idnits 2.17.00 (12 Aug 2021) /tmp/idnits32624/draft-ietf-pki4ipsec-ikecert-profile-07.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 2220. -- Found old boilerplate from RFC 3979, Section 5, paragraph 1 on line 2197. -- Found old boilerplate from RFC 3979, Section 5, paragraph 2 on line 2204. -- Found old boilerplate from RFC 3979, Section 5, paragraph 3 on line 2210. ** 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: ---------------------------------------------------------------------------- == Mismatching filename: the document gives the document name as 'draft-ietf-pki4ipsec-ikecert-profile-06', but the file name used is 'draft-ietf-pki4ipsec-ikecert-profile-07' == No 'Intended status' indicated for this document; assuming Proposed Standard Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- == There are 29 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 1197 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 (November 12, 2005) is 6033 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 1880 -- Looks like a reference, but probably isn't: 'IDr' on line 1970 == Unused Reference: '16' is defined on line 1694, 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 (~~), 12 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: May 16, 2006 November 12, 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 May 16, 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 . . . . . . . . . . . 35 105 6. Security Considerations . . . . . . . . . . . . . . . . . . . 35 106 6.1. Certificate Request Payload . . . . . . . . . . . . . . . 35 107 6.2. IKEv1 Main Mode . . . . . . . . . . . . . . . . . . . . . 35 108 6.3. Disabling Certificate Checks . . . . . . . . . . . . . . . 35 109 7. Intellectual Property Rights . . . . . . . . . . . . . . . . . 35 110 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 35 111 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 36 112 9.1. Normative References . . . . . . . . . . . . . . . . . . . 36 113 9.2. Informative References . . . . . . . . . . . . . . . . . . 36 114 Appendix A. Change History . . . . . . . . . . . . . . . . . . . 37 115 Appendix B. The Possible Dangers of Delta CRLs . . . . . . . . . 44 116 Appendix C. More on Empty CERTREQs . . . . . . . . . . . . . . . 45 117 Appendix D. Acknowledgements . . . . . . . . . . . . . . . . . . 47 118 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 48 119 Intellectual Property and Copyright Statements . . . . . . . . . . 49 121 1. Introduction 123 IKE [1], ISAKMP [2] and IKEv2 [3] provide a secure key exchange 124 mechanism for use with IPsec [4]. In many cases the peers 125 authenticate using digital certificates as specified in PKIX [5]. 126 Unfortunately, the combination of these standards leads to an 127 underspecified set of requirements for the use of certificates in the 128 context of IPsec. 130 ISAKMP references PKIX but in many cases merely specifies the 131 contents of various messages without specifying their syntax or 132 semantics. Meanwhile, PKIX provides a large set of certificate 133 mechanisms which are generally applicable for Internet protocols, but 134 little specific guidance for IPsec. Given the numerous 135 underspecified choices, interoperability is hampered if all 136 implementers do not make similar choices, or at least fail to account 137 for implementations which have chosen differently. 139 This profile of the IKE and PKIX frameworks is intended to provide an 140 agreed-upon standard for using PKI technology in the context of IPsec 141 by profiling the PKIX framework for use with IKE and IPsec, and by 142 documenting the contents of the relevant IKE payloads and further 143 specifying their semantics. 145 In addition to providing a profile of IKE and PKIX, this document 146 attempts to incorporate lessons learned from recent experience with 147 both implementation and deployment, as well as the current state of 148 related protocols and technologies. 150 Material from ISAKMP, IKEv1, IKEv2, or PKIX is not repeated here, and 151 readers of this document are assumed to have read and understood 152 those documents. The requirements and security aspects of those 153 documents are fully relevant to this document as well. 155 This document is organized as follows. Section 2 defines special 156 terminology used in the rest of this document, Section 3 provides the 157 profile of IKEv1/ISAKMP and IKEv2, and Section 4 provides the profile 158 of PKIX. Section 5 covers conventions for the out-of-band exchange 159 of keying materials for configuration purposes. 161 This document is being discussed on the pki4ipsec@icsalabs.com 162 mailing list. 164 2. Terms and Definitions 166 Except for those terms which are defined immediately below, all terms 167 used in this document are defined in either the PKIX [5], ISAKMP [2], 168 IKEv1 [1], IKEv2 [3], or DOI [6] documents. 170 o Peer source address: The source address in packets from a peer. 171 This address may be different from any addresses asserted as the 172 "identity" of the peer. 173 o FQDN: Fully qualified domain name. 174 o ID_USER_FQDN: IKEv2 renamed ID_USER_FQDN to ID_RFC822_ADDR. Both 175 are referred to as ID_USER_FQDN in this document. 177 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 178 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 179 document are to be interpreted as described in RFC-2119 [7]. 181 3. Profile of IKEv1/ISAKMP and IKEv2 183 3.1. Identification Payload 185 The Identification (ID) Payload is used to indicate the identity that 186 the sender claims to be speaking for. The recipient can then use the 187 ID as a lookup key for policy and whatever certificate store or 188 directory that it has available. Our primary concern in this section 189 is to profile the ID payload so that it can be safely used to 190 generate or lookup policy. IKE mandates the use of the ID payload in 191 Phase 1. 193 The DOI [6] defines the 11 types of Identification Data that can be 194 used and specifies the syntax for these types. These are discussed 195 below in detail. 197 The ID payload requirements in this document cover only the portion 198 of the explicit policy checks that deal with the Identification 199 Payload specifically. For instance, in the case where ID does not 200 contain an IP address, checks such as verifying that the peer source 201 address is permitted by the relevant policy are not addressed here as 202 they are out of the scope of this document. 204 Implementations SHOULD populate ID with identity information that is 205 contained within the end-entity certificate (This SHOULD does not 206 contradict text in IKEv2 [3] Section 3.5 that implies a looser 207 binding between these two). Populating ID with identity information 208 from the end-entity certificate enables recipients to use ID as a 209 lookup key to find the peer end-entity certificate. The only case 210 where implementations MAY populate ID with information that is not 211 contained in the end-entity certificate is when ID contains the peer 212 source address (a single address, not a subnet or range). 214 Because implementations may use ID as a lookup key to determine which 215 policy to use, all implementations MUST be especially careful to 216 verify the truthfulness of the contents by verifying that they 217 correspond to some keying material demonstrably held by the peer. 218 Failure to do so may result in the use of an inappropriate or 219 insecure policy. The following sections describe the methods for 220 performing this binding. 