idnits 2.17.00 (12 Aug 2021) /tmp/idnits21791/draft-ietf-pki4ipsec-ikecert-profile-06.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 2170. -- Found old boilerplate from RFC 3979, Section 5, paragraph 1 on line 2147. -- Found old boilerplate from RFC 3979, Section 5, paragraph 2 on line 2154. -- Found old boilerplate from RFC 3979, Section 5, paragraph 3 on line 2160. ** 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 25 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 1185 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. -- 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 (October 26, 2005) is 6050 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 1830 -- Looks like a reference, but probably isn't: 'IDr' on line 1920 == Unused Reference: '16' is defined on line 1671, 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: April 25, 2006 October 26, 2005 6 The Internet IP Security PKI Profile of IKEv1/ISAKMP, IKEv2, and PKIX 7 draft-ietf-pki4ipsec-ikecert-profile-06 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 April 25, 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 . . . . . . . . . . . . . . . 14 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 . . . . . . . . . . . 16 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 . . . . . . . . . . . . . . . . . . . 20 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 . . . . . . . . . . . 22 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 . . . . . . . . . . . 23 89 3.3.11. Robustness . . . . . . . . . . . . . . . . . . . . . . 23 90 3.3.12. Optimizations . . . . . . . . . . . . . . . . . . . . 24 91 4. Profile of PKIX . . . . . . . . . . . . . . . . . . . . . . . 25 92 4.1. X.509 Certificates . . . . . . . . . . . . . . . . . . . . 25 93 4.1.1. Versions . . . . . . . . . . . . . . . . . . . . . . . 25 94 4.1.2. SubjectName . . . . . . . . . . . . . . . . . . . . . 25 95 4.1.3. X.509 Certificate Extensions . . . . . . . . . . . . . 26 96 4.2. X.509 Certificate Revocation Lists . . . . . . . . . . . . 32 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 . . . . . . . . . . . 34 101 5.1. Certificates . . . . . . . . . . . . . . . . . . . . . . . 34 102 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 . . . . . . . . . . . . . . . . . . . 35 106 6.1. Certificate Request Payload . . . . . . . . . . . . . . . 35 107 6.2. IKEv1 Main Mode . . . . . . . . . . . . . . . . . . . . . 35 108 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 Appendix A. Change History . . . . . . . . . . . . . . . . . . . 36 114 Appendix B. The Possible Dangers of Delta CRLs . . . . . . . . . 43 115 Appendix C. More on Empty CERTREQs . . . . . . . . . . . . . . . 44 116 Appendix D. Acknowledgements . . . . . . . . . . . . . . . . . . 46 117 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 47 118 Intellectual Property and Copyright Statements . . . . . . . . . . 48 120 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. 217 Failure to do so may result in the use of an inappropriate or 218 insecure policy. The following sections describe the methods for 219 performing this binding. 221 The following table summarizes the binding of the Identification 222 Payload to the contents of end-entity certificates and of identity 223 information to policy. Each ID type is covered more thoroughly in 224 the following sections. 226 ID type | Support | Correspond | Cert | SPD lookup 227 | for send | PKIX Attrib | matching | rules 228 ------------------------------------------------------------------- 229 | | | | 230 IP*_ADDR | MUST [1] | SubjAltName | MUST [2] | [3], [4] 231 | | iPAddress | | 232 | | | | 233 FQDN | MUST [1] | SubjAltName | MUST [2] | [3], [4] 234 | | dNSName | | 235 | | | | 236 USER_FQDN| MUST [1] | SubjAltName | MUST [2] | [3], [4] 237 | | rfc822Name | | 238 | | | | 239 DN | MUST [1] | Entire | MUST [2] | MUST support lookup 240 | | Subject, | | on any combination 241 | | bitwise | | of C, CN, O, or OU 242 | | compare | | 243 | | | | 244 IP range | MUST NOT | n/a | n/a | n/a 245 | | | | 246 | | | | 247 KEY_ID | MUST NOT | n/a | n/a | n/a 248 | | | | 250 [1] = Implementation MUST have the configuration option to send this 251 ID type in the ID payload. Whether or not the ID type is used is a 252 matter of local configuration. 254 [2] = The ID in the ID payload MUST match the contents of the 255 corresponding field (listed) in the certificate exactly, with no 256 other lookup. The matched ID MAY be used for SPD lookup, but is not 257 required to be used for this. See 2401bis [10], section 4.4.3.2 for 258 more details. 260 [3] = At a minimum, Implementation MUST be capable of being 261 configured to perform exact matching of the ID payload contents to an 262 entry in the local SPD. 264 [4] = In addition, the implementation MAY also be configurable to 265 perform substring or wildcard matches of ID payload contents to 266 entries in the local SPD. (More on this in Section 3.1.5). 268 When sending an IPV4_ADDR, IPV6_ADDR, FQDN, or USER_FQDN, 269 implementations MUST be able to be configured to send the same string 270 as appears in the corresponding SubjectAltName attribute. This 271 document RECOMMENDS that deployers use this configuration option. 272 All these ID types are treated the same: as strings that can be 273 compared easily and quickly to a corresponding string in an explicit 274 attribute in the certificate. Of these types, FQDN and USER_FQDN are 275 RECOMMENDED over IP addresses (see discussion in Section 3.1.1). 277 When sending a DN as ID, implementations MUST send the entire DN in 278 ID. Also, implementations MUST support at least the C, CN, O, and OU 279 attributes for SPD matching. See Section 3.1.5 for more details 280 about DN, including SPD matching. 282 Recipients MUST be able to perform SPD matching on the exact contents 283 of the ID, and this SHOULD be the default setting. In addition, 284 implementations MAY use substrings or wildcards in local policy 285 configuration to do the SPD matching against the ID contents. In 286 other words, implementations MUST be able to do exact matches of ID 287 to SPD, but MAY also be configurable to do substring or wildcard 288 matches of ID to SPD. 290 IKEv2 adds an optional IDr payload in the second exchange that the 291 initiator may send to the responder in order to specify which of the 292 responder's multiple identities should be used. The responder MAY 293 choose to send an IDr in the 3rd exchange that differs in type or 294 content from the initiator-generated IDr. The initiator MUST be able 295 to receive a responder-generated IDr that is a different type from 296 the one the initiator generated. 298 3.1.1. ID_IPV4_ADDR and ID_IPV6_ADDR 300 Implementations MUST support either the ID_IPV4_ADDR or ID_IPV6_ADDR 301 ID type, depending on whether the implementation supports IPv4, IPv6 302 or both. These addresses MUST be encoded in "network byte order," as 303 specified in IP [8]: The least significant bit (LSB) of each octet is 304 the LSB of the corresponding byte in the network address. For the 305 ID_IPV4_ADDR type, the payload MUST contain exactly four octets [8]. 306 For the ID_IPV6_ADDR type, the payload MUST contain exactly sixteen 307 octets [11]. 309 Implementations SHOULD NOT populate ID payload with IP addresses due 310 to interoperability issues such as problems with NAT traversal, and 311 problems with IP verification behavior. 313 Deployments may only want to consider using the IP address as ID if 314 the following are true: 316 o the peer's IP address is static, not dynamically changing 317 o the peer is NOT behind a NAT'ing device 318 o the administrator intends the implementation to verify that the 319 peer source address matches the IP address in the ID received, and 320 that in the iPAddress field in the peer certificate's 321 SubjectAltName extension. 323 Implementations MUST be capable of verifying that the IP address 324 presented in ID matches via bitwise comparison the IP address present 325 in the certificate's iPAddress field of the SubjectAltName extension. 326 Implementations MUST perform this verification by default. When 327 comparing the contents of ID with the iPAddress field in the 328 SubjectAltName extension for equality, binary comparison MUST be 329 performed. Note that certificates may contain multiple address 330 identity types in which case at least one must match the source IP. 331 If the default is enabled, then a mismatch between the two addresses 332 MUST be treated as an error and security association setup MUST be 333 aborted. This event SHOULD be auditable. Implementations MAY 334 provide a configuration option to (i.e. local policy configuration 335 can enable) skip that verification step, but that option MUST be off 336 by default. We include the "option-to-skip-validation" in order to 337 permit better interoperability, as today implementations vary greatly 338 in how they behave on this topic. 340 In addition, implementations MUST be capable of verifying that the 341 address contained in the ID is the same as the peer source address, 342 contained in the outer most IP header. If ID is one of the IP 343 address types, then implementations MUST perform this verification by 344 default. If this default is enabled, then a mismatch MUST be treated 345 as an error and security association setup MUST be aborted. This 346 event SHOULD be auditable. Implementations MAY provide a 347 configuration option to (i.e. local policy configuration can enable) 348 skip that verification step, but that option MUST be off by default. 349 We include the "option-to-skip-validation" in order to permit better 350 interoperability, as today implementations vary greatly in how they 351 behave on the topic of verification of source IP. 353 If the default for both the verifications above are enabled, then, by 354 transitive property, the implementation will also be verifying that 355 the peer source IP address matches via a bitwise comparison the 356 contents of the iPAddress field in the SubjectAltName extension in 357 the certificate. In addition, implementations MAY allow 358 administrators to configure a local policy that explicitly requires 359 that the peer source IP address match via a bitwise comparison the 360 contents of the iPAddress field in the SubjectAltName extension in 361 the certificate. Implementations SHOULD allow administrators to 362 configure a local policy that skips this validation check. 364 Implementations MAY support substring, wildcard, or regular 365 expression matching of the contents of ID to lookup policy in the 366 SPD, and such would be a matter of local security policy 367 configuration. 369 Implementations MAY use the IP address found in the header of packets 370 received from the peer to lookup the policy, but such implementations 371 MUST still perform verification of the ID payload. Although packet 372 IP addresses are inherently untrustworthy and must therefore be 373 independently verified, it is often useful to use the apparent IP 374 address of the peer to locate a general class of policies that will 375 be used until the mandatory identity-based policy lookup can be 376 performed. 378 For instance, if the IP address of the peer is unrecognized, a VPN 379 gateway device might load a general "road warrior" policy that 380 specifies a particular CA that is trusted to issue certificates which 381 contain a valid rfc822Name which can be used by that implementation 382 to perform authorization based on access control lists (ACLs) after 383 the peer's certificate has been validated. The rfc822Name can then 384 be used to determine the policy that provides specific authorization 385 to access resources (such as IP addresses, ports, and so forth). 387 As another example, if the IP address of the peer is recognized to be 388 a known peer VPN endpoint, policy may be determined using that 389 address, but until the identity (address) is validated by validating 390 the peer certificate, the policy MUST NOT be used to authorize any 391 IPsec traffic. 