idnits 2.17.00 (12 Aug 2021) /tmp/idnits31229/draft-ietf-pki4ipsec-ikecert-profile-05.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 on line 14. -- Found old boilerplate from RFC 3978, Section 5.5 on line 2168. -- Found old boilerplate from RFC 3979, Section 5, paragraph 1 on line 2145. -- Found old boilerplate from RFC 3979, Section 5, paragraph 2 on line 2152. -- Found old boilerplate from RFC 3979, Section 5, paragraph 3 on line 2158. ** 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. 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 1188 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). -- 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 (July 27, 2005) is 6141 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 1839 -- Looks like a reference, but probably isn't: 'IDr' on line 1928 == Unused Reference: '16' is defined on line 1672, 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: draft-ietf-ipsec-ikev2 has been published as RFC 4306 ** 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) == Outdated reference: draft-ietf-ipsec-rfc2401bis has been published as RFC 4301 -- Obsolete informational reference (is this intentional?): RFC 1883 (ref. '11') (Obsoleted by RFC 2460) -- Obsolete informational reference (is this intentional?): RFC 2535 (ref. '12') (Obsoleted by RFC 4033, RFC 4034, RFC 4035) == Outdated reference: draft-ietf-pkix-x509-ipaddr-as-extn has been published as RFC 3779 -- Obsolete informational reference (is this intentional?): RFC 1519 (ref. '14') (Obsoleted by RFC 4632) -- Obsolete informational reference (is this intentional?): RFC 2560 (ref. '15') (Obsoleted by RFC 6960) Summary: 9 errors (**), 0 flaws (~~), 11 warnings (==), 13 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 pki4ipsec B. Korver 3 Internet-Draft Network Resonance, Inc. 4 Expires: January 28, 2006 July 27, 2005 6 The Internet IP Security PKI Profile of IKEv1/ISAKMP, IKEv2, and PKIX 7 draft-ietf-pki4ipsec-ikecert-profile-05 9 Status of this Memo 11 By submitting this Internet-Draft, each author represents that any 12 applicable patent or other IPR claims of which he or she is aware 13 have been or will be disclosed, and any of which he or she becomes 14 aware will be disclosed, in accordance with Section 6 of BCP 79. 16 Internet-Drafts are working documents of the Internet Engineering 17 Task Force (IETF), its areas, and its working groups. Note that 18 other groups may also distribute working documents as Internet- 19 Drafts. 21 Internet-Drafts are draft documents valid for a maximum of six months 22 and may be updated, replaced, or obsoleted by other documents at any 23 time. It is inappropriate to use Internet-Drafts as reference 24 material or to cite them other than as "work in progress." 26 The list of current Internet-Drafts can be accessed at 27 http://www.ietf.org/ietf/1id-abstracts.txt. 29 The list of Internet-Draft Shadow Directories can be accessed at 30 http://www.ietf.org/shadow.html. 32 This Internet-Draft will expire on January 28, 2006. 34 Copyright Notice 36 Copyright (C) The Internet Society (2005). 38 Abstract 40 IKE and PKIX both provide frameworks that must be profiled for use in 41 a given application. This document provides a profile of IKE and 42 PKIX that defines the requirements for using PKI technology in the 43 context of IKE/IPsec. The document complements protocol 44 specifications such as IKEv1 and IKEv2, which assume the existence of 45 public key certificates and related keying materials, but which do 46 not address PKI issues explicitly. This document addresses those 47 issues. 49 Table of Contents 51 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 52 2. Terms and Definitions . . . . . . . . . . . . . . . . . . . 4 53 3. Profile of IKEv1/ISAKMP and IKEv2 . . . . . . . . . . . . . 5 54 3.1 Identification Payload . . . . . . . . . . . . . . . . . . 5 55 3.1.1 ID_IPV4_ADDR and ID_IPV6_ADDR . . . . . . . . . . . . 7 56 3.1.2 ID_FQDN . . . . . . . . . . . . . . . . . . . . . . . 9 57 3.1.3 ID_USER_FQDN . . . . . . . . . . . . . . . . . . . . . 10 58 3.1.4 ID_IPV4_ADDR_SUBNET, ID_IPV6_ADDR_SUBNET, 59 ID_IPV4_ADDR_RANGE, ID_IPV6_ADDR_RANGE . . . . . . . . 11 60 3.1.5 ID_DER_ASN1_DN . . . . . . . . . . . . . . . . . . . . 11 61 3.1.6 ID_DER_ASN1_GN . . . . . . . . . . . . . . . . . . . . 12 62 3.1.7 ID_KEY_ID . . . . . . . . . . . . . . . . . . . . . . 12 63 3.1.8 Selecting an Identity from a Certificate . . . . . . . 12 64 3.1.9 SubjectName for DN Only . . . . . . . . . . . . . . . 12 65 3.1.10 Binding Identity to Policy . . . . . . . . . . . . . 13 66 3.2 Certificate Request Payload . . . . . . . . . . . . . . . 13 67 3.2.1 Certificate Type . . . . . . . . . . . . . . . . . . . 14 68 3.2.2 X.509 Certificate - Signature . . . . . . . . . . . . 14 69 3.2.3 Revocation Lists (CRL and ARL) . . . . . . . . . . . . 14 70 3.2.4 PKCS #7 wrapped X.509 certificate . . . . . . . . . . 15 71 3.2.5 IKEv2's Hash and URL of X.509 certificate . . . . . . 15 72 3.2.6 Location of Certificate Payloads . . . . . . . . . . . 15 73 3.2.7 Presence or Absence of Certificate Request Payloads . 16 74 3.2.8 Certificate Requests . . . . . . . . . . . . . . . . . 16 75 3.2.9 Robustness . . . . . . . . . . . . . . . . . . . . . . 18 76 3.2.10 Optimizations . . . . . . . . . . . . . . . . . . . 18 77 3.3 Certificate Payload . . . . . . . . . . . . . . . . . . . 19 78 3.3.1 Certificate Type . . . . . . . . . . . . . . . . . . . 20 79 3.3.2 X.509 Certificate - Signature . . . . . . . . . . . . 21 80 3.3.3 Revocation Lists (CRL and ARL) . . . . . . . . . . . . 21 81 3.3.4 IKEv2's Hash and URL of X.509 Certificate . . . . . . 21 82 3.3.5 PKCS #7 wrapped X.509 certificate . . . . . . . . . . 21 83 3.3.6 Location of Certificate Payloads . . . . . . . . . . . 21 84 3.3.7 Certificate Payloads Not Mandatory . . . . . . . . . . 22 85 3.3.8 Response to Multiple Certification Authority 86 Proposals . . . . . . . . . . . . . . . . . . . . . . 22 87 3.3.9 Using Local Keying Materials . . . . . . . . . . . . . 22 88 3.3.10 Multiple End-Entity Certificates . . . . . . . . . . 22 89 3.3.11 Robustness . . . . . . . . . . . . . . . . . . . . . 23 90 3.3.12 Optimizations . . . . . . . . . . . . . . . . . . . 24 91 4. Profile of PKIX . . . . . . . . . . . . . . . . . . . . . . 24 92 4.1 X.509 Certificates . . . . . . . . . . . . . . . . . . . . 24 93 4.1.1 Versions . . . . . . . . . . . . . . . . . . . . . . . 24 94 4.1.2 SubjectName . . . . . . . . . . . . . . . . . . . . . 25 95 4.1.3 X.509 Certificate Extensions . . . . . . . . . . . . . 25 96 4.2 X.509 Certificate Revocation Lists . . . . . . . . . . . . 31 97 4.2.1 Multiple Sources of Certificate Revocation 98 Information . . . . . . . . . . . . . . . . . . . . . 32 99 4.2.2 X.509 Certificate Revocation List Extensions . . . . . 32 100 5. Configuration Data Exchange Conventions . . . . . . . . . . 33 101 5.1 Certificates . . . . . . . . . . . . . . . . . . . . . . . 33 102 5.2 CRLs and ARLs . . . . . . . . . . . . . . . . . . . . . . 34 103 5.3 Public Keys . . . . . . . . . . . . . . . . . . . . . . . 34 104 5.4 PKCS#10 Certificate Signing Requests . . . . . . . . . . . 34 105 6. Security Considerations . . . . . . . . . . . . . . . . . . 34 106 6.1 Certificate Request Payload . . . . . . . . . . . . . . . 34 107 6.2 IKEv1 Main Mode . . . . . . . . . . . . . . . . . . . . . 34 108 7. Intellectual Property Rights . . . . . . . . . . . . . . . . 35 109 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . 35 110 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 35 111 9.1 Normative References . . . . . . . . . . . . . . . . . . . 35 112 9.2 Informative References . . . . . . . . . . . . . . . . . . 36 113 Author's Address . . . . . . . . . . . . . . . . . . . . . . 36 114 A. Change History . . . . . . . . . . . . . . . . . . . . . . . 36 115 B. The Possible Dangers of Delta CRLs . . . . . . . . . . . . . 43 116 C. More on Empty CERTREQs . . . . . . . . . . . . . . . . . . . 44 117 D. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 46 118 Intellectual Property and Copyright Statements . . . . . . . 47 120 1. Introduction 122 IKE [1], ISAKMP [2] and IKEv2 [3] provide a secure key exchange 123 mechanism for use with IPsec [4]. In many cases the peers 124 authenticate using digital certificates as specified in PKIX [5]. 125 Unfortunately, the combination of these standards leads to an 126 underspecified set of requirements for the use of certificates in the 127 context of IPsec. 129 ISAKMP references PKIX but in many cases merely specifies the 130 contents of various messages without specifying their syntax or 131 semantics. Meanwhile, PKIX provides a large set of certificate 132 mechanisms which are generally applicable for Internet protocols, but 133 little specific guidance for IPsec. Given the numerous 134 underspecified choices, interoperability is hampered if all 135 implementers do not make similar choices, or at least fail to account 136 for implementations which have chosen differently. 138 This profile of the IKE and PKIX frameworks is intended to provide an 139 agreed-upon standard for using PKI technology in the context of IPsec 140 by profiling the PKIX framework for use with IKE and IPsec, and by 141 documenting the contents of the relevant IKE payloads and further 142 specifying their semantics. 144 In addition to providing a profile of IKE and PKIX, this document 145 attempts to incorporate lessons learned from recent experience with 146 both implementation and deployment, as well as the current state of 147 related protocols and technologies. 149 Material from ISAKMP, IKEv1, IKEv2, or PKIX is not repeated here, and 150 readers of this document are assumed to have read and understood 151 those documents. The requirements and security aspects of those 152 documents are fully relevant to this document as well. 154 This document is organized as follows. Section 2 defines special 155 terminology used in the rest of this document, Section 3 provides the 156 profile of IKEv1/ISAKMP and IKEv2, and Section 4 provides the profile 157 of PKIX. Section 5 covers conventions for the out-of-band exchange 158 of keying materials for configuration purposes. 160 This document is being discussed on the pki4ipsec@icsalabs.com 161 mailing list. 163 2. Terms and Definitions 165 Except for those terms which are defined immediately below, all terms 166 used in this document are defined in either the PKIX [5], ISAKMP [2], 167 IKEv1 [1], IKEv2 [3], or DOI [6] documents. 169 o Peer source address: The source address in packets from a peer. 170 This address may be different from any addresses asserted as the 171 "identity" of the peer. 172 o FQDN: Fully qualified domain name. 173 o ID_USER_FQDN: IKEv2 renamed ID_USER_FQDN to ID_RFC822_ADDR. Both 174 are referred to as ID_USER_FQDN in this document. 176 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 177 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 178 document are to be interpreted as described in RFC-2119 [7]. 180 3. Profile of IKEv1/ISAKMP and IKEv2 182 3.1 Identification Payload 184 The Identification (ID) Payload is used to indicate the identity that 185 the sender claims to be speaking for. The recipient can then use the 186 ID as a lookup key for policy and whatever certificate store or 187 directory that it has available. Our primary concern in this section 188 is to profile the ID payload so that it can be safely used to 189 generate or lookup policy. IKE mandates the use of the ID payload in 190 Phase 1. 192 The DOI [6] defines the 11 types of Identification Data that can be 193 used and specifies the syntax for these types. These are discussed 194 below in detail. 196 The ID payload requirements in this document cover only the portion 197 of the explicit policy checks that deal with the Identification 198 Payload specifically. For instance, in the case where ID does not 199 contain an IP address, checks such as verifying that the peer source 200 address is permitted by the relevant policy are not addressed here as 201 they are out of the scope of this document. 203 Implementations SHOULD populate ID with identity information that is 204 contained within the end-entity certificate (This SHOULD does not 205 contradict text in IKEv2 [3] Section 3.5 that implies a looser 206 binding between these two). Populating ID with identity information 207 from the end-entity certificate enables recipients to use ID as a 208 lookup key to find the peer end-entity certificate. The only case 209 where implementations MAY populate ID with information that is not 210 contained in the end-entity certificate is when ID contains the peer 211 source address (a single address, not a subnet or range). 213 Because implementations may use ID as a lookup key to determine which 214 policy to use, all implementations MUST be especially careful to 215 verify the truthfulness of the contents by verifying that they 216 correspond to some keying material demonstrably held by the peer. 218 Failure to do so may result in the use of an inappropriate or 219 insecure policy. The following sections describe the methods for 220 performing this binding. 