222 The following table summarizes the binding of the Identification 223 Payload to the contents of end-entity certificates and of identity 224 information to policy. Each ID type is covered more thoroughly in 225 the following sections. 227 ID type | Support | Correspond | Cert | SPD lookup 228 | for send | PKIX Attrib | matching | rules 229 ------------------------------------------------------------------- 230 | | | | 231 IP*_ADDR | MUST [a] | SubjAltName | MUST [b] | [c], [d] 232 | | iPAddress | | 233 | | | | 234 FQDN | MUST [a] | SubjAltName | MUST [b] | [c], [d] 235 | | dNSName | | 236 | | | | 237 USER_FQDN| MUST [a] | SubjAltName | MUST [b] | [c], [d] 238 | | rfc822Name | | 239 | | | | 240 DN | MUST [a] | Entire | MUST [b] | MUST support lookup 241 | | Subject, | | on any combination 242 | | bitwise | | of C, CN, O, or OU 243 | | compare | | 244 | | | | 245 IP range | MUST NOT | n/a | n/a | n/a 246 | | | | 247 | | | | 248 KEY_ID | MUST NOT | n/a | n/a | n/a 249 | | | | 251 [a] = Implementation MUST have the configuration option to send this 252 ID type in the ID payload. Whether or not the ID type is used is a 253 matter of local configuration. 255 [b] = The ID in the ID payload MUST match the contents of the 256 corresponding field (listed) in the certificate exactly, with no 257 other lookup. The matched ID MAY be used for SPD lookup, but is not 258 required to be used for this. See 2401bis [10], section 4.4.3.2 for 259 more details. 261 [c] = At a minimum, Implementation MUST be capable of being 262 configured to perform exact matching of the ID payload contents to an 263 entry in the local SPD. 265 [d] = In addition, the implementation MAY also be configurable to 266 perform substring or wildcard matches of ID payload contents to 267 entries in the local SPD. (More on this in Section 3.1.5). 269 When sending an IPV4_ADDR, IPV6_ADDR, FQDN, or USER_FQDN, 270 implementations MUST be able to be configured to send the same string 271 as appears in the corresponding SubjectAltName attribute. This 272 document RECOMMENDS that deployers use this configuration option. 273 All these ID types are treated the same: as strings that can be 274 compared easily and quickly to a corresponding string in an explicit 275 attribute in the certificate. Of these types, FQDN and USER_FQDN are 276 RECOMMENDED over IP addresses (see discussion in Section 3.1.1). 278 When sending a DN as ID, implementations MUST send the entire DN in 279 ID. Also, implementations MUST support at least the C, CN, O, and OU 280 attributes for SPD matching. See Section 3.1.5 for more details 281 about DN, including SPD matching. 283 Recipients MUST be able to perform SPD matching on the exact contents 284 of the ID, and this SHOULD be the default setting. In addition, 285 implementations MAY use substrings or wildcards in local policy 286 configuration to do the SPD matching against the ID contents. In 287 other words, implementations MUST be able to do exact matches of ID 288 to SPD, but MAY also be configurable to do substring or wildcard 289 matches of ID to SPD. 291 IKEv2 adds an optional IDr payload in the second exchange that the 292 initiator may send to the responder in order to specify which of the 293 responder's multiple identities should be used. The responder MAY 294 choose to send an IDr in the 3rd exchange that differs in type or 295 content from the initiator-generated IDr. The initiator MUST be able 296 to receive a responder-generated IDr that is a different type from 297 the one the initiator generated. 299 3.1.1. ID_IPV4_ADDR and ID_IPV6_ADDR 301 Implementations MUST support either the ID_IPV4_ADDR or ID_IPV6_ADDR 302 ID type, depending on whether the implementation supports IPv4, IPv6 303 or both. These addresses MUST be encoded in "network byte order," as 304 specified in IP [8]: The least significant bit (LSB) of each octet is 305 the LSB of the corresponding byte in the network address. For the 306 ID_IPV4_ADDR type, the payload MUST contain exactly four octets [8]. 307 For the ID_IPV6_ADDR type, the payload MUST contain exactly sixteen 308 octets [11]. 310 Implementations SHOULD NOT populate ID payload with IP addresses due 311 to interoperability issues such as problems with NAT traversal, and 312 problems with IP verification behavior. 314 Deployments may only want to consider using the IP address as ID if 315 the following are true: 317 o the peer's IP address is static, not dynamically changing 318 o the peer is NOT behind a NAT'ing device 319 o the administrator intends the implementation to verify that the 320 peer source address matches the IP address in the ID received, and 321 that in the iPAddress field in the peer certificate's 322 SubjectAltName extension. 324 Implementations MUST be capable of verifying that the IP address 325 presented in ID matches via bitwise comparison the IP address present 326 in the certificate's iPAddress field of the SubjectAltName extension. 327 Implementations MUST perform this verification by default. When 328 comparing the contents of ID with the iPAddress field in the 329 SubjectAltName extension for equality, binary comparison MUST be 330 performed. Note that certificates may contain multiple address 331 identity types in which case at least one must match the source IP. 332 If the default is enabled, then a mismatch between the two addresses 333 MUST be treated as an error and security association setup MUST be 334 aborted. This event SHOULD be auditable. Implementations MAY 335 provide a configuration option to (i.e. local policy configuration 336 can enable) skip that verification step, but that option MUST be off 337 by default. We include the "option-to-skip-validation" in order to 338 permit better interoperability, as today implementations vary greatly 339 in how they behave on this topic. 341 In addition, implementations MUST be capable of verifying that the 342 address contained in the ID is the same as the peer source address, 343 contained in the outer most IP header. If ID is one of the IP 344 address types, then implementations MUST perform this verification by 345 default. If this default is enabled, then a mismatch MUST be treated 346 as an error and security association setup MUST be aborted. This 347 event SHOULD be auditable. Implementations MAY provide a 348 configuration option to (i.e. local policy configuration can enable) 349 skip that verification step, but that option MUST be off by default. 350 We include the "option-to-skip-validation" in order to permit better 351 interoperability, as today implementations vary greatly in how they 352 behave on the topic of verification of source IP. 354 If the default for both the verifications above are enabled, then, by 355 transitive property, the implementation will also be verifying that 356 the peer source IP address matches via a bitwise comparison the 357 contents of the iPAddress field in the SubjectAltName extension in 358 the certificate. In addition, implementations MAY allow 359 administrators to configure a local policy that explicitly requires 360 that the peer source IP address match via a bitwise comparison the 361 contents of the iPAddress field in the SubjectAltName extension in 362 the certificate. Implementations SHOULD allow administrators to 363 configure a local policy that skips this validation check. 