393 3.1.2. ID_FQDN 395 Implementations MUST support the ID_FQDN ID type, generally to 396 support host-based access control lists for hosts without fixed IP 397 addresses. However, implementations SHOULD NOT use the DNS to map 398 the FQDN to IP addresses for input into any policy decisions, unless 399 that mapping is known to be secure, for example if DNSSEC [12] were 400 employed. 402 If ID contains an ID_FQDN, implementations MUST be capable of 403 verifying that the identity contained in the ID payload matches 404 identity information contained in the peer end-entity certificate, in 405 the dNSName field in the SubjectAltName extension. Implementations 406 MUST perform this verification by default. When comparing the 407 contents of ID with the dNSName field in the SubjectAltName extension 408 for equality, caseless string comparison MUST be performed. 409 Substring, wildcard, or regular expression matching MUST NOT be 410 performed for this comparison. If this default is enabled, then a 411 mismatch MUST be treated as an error and security association setup 412 MUST be aborted. This event SHOULD be auditable. Implementations 413 MAY provide a configuration option to (i.e. local policy 414 configuration can enable) skip that verification step, but that 415 option MUST be off by default. We include the "option-to-skip- 416 validation" in order to permit better interoperability, as today 417 implementations vary greatly in how they behave on this topic. 419 Implementations MAY support substring, wildcard, or regular 420 expression matching of the contents of ID to lookup policy in the 421 SPD, and such would be a matter of local security policy 422 configuration. 424 3.1.3. ID_USER_FQDN 426 Implementations MUST support the ID_USER_FQDN ID type, generally to 427 support user-based access control lists for users without fixed IP 428 addresses. However, implementations SHOULD NOT use the DNS to map 429 the FQDN portion to IP addresses for input into any policy decisions, 430 unless that mapping is known to be secure, for example if DNSSEC [12] 431 were employed. 433 Implementations MUST be capable of verifying that the identity 434 contained in the ID payload matches identity information contained in 435 the peer end-entity certificate, in the rfc822Name field in the 436 SubjectAltName extension. Implementations MUST perform this 437 verification by default. When comparing the contents of ID with the 438 rfc822Name field in the SubjectAltName extension for equality, 439 caseless string comparison MUST be performed. Substring, wildcard, 440 or regular expression matching MUST NOT be performed for this 441 comparison. If this default is enabled, then a mismatch MUST be 442 treated as an error and security association setup MUST be aborted. 443 This event SHOULD be auditable. Implementations MAY provide a 444 configuration option to (i.e. local policy configuration can enable) 445 skip that verification step, but that option MUST be off by default. 446 We include the "option-to-skip-validation" in order to permit better 447 interoperability, as today implementations vary greatly in how they 448 behave on this topic. 450 Implementations MAY support substring, wildcard, or regular 451 expression matching of the contents of ID to lookup policy in the 452 SPD, and such would be a matter of local security policy 453 configuration. 455 3.1.4. ID_IPV4_ADDR_SUBNET, ID_IPV6_ADDR_SUBNET, ID_IPV4_ADDR_RANGE, 456 ID_IPV6_ADDR_RANGE 458 Historically there was no standard method for putting address subnet 459 or range identity information into certificates, nor are there any 460 implementations known to support these ID types. Therefore, use of 461 these ID types is currently undefined. Implementations MUST NOT 462 generate these ID types. 464 Note that work in SBGP [13] for defining blocks of addresses using 465 the certificate extension identified by: 467 id-pe-ipAddrBlock OBJECT IDENTIFIER ::= { id-pe 7 } 469 is experimental at this time. 471 3.1.5. ID_DER_ASN1_DN 473 Implementations MUST support receiving the ID_DER_ASN1_DN ID type. 474 Implementations MUST be capable of generating this type, and the 475 decision to do so will be a matter of local security policy 476 configuration. When generating this type, implementations MUST 477 populate the contents of ID with the SubjectName from the end-entity 478 certificate, and MUST do so such that a binary comparison of the two 479 will succeed. If there is not a match, this MUST be treated as an 480 error and security association setup MUST be aborted. This event 481 SHOULD be auditable. Note, if the certificate was erroneously 482 created such that the encoding of the SubjectName DN varies from the 483 constraints set by DER, that non-conformant DN MUST be used to 484 populate the ID payload: in other words, implementations MUST NOT re- 485 encode the DN for the purposes of making it DER if it does not appear 486 in the certificate as DER. 488 Implementations MUST NOT populate ID with the SubjectName from the 489 end-entity certificate if it is empty, even though an empty 490 certificate SubjectName is explicitly allowed in the "Subject" 491 section of PKIX. 493 Regarding SPD matching, implementations MUST be able to perform 494 matching based on a bitwise comparison of the entire DN in ID to its 495 entry in the SPD. However, operational experience has shown that 496 using the entire DN in local configuration is difficult, especially 497 in large scale deployments. Therefore, implementations also MUST be 498 able to perform SPD matches of any combination of one or more of the 499 C, CN, O, OU attributes within Subject DN in the ID to the same in 500 the SPD. Implementations MAY support matching using additional DN 501 attributes in any combination, although interoperability is far from 502 certain and dubious. Implementations MAY also support performing 503 substring, wildcard, or regular expression matches for any of its 504 supported DN attributes from ID, in any combination, to the SPD. 505 Such flexibility allows deployers to create one SPD entry on the 506 gateway for an entire department of a company (e.g. O=Foobar Inc., 507 OU=Engineering) while still allowing them to draw out other details 508 from the DN (e.g. CN=John Doe) for auditing purposes. All the above 509 is a matter of local implementation and local policy definition and 510 enforcement capability, not bits on the wire, but will have a great 511 impact on interoperability. 513 3.1.6. ID_DER_ASN1_GN 515 Implementations MUST NOT generate this type. 517 3.1.7. ID_KEY_ID 519 The ID_KEY_ID type used to specify pre-shared keys and thus is out of 520 scope. 522 3.1.8. Selecting an Identity from a Certificate 524 Implementations MUST support certificates that contain more than a 525 single identity, such as when SubjectName and the SubjectAltName 526 extension are both populated, or the SubjectAltName extension 527 contains multiple identities irrespective of whether SubjectName is 528 empty or not. In many cases a certificate will contain an identity 529 such as an IP address in the SubjectAltName extension in addition to 530 a non-empty SubjectName. 532 Implementations SHOULD populate ID with whichever identity is likely 533 to be named in the peer's policy. In practice, this generally means 534 FQDN, or USER_FQDN, but this information may also be available to the 535 administrator through some out-of-band means. In the absence of such 536 out-of-band configuration information, the identity with which an 537 implementation chooses to populate the ID payload is a local matter. 539 3.1.9. SubjectName for DN Only 541 If an FQDN is intended to be processed as an identity for the 542 purposes ID matching, it MUST be placed in the dNSName field of the 543 SubjectAltName extension. Implementations MUST NOT populate 544 SubjectName with an FQDN in place of populating the dNSName field of 545 the SubjectAltName extension. 547 While nothing prevents an FQDN, USER_FQDN, or IP address information 548 from appearing somewhere in the SubjectName contents, such entries 549 MUST NOT be interpreted as identity information for the purposes of 550 matching with ID or for policy lookup. 552 3.1.10. Binding Identity to Policy 554 In the presence of certificates that contain multiple identities, 555 implementations MUST select the most appropriate identity from the 556 certificate and populate the ID with that. The recipient MUST use 557 the identity sent as a first key when selecting the policy. The 558 recipient MUST also use the most specific policy from that database 559 if there are overlapping policies caused by wildcards (or the 560 implementation can de-correlate the policy database so there will not 561 be overlapping entries, or it can also forbid creation of overlapping 562 policies and leave the de-correlation process to the administrator, 563 but as this moves the problem to the administrator it is NOT 564 RECOMMENDED). 566 For example, imagine that a implementation is configured with a 567 certificate that contains both a non-empty SubjectName and a dNSName. 568 The sender's policy may specify which of those to use, and it 569 indicates the policy to the other end by sending that ID. If the 570 recipient has both a specific policy for the dNSName for this host 571 and generic wildcard rule for some attributes present in the 572 SubjectName, it will match a different policy depending which ID is 573 sent. As the sender knows why it wanted to connect the peer, it also 574 knows what identity it should use to match the policy it needs to the 575 operation it tries to perform; it is the only party who can select 576 the ID adequately. 578 In the event the policy cannot be found in the recipient's SPD using 579 the ID sent, then the recipient MAY use the other identities in the 580 certificate when attempting to match a suitable policy. For example, 581 say the certificate contains non-empty SubjectName, a dNSName and an 582 iPAddress. If an iPAddress is sent in ID but no specific entry 583 exists for the address in the policy database, the recipient MAY 584 search in the policy database based on the SubjectName or the dNSName 585 contained in the certificate. 587 The Peer Authorization Database (PAD) as described in 2401bis [10] 588 provides a more formal model for the binding of identity to policy in 589 addition to providing services that deal more specifically with the 590 details of policy enforcement, which are generally out of scope of 591 this document. The PAD is intended to provide a link between the SPD 592 and the security association management in protocols such as IKE. 593 See 2401bis [10], section 4.4.3 for more details. 595 3.2. Certificate Request Payload 597 The Certificate Request (CERTREQ) Payload allows an implementation to 598 request that a peer provide some set of certificates or certificate 599 revocation lists. It is not clear from ISAKMP exactly how that set 600 should be specified or how the peer should respond. We describe the 601 semantics on both sides. 603 3.2.1. Certificate Type 605 The Certificate Type field identifies to the peer the type of 606 certificate keying materials that are desired. ISAKMP defines 10 607 types of Certificate Data that can be requested and specifies the 608 syntax for these types, and IKEv2 specifies 3 additional types. For 609 the purposes of this document, only the following types are relevant: 611 o X.509 Certificate - Signature 612 o Revocation Lists (CRL and ARL) 613 o PKCS #7 wrapped X.509 certificate 614 o IKEv2's Hash and URL of X.509 certificate 616 The use of the other types: 618 o X.509 Certificate - Key Exchange 619 o PGP Certificate 620 o DNS Signed Key 621 o Kerberos Tokens 622 o SPKI Certificate 623 o X.509 Certificate Attribute 624 o IKEv2's Raw RSA Key 625 o IKEv2's Hash and URL of X.509 bundle 627 are out of the scope of this document. 629 3.2.2. X.509 Certificate - Signature 631 This type requests that the end-entity certificate be a signing 632 certificate. 