222 The following table summarizes the binding of the Identification 223 Payload to the contents of end-entity certificates and of identity 224 information to policy. Each ID type is covered more thoroughly in 225 the following sections. 227 ID type | Support | Correspond | Cert | SPD lookup 228 | for send | PKIX Attrib | matching | rules 229 ------------------------------------------------------------------- 230 | | | | 231 IP*_ADDR | MUST [1] | SubjAltName | MUST [2] | [3], [4] 232 | | iPAddress | | 233 | | | | 234 FQDN | MUST [1] | SubjAltName | MUST [2] | [3], [4] 235 | | dNSName | | 236 | | | | 237 USER_FQDN| MUST [1] | SubjAltName | MUST [2] | [3], [4] 238 | | rfc822Name | | 239 | | | | 240 DN | MUST [1] | Entire | MUST [2] | MUST support lookup 241 | | Subject, | | on any combination 242 | | bitwise | | of C, CN, O, or OU 243 | | compare | | 244 | | | | 245 IP range | MUST NOT | n/a | n/a | n/a 246 | | | | 247 | | | | 248 KEY_ID | MUST NOT | n/a | n/a | n/a 249 | | | | 251 [1] = Implementation MUST have the configuration option to send this 252 ID type in the ID payload. Whether or not the ID type is used is a 253 matter of local configuration. 255 [2] = The ID in the ID payload MUST match the contents of the 256 corresponding field (listed) in the certificate exactly, with no 257 other lookup. The matched ID MAY be used for SPD lookup, but is not 258 required to be used for this. See 2401bis [10], section 4.4.3.2 for 259 more details. 261 [3] = At a minimum, Implementation MUST be capable of being 262 configured to perform exact matching of the ID payload contents to an 263 entry in the local SPD. 265 [4] = In addition, the implementation MAY also be configurable to 266 perform substring or wildcard matches of ID payload contents to 267 entries in the local SPD. (More on this in Section 3.1.5). 269 When sending an IPV4_ADDR, IPV6_ADDR, FQDN, or USER_FQDN, 270 implementations MUST be able to be configured to send the same string 271 as appears in the corresponding SubjectAltName attribute. This 272 document RECOMMENDS that deployers use this configuration option. 273 All these ID types are treated the same: as strings that can be 274 compared easily and quickly to a corresponding string in an explicit 275 attribute in the certificate. Of these types, FQDN and USER_FQDN are 276 RECOMMENDED over IP addresses (see discussion in Section 3.1.1). 278 When sending a DN as ID, implementations MUST send the entire DN in 279 ID. Also, implementations MUST support at least the C, CN, O, and OU 280 attributes for SPD matching. See Section 3.1.5 for more details 281 about DN, including SPD matching. 283 Recipients MUST be able to perform SPD matching on the exact contents 284 of the ID, and this SHOULD be the default setting. In addition, 285 implementations MAY use substrings or wildcards in local policy 286 configuration to do the SPD matching against the ID contents. In 287 other words, implementations MUST be able to do exact matches of ID 288 to SPD, but MAY also be configurable to do substring or wildcard 289 matches of ID to SPD. 291 IKEv2 adds an optional IDr payload in the second exchange that the 292 initiator may send to the responder in order to specify which of the 293 responder's multiple identities should be used. The responder MAY 294 choose to send an IDr in the 3rd exchange that differs in type or 295 content from the initiator-generated IDr. The initiator MUST be able 296 to receive a responder-generated IDr that is a different type from 297 the one the initiator generated. 299 3.1.1 ID_IPV4_ADDR and ID_IPV6_ADDR 301 Implementations MUST support either the ID_IPV4_ADDR or ID_IPV6_ADDR 302 ID type, depending on whether the implementation supports IPv4, IPv6 303 or both. These addresses MUST be encoded in "network byte order," as 304 specified in IP [8]: The least significant bit (LSB) of each octet is 305 the LSB of the corresponding byte in the network address. For the 306 ID_IPV4_ADDR type, the payload MUST contain exactly four octets [8]. 307 For the ID_IPV6_ADDR type, the payload MUST contain exactly sixteen 308 octets [11]. 310 Implementations SHOULD NOT populate ID payload with IP addresses due 311 to interoperability issues such as problems with NAT traversal, and 312 problems with IP verification behavior. 314 Deployments may only want to consider using the IP address as ID if 315 the following are true: 317 o the peer's IP address is static, not dynamically changing 318 o the peer is NOT behind a NAT'ing device 319 o the administrator intends the implementation to verify that the 320 peer source address matches the IP address in the ID received, and 321 that in the iPAddress field in the peer certificate's 322 SubjectAltName extension. 324 Implementations MUST be capable of verifying that the IP address 325 presented in ID matches via bitwise comparison the IP address present 326 in the certificate's iPAddress field of the SubjectAltName extension. 327 Implementations MUST perform this verification by default. When 328 comparing the contents of ID with the iPAddress field in the 329 SubjectAltName extension for equality, binary comparison MUST be 330 performed. Note that certificates may contain multiple address 331 identity types in which case at least one must match the source IP. 332 If the default is enabled, then a mismatch between the two addresses 333 MUST be treated as an error and security association setup MUST be 334 aborted. This event SHOULD be auditable. Implementations MAY 335 provide a configuration option to (i.e. local policy configuration 336 can enable) skip that verification step, but that option MUST be off 337 by default. We include the "option-to-skip-validation" in order to 338 permit better interoperability, as today implementations vary greatly 339 in how they behave on this topic. 341 In addition, implementations MUST be capable of verifying that the 342 address contained in the ID is the same as the peer source address, 343 contained in the outer most IP header. If ID is one of the IP 344 address types, then implementations MUST perform this verification by 345 default. If this default is enabled, then a mismatch MUST be treated 346 as an error and security association setup MUST be aborted. This 347 event SHOULD be auditable. Implementations MAY provide a 348 configuration option to (i.e. local policy configuration can enable) 349 skip that verification step, but that option MUST be off by default. 350 We include the "option-to-skip-validation" in order to permit better 351 interoperability, as today implementations vary greatly in how they 352 behave on the topic of verification of source IP. 354 If the default for both the verifications above are enabled, then, by 355 transitive property, the implementation will also be verifying that 356 the peer source IP address matches via a bitwise comparison the 357 contents of the iPAddress field in the SubjectAltName extension in 358 the certificate. In addition, implementations MAY allow 359 administrators to configure a local policy that explicitly requires 360 that the peer source IP address match via a bitwise comparison the 361 contents of the iPAddress field in the SubjectAltName extension in 362 the certificate. Implementations SHOULD allow administrators to 363 configure a local policy that skips this validation check. 365 Implementations MAY support substring, wildcard, or regular 366 expression matching of the contents of ID to lookup policy in the 367 SPD, and such would be a matter of local security policy 368 configuration. 370 Implementations MAY use the IP address found in the header of packets 371 received from the peer to lookup the policy, but such implementations 372 MUST still perform verification of the ID payload. Although packet 373 IP addresses are inherently untrustworthy and must therefore be 374 independently verified, it is often useful to use the apparent IP 375 address of the peer to locate a general class of policies that will 376 be used until the mandatory identity-based policy lookup can be 377 performed. 379 For instance, if the IP address of the peer is unrecognized, a VPN 380 gateway device might load a general "road warrior" policy that 381 specifies a particular CA that is trusted to issue certificates which 382 contain a valid rfc822Name which can be used by that implementation 383 to perform authorization based on access control lists (ACLs) after 384 the peer's certificate has been validated. The rfc822Name can then 385 be used to determine the policy that provides specific authorization 386 to access resources (such as IP addresses, ports, and so forth). 388 As another example, if the IP address of the peer is recognized to be 389 a known peer VPN endpoint, policy may be determined using that 390 address, but until the identity (address) is validated by validating 391 the peer certificate, the policy MUST NOT be used to authorize any 392 IPsec traffic. 394 3.1.2 ID_FQDN 396 Implementations MUST support the ID_FQDN ID type, generally to 397 support host-based access control lists for hosts without fixed IP 398 addresses. However, implementations SHOULD NOT use the DNS to map 399 the FQDN to IP addresses for input into any policy decisions, unless 400 that mapping is known to be secure, for example if DNSSEC [12] were 401 employed. 403 If ID contains an ID_FQDN, implementations MUST be capable of 404 verifying that the identity contained in the ID payload matches 405 identity information contained in the peer end-entity certificate, in 406 the dNSName field in the SubjectAltName extension. Implementations 407 MUST perform this verification by default. When comparing the 408 contents of ID with the dNSName field in the SubjectAltName extension 409 for equality, caseless string comparison MUST be performed. 411 Substring, wildcard, or regular expression matching MUST NOT be 412 performed for this comparison. If this default is enabled, then a 413 mismatch MUST be treated as an error and security association setup 414 MUST be aborted. This event SHOULD be auditable. Implementations 415 MAY provide a configuration option to (i.e. local policy 416 configuration can enable) skip that verification step, but that 417 option MUST be off by default. We include the "option-to-skip- 418 validation" in order to permit better interoperability, as today 419 implementations vary greatly in how they behave on this topic. 421 Implementations MAY support substring, wildcard, or regular 422 expression matching of the contents of ID to lookup policy in the 423 SPD, and such would be a matter of local security policy 424 configuration. 426 3.1.3 ID_USER_FQDN 428 Implementations MUST support the ID_USER_FQDN ID type, generally to 429 support user-based access control lists for users without fixed IP 430 addresses. However, implementations SHOULD NOT use the DNS to map 431 the FQDN portion to IP addresses for input into any policy decisions, 432 unless that mapping is known to be secure, for example if DNSSEC [12] 433 were employed. 435 Implementations MUST be capable of verifying that the identity 436 contained in the ID payload matches identity information contained in 437 the peer end-entity certificate, in the rfc822Name field in the 438 SubjectAltName extension. Implementations MUST perform this 439 verification by default. When comparing the contents of ID with the 440 rfc822Name field in the SubjectAltName extension for equality, 441 caseless string comparison MUST be performed. Substring, wildcard, 442 or regular expression matching MUST NOT be performed for this 443 comparison. If this default is enabled, then a mismatch MUST be 444 treated as an error and security association setup MUST be aborted. 445 This event SHOULD be auditable. Implementations MAY provide a 446 configuration option to (i.e. local policy configuration can enable) 447 skip that verification step, but that option MUST be off by default. 448 We include the "option-to-skip-validation" in order to permit better 449 interoperability, as today implementations vary greatly in how they 450 behave on this topic. 452 Implementations MAY support substring, wildcard, or regular 453 expression matching of the contents of ID to lookup policy in the 454 SPD, and such would be a matter of local security policy 455 configuration. 457 3.1.4 ID_IPV4_ADDR_SUBNET, ID_IPV6_ADDR_SUBNET, ID_IPV4_ADDR_RANGE, 458 ID_IPV6_ADDR_RANGE 460 Historically there was no standard method for putting address subnet 461 or range identity information into certificates, nor are there any 462 implementations known to support these ID types. Therefore, use of 463 these ID types is currently undefined. Implementations MUST NOT 464 generate these ID types. 