs using a CREATE_CHILD_SA exchange 1503 The CREATE_CHILD_SA exchange can be used to rekey an existing IKE_SA 1504 (see section 2.8). New Initiator and Responder SPIs are supplied in 1505 the SPI fields. The TS payloads are omitted when rekeying an IKE_SA. 1506 SKEYSEED for the new IKE_SA is computed using SK_d from the existing 1507 IKE_SA as follows: 1509 SKEYSEED = prf(SK_d (old), [g^ir (new)] | Ni | Nr) 1511 where g^ir (new) is the shared secret from the ephemeral Diffie- 1512 Hellman exchange of this CREATE_CHILD_SA exchange (represented as an 1513 octet string in big endian order padded with zeros if necessary to 1514 make it the length of the modulus) and Ni and Nr are the two nonces 1515 stripped of any headers. 1517 The new IKE_SA MUST reset its message counters to 0. 1519 SK_d, SK_ai, SK_ar, and SK_ei, and SK_er are computed from SKEYSEED 1520 as specified in section 2.14. 1522 2.19 Requesting an internal address on a remote network 1524 Most commonly occurring in the endpoint to security gateway scenario, 1525 an endpoint may need an IP address in the network protected by the 1526 security gateway, and may need to have that address dynamically 1527 assigned. A request for such a temporary address can be included in 1528 any request to create a CHILD_SA (including the implicit request in 1529 message 3) by including a CP payload. 1531 This function provides address allocation to an IRAC (IPsec Remote 1532 Access Client) trying to tunnel into a network protected by an IRAS 1533 (IPsec Remote Access Server). Since the IKE_AUTH exchange creates an 1534 IKE_SA and a CHILD_SA, the IRAC MUST request the IRAS controlled 1535 address (and optionally other information concerning the protected 1536 network) in the IKE_AUTH exchange. The IRAS may procure an address 1537 for the IRAC from any number of sources such as a DHCP/BOOTP server 1538 or its own address pool. 1540 Initiator Responder 1541 ----------------------------- --------------------------- 1542 HDR, SK {IDi, [CERT,] [CERTREQ,] 1543 [IDr,] AUTH, CP(CFG_REQUEST), 1544 SAi2, TSi, TSr} --> 1546 <-- HDR, SK {IDr, [CERT,] AUTH, 1547 CP(CFG_REPLY), SAr2, 1548 TSi, TSr} 1550 In all cases, the CP payload MUST be inserted before the SA payload. 1551 In variations of the protocol where there are multiple IKE_AUTH 1552 exchanges, the CP payloads MUST be inserted in the messages 1553 containing the SA payloads. 1555 CP(CFG_REQUEST) MUST contain at least an INTERNAL_ADDRESS attribute 1556 (either IPv4 or IPv6) but MAY contain any number of additional 1557 attributes the initiator wants returned in the response. 1559 For example, message from Initiator to Responder: 1560 CP(CFG_REQUEST) 1561 INTERNAL_ADDRESS(0.0.0.0) 1562 INTERNAL_NETMASK(0.0.0.0) 1563 INTERNAL_DNS(0.0.0.0) 1564 TSi = (0, 0-65536,0.0.0.0-255.255.255.255) 1565 TSr = (0, 0-65536,0.0.0.0-255.255.255.255) 1567 NOTE: Traffic Selectors contain (protocol, port range, address range) 1569 Message from Responder to Initiator: 1571 CP(CFG_REPLY) 1572 INTERNAL_ADDRESS(10.168.219.202) 1573 INTERNAL_NETMASK(255.255.255.0) 1574 INTERNAL_SUBNET(10.168.219.0/255.255.255.0) 1575 TSi = (0, 0-65536,10.168.219.202-10.168.219.202) 1576 TSr = (0, 0-65536,10.168.219.0-10.168.219.255) 1578 All returned values will be implementation dependent. As can be seen 1579 in the above example, the IRAS MAY also send other attributes that 1580 were not included in CP(CFG_REQUEST) and MAY ignore the non- 1581 mandatory attributes that it does not support. 1583 The responder MUST NOT send a CFG_REPLY without having first received 1584 a CP(CFG_REQUEST) from the initiator, because we do not want the IRAS 1585 to perform an unnecessary configuration lookup if the IRAC cannot 1586 process the REPLY. In the case where the IRAS's configuration 1587 requires that CP be used for a given identity IDi, but IRAC has 1588 failed to send a CP(CFG_REQUEST), IRAS MUST fail the request, and 1589 terminate the IKE exchange with a FAILED_CP_REQUIRED error. 1591 2.20 Requesting the Peer's Version 1593 An IKE peer wishing to inquire about the other peer's IKE software 1594 version information MAY use the method below. This is an example of 1595 a configuration request within an INFORMATIONAL Exchange, after the 1596 IKE_SA and first CHILD_SA have been created. 1598 An IKE implementation MAY decline to give out version information 1599 prior to authentication or even after authentication to prevent 1600 trolling in case some implementation is known to have some security 1601 weakness. In that case, it MUST either return an empty string or no 1602 CP payload if CP is not supported. 1604 Initiator Responder 1605 ----------------------------- -------------------------- 1606 HDR, SK{CP(CFG_REQUEST)} --> 1607 <-- HDR, SK{CP(CFG_REPLY)} 1609 CP(CFG_REQUEST) 1610 APPLICATION_VERSION("") 1612 CP(CFG_REPLY) 1613 APPLICATION_VERSION("foobar v1.3beta, (c) Foo Bar Inc.") 1615 2.21 Error Handling 1617 There are many kinds of errors that can occur during IKE processing. 1618 If a request is received that is badly formatted or unacceptable for 1619 reasons of policy (e.g., no matching cryptographic algorithms), the 1620 response MUST contain a Notify payload indicating the error. If an 1621 error occurs outside the context of an IKE request (e.g., the node is 1622 getting ESP messages on a nonexistent SPI), the node SHOULD initiate 1623 an INFORMATIONAL Exchange with a Notify payload describing the 1624 problem. 1626 Errors that occur before a cryptographically protected IKE_SA is 1627 established must be handled very carefully. There is a trade-off 1628 between wanting to be helpful in diagnosing a problem and responding 1629 to it and wanting to avoid being a dupe in a denial of service attack 1630 based on forged messages. 1632 If a node receives a message on UDP port 500 outside the context of 1633 an IKE_SA known to it (and not a request to start one), it may be the 1634 result of a recent crash of the node. If the message is marked as a 1635 response, the node MAY audit the suspicious event but MUST NOT 1636 respond. If the message is marked as a request, the node MAY audit 1637 the suspicious event and MAY send a response. If a response is sent, 1638 the response MUST be sent to the IP address and port from whence it 1639 came with the same IKE SPIs and the Message ID copied. The response 1640 MUST NOT be cryptographically protected and MUST contain a Notify 1641 payload indicating INVALID_IKE_SPI. 1643 A node receiving such an unprotected Notify payload MUST NOT respond 1644 and MUST NOT change the state of any existing SAs. The message might 1645 be a forgery or might be a response the genuine correspondent was 1646 tricked into sending. A node SHOULD treat such a message (and also a 1647 network message like ICMP destination unreachable) as a hint that 1648 there might be problems with SAs to that IP address and SHOULD 1649 initiate a liveness test for any such IKE_SA. An implementation 1650 SHOULD limit the frequency of such tests to avoid being tricked into 1651 participating in a denial of service attack. 1653 A node receiving a suspicious message from an IP address with which 1654 it has an IKE_SA MAY send an IKE Notify payload in an IKE 1655 INFORMATIONAL exchange over that SA. The recipient MUST NOT change 1656 the state of any SA's as a result but SHOULD audit the event to aid 1657 in diagnosing malfunctions. A node MUST limit the rate at which it 1658 will send messages in response to unprotected messages. 1660 2.22 IPComp 1662 Use of IP compression [IPCOMP] can be negotiated as part of the setup 1663 of a CHILD_SA. While IP compression involves an extra header in each 1664 packet and a CPI (compression parameter index), the virtual 1665 "compression association" has no life outside the ESP or AH SA that 1666 contains it. Compression associations disappear when the 1667 corresponding ESP or AH SA goes away, and is not explicitly mentioned 1668 in any DELETE payload. 1670 Negotiation of IP compression is separate from the negotiation of 1671 cryptographic parameters associated with a CHILD_SA. A node 1672 requesting a CHILD_SA MAY advertise its support for one or more 1673 compression algorithms though one or more Notify payloads of type 1674 IPCOMP_SUPPORTED. The response MAY indicate acceptance of a single 1675 compression algorithm with a Notify payload of type IPCOMP_SUPPORTED. 1676 These payloads MUST NOT occur messages that do not contain SA 1677 payloads. 1679 While there has been discussion of allowing multiple compression 1680 algorithms to be accepted and to have different compression 1681 algorithms available for the two directions of a CHILD_SA, 1682 implementations of this specification MUST NOT accept an IPComp 1683 algorithm that was not proposed, MUST NOT accept more than one, and 1684 MUST NOT compress using an algorithm other than one proposed and 1685 accepted in the setup of the CHILD_SA. 1687 A side effect of separating the negotiation of IPComp from 1688 cryptographic parameters is that it is not possible to propose 1689 multiple cryptographic suites and propose IP compression with some of 1690 them but not others. 1692 2.23 NAT Traversal 1694 NAT (Network Address Translation) gateways are a controversial 1695 subject. This section briefly describes what they are and how they 1696 are likely to act on IKE traffic. Many people believe that NATs are 1697 evil and that we should not design our protocols so as to make them 1698 work better. IKEv2 does specify some unintuitive processing rules in 1699 order that NATs are more likely to work. 1701 NATs exist primarily because of the shortage of IPv4 addresses, 1702 though there are other rationales. IP nodes that are "behind" a NAT 1703 have IP addresses that are not globally unique, but rather are 1704 assigned from some space that is unique within the network behind the 1705 NAT but which are likely to be reused by nodes behind other NATs. 1706 Generally, nodes behind NATs can communicate with other nodes behind 1707 the same NAT and with nodes with globally unique addresses, but not 1708 with nodes behind other NATs. There are exceptions to that rule. 1709 When those nodes make connections to nodes on the real Internet, the 1710 NAT gateway "translates" the IP source address to an address that 1711 will be routed back to the gateway. Messages to the gateway from the 1712 Internet have their destination addresses "translated" to the 1713 internal address that will route the packet to the correct endnode. 1715 NATs are designed to be "transparent" to endnodes. Neither software 1716 on the node behind the NAT nor the node on the Internet require 1717 modification to communicate through the NAT. Achieving this 1718 transparency is more difficult with some protocols than with others. 1719 Protocols that include IP addresses of the endpoints within the 1720 payloads of the packet will fail unless the NAT gateway understands 1721 the protocol and modifies the internal references as well as those in 1722 the headers. Such knowledge is inherently unreliable, is a network 1723 layer violation, and often results in subtle problems. 1725 Opening an IPsec connection through a NAT introduces special 1726 problems. If the connection runs in transport mode, changing the IP 1727 addresses on packets will cause the checksums to fail and the NAT 1728 cannot correct the checksums because they are cryptographically 1729 protected. Even in tunnel mode, there are routing problems because 1730 transparently translating the addresses of AH and ESP packets 1731 requires special logic in the NAT and that logic is heuristic and 1732 unreliable in nature. For that reason, IKEv2 can negotiate UDP 1733 encapsulation of IKE, ESP, and AH packets. This encoding is slightly 1734 less efficient but is easier for NATs to process. In addition, 1735 firewalls may be configured to pass IPsec traffic over UDP but not 1736 ESP/AH or vice versa. 1738 It is a common practice of NATs to translate TCP and UDP port numbers 1739 as well as addresses and use the port numbers of inbound packets to 1740 decide which internal node should get a given packet. For this 1741 reason, even though IKE packets MUST be sent from and to UDP port 1742 500, they MUST be accepted coming from any port and responses MUST be 1743 sent to the port from whence they came. This is because the ports may 1744 be modified as the packets pass through NATs. Similarly, IP addresses 1745 of the IKE endpoints are generally not included in the IKE payloads 1746 because the payloads are cryptographically protected and could not be 1747 transparently modified by NATs. 1749 Port 4500 is reserved for UDP encapsulated ESP, AH, and IKE. When 1750 working through a NAT, it is generally better to pass IKE packets 1751 over port 4500 because some older NATs handle IKE traffic on port 500 1752 cleverly in an attempt to transparently establish IPsec connections 1753 between endpoints that don't handle NAT traversal themselves. Such 1754 NATs may interfere with the straightforward NAT traversal envisioned 1755 by this document, so an IPsec endpoint that discovers a NAT between 1756 it and its correspondent MUST send all subsequent traffic to and from 1757 port 4500, which NATs should not treat specially (as they might with 1758 port 500). 1760 The specific requirements for supporting NAT traversal are listed 1761 below. Support for NAT traversal is optional. In this section only, 1762 requirements listed as MUST only apply to implementations supporting 1763 NAT traversal. 1765 IKE MUST listen on port 4500 as well as port 500. IKE MUST respond 1766 to the IP address and port from which packets arrived. 1768 Both IKE initiator and responder MUST include in their IKE_SA_INIT 1769 packets Notify payloads of type NAT_DETECTION_SOURCE_IP and 1770 NAT_DETECTION_DESTINATION_IP. Those payloads can be used to detect 1771 if there is NAT between the hosts, and which end is behind the 1772 NAT. The location of the payloads in the IKE_SA_INIT packets are 1773 just after the Ni and Nr payloads (before the optional CERTREQ 1774 payload). 1776 If none of the NAT_DETECTION_SOURCE_IP payload(s) received matches 1777 the hash of the source IP and port found from the IP header of the 1778 packet containing the payload, it means that the other end is 1779 behind NAT (i.e., someone along the route changed the source 1780 address of the original packet to match the address of the NAT 1781 box). In this case this end should allow dynamic update of the 1782 other ends IP address, as described later. 1784 If the NAT_DETECTION_DESTINATION_IP payload received does not 1785 match the hash of the destination IP and port found from the IP 1786 header of the packet containing the payload, it means that this 1787 end is behind NAT (i.e., the original sender sent the packet to 1788 address of the NAT box, which then changed the destination address 1789 to this host). In this case the this end should start sending 1790 keepalive packets as explained in [Hutt04]. 1792 The IKE initiator MUST check these payloads if present and if they 1793 do not match the addresses in the outer packet MUST tunnel all 1794 future IKE, ESP, and AH packets associated with this IKE_SA over 1795 UDP port 4500. 1797 To tunnel IKE packets over UDP port 4500, the IKE header has four 1798 octets of zero prepended and the result immediately follows the 1799 UDP header. To tunnel ESP packets over UDP port 4500, the ESP 1800 header immediately follows the UDP header. Since the first four 1801 bytes of the ESP header contain the SPI, and the SPI cannot 1802 validly be zero, it is always possible to distinguish ESP and IKE 1803 messages. 1805 The original source and destination IP address required for the 1806 transport mode TCP and UDP packet checksum fixup (see [Hutt04]) 1807 are obtained from the Traffic Selectors associated with the 1808 exchange. In the case of NAT-T, the Traffic Selectors MUST contain 1809 exactly one IP address which is then used as the original IP 1810 address. 1812 There are cases where a NAT box decides to remove mappings that 1813 are still alive (for example, the keepalive interval is too long, 1814 or the NAT box is rebooted). To recover in these cases, hosts that 1815 are not behind a NAT SHOULD send all packets (including 1816 retransmission packets) to the IP address and port from the last 1817 valid authenticated packet from the other end (i.e., dynamically 1818 update the address). A host behind a NAT SHOULD NOT do this 1819 because it opens a DoS attack possibility. Any authenticated IKE 1820 packet or any authenticated UDP encapsulated ESP packet can be 1821 used to detect that the IP address or the port has changed. 1823 Note that similar but probably not identical actions will likely 1824 be needed to make IKE work with Mobile IP, but such processing is 1825 not addressed by this document. 1827 2.24 ECN (Explicit Congestion Notification) 1829 When IPsec tunnels behave as originally specified in [RFC2401], ECN 1830 usage is not appropriate for the outer IP headers because tunnel 1831 decapsulation processing discards ECN congestion indications to the 1832 detriment of the network. ECN support for IPsec tunnels for 1833 IKEv1-based IPsec requires multiple operating modes and negotiation 1834 (see RFC3168]). IKEv2 simplifies this situation by requiring that 1835 ECN be usable in the outer IP headers of all tunnel-mode IPsec SAs 1836 created by IKEv2. Specifically, tunnel encapsulators and 1837 decapsulators for all tunnel-mode Security Associations (SAs) created 1838 by IKEv2 MUST support the ECN full-functionality option for tunnels 1839 specified in [RFC3168] and MUST implement the tunnel encapsulation 1840 and decapsulation processing specified in [RFC2401bis] to prevent 1841 discarding of ECN congestion indications. 1843 3 Header and Payload Formats 1845 3.1 The IKE Header 1847 IKE messages use UDP ports 500 and/or 4500, with one IKE message per 1848 UDP datagram. Information from the UDP header is largely ignored 1849 except that the IP addresses and UDP ports from the headers are 1850 reversed and used for return packets. When sent on UDP port 500, IKE 1851 messages begin immediately following the UDP header. When sent on UDP 1852 port 4500, IKE messages have prepended four octets of zero. These 1853 four octets of zero are not part of the IKE message and are not 1854 included in any of the length fields or checksums defined by IKE. 1855 Each IKE message begins with the IKE header, denoted HDR in this 1856 memo. Following the header are one or more IKE payloads each 1857 identified by a "Next Payload" field in the preceding payload. 