idnits 2.17.1 draft-ietf-pki4ipsec-ikecert-profile-04.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 5.1.a on line 16. -- Found old boilerplate from RFC 3978, Section 5.5 on line 2149. -- Found old boilerplate from RFC 3979, Section 5, paragraph 1 on line 2126. -- Found old boilerplate from RFC 3979, Section 5, paragraph 2 on line 2133. -- Found old boilerplate from RFC 3979, Section 5, paragraph 3 on line 2139. ** 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. ** 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. ** The document uses RFC 3667 boilerplate or RFC 3978-like boilerplate instead of verbatim RFC 3978 boilerplate. After 6 May 2005, submission of drafts without verbatim RFC 3978 boilerplate is not accepted. The following non-3978 patterns matched text found in the document. That text should be removed or replaced: This document is an Internet-Draft and is subject to all provisions of Section 3 of RFC 3667. By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- == No 'Intended status' indicated for this document; assuming Proposed Standard Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- == There are 12 instances of lines with non-RFC6890-compliant IPv4 addresses in the document. If these are example addresses, they should be changed. == There are 1 instance 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. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the RFC 3978 Section 5.4 Copyright Line does not match the current year == Line 1182 has weird spacing: '...lements bit...' == The document seems to use 'NOT RECOMMENDED' as an RFC 2119 keyword, but does not include the phrase in its RFC 2119 key words list. == 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: * Changed ISAKMP references in Abstract and Intro to IKE. * Editorial changes to make the text conform with the summary table in 3.1, especially in the text following the table in 3.1. Particular note should be paid to changes in section 3.5.1. * Sect 3.1.1 - editorial changes to aid in clarification. Added text on when deployers might consider using IP addr, but strongly encouraged not to. * Sect 3.1.8 removed IP address from list of practically used ID types. * 3.1.9 overhauled (per Kivinen, July 18) * 3.2 - added IKEv2's Hash and URL of x.509 to list of those profiled and gave it its own section, now 3.2.5 * added note in CRL/ARL section about revocation occurring OOB of IKE * deleted ARL as its own section and collapsed it into Revocation Lists (CRL and ARL) for consciseness. Renumbered accordingly. * Sect 3.2.7.2 - Changed from MUST not send empty certreqs to SHOULD send CERTREQs which contain CA fields with direction on how, but MAY send empty CERTREQs in certain case. Use case added, and specifics of both initiator and responder behavior listed. * APPENDIX C added to fill out the explanation (mostly discussion from list). * 3.3 - clarified that sending CRLs and chaining certs is deprecated. * added IKEv2's Hash and URL of x.509 to list of those profiled and gave it its own section. Condensed ARL into CRL and renumbered accordingly. * duplicate section was removed, renumbered accordingly * 3.3.10.2 - title changed. sending chaining becomes SHOULD NOT. * 4.1.2 added text to explicity call out support for CN, C, O, OU * collapsed 4.1.2.3 into 4.1.2.2 and renumbered accordingly. * Collapsed 4.1.3.2 into 4.1.3.1 and renumbered accordingly * Edited 4.1.3.2 Key Usage and 4.1.3.12 ExtKey Usage according to Hoffman, July18 * 4.1.3.3 if receive cert w/ PKUP, ignore it. * 4.1.3.13 - CDP changed text to represent SHOULD issue, and how important CDP becomes when we do not send CRLs in-band. Added SHOULD for CDPs actually being resolvable (reilly email). * Reordered 6.4 for better clarity. * Added Rescorla to Acknowledgements section, as he is no longer listed as an editor, since -00. -- 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 (December 2004) is 7044 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- Looks like a reference, but probably isn't: 'IKEv2' on line 1821 -- Looks like a reference, but probably isn't: 'IDr' on line 1910 == Unused Reference: '15' is defined on line 1664, but no explicit reference was found in the text ** Obsolete normative reference: RFC 2409 (ref. '1') (Obsoleted by RFC 4306) ** Obsolete normative reference: RFC 2408 (ref. '2') (Obsoleted by RFC 4306) == Outdated reference: A later version (-17) exists of draft-ietf-ipsec-ikev2-15 ** Obsolete normative reference: RFC 2401 (ref. '4') (Obsoleted by RFC 4301) ** Obsolete normative reference: RFC 3280 (ref. '5') (Obsoleted by RFC 5280) ** Obsolete normative reference: RFC 2407 (ref. '6') (Obsoleted by RFC 4306) ** Obsolete normative reference: RFC 2314 (ref. '9') (Obsoleted by RFC 2986) -- Obsolete informational reference (is this intentional?): RFC 1883 (ref. '10') (Obsoleted by RFC 2460) -- Obsolete informational reference (is this intentional?): RFC 2535 (ref. '11') (Obsoleted by RFC 4033, RFC 4034, RFC 4035) -- Obsolete informational reference (is this intentional?): RFC 1519 (ref. '13') (Obsoleted by RFC 4632) -- Obsolete informational reference (is this intentional?): RFC 2560 (ref. '14') (Obsoleted by RFC 6960) Summary: 11 errors (**), 0 flaws (~~), 9 warnings (==), 13 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 pki4ipsec B. Korver 3 Internet-Draft Xythos Software, Inc. 4 Expires: June 4, 2005 December 2004 6 The Internet IP Security PKI Profile of IKEv1/ISAKMP, IKEv2, and PKIX 7 draft-ietf-pki4ipsec-ikecert-profile-04 9 Status of this Memo 11 This document is an Internet-Draft and is subject to all provisions 12 of Section 3 of RFC 3667. By submitting this Internet-Draft, each 13 author represents that any applicable patent or other IPR claims of 14 which he or she is aware have been or will be disclosed, and any of 15 which he or she become aware will be disclosed, in accordance with 16 RFC 3668. 18 Internet-Drafts are working documents of the Internet Engineering 19 Task Force (IETF), its areas, and its working groups. Note that 20 other groups may also distribute working documents as 21 Internet-Drafts. 23 Internet-Drafts are draft documents valid for a maximum of six months 24 and may be updated, replaced, or obsoleted by other documents at any 25 time. It is inappropriate to use Internet-Drafts as reference 26 material or to cite them other than as "work in progress." 28 The list of current Internet-Drafts can be accessed at 29 http://www.ietf.org/ietf/1id-abstracts.txt. 31 The list of Internet-Draft Shadow Directories can be accessed at 32 http://www.ietf.org/shadow.html. 34 This Internet-Draft will expire on June 4, 2005. 36 Copyright Notice 38 Copyright (C) The Internet Society (2004). 40 Abstract 42 IKE and PKIX both provide frameworks that must be profiled for use in 43 a given application. This document provides a profile of IKE and 44 PKIX that defines the requirements for using PKI technology in the 45 context of IKE/IPsec. The document complements protocol 46 specifications such as IKEv1 and IKEv2, which assume the existence of 47 public key certificates and related keying materials, but which do 48 not address PKI issues explicitly. This document addresses those 49 issues. 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 54 2. Terms and Definitions . . . . . . . . . . . . . . . . . . . 4 55 3. Profile of IKEv1/ISAKMP and IKEv2 . . . . . . . . . . . . . 5 56 3.1 Identification Payload . . . . . . . . . . . . . . . . . . 5 57 3.1.1 ID_IPV4_ADDR and ID_IPV6_ADDR . . . . . . . . . . . . 7 58 3.1.2 ID_FQDN . . . . . . . . . . . . . . . . . . . . . . . 9 59 3.1.3 ID_USER_FQDN . . . . . . . . . . . . . . . . . . . . . 10 60 3.1.4 ID_IPV4_ADDR_SUBNET, ID_IPV6_ADDR_SUBNET, 61 ID_IPV4_ADDR_RANGE, ID_IPV6_ADDR_RANGE . . . . . . . . 11 62 3.1.5 ID_DER_ASN1_DN . . . . . . . . . . . . . . . . . . . . 11 63 3.1.6 ID_DER_ASN1_GN . . . . . . . . . . . . . . . . . . . . 12 64 3.1.7 ID_KEY_ID . . . . . . . . . . . . . . . . . . . . . . 12 65 3.1.8 Selecting an Identity from a Certificate . . . . . . . 12 66 3.1.9 SubjectName for DN Only . . . . . . . . . . . . . . . 12 67 3.1.10 Binding Identity to Policy . . . . . . . . . . . . . 13 68 3.2 Certificate Request Payload . . . . . . . . . . . . . . . 13 69 3.2.1 Certificate Type . . . . . . . . . . . . . . . . . . . 13 70 3.2.2 X.509 Certificate - Signature . . . . . . . . . . . . 14 71 3.2.3 Revocation Lists (CRL and ARL) . . . . . . . . . . . . 14 72 3.2.4 PKCS #7 wrapped X.509 certificate . . . . . . . . . . 15 73 3.2.5 IKEv2's Hash and URL of X.509 certificate . . . . . . 15 74 3.2.6 Location of Certificate Payloads . . . . . . . . . . . 15 75 3.2.7 Presence or Absence of Certificate Request Payloads . 15 76 3.2.8 Certificate Requests . . . . . . . . . . . . . . . . . 16 77 3.2.9 Robustness . . . . . . . . . . . . . . . . . . . . . . 18 78 3.2.10 Optimizations . . . . . . . . . . . . . . . . . . . 18 79 3.3 Certificate Payload . . . . . . . . . . . . . . . . . . . 19 80 3.3.1 Certificate Type . . . . . . . . . . . . . . . . . . . 20 81 3.3.2 X.509 Certificate - Signature . . . . . . . . . . . . 20 82 3.3.3 Revocation Lists (CRL and ARL) . . . . . . . . . . . . 20 83 3.3.4 IKEv2's Hash and URL of X.509 Certificate . . . . . . 21 84 3.3.5 PKCS #7 wrapped X.509 certificate . . . . . . . . . . 21 85 3.3.6 Location of Certificate Payloads . . . . . . . . . . . 21 86 3.3.7 Certificate Payloads Not Mandatory . . . . . . . . . . 21 87 3.3.8 Response to Multiple Certification Authority 88 Proposals . . . . . . . . . . . . . . . . . . . . . . 22 89 3.3.9 Using Local Keying Materials . . . . . . . . . . . . . 22 90 3.3.10 Multiple End-Entity Certificates . . . . . . . . . . 22 91 3.3.11 Robustness . . . . . . . . . . . . . . . . . . . . . 22 92 3.3.12 Optimizations . . . . . . . . . . . . . . . . . . . 24 93 4. Profile of PKIX . . . . . . . . . . . . . . . . . . . . . . 24 94 4.1 X.509 Certificates . . . . . . . . . . . . . . . . . . . . 24 95 4.1.1 Versions . . . . . . . . . . . . . . . . . . . . . . . 24 96 4.1.2 SubjectName . . . . . . . . . . . . . . . . . . . . . 25 97 4.1.3 X.509 Certificate Extensions . . . . . . . . . . . . . 25 98 4.2 X.509 Certificate Revocation Lists . . . . . . . . . . . . 31 99 4.2.1 Multiple Sources of Certificate Revocation 100 Information . . . . . . . . . . . . . . . . . . . . . 31 101 4.2.2 X.509 Certificate Revocation List Extensions . . . . . 32 102 5. Configuration Data Exchange Conventions . . . . . . . . . . 33 103 5.1 Certificates . . . . . . . . . . . . . . . . . . . . . . . 33 104 5.2 CRLs and ARLs . . . . . . . . . . . . . . . . . . . . . . 33 105 5.3 Public Keys . . . . . . . . . . . . . . . . . . . . . . . 34 106 5.4 PKCS#10 Certificate Signing Requests . . . . . . . . . . . 34 107 6. Security Considerations . . . . . . . . . . . . . . . . . . 34 108 6.1 Certificate Request Payload . . . . . . . . . . . . . . . 34 109 6.2 IKEv1 Main Mode . . . . . . . . . . . . . . . . . . . . . 34 110 7. Intellectual Property Rights . . . . . . . . . . . . . . . . 34 111 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . 35 112 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 35 113 9.1 Normative References . . . . . . . . . . . . . . . . . . . 35 114 9.2 Informative References . . . . . . . . . . . . . . . . . . 35 115 Author's Address . . . . . . . . . . . . . . . . . . . . . . 36 116 A. Change History . . . . . . . . . . . . . . . . . . . . . . . 36 117 B. The Possible Dangers of Delta CRLs . . . . . . . . . . . . . 43 118 C. More on Empty CERTREQs . . . . . . . . . . . . . . . . . . . 43 119 D. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 45 120 Intellectual Property and Copyright Statements . . . . . . . 47 122 1. Introduction 124 IKE [1], ISAKMP [2] and IKEv2 [3] provide a secure key exchange 125 mechanism for use with IPsec [4]. In many cases the peers 126 authenticate using digital certificates as specified in PKIX [5]. 127 Unfortunately, the combination of these standards leads to an 128 underspecified set of requirements for the use of certificates in the 129 context of IPsec. 131 ISAKMP references PKIX but in many cases merely specifies the 132 contents of various messages without specifying their syntax or 133 semantics. Meanwhile, PKIX provides a large set of certificate 134 mechanisms which are generally applicable for Internet protocols, but 135 little specific guidance for IPsec. Given the numerous 136 underspecified choices, interoperability is hampered if all 137 implementers do not make similar choices, or at least fail to account 138 for implementations which have chosen differently. 140 This profile of the IKE and PKIX frameworks is intended to provide an 141 agreed-upon standard for using PKI technology in the context of IPsec 142 by profiling the PKIX framework for use with IKE and IPsec, and by 143 documenting the contents of the relevant IKE payloads and further 144 specifying their semantics. 146 In addition to providing a profile of IKE and PKIX, this document 147 attempts to incorporate lessons learned from recent experience with 148 both implementation and deployment, as well as the current state of 149 related protocols and technologies. 151 Material from ISAKMP, IKEv1, IKEv2, or PKIX is not repeated here, and 152 readers of this document are assumed to have read and understood 153 those documents. The requirements and security aspects of those 154 documents are fully relevant to this document as well. 156 This document is organized as follows. Section 2 defines special 157 terminology used in the rest of this document, Section 3 provides the 158 profile of IKEv1/ISAKMP and IKEv2, and Section 4 provides the profile 159 of PKIX. Section 5 covers conventions for the out-of-band exchange 160 of keying materials for configuration purposes. 