634 3.2.3. Revocation Lists (CRL and ARL) 636 ISAKMP and IKEv2 do not support Certificate Payload sizes over 637 approximately 64K, which is too small for many CRLs. Therefore, the 638 acquisition of revocation material is to be dealt with out-of-band of 639 IKE. For this and other reasons, implementations SHOULD NOT generate 640 CERTREQs where the Certificate Type is "Certificate Revocation List 641 (CRL)" or "Authority Revocation List (ARL)". Implementations that do 642 generate such CERTREQs MUST NOT require the recipient to respond with 643 a CRL or ARL, and MUST NOT fail when not receiving any. Upon receipt 644 of such a CERTREQ, implementations MAY ignore the request. 646 In lieu of exchanging revocation lists in-band, a pointer to 647 revocation checking SHOULD be listed in either the 648 CRLDistributionPoints (CDP) or the AuthorityInfoAccess (AIA) 649 certificate extensions (see Section 4 for details). Unless other 650 methods for obtaining revocation information are available, 651 implementations SHOULD be able to process these attributes, and from 652 them be able to identify cached revocation material, or retrieve the 653 relevant revocation material from a URL, for validation processing. 654 In addition, implementations MUST have the ability to configure 655 validation checking information for each certification authority. 656 Regardless of the method (CDP, AIA, or static configuration), the 657 acquisition of revocation material SHOULD occur out-of-band of IKE. 659 3.2.4. PKCS #7 wrapped X.509 certificate 661 This ID type defines a particular encoding (not a particular 662 certificate type), some current implementations may ignore CERTREQs 663 they receive which contain this ID type, and the authors are unaware 664 of any implementations that generate such CERTREQ messages. 665 Therefore, the use of this type is deprecated. Implementations 666 SHOULD NOT require CERTREQs that contain this Certificate Type. 667 Implementations which receive CERTREQs which contain this ID type MAY 668 treat such payloads as synonymous with "X.509 Certificate - 669 Signature". 671 3.2.5. IKEv2's Hash and URL of X.509 certificate 673 This ID type defines a request for the peer to send a hash and URL of 674 it X.509 certificate, instead of the actual certificate itself. This 675 is a particularly useful mechanism when the peer is a device with 676 little memory and lower bandwidth, e.g. a mobile handset or consumer 677 electronics device. 679 If the IKEv2 implementation supports URL lookups, and prefers such a 680 URL to receiving actual certificates, then the implementation will 681 want to send a notify of type HTTP_CERT_LOOKUP_SUPPORTED. From IKEv2 682 [3], section 3.10.1, "This notification MAY be included in any 683 message that can include a CERTREQ payload and indicates that the 684 sender is capable of looking up certificates based on an HTTP-based 685 URL (and hence presumably would prefer to receive certificate 686 specifications in that format)." If an HTTP_LOOKUP_SUPPORTED 687 notification is sent the sender MUST support the http scheme. See 688 Section 3.3.4 for more discussion. 690 3.2.6. Location of Certificate Payloads 692 In IKEv1, the CERTREQ payload MUST be in messages 4 and 5. In IKEv2, 693 the CERTREQ payload must be in messages 2 and 3. Note that in IKEv2, 694 it is possible to have one side authenticating with certificates 695 while the other side authenticates with preshared keys. 697 3.2.7. Presence or Absence of Certificate Request Payloads 699 When in-band exchange of certificate keying materials is desired, 700 implementations MUST inform the peer of this by sending at least one 701 CERTREQ. In other words, an implementation which does not send any 702 CERTREQs during an exchange SHOULD NOT expect to receive any CERT 703 payloads. 705 3.2.8. Certificate Requests 707 3.2.8.1. Specifying Certification Authorities 709 When requesting in-band exchange of keying materials, implementations 710 SHOULD generate CERTREQs for every peer trust anchor that local 711 policy explicitly deems trusted during a given exchange. For IKEv1, 712 implementations SHOULD populate the Certification Authority field 713 with the SubjectName of the trust anchor, populated such that binary 714 comparison of the SubjectName and the Certification Authority will 715 succeed. For IKEv2, implementations MUST populate the Certification 716 Authority field as specified in IKEv2 [3]. 718 Upon receipt of a CERTREQ, implementations MUST respond by sending at 719 least the end-entity certificate corresponding to the Certification 720 Authority listed in the CERTREQ unless local security policy 721 configuration specifies that keying materials must be exchanged out- 722 of-band. Implementations MAY send certificates other than the end- 723 entity certificate (see Section 3.3 for discussion). 725 Note, in the case where multiple end-entity certificates may be 726 available which chain to different trust anchors, implementations 727 SHOULD resort to local heuristics to determine which trust anchor is 728 most appropriate to use for generating the CERTREQ. Such heuristics 729 are out of the scope of this document. 731 3.2.8.2. Empty Certification Authority Field 733 Implementations SHOULD generate CERTREQs where the Certificate Type 734 is "X.509 Certificate - Signature" and where a the Certification 735 Authority field is not empty. However, implementations MAY generate 736 CERTREQs with an empty Certification Authority field under special 737 conditions. Although PKIX prohibits certificates with empty 738 IssuerName fields, there does exist a use case where doing so is 739 appropriate, and carries special meaning in the IKE context. This 740 has become a convention within the IKE interoperability tests and 741 usage space, and so its use is specified, explained here for the sake 742 of interoperability. 744 USE CASE: Consider the rare case where you have a gateway with 745 multiple policies for a large number of IKE peers: some of these 746 peers are business partners, some are remote access employees, some 747 are teleworkers, some are branch offices, and/or the gateway may be 748 simultaneously serving many customers (e.g. Virtual Routers). The 749 total number of certificates, and corresponding trust anchors, is 750 very high, say hundreds. Each of these policies is configured with 751 one or more acceptable trust anchors, so that in total, the gateway 752 has one hundred (100) trust anchors that could possibly used to 753 authenticate an incoming connection. Assume that many of those 754 connections originate from hosts/gateways with dynamically assigned 755 IP addresses, so that the source IP of the IKE initiator is not known 756 to the gateway, nor is the identity of the initiator (until it is 757 revealed in Main Mode message 5). In IKE main mode message 4, the 758 responder gateway will need to send a CERTREQ to the initiator. 759 Given this example, the gateway will have no idea which of the 760 hundred possible Certification Authorities to send in the CERTREQ. 761 Sending all possible Certification Authorities will cause significant 762 processing delays, bandwidth consumption, and UDP fragmentation, so 763 this tactic is ruled out. 765 In such a deployment, the responder gateway implementation should be 766 able to do all it can to indicate a Certification Authority in the 767 CERTREQ. This means the responder SHOULD first check SPD to see if 768 it can match the source IP, and find some indication of which CA is 769 associated with that IP. If this fails (because the source IP is not 770 familiar, as in the case above), then the responder SHOULD have a 771 configuration option specifying which CA's are the default CAs to 772 indicate in CERTREQ during such ambiguous connections (e.g. send 773 CERTREQ with these N CAs if there is an unknown source IP). If such 774 a fall-back is not configured or impractical in a certain deployment 775 scenario, then the responder implementation SHOULD have both of the 776 following configuration options: 778 o send a CERTREQ payload with an empty Certification Authority 779 field, or 780 o terminate the negotiation with an appropriate error message and 781 audit log entry. 783 Receiving a CERTREQ payload with an empty Certification Authority 784 field indicates that the recipient should send all/any end-entity 785 certificates it has, regardless of the trust anchor. The initiator 786 should be aware of what policy and which identity it will use, as it 787 initiated the connection on a matched policy to begin with, and can 788 thus respond with the appropriate certificate. 790 If, after sending an empty CERTREQ in Main Mode message 4, a 791 responder receives a certificate in message 5 that chains to a trust 792 anchor that the responder either (a) does NOT support, or (b) was not 793 configured for the policy (that policy was now able to be matched due 794 to having the initiator's certificate present), this MUST be treated 795 as an error and security association setup MUST be aborted. This 796 event SHOULD be auditable. 798 Instead of sending a empty CERTREQ, the responder implementation MAY 799 be configured to terminate the negotiation on the grounds of a 800 conflict with locally configured security policy. 802 The decision of which to configure is a matter of local security 803 policy, this document RECOMMENDS that both options be presented to 804 administrators. 806 More examples, and explanation on this issue are included in "More on 807 Empty CERTREQs" (Appendix C). 809 3.2.9. Robustness 811 3.2.9.1. Unrecognized or Unsupported Certificate Types 813 Implementations MUST be able to deal with receiving CERTREQs with 814 unsupported Certificate Types. Absent any recognized and supported 815 CERTREQ types, implementations MAY treat them as if they are of a 816 supported type with the Certification Authority field left empty, 817 depending on local policy. ISAKMP [2] Section 5.10 "Certificate 818 Request Payload Processing" specifies additional processing. 820 3.2.9.2. Undecodable Certification Authority Fields 822 Implementations MUST be able to deal with receiving CERTREQs with 823 undecodable Certification Authority fields. Implementations MAY 824 ignore such payloads, depending on local policy. ISAKMP specifies 825 other actions which may be taken. 827 3.2.9.3. Ordering of Certificate Request Payloads 829 Implementations MUST NOT assume that CERTREQs are ordered in any way. 831 3.2.10. Optimizations 832 3.2.10.1. Duplicate Certificate Request Payloads 834 Implementations SHOULD NOT send duplicate CERTREQs during an 835 exchange. 837 3.2.10.2. Name Lowest 'Common' Certification Authorities 839 When a peer's certificate keying materials have been cached, an 840 implementation can send a hint to the peer to elide some of the 841 certificates the peer would normally respond with. In addition to 842 the normal set of CERTREQs that are sent specifying the trust 843 anchors, an implementation MAY send CERTREQs specifying the relevant 844 cached end-entity certificates. When sending these hints, it is 845 still necessary to send the normal set of trust anchor CERTREQs 846 because the hints do not sufficiently convey all of the information 847 required by the peer. Specifically, either the peer may not support 848 this optimization or there may be additional chains that could be 849 used in this context but will not be if only the end-entity 850 certificate is specified. 852 No special processing is required on the part of the recipient of 853 such a CERTREQ, and the end-entity certificates will still be sent. 854 On the other hand, the recipient MAY elect to elide certificates 855 based on receipt of such hints. 