466 Note that work in SBGP [13] for defining blocks of addresses using 467 the certificate extension identified by: 469 id-pe-ipAddrBlock OBJECT IDENTIFIER ::= { id-pe 7 } 471 is experimental at this time. 473 3.1.5 ID_DER_ASN1_DN 475 Implementations MUST support receiving the ID_DER_ASN1_DN ID type. 476 Implementations MUST be capable of generating this type, and the 477 decision to do so will be a matter of local security policy 478 configuration. When generating this type, implementations MUST 479 populate the contents of ID with the SubjectName from the end-entity 480 certificate, and MUST do so such that a binary comparison of the two 481 will succeed. If there is not a match, this MUST be treated as an 482 error and security association setup MUST be aborted. This event 483 SHOULD be auditable. Note, if the certificate was erroneously 484 created such that the encoding of the SubjectName DN varies from the 485 constraints set by DER, that non-conformant DN MUST be used to 486 populate the ID payload: in other words, implementations MUST NOT re- 487 encode the DN for the purposes of making it DER if it does not appear 488 in the certificate as DER. 490 Implementations MUST NOT populate ID with the SubjectName from the 491 end-entity certificate if it is empty, even though an empty 492 certificate SubjectName is explicitly allowed in the "Subject" 493 section of PKIX. 495 Regarding SPD matching, implementations MUST be able to perform 496 matching based on a bitwise comparison of the entire DN in ID to its 497 entry in the SPD. However, operational experience has shown that 498 using the entire DN in local configuration is difficult, especially 499 in large scale deployments. Therefore, implementations also MUST be 500 able to perform SPD matches of any combination of one or more of the 501 C, CN, O, OU attributes within Subject DN in the ID to the same in 502 the SPD. Implementations MAY support matching using additional DN 503 attributes in any combination, although interoperability is far from 504 certain and dubious. Implementations MAY also support performing 505 substring, wildcard, or regular expression matches for any of its 506 supported DN attributes from ID, in any combination, to the SPD. 507 Such flexibility allows deployers to create one SPD entry on the 508 gateway for an entire department of a company (e.g. O=Foobar Inc., 509 OU=Engineering) while still allowing them to draw out other details 510 from the DN (e.g. CN=John Doe) for auditing purposes. All the above 511 is a matter of local implementation and local policy definition and 512 enforcement capability, not bits on the wire, but will have a great 513 impact on interoperability. 515 3.1.6 ID_DER_ASN1_GN 517 Implementations MUST NOT generate this type. 519 3.1.7 ID_KEY_ID 521 The ID_KEY_ID type used to specify pre-shared keys and thus is out of 522 scope. 524 3.1.8 Selecting an Identity from a Certificate 526 Implementations MUST support certificates that contain more than a 527 single identity, such as when SubjectName and the SubjectAltName 528 extension are both populated, or the SubjectAltName extension 529 contains multiple identities irrespective of whether SubjectName is 530 empty or not. In many cases a certificate will contain an identity 531 such as an IP address in the SubjectAltName extension in addition to 532 a non-empty SubjectName. 534 Implementations SHOULD populate ID with whichever identity is likely 535 to be named in the peer's policy. In practice, this generally means 536 FQDN, or USER_FQDN, but this information may also be available to the 537 administrator through some out-of-band means. In the absence of such 538 out-of-band configuration information, the identity with which an 539 implementation chooses to populate the ID payload is a local matter. 541 3.1.9 SubjectName for DN Only 543 If an FQDN is intended to be processed as an identity for the 544 purposes ID matching, it MUST be placed in the dNSName field of the 545 SubjectAltName extension. Implementations MUST NOT populate 546 SubjectName with an FQDN in place of populating the dNSName field of 547 the SubjectAltName extension. 549 While nothing prevents an FQDN, USER_FQDN, or IP address information 550 from appearing somewhere in the SubjectName contents, such entries 551 MUST NOT be interpreted as identity information for the purposes of 552 matching with ID or for policy lookup. 554 3.1.10 Binding Identity to Policy 556 In the presence of certificates that contain multiple identities, 557 implementations MUST select the most appropriate identity from the 558 certificate and populate the ID with that. The recipient MUST use 559 the identity sent as a first key when selecting the policy. The 560 recipient MUST also use the most specific policy from that database 561 if there are overlapping policies caused by wildcards (or the 562 implementation can de-correlate the policy database so there will not 563 be overlapping entries, or it can also forbid creation of overlapping 564 policies and leave the de-correlation process to the administrator, 565 but as this moves the problem to the administrator it is NOT 566 RECOMMENDED). 568 For example, imagine that a implementation is configured with a 569 certificate that contains both a non-empty SubjectName and a dNSName. 570 The sender's policy may specify which of those to use, and it 571 indicates the policy to the other end by sending that ID. If the 572 recipient has both a specific policy for the dNSName for this host 573 and generic wildcard rule for some attributes present in the 574 SubjectName, it will match a different policy depending which ID is 575 sent. As the sender knows why it wanted to connect the peer, it also 576 knows what identity it should use to match the policy it needs to the 577 operation it tries to perform; it is the only party who can select 578 the ID adequately. 580 In the event the policy cannot be found in the recipient's SPD using 581 the ID sent, then the recipient MAY use the other identities in the 582 certificate when attempting to match a suitable policy. For example, 583 say the certificate contains non-empty SubjectName, a dNSName and an 584 iPAddress. If an iPAddress is sent in ID but no specific entry 585 exists for the address in the policy database, the recipient MAY 586 search in the policy database based on the SubjectName or the dNSName 587 contained in the certificate. 589 The Peer Authorization Database (PAD) as described in 2401bis [10] 590 provides a more formal model for the binding of identity to policy in 591 addition to providing services that deal more specifically with the 592 details of policy enforcement, which are generally out of scope of 593 this document. The PAD is intended to provide a link between the SPD 594 and the security association management in protocols such as IKE. 595 See 2401bis [10], section 4.4.3 for more details. 597 3.2 Certificate Request Payload 599 The Certificate Request (CERTREQ) Payload allows an implementation to 600 request that a peer provide some set of certificates or certificate 601 revocation lists. It is not clear from ISAKMP exactly how that set 602 should be specified or how the peer should respond. We describe the 603 semantics on both sides. 605 3.2.1 Certificate Type 607 The Certificate Type field identifies to the peer the type of 608 certificate keying materials that are desired. ISAKMP defines 10 609 types of Certificate Data that can be requested and specifies the 610 syntax for these types, and IKEv2 specifies 3 additional types. For 611 the purposes of this document, only the following types are relevant: 613 o X.509 Certificate - Signature 614 o Revocation Lists (CRL and ARL) 615 o PKCS #7 wrapped X.509 certificate 616 o IKEv2's Hash and URL of X.509 certificate 618 The use of the other types: 620 o X.509 Certificate - Key Exchange 621 o PGP Certificate 622 o DNS Signed Key 623 o Kerberos Tokens 624 o SPKI Certificate 625 o X.509 Certificate Attribute 626 o IKEv2's Raw RSA Key 627 o IKEv2's Hash and URL of X.509 bundle 629 are out of the scope of this document. 631 3.2.2 X.509 Certificate - Signature 633 This type requests that the end-entity certificate be a signing 634 certificate. 636 3.2.3 Revocation Lists (CRL and ARL) 638 ISAKMP and IKEv2 do not support Certificate Payload sizes over 639 approximately 64K, which is too small for many CRLs. Therefore, the 640 acquisition of revocation material is to be dealt with out-of-band of 641 IKE. For this and other reasons, implementations SHOULD NOT generate 642 CERTREQs where the Certificate Type is "Certificate Revocation List 643 (CRL)" or "Authority Revocation List (ARL)". Implementations that do 644 generate such CERTREQs MUST NOT require the recipient to respond with 645 a CRL or ARL, and MUST NOT fail when not receiving any. Upon receipt 646 of such a CERTREQ, implementations MAY ignore the request. 648 In lieu of exchanging revocation lists in-band, a pointer to 649 revocation checking SHOULD be listed in either the 650 CRLDistributionPoints (CDP) or the AuthorityInfoAccess (AIA) 651 certificate extensions (see Section 4 for details). Unless other 652 methods for obtaining revocation information are available, 653 implementations SHOULD be able to process these attributes, and from 654 them be able to identify cached revocation material, or retrieve the 655 relevant revocation material from a URL, for validation processing. 656 In addition, implementations MUST have the ability to configure 657 validation checking information for each certification authority. 658 Regardless of the method (CDP, AIA, or static configuration), the 659 acquisition of revocation material SHOULD occur out-of-band of IKE. 661 3.2.4 PKCS #7 wrapped X.509 certificate 663 This ID type defines a particular encoding (not a particular 664 certificate type), some current implementations may ignore CERTREQs 665 they receive which contain this ID type, and the authors are unaware 666 of any implementations that generate such CERTREQ messages. 667 Therefore, the use of this type is deprecated. Implementations 668 SHOULD NOT require CERTREQs that contain this Certificate Type. 669 Implementations which receive CERTREQs which contain this ID type MAY 670 treat such payloads as synonymous with "X.509 Certificate - 671 Signature". 673 3.2.5 IKEv2's Hash and URL of X.509 certificate 675 This ID type defines a request for the peer to send a hash and URL of 676 it X.509 certificate, instead of the actual certificate itself. This 677 is a particularly useful mechanism when the peer is a device with 678 little memory and lower bandwidth, e.g. a mobile handset or consumer 679 electronics device. 681 If the IKEv2 implementation supports URL lookups, and prefers such a 682 URL to receiving actual certificates, then the implementation will 683 want to send a notify of type HTTP_CERT_LOOKUP_SUPPORTED. From IKEv2 684 [3], section 3.10.1, "This notification MAY be included in any 685 message that can include a CERTREQ payload and indicates that the 686 sender is capable of looking up certificates based on an HTTP-based 687 URL (and hence presumably would prefer to receive certificate 688 specifications in that format)." If an HTTP_LOOKUP_SUPPORTED 689 notification is sent the sender MUST support the http scheme. See 690 Section 3.3.4 for more discussion. 692 3.2.6 Location of Certificate Payloads 694 In IKEv1, the CERTREQ payload MUST be in messages 4 and 5. In IKEv2, 695 the CERTREQ payload must be in messages 2 and 3. Note that in IKEv2, 696 it is possible to have one side authenticating with certificates 697 while the other side authenticates with preshared keys. 699 3.2.7 Presence or Absence of Certificate Request Payloads 701 When in-band exchange of certificate keying materials is desired, 702 implementations MUST inform the peer of this by sending at least one 703 CERTREQ. In other words, an implementation which does not send any 704 CERTREQs during an exchange SHOULD NOT expect to receive any CERT 705 payloads. 707 3.2.8 Certificate Requests 709 3.2.8.1 Specifying Certification Authorities 711 When requesting in-band exchange of keying materials, implementations 712 SHOULD generate CERTREQs for every peer trust anchor that local 713 policy explicitly deems trusted during a given exchange. For IKEv1, 714 implementations SHOULD populate the Certification Authority field 715 with the SubjectName of the trust anchor, populated such that binary 716 comparison of the SubjectName and the Certification Authority will 717 succeed. For IKEv2, implementations MUST populate the Certification 718 Authority field as specified in IKEv2 [3]. 720 Upon receipt of a CERTREQ, implementations MUST respond by sending at 721 least the end-entity certificate corresponding to the Certification 722 Authority listed in the CERTREQ unless local security policy 723 configuration specifies that keying materials must be exchanged out- 724 of-band. Implementations MAY send certificates other than the end- 725 entity certificate (see Section 3.3 for discussion). 