162 This document is being discussed on the pki4ipsec@icsalabs.com 163 mailing list. 165 2. Terms and Definitions 167 Except for those terms which are defined immediately below, all terms 168 used in this document are defined in either the PKIX [5], ISAKMP [2], 169 IKEv1 [1], IKEv2 [3], or DOI [6] documents. 171 o Peer source address: The source address in packets from a peer. 172 This address may be different from any addresses asserted as the 173 "identity" of the peer. 174 o FQDN: Fully qualified domain name. 175 o ID_USER_FQDN: IKEv2 renamed ID_USER_FQDN to ID_RFC822_ADDR. Both 176 are referred to as ID_USER_FQDN in this document. 178 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 179 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 180 document are to be interpreted as described in RFC-2119 [7]. 182 3. Profile of IKEv1/ISAKMP and IKEv2 184 3.1 Identification Payload 186 The Identification (ID) Payload is used to indicate the identity that 187 the sender claims to be speaking for. The recipient can then use the 188 ID as a lookup key for policy and whatever certificate store or 189 directory that it has available. Our primary concern in this section 190 is to profile the ID payload so that it can be safely used to 191 generate or lookup policy. IKE mandates the use of the ID payload in 192 Phase 1. 194 The DOI [6] defines the 11 types of Identification Data that can be 195 used and specifies the syntax for these types. These are discussed 196 below in detail. 198 The ID payload requirements in this document cover only the portion 199 of the explicit policy checks that deal with the Identification 200 Payload specifically. For instance, in the case where ID does not 201 contain an IP address, checks such as verifying that the peer source 202 address is permitted by the relevant policy are not addressed here as 203 they are out of the scope of this document. 205 Implementations SHOULD populate ID with identity information that is 206 contained within the end-entity certificate (This SHOULD does not 207 contradict text in IKEv2 [3] Section 3.5 that implies a looser 208 binding between these two). Populating ID with identity information 209 from the end-entity certificate enables recipients to use ID as a 210 lookup key to find the peer end-entity certificate. The only case 211 where implementations MAY populate ID with information that is not 212 contained in the end-entity certificate is when ID contains the peer 213 source address (a single address, not a subnet or range). 215 Because implementations may use ID as a lookup key to determine which 216 policy to use, all implementations MUST be especially careful to 217 verify the truthfulness of the contents by verifying that they 218 correspond to some keying material demonstrably held by the peer. 220 Failure to do so may result in the use of an inappropriate or 221 insecure policy. The following sections describe the methods for 222 performing this binding. 224 The following table summarizes the binding of the Identification 225 Payload to the contents of end-entity certificates and of identity 226 information to policy. Each ID type is covered more thoroughly in 227 the following sections. 229 ID type | Support | Correspond | Cert | SPD lookup 230 | for send | PKIX Attrib | matching | rules 231 ------------------------------------------------------------------- 232 | | | | 233 IP*_ADDR | MUST [1] | SubjAltName | MUST [2] | [3], [4] 234 | | iPAddress | | 235 | | | | 236 FQDN | MUST [1] | SubjAltName | MUST [2] | [3], [4] 237 | | dNSName | | 238 | | | | 239 USER_FQDN| MUST [1] | SubjAltName | MUST [2] | [3], [4] 240 | | rfc822Name | | 241 | | | | 242 DN | MUST [1] | Entire | MUST [2] | MUST support lookup 243 | | Subject, | | on any combination 244 | | bitwise | | of C, CN, O, or OU 245 | | compare | | 246 | | | | 247 IP range | MUST NOT | n/a | n/a | n/a 248 | | | | 249 | | | | 250 KEY_ID | MUST NOT | n/a | n/a | n/a 251 | | | | 253 [1] = Implementation MUST have the configuration option to send this 254 ID type in the ID payload. Whether or not the ID type is used is a 255 matter of local configuration. 257 [2] = The ID in the ID payload MUST match the contents of the 258 corresponding field (listed) in the certificate exactly, with no 259 other lookup. The matched ID MAY be used for SPD lookup, but is not 260 required to be used for this. 262 [3] = At a minimum, Implementation MUST be capable of being 263 configured to perform exact matching of the ID payload contents to an 264 entry in the local SPD. 266 [4] = In addition, the implementation MAY also be configurable to 267 perform substring or wildcard matches of ID payload contents to 268 entries in the local SPD. (More on this in Section 3.1.5). 270 When sending an IPV4_ADDR, IPV6_ADDR, FQDN, or USER_FQDN, 271 implementations MUST be able to be configured to send the same string 272 as appears in the corresponding SubjectAltName attribute. This 273 document RECOMMENDS that deployers use this configuration option. 274 All these ID types are treated the same: as strings that can be 275 compared easily and quickly to a corresponding string in an explicit 276 attribute in the certificate. Of these types, FQDN and USER_FQDN are 277 RECOMMENDED over IP addresses (see discussion in Section 3.1.1). 279 When sending a DN as ID, implementations MUST send the entire DN in 280 ID. Also, implementations MUST support at least the C, CN, O, and OU 281 attributes for SPD matching. See Section 3.1.5 for more details 282 about DN, including SPD matching. 284 Recipients MUST be able to perform SPD matching on the exact contents 285 of the ID, and this SHOULD be the default setting. In addition, 286 implementations MAY use substrings or wildcards in local policy 287 configuration to do the SPD matching against the ID contents. In 288 other words, implementations MUST be able to do exact matches of ID 289 to SPD, but MAY also be configurable to do substring or wildcard 290 matches of ID to SPD. 292 IKEv2 adds an optional IDr payload in the second exchange that the 293 initiator may send to the responder in order to specify which of the 294 responder's multiple identities should be used. The responder MAY 295 choose to send an IDr in the 3rd exchange that differs in type or 296 content from the initiator-generated IDr. The initiator MUST be able 297 to receive a responder-generated IDr that is a different type from 298 the one the initiator generated. 300 3.1.1 ID_IPV4_ADDR and ID_IPV6_ADDR 302 Implementations MUST support either the ID_IPV4_ADDR or ID_IPV6_ADDR 303 ID type, depending on whether the implementation supports IPv4, IPv6 304 or both. These addresses MUST be encoded in "network byte order," as 305 specified in IP [8]: The least significant bit (LSB) of each octet is 306 the LSB of the corresponding byte in the network address. For the 307 ID_IPV4_ADDR type, the payload MUST contain exactly four octets [8]. 308 For the ID_IPV6_ADDR type, the payload MUST contain exactly sixteen 309 octets [10]. 311 Implementations SHOULD NOT populate ID payload with IP addresses due 312 to interoperability issues such as problems with NAT traversal, and 313 problems with IP verification behavior. 315 Deployments may only want to consider using the IP address as ID if 316 the following are true: 318 o the peer's IP address is static, not dynamically changing 319 o the peer is NOT behind a NAT'ing device 320 o the administrator intends the implementation to verify that the 321 peer source address matches the IP address in the ID received, and 322 that in the iPAddress field in the peer certificate's 323 SubjectAltName extension. 325 Implementations MUST be capable of verifying that the IP address 326 presented in ID matches via bitwise comparison the IP address present 327 in the certificate's iPAddress field of the SubjectAltName extension. 328 Implementations MUST perform this verification by default. When 329 comparing the contents of ID with the iPAddress field in the 330 SubjectAltName extension for equality, binary comparison MUST be 331 performed. Note that certificates may contain multiple address 332 identity types in which case at least one must match the source IP. 333 If the default is enabled, then a mismatch between the two addresses 334 MUST be treated as an error and security association setup MUST be 335 aborted. This event SHOULD be auditable. Implementations MAY 336 provide a configuration option to (i.e. local policy configuration 337 can enable) skip that verification step, but that option MUST be off 338 by default. We include the "option-to-skip-validation" in order to 339 permit better interoperability, as today implementations vary greatly 340 in how they behave on this topic. 342 In addition, implementations MUST be capable of verifying that the 343 address contained in the ID is the same as the peer source address, 344 contained in the outer most IP header. If ID is one of the IP 345 address types, then implementations MUST perform this verification by 346 default. If this default is enabled, then a mismatch MUST be treated 347 as an error and security association setup MUST be aborted. This 348 event SHOULD be auditable. Implementations MAY provide a 349 configuration option to (i.e. local policy configuration can enable) 350 skip that verification step, but that option MUST be off by default. 351 We include the "option-to-skip-validation" in order to permit better 352 interoperability, as today implementations vary greatly in how they 353 behave on the topic of verification of source IP. 355 If the default for both the verifications above are enabled, then, by 356 transitive property, the implementation will also be verifying that 357 the peer source IP address matches via a bitwise comparison the 358 contents of the iPAddress field in the SubjectAltName extension in 359 the certificate. In addition, implementations MAY allow 360 administrators to configure a local policy that explicitly requires 361 that the peer source IP address match via a bitwise comparison the 362 contents of the iPAddress field in the SubjectAltName extension in 363 the certificate. Implementations SHOULD allow administrators to 364 configure a local policy that skips this validation check. 366 Implementations MAY support substring, wildcard, or regular 367 expression matching of the contents of ID to lookup policy in the 368 SPD, and such would be a matter of local security policy 369 configuration. 371 Implementations MAY use the IP address found in the header of packets 372 received from the peer to lookup the policy, but such implementations 373 MUST still perform verification of the ID payload. Although packet 374 IP addresses are inherently untrustworthy and must therefore be 375 independently verified, it is often useful to use the apparent IP 376 address of the peer to locate a general class of policies that will 377 be used until the mandatory identity-based policy lookup can be 378 performed. 380 For instance, if the IP address of the peer is unrecognized, a VPN 381 gateway device might load a general "road warrior" policy that 382 specifies a particular CA that is trusted to issue certificates which 383 contain a valid rfc822Name which can be used by that implementation 384 to perform authorization based on access control lists (ACLs) after 385 the peer's certificate has been validated. The rfc822Name can then 386 be used to determine the policy that provides specific authorization 387 to access resources (such as IP addresses, ports, and so forth). 389 As another example, if the IP address of the peer is recognized to be 390 a known peer VPN endpoint, policy may be determined using that 391 address, but until the identity (address) is validated by validating 392 the peer certificate, the policy MUST NOT be used to authorize any 393 IPsec traffic. 395 3.1.2 ID_FQDN 397 Implementations MUST support the ID_FQDN ID type, generally to 398 support host-based access control lists for hosts without fixed IP 399 addresses. However, implementations SHOULD NOT use the DNS to map 400 the FQDN to IP addresses for input into any policy decisions, unless 401 that mapping is known to be secure, for example if DNSSEC [11] were 402 employed. 404 If ID contains an ID_FQDN, implementations MUST be capable of 405 verifying that the identity contained in the ID payload matches 406 identity information contained in the peer end-entity certificate, in 407 the dNSName field in the SubjectAltName extension. Implementations 408 MUST perform this verification by default. When comparing the 409 contents of ID with the dNSName field in the SubjectAltName extension 410 for equality, caseless string comparison MUST be performed. 412 Substring, wildcard, or regular expression matching MUST NOT be 413 performed for this comparison. If this default is enabled, then a 414 mismatch MUST be treated as an error and security association setup 415 MUST be aborted. This event SHOULD be auditable. Implementations 416 MAY provide a configuration option to (i.e. local policy 417 configuration can enable) skip that verification step, but that 418 option MUST be off by default. We include the 419 "option-to-skip-validation" in order to permit better 420 interoperability, as today implementations vary greatly in how they 421 behave on this topic. 