1858 Payloads are processed in the order in which they appear in an IKE 1859 message by invoking the appropriate processing routine according to 1860 the "Next Payload" field in the IKE header and subsequently according 1861 to the "Next Payload" field in the IKE payload itself until a "Next 1862 Payload" field of zero indicates that no payloads follow. If a 1863 payload of type "Encrypted" is found, that payload is decrypted and 1864 its contents parsed as additional payloads. An Encrypted payload MUST 1865 be the last payload in a packet and an encrypted payload MUST NOT 1866 contain another encrypted payload. 1868 The Recipient SPI in the header identifies an instance of an IKE 1869 security association. It is therefore possible for a single instance 1870 of IKE to multiplex distinct sessions with multiple peers. 1872 All multi-octet fields representing integers are laid out in big 1873 endian order (aka most significant byte first, or network byte 1874 order). 1876 The format of the IKE header is shown in Figure 4. 1877 1 2 3 1878 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 1879 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1880 ! IKE_SA Initiator's SPI ! 1881 ! ! 1882 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1883 ! IKE_SA Responder's SPI ! 1884 ! ! 1885 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1886 ! Next Payload ! MjVer ! MnVer ! Exchange Type ! Flags ! 1887 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1888 ! Message ID ! 1889 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1890 ! Length ! 1891 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1893 Figure 4: IKE Header Format 1895 o Initiator's SPI (8 octets) - A value chosen by the 1896 initiator to identify a unique IKE security association. This 1897 value MUST NOT be zero. 1899 o Responder's SPI (8 octets) - A value chosen by the 1900 responder to identify a unique IKE security association. This 1901 value MUST be zero in the first message of an IKE Initial 1902 Exchange (including repeats of that message including a 1903 cookie) and MUST NOT be zero in any other message. 1905 o Next Payload (1 octet) - Indicates the type of payload that 1906 immediately follows the header. The format and value of each 1907 payload is defined below. 1909 o Major Version (4 bits) - indicates the major version of the IKE 1910 protocol in use. Implementations based on this version of IKE 1911 MUST set the Major Version to 2. Implementations based on 1912 previous versions of IKE and ISAKMP MUST set the Major Version 1913 to 1. Implementations based on this version of IKE MUST reject 1914 or ignore messages containing a version number greater than 1915 2. 1917 o Minor Version (4 bits) - indicates the minor version of the 1918 IKE protocol in use. Implementations based on this version of 1919 IKE MUST set the Minor Version to 0. They MUST ignore the minor 1920 version number of received messages. 1922 o Exchange Type (1 octet) - indicates the type of exchange being 1923 used. This constrains the payloads sent in each message and 1924 orderings of messages in an exchange. 1926 Exchange Type Value 1928 RESERVED 0-33 1929 IKE_SA_INIT 34 1930 IKE_AUTH 35 1931 CREATE_CHILD_SA 36 1932 INFORMATIONAL 37 1933 Reserved for IKEv2+ 38-239 1934 Reserved for private use 240-255 1936 o Flags (1 octet) - indicates specific options that are set 1937 for the message. Presence of options are indicated by the 1938 appropriate bit in the flags field being set. The bits are 1939 defined LSB first, so bit 0 would be the least significant 1940 bit of the Flags octet. In the description below, a bit 1941 being 'set' means its value is '1', while 'cleared' means 1942 its value is '0'. 1944 -- X(reserved) (bits 0-2) - These bits MUST be cleared 1945 when sending and MUST be ignored on receipt. 1947 -- I(nitiator) (bit 3 of Flags) - This bit MUST be set in 1948 messages sent by the original Initiator of the IKE_SA 1949 and MUST be cleared in messages sent by the original 1950 Responder. It is used by the recipient to determine 1951 which eight octets of the SPI was generated by the 1952 recipient. 1954 -- V(ersion) (bit 4 of Flags) - This bit indicates that 1955 the transmitter is capable of speaking a higher major 1956 version number of the protocol than the one indicated 1957 in the major version number field. Implementations of 1958 IKEv2 must clear this bit when sending and MUST ignore 1959 it in incoming messages. 1961 -- R(esponse) (bit 5 of Flags) - This bit indicates that 1962 this message is a response to a message containing 1963 the same message ID. This bit MUST be cleared in all 1964 request messages and MUST be set in all responses. 1965 An IKE endpoint MUST NOT generate a response to a 1966 message that is marked as being a response. 1968 -- X(reserved) (bits 6-7 of Flags) - These bits MUST be 1969 cleared when sending and MUST be ignored on receipt. 1971 o Message ID (4 octets) - Message identifier used to control 1972 retransmission of lost packets and matching of requests and 1973 responses. It is essential to the security of the protocol 1974 because it is used to prevent message replay attacks. 1975 See sections 2.1 and 2.2. 1977 o Length (4 octets) - Length of total message (header + payloads) 1978 in octets. 1980 3.2 Generic Payload Header 1982 Each IKE payload defined in sections 3.3 through 3.16 begins with a 1983 generic payload header, shown in Figure 5. Figures for each payload 1984 below will include the generic payload header but for brevity the 1985 description of each field will be omitted. 1987 1 2 3 1988 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 1989 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1990 ! Next Payload !C! RESERVED ! Payload Length ! 1991 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1993 Figure 5: Generic Payload Header 1995 The Generic Payload Header fields are defined as follows: 1997 o Next Payload (1 octet) - Identifier for the payload type of the 1998 next payload in the message. If the current payload is the last 1999 in the message, then this field will be 0. This field provides 2000 a "chaining" capability whereby additional payloads can be 2001 added to a message by appending it to the end of the message 2002 and setting the "Next Payload" field of the preceding payload 2003 to indicate the new payload's type. An Encrypted payload, 2004 which must always be the last payload of a message, is an 2005 exception. It contains data structures in the format of 2006 additional payloads. In the header of an Encrypted payload, 2007 the Next Payload field is set to the payload type of the first 2008 contained payload (instead of 0). 2010 Payload Type Values 2012 Next Payload Type Notation Value 2014 No Next Payload 0 2015 RESERVED 1-32 2016 Security Association SA 33 2017 Key Exchange KE 34 2018 Identification - Initiator IDi 35 2019 Identification - Responder IDr 36 2020 Certificate CERT 37 2021 Certificate Request CERTREQ 38 2022 Authentication AUTH 39 2023 Nonce Ni, Nr 40 2024 Notify N 41 2025 Delete D 42 2026 Vendor ID V 43 2027 Traffic Selector - Initiator TSi 44 2028 Traffic Selector - Responder TSr 45 2029 Encrypted E 46 2030 Configuration CP 47 2031 Extended Authentication EAP 48 2032 RESERVED TO IANA 49-127 2033 PRIVATE USE 128-255 2035 Payload type values 1-32 should not be used so that there is no 2036 overlap with the code assignments for IKEv1. Payload type values 2037 49-127 are reserved to IANA for future assignment in IKEv2 (see 2038 section 6). Payload type values 128-255 are for private use among 2039 mutually consenting parties. 2041 o Critical (1 bit) - MUST be set to zero if the sender wants 2042 the recipient to skip this payload if he does not 2043 understand the payload type code in the Next Payload field 2044 of the previous payload. MUST be set to one if the 2045 sender wants the recipient to reject this entire message 2046 if he does not understand the payload type. MUST be ignored 2047 by the recipient if the recipient understands the payload type 2048 code. MUST be set to zero for payload types defined in this 2049 document. Note that the critical bit applies to the current 2050 payload rather than the "next" payload whose type code 2051 appears in the first octet. The reasoning behind not setting 2052 the critical bit for payloads defined in this document is 2053 that all implementations MUST understand all payload types 2054 defined in this document and therefore must ignore the 2055 Critical bit's value. Skipped payloads are expected to 2056 have valid Next Payload and Payload Length fields. 2058 o RESERVED (7 bits) - MUST be sent as zero; MUST be ignored on 2059 receipt. 2061 o Payload Length (2 octets) - Length in octets of the current 2062 payload, including the generic payload header. 2064 3.3 Security Association Payload 2066 The Security Association Payload, denoted SA in this memo, is used to 2067 negotiate attributes of a security association. Assembly of Security 2068 Association Payloads requires great peace of mind. An SA payload MAY 2069 contain multiple proposals. If there is more than one, they MUST be 2070 ordered from most preferred to least preferred. Each proposal may 2071 contain multiple IPsec protocols (where a protocol is IKE, ESP, or 2072 AH), each protocol MAY contain multiple transforms, and each 2073 transform MAY contain multiple attributes. When parsing an SA, an 2074 implementation MUST check that the total Payload Length is consistent 2075 with the payload's internal lengths and counts. Proposals, 2076 Transforms, and Attributes each have their own variable length 2077 encodings. They are nested such that the Payload Length of an SA 2078 includes the combined contents of the SA, Proposal, Transform, and 2079 Attribute information. The length of a Proposal includes the lengths 2080 of all Transforms and Attributes it contains. The length of a 2081 Transform includes the lengths of all Attributes it contains. 2083 The syntax of Security Associations, Proposals, Transforms, and 2084 Attributes is based on ISAKMP, however the semantics are somewhat 2085 different. The reason for the complexity and the hierarchy is to 2086 allow for multiple possible combinations of algorithms to be encoded 2087 in a single SA. Sometimes there is a choice of multiple algorithms, 2088 while other times there is a combination of algorithms. For example, 2089 an Initiator might want to propose using (AH w/MD5 and ESP w/3DES) OR 2090 (ESP w/MD5 and 3DES). 2092 One of the reasons the semantics of the SA payload has changed from 2093 ISAKMP and IKEv1 is to make the encodings more compact in common 2094 cases. 2096 The Proposal structure contains within it a Proposal # and an IPsec 2097 protocol ID. Each structure MUST have the same Proposal # as the 2098 previous one or be one (1) greater. The first Proposal MUST have a 2099 Proposal # of one (1). If two successive structures have the same 2100 Proposal number, it means that the proposal consists of the first 2101 structure AND the second. So a proposal of AH AND ESP would have two 2102 proposal structures, one for AH and one for ESP and both would have 2103 Proposal #1. A proposal of AH OR ESP would have two proposal 2104 structures, one for AH with proposal #1 and one for ESP with proposal 2105 #2. 2107 Each Proposal/Protocol structure is followed by one or more transform 2108 structures. The number of different transforms is generally 2109 determined by the Protocol. AH generally has a single transform: an 2110 integrity check algorithm. ESP generally has two: an encryption 2111 algorithm and an integrity check algorithm. IKE generally has four 2112 transforms: a Diffie-Hellman group, an integrity check algorithm, a 2113 prf algorithm, and an encryption algorithm. If an algorithm that 2114 combines encryption and integrity protection is proposed, it MUST be 2115 proposed as an encryption algorithm and an integrity protection 2116 algorithm MUST NOT be proposed. For each Protocol, the set of 2117 permissible transforms are assigned transform ID numbers, which 2118 appear in the header of each transform. 2120 If there are multiple transforms with the same Transform Type, the 2121 proposal is an OR of those transforms. If there are multiple 2122 Transforms with different Transform Types, the proposal is an AND of 2123 the different groups. For example, to propose ESP with (3DES or IDEA) 2124 and (HMAC_MD5 or HMAC_SHA), the ESP proposal would contain two 2125 Transform Type 1 candidates (one for 3DES and one for IDEA) and two 2126 Transform Type 2 candidates (one for HMAC_MD5 and one for HMAC_SHA). 2127 This effectively proposes four combinations of algorithms. If the 2128 Initiator wanted to propose only a subset of those - say (3DES and 2129 HMAC_MD5) or (IDEA and HMAC_SHA), there is no way to encode that as 2130 multiple transforms within a single Proposal. Instead, the Initiator 2131 would have to construct two different Proposals, each with two 2132 transforms. 2134 A given transform MAY have one or more Attributes. Attributes are 2135 necessary when the transform can be used in more than one way, as 2136 when an encryption algorithm has a variable key size. The transform 2137 would specify the algorithm and the attribute would specify the key 2138 size. Most transforms do not have attributes. A transform MUST NOT 2139 have multiple attributes of the same type. To propose alternate 2140 values for an attribute (for example, multiple key sizes for the AES 2141 encryption algorithm), and implementation MUST include multiple 2142 Transforms with the same Transform Type each with a single Attribute. 2144 Note that the semantics of Transforms and Attributes are quite 2145 different than in IKEv1. In IKEv1, a single Transform carried 2146 multiple algorithms for a protocol with one carried in the Transform 2147 and the others carried in the Attributes. 2149 1 2 3 2150 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 2151 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2152 ! Next Payload !C! RESERVED ! Payload Length ! 2153 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2154 ! ! 2155 ~ ~ 2156 ! ! 2157 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2159 Figure 6: Security Association Payload 2161 o Proposals (variable) - one or more proposal substructures. 2163 The payload type for the Security Association Payload is thirty 2164 three (33). 2166 3.3.1 Proposal Substructure 2168 1 2 3 2169 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 2170 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2171 ! 0 (last) or 2 ! RESERVED ! Proposal Length ! 2172 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2173 ! Proposal # ! Protocol ID ! SPI Size !# of Transforms! 2174 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2175 ~ SPI (variable) ~ 2176 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2177 ! ! 2178 ~ ~ 2179 ! ! 2180 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2182 Figure 7: Proposal Substructure 2184 o 0 (last) or 2 (more) (1 octet) - Specifies whether this is the 2185 last Proposal Substructure in the SA. This syntax is inherited 2186 from ISAKMP, but is unnecessary because the last Proposal 2187 could be identified from the length of the SA. The value (2) 2188 corresponds to a Payload Type of Proposal in IKEv1, and the 2189 first four octets of the Proposal structure are designed to 2190 look somewhat like the header of a Payload. 2192 o RESERVED (1 octet) - MUST be sent as zero; MUST be ignored on 2193 receipt. 2195 o Proposal Length (2 octets) - Length of this proposal, 2196 including all transforms and attributes that follow. 2198 o Proposal # (1 octet) - When a proposal is made, the first 2199 proposal in an SA MUST be #1, and subsequent proposals 2200 MUST either be the same as the previous proposal (indicating 2201 an AND of the two proposals) or one more than the previous 2202 proposal (indicating an OR of the two proposals). When a 2203 proposal is accepted, all of the proposal numbers in the 2204 SA MUST be the same and MUST match the number on the 2205 proposal sent that was accepted. 2207 o Protocol ID (1 octet) - Specifies the IPsec protocol 2208 identifier for the current negotiation. The defined values 2209 are: 2211 Protocol Protocol ID 2212 RESERVED 0 2213 IKE 1 2214 AH 2 2215 ESP 3 2216 RESERVED TO IANA 4-200 2217 PRIVATE USE 201-255 2219 o SPI Size (1 octet) - For an initial IKE_SA negotiation, 2220 this field MUST be zero; the SPI is obtained from the 2221 outer header. During subsequent negotiations, 2222 it is equal to the size, in octets, of the SPI of the 2223 corresponding protocol (8 for IKE, 4 for ESP and AH). 2225 o # of Transforms (1 octet) - Specifies the number of 2226 transforms in this proposal. 2228 o SPI (variable) - The sending entity's SPI. Even if the SPI 2229 Size is not a multiple of 4 octets, there is no padding 2230 applied to the payload. When the SPI Size field is zero, 2231 this field is not present in the Security Association 2232 payload. 2234 o Transforms (variable) - one or more transform substructures. 2236 3.3.2 Transform Substructure 2238 1 2 3 2239 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 2240 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2241 ! 0 (last) or 3 ! RESERVED ! Transform Length ! 2242 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2243 !Transform Type ! RESERVED ! Transform ID ! 2244 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2245 ! ! 2246 ~ Transform Attributes ~ 2247 ! ! 2248 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2250 Figure 8: Transform Substructure 2252 o 0 (last) or 3 (more) (1 octet) - Specifies whether this is the 2253 last Transform Substructure in the Proposal. This syntax is 2254 inherited from ISAKMP, but is unnecessary because the last 2255 Proposal could be identified from the length of the SA. The 2256 value (3) corresponds to a Payload Type of Transform in IKEv1, 2257 and the first four octets of the Transform structure are 2258 designed to look somewhat like the header of a Payload. 2260 o RESERVED - MUST be sent as zero; MUST be ignored on receipt. 2262 o Transform Length - The length (in octets) of the Transform 2263 Substructure including Header and Attributes. 