857 CERTREQs must contain information that identifies a Certification 858 Authority certificate, which results in the peer always sending at 859 least the end-entity certificate. Always sending the end-entity 860 certificate allows implementations to determine unambiguously when a 861 new certificate is being used by a peer (perhaps because the previous 862 certificate has just expired), which may result in a failure because 863 a new intermediate CA certificate might not be available to validate 864 the new end-entity certificate). Implementations which implement 865 this optimization MUST recognize when the end-entity certificate has 866 changed and respond to it by not performing this optimization if the 867 exchange must be retried so that any missing keying materials will be 868 sent during retry. 870 3.2.10.3. Example 872 Imagine that an IKEv1 implementation has previously received and 873 cached the peer certificate chain TA->CA1->CA2->EE. If during a 874 subsequent exchange this implementation sends a CERTREQ containing 875 the SubjectName in certificate TA, this implementation is requesting 876 that the peer send at least 3 certificates: CA1, CA2, and EE. On the 877 other hand, if this implementation also sends a CERTREQ containing 878 the SubjectName of CA2, the implementation is providing a hint that 879 only 1 certificate needs to be sent: EE. Note that in this example, 880 the fact that TA is a trust anchor should not be construed to imply 881 that TA is a self-signed certificate. 883 3.3. Certificate Payload 885 The Certificate (CERT) Payload allows the peer to transmit a single 886 certificate or CRL. Multiple certificates should be transmitted in 887 multiple payloads. For backwards compatibility reasons, 888 implementations MAY send intermediate CA certificates in addition to 889 the appropriate end-entity certificate(s), but SHOULD NOT send any 890 CRLs, ARLs, or trust anchors. The reason for not exchanging CRLs or 891 ARLs in IKE is to: 893 o decrease UDP fragmentation 894 o simplify the IKE exchange 895 o reduce bandwidth requirements for IKE exchanges 897 Note, however, that while the sender of the CERT payloads SHOULD NOT 898 send any trust anchors, it's possible that the recipient may consider 899 any given intermediate CA certificate to be a trust anchor. For 900 instance, imagine the sender has the certificate chain TA1->CA1->EE1 901 while the recipient has the certificate chain TA2->EE2 where TA2=CA1. 902 The sender is merely including an intermdiate CA certificate, while 903 the recipient receives a trust anchor. 905 However, not all certificate forms that are legal in PKIX make sense 906 in the context of IPsec. The issue of how to represent IKE- 907 meaningful name-forms in a certificate is especially problematic. 908 This document provides a profile for a subset of PKIX that makes 909 sense for IKEv1/ISAKMP and IKEv2. 911 3.3.1. Certificate Type 913 The Certificate Type field identifies to the peer the type of 914 certificate keying materials that are included. ISAKMP defines 10 915 types of Certificate Data that can be sent and specifies the syntax 916 for these types, and IKEv2 specifies 3 additional types. For the 917 purposes of this document, only the following types are relevant: 919 o X.509 Certificate - Signature 920 o Revocation Lists (CRL and ARL) 921 o PKCS #7 wrapped X.509 certificate 922 o IKEv2's Hash and URL of X.509 certificate 924 The use of the other types: 926 o X.509 Certificate - Key Exchange 927 o PGP Certificate 928 o DNS Signed Key 929 o Kerberos Tokens 930 o SPKI Certificate 931 o X.509 Certificate Attribute 932 o IKEv2's Raw RSA Key 933 o IKEv2's Hash and URL of X.509 bundle 935 are out of the scope of this document. 937 3.3.2. X.509 Certificate - Signature 939 This type specifies that Certificate Data contains a certificate used 940 for signing. 942 3.3.3. Revocation Lists (CRL and ARL) 944 These types specify that Certificate Data contains an X.509 CRL or 945 ARL. These types SHOULD NOT be sent in IKE. See Section 3.2.3 for 946 discussion. 948 3.3.4. IKEv2's Hash and URL of X.509 Certificate 950 This type specifies that Certificate Data contains a hash and the URL 951 to a repository where an X.509 certificate can be retrieved. 953 An implementation that sends a HTTP_LOOKUP_SUPPORTED notification 954 MUST support the http scheme and MAY support the ftp scheme, and MUST 955 NOT require any specific form of the url-path and it SHOULD support 956 having user-name, password and port parts in the URL. The following 957 are examples of mandatory forms: 959 o http://certs.example.com/certificate.crt 960 o http://certs.example.com/certs/cert.pl?u=foo;a=pw;valid-to=+86400 961 o http://certs.example.com/%0a/../foo/bar/zappa 963 while the following is an example of a form that SHOULD be supported: 965 o http://user:password@certs.example.com:8888/certificate.crt 967 The following is an example of the ftp scheme that MAY be supported: 969 o ftp://ftp.example.com/pub/certificate.crt 971 3.3.5. PKCS #7 wrapped X.509 certificate 973 This type defines a particular encoding, not a particular certificate 974 type. Implementations SHOULD NOT generate CERTs that contain this 975 Certificate Type. Implementations SHOULD accept CERTs that contain 976 this Certificate Type because several implementations are known to 977 generate them. Note that those implementations sometimes include 978 entire certificate hierarchies inside a single CERT PKCS #7 payload, 979 which violates the requirement specified in ISAKMP that this payload 980 contain a single certificate. 982 3.3.6. Location of Certificate Payloads 984 In IKEv1, the CERT payload MUST be in messages 5 and 6. In IKEv2, 985 the CERT payload must be in messages 3 and 4. Note that in IKEv2, it 986 is possible to have one side authenticating with certificates while 987 the other side authenticates with preshared keys. 989 3.3.7. Certificate Payloads Not Mandatory 991 An implementation which does not receive any CERTREQs during an 992 exchange SHOULD NOT send any CERT payloads, except when explicitly 993 configured to proactively send CERT payloads in order to interoperate 994 with non-compliant implementations which fail to send CERTREQs even 995 when certificates are desired. In this case, an implementation MAY 996 send the certificate chain (not including the trust anchor) 997 associated with the end-entity certificate. This MUST NOT be the 998 default behavior of implementations. 1000 Implementations whose local security policy configuration expects 1001 that a peer must receive certificates through out-of-band means 1002 SHOULD ignore any CERTREQ messages that are received. 1004 Implementations that receive CERTREQs from a peer which contain only 1005 unrecognized Certification Authorities SHOULD NOT continue the 1006 exchange, in order to avoid unnecessary and potentially expensive 1007 cryptographic processing, denial of service (resource starvation) 1008 attacks. 1010 3.3.8. Response to Multiple Certification Authority Proposals 1012 In response to multiple CERTREQs which contain different 1013 Certification Authority identities, implementations MAY respond using 1014 an end-entity certificate which chains to a CA that matches any of 1015 the identities provided by the peer. 1017 3.3.9. Using Local Keying Materials 1019 Implementations MAY elect to skip parsing or otherwise decoding a 1020 given set of CERTs if equivalent keying materials are available via 1021 some preferable means, such as the case where certificates from a 1022 previous exchange have been cached. 1024 3.3.10. Multiple End-Entity Certificates 1026 Implementations SHOULD NOT send multiple end-entity certificates and 1027 recipients SHOULD NOT be expected to iterate over multiple end-entity 1028 certificates. 1030 If multiple end-entity certificates are sent, they MUST have the same 1031 public key, otherwise the responder does not know which key was used 1032 in the Main Mode message 5. 1034 3.3.11. Robustness 1036 3.3.11.1. Unrecognized or Unsupported Certificate Types 1038 Implementations MUST be able to deal with receiving CERTs with 1039 unrecognized or unsupported Certificate Types. Implementations MAY 1040 discard such payloads, depending on local policy. ISAKMP [2] Section 1041 5.10 "Certificate Request Payload Processing" specifies additional 1042 processing. 1044 3.3.11.2. Undecodable Certificate Data Fields 1046 Implementations MUST be able to deal with receiving CERTs with 1047 undecodable Certificate Data fields. Implementations MAY discard 1048 such payloads, depending on local policy. ISAKMP specifies other 1049 actions which may be taken. 1051 3.3.11.3. Ordering of Certificate Payloads 1053 For IKEv1, implementations MUST NOT assume that CERTs are ordered in 1054 any way. For IKEv2, implementations MUST NOT assume that any except 1055 the first CERT is ordered in any way. IKEv2 specifies that the first 1056 CERT contain an end-entity certificate which can be used to 1057 authenticate the peer. 1059 3.3.11.4. Duplicate Certificate Payloads 1061 Implementations MUST support receiving multiple identical CERTs 1062 during an exchange. 1064 3.3.11.5. Irrelevant Certificates 1066 Implementations MUST be prepared to receive certificates and CRLs 1067 which are not relevant to the current exchange. Implementations MAY 1068 discard such extraneous certificates and CRLs. 1070 Implementations MAY send certificates which are irrelevant to an 1071 exchange. One reason for including certificates which are irrelevant 1072 to an exchange is to minimize the threat of leaking identifying 1073 information in exchanges where CERT is not encrypted. It should be 1074 noted, however, that this probably provides rather poor protection 1075 against leaking the identity. 1077 Another reason for including certificates that seem irrelevant to an 1078 exchange is that there may be two chains from the Certification 1079 Authority to the end entity, each of which is only valid with certain 1080 validation parameters (such as acceptable policies). Since the end- 1081 entity doesn't know which parameters the relying party is using, it 1082 should send the certificates needed for both chains (even if there's 1083 only one CERTREQ). 1085 Implementations SHOULD NOT send multiple end-entity certificates and 1086 recipients SHOULD NOT be expected to iterate over multiple end-entity 1087 certificates. 1089 3.3.12. Optimizations 1091 3.3.12.1. Duplicate Certificate Payloads 1093 Implementations SHOULD NOT send duplicate CERTs during an exchange. 1094 Such payloads should be suppressed. 1096 3.3.12.2. Send Lowest 'Common' Certificates 1098 When multiple CERTREQs are received which specify certificate 1099 authorities within the end-entity certificate chain, implementations 1100 MAY send the shortest chain possible. However, implementations 1101 SHOULD always send the end-entity certificate. See Section 3.2.10.2 1102 for more discussion of this optimization. 1104 3.3.12.3. Ignore Duplicate Certificate Payloads 1106 Implementations MAY employ local means to recognize CERTs that have 1107 already been received and SHOULD discard these duplicate CERTs. 1109 3.3.12.4. Hash Payload 1111 IKEv1 specifies the optional use of the Hash Payload to carry a 1112 pointer to a certificate in either of the Phase 1 public key 1113 encryption modes. This pointer is used by an implementation to 1114 locate the end-entity certificate that contains the public key that a 1115 peer should use for encrypting payloads during the exchange. 1117 Implementations SHOULD include this payload whenever the public 1118 portion of the keypair has been placed in a certificate. 1120 4. Profile of PKIX 1122 Except where specifically stated in this document, implementations 1123 MUST conform to the requirements of PKIX [5]. 1125 4.1. X.509 Certificates 1127 4.1.1. Versions 1129 Although PKIX states that "implementations SHOULD be prepared to 1130 accept any version certificate", in practice this profile requires 1131 certain extensions that necessitate the use of Version 3 certificates 1132 for all but self-signed certificates used as trust anchors. 1133 Implementations that conform to this document MAY therefore reject 1134 Version 1 and Version 2 certificates in all other cases. 