423 Implementations MAY support substring, wildcard, or regular 424 expression matching of the contents of ID to lookup policy in the 425 SPD, and such would be a matter of local security policy 426 configuration. 428 3.1.3 ID_USER_FQDN 430 Implementations MUST support the ID_USER_FQDN ID type, generally to 431 support user-based access control lists for users without fixed IP 432 addresses. However, implementations SHOULD NOT use the DNS to map 433 the FQDN portion to IP addresses for input into any policy decisions, 434 unless that mapping is known to be secure, for example if DNSSEC [11] 435 were employed. 437 Implementations MUST be capable of verifying that the identity 438 contained in the ID payload matches identity information contained in 439 the peer end-entity certificate, in the rfc822Name field in the 440 SubjectAltName extension. Implementations MUST perform this 441 verification by default. When comparing the contents of ID with the 442 rfc822Name field in the SubjectAltName extension for equality, 443 caseless string comparison MUST be performed. Substring, wildcard, 444 or regular expression matching MUST NOT be performed for this 445 comparison. If this default is enabled, then a mismatch MUST be 446 treated as an error and security association setup MUST be aborted. 447 This event SHOULD be auditable. Implementations MAY provide a 448 configuration option to (i.e. local policy configuration can enable) 449 skip that verification step, but that option MUST be off by default. 450 We include the "option-to-skip-validation" in order to permit better 451 interoperability, as today implementations vary greatly in how they 452 behave on this topic. 454 Implementations MAY support substring, wildcard, or regular 455 expression matching of the contents of ID to lookup policy in the 456 SPD, and such would be a matter of local security policy 457 configuration. 459 3.1.4 ID_IPV4_ADDR_SUBNET, ID_IPV6_ADDR_SUBNET, ID_IPV4_ADDR_RANGE, 460 ID_IPV6_ADDR_RANGE 462 Historically there was no standard method for putting address subnet 463 or range identity information into certificates, nor are there any 464 implementations known to support these ID types. Therefore, use of 465 these ID types is currently undefined. Implementations MUST NOT 466 generate these ID types. 468 Note that work in SBGP [12] for defining blocks of addresses using 469 the certificate extension identified by: 471 id-pe-ipAddrBlock OBJECT IDENTIFIER ::= { id-pe 7 } 473 is experimental at this time. 475 3.1.5 ID_DER_ASN1_DN 477 Implementations MUST support receiving the ID_DER_ASN1_DN ID type. 478 Implementations MUST be capable of generating this type, and the 479 decision to do so will be a matter of local security policy 480 configuration. When generating this type, implementations MUST 481 populate the contents of ID with the SubjectName from the end-entity 482 certificate, and MUST do so such that a binary comparison of the two 483 will succeed. If there is not a match, this MUST be treated as an 484 error and security association setup MUST be aborted. This event 485 SHOULD be auditable. Note, if the certificate was erroneously 486 created such that the encoding of the SubjectName DN varies from the 487 constraints set by DER, that non-conformant DN MUST be used to 488 populate the ID payload: in other words, implementations MUST NOT 489 re-encode the DN for the purposes of making it DER if it does not 490 appear in the certificate as DER. 492 Implementations MUST NOT populate ID with the SubjectName from the 493 end-entity certificate if it is empty, even though an empty 494 certificate SubjectName is explicitly allowed in the "Subject" 495 section of PKIX. 497 Regarding SPD matching, implementations MUST be able to perform 498 matching based on a bitwise comparison of the entire DN in ID to its 499 entry in the SPD. However, operational experience has shown that 500 using the entire DN in local configuration is difficult, especially 501 in large scale deployments. Therefore, implementations also MUST be 502 able to perform SPD matches of any combination of one or more of the 503 C, CN, O, OU attributes within Subject DN in the ID to the same in 504 the SPD. Implementations MAY support matching using additional DN 505 attributes in any combination, although interoperability is far from 506 certain and dubious. Implementations MAY also support performing 507 substring, wildcard, or regular expression matches for any of its 508 supported DN attributes from ID, in any combination, to the SPD. 509 Such flexibility allows deployers to create one SPD entry on the 510 gateway for an entire department of a company (e.g. O=Foobar Inc., 511 OU=Engineering) while still allowing them to draw out other details 512 from the DN (e.g. CN=John Doe) for auditing purposes. All the above 513 is a matter of local implementation and local policy definition and 514 enforcement capability, not bits on the wire, but will have a great 515 impact on interoperability. 517 3.1.6 ID_DER_ASN1_GN 519 Implementations MUST NOT generate this type. 521 3.1.7 ID_KEY_ID 523 The ID_KEY_ID type used to specify pre-shared keys and thus is out of 524 scope. 526 3.1.8 Selecting an Identity from a Certificate 528 Implementations MUST support certificates that contain more than a 529 single identity, such as when SubjectName and the SubjectAltName 530 extension are both populated, or the SubjectAltName extension 531 contains multiple identities irrespective of whether SubjectName is 532 empty or not. In many cases a certificate will contain an identity 533 such as an IP address in the SubjectAltName extension in addition to 534 a non-empty SubjectName. 536 Implementations SHOULD populate ID with whichever identity is likely 537 to be named in the peer's policy. In practice, this generally means 538 FQDN, or USER_FQDN, but this information may also be available to the 539 administrator through some out-of-band means. In the absence of such 540 out-of-band configuration information, the identity with which an 541 implementation chooses to populate the ID payload is a local matter. 543 3.1.9 SubjectName for DN Only 545 If an FQDN is intended to be processed as an identity for the 546 purposes ID matching, it MUST be placed in the dNSName field of the 547 SubjectAltName extension. Implementations MUST NOT populate 548 SubjectName with an FQDN in place of populating the dNSName field of 549 the SubjectAltName extension. 551 While nothing prevents an FQDN, USER_FQDN, or IP address information 552 from appearing somewhere in the SubjectName contents, such entries 553 MUST NOT be interpreted as identity information for the purposes of 554 matching with ID or for policy lookup. 556 3.1.10 Binding Identity to Policy 558 In the presence of certificates that contain multiple identities, 559 implementations MUST select the most appropriate identity from the 560 certificate and populate the ID with that. The recipient MUST use 561 the identity sent as a first key when selecting the policy. The 562 recipient MUST also use the most specific policy from that database 563 if there are overlapping policies caused by wildcards (or the 564 implementation can de-correlate the policy database so there will not 565 be overlapping entries, or it can also forbid creation of overlapping 566 policies and leave the de-correlation process to the administrator, 567 but as this moves the problem to the administrator it is NOT 568 RECOMMENDED). 570 For example, imagine that a implementation is configured with a 571 certificate that contains both a non-empty SubjectName and a dNSName. 572 The sender's policy may specify which of those to use, and it 573 indicates the policy to the other end by sending that ID. If the 574 recipient has both a specific policy for the dNSName for this host 575 and generic wildcard rule for some attributes present in the 576 SubjectName, it will match a different policy depending which ID is 577 sent. As the sender knows why it wanted to connect the peer, it also 578 knows what identity it should use to match the policy it needs to the 579 operation it tries to perform; it is the only party who can select 580 the ID adequately. 582 In the event the policy cannot be found in the recipient's SPD using 583 the ID sent, then the recipient MAY use the other identities in the 584 certificate when attempting to match a suitable policy. For example, 585 say the certificate contains non-empty SubjectName, a dNSName and an 586 iPAddress. If an iPAddress is sent in ID but no specific entry 587 exists for the address in the policy database, the recipient MAY 588 search in the policy database based on the SubjectName or the dNSName 589 contained in the certificate. 591 3.2 Certificate Request Payload 593 The Certificate Request (CERTREQ) Payload allows an implementation to 594 request that a peer provide some set of certificates or certificate 595 revocation lists. It is not clear from ISAKMP exactly how that set 596 should be specified or how the peer should respond. We describe the 597 semantics on both sides. 599 3.2.1 Certificate Type 601 The Certificate Type field identifies to the peer the type of 602 certificate keying materials that are desired. ISAKMP defines 10 603 types of Certificate Data that can be requested and specifies the 604 syntax for these types, and IKEv2 specifies 3 additional types. For 605 the purposes of this document, only the following types are relevant: 607 o X.509 Certificate - Signature 608 o Revocation Lists (CRL and ARL) 609 o PKCS #7 wrapped X.509 certificate 610 o IKEv2's Hash and URL of X.509 certificate 612 The use of the other types: 614 o X.509 Certificate - Key Exchange 615 o PGP Certificate 616 o DNS Signed Key 617 o Kerberos Tokens 618 o SPKI Certificate 619 o X.509 Certificate Attribute 620 o IKEv2's Raw RSA Key 621 o IKEv2's Hash and URL of X.509 bundle 623 are out of the scope of this document. 625 3.2.2 X.509 Certificate - Signature 627 This type requests that the end-entity certificate be a signing 628 certificate. 630 3.2.3 Revocation Lists (CRL and ARL) 632 ISAKMP and IKEv2 do not support Certificate Payload sizes over 633 approximately 64K, which is too small for many CRLs. Therefore, the 634 acquisition of revocation material is to be dealt with out-of-band of 635 IKE. For this and other reasons, implementations SHOULD NOT generate 636 CERTREQs where the Certificate Type is "Certificate Revocation List 637 (CRL)" or "Authority Revocation List (ARL)". Implementations that do 638 generate such CERTREQs MUST NOT require the recipient to respond with 639 a CRL or ARL, and MUST NOT fail when not receiving any. Upon receipt 640 of such a CERTREQ, implementations MAY ignore the request. 642 In lieu of exchanging revocation lists in-band, a pointer to 643 revocation checking SHOULD be listed in either the 644 CRLDistributionPoints (CDP) or the AuthorityInfoAccess (AIA) 645 certificate extensions (see Section 4 for details). Unless other 646 methods for obtaining revocation information are available, 647 implementations SHOULD be able to process these attributes, and from 648 them be able to identify cached revocation material, or retrieve the 649 relevant revocation material from a URL, for validation processing. 650 In addition, implementations MUST have the ability to configure 651 validation checking information for each certification authority. 653 Regardless of the method (CDP, AIA, or static configuration), the 654 acquisition of revocation material SHOULD occur out-of-band of IKE. 656 3.2.4 PKCS #7 wrapped X.509 certificate 658 This ID type defines a particular encoding (not a particular 659 certificate type), some current implementations may ignore CERTREQs 660 they receive which contain this ID type, and the authors are unaware 661 of any implementations that generate such CERTREQ messages. 662 Therefore, the use of this type is deprecated. Implementations 663 SHOULD NOT require CERTREQs that contain this Certificate Type. 664 Implementations which receive CERTREQs which contain this ID type MAY 665 treat such payloads as synonymous with "X.509 Certificate - 666 Signature". 668 3.2.5 IKEv2's Hash and URL of X.509 certificate 670 This ID type defines a request for the peer to send a hash and URL of 671 it X.509 certificate, instead of the actual certificate itself. This 672 is a particularly useful mechanism when the peer is a device with 673 little memory and lower bandwidth, e.g. a mobile handset or consumer 674 electronics device. 676 If the IKEv2 implementation supports URL lookups, and prefers such a 677 URL to receiving actual certificates, then the implementation will 678 want to send a notify of type HTTP_CERT_LOOKUP_SUPPORTED. From IKEv2 679 [3], section 3.10.1, "This notification MAY be included in any 680 message that can include a CERTREQ payload and indicates that the 681 sender is capable of looking up certificates based on an HTTP-based 682 URL (and hence presumably would prefer to receive certificate 683 specifications in that format)." If an HTTP_LOOKUP_SUPPORTED 684 notification is sent the sender MUST support the http scheme. See 685 Section 3.3.4 for more discussion. 687 3.2.6 Location of Certificate Payloads 689 In IKEv1, the CERTREQ payload MUST be in messages 4 and 5. In IKEv2, 690 the CERTREQ payload must be in messages 2 and 3. Note that in IKEv2, 691 it is possible to have one side authenticating with certificates 692 while the other side authenticates with preshared keys. 694 3.2.7 Presence or Absence of Certificate Request Payloads 696 When in-band exchange of certificate keying materials is desired, 697 implementations MUST inform the peer of this by sending at least one 698 CERTREQ. In other words, an implementation which does not send any 699 CERTREQs during an exchange SHOULD NOT expect to receive any CERT 700 payloads. 