365 Implementations MAY support substring, wildcard, or regular 366 expression matching of the contents of ID to lookup policy in the 367 SPD, and such would be a matter of local security policy 368 configuration. 370 Implementations MAY use the IP address found in the header of packets 371 received from the peer to lookup the policy, but such implementations 372 MUST still perform verification of the ID payload. Although packet 373 IP addresses are inherently untrustworthy and must therefore be 374 independently verified, it is often useful to use the apparent IP 375 address of the peer to locate a general class of policies that will 376 be used until the mandatory identity-based policy lookup can be 377 performed. 379 For instance, if the IP address of the peer is unrecognized, a VPN 380 gateway device might load a general "road warrior" policy that 381 specifies a particular CA that is trusted to issue certificates which 382 contain a valid rfc822Name which can be used by that implementation 383 to perform authorization based on access control lists (ACLs) after 384 the peer's certificate has been validated. The rfc822Name can then 385 be used to determine the policy that provides specific authorization 386 to access resources (such as IP addresses, ports, and so forth). 388 As another example, if the IP address of the peer is recognized to be 389 a known peer VPN endpoint, policy may be determined using that 390 address, but until the identity (address) is validated by validating 391 the peer certificate, the policy MUST NOT be used to authorize any 392 IPsec traffic. 394 3.1.2. ID_FQDN 396 Implementations MUST support the ID_FQDN ID type, generally to 397 support host-based access control lists for hosts without fixed IP 398 addresses. However, implementations SHOULD NOT use the DNS to map 399 the FQDN to IP addresses for input into any policy decisions, unless 400 that mapping is known to be secure, for example if DNSSEC [12] were 401 employed. 403 If ID contains an ID_FQDN, implementations MUST be capable of 404 verifying that the identity contained in the ID payload matches 405 identity information contained in the peer end-entity certificate, in 406 the dNSName field in the SubjectAltName extension. Implementations 407 MUST perform this verification by default. When comparing the 408 contents of ID with the dNSName field in the SubjectAltName extension 409 for equality, caseless string comparison MUST be performed. 410 Substring, wildcard, or regular expression matching MUST NOT be 411 performed for this comparison. If this default is enabled, then a 412 mismatch MUST be treated as an error and security association setup 413 MUST be aborted. This event SHOULD be auditable. Implementations 414 MAY provide a configuration option to (i.e. local policy 415 configuration can enable) skip that verification step, but that 416 option MUST be off by default. We include the "option-to-skip- 417 validation" in order to permit better interoperability, as today 418 implementations vary greatly in how they behave on this topic. 420 Implementations MAY support substring, wildcard, or regular 421 expression matching of the contents of ID to lookup policy in the 422 SPD, and such would be a matter of local security policy 423 configuration. 425 3.1.3. ID_USER_FQDN 427 Implementations MUST support the ID_USER_FQDN ID type, generally to 428 support user-based access control lists for users without fixed IP 429 addresses. However, implementations SHOULD NOT use the DNS to map 430 the FQDN portion to IP addresses for input into any policy decisions, 431 unless that mapping is known to be secure, for example if DNSSEC [12] 432 were employed. 434 Implementations MUST be capable of verifying that the identity 435 contained in the ID payload matches identity information contained in 436 the peer end-entity certificate, in the rfc822Name field in the 437 SubjectAltName extension. Implementations MUST perform this 438 verification by default. When comparing the contents of ID with the 439 rfc822Name field in the SubjectAltName extension for equality, 440 caseless string comparison MUST be performed. Substring, wildcard, 441 or regular expression matching MUST NOT be performed for this 442 comparison. If this default is enabled, then a mismatch MUST be 443 treated as an error and security association setup MUST be aborted. 444 This event SHOULD be auditable. Implementations MAY provide a 445 configuration option to (i.e. local policy configuration can enable) 446 skip that verification step, but that option MUST be off by default. 447 We include the "option-to-skip-validation" in order to permit better 448 interoperability, as today implementations vary greatly in how they 449 behave on this topic. 451 Implementations MAY support substring, wildcard, or regular 452 expression matching of the contents of ID to lookup policy in the 453 SPD, and such would be a matter of local security policy 454 configuration. 456 3.1.4. ID_IPV4_ADDR_SUBNET, ID_IPV6_ADDR_SUBNET, ID_IPV4_ADDR_RANGE, 457 ID_IPV6_ADDR_RANGE 459 Historically there was no standard method for putting address subnet 460 or range identity information into certificates, nor are there any 461 implementations known to support these ID types. Therefore, use of 462 these ID types is currently undefined. Implementations MUST NOT 463 generate these ID types. 465 Note that work in SBGP [13] for defining blocks of addresses using 466 the certificate extension identified by: 468 id-pe-ipAddrBlock OBJECT IDENTIFIER ::= { id-pe 7 } 470 is experimental at this time. 472 3.1.5. ID_DER_ASN1_DN 474 Implementations MUST support receiving the ID_DER_ASN1_DN ID type. 475 Implementations MUST be capable of generating this type, and the 476 decision to do so will be a matter of local security policy 477 configuration. When generating this type, implementations MUST 478 populate the contents of ID with the SubjectName from the end-entity 479 certificate, and MUST do so such that a binary comparison of the two 480 will succeed. If there is not a match, this MUST be treated as an 481 error and security association setup MUST be aborted. This event 482 SHOULD be auditable. Note, if the certificate was erroneously 483 created such that the encoding of the SubjectName DN varies from the 484 constraints set by DER, that non-conformant DN MUST be used to 485 populate the ID payload: in other words, implementations MUST NOT re- 486 encode the DN for the purposes of making it DER if it does not appear 487 in the certificate as DER. 489 Implementations MUST NOT populate ID with the SubjectName from the 490 end-entity certificate if it is empty, even though an empty 491 certificate SubjectName is explicitly allowed in the "Subject" 492 section of PKIX. 494 Regarding SPD matching, implementations MUST be able to perform 495 matching based on a bitwise comparison of the entire DN in ID to its 496 entry in the SPD. However, operational experience has shown that 497 using the entire DN in local configuration is difficult, especially 498 in large scale deployments. Therefore, implementations also MUST be 499 able to perform SPD matches of any combination of one or more of the 500 C, CN, O, OU attributes within Subject DN in the ID to the same in 501 the SPD. Implementations MAY support matching using additional DN 502 attributes in any combination, although interoperability is far from 503 certain and dubious. Implementations MAY also support performing 504 substring, wildcard, or regular expression matches for any of its 505 supported DN attributes from ID, in any combination, to the SPD. 506 Such flexibility allows deployers to create one SPD entry on the 507 gateway for an entire department of a company (e.g. O=Foobar Inc., 508 OU=Engineering) while still allowing them to draw out other details 509 from the DN (e.g. CN=John Doe) for auditing purposes. All the above 510 is a matter of local implementation and local policy definition and 511 enforcement capability, not bits on the wire, but will have a great 512 impact on interoperability. 