2265 o Transform Type (1 octet) - The type of transform being specified 2266 in this transform. Different protocols support different 2267 transform types. For some protocols, some of the transforms 2268 may be optional. If a transform is optional and the initiator 2269 wishes to propose that the transform be omitted, no transform 2270 of the given type is included in the proposal. If the 2271 initiator wishes to make use of the transform optional to 2272 the responder, she includes a transform substructure with 2273 transform ID = 0 as one of the options. 2275 o Transform ID (2 octets) - The specific instance of the transform 2276 type being proposed. 2278 Transform Type Values 2280 Transform Used In 2281 Type 2282 Encryption Algorithm 1 (IKE and ESP) 2283 Pseudo-random Function 2 (IKE) 2284 Integrity Algorithm 3 (IKE, AH, and optional in ESP) 2285 Diffie-Hellman Group 4 (IKE and optional in AH and ESP) 2286 Extended Sequence Numbers 5 (Optional in AH and ESP) 2287 RESERVED TO IANA 6-240 2288 PRIVATE USE 241-255 2290 For Transform Type 1 (Encryption Algorithm), defined Transform IDs 2291 are: 2293 Name Number Defined In 2294 RESERVED 0 2295 ENCR_DES_IV64 1 (RFC1827) 2296 ENCR_DES 2 (RFC2405) 2297 ENCR_3DES 3 (RFC2451) 2298 ENCR_RC5 4 (RFC2451) 2299 ENCR_IDEA 5 (RFC2451) 2300 ENCR_CAST 6 (RFC2451) 2301 ENCR_BLOWFISH 7 (RFC2451) 2302 ENCR_3IDEA 8 (RFC2451) 2303 ENCR_DES_IV32 9 2304 ENCR_RC4 10 2305 ENCR_NULL 11 (RFC2410) 2306 ENCR_AES_CBC 12 2307 ENCR_AES_CTR 13 2309 values 14-1023 are reserved to IANA. Values 1024-65535 are for 2310 private use among mutually consenting parties. 2312 For Transform Type 2 (Pseudo-random Function), defined Transform IDs 2313 are: 2315 Name Number Defined In 2316 RESERVED 0 2317 PRF_HMAC_MD5 1 (RFC2104) 2318 PRF_HMAC_SHA1 2 (RFC2104) 2319 PRF_HMAC_TIGER 3 (RFC2104) 2320 PRF_AES_CBC 4 2322 values 5-1023 are reserved to IANA. Values 1024-65535 are for 2323 private use among mutually consenting parties. 2325 For Transform Type 3 (Integrity Algorithm), defined Transform IDs 2326 are: 2328 Name Number Defined In 2329 NONE 0 2330 AUTH_HMAC_MD5_96 1 (RFC2403) 2331 AUTH_HMAC_SHA1_96 2 (RFC2404) 2332 AUTH_DES_MAC 3 2333 AUTH_KPDK_MD5 4 (RFC1826) 2334 AUTH_AES_PRF_128 5 (RFC3664) 2336 values 6-1023 are reserved to IANA. Values 1024-65535 are for 2337 private use among mutually consenting parties. 2339 For Transform Type 4 (Diffie-Hellman Group), defined Transform IDs 2340 are: 2342 Name Number 2343 NONE 0 2344 Defined in Appendix B 1 - 4 2345 Defined in [ADDGROUP] 5, 14 - 18 2346 values 6-13 and 19-1023 are reserved to IANA for new MODP, ECP 2347 or EC2N groups. Values 1024-65535 are for private use among 2348 mutually consenting parties. 2350 For Transform Type 5 (Extended Sequence Numbers), defined Transform 2351 IDs are: 2353 Name Number 2354 No Extended Sequence Numbers 0 2355 Extended Sequence Numbers 1 2356 RESERVED 2 - 65535 2358 If Transform Type 5 is not included in a proposal, use of 2359 Extended Sequence Numbers is assumed. 2361 3.3.3 Valid Transform Types by Protocol 2363 The number and type of transforms that accompany an SA payload are 2364 dependent on the protocol in the SA itself. An SA payload proposing 2365 the establishment of an SA has the following mandatory and optional 2366 transform types. A compliant implementation MUST understand all 2367 mandatory and optional types for each protocol it supports (though it 2368 need not accept proposals with unacceptable suites). A proposal MAY 2369 omit the optional types if the only value for them it will accept is 2370 NONE. 2372 Protocol Mandatory Types Optional Types 2373 IKE ENCR, PRF, INTEG, D-H 2374 ESP ENCR INTEG, D-H, ESN 2375 AH INTEG D-H, ESN 2377 3.3.4 Mandatory Transform IDs 2378 The specification of suites that MUST and SHOULD be supported for 2379 interoperability has been removed from this document because they are 2380 likely to change more rapidly than this document evolves. 2382 An important lesson learned from IKEv1 is that no system should only 2383 implement the mandatory algorithms and expect them to be the best 2384 choice for all customers. For example, at the time that this document 2385 was being written, many IKEv1 implementers are starting to migrate to 2386 AES in CBC mode for VPN applications. Many IPsec systems based on 2387 IKEv2 will implement AES, additional Diffie-Hellman groups, and 2388 additional hash algorithms, and some IPsec customers already require 2389 these algorithms in addition to the ones listed above. 2391 It is likely that IANA will add additional transforms in the future, 2392 and some users may want to use private suites, especially for IKE 2393 where implementations should be capable of supporting different 2394 parameters, up to certain size limits. In support of this goal, all 2395 implementations of IKEv2 SHOULD include a management facility that 2396 allows specification (by a user or system administrator) of Diffie- 2397 Hellman parameters (the generator, modulus, and exponent lengths and 2398 values) for new DH groups. Implementations SHOULD provide a 2399 management interface via which these parameters and the associated 2400 transform IDs may be entered (by a user or system administrator), to 2401 enable negotiating such groups. 2403 All implementations of IKEv2 MUST include a management facility that 2404 enables a user or system administrator to specify the suites that are 2405 acceptable for use with IKE. Upon receipt of a payload with a set of 2406 transform IDs, the implementation MUST compare the transmitted 2407 transform IDs against those locally configured via the management 2408 controls, to verify that the proposed suite is acceptable based on 2409 local policy. The implementation MUST reject SA proposals that are 2410 not authorized by these IKE suite controls. 2412 3.3.5 Transform Attributes 2414 Each transform in a Security Association payload may include 2415 attributes that modify or complete the specification of the 2416 transform. These attributes are type/value pairs and are defined 2417 below. For example, if an encryption algorithm has a variable length 2418 key, the key length to be used may be specified as an attribute. 2419 Attributes can have a value with a fixed two octet length or a 2420 variable length value. For the latter, the attribute is encoded as 2421 type/length/value. 2423 1 2 3 2424 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 2425 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2426 !A! Attribute Type ! AF=0 Attribute Length ! 2427 !F! ! AF=1 Attribute Value ! 2428 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2429 ! AF=0 Attribute Value ! 2430 ! AF=1 Not Transmitted ! 2431 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2433 Figure 9: Data Attributes 2435 o Attribute Type (2 octets) - Unique identifier for each type of 2436 attribute (see below). 2438 The most significant bit of this field is the Attribute Format 2439 bit (AF). It indicates whether the data attributes follow the 2440 Type/Length/Value (TLV) format or a shortened Type/Value (TV) 2441 format. If the AF bit is zero (0), then the Data Attributes 2442 are of the Type/Length/Value (TLV) form. If the AF bit is a 2443 one (1), then the Data Attributes are of the Type/Value form. 2445 o Attribute Length (2 octets) - Length in octets of the Attribute 2446 Value. When the AF bit is a one (1), the Attribute Value is 2447 only 2 octets and the Attribute Length field is not present. 2449 o Attribute Value (variable length) - Value of the Attribute 2450 associated with the Attribute Type. If the AF bit is a 2451 zero (0), this field has a variable length defined by the 2452 Attribute Length field. If the AF bit is a one (1), the 2453 Attribute Value has a length of 2 octets. 2455 Note that only a single attribute type (Key Length) is defined, and 2456 it is fixed length. The variable length encoding specification is 2457 included only for future extensions. The only algorithms defined in 2458 this document that accept attributes are the AES based encryption, 2459 integrity, and pseudo-random functions, which require a single 2460 attribute specifying key width. 2462 Attributes described as basic MUST NOT be encoded using the variable 2463 length encoding. Variable length attributes MUST NOT be encoded as 2464 basic even if their value can fit into two octets. NOTE: This is a 2465 change from IKEv1, where increased flexibility may have simplified 2466 the composer of messages but certainly complicated the parser. 2468 Attribute Type value Attribute Format 2469 -------------------------------------------------------------- 2470 RESERVED 0-13 2471 Key Length (in bits) 14 TV 2472 RESERVED 15-17 2473 RESERVED TO IANA 18-16383 2474 PRIVATE USE 16384-32767 2476 Values 0-13 and 15-17 were used in a similar context in IKEv1, and 2477 should not be assigned except to matching values. Values 18-16383 are 2478 reserved to IANA. Values 16384-32767 are for private use among 2479 mutually consenting parties. 2481 - Key Length 2483 When using an Encryption Algorithm that has a variable length key, 2484 this attribute specifies the key length in bits. (MUST use network 2485 byte order). This attribute MUST NOT be used when the specified 2486 Encryption Algorithm uses a fixed length key. 2488 3.3.6 Attribute Negotiation 2490 During security association negotiation Initiators present offers to 2491 Responders. Responders MUST select a single complete set of 2492 parameters from the offers (or reject all offers if none are 2493 acceptable). If there are multiple proposals, the Responder MUST 2494 choose a single proposal number and return all of the Proposal 2495 substructures with that Proposal number. If there are multiple 2496 Transforms with the same type the Responder MUST choose a single one. 2497 Any attributes of a selected transform MUST be returned unmodified. 2498 The Initiator of an exchange MUST check that the accepted offer is 2499 consistent with one of its proposals, and if not that response MUST 2500 be rejected. 2502 Negotiating Diffie-Hellman groups presents some special challenges. 2503 SA offers include proposed attributes and a Diffie-Hellman public 2504 number (KE) in the same message. If in the initial exchange the 2505 Initiator offers to use one of several Diffie-Hellman groups, it 2506 SHOULD pick the one the Responder is most likely to accept and 2507 include a KE corresponding to that group. If the guess turns out to 2508 be wrong, the Responder will indicate the correct group in the 2509 response and the Initiator SHOULD pick an element of that group for 2510 its KE value when retrying the first message. It SHOULD, however, 2511 continue to propose its full supported set of groups in order to 2512 prevent a man in the middle downgrade attack. 2514 Implementation Note: 2516 Certain negotiable attributes can have ranges or could have 2517 multiple acceptable values. These include the key length of a 2518 variable key length symmetric cipher. To further interoperability 2519 and to support upgrading endpoints independently, implementers of 2520 this protocol SHOULD accept values which they deem to supply 2521 greater security. For instance if a peer is configured to accept a 2522 variable lengthed cipher with a key length of X bits and is 2523 offered that cipher with a larger key length, the implementation 2524 SHOULD accept the offer if it supports use of the longer key. 2526 Support of this capability allows an implementation to express a 2527 concept of "at least" a certain level of security-- "a key length of 2528 _at least_ X bits for cipher Y". 2530 3.4 Key Exchange Payload 2532 The Key Exchange Payload, denoted KE in this memo, is used to 2533 exchange Diffie-Hellman public numbers as part of a Diffie-Hellman 2534 key exchange. The Key Exchange Payload consists of the IKE generic 2535 payload header followed by the Diffie-Hellman public value itself. 2537 1 2 3 2538 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 2539 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2540 ! Next Payload !C! RESERVED ! Payload Length ! 2541 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2542 ! DH Group # ! RESERVED ! 2543 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2544 ! ! 2545 ~ Key Exchange Data ~ 2546 ! ! 2547 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2549 Figure 10: Key Exchange Payload Format 2551 A key exchange payload is constructed by copying one's Diffie-Hellman 2552 public value into the "Key Exchange Data" portion of the payload. 2553 The length of the Diffie-Hellman public value MUST be equal to the 2554 length of the prime modulus over which the exponentiation was 2555 performed, prepending zero bits to the value if necessary. 2557 The DH Group # identifies the Diffie-Hellman group in which the Key 2558 Exchange Data was computed (see section 3.3.2). If the selected 2559 proposal uses a different Diffie-Hellman group, the message MUST be 2560 rejected with a Notify payload of type INVALID_KE_PAYLOAD. 2562 The payload type for the Key Exchange payload is thirty four (34). 2564 3.5 Identification Payloads 2566 The Identification Payloads, denoted IDi and IDr in this memo, allow 2567 peers to assert an identity to one another. This identity may be used 2568 for policy lookup, but does not necessarily have to match anything in 2569 the CERT payload; both fields may be used by an implementation to 2570 perform access control decisions. 2572 NOTE: In IKEv1, two ID payloads were used in each direction to hold 2573 Traffic Selector information for data passing over the SA. In IKEv2, 2574 this information is carried in Traffic Selector (TS) payloads (see 2575 section 3.13). 2577 The Identification Payload consists of the IKE generic payload header 2578 followed by identification fields as follows: 2580 1 2 3 2581 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 2582 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2583 ! Next Payload !C! RESERVED ! Payload Length ! 2584 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2585 ! ID Type ! RESERVED | 2586 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2587 ! ! 2588 ~ Identification Data ~ 2589 ! ! 2590 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2592 Figure 11: Identification Payload Format 2594 o ID Type (1 octet) - Specifies the type of Identification being 2595 used. 2597 o RESERVED - MUST be sent as zero; MUST be ignored on receipt. 2599 o Identification Data (variable length) - Value, as indicated by 2600 the Identification Type. The length of the Identification Data 2601 is computed from the size in the ID payload header. 2603 The payload types for the Identification Payload are thirty five (35) 2604 for IDi and thirty six (36) for IDr. 2606 The following table lists the assigned values for the Identification 2607 Type field, followed by a description of the Identification Data 2608 which follows: 2610 ID Type Value 2611 ------- ----- 2612 RESERVED 0 2614 ID_IPV4_ADDR 1 2616 A single four (4) octet IPv4 address. 2618 ID_FQDN 2 2620 A fully-qualified domain name string. An example of a 2621 ID_FQDN is, "example.com". The string MUST not contain any 2622 terminators (e.g., NULL, CR, etc.). 2624 ID_RFC822_ADDR 3 2626 A fully-qualified RFC822 email address string, An example of 2627 a ID_RFC822_ADDR is, "jsmith@example.com". The string MUST 2628 not contain any terminators. 2630 ID_IPV6_ADDR 5 2632 A single sixteen (16) octet IPv6 address. 2634 ID_DER_ASN1_DN 9 2636 The binary DER encoding of an ASN.1 X.500 Distinguished Name 2637 [X.501]. 2639 ID_DER_ASN1_GN 10 2641 The binary DER encoding of an ASN.1 X.500 GeneralName 2642 [X.509]. 2644 ID_KEY_ID 11 2646 An opaque octet stream which may be used to pass vendor- 2647 specific information necessary to do certain proprietary 2648 types of identification. 2650 Reserved to IANA 12-200 2652 Reserved for private use 201-255 2654 Two implementations will interoperate only if each can generate a 2655 type of ID acceptable to the other. To assure maximum 2656 interoperability, implementations MUST be configurable to send at 2657 least one of ID_IPV4_ADDR, ID_FQDN, ID_RFC822_ADDR, or ID_KEY_ID, and 2658 MUST be configurable to accept all of these types. Implementations 2659 SHOULD be capable of generating and accepting all of these types. 2661 3.6 Certificate Payload 2663 The Certificate Payload, denoted CERT in this memo, provides a means 2664 to transport certificates or other authentication related information 2665 via IKE. Certificate payloads SHOULD be included in an exchange if 2666 certificates are available to the sender unless the peer has 2667 indicated an ability to retrieve this information from elsewhere 2668 using an HTTP_CERT_LOOKUP_SUPPORTED Notify payload. Note that the 2669 term "Certificate Payload" is somewhat misleading, because not all 2670 authentication mechanisms use certificates and data other than 2671 certificates may be passed in this payload. 2673 The Certificate Payload is defined as follows: 2675 1 2 3 2676 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 2677 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2678 ! Next Payload !C! RESERVED ! Payload Length ! 2679 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2680 ! Cert Encoding ! ! 2681 +-+-+-+-+-+-+-+-+ ! 2682 ~ Certificate Data ~ 2683 ! ! 2684 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2686 Figure 12: Certificate Payload Format 2688 o Certificate Encoding (1 octet) - This field indicates the type 2689 of certificate or certificate-related information contained 2690 in the Certificate Data field. 2692 Certificate Encoding Value 2693 -------------------- ----- 2694 RESERVED 0 2695 PKCS #7 wrapped X.509 certificate 1 2696 PGP Certificate 2 2697 DNS Signed Key 3 2698 X.509 Certificate - Signature 4 2699 Kerberos Token 6 2700 Certificate Revocation List (CRL) 7 2701 Authority Revocation List (ARL) 8 2702 SPKI Certificate 9 2703 X.509 Certificate - Attribute 10 2704 Raw RSA Key 11 2705 Hash and URL of X.509 certificate 12 2706 Hash and URL of X.509 bundle 13 2707 RESERVED to IANA 14 - 200 2708 PRIVATE USE 201 - 255 2710 o Certificate Data (variable length) - Actual encoding of 2711 certificate data. The type of certificate is indicated 2712 by the Certificate Encoding field. 2714 The payload type for the Certificate Payload is thirty seven (37). 2716 Specific syntax is for some of the certificate type codes above is 2717 not defined in this document. The types whose syntax is defined in 2718 this document are: 2720 X.509 Certificate - Signature (4) contains a BER encoded X.509 2721 certificate whose public key is used to validate the sender's AUTH 2722 payload. 