702 3.2.8 Certificate Requests 704 3.2.8.1 Specifying Certification Authorities 706 When requesting in-band exchange of keying materials, implementations 707 SHOULD generate CERTREQs for every peer trust anchor that local 708 policy explicitly deems trusted during a given exchange. For IKEv1, 709 implementations SHOULD populate the Certification Authority field 710 with the SubjectName of the trust anchor, populated such that binary 711 comparison of the SubjectName and the Certification Authority will 712 succeed. For IKEv2, implementations MUST populate the Certification 713 Authority field as specified in IKEv2 [3]. 715 Upon receipt of a CERTREQ, implementations MUST respond by sending at 716 least the end-entity certificate corresponding to the Certification 717 Authority listed in the CERTREQ unless local security policy 718 configuration specifies that keying materials must be exchanged 719 out-of-band. Implementations MAY send certificates other than the 720 end-entity certificate (see Section 3.3 for discussion). 722 Note, in the case where multiple end-entity certificates may be 723 available which chain to different trust anchors, implementations 724 SHOULD resort to local heuristics to determine which trust anchor is 725 most appropriate to use for generating the CERTREQ. Such heuristics 726 are out of the scope of this document. 728 3.2.8.2 Empty Certification Authority Field 730 Implementations SHOULD generate CERTREQs where the Certificate Type 731 is "X.509 Certificate - Signature" and where a the Certification 732 Authority field is not empty. However, implementations MAY generate 733 CERTREQs with an empty Certification Authority field under special 734 conditions. Although PKIX prohibits certificates with empty 735 IssuerName fields, there does exist a use case where doing so is 736 appropriate, and carries special meaning in the IKE context. This 737 has become a convention within the IKE interoperability tests and 738 usage space, and so its use is specified, explained here for the sake 739 of interoperability. 741 USE CASE: Consider the rare case where you have a gateway with 742 multiple policies for a large number of IKE peers: some of these 743 peers are business partners, some are remote access employees, some 744 are teleworkers, some are branch offices, and/or the gateway may be 745 simultaneously serving many customers (e.g. Virtual Routers). The 746 total number of certificates, and corresponding trust anchors, is 747 very high, say hundreds. Each of these policies is configured with 748 one or more acceptable trust anchors, so that in total, the gateway 749 has one hundred (100) trust anchors that could possibly used to 750 authenticate an incoming connection. Assume that many of those 751 connections originate from hosts/gateways with dynamically assigned 752 IP addresses, so that the source IP of the IKE initiator is not known 753 to the gateway, nor is the identity of the initiator (until it is 754 revealed in Main Mode message 5). In IKE main mode message 4, the 755 responder gateway will need to send a CERTREQ to the initiator. 756 Given this example, the gateway will have no idea which of the 757 hundred possible Certification Authorities to send in the CERTREQ. 758 Sending all possible Certification Authorities will cause significant 759 processing delays, bandwidth consumption, and UDP fragmentation, so 760 this tactic is ruled out. 762 In such a deployment, the responder gateway implementation should be 763 able to do all it can to indicate a Certification Authority in the 764 CERTREQ. This means the responder SHOULD first check SPD to see if 765 it can match the source IP, and find some indication of which CA is 766 associated with that IP. If this fails (because the source IP is not 767 familiar, as in the case above), then the responder SHOULD have a 768 configuration option specifying which CA's are the default CAs to 769 indicate in CERTREQ during such ambiguous connections (e.g. send 770 CERTREQ with these N CAs if there is an unknown source IP). If such 771 a fall-back is not configured or impractical in a certain deployment 772 scenario, then the responder implementation SHOULD have both of the 773 following configuration options: 775 o send a CERTREQ payload with an empty Certification Authority 776 field, or 777 o terminate the negotiation with an appropriate error message and 778 audit log entry. 780 Receiving a CERTREQ payload with an empty Certification Authority 781 field indicates that the recipient should send all/any end-entity 782 certificates it has, regardless of the trust anchor. The initiator 783 should be aware of what policy and which identity it will use, as it 784 initiated the connection on a matched policy to begin with, and can 785 thus respond with the appropriate certificate. 787 If, after sending an empty CERTREQ in Main Mode message 4, a 788 responder receives a certificate in message 5 that chains to a trust 789 anchor that the responder either (a) does NOT support, or (b) was not 790 configured for the policy (that policy was now able to be matched due 791 to having the initiator's certificate present), this MUST be treated 792 as an error and security association setup MUST be aborted. This 793 event SHOULD be auditable. 795 Instead of sending a empty CERTREQ, the responder implementation MAY 796 be configured to terminate the negotiation on the grounds of a 797 conflict with locally configured security policy. 799 The decision of which to configure is a matter of local security 800 policy, this document RECOMMENDS that both options be presented to 801 administrators. 803 More examples, and explanation on this issue are included in "More on 804 Empty CERTREQs" (Appendix C). 806 3.2.9 Robustness 808 3.2.9.1 Unrecognized or Unsupported Certificate Types 810 Implementations MUST be able to deal with receiving CERTREQs with 811 unsupported Certificate Types. Absent any recognized and supported 812 CERTREQ types, implementations MAY treat them as if they are of a 813 supported type with the Certification Authority field left empty, 814 depending on local policy. ISAKMP [2] Section 5.10 "Certificate 815 Request Payload Processing" specifies additional processing. 817 3.2.9.2 Undecodable Certification Authority Fields 819 Implementations MUST be able to deal with receiving CERTREQs with 820 undecodable Certification Authority fields. Implementations MAY 821 ignore such payloads, depending on local policy. ISAKMP specifies 822 other actions which may be taken. 824 3.2.9.3 Ordering of Certificate Request Payloads 826 Implementations MUST NOT assume that CERTREQs are ordered in any way. 828 3.2.10 Optimizations 830 3.2.10.1 Duplicate Certificate Request Payloads 832 Implementations SHOULD NOT send duplicate CERTREQs during an 833 exchange. 835 3.2.10.2 Name Lowest 'Common' Certification Authorities 837 When a peer's certificate keying materials have been cached, an 838 implementation can send a hint to the peer to elide some of the 839 certificates the peer would normally respond with. In addition to 840 the normal set of CERTREQs that are sent specifying the trust 841 anchors, an implementation MAY send CERTREQs specifying the relevant 842 cached end-entity certificates. When sending these hints, it is 843 still necessary to send the normal set of trust anchor CERTREQs 844 because the hints do not sufficiently convey all of the information 845 required by the peer. Specifically, either the peer may not support 846 this optimization or there may be additional chains that could be 847 used in this context but will not be if only the end-entity 848 certificate is specified. 850 No special processing is required on the part of the recipient of 851 such a CERTREQ, and the end-entity certificates will still be sent. 852 On the other hand, the recipient MAY elect to elide certificates 853 based on receipt of such hints. 855 CERTREQs must contain information that identifies a Certification 856 Authority certificate, which results in the peer always sending at 857 least the end-entity certificate. Always sending the end-entity 858 certificate allows implementations to determine unambiguously when a 859 new certificate is being used by a peer (perhaps because the previous 860 certificate has just expired), which may result in a failure because 861 a new intermediate CA certificate might not be available to validate 862 the new end-entity certificate). Implementations which implement 863 this optimization MUST recognize when the end-entity certificate has 864 changed and respond to it by not performing this optimization if the 865 exchange must be retried so that any missing keying materials will be 866 sent during retry. 868 3.2.10.3 Example 870 Imagine that an IKEv1 implementation has previously received and 871 cached the peer certificate chain TA->CA1->CA2->EE. If during a 872 subsequent exchange this implementation sends a CERTREQ containing 873 the SubjectName in certificate TA, this implementation is requesting 874 that the peer send at least 3 certificates: CA1, CA2, and EE. On the 875 other hand, if this implementation also sends a CERTREQ containing 876 the SubjectName of CA2, the implementation is providing a hint that 877 only 1 certificate needs to be sent: EE. Note that in this example, 878 the fact that TA is a trust anchor should not be construed to imply 879 that TA is a self-signed certificate. 881 3.3 Certificate Payload 883 The Certificate (CERT) Payload allows the peer to transmit a single 884 certificate or CRL. Multiple certificates should be transmitted in 885 multiple payloads. For backwards compatibility reasons, 886 implementations MAY send intermediate CA certificates in addition to 887 the appropriate end-entity certificate(s), but SHOULD NOT send any 888 CRLs, ARLs, or trust anchors. The reason for not exchanging CRLs or 889 ARLs in IKE is to: 891 o decrease UDP fragmentation 892 o simplify the IKE exchange 893 o reduce bandwidth requirements for IKE exchanges 894 Note, however, that while the sender of the CERT payloads SHOULD NOT 895 send any trust anchors, it's possible that the recipient may consider 896 any given intermediate CA certificate to be a trust anchor. For 897 instance, imagine the sender has the certificate chain TA1->CA1->EE1 898 while the recipient has the certificate chain TA2->EE2 where TA2=CA1. 899 The sender is merely including an intermdiate CA certificate, while 900 the recipient receives a trust anchor. 902 However, not all certificate forms that are legal in PKIX make sense 903 in the context of IPsec. The issue of how to represent 904 IKE-meaningful name-forms in a certificate is especially problematic. 905 This document provides a profile for a subset of PKIX that makes 906 sense for IKEv1/ISAKMP and IKEv2. 908 3.3.1 Certificate Type 910 The Certificate Type field identifies to the peer the type of 911 certificate keying materials that are included. ISAKMP defines 10 912 types of Certificate Data that can be sent and specifies the syntax 913 for these types, and IKEv2 specifies 3 additional types. For the 914 purposes of this document, only the following types are relevant: 916 o X.509 Certificate - Signature 917 o Revocation Lists (CRL and ARL) 918 o PKCS #7 wrapped X.509 certificate 919 o IKEv2's Hash and URL of X.509 certificate 921 The use of the other types: 923 o X.509 Certificate - Key Exchange 924 o PGP Certificate 925 o DNS Signed Key 926 o Kerberos Tokens 927 o SPKI Certificate 928 o X.509 Certificate Attribute 929 o IKEv2's Raw RSA Key 930 o IKEv2's Hash and URL of X.509 bundle 932 are out of the scope of this document. 934 3.3.2 X.509 Certificate - Signature 936 This type specifies that Certificate Data contains a certificate used 937 for signing. 939 3.3.3 Revocation Lists (CRL and ARL) 941 These types specify that Certificate Data contains an X.509 CRL or 942 ARL. These types SHOULD NOT be sent in IKE. See Section 3.2.3 for 943 discussion. 945 3.3.4 IKEv2's Hash and URL of X.509 Certificate 947 This type specifies that Certificate Data contains a hash and the URL 948 to a repository where an X.509 certificate can be retrieved. 950 An implementation that sends a HTTP_LOOKUP_SUPPORTED notification 951 MUST support the http scheme and MAY support the ftp scheme, and MUST 952 NOT require any specific form of the url-path and it SHOULD support 953 having user-name, password and port parts in the URL. The following 954 are examples of mandatory forms: 956 o http://certs.example.com/certificate.crt 957 o http://certs.example.com/certs/cert.pl?u=foo;a=pw;valid-to=+86400 958 o http://certs.example.com/%0a/../foo/bar/zappa 960 while the following is an example of a form that SHOULD be supported: 962 o http://user:password@certs.example.com:8888/certificate.crt 964 The following is an example of the ftp scheme that MAY be supported: 966 o ftp://ftp.example.com/pub/certificate.crt 968 3.3.5 PKCS #7 wrapped X.509 certificate 970 This type defines a particular encoding, not a particular certificate 971 type. Implementations SHOULD NOT generate CERTs that contain this 972 Certificate Type. Implementations SHOULD accept CERTs that contain 973 this Certificate Type because several implementations are known to 974 generate them. Note that those implementations sometimes include 975 entire certificate hierarchies inside a single CERT PKCS #7 payload, 976 which violates the requirement specified in ISAKMP that this payload 977 contain a single certificate. 