514 3.1.6. ID_DER_ASN1_GN 516 Implementations MUST NOT generate this type. 518 3.1.7. ID_KEY_ID 520 The ID_KEY_ID type used to specify pre-shared keys and thus is out of 521 scope. 523 3.1.8. Selecting an Identity from a Certificate 525 Implementations MUST support certificates that contain more than a 526 single identity, such as when SubjectName and the SubjectAltName 527 extension are both populated, or the SubjectAltName extension 528 contains multiple identities irrespective of whether SubjectName is 529 empty or not. In many cases a certificate will contain an identity 530 such as an IP address in the SubjectAltName extension in addition to 531 a non-empty SubjectName. 533 Implementations SHOULD populate ID with whichever identity is likely 534 to be named in the peer's policy. In practice, this generally means 535 FQDN, or USER_FQDN, but this information may also be available to the 536 administrator through some out-of-band means. In the absence of such 537 out-of-band configuration information, the identity with which an 538 implementation chooses to populate the ID payload is a local matter. 540 3.1.9. SubjectName for DN Only 542 If an FQDN is intended to be processed as an identity for the 543 purposes ID matching, it MUST be placed in the dNSName field of the 544 SubjectAltName extension. Implementations MUST NOT populate 545 SubjectName with an FQDN in place of populating the dNSName field of 546 the SubjectAltName extension. 548 While nothing prevents an FQDN, USER_FQDN, or IP address information 549 from appearing somewhere in the SubjectName contents, such entries 550 MUST NOT be interpreted as identity information for the purposes of 551 matching with ID or for policy lookup. 553 3.1.10. Binding Identity to Policy 555 In the presence of certificates that contain multiple identities, 556 implementations MUST select the most appropriate identity from the 557 certificate and populate the ID with that. The recipient MUST use 558 the identity sent as a first key when selecting the policy. The 559 recipient MUST also use the most specific policy from that database 560 if there are overlapping policies caused by wildcards (or the 561 implementation can de-correlate the policy database so there will not 562 be overlapping entries, or it can also forbid creation of overlapping 563 policies and leave the de-correlation process to the administrator, 564 but as this moves the problem to the administrator it is NOT 565 RECOMMENDED). 567 For example, imagine that a implementation is configured with a 568 certificate that contains both a non-empty SubjectName and a dNSName. 569 The sender's policy may specify which of those to use, and it 570 indicates the policy to the other end by sending that ID. If the 571 recipient has both a specific policy for the dNSName for this host 572 and generic wildcard rule for some attributes present in the 573 SubjectName, it will match a different policy depending which ID is 574 sent. As the sender knows why it wanted to connect the peer, it also 575 knows what identity it should use to match the policy it needs to the 576 operation it tries to perform; it is the only party who can select 577 the ID adequately. 579 In the event the policy cannot be found in the recipient's SPD using 580 the ID sent, then the recipient MAY use the other identities in the 581 certificate when attempting to match a suitable policy. For example, 582 say the certificate contains non-empty SubjectName, a dNSName and an 583 iPAddress. If an iPAddress is sent in ID but no specific entry 584 exists for the address in the policy database, the recipient MAY 585 search in the policy database based on the SubjectName or the dNSName 586 contained in the certificate. 588 The Peer Authorization Database (PAD) as described in 2401bis [10] 589 provides a more formal model for the binding of identity to policy in 590 addition to providing services that deal more specifically with the 591 details of policy enforcement, which are generally out of scope of 592 this document. The PAD is intended to provide a link between the SPD 593 and the security association management in protocols such as IKE. 594 See 2401bis [10], section 4.4.3 for more details. 596 3.2. Certificate Request Payload 598 The Certificate Request (CERTREQ) Payload allows an implementation to 599 request that a peer provide some set of certificates or certificate 600 revocation lists. It is not clear from ISAKMP exactly how that set 601 should be specified or how the peer should respond. We describe the 602 semantics on both sides. 604 3.2.1. Certificate Type 606 The Certificate Type field identifies to the peer the type of 607 certificate keying materials that are desired. ISAKMP defines 10 608 types of Certificate Data that can be requested and specifies the 609 syntax for these types, and IKEv2 specifies 3 additional types. For 610 the purposes of this document, only the following types are relevant: 612 o X.509 Certificate - Signature 613 o Revocation Lists (CRL and ARL) 614 o PKCS #7 wrapped X.509 certificate 615 o IKEv2's Hash and URL of X.509 certificate 617 The use of the other types: 619 o X.509 Certificate - Key Exchange 620 o PGP Certificate 621 o DNS Signed Key 622 o Kerberos Tokens 623 o SPKI Certificate 624 o X.509 Certificate Attribute 625 o IKEv2's Raw RSA Key 626 o IKEv2's Hash and URL of X.509 bundle 628 are out of the scope of this document. 630 3.2.2. X.509 Certificate - Signature 632 This type requests that the end-entity certificate be a certificate 633 used for signing. 635 3.2.3. Revocation Lists (CRL and ARL) 637 ISAKMP and IKEv2 do not support Certificate Payload sizes over 638 approximately 64K, which is too small for many CRLs. Therefore, the 639 acquisition of revocation material is to be dealt with out-of-band of 640 IKE. For this and other reasons, implementations SHOULD NOT generate 641 CERTREQs where the Certificate Type is "Certificate Revocation List 642 (CRL)" or "Authority Revocation List (ARL)". Implementations that do 643 generate such CERTREQs MUST NOT require the recipient to respond with 644 a CRL or ARL, and MUST NOT fail when not receiving any. Upon receipt 645 of such a CERTREQ, implementations MAY ignore the request. 647 In lieu of exchanging revocation lists in-band, a pointer to 648 revocation checking SHOULD be listed in either the 649 CRLDistributionPoints (CDP) or the AuthorityInfoAccess (AIA) 650 certificate extensions (see Section 4 for details). Unless other 651 methods for obtaining revocation information are available, 652 implementations SHOULD be able to process these attributes, and from 653 them be able to identify cached revocation material, or retrieve the 654 relevant revocation material from a URL, for validation processing. 