2724 Certificate Revocation List (7) contains a BER encoded X.509 2725 certificate revocation list. 2727 Raw RSA Key (11) contains a PKCS #1 encoded RSA key. 2729 Hash and URL encodings (12-13) allow IKE messages to remain short 2730 by replacing long data structures with a 20 octet SHA-1 hash of 2731 the replaced value followed by a variable length URL that resolves 2732 to the BER encoded data structure itself. This improves efficiency 2733 when the endpoints have certificate data cached and makes IKE less 2734 subject to denial of service attacks that become easier to mount 2735 when IKE messages are large enough to require IP fragmentation 2736 [KPS03]. 2738 Use the following ASN.1 definition for an X.509 bundle: 2740 CertBundle 2741 { iso(1) identified-organization(3) dod(6) internet(1) 2742 security(5) mechanisms(5) pkix(7) id-mod(0) 2743 id-mod-cert-bundle(34) } 2745 DEFINITIONS EXPLICIT TAGS :: 2746 BEGIN 2748 IMPORTS 2749 Certificate, CertificateList 2750 FROM PKIX1Explicit88 2751 { iso(1) identified-organization(3) dod(6) 2752 internet(1) security(5) mechanisms(5) pkix(7) 2753 id-mod(0) id-pkix1-explicit(18) } ; 2755 CertificateOrCRL ::= CHOICE { 2756 cert [0] Certificate, 2757 crl [1] CertificateList } 2759 CertificateBundle ::= SEQUENCE OF CertificateOrCRL 2761 END 2763 Implementations MUST be capable of being configured to send and 2764 accept up to four X.509 certificates in support of authentication. 2765 Implementations SHOULD be capable of being configured to send and 2766 accept Raw RSA keys and the first two Hash and URL formats. If 2767 multiple certificates are sent, the first certificate MUST contain 2768 the public key used to sign the AUTH payload. The other certificates 2769 may be sent in any order. 2771 3.7 Certificate Request Payload 2773 The Certificate Request Payload, denoted CERTREQ in this memo, 2774 provides a means to request preferred certificates via IKE and can 2775 appear in the IKE_INIT_SA response and/or the IKE_AUTH request. 2776 Certificate Request payloads MAY be included in an exchange when the 2777 sender needs to get the certificate of the receiver. If multiple CAs 2778 are trusted and the cert encoding does not allow a list, then 2779 multiple Certificate Request payloads SHOULD be transmitted. 2781 The Certificate Request Payload is defined as follows: 2783 1 2 3 2784 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 2785 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2786 ! Next Payload !C! RESERVED ! Payload Length ! 2787 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2788 ! Cert Encoding ! ! 2789 +-+-+-+-+-+-+-+-+ ! 2790 ~ Certification Authority ~ 2791 ! ! 2792 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2794 Figure 13: Certificate Request Payload Format 2796 o Certificate Encoding (1 octet) - Contains an encoding of the type 2797 or format of certificate requested. Values are listed in section 2798 3.6. 2800 o Certification Authority (variable length) - Contains an encoding 2801 of an acceptable certification authority for the type of 2802 certificate requested. 2804 The payload type for the Certificate Request Payload is thirty eight 2805 (38). 2807 The Certificate Encoding field has the same values as those defined 2808 in section 3.6. The Certification Authority field contains an 2809 indicator of trusted authorities for this certificate type. The 2810 Certification Authority value is a concatenated list of SHA-1 hashes 2811 of the public keys of trusted CAs. Each is encoded as the SHA-1 hash 2812 of the Subject Public Key Info element (see section 4.1.2.7 of 2813 [RFC3280]) from each Trust Anchor certificate. The twenty-octet 2814 hashes are concatenated and included with no other formatting. 2816 Note that the term "Certificate Request" is somewhat misleading, in 2817 that values other than certificates are defined in a "Certificate" 2818 payload and requests for those values can be present in a Certificate 2819 Request Payload. The syntax of the Certificate Request payload in 2820 such cases is not defined in this document. 2822 The Certificate Request Payload is processed by inspecting the "Cert 2823 Encoding" field to determine whether the processor has any 2824 certificates of this type. If so the "Certification Authority" field 2825 is inspected to determine if the processor has any certificates which 2826 can be validated up to one of the specified certification 2827 authorities. This can be a chain of certificates. 2829 If an end-entity certificate exists which satisfies the criteria 2830 specified in the CERTREQ, a certificate or certificate chain SHOULD 2831 be sent back to the certificate requestor if: 2833 - the recipient of the CERTREQ is configured to use certificate 2834 authentication, 2836 - is allowed to send a CERT payload, 2838 - has matching CA trust policy governing the current negotiation, 2839 and 2841 - has at least one time-wise and usage appropriate end-entity 2842 certificate chaining to a CA provided in the CERTREQ. 2844 Certificate revocation checking must be considered during the 2845 chaining process used to select a certificate. Note that even if two 2846 peers are configured to use two different CAs, cross-certification 2847 relationships should be supported by appropriate selection logic. The 2848 intent is not to prevent communication through the strict adherence 2849 of selection of a certificate based on CERTREQ, when an alternate 2850 certificate could be selected by the sender which would still enable 2851 the recipient to successfully validate and trust it through trust 2852 conveyed by cross-certification, CRLs or other out-of-band configured 2853 means. Thus the processing of a CERTREQ CA name should be seen as a 2854 suggestion for a certificate to select, not a mandated one. If no 2855 certificates exist then the CERTREQ is ignored. This is not an error 2856 condition of the protocol. There may be cases where there is a 2857 preferred CA sent in the CERTREQ, but an alternate might be 2858 acceptable (perhaps after prompting a human operator)." 2860 3.8 Authentication Payload 2862 The Authentication Payload, denoted AUTH in this memo, contains data 2863 used for authentication purposes. The syntax of the Authentication 2864 data varies according to the Auth Method as specified below. 2866 The Authentication Payload is defined as follows: 2868 1 2 3 2869 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 2870 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2871 ! Next Payload !C! RESERVED ! Payload Length ! 2872 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2873 ! Auth Method ! RESERVED ! 2874 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2875 ! ! 2876 ~ Authentication Data ~ 2877 ! ! 2878 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2880 Figure 14: Authentication Payload Format 2882 o Auth Method (1 octet) - Specifies the method of authentication 2883 used. Values defined are: 2885 RSA Digital Signature (1) - Computed as specified in section 2886 2.15 using an RSA private key over a PKCS#1 padded hash. 2888 Shared Key Message Integrity Code (2) - Computed as specified in 2889 section 2.15 using the shared key associated with the identity 2890 in the ID payload and the negotiated prf function 2892 DSS Digital Signature (3) - Computed as specified in section 2893 2.15 using a DSS private key over a SHA-1 hash. 2895 The values 0 and 4-200 are reserved to IANA. The values 201-255 2896 are available for private use. 2898 o Authentication Data (variable length) - see section 2.15. 2900 The payload type for the Authentication Payload is thirty nine (39). 2902 3.9 Nonce Payload 2904 The Nonce Payload, denoted Ni and Nr in this memo for the Initiator's 2905 and Responder's nonce respectively, contains random data used to 2906 guarantee liveness during an exchange and protect against replay 2907 attacks. 2909 The Nonce Payload is defined as follows: 2911 1 2 3 2912 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 2913 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2914 ! Next Payload !C! RESERVED ! Payload Length ! 2915 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2916 ! ! 2917 ~ Nonce Data ~ 2918 ! ! 2919 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2921 Figure 15: Nonce Payload Format 2923 o Nonce Data (variable length) - Contains the random data generated 2924 by the transmitting entity. 2926 The payload type for the Nonce Payload is forty (40). 2928 The size of a Nonce MUST be between 16 and 256 octets inclusive. 2929 Nonce values MUST NOT be reused. 2931 3.10 Notify Payload 2933 The Notify Payload, denoted N in this document, is used to transmit 2934 informational data, such as error conditions and state transitions, 2935 to an IKE peer. A Notify Payload may appear in a response message 2936 (usually specifying why a request was rejected), in an INFORMATIONAL 2937 Exchange (to report an error not in an IKE request), or in any other 2938 message to indicate sender capabilities or to modify the meaning of 2939 the request. 2941 The Notify Payload is defined as follows: 2943 1 2 3 2944 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 2945 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2946 ! Next Payload !C! RESERVED ! Payload Length ! 2947 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2948 ! Protocol ID ! SPI Size ! Notify Message Type ! 2949 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2950 ! ! 2951 ~ Security Parameter Index (SPI) ~ 2952 ! ! 2953 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2954 ! ! 2955 ~ Notification Data ~ 2956 ! ! 2957 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2959 Figure 16: Notification Payload Format 2961 o Protocol ID (1 octet) - If this notification concerns 2962 an existing SA, this field indicates the type of that SA. 2963 For IKE_SA notifications, this field MUST be one (1). For 2964 notifications concerning IPsec SAs this field MUST contain 2965 either (2) to indicate AH or (3) to indicate ESP. For 2966 notifications which do not relate to an existing SA, this 2967 field MUST be sent as zero and MUST be ignored on receipt. 2968 All other values for this field are reserved to IANA for future 2969 assignment. 2971 o SPI Size (1 octet) - Length in octets of the SPI as defined by 2972 the IPsec protocol ID or zero if no SPI is applicable. For a 2973 notification concerning the IKE_SA, the SPI Size MUST be zero. 2975 o Notify Message Type (2 octets) - Specifies the type of 2976 notification message. 2978 o SPI (variable length) - Security Parameter Index. 2980 o Notification Data (variable length) - Informational or error data 2981 transmitted in addition to the Notify Message Type. Values for 2982 this field are type specific (see below). 2984 The payload type for the Notification Payload is forty one (41). 2986 3.10.1 Notify Message Types 2988 Notification information can be error messages specifying why an SA 2989 could not be established. It can also be status data that a process 2990 managing an SA database wishes to communicate with a peer process. 2991 The table below lists the Notification messages and their 2992 corresponding values. The number of different error statuses was 2993 greatly reduced from IKE V1 both for simplification and to avoid 2994 giving configuration information to probers. 2996 Types in the range 0 - 16383 are intended for reporting errors. An 2997 implementation receiving a Notify payload with one of these types 2998 that it does not recognize in a response MUST assume that the 2999 corresponding request has failed entirely. Unrecognized error types 3000 in a request and status types in a request or response MUST be 3001 ignored except that they SHOULD be logged. 3003 Notify payloads with status types MAY be added to any message and 3004 MUST be ignored if not recognized. They are intended to indicate 3005 capabilities, and as part of SA negotiation are used to negotiate 3006 non-cryptographic parameters. 3008 NOTIFY MESSAGES - ERROR TYPES Value 3009 ----------------------------- ----- 3010 UNSUPPORTED_CRITICAL_PAYLOAD 1 3012 Sent if the payload has the "critical" bit set and the 3013 payload type is not recognized. Notification Data contains 3014 the one octet payload type. 3016 INVALID_IKE_SPI 4 3018 Indicates an IKE message was received with an unrecognized 3019 destination SPI. This usually indicates that the recipient 3020 has rebooted and forgotten the existence of an IKE_SA. 3022 INVALID_MAJOR_VERSION 5 3024 Indicates the recipient cannot handle the version of IKE 3025 specified in the header. The closest version number that the 3026 recipient can support will be in the reply header. 3028 INVALID_SYNTAX 7 3030 Indicates the IKE message was received was invalid because 3031 some type, length, or value was out of range or because the 3032 request was rejected for policy reasons. To avoid a denial 3033 of service attack using forged messages, this status may 3034 only be returned for and in an encrypted packet if the 3035 message ID and cryptographic checksum were valid. To avoid 3036 leaking information to someone probing a node, this status 3037 MUST be sent in response to any error not covered by one of 3038 the other status types. To aid debugging, more detailed 3039 error information SHOULD be written to a console or log. 3041 INVALID_MESSAGE_ID 9 3043 Sent when an IKE message ID outside the supported window is 3044 received. This Notify MUST NOT be sent in a response; the 3045 invalid request MUST NOT be acknowledged. Instead, inform 3046 the other side by initiating an INFORMATIONAL exchange with 3047 Notification data containing the four octet invalid message 3048 ID. Sending this notification is optional and notifications 3049 of this type MUST be rate limited. 3051 INVALID_SPI 11 3053 MAY be sent in an IKE INFORMATIONAL Exchange when a node 3054 receives an ESP or AH packet with an invalid SPI. The 3055 Notification Data contains the SPI of the invalid packet. 3056 This usually indicates a node has rebooted and forgotten an 3057 SA. If this Informational Message is sent outside the 3058 context of an IKE_SA, it should only be used by the 3059 recipient as a "hint" that something might be wrong (because 3060 it could easily be forged). 3062 NO_PROPOSAL_CHOSEN 14 3064 None of the proposed crypto suites was acceptable. 3066 INVALID_KE_PAYLOAD 17 3068 The D-H Group # field in the KE payload is not the group # 3069 selected by the responder for this exchange. There are two 3070 octets of data associated with this notification: the 3071 accepted D-H Group # in big endian order. 3073 AUTHENTICATION_FAILED 24 3075 Sent in the response to an IKE_AUTH message when for some 3076 reason the authentication failed. There is no associated 3077 data. 3079 SINGLE_PAIR_REQUIRED 34 3081 This error indicates that a CREATE_CHILD_SA request is 3082 unacceptable because its sender is only willing to accept 3083 traffic selectors specifying a single pair of addresses. 3084 The requestor is expected to respond by requesting an SA for 3085 only the specific traffic he is trying to forward. 3087 NO_ADDITIONAL_SAS 35 3089 This error indicates that a CREATE_CHILD_SA request is 3090 unacceptable because the Responder is unwilling to accept 3091 any more CHILD_SAs on this IKE_SA. Some minimal 3092 implementations may only accept a single CHILD_SA setup in 3093 the context of an initial IKE exchange and reject any 3094 subsequent attempts to add more. 3096 INTERNAL_ADDRESS_FAILURE 36 3098 Indicates an error assigning an internal address (i.e., 3099 INTERNAL_IP4_ADDRESS or INTERNAL_IP6_ADDRESS) during the 3100 processing of a Configuration Payload by a Responder. If 3101 this error is generated within an IKE_AUTH exchange no 3102 CHILD_SA will be created. 3104 FAILED_CP_REQUIRED 37 3106 Sent by responder in the case where CP(CFG_REQUEST) was 3107 expected but not received, and so is a conflict with locally 3108 configured policy. There is no associated data. 3110 TS_UNACCEPTABLE 38 3112 Indicates that none of the addresses/protocols/ports in the 3113 supplied traffic selectors is acceptable. 3115 INVALID_SELECTORS 39 3117 MAY be sent in an IKE INFORMATIONAL Exchange when a node 3118 receives an ESP or AH packet whose selectors do not match 3119 those of the SA on which it was delivered (and which caused 3120 the packet to be dropped). The Notification Data contains 3121 the start of the offending packet (as in ICMP messages) and 3122 the SPI field of the notification is set to match the SPI of 3123 the IPsec SA. 3124 RESERVED TO IANA - Error types 39 - 8191 3126 Private Use - Errors 8192 - 16383 3127 NOTIFY MESSAGES - STATUS TYPES Value 3128 ------------------------------ ----- 3130 INITIAL_CONTACT 16384 3132 This notification asserts that this IKE_SA is the only 3133 IKE_SA currently active between the authenticated 3134 identities. It MAY be sent when an IKE_SA is established 3135 after a crash, and the recipient MAY use this information to 3136 delete any other IKE_SAs it has to the same authenticated 3137 identity without waiting for a timeout. This notification 3138 MUST NOT be sent by an entity that may be replicated (e.g., 3139 a roaming user's credentials where the user is allowed to 3140 connect to the corporate firewall from two remote systems at 3141 the same time). 3143 SET_WINDOW_SIZE 16385 3145 This notification asserts that the sending endpoint is 3146 capable of keeping state for multiple outstanding exchanges, 3147 permitting the recipient to send multiple requests before 3148 getting a response to the first. The data associated with a 3149 SET_WINDOW_SIZE notification MUST be 4 octets long and 3150 contain the big endian representation of the number of 3151 messages the sender promises to keep. Window size is always 3152 one until the initial exchanges complete. 