1136 4.1.2. SubjectName 1138 Certification Authority implementations MUST be able to create 1139 certificates with SubjectName fields with at least the following four 1140 attributes: CN, C, O, OU. Implementations MAY support other 1141 SubjectName attributes as well. The contents of these attributes 1142 SHOULD be configurable on a certificate by certificate basis, as 1143 these fields will likely be used by IKE implementations to match SPD 1144 policy. 1146 See Section 3.1.5 for details on how IKE implementations need to be 1147 able to process SubjectName field attributes for SPD policy lookup. 1149 4.1.2.1. Empty SubjectName 1151 IKE Implementations MUST accept certificates which contain an empty 1152 SubjectName field, as specified in PKIX. Identity information in 1153 such certificates will be contained entirely in the SubjectAltName 1154 extension. 1156 4.1.2.2. Specifying Hosts and not FQDN in SubjectName 1158 Implementations which desire to place host names that are not 1159 intended to be processed by recipients as FQDNs (for instance 1160 "Gateway Router") in the SubjectName MUST use the commonName 1161 attribute. 1163 4.1.2.3. EmailAddress 1165 As specified in PKIX, implementations MUST NOT populate 1166 DistinguishedNames with the emailAddress attribute. 1168 4.1.3. X.509 Certificate Extensions 1170 Conforming IKE implementations MUST recognize extensions which must 1171 or may be marked critical according to this specification. These 1172 extensions are: KeyUsage, SubjectAltName, and BasicConstraints. 1174 Certification Authority implementations SHOULD generate certificates 1175 such that the extension criticality bits are set in accordance with 1176 PKIX and this document. With respect to PKIX compliance, IKE 1177 implementations processing certificates MAY ignore the value of the 1178 criticality bit for extensions that are supported by that 1179 implementation, but MUST support the criticality bit for extensions 1180 that are not supported by that implementation. That is, a relying 1181 party processes all the extensions it is aware of whether the bit is 1182 true or false -- the bit says what happens when a relying party 1183 cannot process an extension. 1185 implements bit in cert PKIX mandate behavior 1186 ------------------------------------------------------ 1187 yes true true ok 1188 yes true false ok or reject 1189 yes false true ok or reject 1190 yes false false ok 1191 no true true reject 1192 no true false reject 1193 no false true reject 1194 no false false ok 1196 4.1.3.1. AuthorityKeyIdentifier and SubjectKeyIdentifier 1198 Implementations SHOULD NOT assume support for the 1199 AuthorityKeyIdentifier or SubjectKeyIdentifier extensions, and thus 1200 Certification Authority implementations SHOULD NOT generate 1201 certificate hierarchies which are overly complex to process in the 1202 absence of these extensions, such as those that require possibly 1203 verifying a signature against a large number of similarly named CA 1204 certificates in order to find the CA certificate which contains the 1205 key that was used to generate the signature. 1207 4.1.3.2. KeyUsage 1209 IKE uses an end-entity certificate in the authentication process. 1210 The end-entity certificate may be used for multiple applications. As 1211 such, the CA can impose some constraints on the manner that a public 1212 key ought to be used. The KeyUsage and ExtendedKeyUsage extensions 1213 apply in this situation. 1215 Since we are talking about using the public key to validate a 1216 signature, if the KeyUsage extension is present, then at least one of 1217 the digitalSignature or the nonRepudiation bits in the KeyUsage 1218 extension MUST be set (both can be set as well). It is also fine if 1219 other KeyUsage bits are set. 1221 A summary of the logic flow for peer cert validation follows: 1223 o If told (by configuration) to ignore KeyUsage (KU), accept cert 1224 regardless of its markings. 1225 o If no KU extension, accept cert. 1226 o If KU present and doesn't mention digitalSignature or 1227 nonRepudiation (both, in addition to other KUs, is also fine), 1228 reject cert. 1229 o If none of the above, accept cert. 1231 4.1.3.3. PrivateKeyUsagePeriod 1233 PKIX recommends against the use of this extension. The 1234 PrivateKeyUsageExtension is intended to be used when signatures will 1235 need to be verified long past the time when signatures using the 1236 private keypair may be generated. Since IKE SAs are short-lived 1237 relative to the intended use of this extension in addition to the 1238 fact that each signature is validated only a single time, the 1239 usefulness of this extension in the context of IKE is unclear. 1240 Therefore, Certification Authority implementations MUST NOT generate 1241 certificates that contain the PrivateKeyUsagePeriod extension. If an 1242 IKE implementation receives a certificate with this set, it SHOULD 1243 ignore it. 1245 4.1.3.4. CertificatePolicies 1247 Many IKE implementations do not currently provide support for the 1248 CertificatePolicies extension. Therefore, Certification Authority 1249 implementations that generate certificates which contain this 1250 extension SHOULD NOT mark the extension as critical. 1252 4.1.3.5. PolicyMappings 1254 Many IKE implementations do not support the PolicyMappings extension. 1256 Therefore, implementations that generate certificates which contain 1257 this extension SHOULD NOT mark the extension as critical. 1259 4.1.3.6. SubjectAltName 1261 Deployments that intend to use an ID of either FQDN, USER_FQDN, 1262 IPV4_ADDR or IPV6_ADDR MUST issue certificates with the corresponding 1263 SubjectAltName fields populated with the same data. Implementations 1264 SHOULD generate only the following GeneralName choices in the 1265 SubjectAltName extension, as these choices map to legal IKEv1/ISAKMP/ 1266 IKEv2 Identification Payload types: rfc822Name, dNSName, or 1267 iPAddress. Although it is possible to specify any GeneralName choice 1268 in the Identification Payload by using the ID_DER_ASN1_GN ID type, 1269 implementations SHOULD NOT assume support for such functionality, and 1270 SHOULD NOT generate certificates that do so. 1272 4.1.3.6.1. dNSName 1274 This field MUST contain a fully qualified domain name. If the IKE ID 1275 type is FQDN then the dNSName field MUST match its contents. 1276 Implementations MUST NOT generate names that contain wildcards. 1277 Implementations MAY treat certificates that contain wildcards in this 1278 field as syntactically invalid. 1280 Although this field is in the form of an FQDN, IKE implementations 1281 SHOULD NOT assume that this field contains an FQDN that will resolve 1282 via the DNS, unless this is known by way of some out-of-band 1283 mechanism. Such a mechanism is out of the scope of this document. 1284 Implementations SHOULD NOT treat the failure to resolve as an error. 1286 4.1.3.6.2. iPAddress 1288 If the IKE ID type is IPV4_ADDR or IPV6_ADDR then the iPAddress field 1289 MUST match its contents. Note that although PKIX permits CIDR [14] 1290 notation in the "Name Constraints" extension, PKIX explicitly 1291 prohibits using CIDR notation for conveying identity information. In 1292 other words, the CIDR notation MUST NOT be used in the SubjectAltName 1293 extension. 1295 4.1.3.6.3. rfc822Name 1297 If the IKE ID type is USER_FQDN then the rfc822Name field MUST match 1298 its contents. Although this field is in the form of an Internet mail 1299 address, IKE implementations SHOULD NOT assume that this field 1300 contains a valid email address, unless this is known by way of some 1301 out-of-band mechanism. Such a mechanism is out of the scope of this 1302 document. 1304 4.1.3.7. IssuerAltName 1306 Certification Authority implementations SHOULD NOT assume that other 1307 implementations support the IssuerAltName extension, and especially 1308 should not assume that information contained in this extension will 1309 be displayed to end users. 1311 4.1.3.8. SubjectDirectoryAttributes 1313 The SubjectDirectoryAttributes extension is intended to convey 1314 identification attributes of the subject. IKE implementations MAY 1315 ignore this extension when it is marked non-critical, as PKIX 1316 mandates. 1318 4.1.3.9. BasicConstraints 1320 PKIX mandates that CA certificates contain this extension and that it 1321 be marked critical. IKE implementations SHOULD reject CA 1322 certificates that do not contain this extension. For backwards 1323 compatibility, implementations may accept such certificates if 1324 explicitly configured to do so, but the default for this setting MUST 1325 be to reject such certificates. 1327 4.1.3.10. NameConstraints 1329 Many IKE implementations do not support the NameConstraints 1330 extension. Since PKIX mandates that this extension be marked 1331 critical when present, Certification Authority implementations which 1332 are interested in maximal interoperability for IKE SHOULD NOT 1333 generate certificates which contain this extension. 1335 4.1.3.11. PolicyConstraints 1337 Many IKE implementations do not support the PolicyConstraints 1338 extension. Since PKIX mandates that this extension be marked 1339 critical when present, Certification Authority implementations which 1340 are interested in maximal interoperability for IKE SHOULD NOT 1341 generate certificates which contain this extension. 1343 4.1.3.12. ExtendedKeyUsage 1345 The CA SHOULD NOT include the ExtendedKeyUsage (EKU) extension in 1346 certificates for use with IKE. Note that there were three IPsec 1347 related object identifiers in EKU that were assigned in 1999. The 1348 semantics of these values were never clearly defined. The use of 1349 these three EKU values in IKE/IPsec is obsolete and explicitly 1350 deprecated by this specification. CAs SHOULD NOT issue certificates 1351 for use in IKE with them. (For historical reference only, those 1352 values were id-kp-ipsecEndSystem, id-kp-ipsecTunnel, and id-kp- 1353 ipsecUser.) 1355 The CA SHOULD NOT mark the EKU extension in certificates for use with 1356 IKE and one or more other applications. Nevertheless, this document 1357 defines an ExtendedKeyUsage keyPurposeID that MAY be used to limit a 1358 certificate's use: 1360 id-kp-ipsecIKE OBJECT IDENTIFIER ::= { id-kp 17 } 1362 where id-kp is defined in RFC-3280 [5]. If the CA administrator 1363 feels they must use an EKU for some other application, then such 1364 certificates MUST contain either the keyPurposeID id-kp-ipsecIKE or 1365 anyExtendedKeyUsage [5] as well as the keyPurposeID values associated 1366 with the other applications for which the certificate is intended to 1367 be used. Recall however, EKU extensions in certificates meant for 1368 use in IKE are NOT RECOMMENDED. 1370 A summary of the logic flow for peer certificate validation regarding 1371 the EKU extension follows: 1373 o If told (by configuration) to ignore ExtendedKeyUsage (EKU), 1374 accept cert regardless of the presence or absence of the 1375 extension. 1376 o If no EKU extension, accept cert. 1377 o If EKU present AND contains either id-kp-ipsecIKE or 1378 anyExtendedKeyUsage, accept cert. 1379 o Otherwise, reject cert. 1381 4.1.3.13. CRLDistributionPoints 1383 Because this document deprecates the sending of CRLs in-band, the use 1384 of CRLDistributionPoints (CDP) becomes very important if CRLs are 1385 used for revocation checking (as opposed to say Online Certificate 1386 Status Protocol - OCSP [15]). The IPsec peer either needs to have a 1387 URL for a CRL written into its local configuration, or it needs to 1388 learn it from CDP. Therefore, Certification Authority 1389 implementations SHOULD issue certificates with a populated CDP. 1391 Failure to validate the CRLDistributionPoints/ 1392 IssuingDistributionPoint pair can result in CRL substitution where an 1393 entity knowingly substitutes a known good CRL from a different 1394 distribution point for the CRL which is supposed to be used which 1395 would show the entity as revoked. IKE implementations MUST support 1396 validating that the contents of CRLDistributionPoints match those of 1397 the IssuingDistributionPoint to prevent CRL substitution when the 1398 issuing CA is using them. At least one CA is known to default to 1399 this type of CRL use. See Section 4.2.2.5 for more information. 