727 Note, in the case where multiple end-entity certificates may be 728 available which chain to different trust anchors, implementations 729 SHOULD resort to local heuristics to determine which trust anchor is 730 most appropriate to use for generating the CERTREQ. Such heuristics 731 are out of the scope of this document. 733 3.2.8.2 Empty Certification Authority Field 735 Implementations SHOULD generate CERTREQs where the Certificate Type 736 is "X.509 Certificate - Signature" and where a the Certification 737 Authority field is not empty. However, implementations MAY generate 738 CERTREQs with an empty Certification Authority field under special 739 conditions. Although PKIX prohibits certificates with empty 740 IssuerName fields, there does exist a use case where doing so is 741 appropriate, and carries special meaning in the IKE context. This 742 has become a convention within the IKE interoperability tests and 743 usage space, and so its use is specified, explained here for the sake 744 of interoperability. 746 USE CASE: Consider the rare case where you have a gateway with 747 multiple policies for a large number of IKE peers: some of these 748 peers are business partners, some are remote access employees, some 749 are teleworkers, some are branch offices, and/or the gateway may be 750 simultaneously serving many customers (e.g. Virtual Routers). The 751 total number of certificates, and corresponding trust anchors, is 752 very high, say hundreds. Each of these policies is configured with 753 one or more acceptable trust anchors, so that in total, the gateway 754 has one hundred (100) trust anchors that could possibly used to 755 authenticate an incoming connection. Assume that many of those 756 connections originate from hosts/gateways with dynamically assigned 757 IP addresses, so that the source IP of the IKE initiator is not known 758 to the gateway, nor is the identity of the initiator (until it is 759 revealed in Main Mode message 5). In IKE main mode message 4, the 760 responder gateway will need to send a CERTREQ to the initiator. 761 Given this example, the gateway will have no idea which of the 762 hundred possible Certification Authorities to send in the CERTREQ. 763 Sending all possible Certification Authorities will cause significant 764 processing delays, bandwidth consumption, and UDP fragmentation, so 765 this tactic is ruled out. 767 In such a deployment, the responder gateway implementation should be 768 able to do all it can to indicate a Certification Authority in the 769 CERTREQ. This means the responder SHOULD first check SPD to see if 770 it can match the source IP, and find some indication of which CA is 771 associated with that IP. If this fails (because the source IP is not 772 familiar, as in the case above), then the responder SHOULD have a 773 configuration option specifying which CA's are the default CAs to 774 indicate in CERTREQ during such ambiguous connections (e.g. send 775 CERTREQ with these N CAs if there is an unknown source IP). If such 776 a fall-back is not configured or impractical in a certain deployment 777 scenario, then the responder implementation SHOULD have both of the 778 following configuration options: 780 o send a CERTREQ payload with an empty Certification Authority 781 field, or 782 o terminate the negotiation with an appropriate error message and 783 audit log entry. 785 Receiving a CERTREQ payload with an empty Certification Authority 786 field indicates that the recipient should send all/any end-entity 787 certificates it has, regardless of the trust anchor. The initiator 788 should be aware of what policy and which identity it will use, as it 789 initiated the connection on a matched policy to begin with, and can 790 thus respond with the appropriate certificate. 792 If, after sending an empty CERTREQ in Main Mode message 4, a 793 responder receives a certificate in message 5 that chains to a trust 794 anchor that the responder either (a) does NOT support, or (b) was not 795 configured for the policy (that policy was now able to be matched due 796 to having the initiator's certificate present), this MUST be treated 797 as an error and security association setup MUST be aborted. This 798 event SHOULD be auditable. 800 Instead of sending a empty CERTREQ, the responder implementation MAY 801 be configured to terminate the negotiation on the grounds of a 802 conflict with locally configured security policy. 804 The decision of which to configure is a matter of local security 805 policy, this document RECOMMENDS that both options be presented to 806 administrators. 808 More examples, and explanation on this issue are included in "More on 809 Empty CERTREQs" (Appendix C). 811 3.2.9 Robustness 813 3.2.9.1 Unrecognized or Unsupported Certificate Types 815 Implementations MUST be able to deal with receiving CERTREQs with 816 unsupported Certificate Types. Absent any recognized and supported 817 CERTREQ types, implementations MAY treat them as if they are of a 818 supported type with the Certification Authority field left empty, 819 depending on local policy. ISAKMP [2] Section 5.10 "Certificate 820 Request Payload Processing" specifies additional processing. 822 3.2.9.2 Undecodable Certification Authority Fields 824 Implementations MUST be able to deal with receiving CERTREQs with 825 undecodable Certification Authority fields. Implementations MAY 826 ignore such payloads, depending on local policy. ISAKMP specifies 827 other actions which may be taken. 829 3.2.9.3 Ordering of Certificate Request Payloads 831 Implementations MUST NOT assume that CERTREQs are ordered in any way. 833 3.2.10 Optimizations 835 3.2.10.1 Duplicate Certificate Request Payloads 837 Implementations SHOULD NOT send duplicate CERTREQs during an 838 exchange. 840 3.2.10.2 Name Lowest 'Common' Certification Authorities 842 When a peer's certificate keying materials have been cached, an 843 implementation can send a hint to the peer to elide some of the 844 certificates the peer would normally respond with. In addition to 845 the normal set of CERTREQs that are sent specifying the trust 846 anchors, an implementation MAY send CERTREQs specifying the relevant 847 cached end-entity certificates. When sending these hints, it is 848 still necessary to send the normal set of trust anchor CERTREQs 849 because the hints do not sufficiently convey all of the information 850 required by the peer. Specifically, either the peer may not support 851 this optimization or there may be additional chains that could be 852 used in this context but will not be if only the end-entity 853 certificate is specified. 855 No special processing is required on the part of the recipient of 856 such a CERTREQ, and the end-entity certificates will still be sent. 857 On the other hand, the recipient MAY elect to elide certificates 858 based on receipt of such hints. 860 CERTREQs must contain information that identifies a Certification 861 Authority certificate, which results in the peer always sending at 862 least the end-entity certificate. Always sending the end-entity 863 certificate allows implementations to determine unambiguously when a 864 new certificate is being used by a peer (perhaps because the previous 865 certificate has just expired), which may result in a failure because 866 a new intermediate CA certificate might not be available to validate 867 the new end-entity certificate). Implementations which implement 868 this optimization MUST recognize when the end-entity certificate has 869 changed and respond to it by not performing this optimization if the 870 exchange must be retried so that any missing keying materials will be 871 sent during retry. 873 3.2.10.3 Example 875 Imagine that an IKEv1 implementation has previously received and 876 cached the peer certificate chain TA->CA1->CA2->EE. If during a 877 subsequent exchange this implementation sends a CERTREQ containing 878 the SubjectName in certificate TA, this implementation is requesting 879 that the peer send at least 3 certificates: CA1, CA2, and EE. On the 880 other hand, if this implementation also sends a CERTREQ containing 881 the SubjectName of CA2, the implementation is providing a hint that 882 only 1 certificate needs to be sent: EE. Note that in this example, 883 the fact that TA is a trust anchor should not be construed to imply 884 that TA is a self-signed certificate. 886 3.3 Certificate Payload 888 The Certificate (CERT) Payload allows the peer to transmit a single 889 certificate or CRL. Multiple certificates should be transmitted in 890 multiple payloads. For backwards compatibility reasons, 891 implementations MAY send intermediate CA certificates in addition to 892 the appropriate end-entity certificate(s), but SHOULD NOT send any 893 CRLs, ARLs, or trust anchors. The reason for not exchanging CRLs or 894 ARLs in IKE is to: 896 o decrease UDP fragmentation 897 o simplify the IKE exchange 898 o reduce bandwidth requirements for IKE exchanges 900 Note, however, that while the sender of the CERT payloads SHOULD NOT 901 send any trust anchors, it's possible that the recipient may consider 902 any given intermediate CA certificate to be a trust anchor. For 903 instance, imagine the sender has the certificate chain TA1->CA1->EE1 904 while the recipient has the certificate chain TA2->EE2 where TA2=CA1. 905 The sender is merely including an intermdiate CA certificate, while 906 the recipient receives a trust anchor. 908 However, not all certificate forms that are legal in PKIX make sense 909 in the context of IPsec. The issue of how to represent IKE- 910 meaningful name-forms in a certificate is especially problematic. 911 This document provides a profile for a subset of PKIX that makes 912 sense for IKEv1/ISAKMP and IKEv2. 914 3.3.1 Certificate Type 916 The Certificate Type field identifies to the peer the type of 917 certificate keying materials that are included. ISAKMP defines 10 918 types of Certificate Data that can be sent and specifies the syntax 919 for these types, and IKEv2 specifies 3 additional types. For the 920 purposes of this document, only the following types are relevant: 922 o X.509 Certificate - Signature 923 o Revocation Lists (CRL and ARL) 924 o PKCS #7 wrapped X.509 certificate 925 o IKEv2's Hash and URL of X.509 certificate 927 The use of the other types: 929 o X.509 Certificate - Key Exchange 930 o PGP Certificate 931 o DNS Signed Key 932 o Kerberos Tokens 933 o SPKI Certificate 934 o X.509 Certificate Attribute 935 o IKEv2's Raw RSA Key 936 o IKEv2's Hash and URL of X.509 bundle 938 are out of the scope of this document. 940 3.3.2 X.509 Certificate - Signature 942 This type specifies that Certificate Data contains a certificate used 943 for signing. 945 3.3.3 Revocation Lists (CRL and ARL) 947 These types specify that Certificate Data contains an X.509 CRL or 948 ARL. These types SHOULD NOT be sent in IKE. See Section 3.2.3 for 949 discussion. 951 3.3.4 IKEv2's Hash and URL of X.509 Certificate 953 This type specifies that Certificate Data contains a hash and the URL 954 to a repository where an X.509 certificate can be retrieved. 956 An implementation that sends a HTTP_LOOKUP_SUPPORTED notification 957 MUST support the http scheme and MAY support the ftp scheme, and MUST 958 NOT require any specific form of the url-path and it SHOULD support 959 having user-name, password and port parts in the URL. The following 960 are examples of mandatory forms: 962 o http://certs.example.com/certificate.crt 963 o http://certs.example.com/certs/cert.pl?u=foo;a=pw;valid-to=+86400 964 o http://certs.example.com/%0a/../foo/bar/zappa 966 while the following is an example of a form that SHOULD be supported: 968 o http://user:password@certs.example.com:8888/certificate.crt 970 The following is an example of the ftp scheme that MAY be supported: 972 o ftp://ftp.example.com/pub/certificate.crt 974 3.3.5 PKCS #7 wrapped X.509 certificate 976 This type defines a particular encoding, not a particular certificate 977 type. Implementations SHOULD NOT generate CERTs that contain this 978 Certificate Type. Implementations SHOULD accept CERTs that contain 979 this Certificate Type because several implementations are known to 980 generate them. Note that those implementations sometimes include 981 entire certificate hierarchies inside a single CERT PKCS #7 payload, 982 which violates the requirement specified in ISAKMP that this payload 983 contain a single certificate. 985 3.3.6 Location of Certificate Payloads 987 In IKEv1, the CERT payload MUST be in messages 5 and 6. In IKEv2, 988 the CERT payload must be in messages 3 and 4. Note that in IKEv2, it 989 is possible to have one side authenticating with certificates while 990 the other side authenticates with preshared keys. 992 3.3.7 Certificate Payloads Not Mandatory 994 An implementation which does not receive any CERTREQs during an 995 exchange SHOULD NOT send any CERT payloads, except when explicitly 996 configured to proactively send CERT payloads in order to interoperate 997 with non-compliant implementations which fail to send CERTREQs even 998 when certificates are desired. In this case, an implementation MAY 999 send the certificate chain (not including the trust anchor) 1000 associated with the end-entity certificate. This MUST NOT be the 1001 default behavior of implementations. 