3154 ADDITIONAL_TS_POSSIBLE 16386 3156 This notification asserts that the sending endpoint narrowed 3157 the proposed traffic selectors but that other traffic 3158 selectors would also have been acceptable, though only in a 3159 separate SA (see section 2.9). There is no data associated 3160 with this Notify type. It may only be sent as an additional 3161 payload in a message including accepted TSs. 3163 IPCOMP_SUPPORTED 16387 3165 This notification may only be included in a message 3166 containing an SA payload negotiating a CHILD_SA and 3167 indicates a willingness by its sender to use IPComp on this 3168 SA. The data associated with this notification includes a 3169 two octet IPComp CPI followed by a one octet transform ID 3170 optionally followed by attributes whose length and format is 3171 defined by that transform ID. A message proposing an SA may 3172 contain multiple IPCOMP_SUPPORTED notifications to indicate 3173 multiple supported algorithms. A message accepting an SA may 3174 contain at most one. 3176 The transform IDs currently defined are: 3178 NAME NUMBER DEFINED IN 3179 ----------- ------ ----------- 3180 RESERVED 0 3181 IPCOMP_OUI 1 3182 IPCOMP_DEFLATE 2 RFC 2394 3183 IPCOMP_LZS 3 RFC 2395 3184 IPCOMP_LZJH 4 RFC 3051 3186 values 5-240 are reserved to IANA. Values 241-255 are 3187 for private use among mutually consenting parties. 3189 NAT_DETECTION_SOURCE_IP 16388 3191 This notification is used by its recipient to determine 3192 whether the source is behind a NAT box. The data associated 3193 with this notification is a SHA-1 digest of the SPIs (in the 3194 order they appear in the header), IP address and port on 3195 which this packet was sent. There MAY be multiple Notify 3196 payloads of this type in a message if the sender does not 3197 know which of several network attachments will be used to 3198 send the packet. The recipient of this notification MAY 3199 compare the supplied value to a SHA-1 hash of the SPIs, 3200 source IP address and port and if they don't match it SHOULD 3201 enable NAT traversal (see section 2.23). Alternately, it 3202 MAY reject the connection attempt if NAT traversal is not 3203 supported. 3205 NAT_DETECTION_DESTINATION_IP 16389 3207 This notification is used by its recipient to determine 3208 whether it is behind a NAT box. The data associated with 3209 this notification is a SHA-1 digest of the SPIs (in the 3210 order they appear in the header), IP address and port to 3211 which this packet was sent. The recipient of this 3212 notification MAY compare the supplied value to a hash of the 3213 SPIs, destination IP address and port and if they don't 3214 match it SHOULD invoke NAT traversal (see section 2.23). If 3215 they don't match, it means that this end is behind a NAT and 3216 this end SHOULD start sending keepalive packets as defined 3217 in [Hutt04]. Alternately, it MAY reject the connection 3218 attempt if NAT traversal is not supported. 3220 COOKIE 16390 3222 This notification MAY be included in an IKE_SA_INIT 3223 response. It indicates that the request should be retried 3224 with a copy of this notification as the first payload. This 3225 notification MUST be included in an IKE_SA_INIT request 3226 retry if a COOKIE notification was included in the initial 3227 response. The data associated with this notification MUST 3228 be between 1 and 64 octets in length (inclusive). 3230 USE_TRANSPORT_MODE 16391 3232 This notification MAY be included in a request message that 3233 also includes an SA requesting a CHILD_SA. It requests that 3234 the CHILD_SA use transport mode rather than tunnel mode for 3235 the SA created. If the request is accepted, the response 3236 MUST also include a notification of type USE_TRANSPORT_MODE. 3237 If the responder declines the request, the CHILD_SA will be 3238 established in tunnel mode. If this is unacceptable to the 3239 initiator, the initiator MUST delete the SA. Note: except 3240 when using this option to negotiate transport mode, all 3241 CHILD_SAs will use tunnel mode. 3243 Note: The ECN decapsulation modifications specified in 3244 [RFC2401bis] MUST be performed for every tunnel mode SA 3245 created by IKEv2. 3247 HTTP_CERT_LOOKUP_SUPPORTED 16392 3249 This notification MAY be included in any message that can 3250 include a CERTREQ payload and indicates that the sender is 3251 capable of looking up certificates based on an HTTP-based 3252 URL (and hence presumably would prefer to receive 3253 certificate specifications in that format). 3255 REKEY_SA 16393 3257 This notification MUST be included in a CREATE_CHILD_SA 3258 exchange if the purpose of the exchange is to replace an 3259 existing ESP or AH SA. The SPI field identifies the SA being 3260 rekeyed. There is no data. 3262 ESP_TFC_PADDING_NOT_SUPPORTED 16394 3264 This notification asserts that the sending endpoint will NOT 3265 accept packets that contain Flow Confidentiality (TFC) 3266 padding. 3268 NON_FIRST_FRAGMENTS_ALSO 16395 3270 Used for fragmentation control. See [2401bis] for 3271 explanation. 3273 RESERVED TO IANA - STATUS TYPES 16396 - 40959 3275 Private Use - STATUS TYPES 40960 - 65535 3277 3.11 Delete Payload 3279 The Delete Payload, denoted D in this memo, contains a protocol 3280 specific security association identifier that the sender has removed 3281 from its security association database and is, therefore, no longer 3282 valid. Figure 17 shows the format of the Delete Payload. It is 3283 possible to send multiple SPIs in a Delete payload, however, each SPI 3284 MUST be for the same protocol. Mixing of protocol identifiers MUST 3285 NOT be performed in a the Delete payload. It is permitted, however, 3286 to include multiple Delete payloads in a single INFORMATIONAL 3287 Exchange where each Delete payload lists SPIs for a different 3288 protocol. 3290 Deletion of the IKE_SA is indicated by a protocol ID of 1 (IKE) but 3291 no SPIs. Deletion of a CHILD_SA, such as ESP or AH, will contain the 3292 IPsec protocol ID of that protocol (2 for AH, 3 for ESP) and the SPI 3293 is the SPI the sending endpoint would expect in inbound ESP or AH 3294 packets. 3296 The Delete Payload is defined as follows: 3298 1 2 3 3299 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 3300 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3301 ! Next Payload !C! RESERVED ! Payload Length ! 3302 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3303 ! Protocol ID ! SPI Size ! # of SPIs ! 3304 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3305 ! ! 3306 ~ Security Parameter Index(es) (SPI) ~ 3307 ! ! 3308 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3310 Figure 17: Delete Payload Format 3312 o Protocol ID (1 octet) - Must be 1 for an IKE_SA, 2 for AH, or 3313 3 for ESP. 3315 o SPI Size (1 octet) - Length in octets of the SPI as defined by 3316 the protocol ID. It MUST be zero for IKE (SPI is in message 3317 header) or four for AH and ESP. 3319 o # of SPIs (2 octets) - The number of SPIs contained in the Delete 3320 payload. The size of each SPI is defined by the SPI Size field. 3322 o Security Parameter Index(es) (variable length) - Identifies the 3323 specific security association(s) to delete. The length of this 3324 field is determined by the SPI Size and # of SPIs fields. 3326 The payload type for the Delete Payload is forty two (42). 3328 3.12 Vendor ID Payload 3330 The Vendor ID Payload contains a vendor defined constant. The 3331 constant is used by vendors to identify and recognize remote 3332 instances of their implementations. This mechanism allows a vendor 3333 to experiment with new features while maintaining backwards 3334 compatibility. 3336 A Vendor ID payload MAY announce that the sender is capable to 3337 accepting certain extensions to the protocol, or it MAY simply 3338 identify the implementation as an aid in debugging. A Vendor ID 3339 payload MUST NOT change the interpretation of any information defined 3340 in this specification (i.e., it MUST be non-critical). Multiple 3341 Vendor ID payloads MAY be sent. An implementation is NOT REQUIRED to 3342 send any Vendor ID payload at all. 3344 A Vendor ID payload may be sent as part of any message. Reception of 3345 a familiar Vendor ID payload allows an implementation to make use of 3346 Private USE numbers described throughout this memo-- private 3347 payloads, private exchanges, private notifications, etc. Unfamiliar 3348 Vendor IDs MUST be ignored. 3350 Writers of Internet-Drafts who wish to extend this protocol MUST 3351 define a Vendor ID payload to announce the ability to implement the 3352 extension in the Internet-Draft. It is expected that Internet-Drafts 3353 which gain acceptance and are standardized will be given "magic 3354 numbers" out of the Future Use range by IANA and the requirement to 3355 use a Vendor ID will go away. 3357 The Vendor ID Payload fields are defined as follows: 3359 1 2 3 3360 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 3361 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3362 ! Next Payload !C! RESERVED ! Payload Length ! 3363 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3364 ! ! 3365 ~ Vendor ID (VID) ~ 3366 ! ! 3367 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3369 Figure 18: Vendor ID Payload Format 3371 o Vendor ID (variable length) - It is the responsibility of 3372 the person choosing the Vendor ID to assure its uniqueness 3373 in spite of the absence of any central registry for IDs. 3374 Good practice is to include a company name, a person name 3375 or some such. If you want to show off, you might include 3376 the latitude and longitude and time where you were when 3377 you chose the ID and some random input. A message digest 3378 of a long unique string is preferable to the long unique 3379 string itself. 3381 The payload type for the Vendor ID Payload is forty three (43). 3383 3.13 Traffic Selector Payload 3385 The Traffic Selector Payload, denoted TS in this memo, allows peers 3386 to identify packet flows for processing by IPsec security services. 3387 The Traffic Selector Payload consists of the IKE generic payload 3388 header followed by individual traffic selectors as follows: 3390 1 2 3 3391 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 3392 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3393 ! Next Payload !C! RESERVED ! Payload Length ! 3394 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3395 ! Number of TSs ! RESERVED ! 3396 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3397 ! ! 3398 ~ ~ 3399 ! ! 3400 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3402 Figure 19: Traffic Selectors Payload Format 3404 o Number of TSs (1 octet) - Number of traffic selectors 3405 being provided. 3407 o RESERVED - This field MUST be sent as zero and MUST be ignored 3408 on receipt. 3410 o Traffic Selectors (variable length) - one or more individual 3411 traffic selectors. 3413 The length of the Traffic Selector payload includes the TS header and 3414 all the traffic selectors. 3416 The payload type for the Traffic Selector payload is forty four (44) 3417 for addresses at the initiator's end of the SA and forty five (45) 3418 for addresses at the responder's end. 3420 3.13.1 Traffic Selector 3422 1 2 3 3423 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 3424 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3425 ! TS Type !IP Protocol ID*| Selector Length | 3426 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3427 | Start Port* | End Port* | 3428 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3429 ! ! 3430 ~ Starting Address* ~ 3431 ! ! 3432 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3433 ! ! 3434 ~ Ending Address* ~ 3435 ! ! 3436 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3438 Figure 20: Traffic Selector 3440 *Note: all fields other than TS Type and Selector Length depend on 3441 the TS Type. The fields shown are for TS Types 7 and 8, the only two 3442 values currently defined. 3444 o TS Type (one octet) - Specifies the type of traffic selector. 3446 o IP protocol ID (1 octet) - Value specifying an associated IP 3447 protocol ID (e.g., UDP/TCP/ICMP). A value of zero means that 3448 the protocol ID is not relevant to this traffic selector-- 3449 the SA can carry all protocols. 3451 o Selector Length - Specifies the length of this Traffic 3452 Selector Substructure including the header. 3454 o Start Port (2 octets) - Value specifying the smallest port 3455 number allowed by this Traffic Selector. For protocols for 3456 which port is undefined, or if all ports are allowed, 3457 this field MUST be zero. For the 3458 ICMP protocol, the two one octet fields Type and Code are 3459 treated as a single 16 bit integer (with Type in the most 3460 significant eight bits and Code in the least significant 3461 eight bits) port number for the purposes of filtering based 3462 on this field. 3464 o End Port (2 octets) - Value specifying the largest port 3465 number allowed by this Traffic Selector. For protocols for 3466 which port is undefined, or if all ports are allowed, 3467 this field MUST be 65535. For the 3468 ICMP protocol, the two one octet fields Type and Code are 3469 treated as a single 16 bit integer (with Type in the most 3470 significant eight bits and Code in the least significant 3471 eight bits) port number for the purposed of filtering based 3472 on this field. 3474 o Starting Address - The smallest address included in this 3475 Traffic Selector (length determined by TS type). 3477 o Ending Address - The largest address included in this 3478 Traffic Selector (length determined by TS type). 3480 Systems that are complying with [RFC2401bis] that wish to indicate 3481 "ANY" ports MUST set the start port to 0 and the end port to 65535; 3482 note that according to [RFC2401bis], "ANY" includes "OPAQUE". Systems 3483 working with [RFC2401bis] that wish to indicate "OPAQUE" ports, but 3484 not "ANY" ports, MUST set the start port to 65535 and the end port to 3485 0. 3487 The following table lists the assigned values for the Traffic 3488 Selector Type field and the corresponding Address Selector Data. 3490 TS Type Value 3491 ------- ----- 3492 RESERVED 0-6 3494 TS_IPV4_ADDR_RANGE 7 3496 A range of IPv4 addresses, represented by two four (4) octet 3497 values. The first value is the beginning IPv4 address 3498 (inclusive) and the second value is the ending IPv4 address 3499 (inclusive). All addresses falling between the two specified 3500 addresses are considered to be within the list. 3502 TS_IPV6_ADDR_RANGE 8 3504 A range of IPv6 addresses, represented by two sixteen (16) 3505 octet values. The first value is the beginning IPv6 address 3506 (inclusive) and the second value is the ending IPv6 address 3507 (inclusive). All addresses falling between the two specified 3508 addresses are considered to be within the list. 3510 RESERVED TO IANA 9-240 3511 PRIVATE USE 241-255 3513 3.14 Encrypted Payload 3515 The Encrypted Payload, denoted SK{...} in this memo, contains other 3516 payloads in encrypted form. The Encrypted Payload, if present in a 3517 message, MUST be the last payload in the message. Often, it is the 3518 only payload in the message. 3520 The algorithms for encryption and integrity protection are negotiated 3521 during IKE_SA setup, and the keys are computed as specified in 3522 sections 2.14 and 2.18. 3524 The encryption and integrity protection algorithms are modeled after 3525 the ESP algorithms described in RFCs 2104, 2406, 2451. This document 3526 completely specifies the cryptographic processing of IKE data, but 3527 those documents should be consulted for design rationale. We assume a 3528 block cipher with a fixed block size and an integrity check algorithm 3529 that computes a fixed length checksum over a variable size message. 3531 The payload type for an Encrypted payload is forty six (46). The 3532 Encrypted Payload consists of the IKE generic payload header followed 3533 by individual fields as follows: 3535 1 2 3 3536 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 3537 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3538 ! Next Payload !C! RESERVED ! Payload Length ! 3539 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3540 ! Initialization Vector ! 3541 ! (length is block size for encryption algorithm) ! 3542 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3543 ! Encrypted IKE Payloads ! 3544 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3545 ! ! Padding (0-255 octets) ! 3546 +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+ 3547 ! ! Pad Length ! 3548 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3549 ~ Integrity Checksum Data ~ 3550 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3552 Figure 21: Encrypted Payload Format 3554 o Next Payload - The payload type of the first embedded payload. 3555 Note that this is an exception in the standard header format, 3556 since the Encrypted payload is the last payload in the 3557 message and therefore the Next Payload field would normally 3558 be zero. But because the content of this payload is embedded 3559 payloads and there was no natural place to put the type of 3560 the first one, that type is placed here. 3562 o Payload Length - Includes the lengths of the header, IV, 3563 Encrypted IKE Payloads, Padding, Pad Length and Integrity 3564 Checksum Data. 3566 o Initialization Vector - A randomly chosen value whose length 3567 is equal to the block length of the underlying encryption 3568 algorithm. Recipients MUST accept any value. Senders SHOULD 3569 either pick this value pseudo-randomly and independently for 3570 each message or use the final ciphertext block of the previous 3571 message sent. Senders MUST NOT use the same value for each 3572 message, use a sequence of values with low hamming distance 3573 (e.g., a sequence number), or use ciphertext from a received 3574 message. 3576 o IKE Payloads are as specified earlier in this section. This 3577 field is encrypted with the negotiated cipher. 3579 o Padding MAY contain any value chosen by the sender, and MUST 3580 have a length that makes the combination of the Payloads, the 3581 Padding, and the Pad Length to be a multiple of the encryption 3582 block size. This field is encrypted with the negotiated 3583 cipher. 3585 o Pad Length is the length of the Padding field. The sender 3586 SHOULD set the Pad Length to the minimum value that makes 3587 the combination of the Payloads, the Padding, and the Pad 3588 Length a multiple of the block size, but the recipient MUST 3589 accept any length that results in proper alignment. This 3590 field is encrypted with the negotiated cipher. 3592 o Integrity Checksum Data is the cryptographic checksum of 3593 the entire message starting with the Fixed IKE Header 3594 through the Pad Length. The checksum MUST be computed over 3595 the encrypted message. Its length is determined by the 3596 integrity algorithm negotiated. 