1401 CDPs SHOULD be "resolvable". Several non-compliant Certification 1402 Authority implementations are well known for including unresolvable 1403 CDPs like http://localhost/path_to_CRL and http:///path_to_CRL which 1404 are equivalent to failing to include the CDP extension in the 1405 certificate. 1407 See PKIX docs for CRLDistributionPoints intellectual property rights 1408 (IPR) information. Note that both the CRLDistributionPoints and 1409 IssuingDistributionPoint extensions are RECOMMENDED but not REQUIRED 1410 by PKIX, so there is no requirement to license any IPR. 1412 4.1.3.14. InhibitAnyPolicy 1414 Many IKE implementations do not support the InhibitAnyPolicy 1415 extension. Since PKIX mandates that this extension be marked 1416 critical when present, Certification Authority implementations which 1417 are interested in maximal interoperability for IKE SHOULD NOT 1418 generate certificates which contain this extension. 1420 4.1.3.15. FreshestCRL 1422 IKE implementations MUST NOT assume that the FreshestCRL extension 1423 will exist in peer certificates. Note that most IKE implementations 1424 do not support delta CRLs. 1426 4.1.3.16. AuthorityInfoAccess 1428 PKIX defines the AuthorityInfoAccess extension, which is used to 1429 indicate "how to access CA information and services for the issuer of 1430 the certificate in which the extension appears." Because this 1431 document deprecates the sending of CRLs in band, the use of 1432 AuthorityInfoAccess (AIA) becomes very important if OCSP [15] is to 1433 be used for revocation checking (as opposed to CRLs). The IPsec peer 1434 either needs to have a URI for the OCSP query written into its local 1435 configuration, or it needs to learn it from AIA. Therefore, 1436 implementations SHOULD support this extension, especially if OCSP 1437 will be used. 1439 4.1.3.17. SubjectInfoAccess 1441 PKIX defines the SubjectInfoAccess private certificate extension, 1442 which is used to indicate "how to access information and services for 1443 the subject of the certificate in which the extension appears." This 1444 extension has no known use in the context of IPsec. Conformant IKE 1445 implementations SHOULD ignore this extension when present. 1447 4.2. X.509 Certificate Revocation Lists 1449 When validating certificates, IKE implementations MUST make use of 1450 certificate revocation information, and SHOULD support such 1451 revocation information in the form of CRLs, unless non-CRL revocation 1452 information is known to be the only method for transmitting this 1453 information. Deployments that intend to use CRLs for revocation 1454 SHOULD populate the CRLDistributionPoints extension. Therefore 1455 Certification Authority implementations MUST support issuing 1456 certificates with this field populated according to administrator's 1457 needs. IKE implementations MAY provide a configuration option to 1458 disable use of certain types of revocation information, but that 1459 option MUST be off by default. Such an option is often valuable in 1460 lab testing environments. 1462 4.2.1. Multiple Sources of Certificate Revocation Information 1464 IKE implementations which support multiple sources of obtaining 1465 certificate revocation information MUST act conservatively when the 1466 information provided by these sources is inconsistent: when a 1467 certificate is reported as revoked by one trusted source, the 1468 certificate MUST be considered revoked. 1470 4.2.2. X.509 Certificate Revocation List Extensions 1472 4.2.2.1. AuthorityKeyIdentifier 1474 Certification Authority implementations SHOULD NOT assume that IKE 1475 implementations support the AuthorityKeyIdentifier extension, and 1476 thus SHOULD NOT generate certificate hierarchies which are overly 1477 complex to process in the absence of this extension, such as those 1478 that require possibly verifying a signature against a large number of 1479 similarly named CA certificates in order to find the CA certificate 1480 which contains the key that was used to generate the signature. 1482 4.2.2.2. IssuerAltName 1484 Certification Authority implementations SHOULD NOT assume that IKE 1485 implementations support the IssuerAltName extension, and especially 1486 should not assume that information contained in this extension will 1487 be displayed to end users. 1489 4.2.2.3. CRLNumber 1491 As stated in PKIX, all issuers conforming to PKIX MUST include this 1492 extension in all CRLs. 1494 4.2.2.4. DeltaCRLIndicator 1496 4.2.2.4.1. If Delta CRLs Are Unsupported 1498 IKE implementations that do not support delta CRLs MUST reject CRLs 1499 which contain the DeltaCRLIndicator (which MUST be marked critical 1500 according to PKIX) and MUST make use of a base CRL if it is 1501 available. Such implementations MUST ensure that a delta CRL does 1502 not "overwrite" a base CRL, for instance in the keying material 1503 database. 1505 4.2.2.4.2. Delta CRL Recommendations 1507 Since some IKE implementations that do not support delta CRLs may 1508 behave incorrectly or insecurely when presented with delta CRLs, 1509 administrators and deployers should consider whether issuing delta 1510 CRLs increases security before issuing such CRLs. And, if all the 1511 elements in the VPN and PKI systems do not adequately support Delta 1512 CRLs, then their use should be questioned. 1514 The authors are aware of several implementations which behave in an 1515 incorrect or insecure manner when presented with delta CRLs. See 1516 Appendix B for a description of the issue. Therefore, this 1517 specification RECOMMENDS NOT issuing delta CRLs at this time. On the 1518 other hand, failure to issue delta CRLs exposes a larger window of 1519 vulnerability. See the Security Considerations section of PKIX [5] 1520 for additional discussion. Implementors as well as administrators 1521 are encouraged to consider these issues. 1523 4.2.2.5. IssuingDistributionPoint 1525 A CA that is using CRLDistributionPoints may do so to provide many 1526 "small" CRLs, each only valid for a particular set of certificates 1527 issued by that CA. To associate a CRL with a certificate, the CA 1528 places the CRLDistributionPoints extension in the certificate, and 1529 places the IssuingDistributionPoint in the CRL. The 1530 distributionPointName field in the CRLDistributionPoints extension 1531 MUST be identical to the distributionPoint field in the 1532 IssuingDistributionPoint extension. At least one CA is known to 1533 default to this type of CRL use. See Section 4.1.3.13 for more 1534 information. 1536 4.2.2.6. FreshestCRL 1538 Given the recommendations against Certification Authority 1539 implementations generating delta CRLs, this specification RECOMMENDS 1540 that implementations do not populate CRLs with the FreshestCRL 1541 extension, which is used to obtain delta CRLs. 1543 5. Configuration Data Exchange Conventions 1545 Below we present a common format for exchanging configuration data. 1546 Implementations MUST support these formats, MUST support receiving 1547 arbitrary whitespace at the beginning and end of any line, MUST 1548 support receiving arbitrary line lengths although they SHOULD 1549 generate lines less than 76 characters, and MUST support receiving 1550 the following three line-termination disciplines: LF (US-ASCII 10), 1551 CR (US-ASCII 13), and CRLF. 1553 5.1. Certificates 1555 Certificates MUST be Base64 encoded and appear between the following 1556 delimiters: 1558 -----BEGIN CERTIFICATE----- 1559 -----END CERTIFICATE----- 1561 5.2. CRLs and ARLs 1563 CRLs and ARLs MUST be Base64 encoded and appear between the following 1564 delimiters: 1566 -----BEGIN CRL----- 1567 -----END CRL----- 1569 5.3. Public Keys 1571 IKE implementations MUST support two forms of public keys: 1572 certificates and so-called "raw" keys. Certificates should be 1573 transferred in the same form as above. A raw key is only the 1574 SubjectPublicKeyInfo portion of the certificate, and MUST be Base64 1575 encoded and appear between the following delimiters: 1577 -----BEGIN PUBLIC KEY----- 1578 -----END PUBLIC KEY----- 1580 5.4. PKCS#10 Certificate Signing Requests 1582 A PKCS#10 [9] Certificate Signing Request MUST be Base64 encoded and 1583 appear between the following delimiters: 1585 -----BEGIN CERTIFICATE REQUEST----- 1586 -----END CERTIFICATE REQUEST----- 1588 6. Security Considerations 1590 6.1. Certificate Request Payload 1592 The Contents of CERTREQ are not encrypted in IKE. In some 1593 environments this may leak private information. Administrators in 1594 some environments may wish to use the empty Certification Authority 1595 option to prevent such information from leaking, at the cost of 1596 performance. 1598 6.2. IKEv1 Main Mode 1600 Certificates may be included in any message, and therefore 1601 implementations may wish to respond with CERTs in a message that 1602 offers privacy protection, in Main Mode messages 5 and 6. 1603 Implementations may not wish to respond with CERTs in the second 1604 message, thereby violating the identity protection feature of Main 1605 Mode in IKEv1. 1607 7. Intellectual Property Rights 1609 No new intellectual property rights are introduced by this document. 1611 8. IANA Considerations 1613 There are no known numbers which IANA will need to manage. 1615 9. References 1617 9.1. Normative References 1619 [1] Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)", 1620 RFC 2409, November 1998. 1622 [2] Maughan, D., Schneider, M., and M. Schertler, "Internet Security 1623 Association and Key Management Protocol (ISAKMP)", RFC 2408, 1624 November 1998. 1626 [3] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", 1627 draft-ietf-ipsec-ikev2-15 (work in progress), August 2004. 1629 [4] Kent, S. and R. Atkinson, "Security Architecture for the 1630 Internet Protocol", RFC 2401, November 1998. 1632 [5] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet X.509 1633 Public Key Infrastructure Certificate and Certificate Revocation 1634 List (CRL) Profile", RFC 3280, April 2002. 1636 [6] Piper, D., "The Internet IP Security Domain of Interpretation 1637 for ISAKMP", RFC 2407, November 1998. 1639 [7] Bradner, S., "Key words for use in RFCs to Indicate Requirement 1640 Levels", BCP 14, RFC 2119, March 1997. 1642 [8] Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981. 1644 [9] Kaliski, B., "PKCS #10: Certification Request Syntax Version 1645 1.5", RFC 2314, March 1998. 1647 9.2. Informative References 1649 [10] Kent, S. and K. Seo, "Security Architecture for the Internet 1650 Protocol", draft-ietf-ipsec-rfc2401bis-06 (work in progress), 1651 March 2005. 1653 [11] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) 1654 Specification", RFC 1883, December 1995. 1656 [12] Eastlake, D., "Domain Name System Security Extensions", 1657 RFC 2535, March 1999. 1659 [13] Lynn, C., "X.509 Extensions for IP Addresses and AS 1660 Identifiers", draft-ietf-pkix-x509-ipaddr-as-extn-03 (work in 1661 progress), September 2003. 1663 [14] Fuller, V., Li, T., Yu, J., and K. Varadhan, "Classless Inter- 1664 Domain Routing (CIDR): an Address Assignment and Aggregation 1665 Strategy", RFC 1519, September 1993. 1667 [15] Myers, M., Ankney, R., Malpani, A., Galperin, S., and C. Adams, 1668 "X.509 Internet Public Key Infrastructure Online Certificate 1669 Status Protocol - OCSP", RFC 2560, June 1999. 1671 [16] Arsenault, A. and S. Turner, "Internet X.509 Public Key 1672 Infrastructure: Roadmap", draft-ietf-pkix-roadmap-09 (work in 1673 progress), July 2002. 1675 Appendix A. Change History 1676 October 2005 (-06) 1678 * 4.1.3.12 - added text re: id-kp-ipsecIKE 1680 July 2005 (-05) 1682 * 3.1 - added "See 2401bis [10], section 4.4.3.2 for more 1683 details." to resolve issue #561. 1684 * 3.1.10 - added text pointing to PAD in 2401bis [10] to 1685 discussion of binding identity to policy. 