1003 Implementations whose local security policy configuration expects 1004 that a peer must receive certificates through out-of-band means 1005 SHOULD ignore any CERTREQ messages that are received. 1007 Implementations that receive CERTREQs from a peer which contain only 1008 unrecognized Certification Authorities SHOULD NOT continue the 1009 exchange, in order to avoid unnecessary and potentially expensive 1010 cryptographic processing, denial of service (resource starvation) 1011 attacks. 1013 3.3.8 Response to Multiple Certification Authority Proposals 1015 In response to multiple CERTREQs which contain different 1016 Certification Authority identities, implementations MAY respond using 1017 an end-entity certificate which chains to a CA that matches any of 1018 the identities provided by the peer. 1020 3.3.9 Using Local Keying Materials 1022 Implementations MAY elect to skip parsing or otherwise decoding a 1023 given set of CERTs if equivalent keying materials are available via 1024 some preferable means, such as the case where certificates from a 1025 previous exchange have been cached. 1027 3.3.10 Multiple End-Entity Certificates 1029 Implementations SHOULD NOT send multiple end-entity certificates and 1030 recipients SHOULD NOT be expected to iterate over multiple end-entity 1031 certificates. 1033 If multiple end-entity certificates are sent, they MUST have the same 1034 public key, otherwise the responder does not know which key was used 1035 in the Main Mode message 5. 1037 3.3.11 Robustness 1039 3.3.11.1 Unrecognized or Unsupported Certificate Types 1041 Implementations MUST be able to deal with receiving CERTs with 1042 unrecognized or unsupported Certificate Types. Implementations MAY 1043 discard such payloads, depending on local policy. ISAKMP [2] Section 1044 5.10 "Certificate Request Payload Processing" specifies additional 1045 processing. 1047 3.3.11.2 Undecodable Certificate Data Fields 1049 Implementations MUST be able to deal with receiving CERTs with 1050 undecodable Certificate Data fields. Implementations MAY discard 1051 such payloads, depending on local policy. ISAKMP specifies other 1052 actions which may be taken. 1054 3.3.11.3 Ordering of Certificate Payloads 1056 For IKEv1, implementations MUST NOT assume that CERTs are ordered in 1057 any way. For IKEv2, implementations MUST NOT assume that any except 1058 the first CERT is ordered in any way. IKEv2 specifies that the first 1059 CERT contain an end-entity certificate which can be used to 1060 authenticate the peer. 1062 3.3.11.4 Duplicate Certificate Payloads 1064 Implementations MUST support receiving multiple identical CERTs 1065 during an exchange. 1067 3.3.11.5 Irrelevant Certificates 1069 Implementations MUST be prepared to receive certificates and CRLs 1070 which are not relevant to the current exchange. Implementations MAY 1071 discard such extraneous certificates and CRLs. 1073 Implementations MAY send certificates which are irrelevant to an 1074 exchange. One reason for including certificates which are irrelevant 1075 to an exchange is to minimize the threat of leaking identifying 1076 information in exchanges where CERT is not encrypted. It should be 1077 noted, however, that this probably provides rather poor protection 1078 against leaking the identity. 1080 Another reason for including certificates that seem irrelevant to an 1081 exchange is that there may be two chains from the Certification 1082 Authority to the end entity, each of which is only valid with certain 1083 validation parameters (such as acceptable policies). Since the end- 1084 entity doesn't know which parameters the relying party is using, it 1085 should send the certificates needed for both chains (even if there's 1086 only one CERTREQ). 1088 Implementations SHOULD NOT send multiple end-entity certificates and 1089 recipients SHOULD NOT be expected to iterate over multiple end-entity 1090 certificates. 1092 3.3.12 Optimizations 1094 3.3.12.1 Duplicate Certificate Payloads 1096 Implementations SHOULD NOT send duplicate CERTs during an exchange. 1097 Such payloads should be suppressed. 1099 3.3.12.2 Send Lowest 'Common' Certificates 1101 When multiple CERTREQs are received which specify certificate 1102 authorities within the end-entity certificate chain, implementations 1103 MAY send the shortest chain possible. However, implementations 1104 SHOULD always send the end-entity certificate. See Section 3.2.10.2 1105 for more discussion of this optimization. 1107 3.3.12.3 Ignore Duplicate Certificate Payloads 1109 Implementations MAY employ local means to recognize CERTs that have 1110 already been received and SHOULD discard these duplicate CERTs. 1112 3.3.12.4 Hash Payload 1114 IKEv1 specifies the optional use of the Hash Payload to carry a 1115 pointer to a certificate in either of the Phase 1 public key 1116 encryption modes. This pointer is used by an implementation to 1117 locate the end-entity certificate that contains the public key that a 1118 peer should use for encrypting payloads during the exchange. 1120 Implementations SHOULD include this payload whenever the public 1121 portion of the keypair has been placed in a certificate. 1123 4. Profile of PKIX 1125 Except where specifically stated in this document, implementations 1126 MUST conform to the requirements of PKIX [5]. 1128 4.1 X.509 Certificates 1130 4.1.1 Versions 1132 Although PKIX states that "implementations SHOULD be prepared to 1133 accept any version certificate", in practice this profile requires 1134 certain extensions that necessitate the use of Version 3 certificates 1135 for all but self-signed certificates used as trust anchors. 1136 Implementations that conform to this document MAY therefore reject 1137 Version 1 and Version 2 certificates in all other cases. 1139 4.1.2 SubjectName 1141 Certification Authority implementations MUST be able to create 1142 certificates with SubjectName fields with at least the following four 1143 attributes: CN, C, O, OU. Implementations MAY support other 1144 SubjectName attributes as well. The contents of these attributes 1145 SHOULD be configurable on a certificate by certificate basis, as 1146 these fields will likely be used by IKE implementations to match SPD 1147 policy. 1149 See Section 3.1.5 for details on how IKE implementations need to be 1150 able to process SubjectName field attributes for SPD policy lookup. 1152 4.1.2.1 Empty SubjectName 1154 IKE Implementations MUST accept certificates which contain an empty 1155 SubjectName field, as specified in PKIX. Identity information in 1156 such certificates will be contained entirely in the SubjectAltName 1157 extension. 1159 4.1.2.2 Specifying Hosts and not FQDN in SubjectName 1161 Implementations which desire to place host names that are not 1162 intended to be processed by recipients as FQDNs (for instance 1163 "Gateway Router") in the SubjectName MUST use the commonName 1164 attribute. 1166 4.1.2.3 EmailAddress 1168 As specified in PKIX, implementations MUST NOT populate 1169 DistinguishedNames with the emailAddress attribute. 1171 4.1.3 X.509 Certificate Extensions 1173 Conforming IKE implementations MUST recognize extensions which must 1174 or may be marked critical according to this specification. These 1175 extensions are: KeyUsage, SubjectAltName, and BasicConstraints. 1177 Certification Authority implementations SHOULD generate certificates 1178 such that the extension criticality bits are set in accordance with 1179 PKIX and this document. With respect to PKIX compliance, IKE 1180 implementations processing certificates MAY ignore the value of the 1181 criticality bit for extensions that are supported by that 1182 implementation, but MUST support the criticality bit for extensions 1183 that are not supported by that implementation. That is, a relying 1184 party processes all the extensions it is aware of whether the bit is 1185 true or false -- the bit says what happens when a relying party 1186 cannot process an extension. 1188 implements bit in cert PKIX mandate behavior 1189 ------------------------------------------------------ 1190 yes true true ok 1191 yes true false ok or reject 1192 yes false true ok or reject 1193 yes false false ok 1194 no true true reject 1195 no true false reject 1196 no false true reject 1197 no false false ok 1199 4.1.3.1 AuthorityKeyIdentifier and SubjectKeyIdentifier 1201 Implementations SHOULD NOT assume support for the 1202 AuthorityKeyIdentifier or SubjectKeyIdentifier extensions, and thus 1203 Certification Authority implementations SHOULD NOT generate 1204 certificate hierarchies which are overly complex to process in the 1205 absence of these extensions, such as those that require possibly 1206 verifying a signature against a large number of similarly named CA 1207 certificates in order to find the CA certificate which contains the 1208 key that was used to generate the signature. 1210 4.1.3.2 KeyUsage 1212 IKE uses an end-entity certificate in the authentication process. 1213 The end-entity certificate may be used for multiple applications. As 1214 such, the CA can impose some constraints on the manner that a public 1215 key ought to be used. The KeyUsage and ExtendedKeyUsage extensions 1216 apply in this situation. 1218 Since we are talking about using the public key to validate a 1219 signature, if the KeyUsage extension is present, then at least one of 1220 the digitalSignature or the nonRepudiation bits in the KeyUsage 1221 extension MUST be set (both can be set as well). It is also fine if 1222 other KeyUsage bits are set. 1224 A summary of the logic flow for peer cert validation follows: 1226 o If told (by configuration) to ignore KeyUsage (KU), accept cert 1227 regardless of its markings. 1228 o If no KU extension, accept cert. 1229 o If KU present and doesn't mention digitalSignature or 1230 nonRepudiation (both, in addition to other KUs, is also fine), 1231 reject cert. 1232 o If none of the above, accept cert. 1234 4.1.3.3 PrivateKeyUsagePeriod 1236 PKIX recommends against the use of this extension. The 1237 PrivateKeyUsageExtension is intended to be used when signatures will 1238 need to be verified long past the time when signatures using the 1239 private keypair may be generated. Since IKE SAs are short-lived 1240 relative to the intended use of this extension in addition to the 1241 fact that each signature is validated only a single time, the 1242 usefulness of this extension in the context of IKE is unclear. 1243 Therefore, Certification Authority implementations MUST NOT generate 1244 certificates that contain the PrivateKeyUsagePeriod extension. If an 1245 IKE implementation receives a certificate with this set, it SHOULD 1246 ignore it. 1248 4.1.3.4 CertificatePolicies 1250 Many IKE implementations do not currently provide support for the 1251 CertificatePolicies extension. Therefore, Certification Authority 1252 implementations that generate certificates which contain this 1253 extension SHOULD NOT mark the extension as critical. 1255 4.1.3.5 PolicyMappings 1257 Many IKE implementations do not support the PolicyMappings extension. 1258 Therefore, implementations that generate certificates which contain 1259 this extension SHOULD NOT mark the extension as critical. 1261 4.1.3.6 SubjectAltName 1263 Deployments that intend to use an ID of either FQDN, USER_FQDN, 1264 IPV4_ADDR or IPV6_ADDR MUST issue certificates with the corresponding 1265 SubjectAltName fields populated with the same data. Implementations 1266 SHOULD generate only the following GeneralName choices in the 1267 SubjectAltName extension, as these choices map to legal IKEv1/ISAKMP/ 1268 IKEv2 Identification Payload types: rfc822Name, dNSName, or 1269 iPAddress. Although it is possible to specify any GeneralName choice 1270 in the Identification Payload by using the ID_DER_ASN1_GN ID type, 1271 implementations SHOULD NOT assume support for such functionality, and 1272 SHOULD NOT generate certificates that do so. 1274 4.1.3.6.1 dNSName 1276 This field MUST contain a fully qualified domain name. If the IKE ID 1277 type is FQDN then the dNSName field MUST match its contents. 1278 Implementations MUST NOT generate names that contain wildcards. 1279 Implementations MAY treat certificates that contain wildcards in this 1280 field as syntactically invalid. 1282 Although this field is in the form of an FQDN, IKE implementations 1283 SHOULD NOT assume that this field contains an FQDN that will resolve 1284 via the DNS, unless this is known by way of some out-of-band 1285 mechanism. Such a mechanism is out of the scope of this document. 1286 Implementations SHOULD NOT treat the failure to resolve as an error. 