655 In addition, implementations MUST have the ability to configure 656 validation checking information for each certification authority. 657 Regardless of the method (CDP, AIA, or static configuration), the 658 acquisition of revocation material SHOULD occur out-of-band of IKE. 660 3.2.4. PKCS #7 wrapped X.509 certificate 662 This ID type defines a particular encoding (not a particular 663 certificate type), some current implementations may ignore CERTREQs 664 they receive which contain this ID type, and the authors are unaware 665 of any implementations that generate such CERTREQ messages. 666 Therefore, the use of this type is deprecated. Implementations 667 SHOULD NOT require CERTREQs that contain this Certificate Type. 668 Implementations which receive CERTREQs which contain this ID type MAY 669 treat such payloads as synonymous with "X.509 Certificate - 670 Signature". 672 3.2.5. IKEv2's Hash and URL of X.509 certificate 674 This ID type defines a request for the peer to send a hash and URL of 675 it X.509 certificate, instead of the actual certificate itself. This 676 is a particularly useful mechanism when the peer is a device with 677 little memory and lower bandwidth, e.g. a mobile handset or consumer 678 electronics device. 680 If the IKEv2 implementation supports URL lookups, and prefers such a 681 URL to receiving actual certificates, then the implementation will 682 want to send a notify of type HTTP_CERT_LOOKUP_SUPPORTED. From IKEv2 683 [3], section 3.10.1, "This notification MAY be included in any 684 message that can include a CERTREQ payload and indicates that the 685 sender is capable of looking up certificates based on an HTTP-based 686 URL (and hence presumably would prefer to receive certificate 687 specifications in that format)." If an HTTP_LOOKUP_SUPPORTED 688 notification is sent the sender MUST support the http scheme. See 689 Section 3.3.4 for more discussion. 691 3.2.6. Location of Certificate Payloads 693 In IKEv1, the CERTREQ payload MUST be in messages 4 and 5. In IKEv2, 694 the CERTREQ payload must be in messages 2 and 3. Note that in IKEv2, 695 it is possible to have one side authenticating with certificates 696 while the other side authenticates with preshared keys. 698 3.2.7. Presence or Absence of Certificate Request Payloads 700 When in-band exchange of certificate keying materials is desired, 701 implementations MUST inform the peer of this by sending at least one 702 CERTREQ. In other words, an implementation which does not send any 703 CERTREQs during an exchange SHOULD NOT expect to receive any CERT 704 payloads. 706 3.2.8. Certificate Requests 708 3.2.8.1. Specifying Certification Authorities 710 When requesting in-band exchange of keying materials, implementations 711 SHOULD generate CERTREQs for every peer trust anchor that local 712 policy explicitly deems trusted during a given exchange. For IKEv1, 713 implementations SHOULD populate the Certification Authority field 714 with the SubjectName of the trust anchor, populated such that binary 715 comparison of the SubjectName and the Certification Authority will 716 succeed. For IKEv2, implementations MUST populate the Certification 717 Authority field as specified in IKEv2 [3]. 719 Upon receipt of a CERTREQ, implementations MUST respond by sending at 720 least the end-entity certificate corresponding to the Certification 721 Authority listed in the CERTREQ unless local security policy 722 configuration specifies that keying materials must be exchanged out- 723 of-band. Implementations MAY send certificates other than the end- 724 entity certificate (see Section 3.3 for discussion). 726 Note, in the case where multiple end-entity certificates may be 727 available which chain to different trust anchors, implementations 728 SHOULD resort to local heuristics to determine which trust anchor is 729 most appropriate to use for generating the CERTREQ. Such heuristics 730 are out of the scope of this document. 732 3.2.8.2. Empty Certification Authority Field 734 Implementations SHOULD generate CERTREQs where the Certificate Type 735 is "X.509 Certificate - Signature" and where a the Certification 736 Authority field is not empty. However, implementations MAY generate 737 CERTREQs with an empty Certification Authority field under special 738 conditions. Although PKIX prohibits certificates with empty 739 IssuerName fields, there does exist a use case where doing so is 740 appropriate, and carries special meaning in the IKE context. This 741 has become a convention within the IKE interoperability tests and 742 usage space, and so its use is specified, explained here for the sake 743 of interoperability. 745 USE CASE: Consider the rare case where you have a gateway with 746 multiple policies for a large number of IKE peers: some of these 747 peers are business partners, some are remote access employees, some 748 are teleworkers, some are branch offices, and/or the gateway may be 749 simultaneously serving many customers (e.g. Virtual Routers). The 750 total number of certificates, and corresponding trust anchors, is 751 very high, say hundreds. Each of these policies is configured with 752 one or more acceptable trust anchors, so that in total, the gateway 753 has one hundred (100) trust anchors that could possibly used to 754 authenticate an incoming connection. Assume that many of those 755 connections originate from hosts/gateways with dynamically assigned 756 IP addresses, so that the source IP of the IKE initiator is not known 757 to the gateway, nor is the identity of the initiator (until it is 758 revealed in Main Mode message 5). In IKE main mode message 4, the 759 responder gateway will need to send a CERTREQ to the initiator. 760 Given this example, the gateway will have no idea which of the 761 hundred possible Certification Authorities to send in the CERTREQ. 762 Sending all possible Certification Authorities will cause significant 763 processing delays, bandwidth consumption, and UDP fragmentation, so 764 this tactic is ruled out. 766 In such a deployment, the responder gateway implementation should be 767 able to do all it can to indicate a Certification Authority in the 768 CERTREQ. This means the responder SHOULD first check SPD to see if 769 it can match the source IP, and find some indication of which CA is 770 associated with that IP. If this fails (because the source IP is not 771 familiar, as in the case above), then the responder SHOULD have a 772 configuration option specifying which CA's are the default CAs to 773 indicate in CERTREQ during such ambiguous connections (e.g. send 774 CERTREQ with these N CAs if there is an unknown source IP). If such 775 a fall-back is not configured or impractical in a certain deployment 776 scenario, then the responder implementation SHOULD have both of the 777 following configuration options: 779 o send a CERTREQ payload with an empty Certification Authority 780 field, or 781 o terminate the negotiation with an appropriate error message and 782 audit log entry. 784 Receiving a CERTREQ payload with an empty Certification Authority 785 field indicates that the recipient should send all/any end-entity 786 certificates it has, regardless of the trust anchor. The initiator 787 should be aware of what policy and which identity it will use, as it 788 initiated the connection on a matched policy to begin with, and can 789 thus respond with the appropriate certificate. 