3598 3.15 Configuration Payload 3600 The Configuration payload, denoted CP in this document, is used to 3601 exchange configuration information between IKE peers. The exchange is 3602 for an IRAC to request an internal IP address from an IRAS and to 3603 exchange other information of the sort that one would acquire with 3604 DHCP if the IRAC were directly connected to a LAN. 3606 Configuration payloads are of type CFG_REQUEST/CFG_REPLY or 3607 CFG_SET/CFG_ACK (see CFG Type in the payload description below). 3608 CFG_REQUEST and CFG_SET payloads may optionally be added to any IKE 3609 request. The IKE response MUST include either a corresponding 3610 CFG_REPLY or CFG_ACK or a Notify payload with an error type 3611 indicating why the request could not be honored. An exception is that 3612 a minimal implementation MAY ignore all CFG_REQUEST and CFG_SET 3613 payloads, so a response message without a corresponding CFG_REPLY or 3614 CFG_ACK MUST be accepted as an indication that the request was not 3615 supported. 3617 "CFG_REQUEST/CFG_REPLY" allows an IKE endpoint to request information 3618 from its peer. If an attribute in the CFG_REQUEST Configuration 3619 Payload is not zero length it is taken as a suggestion for that 3620 attribute. The CFG_REPLY Configuration Payload MAY return that 3621 value, or a new one. It MAY also add new attributes and not include 3622 some requested ones. Requestors MUST ignore returned attributes that 3623 they do not recognize. 3625 Some attributes MAY be multi-valued, in which case multiple attribute 3626 values of the same type are sent and/or returned. Generally, all 3627 values of an attribute are returned when the attribute is requested. 3628 For some attributes (in this version of the specification only 3629 internal addresses), multiple requests indicates a request that 3630 multiple values be assigned. For these attributes, the number of 3631 values returned SHOULD NOT exceed the number requested. 3633 If the data type requested in a CFG_REQUEST is not recognized or not 3634 supported, the responder MUST NOT return an error type but rather 3635 MUST either send a CFG_REPLY which MAY be empty or a reply not 3636 containing a CFG_REPLY payload at all. Error returns are reserved for 3637 cases where the request is recognized but cannot be performed as 3638 requested or the request is badly formatted. 3640 "CFG_SET/CFG_ACK" allows an IKE endpoint to push configuration data 3641 to its peer. In this case the CFG_SET Configuration Payload contains 3642 attributes the initiator wants its peer to alter. The responder MUST 3643 return a Configuration Payload if it accepted any of the 3644 configuration data and it MUST contain the attributes that the 3645 responder accepted with zero length data. Those attributes that it 3646 did not accept MUST NOT be in the CFG_ACK Configuration Payload. If 3647 no attributes were accepted, the responder MUST return either an 3648 empty CFG_ACK payload or a response message without a CFG_ACK 3649 payload. There are currently no defined uses for the CFG_SET/CFG_ACK 3650 exchange, though they may be used in connection with extensions based 3651 on Vendor IDs. An minimal implementation of this specification MAY 3652 ignore CFG_SET payloads. 3654 Extensions via the CP payload SHOULD NOT be used for general purpose 3655 management. Its main intent is to provide a bootstrap mechanism to 3656 exchange information within IPsec from IRAS to IRAC. While it MAY be 3657 useful to use such a method to exchange information between some 3658 Security Gateways (SGW) or small networks, existing management 3659 protocols such as DHCP [DHCP], RADIUS [RADIUS], SNMP or LDAP [LDAP] 3660 should be preferred for enterprise management as well as subsequent 3661 information exchanges. 3663 The Configuration Payload is defined as follows: 3665 1 2 3 3666 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 3667 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3668 ! Next Payload !C! RESERVED ! Payload Length ! 3669 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3670 ! CFG Type ! RESERVED ! 3671 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3672 ! ! 3673 ~ Configuration Attributes ~ 3674 ! ! 3675 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3677 Figure 22: Configuration Payload Format 3679 The payload type for the Configuration Payload is forty seven (47). 3681 o CFG Type (1 octet) - The type of exchange represented by the 3682 Configuration Attributes. 3684 CFG Type Value 3685 =========== ==== 3686 RESERVED 0 3687 CFG_REQUEST 1 3688 CFG_REPLY 2 3689 CFG_SET 3 3690 CFG_ACK 4 3692 values 5-127 are reserved to IANA. Values 128-255 are for private 3693 use among mutually consenting parties. 3695 o RESERVED (3 octets) - MUST be sent as zero; MUST be ignored on 3696 receipt. 3698 o Configuration Attributes (variable length) - These are type 3699 length values specific to the Configuration Payload and are 3700 defined below. There may be zero or more Configuration 3701 Attributes in this payload. 3703 3.15.1 Configuration Attributes 3705 1 2 3 3706 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 3707 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3708 !R| Attribute Type ! Length | 3709 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3710 | | 3711 ~ Value ~ 3712 | | 3713 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3715 Figure 23: Configuration Attribute Format 3717 o Reserved (1 bit) - This bit MUST be set to zero and MUST be 3718 ignored on receipt. 3720 o Attribute Type (7 bits) - A unique identifier for each of the 3721 Configuration Attribute Types. 3723 o Length (2 octets) - Length in octets of Value. 3725 o Value (0 or more octets) - The variable length value of this 3726 Configuration Attribute. 3728 The following attribute types have been defined: 3730 Multi- 3731 Attribute Type Value Valued Length 3732 ======================= ===== ====== ================= 3733 RESERVED 0 3734 INTERNAL_IP4_ADDRESS 1 YES* 0 or 4 octets 3735 INTERNAL_IP4_NETMASK 2 NO 0 or 4 octets 3736 INTERNAL_IP4_DNS 3 YES 0 or 4 octets 3737 INTERNAL_IP4_NBNS 4 YES 0 or 4 octets 3738 INTERNAL_ADDRESS_EXPIRY 5 NO 0 or 4 octets 3739 INTERNAL_IP4_DHCP 6 YES 0 or 4 octets 3740 APPLICATION_VERSION 7 NO 0 or more 3741 INTERNAL_IP6_ADDRESS 8 YES* 0 or 17 octets 3742 RESERVED 9 3743 INTERNAL_IP6_DNS 10 YES 0 or 16 octets 3744 INTERNAL_IP6_NBNS 11 YES 0 or 16 octets 3745 INTERNAL_IP6_DHCP 12 YES 0 or 16 octets 3746 INTERNAL_IP4_SUBNET 13 NO 0 or 8 octets 3747 SUPPORTED_ATTRIBUTES 14 NO Multiple of 2 3748 INTERNAL_IP6_SUBNET 15 NO 17 octets 3750 * These attributes may be multi-valued on return only if 3751 multiple values were requested. 3753 Types 16-16383 are reserved to IANA. Values 16384-32767 are for 3754 private use among mutually consenting parties. 3756 o INTERNAL_IP4_ADDRESS, INTERNAL_IP6_ADDRESS - An address on the 3757 internal network, sometimes called a red node address or 3758 private address and MAY be a private address on the Internet. 3759 Multiple internal addresses MAY be requested by requesting 3760 multiple internal address attributes. The responder MAY only 3761 send up to the number of addresses requested. The 3762 INTERNAL_IP6_ADDRESS is made up of two fields; the first 3763 being a 16 octet IPv6 address and the second being a one octet 3764 prefix-length as defined in [ADDRIPV6]. 3766 The requested address is valid until the expiry time defined 3767 with the INTERNAL_ADDRESS EXPIRY attribute or there are no 3768 IKE_SAs between the peers. 3770 o INTERNAL_IP4_NETMASK - The internal network's netmask. Only 3771 one netmask is allowed in the request and reply messages 3772 (e.g., 255.255.255.0) and it MUST be used only with an 3773 INTERNAL_IP4_ADDRESS attribute. 3775 o INTERNAL_IP4_DNS, INTERNAL_IP6_DNS - Specifies an address of a 3776 DNS server within the network. Multiple DNS servers MAY be 3777 requested. The responder MAY respond with zero or more DNS 3778 server attributes. 3780 o INTERNAL_IP4_NBNS, INTERNAL_IP6_NBNS - Specifies an address of 3781 a NetBios Name Server (WINS) within the network. Multiple NBNS 3782 servers MAY be requested. The responder MAY respond with zero 3783 or more NBNS server attributes. 3785 o INTERNAL_ADDRESS_EXPIRY - Specifies the number of seconds that 3786 the host can use the internal IP address. The host MUST renew 3787 the IP address before this expiry time. Only one of these 3788 attributes MAY be present in the reply. 3790 o INTERNAL_IP4_DHCP, INTERNAL_IP6_DHCP - Instructs the host to 3791 send any internal DHCP requests to the address contained within 3792 the attribute. Multiple DHCP servers MAY be requested. The 3793 responder MAY respond with zero or more DHCP server attributes. 3795 o APPLICATION_VERSION - The version or application information of 3796 the IPsec host. This is a string of printable ASCII characters 3797 that is NOT null terminated. 3799 o INTERNAL_IP4_SUBNET - The protected sub-networks that this 3800 edge-device protects. This attribute is made up of two fields; 3801 the first being an IP address and the second being a netmask. 3802 Multiple sub-networks MAY be requested. The responder MAY 3803 respond with zero or more sub-network attributes. 3805 o SUPPORTED_ATTRIBUTES - When used within a Request, this 3806 attribute MUST be zero length and specifies a query to the 3807 responder to reply back with all of the attributes that it 3808 supports. The response contains an attribute that contains a 3809 set of attribute identifiers each in 2 octets. The length 3810 divided by 2 (octets) would state the number of supported 3811 attributes contained in the response. 3813 o INTERNAL_IP6_SUBNET - The protected sub-networks that this 3814 edge-device protects. This attribute is made up of two fields; 3815 the first being a 16 octet IPv6 address the second being a one 3816 octet prefix-length as defined in [ADDRIPV6]. Multiple 3817 sub-networks MAY be requested. The responder MAY respond with 3818 zero or more sub-network attributes. 3820 Note that no recommendations are made in this document how an 3821 implementation actually figures out what information to send in a 3822 reply. i.e., we do not recommend any specific method of an IRAS 3823 determining which DNS server should be returned to a requesting 3824 IRAC. 3826 3.16 Extended Authentication Protocol (EAP) Payload 3828 The Extended Authentication Protocol Payload, denoted EAP in this 3829 memo, allows IKE_SAs to be authenticated using the protocol defined 3830 in RFC 2284 [EAP] and subsequent extensions to that protocol. The 3831 full set of acceptable values for the payload are defined elsewhere, 3832 but a short summary of RFC 2284 is included here to make this 3833 document stand alone in the common cases. 3835 1 2 3 3836 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 3837 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3838 ! Next Payload !C! RESERVED ! Payload Length ! 3839 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3840 ! ! 3841 ~ EAP Message ~ 3842 ! ! 3843 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3845 Figure 24: EAP Payload Format 3847 The payload type for an EAP Payload is forty eight (48). 3849 1 2 3 3850 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 3851 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3852 ! Code ! Identifier ! Length ! 3853 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3854 ! Type ! Type_Data... 3855 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 3857 Figure 25: EAP Message Format 3859 o Code (one octet) indicates whether this message is a 3860 Request (1), Response (2), Success (3), or Failure (4). 3862 o Identifier (one octet) is used in PPP to distinguish replayed 3863 messages from repeated ones. Since in IKE, EAP runs over a 3864 reliable protocol, it serves no function here. In a response 3865 message this octet MUST be set to match the identifier in the 3866 corresponding request. In other messages, this field MAY 3867 be set to any value. 3869 o Length (two octets) is the length of the EAP message and MUST 3870 be four less than the Payload Length of the encapsulating 3871 payload. 3873 o Type (one octet) is present only if the Code field is Request 3874 (1) or Response (2). For other codes, the EAP message length 3875 MUST be four octets and the Type and Type_Data fields MUST NOT 3876 be present. In a Request (1) message, Type indicates the 3877 data being requested. In a Response (2) message, Type MUST 3878 either be NAC or match the type of the data requested. The 3879 following types are defined in RFC 2284: 3881 1 Identity 3882 2 Notification 3883 3 NAK (Response Only) 3884 4 MD5-Challenge 3885 5 One-Time Password (OTP) 3886 6 Generic Token Card 3888 o Type_Data (Variable Length) contains data depending on the Code 3889 and Type. In Requests other than MD5-Challenge, this field 3890 contains a prompt to be displayed to a human user. For NAK, it 3891 contains one octet suggesting the type of authentication the 3892 Initiator would prefer to use. For most other responses, it 3893 contains the authentication code typed by the human user. 3895 Note that since IKE passes an indication of initiator identity in 3896 message 3 of the protocol, EAP based prompts for Identity SHOULD NOT 3897 be used. 3899 4 Conformance Requirements 3901 In order to assure that all implementations of IKEv2 can 3902 interoperate, there are MUST support requirements in addition to 3903 those listed elsewhere. Of course, IKEv2 is a security protocol, and 3904 one of its major functions is to only allow authorized parties to 3905 successfully complete establishment of SAs. So a particular 3906 implementation may be configured with any of a number of restrictions 3907 concerning algorithms and trusted authorities that will prevent 3908 universal interoperability. 3910 IKEv2 is designed to permit minimal implementations that can 3911 interoperate with all compliant implementations. There are a series 3912 of optional features that can easily be ignored by a particular 3913 implementation if it does not support that feature. Those features 3914 include: 3916 Ability to negotiate SAs through a NAT and tunnel the resulting 3917 ESP SA over UDP. 3919 Ability to request (and respond to a request for) a temporary IP 3920 address on the remote end of a tunnel. 3922 Ability to support various types of legacy authentication. 3924 Ability to support window sizes greater than one. 3926 Ability to establish multiple ESP and/or AH SAs within a single 3927 IKE_SA. 3929 Ability to rekey SAs. 3931 To assure interoperability, all implementations MUST be capable of 3932 parsing all payload types (if only to skip over them) and to ignore 3933 payload types that it does not support unless the critical bit is set 3934 in the payload header. If the critical bit is set in an unsupported 3935 payload header, all implementations MUST reject the messages 3936 containing those payloads. 3938 Every implementation MUST be capable of doing four message 3939 IKE_SA_INIT and IKE_AUTH exchanges establishing two SAs (one for IKE, 3940 one for ESP and/or AH). Implementations MAY be initiate-only or 3941 respond-only if appropriate for their platform. Every implementation 3942 MUST be capable of responding to an INFORMATIONAL exchange, but a 3943 minimal implementation MAY respond to any INFORMATIONAL message with 3944 an empty INFORMATIONAL reply. A minimal implementation MAY support 3945 the CREATE_CHILD_SA exchange only in so far as to recognize requests 3946 and reject them with a Notify payload of type NO_ADDITIONAL_SAS. A 3947 minimal implementation need not be able to initiate CREATE_CHILD_SA 3948 or INFORMATIONAL exchanges. When an SA expires (based on locally 3949 configured values of either lifetime or octets passed), and 3950 implementation MAY either try to renew it with a CREATE_CHILD_SA 3951 exchange or it MAY delete (close) the old SA and create a new one. If 3952 the responder rejects the CREATE_CHILD_SA request with a 3953 NO_ADDITIONAL_SAS notification, the implementation MUST be capable of 3954 instead closing the old SA and creating a new one. 3956 Implementations are not required to support requesting temporary IP 3957 addresses or responding to such requests. If an implementation does 3958 support issuing such requests, it MUST include a CP payload in 3959 message 3 containing at least a field of type INTERNAL_IP4_ADDRESS or 3960 INTERNAL_IP6_ADDRESS. All other fields are optional. If an 3961 implementation supports responding to such requests, it MUST parse 3962 the CP payload of type CFG_REQUEST in message 3 and recognize a field 3963 of type INTERNAL_IP4_ADDRESS or INTERNAL_IP6_ADDRESS. If it supports 3964 leasing an address of the appropriate type, it MUST return a CP 3965 payload of type CFG_REPLY containing an address of the requested 3966 type. The responder SHOULD include all of the other related 3967 attributes if it has them. 3969 A minimal IPv4 responder implementation will ignore the contents of 3970 the CP payload except to determine that it includes an 3971 INTERNAL_IP4_ADDRESS attribute and will respond with the address and 3972 other related attributes regardless of whether the initiator 3973 requested them. 3975 A minimal IPv4 initiator will generate a CP payload containing only 3976 an INTERNAL_IP4_ADDRESS attribute and will parse the response 3977 ignoring attributes it does not know how to use. The only attribute 3978 it MUST be able to process is INTERNAL_ADDRESS_EXPIRY, which it must 3979 use to bound the lifetime of the SA unless it successfully renews the 3980 lease before it expires. Minimal initiators need not be able to 3981 request lease renewals and minimal responders need not respond to 3982 them. 3984 For an implementation to be called conforming to this specification, 3985 it MUST be possible to configure it to accept the following: 3987 PKIX Certificates containing and signed by RSA keys of size 1024 or 3988 2048 bits, where the ID passed is any of ID_KEY_ID, ID_FQDN, 3989 ID_RFC822_ADDR, or ID_DER_ASN1_DN. 3991 Shared key authentication where the ID passes is any of ID_KEY_ID, 3992 ID_FQDN, or ID_RFC822_ADDR. 3994 Authentication where the responder is authenticated using PKIX 3995 Certificates and the initiator is authenticated using shared key 3996 authentication. 