1687 December 2004 (-04) 1689 * Added Paul Hoffman's text from issue #708 1690 * Added text explaining that it's possible for a recipient to 1691 receive CERT payloads containing certs that the recipient 1692 considers a trust anchor (15 Nov 2004 pki4ipsec email from 1693 Peter Williams) 1694 * Replaced text in 4.1.3 with Kent's text (issue #655) (22 Nov 1695 2004 pki4ipsec email from Stephen Kent, Paul Hoffman) 1697 September 2004 (-03) 1699 * Minor editorial changes in abstract and introduction clarifing 1700 when something is from IPsec, IKE, etc 1701 * Minor editorial changes throughout 1702 * Fixed "Certification Authority" instead of "Certificate 1703 Authority" 1704 * Cleaned up initiator/responder when really referred to sender/ 1705 recipient 1706 * Fixed inconsistancy in text by making sure that all text on the 1707 topic of sending CERTREQs follow Gregory Lebovitz's proposal 1708 for CERT payloads: "should deal with all the CRL, Intermediat 1709 Certs, Trust Anchors, etc OOB of IKE; MUST be able to send and 1710 receive EE cert payload; only real exception is Intermediate 1711 Cets which MAY be sent and SHOULD be able to be receivable (but 1712 in reality there are very few hierarchies in operation, so 1713 really it's a corner case); SHOULD NOT send the other stuff 1714 (CRL, Trust Anchors, etc) in cert payloads in IKE; SHOULD be 1715 able to accept the other stuff if by chance it gets sent, 1716 though we hope they don't get sent" 1717 * 3.1 - removed text suggesting that it would be reasonable to 1718 terminate IKEv2 processing if the initiator were to receive a 1719 responder-generated IDr 1721 * 3.1.1 - noted that certificates may contain multiple IP 1722 addresses 1723 * 3.1.9 - removed (temporarily?) confusing text stating that 1724 overlapping policies was prohibited, text which was 1725 inconsistent with text right above it 1726 * 3.2.7.2 - SHOULD changed to MUST terminate if peer's 1727 certificate chain violates local policy 1728 * 3.3 - removed text implying that pausing in the middle of an 1729 IKE exchange in order to obtain revocation status information 1730 via http or OCSP would reduce latency in IKE 1731 * 4.2 - allow deployments that don't wish to populate CDP (for 1732 instance if a source of revocation information is configured 1733 via some other means) to skip populating CDP, making consistent 1734 with 4.1.3.13 and the issues IPR spelled out in PKIX 1735 * Somehow a CRL out-of-band configuration format had been 1736 omitted. 1737 * #555: Kent-1.0 Introduction - document now references IKEv2 1738 * #559: Kent-Profile Document 3.1.0 - use sender/recipient 1739 instead of agent 1740 * #564: Kent-Profile Document 3.1.1 - specified that support for 1741 ID_IPV4_ADDR and/or ID_IPV6_ADDR are contingent on device 1742 support for IPv4 and/or IPv6 1743 * #568: Kent-Profile document 3.1.4 - specified that there wasn't 1744 a standard and besides no one has implemented it 1745 * #571: Kent-Profile document 3.1.8 - tried to be even more 1746 clearer than was asked for by spelling things out in detail 1747 * #572: Kent-Profile document 3.1.8 Formerly issue #18 - now 1748 specifies that it's only a local matter if that information is 1749 not coordinated with other administrators 1750 * #573: Kent-Profile document 3.2.3/Myers - revocation 1751 information no longer exchanged in-band, plus Mike Myers has 1752 submitted an OCSP w/IKE draft, which is references by this 1753 document. 1754 * #578 Kent-Profile document 4.0.0 - went through entire PKIX 1755 profile section and prefaced "implementation" with "IKE" or 1756 "Certification Authority" wherever it was sure to be one or the 1757 other 1758 * #581: Kent-Profile document 4.1.3.9 - replaced description with 1759 text from RFC 2459 1760 * #584: Maillist-Lebovitz PKI Life Cycle-Revocation - fixed 1761 * #586: Maillist-Allison Empty CertReq - there is now lots of 1762 text dealing with when empty certreqs are permitted 1763 * 3.2.7.1 - CERTREQ only mandatory if in-band exchange of keymat 1764 is desired (28 Jul 2004 pki4ipsec email from jknowles@ 1765 SonicWALL.com) 1766 * 3.3.6 - clarified that "non-compliant" means not sending a 1767 CERTREQ (28 Jul 2004 pki4ipsec email from jknowles@ 1768 SonicWALL.com) 1770 * 3.2.7.1 - fixed contradition: mandatory to respond to CERTREQ 1771 UNLESS configured not to (28 Jul 2004 pki4ipsec email from 1772 jknowles@SonicWALL.com) 1773 * 3.2.9.2 and 3.2.9.3 - CERTREQ contains an issuer name only for 1774 IKEv2 (19 Sep 2004 email from Charlie Kaufman) 1775 * Answered 'Section 3.1.9 para 2: "The initiator MUST know by 1776 policy..." is a difficult to interpret requirement. It could 1777 mean that it must be possible to configure in policy which ID 1778 is to be sent. Did you mean "the initiator must decide...", 1779 where the decision might be wired into a particular 1780 implementation?' by changing it to be merely descriptive, and 1781 to refer to policy configuration (19 Sep 2004 email from 1782 Charlie Kaufman) 1783 * IPSEC -> IPsec (19 Sep 2004 email from Charlie Kaufman) 1784 * 3.1.1 para 1: "MUST be stored" changed to "MUST be encoded" (19 1785 Sep 2004 email from Charlie Kaufman) 1786 * 3.1.5 para 2 - made it clear that empty SubjectNames are 1787 permitted by PKIX in certificates, but this document doesn't 1788 permit them in ID (19 Sep 2004 email from Charlie Kaufman) 1789 * 3.2.7.1 - clarified by specifying that it's a trust anchor 1790 that's being chosen, not end-entity certificate (19 Sep 2004 1791 email from Charlie Kaufman) 1792 * 3.3.9.5 - fixed confusing last paragraph (19 Sep 2004 email 1793 from Charlie Kaufman) 1794 * 3.3.10.3 - made it more clear that this section is really 1795 talking about duplicate certificate payloads (19 Sep 2004 email 1796 from Charlie Kaufman) 1797 * 4.1.2.2 para 2 and 3 - moved to 3.1.x section where is belongs 1798 (19 Sep 2004 email from Charlie Kaufman) 1799 * 4.1.3.5 - the last sentence of 4.1.3.4 copied here (19 Sep 2004 1800 email from Charlie Kaufman) 1801 * 4.2.2.4.2 - SHOULD -> should (19 Sep 2004 email from Charlie 1802 Kaufman) 1803 * 3.2.5 and 3.3.4 - added description of URL scheme support (16 1804 Aug 2004 pki4ipsec email from Tero Kivinen) 1805 * Removed 6.1 and 6.3 because they were either incorrect or 1806 didn't add any new security considerations above and beyond the 1807 IKE documents. 1808 August 2004 (-02) (Edited by Gregory Lebovitz, with XML formatting 1809 and cross-referencing by Paul Knight) 1811 * 3.1.1 the text between the **s was added to paragraph, per the 1812 question that arose in IETF60 WG session: Implementations MUST 1813 be capable of verifying that the address contained in the ID is 1814 the same as the peer source address **contained in the outer 1815 most IP header**. 1817 * 3.2.7 - added HTTP_CERT_LOOKUP_SUPPORTED to this section and 1818 described its use - #38 1819 * 3.3 - changed back sending of intermediate CA certificates from 1820 SHOULD NOT to MAY (for backward compatibility). Added text to 1821 explain further why we want to stay away from actually doing it 1822 though. 1823 * 3.3.8 - changed text per Knowles/Korver 2004.07.28. 1824 * 3.3.9.5 - Change discard of Irrelevant Certificates from may to 1825 SHOULD - #23(Kent 2004.04.26) 1826 * 4.1.3.2 KU - re-worked to reflect discussion on list and in 1827 IETF60 - #36 1828 * 4.1.3.12 EKU - re-worked to reflect discussion on list and in 1829 IETF60 - #36 1830 * [IKEv2] update the reference to the -14 draft of May 29, 2004 1832 July 2004 (-01) (Edited by Gregory Lebovitz) 1834 * Changed ISAKMP references in Abstract and Intro to IKE. 1835 * Editorial changes to make the text conform with the summary 1836 table in 3.1, especially in the text following the table in 1837 3.1. Particular note should be paid to changes in section 1838 3.5.1. 1839 * Sect 3.1.1 - editorial changes to aid in clarification. Added 1840 text on when deployers might consider using IP addr, but 1841 strongly encouraged not to. 1842 * Sect 3.1.8 removed IP address from list of practically used ID 1843 types. 1844 * 3.1.9 overhauled (per Kivinen, July 18) 1845 * 3.2 - added IKEv2's Hash and URL of x.509 to list of those 1846 profiled and gave it its own section, now 3.2.5 1847 * added note in CRL/ARL section about revocation occurring OOB of 1848 IKE 1849 * deleted ARL as its own section and collapsed it into Revocation 1850 Lists (CRL and ARL) for consciseness. Renumbered accordingly. 1851 * Sect 3.2.7.2 - Changed from MUST not send empty certreqs to 1852 SHOULD send CERTREQs which contain CA fields with direction on 1853 how, but MAY send empty CERTREQs in certain case. Use case 1854 added, and specifics of both initiator and responder behavior 1855 listed. 1856 * APPENDIX C added to fill out the explanation (mostly discussion 1857 from list). 1858 * 3.3 - clarified that sending CRLs and chaining certs is 1859 deprecated. 1860 * added IKEv2's Hash and URL of x.509 to list of those profiled 1861 and gave it its own section. Condensed ARL into CRL and 1862 renumbered accordingly. 1864 * duplicate section was removed, renumbered accordingly 1865 * 3.3.10.2 - title changed. sending chaining becomes SHOULD NOT. 1866 * 4.1.2 added text to explicity call out support for CN, C, O, OU 1867 * collapsed 4.1.2.3 into 4.1.2.2 and renumbered accordingly. 1868 * Collapsed 4.1.3.2 into 4.1.3.1 and renumbered accordingly 1869 * Edited 4.1.3.2 Key Usage and 4.1.3.12 ExtKey Usage according to 1870 Hoffman, July18 1871 * 4.1.3.3 if receive cert w/ PKUP, ignore it. 1872 * 4.1.3.13 - CDP changed text to represent SHOULD issue, and how 1873 important CDP becomes when we do not send CRLs in-band. Added 1874 SHOULD for CDPs actually being resolvable (reilly email). 1875 * Reordered 6.4 for better clarity. 1876 * Added Rescorla to Acknowledgements section, as he is no longer 1877 listed as an editor, since -00. 1879 May 2004 (renamed draft-ietf-pki4ipsec-ikecert-profile-00.txt) 1880 (edited by Brian Korver) 1882 * Made it clearer that the format of the ID_IPV4_ADDR payload 1883 comes from RFC791 and is nothing new. (Tero Kivinen Feb 29) 1884 * Permit implementations to skip verifying that the peer source 1885 address matches the contents of ID_IPV{4,6}_ADDR. (Tero 1886 Kivinen Feb 29, Gregory Lebovitz Feb 29) 1887 * Removed paragraph suggesting that implementations favor 1888 unauthenticated peer source addresses over an unauthenticated 1889 ID for initial policy lookup. (Tero Kivinen Feb 29, Gregory 1890 Lebovitz Feb 29) 1891 * Removed some text implying RSA encryption mode was in scope. 1892 (Tero Kivinen Feb 29) 1893 * Relaxed deprecation of PKCS#7 CERT payloads. (Tero Kivinen Feb 1894 29) 1895 * Made it clearer that out-of-scope local heuristics should be 1896 used for picking an EE cert to use when generating CERTREQ, not 1897 when receiving CERTREQ. (Tero Kivinen Feb 29) 1898 * Made it clearer that CERT processing can be skipped when the 1899 contents of a CERT are already known. (Tero Kivinen Feb 29) 1900 * Implementations SHOULD generate BASE64 lines less than 76 1901 characters. (Tero Kivinen Feb 29) 1902 * Added "Except where specifically stated in this document, 1903 implementations MUST conform to the requirements of PKIX" 1904 (Steve Hanna Oct 7, 2003) 1905 * RECOMMENDS against populating the ID payload with IP addresses 1906 due to interoperability issues such as problem with NAT 1907 traversal. (Gregory Lebovitz May 14) 1908 * Changed "as revoked by one source" to "as revoked by one 1909 trusted source". (Michael Myers, May 15) 1911 * Specifying Certificate Authorities section needed to be 1912 regularized with Gregory Lebovitz's CERT proposal from -04. 1913 (Tylor Allison, May 15) 1914 * Added text specifying how recipients SHOULD NOT be expected to 1915 iterate over multiple end-entity certs. (Tylor Allison, May 1916 15) 1917 * Modified text to refer to IKEv2 as well as IKEv1/ISAKMP where 1918 relevant. 1919 * IKEv2: Explained that IDr sent by responder doesn't have to 1920 match the [IDr] sent initiator in second exchange. 