979 3.3.6 Location of Certificate Payloads 981 In IKEv1, the CERT payload MUST be in messages 5 and 6. In IKEv2, 982 the CERT payload must be in messages 3 and 4. Note that in IKEv2, it 983 is possible to have one side authenticating with certificates while 984 the other side authenticates with preshared keys. 986 3.3.7 Certificate Payloads Not Mandatory 988 An implementation which does not receive any CERTREQs during an 989 exchange SHOULD NOT send any CERT payloads, except when explicitly 990 configured to proactively send CERT payloads in order to interoperate 991 with non-compliant implementations which fail to send CERTREQs even 992 when certificates are desired. In this case, an implementation MAY 993 send the certificate chain (not including the trust anchor) 994 associated with the end-entity certificate. This MUST NOT be the 995 default behavior of implementations. 997 Implementations whose local security policy configuration expects 998 that a peer must receive certificates through out-of-band means 999 SHOULD ignore any CERTREQ messages that are received. 1001 Implementations that receive CERTREQs from a peer which contain only 1002 unrecognized Certification Authorities SHOULD NOT continue the 1003 exchange, in order to avoid unnecessary and potentially expensive 1004 cryptographic processing, denial of service (resource starvation) 1005 attacks. 1007 3.3.8 Response to Multiple Certification Authority Proposals 1009 In response to multiple CERTREQs which contain different 1010 Certification Authority identities, implementations MAY respond using 1011 an end-entity certificate which chains to a CA that matches any of 1012 the identities provided by the peer. 1014 3.3.9 Using Local Keying Materials 1016 Implementations MAY elect to skip parsing or otherwise decoding a 1017 given set of CERTs if equivalent keying materials are available via 1018 some preferable means, such as the case where certificates from a 1019 previous exchange have been cached. 1021 3.3.10 Multiple End-Entity Certificates 1023 Implementations SHOULD NOT send multiple end-entity certificates and 1024 recipients SHOULD NOT be expected to iterate over multiple end-entity 1025 certificates. 1027 If multiple end-entity certificates are sent, they MUST have the same 1028 public key, otherwise the responder does not know which key was used 1029 in the Main Mode message 5. 1031 3.3.11 Robustness 1033 3.3.11.1 Unrecognized or Unsupported Certificate Types 1035 Implementations MUST be able to deal with receiving CERTs with 1036 unrecognized or unsupported Certificate Types. Implementations MAY 1037 discard such payloads, depending on local policy. ISAKMP [2] Section 1038 5.10 "Certificate Request Payload Processing" specifies additional 1039 processing. 1041 3.3.11.2 Undecodable Certificate Data Fields 1043 Implementations MUST be able to deal with receiving CERTs with 1044 undecodable Certificate Data fields. Implementations MAY discard 1045 such payloads, depending on local policy. ISAKMP specifies other 1046 actions which may be taken. 1048 3.3.11.3 Ordering of Certificate Payloads 1050 For IKEv1, implementations MUST NOT assume that CERTs are ordered in 1051 any way. For IKEv2, implementations MUST NOT assume that any except 1052 the first CERT is ordered in any way. IKEv2 specifies that the first 1053 CERT contain an end-entity certificate which can be used to 1054 authenticate the peer. 1056 3.3.11.4 Duplicate Certificate Payloads 1058 Implementations MUST support receiving multiple identical CERTs 1059 during an exchange. 1061 3.3.11.5 Irrelevant Certificates 1063 Implementations MUST be prepared to receive certificates and CRLs 1064 which are not relevant to the current exchange. Implementations MAY 1065 discard such extraneous certificates and CRLs. 1067 Implementations MAY send certificates which are irrelevant to an 1068 exchange. One reason for including certificates which are irrelevant 1069 to an exchange is to minimize the threat of leaking identifying 1070 information in exchanges where CERT is not encrypted. It should be 1071 noted, however, that this probably provides rather poor protection 1072 against leaking the identity. 1074 Another reason for including certificates that seem irrelevant to an 1075 exchange is that there may be two chains from the Certification 1076 Authority to the end entity, each of which is only valid with certain 1077 validation parameters (such as acceptable policies). Since the 1078 end-entity doesn't know which parameters the relying party is using, 1079 it should send the certificates needed for both chains (even if 1080 there's only one CERTREQ). 1082 Implementations SHOULD NOT send multiple end-entity certificates and 1083 recipients SHOULD NOT be expected to iterate over multiple end-entity 1084 certificates. 1086 3.3.12 Optimizations 1088 3.3.12.1 Duplicate Certificate Payloads 1090 Implementations SHOULD NOT send duplicate CERTs during an exchange. 1091 Such payloads should be suppressed. 1093 3.3.12.2 Send Lowest 'Common' Certificates 1095 When multiple CERTREQs are received which specify certificate 1096 authorities within the end-entity certificate chain, implementations 1097 MAY send the shortest chain possible. However, implementations 1098 SHOULD always send the end-entity certificate. See Section 3.2.10.2 1099 for more discussion of this optimization. 1101 3.3.12.3 Ignore Duplicate Certificate Payloads 1103 Implementations MAY employ local means to recognize CERTs that have 1104 already been received and SHOULD discard these duplicate CERTs. 1106 3.3.12.4 Hash Payload 1108 IKEv1 specifies the optional use of the Hash Payload to carry a 1109 pointer to a certificate in either of the Phase 1 public key 1110 encryption modes. This pointer is used by an implementation to 1111 locate the end-entity certificate that contains the public key that a 1112 peer should use for encrypting payloads during the exchange. 1114 Implementations SHOULD include this payload whenever the public 1115 portion of the keypair has been placed in a certificate. 1117 4. Profile of PKIX 1119 Except where specifically stated in this document, implementations 1120 MUST conform to the requirements of PKIX [5]. 1122 4.1 X.509 Certificates 1124 4.1.1 Versions 1126 Although PKIX states that "implementations SHOULD be prepared to 1127 accept any version certificate", in practice this profile requires 1128 certain extensions that necessitate the use of Version 3 certificates 1129 for all but self-signed certificates used as trust anchors. 1130 Implementations that conform to this document MAY therefore reject 1131 Version 1 and Version 2 certificates in all other cases. 1133 4.1.2 SubjectName 1135 Certification Authority implementations MUST be able to create 1136 certificates with SubjectName fields with at least the following four 1137 attributes: CN, C, O, OU. Implementations MAY support other 1138 SubjectName attributes as well. The contents of these attributes 1139 SHOULD be configurable on a certificate by certificate basis, as 1140 these fields will likely be used by IKE implementations to match SPD 1141 policy. 1143 See Section 3.1.5 for details on how IKE implementations need to be 1144 able to process SubjectName field attributes for SPD policy lookup. 1146 4.1.2.1 Empty SubjectName 1148 IKE Implementations MUST accept certificates which contain an empty 1149 SubjectName field, as specified in PKIX. Identity information in 1150 such certificates will be contained entirely in the SubjectAltName 1151 extension. 1153 4.1.2.2 Specifying Hosts and not FQDN in SubjectName 1155 Implementations which desire to place host names that are not 1156 intended to be processed by recipients as FQDNs (for instance 1157 "Gateway Router") in the SubjectName MUST use the commonName 1158 attribute. 1160 4.1.2.3 EmailAddress 1162 As specified in PKIX, implementations MUST NOT populate 1163 DistinguishedNames with the emailAddress attribute. 1165 4.1.3 X.509 Certificate Extensions 1167 Conforming IKE implementations MUST recognize extensions which must 1168 or may be marked critical according to this specification. These 1169 extensions are: KeyUsage, SubjectAltName, and BasicConstraints. 1171 Certification Authority implementations SHOULD generate certificates 1172 such that the extension criticality bits are set in accordance with 1173 PKIX and this document. With respect to PKIX compliance, IKE 1174 implementations processing certificates MAY ignore the value of the 1175 criticality bit for extensions that are supported by that 1176 implementation, but MUST support the criticality bit for extensions 1177 that are not supported by that implementation. That is, a relying 1178 party processes all the extensions it is aware of whether the bit is 1179 true or false -- the bit says what happens when a relying party 1180 cannot process an extension. 1182 implements bit in cert PKIX mandate behavior 1183 ------------------------------------------------------ 1184 yes true true ok 1185 yes true false ok or reject 1186 yes false true ok or reject 1187 yes false false ok 1188 no true true reject 1189 no true false reject 1190 no false true reject 1191 no false false ok 1193 4.1.3.1 AuthorityKeyIdentifier and SubjectKeyIdentifier 1195 Implementations SHOULD NOT assume support for the 1196 AuthorityKeyIdentifier or SubjectKeyIdentifier extensions, and thus 1197 Certification Authority implementations SHOULD NOT generate 1198 certificate hierarchies which are overly complex to process in the 1199 absence of these extensions, such as those that require possibly 1200 verifying a signature against a large number of similarly named CA 1201 certificates in order to find the CA certificate which contains the 1202 key that was used to generate the signature. 1204 4.1.3.2 KeyUsage 1206 IKE uses an end-entity certificate in the authentication process. 1207 The end-entity certificate may be used for multiple applications. As 1208 such, the CA can impose some constraints on the manner that a public 1209 key ought to be used. The KeyUsage and ExtendedKeyUsage extensions 1210 apply in this situation. 1212 Since we are talking about using the public key to validate a 1213 signature, if the KeyUsage extension is present, then at least one of 1214 the digitalSignature or the nonRepudiation bits in the KeyUsage 1215 extension MUST be set (both can be set as well). It is also fine if 1216 other KeyUsage bits are set. 1218 A summary of the logic flow for peer cert validation follows: 1220 o If told (by configuration) to ignore KeyUsage (KU), accept cert 1221 regardless of its markings. 1222 o If no KU extension, accept cert. 1223 o If KU present and doesn't mention digitalSignature or 1224 nonRepudiation (both, in addition to other KUs, is also fine), 1225 reject cert. 1226 o If none of the above, accept cert. 1228 4.1.3.3 PrivateKeyUsagePeriod 1230 PKIX recommends against the use of this extension. The 1231 PrivateKeyUsageExtension is intended to be used when signatures will 1232 need to be verified long past the time when signatures using the 1233 private keypair may be generated. Since IKE SAs are short-lived 1234 relative to the intended use of this extension in addition to the 1235 fact that each signature is validated only a single time, the 1236 usefulness of this extension in the context of IKE is unclear. 1237 Therefore, Certification Authority implementations MUST NOT generate 1238 certificates that contain the PrivateKeyUsagePeriod extension. If an 1239 IKE implementation receives a certificate with this set, it SHOULD 1240 ignore it. 1242 4.1.3.4 CertificatePolicies 1244 Many IKE implementations do not currently provide support for the 1245 CertificatePolicies extension. Therefore, Certification Authority 1246 implementations that generate certificates which contain this 1247 extension SHOULD NOT mark the extension as critical. 1249 4.1.3.5 PolicyMappings 1251 Many IKE implementations do not support the PolicyMappings extension. 1252 Therefore, implementations that generate certificates which contain 1253 this extension SHOULD NOT mark the extension as critical. 1255 4.1.3.6 SubjectAltName 1257 Deployments that intend to use an ID of either FQDN, USER_FQDN, 1258 IPV4_ADDR or IPV6_ADDR MUST issue certificates with the corresponding 1259 SubjectAltName fields populated with the same data. Implementations 1260 SHOULD generate only the following GeneralName choices in the 1261 SubjectAltName extension, as these choices map to legal 1262 IKEv1/ISAKMP/IKEv2 Identification Payload types: rfc822Name, dNSName, 1263 or iPAddress. Although it is possible to specify any GeneralName 1264 choice in the Identification Payload by using the ID_DER_ASN1_GN ID 1265 type, implementations SHOULD NOT assume support for such 1266 functionality, and SHOULD NOT generate certificates that do so. 1268 4.1.3.6.1 dNSName 1270 This field MUST contain a fully qualified domain name. If the IKE ID 1271 type is FQDN then the dNSName field MUST match its contents. 1272 Implementations MUST NOT generate names that contain wildcards. 1273 Implementations MAY treat certificates that contain wildcards in this 1274 field as syntactically invalid. 1276 Although this field is in the form of an FQDN, IKE implementations 1277 SHOULD NOT assume that this field contains an FQDN that will resolve 1278 via the DNS, unless this is known by way of some out-of-band 1279 mechanism. Such a mechanism is out of the scope of this document. 1280 Implementations SHOULD NOT treat the failure to resolve as an error. 