3998 5 Security Considerations 4000 While this protocol is designed to minimize disclosure of 4001 configuration information to unauthenticated peers, some such 4002 disclosure is unavoidable. One peer or the other must identify 4003 itself first and prove its identity first. To avoid probing, the 4004 initiator of an exchange is required to identify itself first, and 4005 usually is required to authenticate itself first. The initiator can, 4006 however, learn that the responder supports IKE and what cryptographic 4007 protocols it supports. The responder (or someone impersonating the 4008 responder) can probe the initiator not only for its identity, but 4009 using CERTREQ payloads may be able to determine what certificates the 4010 initiator is willing to use. 4012 Use of EAP authentication changes the probing possibilities somewhat. 4013 When EAP authentication is used, the responder proves its identity 4014 before the initiator does, so an initiator that knew the name of a 4015 valid initiator could probe the responder for both its name and 4016 certificates. 4018 Repeated rekeying using CREATE_CHILD_SA without PFS leaves all SAs 4019 vulnerable to cryptanalysis of a single key or overrun of either 4020 endpoint. Implementers should take note of this fact and set a limit 4021 on CREATE_CHILD_SA exchanges between exponentiations. This memo does 4022 not prescribe such a limit. 4024 The strength of a key derived from a Diffie-Hellman exchange using 4025 any of the groups defined here depends on the inherent strength of 4026 the group, the size of the exponent used, and the entropy provided by 4027 the random number generator used. Due to these inputs it is difficult 4028 to determine the strength of a key for any of the defined groups. 4029 Diffie-Hellman group number two, when used with a strong random 4030 number generator and an exponent no less than 200 bits, is common for 4031 use with 3DES. Group five provides greater security than group two. 4032 Group one is for historic purposes only and does not provide 4033 sufficient strength except for use with DES, which is also for 4034 historic use only. Implementations should make note of these 4035 estimates when establishing policy and negotiating security 4036 parameters. 4038 Note that these limitations are on the Diffie-Hellman groups 4039 themselves. There is nothing in IKE which prohibits using stronger 4040 groups nor is there anything which will dilute the strength obtained 4041 from stronger groups (limited by the strength of the other algorithms 4042 negotiated including the prf function). In fact, the extensible 4043 framework of IKE encourages the definition of more groups; use of 4044 elliptical curve groups may greatly increase strength using much 4045 smaller numbers. 4047 It is assumed that all Diffie-Hellman exponents are erased from 4048 memory after use. In particular, these exponents MUST NOT be derived 4049 from long-lived secrets like the seed to a pseudo-random generator 4050 that is not erased after use. 4052 The strength of all keys are limited by the size of the output of the 4053 negotiated prf function. For this reason, a prf function whose output 4054 is less than 128 bits (e.g., 3DES-CBC) MUST NOT be used with this 4055 protocol. 4057 The security of this protocol is critically dependent on the 4058 randomness of the randomly chosen parameters. These should be 4059 generated by a strong random or properly seeded pseudo-random source 4060 (see [RFC1750]). Implementers should take care to ensure that use of 4061 random numbers for both keys and nonces is engineered in a fashion 4062 that does not undermine the security of the keys. 4064 For information on the rationale of many of the cryptographic design 4065 choices in this protocol, see [SIGMA]. 4067 When using pre-shared keys, a critical consideration is how to assure 4068 the randomness of these secrets. The strongest practice is to ensure 4069 that any pre-shared key contain as much randomness as the strongest 4070 key being negotiated. Deriving a shared secret from a password, name, 4071 or other low entropy source is not secure. These sources are subject 4072 to dictionary and social engineering attacks, among others. 4074 The NAT_DETECTION_*_IP notifications contain a hash of the addresses 4075 and ports in an attempt to hide internal IP addresses behind a NAT. 4076 Since the IPv4 address space is only 32 bits, and it is usually very 4077 sparse, it would be possible for an attacker to find out the internal 4078 address used behind the NAT box by trying all possible IP-addresses 4079 and trying to find the matching hash. The port numbers are normally 4080 fixed to 500, and the SPIs can be extracted from the packet. This 4081 reduces the number of hash calculations to 2^32. With an educated 4082 guess of the use of private address space, the number of hash 4083 calculations is much smaller. Designers should therefore not assume 4084 that use of IKE will not leak internal address information. 4086 When using an EAP authentication method that does not generate a 4087 shared key for protecting a subsequent AUTH payload, certain man-in- 4088 the-middle and server impersonation attacks are possible [EAPMITM]. 4089 These vulnerabilities occur when EAP is also used in protocols which 4090 are not protected with a secure tunnel. Since EAP is a general- 4091 purpose authentication protocol, which is often used to provide 4092 single-signon facilities, a deployed IPsec solution which relies on 4093 an EAP authentication method that does not generate a shared key 4094 (also known as a non-key-generating EAP method) can become 4095 compromised due to the deployment of an entirely unrelated 4096 application that also happens to use the same non-key-generating EAP 4097 method, but in an unprotected fashion. Note that this vulnerability 4098 is not limited to just EAP, but can occur in other scenarios where an 4099 authentication infrastructure is reused. For example, if the EAP 4100 mechanism used by IKEv2 utilizes a token authenticator, a man-in-the- 4101 middle attacker could impersonate the web server, intercept the token 4102 authentication exchange, and use it to initiate an IKEv2 connection. 4103 For this reason, use of non-key-generating EAP methods SHOULD be 4104 avoided where possible. Where they are used, it is extremely 4105 important that all usages of these EAP methods SHOULD utilize a 4106 protected tunnel, where the initiator validates the responder's 4107 certificate before initiating the EAP exchange. Implementers SHOULD 4108 describe the vulnerabilities of using non-key-generating EAP methods 4109 in the documentation of their implementations so that the 4110 administrators deploying IPsec solutions are aware of these dangers. 4112 An implementation using EAP MUST also use a public key based 4113 authentication of the server to the client before the EAP exchange 4114 begins, even if the EAP method offers mutual authentication. This 4115 avoids having additional IKEv2 protocol variations and protects the 4116 EAP data from active attackers. 4118 6 IANA Considerations 4120 This document defines a number of new field types and values where 4121 future assignments will be managed by the IANA. 4123 The following registries should be created: 4125 IKEv2 Exchange Types 4126 IKEv2 Payload Types 4127 IKEv2 Transform Types 4128 IKEv2 Transform Attribute Types 4129 IKEv2 Encryption Transform IDs 4130 IKEv2 Pseudo-random Function Transform IDs 4131 IKEv2 Integrity Algorithm Transform IDs 4132 IKEv2 Diffie-Hellman, ECP and EC2N Transform IDs 4133 IKEv2 Identification Payload ID Types 4134 IKEv2 Certification Encodings 4135 IKEv2 Authentication Method 4136 IKEv2 Notification Payload Types 4137 IKEv2 Notification IPCOMP Transform IDs 4138 IKEv2 Security Protocol Identifiers 4139 IKEv2 Traffic Selector Types 4140 IKEv2 Configuration Payload CFG Types 4141 IKEv2 Configuration Payload Attribute Types 4143 Note: when creating a new Transform Type, a new registry for it must 4144 be created. 4146 New allocations to any of those registries may be allocated by expert 4147 review. 4149 7 Acknowledgements 4151 This document is a collaborative effort of the entire IPsec WG. If 4152 there were no limit to the number of authors that could appear on an 4153 RFC, the following, in alphabetical order, would have been listed: 4154 Bill Aiello, Stephane Beaulieu, Steve Bellovin, Sara Bitan, Matt 4155 Blaze, Ran Canetti, Darren Dukes, Dan Harkins, Paul Hoffman, J. 4156 Ioannidis, Steve Kent, Angelos Keromytis, Tero Kivinen, Hugo 4157 Krawczyk, Andrew Krywaniuk, Radia Perlman, O. Reingold, Michael 4158 Richardson. Many other people contributed to the design. It is an 4159 evolution of IKEv1, ISAKMP, and the IPsec DOI, each of which has its 4160 own list of authors. Hugh Daniel suggested the feature of having the 4161 initiator, in message 3, specify a name for the responder, and gave 4162 the feature the cute name "You Tarzan, Me Jane". David Faucher and 4163 Valery Smyzlov helped refine the design of the traffic selector 4164 negotiation. 4166 8 References 4168 8.1 Normative References 4170 [ADDGROUP] Kivinen, T., and Kojo, M., "More Modular Exponential 4171 (MODP) Diffie-Hellman groups for Internet Key 4172 Exchange (IKE)", RFC 3526, May 2003. 4174 [ADDRIPV6] Hinden, R., and Deering, S., 4175 "Internet Protocol Version 6 (IPv6) Addressing 4176 Architecture", RFC 3513, April 2003. 4178 [Bra97] Bradner, S., "Key Words for use in RFCs to indicate 4179 Requirement Levels", BCP 14, RFC 2119, March 1997. 4181 [EAP] Blunk, L. and Vollbrecht, J., "PPP Extensible 4182 Authentication Protocol (EAP), RFC 2284, March 1998. 4184 [ESPCBC] Pereira, R., Adams, R., "The ESP CBC-Mode Cipher 4185 Algorithms", RFC 2451, November 1998. 4187 [Hutt04] Huttunen, A. et. al., "UDP Encapsulation of IPsec 4188 Packets", draft-ietf-ipsec-udp-encaps-08.txt, February 4189 2004, work in progress. 4191 [RFC2401bis] Kent, S. and Atkinson, R., "Security Architecture 4192 for the Internet Protocol", un-issued Internet 4193 Draft, work in progress. 4195 [RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing 4196 an IANA Considerations Section in RFCs", BCP 26, RFC 2434, 4197 October 1998. 4199 [RFC3168] Ramakrishnan, K., Floyd, S., and Black, D., 4200 "The Addition of Explicit Congestion Notification (ECN) 4201 to IP", RFC 3168, September 2001. 4203 [RFC3280] Housley, R., Polk, W., Ford, W., Solo, D., "Internet 4204 X.509 Public Key Infrastructure Certificate and 4205 Certificate Revocation List (CRL) Profile", RFC 3280, 4206 April 2002. 4208 [RFC3667] Bradner, S., "IETF Rights in Submissions", BCP 78, 4209 RFC 3667, February 2004. 4211 [RFC3668] Bradner, S., "Intellectual Property Rights in IETF 4212 Technology", BCP 79, RFC 3668, February 2004. 4214 8.2 Informative References 4216 [DES] ANSI X3.106, "American National Standard for Information 4217 Systems-Data Link Encryption", American National Standards 4218 Institute, 1983. 4220 [DH] Diffie, W., and Hellman M., "New Directions in 4221 Cryptography", IEEE Transactions on Information Theory, V. 4222 IT-22, n. 6, June 1977. 4224 [DHCP] R. Droms, "Dynamic Host Configuration Protocol", 4225 RFC2131 4227 [DSS] NIST, "Digital Signature Standard", FIPS 186, National 4228 Institute of Standards and Technology, U.S. Department of 4229 Commerce, May, 1994. 4231 [EAPMITM] Asokan, N., Nierni, V., and Nyberg, K., "Man-in-the-Middle 4232 in Tunneled Authentication Protocols", 4233 http://eprint.iacr.org/2002/163, November 2002. 4235 [HC98] Harkins, D., Carrel, D., "The Internet Key Exchange 4236 (IKE)", RFC 2409, November 1998. 4238 [IDEA] Lai, X., "On the Design and Security of Block Ciphers," 4239 ETH Series in Information Processing, v. 1, Konstanz: 4240 Hartung-Gorre Verlag, 1992 4242 [IKEv2IANA]Richardson, M., "Initial IANA registry contents", 4243 draft-ietf-ipsec-ikev2-iana-00.txt, work in progress. 4245 [IPCOMP] Shacham, A., Monsour, R., Pereira, R., and Thomas, M., "IP 4246 Payload Compression Protocol (IPComp)", RFC 3173, 4247 September 2001. 4249 [KPS03] Kaufman, C., Perlman, R., and Sommerfeld, B., "DoS 4250 protection for UDP-based protocols", ACM Conference on 4251 Computer and Communications Security, October 2003. 4253 [Ker01] Keromytis, A., Sommerfeld, B., "The 'Suggested ID' 4254 Extension for IKE", draft-keromytis-ike-id-00.txt, 2001 4256 [KBC96] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- 4257 Hashing for Message Authentication", RFC 2104, February 4258 1997. 4260 [LDAP] M. Wahl, T. Howes, S. Kille., "Lightweight Directory 4261 Access Protocol (v3)", RFC 2251 4263 [MD5] Rivest, R., "The MD5 Message Digest Algorithm", RFC 1321, 4264 April 1992. 4266 [MSST98] Maughhan, D., Schertler, M., Schneider, M., and Turner, J. 4267 "Internet Security Association and Key Management Protocol 4268 (ISAKMP)", RFC 2408, November 1998. 4270 [Orm96] Orman, H., "The Oakley Key Determination Protocol", RFC 4271 2412, November 1998. 4273 [PFKEY] McDonald, D., Metz, C., and Phan, B., "PFKEY Key 4274 Management API, Version 2", RFC 2367, July 1998. 4276 [PKCS1] Kaliski, B., and J. Staddon, "PKCS #1: RSA Cryptography 4277 Specifications Version 2", September 1998. 4279 [PK01] Perlman, R., and Kaufman, C., "Analysis of the IPsec key 4280 exchange Standard", WET-ICE Security Conference, MIT,2001, 4281 http://sec.femto.org/wetice-2001/papers/radia-paper.pdf. 4283 [Pip98] Piper, D., "The Internet IP Security Domain Of 4284 Interpretation for ISAKMP", RFC 2407, November 1998. 4286 [RADIUS] C. Rigney, A. Rubens, W. Simpson, S. Willens, "Remote 4287 Authentication Dial In User Service (RADIUS)", RFC 2138 4289 [RFC1750] Eastlake, D., Crocker, S., and Schiller, J., "Randomness 4290 Recommendations for Security", RFC 1750, December 1994. 4292 [RFC1958] Carpenter, B., "Architectural Principles of the 4293 Internet", RFC 1958, June 1996. 4295 [RFC2401] Kent, S., and Atkinson, R., "Security Architecture for 4296 the Internet Protocol", RFC 2401, November 1998. 4298 [RFC2474] Nichols, K., Blake, S., Baker, F. and Black, D., 4299 "Definition of the Differentiated Services Field (DS 4300 Field) in the IPv4 and IPv6 Headers", RFC 2474, 4301 December 1998. 4303 [RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z. 4304 and Weiss, W., "An Architecture for Differentiated 4305 Services", RFC 2475, December 1998. 4307 [RFC2522] Karn, P., and Simpson, W., "Photuris: Session-Key 4308 Management Protocol", RFC 2522, March 1999. 4310 [RFC2775] Carpenter, B., "Internet Transparency", RFC 2775, 4311 February 2000. 4313 [RFC2983] Black, D., "Differentiated Services and Tunnels", 4314 RFC 2983, October 2000. 4316 [RFC3439] Bush, R. and D. Meyer, "Some Internet Architectural 4317 Guidelines and Philosophy", RFC 3429, December 2002. 4319 [RFC3715] Aboba, B and Dixon, W., "IPsec-Network Address 4320 Translation (NAT) Compatibility Requirements", 4321 RFC 3715, March 2004. 4323 [RSA] Rivest, R., Shamir, A., and Adleman, L., "A Method for 4324 Obtaining Digital Signatures and Public-Key 4325 Cryptosystems", Communications of the ACM, v. 21, n. 2, 4326 February 1978. 4328 [SHA] NIST, "Secure Hash Standard", FIPS 180-1, National 4329 Institute of Standards and Technology, U.S. Department 4330 of Commerce, May 1994. 4332 [SIGMA] Krawczyk, H., "SIGMA: the `SIGn-and-MAc' Approach to 4333 Authenticated Diffie-Hellman and its Use in the IKE 4334 Protocols", in Advances in Cryptography - CRYPTO 2003 4335 Proceedings, LNCS 2729, Springer, 2003. Available at: 4336 http://www.ee.technion.ac.il/~hugo/sigma.html 4338 [SKEME] Krawczyk, H., "SKEME: A Versatile Secure Key Exchange 4339 Mechanism for Internet", from IEEE Proceedings of the 4340 1996 Symposium on Network and Distributed Systems 4341 Security. 4343 [X.501] ITU-T Recommendation X.501: Information Technology - 4344 Open Systems Interconnection - The Directory: Models, 4345 1993. 4347 [X.509] ITU-T Recommendation X.509 (1997 E): Information 4348 Technology - Open Systems Interconnection - The 4349 Directory: Authentication Framework, June 1997. 4351 Appendix A: Summary of changes from IKEv1 4353 The goals of this revision to IKE are: 4355 1) To define the entire IKE protocol in a single document, replacing 4356 RFCs 2407, 2408, and 2409 and incorporating subsequent changes to 4357 support NAT Traversal, Extended Authentication, and Remote Address 4358 acquisition. 4360 2) To simplify IKE by replacing the eight different initial exchanges 4361 with a single four message exchange (with changes in authentication 4362 mechanisms affecting only a single AUTH payload rather than 4363 restructuring the entire exchange); 4365 3) To remove the Domain of Interpretation (DOI), Situation (SIT), and 4366 Labeled Domain Identifier fields, and the Commit and Authentication 4367 only bits; 4369 4) To decrease IKE's latency in the common case by making the initial 4370 exchange be 2 round trips (4 messages), and allowing the ability to 4371 piggyback setup of a CHILD_SA on that exchange; 4373 5) To replace the cryptographic syntax for protecting the IKE 4374 messages themselves with one based closely on ESP to simplify 4375 implementation and security analysis; 4377 6) To reduce the number of possible error states by making the 4378 protocol reliable (all messages are acknowledged) and sequenced. This 4379 allows shortening CREATE_CHILD_SA exchanges from 3 messages to 2; 4381 7) To increase robustness by allowing the responder to not do 4382 significant processing until it receives a message proving that the 4383 initiator can receive messages at its claimed IP address, and not 4384 commit any state to an exchange until the initiator can be 4385 cryptographically authenticated; 4387 8) To fix bugs such as the hash problem documented in [draft-ietf- 4388 ipsec-ike-hash-revised-02.txt]; 4390 9) To specify Traffic Selectors in their own payloads type rather 4391 than overloading ID payloads, and making more flexible the Traffic 4392 Selectors that may be specified; 4394 10) To specify required behavior under certain error conditions or 4395 when data that is not understood is received in order to make it 4396 easier to make future revisions in a way that does not break 4397 backwards compatibility; 4398 11) To incorporate ideas from draft-ietf-ipsec-nat-reqts-04.txt to 4399 allow IKE to negotiate through NAT gateways; 4401 12) To simplify and clarify how shared state is maintained in the 4402 presence of network failures and Denial of Service attacks; and 4404 13) To maintain existing syntax and magic numbers to the extent 4405 possible to make it likely that implementations of IKEv1 can be 4406 enhanced to support IKEv2 with minimum effort. 