791 If, after sending an empty CERTREQ in Main Mode message 4, a 792 responder receives a certificate in message 5 that chains to a trust 793 anchor that the responder either (a) does NOT support, or (b) was not 794 configured for the policy (that policy was now able to be matched due 795 to having the initiator's certificate present), this MUST be treated 796 as an error and security association setup MUST be aborted. This 797 event SHOULD be auditable. 799 Instead of sending a empty CERTREQ, the responder implementation MAY 800 be configured to terminate the negotiation on the grounds of a 801 conflict with locally configured security policy. 803 The decision of which to configure is a matter of local security 804 policy, this document RECOMMENDS that both options be presented to 805 administrators. 807 More examples, and explanation on this issue are included in "More on 808 Empty CERTREQs" (Appendix C). 810 3.2.9. Robustness 812 3.2.9.1. Unrecognized or Unsupported Certificate Types 814 Implementations MUST be able to deal with receiving CERTREQs with 815 unsupported Certificate Types. Absent any recognized and supported 816 CERTREQ types, implementations MAY treat them as if they are of a 817 supported type with the Certification Authority field left empty, 818 depending on local policy. ISAKMP [2] Section 5.10 "Certificate 819 Request Payload Processing" specifies additional processing. 821 3.2.9.2. Undecodable Certification Authority Fields 823 Implementations MUST be able to deal with receiving CERTREQs with 824 undecodable Certification Authority fields. Implementations MAY 825 ignore such payloads, depending on local policy. ISAKMP specifies 826 other actions which may be taken. 828 3.2.9.3. Ordering of Certificate Request Payloads 830 Implementations MUST NOT assume that CERTREQs are ordered in any way. 832 3.2.10. Optimizations 833 3.2.10.1. Duplicate Certificate Request Payloads 835 Implementations SHOULD NOT send duplicate CERTREQs during an 836 exchange. 838 3.2.10.2. Name Lowest 'Common' Certification Authorities 840 When a peer's certificate keying materials have been cached, an 841 implementation can send a hint to the peer to elide some of the 842 certificates the peer would normally respond with. In addition to 843 the normal set of CERTREQs that are sent specifying the trust 844 anchors, an implementation MAY send CERTREQs specifying the relevant 845 cached end-entity certificates. When sending these hints, it is 846 still necessary to send the normal set of trust anchor CERTREQs 847 because the hints do not sufficiently convey all of the information 848 required by the peer. Specifically, either the peer may not support 849 this optimization or there may be additional chains that could be 850 used in this context but will not be if only the end-entity 851 certificate is specified. 853 No special processing is required on the part of the recipient of 854 such a CERTREQ, and the end-entity certificates will still be sent. 855 On the other hand, the recipient MAY elect to elide certificates 856 based on receipt of such hints. 858 CERTREQs must contain information that identifies a Certification 859 Authority certificate, which results in the peer always sending at 860 least the end-entity certificate. Always sending the end-entity 861 certificate allows implementations to determine unambiguously when a 862 new certificate is being used by a peer (perhaps because the previous 863 certificate has just expired), which may result in a failure because 864 a new intermediate CA certificate might not be available to validate 865 the new end-entity certificate). Implementations which implement 866 this optimization MUST recognize when the end-entity certificate has 867 changed and respond to it by not performing this optimization if the 868 exchange must be retried so that any missing keying materials will be 869 sent during retry. 871 3.2.10.3. Example 873 Imagine that an IKEv1 implementation has previously received and 874 cached the peer certificate chain TA->CA1->CA2->EE. If during a 875 subsequent exchange this implementation sends a CERTREQ containing 876 the SubjectName in certificate TA, this implementation is requesting 877 that the peer send at least 3 certificates: CA1, CA2, and EE. On the 878 other hand, if this implementation also sends a CERTREQ containing 879 the SubjectName of CA2, the implementation is providing a hint that 880 only 1 certificate needs to be sent: EE. Note that in this example, 881 the fact that TA is a trust anchor should not be construed to imply 882 that TA is a self-signed certificate. 884 3.3. Certificate Payload 886 The Certificate (CERT) Payload allows the peer to transmit a single 887 certificate or CRL. Multiple certificates should be transmitted in 888 multiple payloads. For backwards compatibility reasons, 889 implementations MAY send intermediate CA certificates in addition to 890 the appropriate end-entity certificate(s), but SHOULD NOT send any 891 CRLs, ARLs, or trust anchors. The reason for not exchanging CRLs or 892 ARLs in IKE is to: 894 o decrease UDP fragmentation 895 o simplify the IKE exchange 896 o reduce bandwidth requirements for IKE exchanges 898 Note, however, that while the sender of the CERT payloads SHOULD NOT 899 send any trust anchors, it's possible that the recipient may consider 900 any given intermediate CA certificate to be a trust anchor. For 901 instance, imagine the sender has the certificate chain TA1->CA1->EE1 902 while the recipient has the certificate chain TA2->EE2 where TA2=CA1. 903 The sender is merely including an intermdiate CA certificate, while 904 the recipient receives a trust anchor. 906 However, not all certificate forms that are legal in PKIX make sense 907 in the context of IPsec. The issue of how to represent IKE- 908 meaningful name-forms in a certificate is especially problematic. 909 This document provides a profile for a subset of PKIX that makes 910 sense for IKEv1/ISAKMP and IKEv2. 912 3.3.1. Certificate Type 914 The Certificate Type field identifies to the peer the type of 915 certificate keying materials that are included. ISAKMP defines 10 916 types of Certificate Data that can be sent and specifies the syntax 917 for these types, and IKEv2 specifies 3 additional types. For the 918 purposes of this document, only the following types are relevant: 920 o X.509 Certificate - Signature 921 o Revocation Lists (CRL and ARL) 922 o PKCS #7 wrapped X.509 certificate 923 o IKEv2's Hash and URL of X.509 certificate 925 The use of the other types: 927 o X.509 Certificate - Key Exchange 928 o PGP Certificate 929 o DNS Signed Key 930 o Kerberos Tokens 931 o SPKI Certificate 932 o X.509 Certificate Attribute 933 o IKEv2's Raw RSA Key 934 o IKEv2's Hash and URL of X.509 bundle 936 are out of the scope of this document. 938 3.3.2. X.509 Certificate - Signature 940 This type specifies that Certificate Data contains a certificate used 941 for signing. 943 3.3.3. Revocation Lists (CRL and ARL) 945 These types specify that Certificate Data contains an X.509 CRL or 946 ARL. These types SHOULD NOT be sent in IKE. See Section 3.2.3 for 947 discussion. 949 3.3.4. IKEv2's Hash and URL of X.509 Certificate 951 This type specifies that Certificate Data contains a hash and the URL 952 to a repository where an X.509 certificate can be retrieved. 