1282 4.1.3.6.2 iPAddress 1284 If the IKE ID type is IPV4_ADDR or IPV6_ADDR then the iPAddress field 1285 MUST match its contents. Note that although PKIX permits CIDR [13] 1286 notation in the "Name Constraints" extension, PKIX explicitly 1287 prohibits using CIDR notation for conveying identity information. In 1288 other words, the CIDR notation MUST NOT be used in the SubjectAltName 1289 extension. 1291 4.1.3.6.3 rfc822Name 1293 If the IKE ID type is USER_FQDN then the rfc822Name field MUST match 1294 its contents. Although this field is in the form of an Internet mail 1295 address, IKE implementations SHOULD NOT assume that this field 1296 contains a valid email address, unless this is known by way of some 1297 out-of-band mechanism. Such a mechanism is out of the scope of this 1298 document. 1300 4.1.3.7 IssuerAltName 1302 Certification Authority implementations SHOULD NOT assume that other 1303 implementations support the IssuerAltName extension, and especially 1304 should not assume that information contained in this extension will 1305 be displayed to end users. 1307 4.1.3.8 SubjectDirectoryAttributes 1309 The SubjectDirectoryAttributes extension is intended to convey 1310 identification attributes of the subject. IKE implementations MAY 1311 ignore this extension when it is marked non-critical, as PKIX 1312 mandates. 1314 4.1.3.9 BasicConstraints 1316 PKIX mandates that CA certificates contain this extension and that it 1317 be marked critical. IKE implementations SHOULD reject CA 1318 certificates that do not contain this extension. For backwards 1319 compatibility, implementations may accept such certificates if 1320 explicitly configured to do so, but the default for this setting MUST 1321 be to reject such certificates. 1323 4.1.3.10 NameConstraints 1325 Many IKE implementations do not support the NameConstraints 1326 extension. Since PKIX mandates that this extension be marked 1327 critical when present, Certification Authority implementations which 1328 are interested in maximal interoperability for IKE SHOULD NOT 1329 generate certificates which contain this extension. 1331 4.1.3.11 PolicyConstraints 1333 Many IKE implementations do not support the PolicyConstraints 1334 extension. Since PKIX mandates that this extension be marked 1335 critical when present, Certification Authority implementations which 1336 are interested in maximal interoperability for IKE SHOULD NOT 1337 generate certificates which contain this extension. 1339 4.1.3.12 ExtendedKeyUsage 1341 The CA SHOULD NOT include the ExtendedKeyUsage (EKU) extension in 1342 certificates for use with IKE. Note that there were three IPsec 1343 related object identifiers in EKU that were assigned in 1999. The 1344 semantics of these values were never clearly defined. The use of 1345 these three EKU values in IKE/IPsec is obsolete and explicitly 1346 deprecated by this specification. CAs SHOULD NOT issue certificates 1347 for use in IKE with them. (For historical reference only, those 1348 values were id-kp-ipsecEndSystem, id-kp-ipsecTunnel, and 1349 id-kp-ipsecUser.) 1351 PKIX [5] section 4.2.1.13 states, "If a CA includes extended key 1352 usages to satisfy such applications, but does not wish to restrict 1353 usages of the key, the CA can include the special keyPurposeID 1354 anyExtendedKeyUsage. If the anyExtendedKeyUsage keyPurposeID is 1355 present, the extension SHOULD NOT be critical." 1357 The CA SHOULD NOT mark the EKU extension in certificates for use with 1358 IKE and one or more other applications. If the CA administrator 1359 feels they must use an EKU for some other application, then such 1360 certificates MUST contain the keyPurposeID anyExtendedKeyUsage as 1361 well as the keyPurposeID values associated with the other 1362 applications for which the certificate is intended to be used. 1363 Recall however, EKU extensions in certificates meant for use in IKE 1364 are NOT RECOMMENDED. 1366 A summary of the logic flow for peer certificate validation regarding 1367 the EKU extension follows: 1369 o If told (by configuration) to ignore ExtendedKeyUsage (EKU), 1370 accept cert regardless of the presence or absence of the 1371 extension. 1372 o If no EKU extension, accept cert. 1373 o If EKU present AND anyExtendedKeyUsage is included, accept cert. 1374 o Otherwise, reject cert. 1376 4.1.3.13 CRLDistributionPoints 1378 Because this document deprecates the sending of CRLs in-band, the use 1379 of CRLDistributionPoints (CDP) becomes very important if CRLs are 1380 used for revocation checking (as opposed to say Online Certificate 1381 Status Protocol - OCSP [14]). The IPsec peer either needs to have a 1382 URL for a CRL written into its local configuration, or it needs to 1383 learn it from CDP. Therefore, Certification Authority 1384 implementations SHOULD issue certificates with a populated CDP. 1386 Failure to validate the 1387 CRLDistributionPoints/IssuingDistributionPoint pair can result in CRL 1388 substitution where an entity knowingly substitutes a known good CRL 1389 from a different distribution point for the CRL which is supposed to 1390 be used which would show the entity as revoked. IKE implementations 1391 MUST support validating that the contents of CRLDistributionPoints 1392 match those of the IssuingDistributionPoint to prevent CRL 1393 substitution when the issuing CA is using them. At least one CA is 1394 known to default to this type of CRL use. See Section 4.2.2.5 for 1395 more information. 1397 CDPs SHOULD be "resolvable". Several non-compliant Certification 1398 Authority implementations are well known for including unresolvable 1399 CDPs like http://localhost/path_to_CRL and http:///path_to_CRL which 1400 are equivalent to failing to include the CDP extension in the 1401 certificate. 1403 See PKIX docs for CRLDistributionPoints intellectual property rights 1404 (IPR) information. Note that both the CRLDistributionPoints and 1405 IssuingDistributionPoint extensions are RECOMMENDED but not REQUIRED 1406 by PKIX, so there is no requirement to license any IPR. 1408 4.1.3.14 InhibitAnyPolicy 1410 Many IKE implementations do not support the InhibitAnyPolicy 1411 extension. Since PKIX mandates that this extension be marked 1412 critical when present, Certification Authority implementations which 1413 are interested in maximal interoperability for IKE SHOULD NOT 1414 generate certificates which contain this extension. 1416 4.1.3.15 FreshestCRL 1418 IKE implementations MUST NOT assume that the FreshestCRL extension 1419 will exist in peer certificates. Note that most IKE implementations 1420 do not support delta CRLs. 1422 4.1.3.16 AuthorityInfoAccess 1424 PKIX defines the AuthorityInfoAccess extension, which is used to 1425 indicate "how to access CA information and services for the issuer of 1426 the certificate in which the extension appears." Because this 1427 document deprecates the sending of CRLs in band, the use of 1428 AuthorityInfoAccess (AIA) becomes very important if OCSP [14] is to 1429 be used for revocation checking (as opposed to CRLs). The IPsec peer 1430 either needs to have a URI for the OCSP query written into its local 1431 configuration, or it needs to learn it from AIA. Therefore, 1432 implementations SHOULD support this extension, especially if OCSP 1433 will be used. 1435 4.1.3.17 SubjectInfoAccess 1437 PKIX defines the SubjectInfoAccess private certificate extension, 1438 which is used to indicate "how to access information and services for 1439 the subject of the certificate in which the extension appears." This 1440 extension has no known use in the context of IPsec. Conformant IKE 1441 implementations SHOULD ignore this extension when present. 1443 4.2 X.509 Certificate Revocation Lists 1445 When validating certificates, IKE implementations MUST make use of 1446 certificate revocation information, and SHOULD support such 1447 revocation information in the form of CRLs, unless non-CRL revocation 1448 information is known to be the only method for transmitting this 1449 information. Deployments that intend to use CRLs for revocation 1450 SHOULD populate the CRLDistributionPoints extension. Therefore 1451 Certification Authority implementations MUST support issuing 1452 certificates with this field populated according to administrator's 1453 needs. IKE implementations MAY provide a configuration option to 1454 disable use of certain types of revocation information, but that 1455 option MUST be off by default. Such an option is often valuable in 1456 lab testing environments. 1458 4.2.1 Multiple Sources of Certificate Revocation Information 1460 IKE implementations which support multiple sources of obtaining 1461 certificate revocation information MUST act conservatively when the 1462 information provided by these sources is inconsistent: when a 1463 certificate is reported as revoked by one trusted source, the 1464 certificate MUST be considered revoked. 1466 4.2.2 X.509 Certificate Revocation List Extensions 1468 4.2.2.1 AuthorityKeyIdentifier 1470 Certification Authority implementations SHOULD NOT assume that IKE 1471 implementations support the AuthorityKeyIdentifier extension, and 1472 thus SHOULD NOT generate certificate hierarchies which are overly 1473 complex to process in the absence of this extension, such as those 1474 that require possibly verifying a signature against a large number of 1475 similarly named CA certificates in order to find the CA certificate 1476 which contains the key that was used to generate the signature. 1478 4.2.2.2 IssuerAltName 1480 Certification Authority implementations SHOULD NOT assume that IKE 1481 implementations support the IssuerAltName extension, and especially 1482 should not assume that information contained in this extension will 1483 be displayed to end users. 1485 4.2.2.3 CRLNumber 1487 As stated in PKIX, all issuers conforming to PKIX MUST include this 1488 extension in all CRLs. 1490 4.2.2.4 DeltaCRLIndicator 1492 4.2.2.4.1 If Delta CRLs Are Unsupported 1494 IKE implementations that do not support delta CRLs MUST reject CRLs 1495 which contain the DeltaCRLIndicator (which MUST be marked critical 1496 according to PKIX) and MUST make use of a base CRL if it is 1497 available. Such implementations MUST ensure that a delta CRL does 1498 not "overwrite" a base CRL, for instance in the keying material 1499 database. 1501 4.2.2.4.2 Delta CRL Recommendations 1503 Since some IKE implementations that do not support delta CRLs may 1504 behave incorrectly or insecurely when presented with delta CRLs, 1505 administrators and deployers should consider whether issuing delta 1506 CRLs increases security before issuing such CRLs. And, if all the 1507 elements in the VPN and PKI systems do not adequately support Delta 1508 CRLs, then their use should be questioned. 1510 The authors are aware of several implementations which behave in an 1511 incorrect or insecure manner when presented with delta CRLs. See 1512 Appendix B for a description of the issue. Therefore, this 1513 specification RECOMMENDS NOT issuing delta CRLs at this time. On the 1514 other hand, failure to issue delta CRLs exposes a larger window of 1515 vulnerability. See the Security Considerations section of PKIX [5] 1516 for additional discussion. Implementors as well as administrators 1517 are encouraged to consider these issues. 1519 4.2.2.5 IssuingDistributionPoint 1521 A CA that is using CRLDistributionPoints may do so to provide many 1522 "small" CRLs, each only valid for a particular set of certificates 1523 issued by that CA. To associate a CRL with a certificate, the CA 1524 places the CRLDistributionPoints extension in the certificate, and 1525 places the IssuingDistributionPoint in the CRL. The 1526 distributionPointName field in the CRLDistributionPoints extension 1527 MUST be identical to the distributionPoint field in the 1528 IssuingDistributionPoint extension. At least one CA is known to 1529 default to this type of CRL use. See Section 4.1.3.13 for more 1530 information. 1532 4.2.2.6 FreshestCRL 1534 Given the recommendations against Certification Authority 1535 implementations generating delta CRLs, this specification RECOMMENDS 1536 that implementations do not populate CRLs with the FreshestCRL 1537 extension, which is used to obtain delta CRLs. 1539 5. Configuration Data Exchange Conventions 1541 Below we present a common format for exchanging configuration data. 1542 Implementations MUST support these formats, MUST support receiving 1543 arbitrary whitespace at the beginning and end of any line, MUST 1544 support receiving arbitrary line lengths although they SHOULD 1545 generate lines less than 76 characters, and MUST support receiving 1546 the following three line-termination disciplines: LF (US-ASCII 10), 1547 CR (US-ASCII 13), and CRLF. 1549 5.1 Certificates 1551 Certificates MUST be Base64 encoded and appear between the following 1552 delimiters: 1554 -----BEGIN CERTIFICATE----- 1555 -----END CERTIFICATE----- 1557 5.2 CRLs and ARLs 1559 CRLs and ARLs MUST be Base64 encoded and appear between the following 1560 delimiters: 1562 -----BEGIN CRL----- 1563 -----END CRL----- 1565 5.3 Public Keys 1567 IKE implementations MUST support two forms of public keys: 1568 certificates and so-called "raw" keys. Certificates should be 1569 transferred in the same form as above. A raw key is only the 1570 SubjectPublicKeyInfo portion of the certificate, and MUST be Base64 1571 encoded and appear between the following delimiters: 1573 -----BEGIN PUBLIC KEY----- 1574 -----END PUBLIC KEY----- 1576 5.4 PKCS#10 Certificate Signing Requests 1578 A PKCS#10 [9] Certificate Signing Request MUST be Base64 encoded and 1579 appear between the following delimiters: 1581 -----BEGIN CERTIFICATE REQUEST----- 1582 -----END CERTIFICATE REQUEST----- 1584 6. Security Considerations 1586 6.1 Certificate Request Payload 1588 The Contents of CERTREQ are not encrypted in IKE. In some 1589 environments this may leak private information. Administrators in 1590 some environments may wish to use the empty Certification Authority 1591 option to prevent such information from leaking, at the cost of 1592 performance. 