1288 4.1.3.6.2 iPAddress 1290 If the IKE ID type is IPV4_ADDR or IPV6_ADDR then the iPAddress field 1291 MUST match its contents. Note that although PKIX permits CIDR [14] 1292 notation in the "Name Constraints" extension, PKIX explicitly 1293 prohibits using CIDR notation for conveying identity information. In 1294 other words, the CIDR notation MUST NOT be used in the SubjectAltName 1295 extension. 1297 4.1.3.6.3 rfc822Name 1299 If the IKE ID type is USER_FQDN then the rfc822Name field MUST match 1300 its contents. Although this field is in the form of an Internet mail 1301 address, IKE implementations SHOULD NOT assume that this field 1302 contains a valid email address, unless this is known by way of some 1303 out-of-band mechanism. Such a mechanism is out of the scope of this 1304 document. 1306 4.1.3.7 IssuerAltName 1308 Certification Authority implementations SHOULD NOT assume that other 1309 implementations support the IssuerAltName extension, and especially 1310 should not assume that information contained in this extension will 1311 be displayed to end users. 1313 4.1.3.8 SubjectDirectoryAttributes 1315 The SubjectDirectoryAttributes extension is intended to convey 1316 identification attributes of the subject. IKE implementations MAY 1317 ignore this extension when it is marked non-critical, as PKIX 1318 mandates. 1320 4.1.3.9 BasicConstraints 1322 PKIX mandates that CA certificates contain this extension and that it 1323 be marked critical. IKE implementations SHOULD reject CA 1324 certificates that do not contain this extension. For backwards 1325 compatibility, implementations may accept such certificates if 1326 explicitly configured to do so, but the default for this setting MUST 1327 be to reject such certificates. 1329 4.1.3.10 NameConstraints 1331 Many IKE implementations do not support the NameConstraints 1332 extension. Since PKIX mandates that this extension be marked 1333 critical when present, Certification Authority implementations which 1334 are interested in maximal interoperability for IKE SHOULD NOT 1335 generate certificates which contain this extension. 1337 4.1.3.11 PolicyConstraints 1339 Many IKE implementations do not support the PolicyConstraints 1340 extension. Since PKIX mandates that this extension be marked 1341 critical when present, Certification Authority implementations which 1342 are interested in maximal interoperability for IKE SHOULD NOT 1343 generate certificates which contain this extension. 1345 4.1.3.12 ExtendedKeyUsage 1347 The CA SHOULD NOT include the ExtendedKeyUsage (EKU) extension in 1348 certificates for use with IKE. Note that there were three IPsec 1349 related object identifiers in EKU that were assigned in 1999. The 1350 semantics of these values were never clearly defined. The use of 1351 these three EKU values in IKE/IPsec is obsolete and explicitly 1352 deprecated by this specification. CAs SHOULD NOT issue certificates 1353 for use in IKE with them. (For historical reference only, those 1354 values were id-kp-ipsecEndSystem, id-kp-ipsecTunnel, and id-kp- 1355 ipsecUser.) 1357 PKIX [5] section 4.2.1.13 states, "If a CA includes extended key 1358 usages to satisfy such applications, but does not wish to restrict 1359 usages of the key, the CA can include the special keyPurposeID 1360 anyExtendedKeyUsage. If the anyExtendedKeyUsage keyPurposeID is 1361 present, the extension SHOULD NOT be critical." 1363 The CA SHOULD NOT mark the EKU extension in certificates for use with 1364 IKE and one or more other applications. If the CA administrator 1365 feels they must use an EKU for some other application, then such 1366 certificates MUST contain the keyPurposeID anyExtendedKeyUsage as 1367 well as the keyPurposeID values associated with the other 1368 applications for which the certificate is intended to be used. 1369 Recall however, EKU extensions in certificates meant for use in IKE 1370 are NOT RECOMMENDED. 1372 A summary of the logic flow for peer certificate validation regarding 1373 the EKU extension follows: 1375 o If told (by configuration) to ignore ExtendedKeyUsage (EKU), 1376 accept cert regardless of the presence or absence of the 1377 extension. 1378 o If no EKU extension, accept cert. 1379 o If EKU present AND anyExtendedKeyUsage is included, accept cert. 1380 o Otherwise, reject cert. 1382 4.1.3.13 CRLDistributionPoints 1384 Because this document deprecates the sending of CRLs in-band, the use 1385 of CRLDistributionPoints (CDP) becomes very important if CRLs are 1386 used for revocation checking (as opposed to say Online Certificate 1387 Status Protocol - OCSP [15]). The IPsec peer either needs to have a 1388 URL for a CRL written into its local configuration, or it needs to 1389 learn it from CDP. Therefore, Certification Authority 1390 implementations SHOULD issue certificates with a populated CDP. 1392 Failure to validate the CRLDistributionPoints/ 1393 IssuingDistributionPoint pair can result in CRL substitution where an 1394 entity knowingly substitutes a known good CRL from a different 1395 distribution point for the CRL which is supposed to be used which 1396 would show the entity as revoked. IKE implementations MUST support 1397 validating that the contents of CRLDistributionPoints match those of 1398 the IssuingDistributionPoint to prevent CRL substitution when the 1399 issuing CA is using them. At least one CA is known to default to 1400 this type of CRL use. See Section 4.2.2.5 for more information. 1402 CDPs SHOULD be "resolvable". Several non-compliant Certification 1403 Authority implementations are well known for including unresolvable 1404 CDPs like http://localhost/path_to_CRL and http:///path_to_CRL which 1405 are equivalent to failing to include the CDP extension in the 1406 certificate. 1408 See PKIX docs for CRLDistributionPoints intellectual property rights 1409 (IPR) information. Note that both the CRLDistributionPoints and 1410 IssuingDistributionPoint extensions are RECOMMENDED but not REQUIRED 1411 by PKIX, so there is no requirement to license any IPR. 1413 4.1.3.14 InhibitAnyPolicy 1415 Many IKE implementations do not support the InhibitAnyPolicy 1416 extension. Since PKIX mandates that this extension be marked 1417 critical when present, Certification Authority implementations which 1418 are interested in maximal interoperability for IKE SHOULD NOT 1419 generate certificates which contain this extension. 1421 4.1.3.15 FreshestCRL 1423 IKE implementations MUST NOT assume that the FreshestCRL extension 1424 will exist in peer certificates. Note that most IKE implementations 1425 do not support delta CRLs. 1427 4.1.3.16 AuthorityInfoAccess 1429 PKIX defines the AuthorityInfoAccess extension, which is used to 1430 indicate "how to access CA information and services for the issuer of 1431 the certificate in which the extension appears." Because this 1432 document deprecates the sending of CRLs in band, the use of 1433 AuthorityInfoAccess (AIA) becomes very important if OCSP [15] is to 1434 be used for revocation checking (as opposed to CRLs). The IPsec peer 1435 either needs to have a URI for the OCSP query written into its local 1436 configuration, or it needs to learn it from AIA. Therefore, 1437 implementations SHOULD support this extension, especially if OCSP 1438 will be used. 1440 4.1.3.17 SubjectInfoAccess 1442 PKIX defines the SubjectInfoAccess private certificate extension, 1443 which is used to indicate "how to access information and services for 1444 the subject of the certificate in which the extension appears." This 1445 extension has no known use in the context of IPsec. Conformant IKE 1446 implementations SHOULD ignore this extension when present. 1448 4.2 X.509 Certificate Revocation Lists 1450 When validating certificates, IKE implementations MUST make use of 1451 certificate revocation information, and SHOULD support such 1452 revocation information in the form of CRLs, unless non-CRL revocation 1453 information is known to be the only method for transmitting this 1454 information. Deployments that intend to use CRLs for revocation 1455 SHOULD populate the CRLDistributionPoints extension. Therefore 1456 Certification Authority implementations MUST support issuing 1457 certificates with this field populated according to administrator's 1458 needs. IKE implementations MAY provide a configuration option to 1459 disable use of certain types of revocation information, but that 1460 option MUST be off by default. Such an option is often valuable in 1461 lab testing environments. 1463 4.2.1 Multiple Sources of Certificate Revocation Information 1465 IKE implementations which support multiple sources of obtaining 1466 certificate revocation information MUST act conservatively when the 1467 information provided by these sources is inconsistent: when a 1468 certificate is reported as revoked by one trusted source, the 1469 certificate MUST be considered revoked. 1471 4.2.2 X.509 Certificate Revocation List Extensions 1473 4.2.2.1 AuthorityKeyIdentifier 1475 Certification Authority implementations SHOULD NOT assume that IKE 1476 implementations support the AuthorityKeyIdentifier extension, and 1477 thus SHOULD NOT generate certificate hierarchies which are overly 1478 complex to process in the absence of this extension, such as those 1479 that require possibly verifying a signature against a large number of 1480 similarly named CA certificates in order to find the CA certificate 1481 which contains the key that was used to generate the signature. 1483 4.2.2.2 IssuerAltName 1485 Certification Authority implementations SHOULD NOT assume that IKE 1486 implementations support the IssuerAltName extension, and especially 1487 should not assume that information contained in this extension will 1488 be displayed to end users. 1490 4.2.2.3 CRLNumber 1492 As stated in PKIX, all issuers conforming to PKIX MUST include this 1493 extension in all CRLs. 1495 4.2.2.4 DeltaCRLIndicator 1497 4.2.2.4.1 If Delta CRLs Are Unsupported 1499 IKE implementations that do not support delta CRLs MUST reject CRLs 1500 which contain the DeltaCRLIndicator (which MUST be marked critical 1501 according to PKIX) and MUST make use of a base CRL if it is 1502 available. Such implementations MUST ensure that a delta CRL does 1503 not "overwrite" a base CRL, for instance in the keying material 1504 database. 1506 4.2.2.4.2 Delta CRL Recommendations 1508 Since some IKE implementations that do not support delta CRLs may 1509 behave incorrectly or insecurely when presented with delta CRLs, 1510 administrators and deployers should consider whether issuing delta 1511 CRLs increases security before issuing such CRLs. And, if all the 1512 elements in the VPN and PKI systems do not adequately support Delta 1513 CRLs, then their use should be questioned. 1515 The authors are aware of several implementations which behave in an 1516 incorrect or insecure manner when presented with delta CRLs. See 1517 Appendix B for a description of the issue. Therefore, this 1518 specification RECOMMENDS NOT issuing delta CRLs at this time. On the 1519 other hand, failure to issue delta CRLs exposes a larger window of 1520 vulnerability. See the Security Considerations section of PKIX [5] 1521 for additional discussion. Implementors as well as administrators 1522 are encouraged to consider these issues. 1524 4.2.2.5 IssuingDistributionPoint 1526 A CA that is using CRLDistributionPoints may do so to provide many 1527 "small" CRLs, each only valid for a particular set of certificates 1528 issued by that CA. To associate a CRL with a certificate, the CA 1529 places the CRLDistributionPoints extension in the certificate, and 1530 places the IssuingDistributionPoint in the CRL. The 1531 distributionPointName field in the CRLDistributionPoints extension 1532 MUST be identical to the distributionPoint field in the 1533 IssuingDistributionPoint extension. At least one CA is known to 1534 default to this type of CRL use. See Section 4.1.3.13 for more 1535 information. 1537 4.2.2.6 FreshestCRL 1539 Given the recommendations against Certification Authority 1540 implementations generating delta CRLs, this specification RECOMMENDS 1541 that implementations do not populate CRLs with the FreshestCRL 1542 extension, which is used to obtain delta CRLs. 1544 5. Configuration Data Exchange Conventions 1546 Below we present a common format for exchanging configuration data. 1547 Implementations MUST support these formats, MUST support receiving 1548 arbitrary whitespace at the beginning and end of any line, MUST 1549 support receiving arbitrary line lengths although they SHOULD 1550 generate lines less than 76 characters, and MUST support receiving 1551 the following three line-termination disciplines: LF (US-ASCII 10), 1552 CR (US-ASCII 13), and CRLF. 1554 5.1 Certificates 1556 Certificates MUST be Base64 encoded and appear between the following 1557 delimiters: 1559 -----BEGIN CERTIFICATE----- 1560 -----END CERTIFICATE----- 1562 5.2 CRLs and ARLs 1564 CRLs and ARLs MUST be Base64 encoded and appear between the following 1565 delimiters: 1567 -----BEGIN CRL----- 1568 -----END CRL----- 1570 5.3 Public Keys 1572 IKE implementations MUST support two forms of public keys: 1573 certificates and so-called "raw" keys. Certificates should be 1574 transferred in the same form as above. A raw key is only the 1575 SubjectPublicKeyInfo portion of the certificate, and MUST be Base64 1576 encoded and appear between the following delimiters: 1578 -----BEGIN PUBLIC KEY----- 1579 -----END PUBLIC KEY----- 1581 5.4 PKCS#10 Certificate Signing Requests 1583 A PKCS#10 [9] Certificate Signing Request MUST be Base64 encoded and 1584 appear between the following delimiters: 1586 -----BEGIN CERTIFICATE REQUEST----- 1587 -----END CERTIFICATE REQUEST----- 1589 6. Security Considerations 1591 6.1 Certificate Request Payload 1593 The Contents of CERTREQ are not encrypted in IKE. In some 1594 environments this may leak private information. Administrators in 1595 some environments may wish to use the empty Certification Authority 1596 option to prevent such information from leaking, at the cost of 1597 performance. 