954 An implementation that sends a HTTP_LOOKUP_SUPPORTED notification 955 MUST support the http scheme and MAY support the ftp scheme, and MUST 956 NOT require any specific form of the url-path and it SHOULD support 957 having user-name, password and port parts in the URL. The following 958 are examples of mandatory forms: 960 o http://certs.example.com/certificate.crt 961 o http://certs.example.com/certs/cert.pl?u=foo;a=pw;valid-to=+86400 962 o http://certs.example.com/%0a/../foo/bar/zappa 964 while the following is an example of a form that SHOULD be supported: 966 o http://user:password@certs.example.com:8888/certificate.crt 968 The following is an example of the ftp scheme that MAY be supported: 970 o ftp://ftp.example.com/pub/certificate.crt 972 3.3.5. PKCS #7 wrapped X.509 certificate 974 This type defines a particular encoding, not a particular certificate 975 type. Implementations SHOULD NOT generate CERTs that contain this 976 Certificate Type. Implementations SHOULD accept CERTs that contain 977 this Certificate Type because several implementations are known to 978 generate them. Note that those implementations sometimes include 979 entire certificate hierarchies inside a single CERT PKCS #7 payload, 980 which violates the requirement specified in ISAKMP that this payload 981 contain a single certificate. 983 3.3.6. Location of Certificate Payloads 985 In IKEv1, the CERT payload MUST be in messages 5 and 6. In IKEv2, 986 the CERT payload must be in messages 3 and 4. Note that in IKEv2, it 987 is possible to have one side authenticating with certificates while 988 the other side authenticates with preshared keys. 990 3.3.7. Certificate Payloads Not Mandatory 992 An implementation which does not receive any CERTREQs during an 993 exchange SHOULD NOT send any CERT payloads, except when explicitly 994 configured to proactively send CERT payloads in order to interoperate 995 with non-compliant implementations which fail to send CERTREQs even 996 when certificates are desired. In this case, an implementation MAY 997 send the certificate chain (not including the trust anchor) 998 associated with the end-entity certificate. This MUST NOT be the 999 default behavior of implementations. 1001 Implementations whose local security policy configuration expects 1002 that a peer must receive certificates through out-of-band means 1003 SHOULD ignore any CERTREQ messages that are received. 1005 Implementations that receive CERTREQs from a peer which contain only 1006 unrecognized Certification Authorities SHOULD NOT continue the 1007 exchange, in order to avoid unnecessary and potentially expensive 1008 cryptographic processing, denial of service (resource starvation) 1009 attacks. 1011 3.3.8. Response to Multiple Certification Authority Proposals 1013 In response to multiple CERTREQs which contain different 1014 Certification Authority identities, implementations MAY respond using 1015 an end-entity certificate which chains to a CA that matches any of 1016 the identities provided by the peer. 1018 3.3.9. Using Local Keying Materials 1020 Implementations MAY elect to skip parsing or otherwise decoding a 1021 given set of CERTs if equivalent keying materials are available via 1022 some preferable means, such as the case where certificates from a 1023 previous exchange have been cached. 1025 3.3.10. Multiple End-Entity Certificates 1027 Implementations SHOULD NOT send multiple end-entity certificates and 1028 recipients SHOULD NOT be expected to iterate over multiple end-entity 1029 certificates. 1031 If multiple end-entity certificates are sent, they MUST have the same 1032 public key, otherwise the responder does not know which key was used 1033 in the Main Mode message 5. 1035 3.3.11. Robustness 1037 3.3.11.1. Unrecognized or Unsupported Certificate Types 1039 Implementations MUST be able to deal with receiving CERTs with 1040 unrecognized or unsupported Certificate Types. Implementations MAY 1041 discard such payloads, depending on local policy. ISAKMP [2] Section 1042 5.10 "Certificate Request Payload Processing" specifies additional 1043 processing. 1045 3.3.11.2. Undecodable Certificate Data Fields 1047 Implementations MUST be able to deal with receiving CERTs with 1048 undecodable Certificate Data fields. Implementations MAY discard 1049 such payloads, depending on local policy. ISAKMP specifies other 1050 actions which may be taken. 1052 3.3.11.3. Ordering of Certificate Payloads 1054 For IKEv1, implementations MUST NOT assume that CERTs are ordered in 1055 any way. For IKEv2, implementations MUST NOT assume that any except 1056 the first CERT is ordered in any way. IKEv2 specifies that the first 1057 CERT contain an end-entity certificate which can be used to 1058 authenticate the peer. 1060 3.3.11.4. Duplicate Certificate Payloads 1062 Implementations MUST support receiving multiple identical CERTs 1063 during an exchange. 1065 3.3.11.5. Irrelevant Certificates 1067 Implementations MUST be prepared to receive certificates and CRLs 1068 which are not relevant to the current exchange. Implementations MAY 1069 discard such extraneous certificates and CRLs. 1071 Implementations MAY send certificates which are irrelevant to an 1072 exchange. One reason for including certificates which are irrelevant 1073 to an exchange is to minimize the threat of leaking identifying 1074 information in exchanges where CERT is not encrypted. It should be 1075 noted, however, that this probably provides rather poor protection 1076 against leaking the identity. 1078 Another reason for including certificates that seem irrelevant to an 1079 exchange is that there may be two chains from the Certification 1080 Authority to the end entity, each of which is only valid with certain 1081 validation parameters (such as acceptable policies). Since the end- 1082 entity doesn't know which parameters the relying party is using, it 1083 should send the certificates needed for both chains (even if there's 1084 only one CERTREQ). 1086 Implementations SHOULD NOT send multiple end-entity certificates and 1087 recipients SHOULD NOT be expected to iterate over multiple end-entity 1088 certificates. 1090 3.3.12. Optimizations 1092 3.3.12.1. Duplicate Certificate Payloads 1094 Implementations SHOULD NOT send duplicate CERTs during an exchange. 1095 Such payloads should be suppressed. 1097 3.3.12.2. Send Lowest 'Common' Certificates 1099 When multiple CERTREQs are received which specify certificate 1100 authorities within the end-entity certificate chain, implementations 1101 MAY send the shortest chain possible. However, implementations 1102 SHOULD always send the end-entity certificate. See Section 3.2.10.2 1103 for more discussion of this optimization. 1105 3.3.12.3. Ignore Duplicate Certificate Payloads 1107 Implementations MAY employ local means to recognize CERTs that have 1108 already been received and SHOULD discard these duplicate CERTs. 1110 3.3.12.4. Hash Payload 1112 IKEv1 specifies the optional use of the Hash Payload to carry a 1113 pointer to a certificate in either of the Phase 1 public key 1114 encryption modes. This pointer is used by an implementation to 1115 locate the end-entity certificate that contains the public key that a 1116 peer should use for encrypting payloads during the exchange. 1118 Implementations SHOULD include this payload whenever the public 1119 portion of the keypair has been placed in a certificate. 