4408 Appendix B: Diffie-Hellman Groups 4410 There are 4 different Diffie-Hellman groups defined here for use in 4411 IKE. These groups were generated by Richard Schroeppel at the 4412 University of Arizona. Properties of these primes are described in 4413 [Orm96]. 4415 The strength supplied by group one may not be sufficient for the 4416 mandatory-to-implement encryption algorithm and is here for historic 4417 reasons. 4419 Additional Diffie-Hellman groups have been defined in [ADDGROUP]. 4421 B.1 Group 1 - 768 Bit MODP 4423 This group is assigned id 1 (one). 4425 The prime is: 2^768 - 2 ^704 - 1 + 2^64 * { [2^638 pi] + 149686 } 4426 Its hexadecimal value is: 4428 FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1 29024E08 4429 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD EF9519B3 CD3A431B 4430 302B0A6D F25F1437 4FE1356D 6D51C245 E485B576 625E7EC6 F44C42E9 4431 A63A3620 FFFFFFFF FFFFFFFF 4433 The generator is 2. 4435 B.2 Group 2 - 1024 Bit MODP 4437 This group is assigned id 2 (two). 4439 The prime is 2^1024 - 2^960 - 1 + 2^64 * { [2^894 pi] + 129093 }. 4440 Its hexadecimal value is: 4442 FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1 29024E08 4443 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD EF9519B3 CD3A431B 4444 302B0A6D F25F1437 4FE1356D 6D51C245 E485B576 625E7EC6 F44C42E9 4445 A637ED6B 0BFF5CB6 F406B7ED EE386BFB 5A899FA5 AE9F2411 7C4B1FE6 4446 49286651 ECE65381 FFFFFFFF FFFFFFFF 4448 The generator is 2. 4450 B.3 Group 3 - 155 Bit EC2N 4452 This group is assigned id 3 (three). The curve is based on the Galois 4453 Field GF[2^155]. The field size is 155. The irreducible polynomial 4454 for the field is: 4455 u^155 + u^62 + 1. 4457 The equation for the elliptic curve is: 4458 y^2 + xy = x^3 + ax^2 + b. 4460 Field Size: 155 4461 Group Prime/Irreducible Polynomial: 4462 0x0800000000000000000000004000000000000001 4463 Group Generator One: 0x7b 4464 Group Curve A: 0x0 4465 Group Curve B: 0x07338f 4466 Group Order: 0x0800000000000000000057db5698537193aef944 4468 The data in the KE payload when using this group is the value x from 4469 the solution (x,y), the point on the curve chosen by taking the 4470 randomly chosen secret Ka and computing Ka*P, where * is the 4471 repetition of the group addition and double operations, P is the 4472 curve point with x coordinate equal to generator 1 and the y 4473 coordinate determined from the defining equation. The equation of 4474 curve is implicitly known by the Group Type and the A and B 4475 coefficients. There are two possible values for the y coordinate; 4476 either one can be used successfully (the two parties need not agree 4477 on the selection). 4479 B.4 Group 4 - 185 Bit EC2N 4481 This group is assigned id 4 (four). The curve is based on the Galois 4482 Field GF[2^185]. The field size is 185. The irreducible polynomial 4483 for the field is: 4484 u^185 + u^69 + 1. 4486 The equation for the elliptic curve is: 4487 y^2 + xy = x^3 + ax^2 + b. 4489 Field Size: 185 4490 Group Prime/Irreducible Polynomial: 4491 0x020000000000000000000000000000200000000000000001 4492 Group Generator One: 0x18 4493 Group Curve A: 0x0 4494 Group Curve B: 0x1ee9 4495 Group Order: 0x01ffffffffffffffffffffffdbf2f889b73e484175f94ebc 4497 The data in the KE payload when using this group will be identical to 4498 that as when using Oakley Group 3 (three). 4500 Change History (To be removed from RFC) 4502 H.1 Changes from IKEv2-00 to IKEv2-01 February 2002 4504 1) Changed Appendix B to specify the encryption and authentication 4505 processing for IKE rather than referencing ESP. Simplified the format 4506 by removing idiosyncrasies not needed for IKE. 4508 2) Added option for authentication via a shared secret key. 4510 3) Specified different keys in the two directions of IKE messages. 4511 Removed requirement of different cookies in the two directions since 4512 now no longer required. 4514 4) Change the quantities signed by the two ends in AUTH fields to 4515 assure the two parties sign different quantities. 4517 5) Changed reference to AES to AES_128. 4519 6) Removed requirement that Diffie-Hellman be repeated when rekeying 4520 IKE_SA. 4522 7) Fixed typos. 4524 8) Clarified requirements around use of port 500 at the remote end in 4525 support of NAT. 4527 9) Clarified required ordering for payloads. 4529 10) Suggested mechanisms for avoiding DoS attacks. 4531 11) Removed claims in some places that the first phase 2 piggybacked 4532 on phase 1 was optional. 4534 H.2 Changes from IKEv2-01 to IKEv2-02 April 2002 4536 1) Moved the Initiator CERTREQ payload from message 1 to message 3. 4538 2) Added a second optional ID payload in message 3 for the Initiator 4539 to name a desired Responder to support the case where multiple named 4540 identities are served by a single IP address. 4542 3) Deleted the optimization whereby the Diffie-Hellman group did not 4543 need to be specified in phase 2 if it was the same as in phase 1 (it 4544 complicated the design with no meaningful benefit). 4546 4) Added a section on the implications of reusing Diffie-Hellman 4547 exponentials 4548 5) Changed the specification of sequence numbers to being at 0 in 4549 both directions. 4551 6) Many editorial changes and corrections, the most significant being 4552 a global replace of "byte" with "octet". 4554 H.3 Changes from IKEv2-02 to IKEv2-03 October 2002 4556 1) Reorganized the document moving introductory material to the 4557 front. 4559 2) Simplified the specification of Traffic Selectors to allow only 4560 IPv4 and IPv6 address ranges, as was done in the JFK spec. 4562 3) Fixed the problem brought up by David Faucher with the fix 4563 suggested by Valery Smyslov. If Bob needs to narrow the selector 4564 range, but has more than one matching narrower range, then if Alice's 4565 first selector is a single address pair, Bob chooses the range that 4566 encompasses that. 4568 4) To harmonize with the JFK spec, changed the exchange so that the 4569 initial exchange can be completed in four messages even if the 4570 responder must invoke an anti-clogging defense and the initiator 4571 incorrectly anticipates the responder's choice of Diffie-Hellman 4572 group. 4574 5) Replaced the hierarchical SA payload with a simplified version 4575 that only negotiates suites of cryptographic algorithms. 4577 H.4 Changes from IKEv2-03 to IKEv2-04 January 2003 4579 1) Integrated NAT traversal changes (including Appendix A). 4581 2) Moved the anti-clogging token (cookie) from the SPI to a NOTIFY 4582 payload; changed negotiation back to 6 messages when a cookie is 4583 needed. 4585 3) Made capitalization of IKE_SA and CHILD_SA consistent. 4587 4) Changed how IPComp was negotiated. 4589 5) Added usage scenarios. 4591 6) Added configuration payload for acquiring internal addresses on 4592 remote networks. 4594 7) Added negotiation of tunnel vs. transport mode. 4596 H.5 Changes from IKEv2-04 to IKEv2-05 February 2003 4598 1) Shortened Abstract 4600 2) Moved NAT Traversal from Appendix to section 2. Moved changes from 4601 IKEv2 to Appendix A. Renumbered sections. 4603 3) Made language more consistent. Removed most references to Phase 1 4604 and Phase 2. 4606 4) Made explicit the requirements for support of NAT Traversal. 4608 5) Added support for Extended Authentication Protocol methods. 4610 6) Added Response bit to message header. 4612 7) Made more explicit the encoding of Diffie-Hellman numbers in key 4613 expansion algorithms. 4615 8) Added ID payloads to AUTH payload computation. 4617 9) Expanded set of defined cryptographic suites. 4619 10) Added text for MUST/SHOULD support for ID payloads. 4621 11) Added new certificate formats and added MUST/SHOULD text. 4623 12) Clarified use of CERTREQ. 4625 13) Deleted "MUST SUPPORT" column in CP payload specification (it was 4626 inconsistent with surrounding text). 4628 14) Extended and clarified Conformance Requirements section, 4629 including specification of a minimal implementation. 4631 15) Added text to specify ECN handling. 4633 H.6 Changes from IKEv2-05 to IKEv2-06 March 2003 4635 1) Changed the suite based crypto negotiation back to ala carte. 4637 2) Eliminated some awkward page breaks, typographical errors, and 4638 other formatting issues. 4640 3) Tightened language describing cryptographic strength. 4642 4) Added references. 4644 5) Added more specific error codes. 4646 6) Added rationale for unintuitive key generation hash with shared 4647 secret based authentication. 4649 7) Changed the computation of the authenticating AUTH payload as 4650 proposed by Hugo Krawczyk. 4652 8) Changed the dashes (-) to underscores (_) in the names of fields 4653 and constants. 4655 H.7 Changes from IKEv2-06 to IKEv2-07 April 2003 4657 1) Added a list of payload types to section 3.2. 4659 2) Clarified use of SET_WINDOW_SIZE Notify payload. 4661 3) Removed references to COOKIE_REQUIRED Notify payload. 4663 4) Specified how to use a prf with a fixed key size. 4665 5) Removed g^ir from data processed by prf+. 4667 6) Strengthened cautions against using passwords as shared keys. 4669 7) Renamed Protocol_id field SECURITY_PROTOCOL_ID when it is not the 4670 Protocol ID from IP, and changed its values for consistency with 4671 IKEv1. 4673 8) Clarified use of ID payload in access control decisions. 4675 9) Gave IDr and TSr their own payload type numbers. 4677 10) Added Intellectual Property rights section. 4679 11) Clarified some issues in NAT Traversal. 4681 H.8 Changes from IKEv2-07 to IKEv2-08 May 2003 4683 1) Numerous editorial corrections and clarifications. 4685 2) Renamed Gateway to Security Gateway. 4687 3) Made explicit that the ability to rekey SAs without restarting IKE 4688 was optional. 4690 4) Removed last references to MUST and SHOULD cipher suites. 4692 5) Changed examples to "example.com". 4694 6) Changed references to status codes to status types. 4696 7) Simplified IANA Considerations section 4698 8) Updated References 4700 H.9 Changes from IKEv2-08 to IKEv2-09 August 2003 4702 1) Numerous editorial corrections and clarifications. 4704 2) Added REKEY_SA notify payload to the first message of a 4705 CREATE_CHILD_SA exchange if the new exchange was rekeying an existing 4706 SA. 4708 3) Renamed AES_ENCR128 to AES_ENCR and made it take a single 4709 parameter that is the key size (which may be 128, 192, or 256 bits). 4711 4) Clarified when a newly created SA is useable. 4713 5) Added additional text to section 2.23 specifying how to negotiate 4714 NAT Traversal. 4716 6) Replaced specification of ECN handling with a reference to 4717 [RFC2401bis]. 4719 7) Renumbered payloads so that numbers would not collide with IKEv1 4720 payload numbers in hopes of making code implementing both protocols 4721 simpler. 4723 8) Expanded the Transform ID field (also referred to as Diffie- 4724 Hellman group number) from one byte to two bytes. 4726 9) Removed ability to negotiate Diffie-Hellman groups by explicitly 4727 passing parameters. They must now be negotiated using Transform IDs. 4729 10) Renumbered status codes to be contiguous. 4731 11) Specified the meaning of the "Port" fields in Traffic Selectors 4732 when the ICMP protocol is being used. 4734 12) Removed the specification of D-H Group #5 since it is already 4735 specified in [ADDGROUP. 4737 H.10 Changes from IKEv2-09 to IKEv2-10 August 2003 4739 1) Numerous boilerplate and formatting corrections to comply with RFC 4740 Editorial Guidelines and procedures. 4742 2) Fixed five typographical errors. 4744 3) Added a sentence to the end of "Security considerations" 4745 discouraging the use of non-key-generating EAP mechanisms. 4747 H.11 Changes from IKEv2-10 to IKEv2-11 October 2003 4749 1) Added SHOULD NOT language concerning use of non-key-generating EAP 4750 authentication methods and added reference [EAPMITM]. 4752 2) Clarified use of parallel SAs with identical traffic selectors for 4753 purposes of QoS handling. 4755 3) Fixed description of ECN handling to make normative references to 4756 [RFC2401bis] and [RFC3168]. 4758 4) Fixed two typos in the description of NAT traversal. 4760 5) Added specific ASN.1 encoding of certificate bundles in section 4761 3.6. 4763 H.12 Changes from IKEv2-11 to IKEv2-12 January 2004 4765 1) Made the values of the one byte IPsec Protocol ID consistent 4766 between payloads and made the naming more nearly consistent. 4768 2) Changed the specification to require that AUTH payloads be 4769 provided in EAP exchanges even when a non-key generating EAP method 4770 is used. This protects against certain obscure cryptographic 4771 threats. 4773 3) Changed all example IP addresses to be within subnet 10. 4775 4) Specified that issues surrounding weak keys and DES key parity 4776 must be addressed in algorithm documents. 4778 5) Removed the unsupported (and probably untrue) claim that Photuris 4779 cookies were given that name because the IETF always supports 4780 proposals involving cookies. 4782 6) Fixed some text that specified that Transform ID was 1 octet while 4783 everywhere else said it was 2 octets. 4785 7) Corrected the ASN.1 specification of the encoding of X.509 4786 certificate bundles. 4788 8) Added an INVALID_SELECTORS error type. 4790 9) Replaced IANA considerations section with a reference to draft- 4791 ietf-ipsec-ikev2-iana-00.txt. 4793 10) Removed 2 obsolete informative references and added one to a 4794 paper on UDP fragmentation problems. 4796 11) 41 Editorial Corrections and Clarifications. 4798 12) 6 Grammatical and Spelling errors fixed. 4800 13) 4 Corrected capitalizations of MAY/MUST/etc. 4802 14) 4 Attempts to make capitalization and use of underscores more 4803 consistent. 4805 H.13 Changes from IKEv2-12 to IKEv2-13 March 2004 4807 1) Updated copyright and intellectual property right sections per RFC 4808 3667. Added normative references to RFC 3667 and RFC 3668. 4810 2) Updated IANA Considerations section and adjusted some assignment 4811 tables to be consistent with the IANA registries document. Added 4812 Michael Richardson to the acknowledgements. 4814 3) Changed the cryptographic formula for computing the AUTH payload 4815 in the case where EAP authentication is used and the EAP algorithm 4816 does not produce a shared key. Clarified the case where it does 4817 produce a shared key. 4819 4) Extended the EAP authentication protocol by two messages so that 4820 the AUTH message is always sent after the success status is received. 4822 5) Updated reference to ESP encapsulation in UDP and made it 4823 normative. 4825 6) Added notification type ESP_TFC_PADDING_NOT_SUPPORTED. 4827 7) Clarified encoding of port number fields in transport selectors in 4828 the cases of ICMP and OPAQUE. 4830 8) Clarified that the length of the integrity checksum is fixed 4831 length and determined by the negotiated integrity algorithm. 4833 9) Added an informative reference to RFC 3715 (NAT Compatibility 4834 Requirements). 4836 10) Fixed 2 typos. 4838 H.14 Changes from IKEv2-13 to IKEv2-14 May 2004 4840 1) ISSUE #99: Clarified use of tunnel mode vs. transport mode. 4842 2) Changed the cryptographic formula for computing the AUTH payload 4843 in response to a suggestion from Hugo Krawczyk. 4845 3) Fixed a wording error in the explanation of why NAT traversal 4846 works as it does related to processing by legacy NAT gateways. 4848 4) Corrected the label AUTH_AES_XCBC_96 to AUTH_AES_PRF_128. 4850 5) Deleted suggestion that ID_KEY_ID field might be used to pass an 4851 account name. 4853 6) Listed the newly allocated OID for certificate bundle. 4855 7) Added NON_FIRST_FRAGMENTS_ALSO notification for negotiating the 4856 ability to send non-initial fragments of packets on the same SA as 4857 the initial fragments. 4859 8) ISSUE #97: Removed language concerning the relative strength of 4860 Diffie-Hellman groups. 4862 9) ISSUE #100: Reduced requirements concerning sending of 4863 certificates to allow implementations to by more coy about their 4864 identities and protect themselves from probing attacks. Listed in 4865 Security Considerations some issues an implementer might consider in 4866 deciding how to deal with such attacks. 4868 10) Made the punctuation of references to RFCs more consistent. 4870 11) Fixed fourteen typos. 4872 Editor's Address 4874 Charlie Kaufman 4875 Microsoft Corporation 4876 1 Microsoft Way 4877 Redmond, WA 98052 4878 1-425-707-3335 4880 charliek@microsoft.com 4882 Full Copyright Statement 4884 Copyright (C) The Internet Society (2004). This document is subject 4885 to the rights, licenses and restrictions contained in BCP 78 and 4886 except as set forth therein, the authors retain all their rights. 4888 This document and the information contained herein are provided on an 4889 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 4890 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET 4891 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, 4892 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE 4893 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 4894 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 4896 Intellectual Property Statement 4898 The IETF takes no position regarding the validity or scope of any 4899 Intellectual Property Rights or other rights that might be claimed to 4900 pertain to the implementation or use of the technology described in 4901 this document or the extent to which any license under such rights 4902 might or might not be available; nor does it represent that it has 4903 made any independent effort to identify any such rights. Information 4904 on the procedures with respect to rights in RFC documents can be 4905 found in BCP 78 and BCP 79. 4907 Copies of IPR disclosures made to the IETF Secretariat and any 4908 assurances of licenses to be made available, or the result of an 4909 attempt made to obtain a general license or permission for the use of 4910 such proprietary rights by implementers or users of this 4911 specification can be obtained from the IETF on-line IPR repository at 4912 http://www.ietf.org/ipr. 4914 The IETF invites any interested party to bring to its attention any 4915 copyrights, patents or patent applications, or other proprietary 4916 rights that may cover technology that may be required to implement 4917 this standard. Please address the information to the IETF at ietf- 4918 ipr@ietf.org. 4920 Acknowledgement 4922 Funding for the RFC Editor function is currently provided by the 4923 Internet Society. 4925 Expiration 4927 This Internet-Draft (draft-ietf-ipsec-ikev2-14.txt) expires in 4928 November 2004.