1594 6.2 IKEv1 Main Mode 1596 Certificates may be included in any message, and therefore 1597 implementations may wish to respond with CERTs in a message that 1598 offers privacy protection, in Main Mode messages 5 and 6. 1599 Implementations may not wish to respond with CERTs in the second 1600 message, thereby violating the identity protection feature of Main 1601 Mode in IKEv1. 1603 7. Intellectual Property Rights 1605 No new intellectual property rights are introduced by this document. 1607 8. IANA Considerations 1609 There are no known numbers which IANA will need to manage. 1611 9. References 1613 9.1 Normative References 1615 [1] Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)", 1616 RFC 2409, November 1998. 1618 [2] Maughan, D., Schneider, M. and M. Schertler, "Internet Security 1619 Association and Key Management Protocol (ISAKMP)", RFC 2408, 1620 November 1998. 1622 [3] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", 1623 Internet-Draft draft-ietf-ipsec-ikev2-15, August 2004. 1625 [4] Kent, S. and R. Atkinson, "Security Architecture for the 1626 Internet Protocol", RFC 2401, November 1998. 1628 [5] Housley, R., Polk, W., Ford, W. and D. Solo, "Internet X.509 1629 Public Key Infrastructure Certificate and Certificate Revocation 1630 List (CRL) Profile", RFC 3280, April 2002. 1632 [6] Piper, D., "The Internet IP Security Domain of Interpretation 1633 for ISAKMP", RFC 2407, November 1998. 1635 [7] Bradner, S., "Key words for use in RFCs to Indicate Requirement 1636 Levels", BCP 14, RFC 2119, March 1997. 1638 [8] Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981. 1640 [9] Kaliski, B., "PKCS #10: Certification Request Syntax Version 1641 1.5", RFC 2314, March 1998. 1643 9.2 Informative References 1645 [10] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) 1646 Specification", RFC 1883, December 1995. 1648 [11] Eastlake, D., "Domain Name System Security Extensions", 1649 RFC 2535, March 1999. 1651 [12] Lynn, C., "X.509 Extensions for IP Addresses and AS 1652 Identifiers", 1653 Internet-Draft draft-ietf-pkix-x509-ipaddr-as-extn-03, 1654 September 2003. 1656 [13] Fuller, V., Li, T., Yu, J. and K. Varadhan, "Classless 1657 Inter-Domain Routing (CIDR): an Address Assignment and 1658 Aggregation Strategy", RFC 1519, September 1993. 1660 [14] Myers, M., Ankney, R., Malpani, A., Galperin, S. and C. Adams, 1661 "X.509 Internet Public Key Infrastructure Online Certificate 1662 Status Protocol - OCSP", RFC 2560, June 1999. 1664 [15] Arsenault, A. and S. Turner, "Internet X.509 Public Key 1665 Infrastructure: Roadmap", 1666 Internet-Draft draft-ietf-pkix-roadmap-09, July 2002. 1668 Author's Address 1670 Brian Korver 1671 Xythos Software, Inc. 1672 One Bush Street, Suite 600 1673 San Francisco, CA 94104 1674 US 1676 Phone: +1 415 248 3800 1677 Email: briank@xythos.com 1679 Appendix A. Change History 1681 September 2004 (-03) 1683 * Added Paul Hoffman's text from issue #708 1684 * Added text explaining that it's possible for a recipient to 1685 receive CERT payloads containing certs that the recipient 1686 considers a trust anchor (15 Nov 2004 pki4ipsec email from 1687 Peter Williams) 1688 * Replaced text in 4.1.3 with Kent's text (issue #655) (22 Nov 1689 2004 pki4ipsec email from Stephen Kent, Paul Hoffman) 1690 September 2004 (-03) 1692 * Minor editorial changes in abstract and introduction clarifing 1693 when something is from IPsec, IKE, etc 1694 * Minor editorial changes throughout 1695 * Fixed "Certification Authority" instead of "Certificate 1696 Authority" 1697 * Cleaned up initiator/responder when really referred to 1698 sender/recipient 1699 * Fixed inconsistancy in text by making sure that all text on the 1700 topic of sending CERTREQs follow Gregory Lebovitz's proposal 1701 for CERT payloads: "should deal with all the CRL, Intermediat 1702 Certs, Trust Anchors, etc OOB of IKE; MUST be able to send and 1703 receive EE cert payload; only real exception is Intermediate 1704 Cets which MAY be sent and SHOULD be able to be receivable (but 1705 in reality there are very few hierarchies in operation, so 1706 really it's a corner case); SHOULD NOT send the other stuff 1707 (CRL, Trust Anchors, etc) in cert payloads in IKE; SHOULD be 1708 able to accept the other stuff if by chance it gets sent, 1709 though we hope they don't get sent" 1710 * 3.1 - removed text suggesting that it would be reasonable to 1711 terminate IKEv2 processing if the initiator were to receive a 1712 responder-generated IDr 1713 * 3.1.1 - noted that certificates may contain multiple IP 1714 addresses 1715 * 3.1.9 - removed (temporarily?) confusing text stating that 1716 overlapping policies was prohibited, text which was 1717 inconsistent with text right above it 1718 * 3.2.7.2 - SHOULD changed to MUST terminate if peer's 1719 certificate chain violates local policy 1720 * 3.3 - removed text implying that pausing in the middle of an 1721 IKE exchange in order to obtain revocation status information 1722 via http or OCSP would reduce latency in IKE 1723 * 4.2 - allow deployments that don't wish to populate CDP (for 1724 instance if a source of revocation information is configured 1725 via some other means) to skip populating CDP, making consistent 1726 with 4.1.3.13 and the issues IPR spelled out in PKIX 1727 * Somehow a CRL out-of-band configuration format had been 1728 omitted. 1729 * #555: Kent-1.0 Introduction - document now references IKEv2 1730 * #559: Kent-Profile Document 3.1.0 - use sender/recipient 1731 instead of agent 1732 * #564: Kent-Profile Document 3.1.1 - specified that support for 1733 ID_IPV4_ADDR and/or ID_IPV6_ADDR are contingent on device 1734 support for IPv4 and/or IPv6 1735 * #568: Kent-Profile document 3.1.4 - specified that there wasn't 1736 a standard and besides no one has implemented it 1737 * #571: Kent-Profile document 3.1.8 - tried to be even more 1738 clearer than was asked for by spelling things out in detail 1739 * #572: Kent-Profile document 3.1.8 Formerly issue #18 - now 1740 specifies that it's only a local matter if that information is 1741 not coordinated with other administrators 1742 * #573: Kent-Profile document 3.2.3/Myers - revocation 1743 information no longer exchanged in-band, plus Mike Myers has 1744 submitted an OCSP w/IKE draft, which is references by this 1745 document. 1746 * #578 Kent-Profile document 4.0.0 - went through entire PKIX 1747 profile section and prefaced "implementation" with "IKE" or 1748 "Certification Authority" wherever it was sure to be one or the 1749 other 1751 * #581: Kent-Profile document 4.1.3.9 - replaced description with 1752 text from RFC 2459 1753 * #584: Maillist-Lebovitz PKI Life Cycle-Revocation - fixed 1754 * #586: Maillist-Allison Empty CertReq - there is now lots of 1755 text dealing with when empty certreqs are permitted 1756 * 3.2.7.1 - CERTREQ only mandatory if in-band exchange of keymat 1757 is desired (28 Jul 2004 pki4ipsec email from 1758 jknowles@SonicWALL.com) 1759 * 3.3.6 - clarified that "non-compliant" means not sending a 1760 CERTREQ (28 Jul 2004 pki4ipsec email from 1761 jknowles@SonicWALL.com) 1762 * 3.2.7.1 - fixed contradition: mandatory to respond to CERTREQ 1763 UNLESS configured not to (28 Jul 2004 pki4ipsec email from 1764 jknowles@SonicWALL.com) 1765 * 3.2.9.2 and 3.2.9.3 - CERTREQ contains an issuer name only for 1766 IKEv2 (19 Sep 2004 email from Charlie Kaufman) 1767 * Answered 'Section 3.1.9 para 2: "The initiator MUST know by 1768 policy..." is a difficult to interpret requirement. It could 1769 mean that it must be possible to configure in policy which ID 1770 is to be sent. Did you mean "the initiator must decide...", 1771 where the decision might be wired into a particular 1772 implementation?' by changing it to be merely descriptive, and 1773 to refer to policy configuration (19 Sep 2004 email from 1774 Charlie Kaufman) 1775 * IPSEC -> IPsec (19 Sep 2004 email from Charlie Kaufman) 1776 * 3.1.1 para 1: "MUST be stored" changed to "MUST be encoded" (19 1777 Sep 2004 email from Charlie Kaufman) 1778 * 3.1.5 para 2 - made it clear that empty SubjectNames are 1779 permitted by PKIX in certificates, but this document doesn't 1780 permit them in ID (19 Sep 2004 email from Charlie Kaufman) 1781 * 3.2.7.1 - clarified by specifying that it's a trust anchor 1782 that's being chosen, not end-entity certificate (19 Sep 2004 1783 email from Charlie Kaufman) 1784 * 3.3.9.5 - fixed confusing last paragraph (19 Sep 2004 email 1785 from Charlie Kaufman) 1786 * 3.3.10.3 - made it more clear that this section is really 1787 talking about duplicate certificate payloads (19 Sep 2004 email 1788 from Charlie Kaufman) 1789 * 4.1.2.2 para 2 and 3 - moved to 3.1.x section where is belongs 1790 (19 Sep 2004 email from Charlie Kaufman) 1791 * 4.1.3.5 - the last sentence of 4.1.3.4 copied here (19 Sep 2004 1792 email from Charlie Kaufman) 1793 * 4.2.2.4.2 - SHOULD -> should (19 Sep 2004 email from Charlie 1794 Kaufman) 1795 * 3.2.5 and 3.3.4 - added description of URL scheme support (16 1796 Aug 2004 pki4ipsec email from Tero Kivinen) 1797 * Removed 6.1 and 6.3 because they were either incorrect or 1798 didn't add any new security considerations above and beyond the 1799 IKE documents. 1800 August 2004 (-02) (Edited by Gregory Lebovitz, with XML formatting 1801 and cross-referencing by Paul Knight) 1803 * 3.1.1 the text between the **s was added to paragraph, per the 1804 question that arose in IETF60 WG session: Implementations MUST 1805 be capable of verifying that the address contained in the ID is 1806 the same as the peer source address **contained in the outer 1807 most IP header**. 1808 * 3.2.7 - added HTTP_CERT_LOOKUP_SUPPORTED to this section and 1809 described its use - #38 1810 * 3.3 - changed back sending of intermediate CA certificates from 1811 SHOULD NOT to MAY (for backward compatibility). Added text to 1812 explain further why we want to stay away from actually doing it 1813 though. 1814 * 3.3.8 - changed text per Knowles/Korver 2004.07.28. 1815 * 3.3.9.5 - Change discard of Irrelevant Certificates from may to 1816 SHOULD - #23(Kent 2004.04.26) 1817 * 4.1.3.2 KU - re-worked to reflect discussion on list and in 1818 IETF60 - #36 1819 * 4.1.3.12 EKU - re-worked to reflect discussion on list and in 1820 IETF60 - #36 1821 * [IKEv2] update the reference to the -14 draft of May 29, 2004 1823 July 2004 (-01) (Edited by Gregory Lebovitz) 1825 * Changed ISAKMP references in Abstract and Intro to IKE. 1826 * Editorial changes to make the text conform with the summary 1827 table in 3.1, especially in the text following the table in 1828 3.1. Particular note should be paid to changes in section 1829 3.5.1. 1830 * Sect 3.1.1 - editorial changes to aid in clarification. Added 1831 text on when deployers might consider using IP addr, but 1832 strongly encouraged not to. 1833 * Sect 3.1.8 removed IP address from list of practically used ID 1834 types. 1835 * 3.1.9 overhauled (per Kivinen, July 18) 1836 * 3.2 - added IKEv2's Hash and URL of x.509 to list of those 1837 profiled and gave it its own section, now 3.2.5 1838 * added note in CRL/ARL section about revocation occurring OOB of 1839 IKE 1840 * deleted ARL as its own section and collapsed it into Revocation 1841 Lists (CRL and ARL) for consciseness. Renumbered accordingly. 1842 * Sect 3.2.7.2 - Changed from MUST not send empty certreqs to 1843 SHOULD send CERTREQs which contain CA fields with direction on 1844 how, but MAY send empty CERTREQs in certain case. Use case 1845 added, and specifics of both initiator and responder behavior 1846 listed. 1847 * APPENDIX C added to fill out the explanation (mostly discussion 1848 from list). 1849 * 3.3 - clarified that sending CRLs and chaining certs is 1850 deprecated. 1851 * added IKEv2's Hash and URL of x.509 to list of those profiled 1852 and gave it its own section. Condensed ARL into CRL and 1853 renumbered accordingly. 1854 * duplicate section was removed, renumbered accordingly 1855 * 3.3.10.2 - title changed. sending chaining becomes SHOULD NOT. 1856 * 4.1.2 added text to explicity call out support for CN, C, O, OU 1857 * collapsed 4.1.2.3 into 4.1.2.2 and renumbered accordingly. 1858 * Collapsed 4.1.3.2 into 4.1.3.1 and renumbered accordingly 1859 * Edited 4.1.3.2 Key Usage and 4.1.3.12 ExtKey Usage according to 1860 Hoffman, July18 1861 * 4.1.3.3 if receive cert w/ PKUP, ignore it. 1862 * 4.1.3.13 - CDP changed text to represent SHOULD issue, and how 1863 important CDP becomes when we do not send CRLs in-band. Added 1864 SHOULD for CDPs actually being resolvable (reilly email). 1865 * Reordered 6.4 for better clarity. 1866 * Added Rescorla to Acknowledgements section, as he is no longer 1867 listed as an editor, since -00. 1869 May 2004 (renamed draft-ietf-pki4ipsec-ikecert-profile-00.txt) 1870 (edited by Brian Korver) 1872 * Made it clearer that the format of the ID_IPV4_ADDR payload 1873 comes from RFC791 and is nothing new. (Tero Kivinen Feb 29) 1874 * Permit implementations to skip verifying that the peer source 1875 address matches the contents of ID_IPV{4,6}_ADDR. (Tero 1876 Kivinen Feb 29, Gregory Lebovitz Feb 29) 1877 * Removed paragraph suggesting that implementations favor 1878 unauthenticated peer source addresses over an unauthenticated 1879 ID for initial policy lookup. (Tero Kivinen Feb 29, Gregory 1880 Lebovitz Feb 29) 1881 * Removed some text implying RSA encryption mode was in scope. 