1599 6.2 IKEv1 Main Mode 1601 Certificates may be included in any message, and therefore 1602 implementations may wish to respond with CERTs in a message that 1603 offers privacy protection, in Main Mode messages 5 and 6. 1604 Implementations may not wish to respond with CERTs in the second 1605 message, thereby violating the identity protection feature of Main 1606 Mode in IKEv1. 1608 7. Intellectual Property Rights 1610 No new intellectual property rights are introduced by this document. 1612 8. IANA Considerations 1614 There are no known numbers which IANA will need to manage. 1616 9. References 1618 9.1 Normative References 1620 [1] Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)", 1621 RFC 2409, November 1998. 1623 [2] Maughan, D., Schneider, M., and M. Schertler, "Internet Security 1624 Association and Key Management Protocol (ISAKMP)", RFC 2408, 1625 November 1998. 1627 [3] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", 1628 draft-ietf-ipsec-ikev2-15 (work in progress), August 2004. 1630 [4] Kent, S. and R. Atkinson, "Security Architecture for the 1631 Internet Protocol", RFC 2401, November 1998. 1633 [5] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet X.509 1634 Public Key Infrastructure Certificate and Certificate Revocation 1635 List (CRL) Profile", RFC 3280, April 2002. 1637 [6] Piper, D., "The Internet IP Security Domain of Interpretation 1638 for ISAKMP", RFC 2407, November 1998. 1640 [7] Bradner, S., "Key words for use in RFCs to Indicate Requirement 1641 Levels", BCP 14, RFC 2119, March 1997. 1643 [8] Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981. 1645 [9] Kaliski, B., "PKCS #10: Certification Request Syntax Version 1646 1.5", RFC 2314, March 1998. 1648 9.2 Informative References 1650 [10] Kent, S. and K. Seo, "Security Architecture for the Internet 1651 Protocol", draft-ietf-ipsec-rfc2401bis-06 (work in progress), 1652 March 2005. 1654 [11] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) 1655 Specification", RFC 1883, December 1995. 1657 [12] Eastlake, D., "Domain Name System Security Extensions", 1658 RFC 2535, March 1999. 1660 [13] Lynn, C., "X.509 Extensions for IP Addresses and AS 1661 Identifiers", draft-ietf-pkix-x509-ipaddr-as-extn-03 (work in 1662 progress), September 2003. 1664 [14] Fuller, V., Li, T., Yu, J., and K. Varadhan, "Classless Inter- 1665 Domain Routing (CIDR): an Address Assignment and Aggregation 1666 Strategy", RFC 1519, September 1993. 1668 [15] Myers, M., Ankney, R., Malpani, A., Galperin, S., and C. Adams, 1669 "X.509 Internet Public Key Infrastructure Online Certificate 1670 Status Protocol - OCSP", RFC 2560, June 1999. 1672 [16] Arsenault, A. and S. Turner, "Internet X.509 Public Key 1673 Infrastructure: Roadmap", draft-ietf-pkix-roadmap-09 (work in 1674 progress), July 2002. 1676 Author's Address 1678 Brian Korver 1679 Network Resonance, Inc. 1680 2483 E. Bayshore Rd. 1681 Palo Alto, CA 94303 1682 US 1684 Phone: +1 415 812 7700 1685 Email: briank@networkresonance.com 1687 Appendix A. Change History 1689 July 2005 (-05) 1691 * 3.1 - added "See 2401bis [10], section 4.4.3.2 for more 1692 details." to resolve issue #561. 1694 * 3.1.10 - added text pointing to PAD in 2401bis [10] to 1695 discussion of binding identity to policy. 1697 December 2004 (-04) 1699 * Added Paul Hoffman's text from issue #708 1700 * Added text explaining that it's possible for a recipient to 1701 receive CERT payloads containing certs that the recipient 1702 considers a trust anchor (15 Nov 2004 pki4ipsec email from 1703 Peter Williams) 1704 * Replaced text in 4.1.3 with Kent's text (issue #655) (22 Nov 1705 2004 pki4ipsec email from Stephen Kent, Paul Hoffman) 1707 September 2004 (-03) 1709 * Minor editorial changes in abstract and introduction clarifing 1710 when something is from IPsec, IKE, etc 1711 * Minor editorial changes throughout 1712 * Fixed "Certification Authority" instead of "Certificate 1713 Authority" 1714 * Cleaned up initiator/responder when really referred to sender/ 1715 recipient 1716 * Fixed inconsistancy in text by making sure that all text on the 1717 topic of sending CERTREQs follow Gregory Lebovitz's proposal 1718 for CERT payloads: "should deal with all the CRL, Intermediat 1719 Certs, Trust Anchors, etc OOB of IKE; MUST be able to send and 1720 receive EE cert payload; only real exception is Intermediate 1721 Cets which MAY be sent and SHOULD be able to be receivable (but 1722 in reality there are very few hierarchies in operation, so 1723 really it's a corner case); SHOULD NOT send the other stuff 1724 (CRL, Trust Anchors, etc) in cert payloads in IKE; SHOULD be 1725 able to accept the other stuff if by chance it gets sent, 1726 though we hope they don't get sent" 1727 * 3.1 - removed text suggesting that it would be reasonable to 1728 terminate IKEv2 processing if the initiator were to receive a 1729 responder-generated IDr 1730 * 3.1.1 - noted that certificates may contain multiple IP 1731 addresses 1732 * 3.1.9 - removed (temporarily?) confusing text stating that 1733 overlapping policies was prohibited, text which was 1734 inconsistent with text right above it 1735 * 3.2.7.2 - SHOULD changed to MUST terminate if peer's 1736 certificate chain violates local policy 1737 * 3.3 - removed text implying that pausing in the middle of an 1738 IKE exchange in order to obtain revocation status information 1739 via http or OCSP would reduce latency in IKE 1741 * 4.2 - allow deployments that don't wish to populate CDP (for 1742 instance if a source of revocation information is configured 1743 via some other means) to skip populating CDP, making consistent 1744 with 4.1.3.13 and the issues IPR spelled out in PKIX 1745 * Somehow a CRL out-of-band configuration format had been 1746 omitted. 1747 * #555: Kent-1.0 Introduction - document now references IKEv2 1748 * #559: Kent-Profile Document 3.1.0 - use sender/recipient 1749 instead of agent 1750 * #564: Kent-Profile Document 3.1.1 - specified that support for 1751 ID_IPV4_ADDR and/or ID_IPV6_ADDR are contingent on device 1752 support for IPv4 and/or IPv6 1753 * #568: Kent-Profile document 3.1.4 - specified that there wasn't 1754 a standard and besides no one has implemented it 1755 * #571: Kent-Profile document 3.1.8 - tried to be even more 1756 clearer than was asked for by spelling things out in detail 1757 * #572: Kent-Profile document 3.1.8 Formerly issue #18 - now 1758 specifies that it's only a local matter if that information is 1759 not coordinated with other administrators 1760 * #573: Kent-Profile document 3.2.3/Myers - revocation 1761 information no longer exchanged in-band, plus Mike Myers has 1762 submitted an OCSP w/IKE draft, which is references by this 1763 document. 1764 * #578 Kent-Profile document 4.0.0 - went through entire PKIX 1765 profile section and prefaced "implementation" with "IKE" or 1766 "Certification Authority" wherever it was sure to be one or the 1767 other 1768 * #581: Kent-Profile document 4.1.3.9 - replaced description with 1769 text from RFC 2459 1770 * #584: Maillist-Lebovitz PKI Life Cycle-Revocation - fixed 1771 * #586: Maillist-Allison Empty CertReq - there is now lots of 1772 text dealing with when empty certreqs are permitted 1773 * 3.2.7.1 - CERTREQ only mandatory if in-band exchange of keymat 1774 is desired (28 Jul 2004 pki4ipsec email from jknowles@ 1775 SonicWALL.com) 1776 * 3.3.6 - clarified that "non-compliant" means not sending a 1777 CERTREQ (28 Jul 2004 pki4ipsec email from jknowles@ 1778 SonicWALL.com) 1779 * 3.2.7.1 - fixed contradition: mandatory to respond to CERTREQ 1780 UNLESS configured not to (28 Jul 2004 pki4ipsec email from 1781 jknowles@SonicWALL.com) 1782 * 3.2.9.2 and 3.2.9.3 - CERTREQ contains an issuer name only for 1783 IKEv2 (19 Sep 2004 email from Charlie Kaufman) 1784 * Answered 'Section 3.1.9 para 2: "The initiator MUST know by 1785 policy..." is a difficult to interpret requirement. It could 1786 mean that it must be possible to configure in policy which ID 1787 is to be sent. Did you mean "the initiator must decide...", 1788 where the decision might be wired into a particular 1789 implementation?' by changing it to be merely descriptive, and 1790 to refer to policy configuration (19 Sep 2004 email from 1791 Charlie Kaufman) 1792 * IPSEC -> IPsec (19 Sep 2004 email from Charlie Kaufman) 1793 * 3.1.1 para 1: "MUST be stored" changed to "MUST be encoded" (19 1794 Sep 2004 email from Charlie Kaufman) 1795 * 3.1.5 para 2 - made it clear that empty SubjectNames are 1796 permitted by PKIX in certificates, but this document doesn't 1797 permit them in ID (19 Sep 2004 email from Charlie Kaufman) 1798 * 3.2.7.1 - clarified by specifying that it's a trust anchor 1799 that's being chosen, not end-entity certificate (19 Sep 2004 1800 email from Charlie Kaufman) 1801 * 3.3.9.5 - fixed confusing last paragraph (19 Sep 2004 email 1802 from Charlie Kaufman) 1803 * 3.3.10.3 - made it more clear that this section is really 1804 talking about duplicate certificate payloads (19 Sep 2004 email 1805 from Charlie Kaufman) 1806 * 4.1.2.2 para 2 and 3 - moved to 3.1.x section where is belongs 1807 (19 Sep 2004 email from Charlie Kaufman) 1808 * 4.1.3.5 - the last sentence of 4.1.3.4 copied here (19 Sep 2004 1809 email from Charlie Kaufman) 1810 * 4.2.2.4.2 - SHOULD -> should (19 Sep 2004 email from Charlie 1811 Kaufman) 1812 * 3.2.5 and 3.3.4 - added description of URL scheme support (16 1813 Aug 2004 pki4ipsec email from Tero Kivinen) 1814 * Removed 6.1 and 6.3 because they were either incorrect or 1815 didn't add any new security considerations above and beyond the 1816 IKE documents. 1817 August 2004 (-02) (Edited by Gregory Lebovitz, with XML formatting 1818 and cross-referencing by Paul Knight) 1820 * 3.1.1 the text between the **s was added to paragraph, per the 1821 question that arose in IETF60 WG session: Implementations MUST 1822 be capable of verifying that the address contained in the ID is 1823 the same as the peer source address **contained in the outer 1824 most IP header**. 1825 * 3.2.7 - added HTTP_CERT_LOOKUP_SUPPORTED to this section and 1826 described its use - #38 1827 * 3.3 - changed back sending of intermediate CA certificates from 1828 SHOULD NOT to MAY (for backward compatibility). Added text to 1829 explain further why we want to stay away from actually doing it 1830 though. 1831 * 3.3.8 - changed text per Knowles/Korver 2004.07.28. 1832 * 3.3.9.5 - Change discard of Irrelevant Certificates from may to 1833 SHOULD - #23(Kent 2004.04.26) 1834 * 4.1.3.2 KU - re-worked to reflect discussion on list and in 1835 IETF60 - #36 1837 * 4.1.3.12 EKU - re-worked to reflect discussion on list and in 1838 IETF60 - #36 1839 * [IKEv2] update the reference to the -14 draft of May 29, 2004 1841 July 2004 (-01) (Edited by Gregory Lebovitz) 1843 * Changed ISAKMP references in Abstract and Intro to IKE. 1844 * Editorial changes to make the text conform with the summary 1845 table in 3.1, especially in the text following the table in 1846 3.1. Particular note should be paid to changes in section 1847 3.5.1. 1848 * Sect 3.1.1 - editorial changes to aid in clarification. Added 1849 text on when deployers might consider using IP addr, but 1850 strongly encouraged not to. 1851 * Sect 3.1.8 removed IP address from list of practically used ID 1852 types. 1853 * 3.1.9 overhauled (per Kivinen, July 18) 1854 * 3.2 - added IKEv2's Hash and URL of x.509 to list of those 1855 profiled and gave it its own section, now 3.2.5 1856 * added note in CRL/ARL section about revocation occurring OOB of 1857 IKE 1858 * deleted ARL as its own section and collapsed it into Revocation 1859 Lists (CRL and ARL) for consciseness. Renumbered accordingly. 1860 * Sect 3.2.7.2 - Changed from MUST not send empty certreqs to 1861 SHOULD send CERTREQs which contain CA fields with direction on 1862 how, but MAY send empty CERTREQs in certain case. Use case 1863 added, and specifics of both initiator and responder behavior 1864 listed. 