1921 * IKEv2: Noted that "The identity ... does not necessarily have 1922 to match anything in the CERT payload" (S3.5) is not 1923 contradicted by SHOULD in this document. 1924 * IKEv2: Noted that ID_USER_FQDN renamed to ID_RFC822_ADDR, and 1925 ID_USER_FQDN would be used exclusively in this document. 1926 * IKEv2: Declared that 3 new CERTREQ and CERT types are not 1927 profiled in this document (well, at least not yet, pending WG 1928 discussion of what to do -- note that they are only SHOULDs in 1929 IKEv2). 1930 * IKEv2: Noted that CERTREQ payload changed from DN to SHA-1 of 1931 SubjectPublicKeyInfo. 1932 * IKEv2: Noted new requirement that specifies that the first 1933 certificate sent MUST be the EE cert (section 3.6). 1935 February 2004 (-04) 1937 * Minor editorial changes to clean up language 1938 * Deprecate in-band exchange of CRLs 1939 * Incorporated Gregory Lebovitz's proposal for CERT payloads: 1940 "should deal with all the CRL, Intermediat Certs, Trust 1941 Anchors, etc OOB of IKE; MUST be able to send and receive EE 1942 cert payload; only real exception is Intermediate Cets which 1943 MAY be sent and SHOULD be able to be receivable (but in reality 1944 there are very few hierarchies in operation, so really it's a 1945 corner case); SHOULD NOT send the other stuff (CRL, Trust 1946 Anchors, etc) in cert payloads in IKE; SHOULD be able to accept 1947 the other stuff if by chance it gets sent, though we hope they 1948 don't get sent" 1949 * Incorporated comments contained in Oct 7, 2003 email from 1950 steve.hanna@sun.com to ipsec@lists.tislabs.com 1951 * Moved text from "Profile of ISAKMP" Background section to each 1952 payload section (removing duplication of these sections) 1953 * Removed "Certificate-Related Playloads in ISAKMP" section since 1954 it was not specific to IKE. 1955 * Incorporated Gregory Lebovitz's table in the "Identification 1956 Payload" section 1958 * Moved text from "binding identity to policy" sections to each 1959 payload section 1960 * Moved text from "IKE" section into now-combined "IKE/ISAKMP" 1961 section 1962 * ID_USER_FQDN and ID_FQDN promoted to MUST from MAY 1963 * Promoted sending ID_DER_ASN1_DN to MAY from SHOULD NOT, and 1964 receiving from MUST from MAY 1965 * Demoted ID_DER_ASN1_GN to MUST NOT 1966 * Demoted populating SubjectName in place of populating the 1967 dNSName from SHOULD NOT to MUST NOT and removed the text 1968 regarding domainComponent 1969 * Revocation information checking MAY now be disabled, although 1970 not by default 1971 * Aggressive Mode removed from this profile 1973 June 2003 (-03) 1975 * Minor editorial changes to clean up language 1976 * Minor additional clarifying text 1977 * Removed hyphenation 1978 * Added requirement that implementations support configuration 1979 data exchange having arbitrary line lengths 1981 February 2003 (-02) 1983 * Word choice: move from use of "root" to "trust anchor", in 1984 accordance with PKIX 1985 * SBGP note and reference for placing address subnet and range 1986 information into certificates 1987 * Clarification of text regarding placing names of hosts into the 1988 Name commonName attribute of SubjectName 1989 * Added table to clarify text regarding processing of the 1990 certificate extension criticality bit 1991 * Added text underscoring processing requirements for 1992 CRLDistributionPoints and IssuingDistributionPoint 1994 October 2002, Reorganization (-01) 1996 June 2002, Initial Draft (-00) 1998 Appendix B. The Possible Dangers of Delta CRLs 2000 The problem is that the CRL processing algorithm is sometimes written 2001 incorrectly with the assumption that all CRLs are base CRLs and it is 2002 assumed that CRLs will pass content validity tests. Specifically, 2003 such implementations fail to check the certificate against all 2004 possible CRLs: if the first CRL that is obtained from the keying 2005 material database fails to decode, no further revocation checks are 2006 performed for the relevant certificate. This problem is compounded 2007 by the fact that implementations which do not understand delta CRLs 2008 may fail to decode such CRLs due to the critical DeltaCRLIndicator 2009 extension. The algorithm that is implemented in this case is 2010 approximately: 2012 o fetch newest CRL 2013 o check validity of CRL signature 2014 o if CRL signature is valid then 2015 o if CRL does not contain unrecognized critical extensions 2016 o and certificate is on CRL then 2017 o set certificate status to revoked 2019 The authors note that a number of PKI toolkits do not even provide a 2020 method for obtaining anything but the newest CRL, which in the 2021 presence of delta CRLs may in fact be a delta CRL, not a base CRL. 2023 Note that the above algorithm is dangerous in many ways. See PKIX 2024 [5] for the correct algorithm. 2026 Appendix C. More on Empty CERTREQs 2028 Sending empty certificate requests is commonly used in 2029 implementations, and in the IPsec interop meetings, vendors have 2030 generally agreed that it means that send all/any end-entity 2031 certificates you have (if multiple end-entity certificates are sent, 2032 they must have same public key, as otherwise the other end does not 2033 know which key was used). For 99% of cases the client have exactly 2034 one certificate and public key, so it really doesn't matter, but the 2035 server might have multiple, thus it simply needs to say to the 2036 client, use any certificate you have. If we are talking about 2037 corporate vpns etc, even if the client have multiple certificates or 2038 keys, all of them would be usable when authenticating to the server, 2039 so client can simply pick one. 2041 If there is some real difference on which cert to use (like ones 2042 giving different permissions), then the client must be configured 2043 anyways, or it might even ask the user which one to use (the user is 2044 the only one who knows whether he needs admin privileges, thus needs 2045 to use admin cert, or is the normal email privileges ok, thus using 2046 email only cert). 2048 99% of the cases the client have exactly one certificate, so it will 2049 send it. In 90% of the rest of the cases, any of the certificates is 2050 ok, as they are simply different certificates from same CA, or 2051 different CAs for the same corporate VPN, thus any of them is ok. 2053 Sending empty certificate requests has been agreed there to mean 2054 "give me your cert; any cert". 2056 Justification: 2058 o Responder first does all it can to send a certreq with a CA, check 2059 for IP match in SPD, have a default set of CAs to use in ambiguous 2060 cases, etc. 2061 o sending empty certreq's is fairly common in implementations today, 2062 and is generally accepted to mean "send me a cert, any cert that 2063 works for you" 2064 o saves responder sending potentially 100's of certs, the 2065 fragmentation problems that follow, etc. 2066 o in +90% of use cases, Initiators have exactly 1 cert 2067 o in +90% of the remaining use cases, the multiple certs it has are 2068 issued by the same CA 2069 o in the remaining use case(s) -- if not all the others above -- the 2070 Initiator will be configured explicitly with which cert to send, 2071 so responding to an empty certreq is easy. 2073 The following example shows why initiators need to have sufficient 2074 policy definition to know which certificate to use for a given 2075 connection it initiates. 2077 EXAMPLE: Your client (initiator) is configured with VPN policies for 2078 gateways A and B (representing perhaps corporate partners). 2080 The policies for the two gateways look something like: 2082 Acme Company policy (gateway A) 2083 Engineering can access 10.1.1.0 2084 Trusted CA: CA-A, Trusted Users: OU=Engineering 2085 Partners can access 20.1.1.0 2086 Trusted CA: CA-B, Trusted Users: OU=AcmePartners 2088 Bizco Company policy (gateway B) 2089 sales can access 30.1.1.0 2090 Trusted CA: CA-C, Trusted Users: OU=Sales 2091 Partners can access 40.1.1.0 2092 Trusted CA: CA-B, Trusted Users: OU=BizcoPartners 2094 You are an employee of Acme and you are issued the following 2095 certificates: 2097 o From CA-A: CN=JoeUser,OU=Engineering 2098 o From CA-B: CN=JoePartner,OU=BizcoPartners 2100 The client MUST be configured locally to know which CA to use when 2101 connecting to either gateway. If your client is not configured to 2102 know the local credential to use for the remote gateway, this 2103 scenario will not work either. If you attempt to connect to Bizco, 2104 everything will work... as you are presented with responding with a 2105 certificate signed by CA-B or CA-C... as you only have a certificate 2106 from CA-B you are OK. If you attempt to connect to Acme, you have an 2107 issue because you are presented with an ambiguous policy selection. 2108 As the initiator, you will be presented with certificate requests 2109 from both CA A and CA B. You have certificates issued by both CAs, 2110 but only one of the certificates will be usable. How does the client 2111 know which certificate it should present? It must have sufficiently 2112 clear local policy specifying which one credential to present for the 2113 connection it initiates. 2115 Appendix D. Acknowledgements 2117 The authors would like to acknowledge the expired draft-ietf-ipsec- 2118 pki-req-05.txt for providing valuable materials for this document. 2120 The authors would like to especially thank Eric Rescorla, one of its 2121 original authors, in addition to Greg Carter, Steve Hanna, Russ 2122 Housley, Charlie Kaufman, Tero Kivinen, and Gregory Lebovitz for 2123 their valuable comments, some of which have been incorporated 2124 verbatim into this document. Paul Knight performed the arduous tasks 2125 of coverting the text to XML format. 2127 Author's Address 2129 Brian Korver 2130 Network Resonance, Inc. 2131 2483 E. Bayshore Rd. 2132 Palo Alto, CA 94303 2133 US 2135 Phone: +1 415 812 7700 2136 Email: briank@networkresonance.com 2138 Intellectual Property Statement 2140 The IETF takes no position regarding the validity or scope of any 2141 Intellectual Property Rights or other rights that might be claimed to 2142 pertain to the implementation or use of the technology described in 2143 this document or the extent to which any license under such rights 2144 might or might not be available; nor does it represent that it has 2145 made any independent effort to identify any such rights. Information 2146 on the procedures with respect to rights in RFC documents can be 2147 found in BCP 78 and BCP 79. 2149 Copies of IPR disclosures made to the IETF Secretariat and any 2150 assurances of licenses to be made available, or the result of an 2151 attempt made to obtain a general license or permission for the use of 2152 such proprietary rights by implementers or users of this 2153 specification can be obtained from the IETF on-line IPR repository at 2154 http://www.ietf.org/ipr. 2156 The IETF invites any interested party to bring to its attention any 2157 copyrights, patents or patent applications, or other proprietary 2158 rights that may cover technology that may be required to implement 2159 this standard. Please address the information to the IETF at 2160 ietf-ipr@ietf.org. 2162 Disclaimer of Validity 2164 This document and the information contained herein are provided on an 2165 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 2166 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET 2167 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, 2168 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE 2169 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 2170 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 2172 Copyright Statement 2174 Copyright (C) The Internet Society (2005). This document is subject 2175 to the rights, licenses and restrictions contained in BCP 78, and 2176 except as set forth therein, the authors retain all their rights. 2178 Acknowledgment 2180 Funding for the RFC Editor function is currently provided by the 2181 Internet Society.