1882 (Tero Kivinen Feb 29) 1883 * Relaxed deprecation of PKCS#7 CERT payloads. (Tero Kivinen Feb 1884 29) 1885 * Made it clearer that out-of-scope local heuristics should be 1886 used for picking an EE cert to use when generating CERTREQ, not 1887 when receiving CERTREQ. (Tero Kivinen Feb 29) 1888 * Made it clearer that CERT processing can be skipped when the 1889 contents of a CERT are already known. (Tero Kivinen Feb 29) 1891 * Implementations SHOULD generate BASE64 lines less than 76 1892 characters. (Tero Kivinen Feb 29) 1893 * Added "Except where specifically stated in this document, 1894 implementations MUST conform to the requirements of PKIX" 1895 (Steve Hanna Oct 7, 2003) 1896 * RECOMMENDS against populating the ID payload with IP addresses 1897 due to interoperability issues such as problem with NAT 1898 traversal. (Gregory Lebovitz May 14) 1899 * Changed "as revoked by one source" to "as revoked by one 1900 trusted source". (Michael Myers, May 15) 1901 * Specifying Certificate Authorities section needed to be 1902 regularized with Gregory Lebovitz's CERT proposal from -04. 1903 (Tylor Allison, May 15) 1904 * Added text specifying how recipients SHOULD NOT be expected to 1905 iterate over multiple end-entity certs. (Tylor Allison, May 1906 15) 1907 * Modified text to refer to IKEv2 as well as IKEv1/ISAKMP where 1908 relevant. 1909 * IKEv2: Explained that IDr sent by responder doesn't have to 1910 match the [IDr] sent initiator in second exchange. 1911 * IKEv2: Noted that "The identity ... does not necessarily have 1912 to match anything in the CERT payload" (S3.5) is not 1913 contradicted by SHOULD in this document. 1914 * IKEv2: Noted that ID_USER_FQDN renamed to ID_RFC822_ADDR, and 1915 ID_USER_FQDN would be used exclusively in this document. 1916 * IKEv2: Declared that 3 new CERTREQ and CERT types are not 1917 profiled in this document (well, at least not yet, pending WG 1918 discussion of what to do -- note that they are only SHOULDs in 1919 IKEv2). 1920 * IKEv2: Noted that CERTREQ payload changed from DN to SHA-1 of 1921 SubjectPublicKeyInfo. 1922 * IKEv2: Noted new requirement that specifies that the first 1923 certificate sent MUST be the EE cert (section 3.6). 1925 February 2004 (-04) 1927 * Minor editorial changes to clean up language 1928 * Deprecate in-band exchange of CRLs 1929 * Incorporated Gregory Lebovitz's proposal for CERT payloads: 1930 "should deal with all the CRL, Intermediat Certs, Trust 1931 Anchors, etc OOB of IKE; MUST be able to send and receive EE 1932 cert payload; only real exception is Intermediate Cets which 1933 MAY be sent and SHOULD be able to be receivable (but in reality 1934 there are very few hierarchies in operation, so really it's a 1935 corner case); SHOULD NOT send the other stuff (CRL, Trust 1936 Anchors, etc) in cert payloads in IKE; SHOULD be able to accept 1937 the other stuff if by chance it gets sent, though we hope they 1938 don't get sent" 1939 * Incorporated comments contained in Oct 7, 2003 email from 1940 steve.hanna@sun.com to ipsec@lists.tislabs.com 1941 * Moved text from "Profile of ISAKMP" Background section to each 1942 payload section (removing duplication of these sections) 1943 * Removed "Certificate-Related Playloads in ISAKMP" section since 1944 it was not specific to IKE. 1945 * Incorporated Gregory Lebovitz's table in the "Identification 1946 Payload" section 1947 * Moved text from "binding identity to policy" sections to each 1948 payload section 1949 * Moved text from "IKE" section into now-combined "IKE/ISAKMP" 1950 section 1951 * ID_USER_FQDN and ID_FQDN promoted to MUST from MAY 1952 * Promoted sending ID_DER_ASN1_DN to MAY from SHOULD NOT, and 1953 receiving from MUST from MAY 1954 * Demoted ID_DER_ASN1_GN to MUST NOT 1955 * Demoted populating SubjectName in place of populating the 1956 dNSName from SHOULD NOT to MUST NOT and removed the text 1957 regarding domainComponent 1958 * Revocation information checking MAY now be disabled, although 1959 not by default 1960 * Aggressive Mode removed from this profile 1962 June 2003 (-03) 1964 * Minor editorial changes to clean up language 1965 * Minor additional clarifying text 1966 * Removed hyphenation 1967 * Added requirement that implementations support configuration 1968 data exchange having arbitrary line lengths 1970 February 2003 (-02) 1972 * Word choice: move from use of "root" to "trust anchor", in 1973 accordance with PKIX 1974 * SBGP note and reference for placing address subnet and range 1975 information into certificates 1976 * Clarification of text regarding placing names of hosts into the 1977 Name commonName attribute of SubjectName 1978 * Added table to clarify text regarding processing of the 1979 certificate extension criticality bit 1981 * Added text underscoring processing requirements for 1982 CRLDistributionPoints and IssuingDistributionPoint 1984 October 2002, Reorganization (-01) 1986 June 2002, Initial Draft (-00) 1988 Appendix B. The Possible Dangers of Delta CRLs 1990 The problem is that the CRL processing algorithm is sometimes written 1991 incorrectly with the assumption that all CRLs are base CRLs and it is 1992 assumed that CRLs will pass content validity tests. Specifically, 1993 such implementations fail to check the certificate against all 1994 possible CRLs: if the first CRL that is obtained from the keying 1995 material database fails to decode, no further revocation checks are 1996 performed for the relevant certificate. This problem is compounded 1997 by the fact that implementations which do not understand delta CRLs 1998 may fail to decode such CRLs due to the critical DeltaCRLIndicator 1999 extension. The algorithm that is implemented in this case is 2000 approximately: 2002 o fetch newest CRL 2003 o check validity of CRL signature 2004 o if CRL signature is valid then 2005 o if CRL does not contain unrecognized critical extensions 2006 o and certificate is on CRL then 2007 o set certificate status to revoked 2009 The authors note that a number of PKI toolkits do not even provide a 2010 method for obtaining anything but the newest CRL, which in the 2011 presence of delta CRLs may in fact be a delta CRL, not a base CRL. 2013 Note that the above algorithm is dangerous in many ways. See PKIX 2014 [5] for the correct algorithm. 2016 Appendix C. More on Empty CERTREQs 2018 Sending empty certificate requests is commonly used in 2019 implementations, and in the IPsec interop meetings, vendors have 2020 generally agreed that it means that send all/any end-entity 2021 certificates you have (if multiple end-entity certificates are sent, 2022 they must have same public key, as otherwise the other end does not 2023 know which key was used). For 99% of cases the client have exactly 2024 one certificate and public key, so it really doesn't matter, but the 2025 server might have multiple, thus it simply needs to say to the 2026 client, use any certificate you have. If we are talking about 2027 corporate vpns etc, even if the client have multiple certificates or 2028 keys, all of them would be usable when authenticating to the server, 2029 so client can simply pick one. 2031 If there is some real difference on which cert to use (like ones 2032 giving different permissions), then the client must be configured 2033 anyways, or it might even ask the user which one to use (the user is 2034 the only one who knows whether he needs admin privileges, thus needs 2035 to use admin cert, or is the normal email privileges ok, thus using 2036 email only cert). 2038 99% of the cases the client have exactly one certificate, so it will 2039 send it. In 90% of the rest of the cases, any of the certificates is 2040 ok, as they are simply different certificates from same CA, or 2041 different CAs for the same corporate VPN, thus any of them is ok. 2043 Sending empty certificate requests has been agreed there to mean 2044 "give me your cert; any cert". 2046 Justification: 2048 o Responder first does all it can to send a certreq with a CA, check 2049 for IP match in SPD, have a default set of CAs to use in ambiguous 2050 cases, etc. 2051 o sending empty certreq's is fairly common in implementations today, 2052 and is generally accepted to mean "send me a cert, any cert that 2053 works for you" 2054 o saves responder sending potentially 100's of certs, the 2055 fragmentation problems that follow, etc. 2056 o in +90% of use cases, Initiators have exactly 1 cert 2057 o in +90% of the remaining use cases, the multiple certs it has are 2058 issued by the same CA 2059 o in the remaining use case(s) -- if not all the others above -- the 2060 Initiator will be configured explicitly with which cert to send, 2061 so responding to an empty certreq is easy. 2063 The following example shows why initiators need to have sufficient 2064 policy definition to know which certificate to use for a given 2065 connection it initiates. 2067 EXAMPLE: Your client (initiator) is configured with VPN policies for 2068 gateways A and B (representing perhaps corporate partners). 2070 The policies for the two gateways look something like: 2072 Acme Company policy (gateway A) 2073 Engineering can access 10.1.1.0 2074 Trusted CA: CA-A, Trusted Users: OU=Engineering 2075 Partners can access 20.1.1.0 2076 Trusted CA: CA-B, Trusted Users: OU=AcmePartners 2078 Bizco Company policy (gateway B) 2079 sales can access 30.1.1.0 2080 Trusted CA: CA-C, Trusted Users: OU=Sales 2081 Partners can access 40.1.1.0 2082 Trusted CA: CA-B, Trusted Users: OU=BizcoPartners 2084 You are an employee of Acme and you are issued the following 2085 certificates: 2087 o From CA-A: CN=JoeUser,OU=Engineering 2088 o From CA-B: CN=JoePartner,OU=BizcoPartners 2090 The client MUST be configured locally to know which CA to use when 2091 connecting to either gateway. If your client is not configured to 2092 know the local credential to use for the remote gateway, this 2093 scenario will not work either. If you attempt to connect to Bizco, 2094 everything will work... as you are presented with responding with a 2095 certificate signed by CA-B or CA-C... as you only have a certificate 2096 from CA-B you are OK. If you attempt to connect to Acme, you have an 2097 issue because you are presented with an ambiguous policy selection. 2098 As the initiator, you will be presented with certificate requests 2099 from both CA A and CA B. You have certificates issued by both CAs, 2100 but only one of the certificates will be usable. How does the client 2101 know which certificate it should present? It must have sufficiently 2102 clear local policy specifying which one credential to present for the 2103 connection it initiates. 2105 Appendix D. Acknowledgements 2107 The authors would like to acknowledge the expired draft-ietf-ipsec- 2108 pki-req-05.txt for providing valuable materials for this document. 2110 The authors would like to especially thank Eric Rescorla, one of its 2111 original authors, in addition to Greg Carter, Steve Hanna, Russ 2112 Housley, Charlie Kaufman, Tero Kivinen, and Gregory Lebovitz for 2113 their valuable comments, some of which have been incorporated 2114 verbatim into this document. Paul Knight performed the arduous tasks 2115 of coverting the text to XML format. 2117 Intellectual Property Statement 2119 The IETF takes no position regarding the validity or scope of any 2120 Intellectual Property Rights or other rights that might be claimed to 2121 pertain to the implementation or use of the technology described in 2122 this document or the extent to which any license under such rights 2123 might or might not be available; nor does it represent that it has 2124 made any independent effort to identify any such rights. Information 2125 on the procedures with respect to rights in RFC documents can be 2126 found in BCP 78 and BCP 79. 2128 Copies of IPR disclosures made to the IETF Secretariat and any 2129 assurances of licenses to be made available, or the result of an 2130 attempt made to obtain a general license or permission for the use of 2131 such proprietary rights by implementers or users of this 2132 specification can be obtained from the IETF on-line IPR repository at 2133 http://www.ietf.org/ipr. 2135 The IETF invites any interested party to bring to its attention any 2136 copyrights, patents or patent applications, or other proprietary 2137 rights that may cover technology that may be required to implement 2138 this standard. Please address the information to the IETF at 2139 ietf-ipr@ietf.org. 2141 Disclaimer of Validity 2143 This document and the information contained herein are provided on an 2144 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 2145 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET 2146 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, 2147 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE 2148 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 2149 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 2151 Copyright Statement 2153 Copyright (C) The Internet Society (2004). This document is subject 2154 to the rights, licenses and restrictions contained in BCP 78, and 2155 except as set forth therein, the authors retain all their rights. 2157 Acknowledgment 2159 Funding for the RFC Editor function is currently provided by the 2160 Internet Society.