1865 * APPENDIX C added to fill out the explanation (mostly discussion 1866 from list). 1867 * 3.3 - clarified that sending CRLs and chaining certs is 1868 deprecated. 1869 * added IKEv2's Hash and URL of x.509 to list of those profiled 1870 and gave it its own section. Condensed ARL into CRL and 1871 renumbered accordingly. 1872 * duplicate section was removed, renumbered accordingly 1873 * 3.3.10.2 - title changed. sending chaining becomes SHOULD NOT. 1874 * 4.1.2 added text to explicity call out support for CN, C, O, OU 1875 * collapsed 4.1.2.3 into 4.1.2.2 and renumbered accordingly. 1876 * Collapsed 4.1.3.2 into 4.1.3.1 and renumbered accordingly 1877 * Edited 4.1.3.2 Key Usage and 4.1.3.12 ExtKey Usage according to 1878 Hoffman, July18 1879 * 4.1.3.3 if receive cert w/ PKUP, ignore it. 1880 * 4.1.3.13 - CDP changed text to represent SHOULD issue, and how 1881 important CDP becomes when we do not send CRLs in-band. Added 1882 SHOULD for CDPs actually being resolvable (reilly email). 1884 * Reordered 6.4 for better clarity. 1885 * Added Rescorla to Acknowledgements section, as he is no longer 1886 listed as an editor, since -00. 1888 May 2004 (renamed draft-ietf-pki4ipsec-ikecert-profile-00.txt) 1889 (edited by Brian Korver) 1891 * Made it clearer that the format of the ID_IPV4_ADDR payload 1892 comes from RFC791 and is nothing new. (Tero Kivinen Feb 29) 1893 * Permit implementations to skip verifying that the peer source 1894 address matches the contents of ID_IPV{4,6}_ADDR. (Tero 1895 Kivinen Feb 29, Gregory Lebovitz Feb 29) 1896 * Removed paragraph suggesting that implementations favor 1897 unauthenticated peer source addresses over an unauthenticated 1898 ID for initial policy lookup. (Tero Kivinen Feb 29, Gregory 1899 Lebovitz Feb 29) 1900 * Removed some text implying RSA encryption mode was in scope. 1901 (Tero Kivinen Feb 29) 1902 * Relaxed deprecation of PKCS#7 CERT payloads. (Tero Kivinen Feb 1903 29) 1904 * Made it clearer that out-of-scope local heuristics should be 1905 used for picking an EE cert to use when generating CERTREQ, not 1906 when receiving CERTREQ. (Tero Kivinen Feb 29) 1907 * Made it clearer that CERT processing can be skipped when the 1908 contents of a CERT are already known. (Tero Kivinen Feb 29) 1909 * Implementations SHOULD generate BASE64 lines less than 76 1910 characters. (Tero Kivinen Feb 29) 1911 * Added "Except where specifically stated in this document, 1912 implementations MUST conform to the requirements of PKIX" 1913 (Steve Hanna Oct 7, 2003) 1914 * RECOMMENDS against populating the ID payload with IP addresses 1915 due to interoperability issues such as problem with NAT 1916 traversal. (Gregory Lebovitz May 14) 1917 * Changed "as revoked by one source" to "as revoked by one 1918 trusted source". (Michael Myers, May 15) 1919 * Specifying Certificate Authorities section needed to be 1920 regularized with Gregory Lebovitz's CERT proposal from -04. 1921 (Tylor Allison, May 15) 1922 * Added text specifying how recipients SHOULD NOT be expected to 1923 iterate over multiple end-entity certs. (Tylor Allison, May 1924 15) 1925 * Modified text to refer to IKEv2 as well as IKEv1/ISAKMP where 1926 relevant. 1927 * IKEv2: Explained that IDr sent by responder doesn't have to 1928 match the [IDr] sent initiator in second exchange. 1930 * IKEv2: Noted that "The identity ... does not necessarily have 1931 to match anything in the CERT payload" (S3.5) is not 1932 contradicted by SHOULD in this document. 1933 * IKEv2: Noted that ID_USER_FQDN renamed to ID_RFC822_ADDR, and 1934 ID_USER_FQDN would be used exclusively in this document. 1935 * IKEv2: Declared that 3 new CERTREQ and CERT types are not 1936 profiled in this document (well, at least not yet, pending WG 1937 discussion of what to do -- note that they are only SHOULDs in 1938 IKEv2). 1939 * IKEv2: Noted that CERTREQ payload changed from DN to SHA-1 of 1940 SubjectPublicKeyInfo. 1941 * IKEv2: Noted new requirement that specifies that the first 1942 certificate sent MUST be the EE cert (section 3.6). 1944 February 2004 (-04) 1946 * Minor editorial changes to clean up language 1947 * Deprecate in-band exchange of CRLs 1948 * Incorporated Gregory Lebovitz's proposal for CERT payloads: 1949 "should deal with all the CRL, Intermediat Certs, Trust 1950 Anchors, etc OOB of IKE; MUST be able to send and receive EE 1951 cert payload; only real exception is Intermediate Cets which 1952 MAY be sent and SHOULD be able to be receivable (but in reality 1953 there are very few hierarchies in operation, so really it's a 1954 corner case); SHOULD NOT send the other stuff (CRL, Trust 1955 Anchors, etc) in cert payloads in IKE; SHOULD be able to accept 1956 the other stuff if by chance it gets sent, though we hope they 1957 don't get sent" 1958 * Incorporated comments contained in Oct 7, 2003 email from 1959 steve.hanna@sun.com to ipsec@lists.tislabs.com 1960 * Moved text from "Profile of ISAKMP" Background section to each 1961 payload section (removing duplication of these sections) 1962 * Removed "Certificate-Related Playloads in ISAKMP" section since 1963 it was not specific to IKE. 1964 * Incorporated Gregory Lebovitz's table in the "Identification 1965 Payload" section 1966 * Moved text from "binding identity to policy" sections to each 1967 payload section 1968 * Moved text from "IKE" section into now-combined "IKE/ISAKMP" 1969 section 1970 * ID_USER_FQDN and ID_FQDN promoted to MUST from MAY 1971 * Promoted sending ID_DER_ASN1_DN to MAY from SHOULD NOT, and 1972 receiving from MUST from MAY 1973 * Demoted ID_DER_ASN1_GN to MUST NOT 1974 * Demoted populating SubjectName in place of populating the 1975 dNSName from SHOULD NOT to MUST NOT and removed the text 1976 regarding domainComponent 1978 * Revocation information checking MAY now be disabled, although 1979 not by default 1980 * Aggressive Mode removed from this profile 1982 June 2003 (-03) 1984 * Minor editorial changes to clean up language 1985 * Minor additional clarifying text 1986 * Removed hyphenation 1987 * Added requirement that implementations support configuration 1988 data exchange having arbitrary line lengths 1990 February 2003 (-02) 1992 * Word choice: move from use of "root" to "trust anchor", in 1993 accordance with PKIX 1994 * SBGP note and reference for placing address subnet and range 1995 information into certificates 1996 * Clarification of text regarding placing names of hosts into the 1997 Name commonName attribute of SubjectName 1998 * Added table to clarify text regarding processing of the 1999 certificate extension criticality bit 2000 * Added text underscoring processing requirements for 2001 CRLDistributionPoints and IssuingDistributionPoint 2003 October 2002, Reorganization (-01) 2005 June 2002, Initial Draft (-00) 2007 Appendix B. The Possible Dangers of Delta CRLs 2009 The problem is that the CRL processing algorithm is sometimes written 2010 incorrectly with the assumption that all CRLs are base CRLs and it is 2011 assumed that CRLs will pass content validity tests. Specifically, 2012 such implementations fail to check the certificate against all 2013 possible CRLs: if the first CRL that is obtained from the keying 2014 material database fails to decode, no further revocation checks are 2015 performed for the relevant certificate. This problem is compounded 2016 by the fact that implementations which do not understand delta CRLs 2017 may fail to decode such CRLs due to the critical DeltaCRLIndicator 2018 extension. The algorithm that is implemented in this case is 2019 approximately: 2021 o fetch newest CRL 2022 o check validity of CRL signature 2023 o if CRL signature is valid then 2024 o if CRL does not contain unrecognized critical extensions 2025 o and certificate is on CRL then 2026 o set certificate status to revoked 2028 The authors note that a number of PKI toolkits do not even provide a 2029 method for obtaining anything but the newest CRL, which in the 2030 presence of delta CRLs may in fact be a delta CRL, not a base CRL. 2032 Note that the above algorithm is dangerous in many ways. See PKIX 2033 [5] for the correct algorithm. 2035 Appendix C. More on Empty CERTREQs 2037 Sending empty certificate requests is commonly used in 2038 implementations, and in the IPsec interop meetings, vendors have 2039 generally agreed that it means that send all/any end-entity 2040 certificates you have (if multiple end-entity certificates are sent, 2041 they must have same public key, as otherwise the other end does not 2042 know which key was used). For 99% of cases the client have exactly 2043 one certificate and public key, so it really doesn't matter, but the 2044 server might have multiple, thus it simply needs to say to the 2045 client, use any certificate you have. If we are talking about 2046 corporate vpns etc, even if the client have multiple certificates or 2047 keys, all of them would be usable when authenticating to the server, 2048 so client can simply pick one. 2050 If there is some real difference on which cert to use (like ones 2051 giving different permissions), then the client must be configured 2052 anyways, or it might even ask the user which one to use (the user is 2053 the only one who knows whether he needs admin privileges, thus needs 2054 to use admin cert, or is the normal email privileges ok, thus using 2055 email only cert). 2057 99% of the cases the client have exactly one certificate, so it will 2058 send it. In 90% of the rest of the cases, any of the certificates is 2059 ok, as they are simply different certificates from same CA, or 2060 different CAs for the same corporate VPN, thus any of them is ok. 2062 Sending empty certificate requests has been agreed there to mean 2063 "give me your cert; any cert". 2065 Justification: 2067 o Responder first does all it can to send a certreq with a CA, check 2068 for IP match in SPD, have a default set of CAs to use in ambiguous 2069 cases, etc. 2070 o sending empty certreq's is fairly common in implementations today, 2071 and is generally accepted to mean "send me a cert, any cert that 2072 works for you" 2073 o saves responder sending potentially 100's of certs, the 2074 fragmentation problems that follow, etc. 2075 o in +90% of use cases, Initiators have exactly 1 cert 2076 o in +90% of the remaining use cases, the multiple certs it has are 2077 issued by the same CA 2078 o in the remaining use case(s) -- if not all the others above -- the 2079 Initiator will be configured explicitly with which cert to send, 2080 so responding to an empty certreq is easy. 2082 The following example shows why initiators need to have sufficient 2083 policy definition to know which certificate to use for a given 2084 connection it initiates. 2086 EXAMPLE: Your client (initiator) is configured with VPN policies for 2087 gateways A and B (representing perhaps corporate partners). 2089 The policies for the two gateways look something like: 2091 Acme Company policy (gateway A) 2092 Engineering can access 10.1.1.0 2093 Trusted CA: CA-A, Trusted Users: OU=Engineering 2094 Partners can access 20.1.1.0 2095 Trusted CA: CA-B, Trusted Users: OU=AcmePartners 2097 Bizco Company policy (gateway B) 2098 sales can access 30.1.1.0 2099 Trusted CA: CA-C, Trusted Users: OU=Sales 2100 Partners can access 40.1.1.0 2101 Trusted CA: CA-B, Trusted Users: OU=BizcoPartners 2103 You are an employee of Acme and you are issued the following 2104 certificates: 2106 o From CA-A: CN=JoeUser,OU=Engineering 2107 o From CA-B: CN=JoePartner,OU=BizcoPartners 2109 The client MUST be configured locally to know which CA to use when 2110 connecting to either gateway. If your client is not configured to 2111 know the local credential to use for the remote gateway, this 2112 scenario will not work either. If you attempt to connect to Bizco, 2113 everything will work... as you are presented with responding with a 2114 certificate signed by CA-B or CA-C... as you only have a certificate 2115 from CA-B you are OK. If you attempt to connect to Acme, you have an 2116 issue because you are presented with an ambiguous policy selection. 2117 As the initiator, you will be presented with certificate requests 2118 from both CA A and CA B. You have certificates issued by both CAs, 2119 but only one of the certificates will be usable. How does the client 2120 know which certificate it should present? It must have sufficiently 2121 clear local policy specifying which one credential to present for the 2122 connection it initiates. 2124 Appendix D. Acknowledgements 2126 The authors would like to acknowledge the expired draft-ietf-ipsec- 2127 pki-req-05.txt for providing valuable materials for this document. 2129 The authors would like to especially thank Eric Rescorla, one of its 2130 original authors, in addition to Greg Carter, Steve Hanna, Russ 2131 Housley, Charlie Kaufman, Tero Kivinen, and Gregory Lebovitz for 2132 their valuable comments, some of which have been incorporated 2133 verbatim into this document. 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