1121 4. Profile of PKIX 1123 Except where specifically stated in this document, implementations 1124 MUST conform to the requirements of PKIX [5]. 1126 4.1. X.509 Certificates 1128 Users deploying IKE and IPsec with certificates have often had little 1129 control over the capabilities of CAs available to them. 1130 Implementations of this specification may include configuration knobs 1131 to disable checks required by this specification in order to permit 1132 use with inflexible and/or noncompliant CAs. However, all checks on 1133 certificates exist for a specific reason involving the security of 1134 the entire system. Therefore, all checks MUST be enabled by default. 1135 Administrators and users ought to understand the security purpose for 1136 the various checks, and be clear on what security will be lost by 1137 disabling the check. 1139 4.1.1. Versions 1141 Although PKIX states that "implementations SHOULD be prepared to 1142 accept any version certificate", in practice this profile requires 1143 certain extensions that necessitate the use of Version 3 certificates 1144 for all but self-signed certificates used as trust anchors. 1145 Implementations that conform to this document MAY therefore reject 1146 Version 1 and Version 2 certificates in all other cases. 1148 4.1.2. SubjectName 1150 Certification Authority implementations MUST be able to create 1151 certificates with SubjectName fields with at least the following four 1152 attributes: CN, C, O, OU. Implementations MAY support other 1153 SubjectName attributes as well. The contents of these attributes 1154 SHOULD be configurable on a certificate by certificate basis, as 1155 these fields will likely be used by IKE implementations to match SPD 1156 policy. 1158 See Section 3.1.5 for details on how IKE implementations need to be 1159 able to process SubjectName field attributes for SPD policy lookup. 1161 4.1.2.1. Empty SubjectName 1163 IKE Implementations MUST accept certificates which contain an empty 1164 SubjectName field, as specified in PKIX. Identity information in 1165 such certificates will be contained entirely in the SubjectAltName 1166 extension. 1168 4.1.2.2. Specifying Hosts and not FQDN in SubjectName 1170 Implementations which desire to place host names that are not 1171 intended to be processed by recipients as FQDNs (for instance 1172 "Gateway Router") in the SubjectName MUST use the commonName 1173 attribute. 1175 4.1.2.3. EmailAddress 1177 As specified in PKIX, implementations MUST NOT populate 1178 DistinguishedNames with the emailAddress attribute. 1180 4.1.3. X.509 Certificate Extensions 1182 Conforming IKE implementations MUST recognize extensions which must 1183 or may be marked critical according to this specification. These 1184 extensions are: KeyUsage, SubjectAltName, and BasicConstraints. 1186 Certification Authority implementations SHOULD generate certificates 1187 such that the extension criticality bits are set in accordance with 1188 PKIX and this document. With respect to PKIX compliance, IKE 1189 implementations processing certificates MAY ignore the value of the 1190 criticality bit for extensions that are supported by that 1191 implementation, but MUST support the criticality bit for extensions 1192 that are not supported by that implementation. That is, a relying 1193 party processes all the extensions it is aware of whether the bit is 1194 true or false -- the bit says what happens when a relying party 1195 cannot process an extension. 1197 implements bit in cert PKIX mandate behavior 1198 ------------------------------------------------------ 1199 yes true true ok 1200 yes true false ok or reject 1201 yes false true ok or reject 1202 yes false false ok 1203 no true true reject 1204 no true false reject 1205 no false true reject 1206 no false false ok 1208 4.1.3.1. AuthorityKeyIdentifier and SubjectKeyIdentifier 1210 Implementations SHOULD NOT assume support for the 1211 AuthorityKeyIdentifier or SubjectKeyIdentifier extensions, and thus 1212 Certification Authority implementations SHOULD NOT generate 1213 certificate hierarchies which are overly complex to process in the 1214 absence of these extensions, such as those that require possibly 1215 verifying a signature against a large number of similarly named CA 1216 certificates in order to find the CA certificate which contains the 1217 key that was used to generate the signature. 1219 4.1.3.2. KeyUsage 1221 IKE uses an end-entity certificate in the authentication process. 1222 The end-entity certificate may be used for multiple applications. As 1223 such, the CA can impose some constraints on the manner that a public 1224 key ought to be used. The KeyUsage and ExtendedKeyUsage extensions 1225 apply in this situation. 1227 Since we are talking about using the public key to validate a 1228 signature, if the KeyUsage extension is present, then at least one of 1229 the digitalSignature or the nonRepudiation bits in the KeyUsage 1230 extension MUST be set (both can be set as well). It is also fine if 1231 other KeyUsage bits are set. 1233 A summary of the logic flow for peer cert validation follows: 1235 o If no KU extension, continue. 1236 o If KU present and doesn't mention digitalSignature or 1237 nonRepudiation (both, in addition to other KUs, is also fine), 1238 reject cert. 1239 o If none of the above, continue. 1241 4.1.3.3. PrivateKeyUsagePeriod 1243 PKIX recommends against the use of this extension. The 1244 PrivateKeyUsageExtension is intended to be used when signatures will 1245 need to be verified long past the time when signatures using the 1246 private keypair may be generated. Since IKE SAs are short-lived 1247 relative to the intended use of this extension in addition to the 1248 fact that each signature is validated only a single time, the 1249 usefulness of this extension in the context of IKE is unclear. 1250 Therefore, Certification Authority implementations MUST NOT generate 1251 certificates that contain the PrivateKeyUsagePeriod extension. If an 1252 IKE implementation receives a certificate with this set, it SHOULD 1253 ignore it. 1255 4.1.3.4. CertificatePolicies 1257 Many IKE implementations do not currently provide support for the 1258 CertificatePolicies extension. Therefore, Certification Authority 1259 implementations that generate certificates which contain this 1260 extension SHOULD NOT mark the extension as critical. 1262 4.1.3.5. PolicyMappings 1264 Many IKE implementations do not support the PolicyMappings extension. 1265 Therefore, implementations that generate certificates which contain 1266 this extension SHOULD NOT mark the extension as critical. 1268 4.1.3.6. SubjectAltName 1270 Deployments that intend to use an ID of either FQDN, USER_FQDN, 1271 IPV4_ADDR or IPV6_ADDR MUST issue certificates with the corresponding 1272 SubjectAltName fields populated with the same data. Implementations 1273 SHOULD generate only the following GeneralName choices in the 1274 SubjectAltName extension, as these choices map to legal IKEv1/ISAKMP/ 1275 IKEv2 Identification Payload types: rfc822Name, dNSName, or 1276 iPAddress. Although it is possible to specify any GeneralName choice 1277 in the Identification Payload by using the ID_DER_ASN1_GN ID type, 1278 implementations SHOULD NOT assume support for such functionality, and 1279 SHOULD NOT generate certificates that do so. 1281 4.1.3.6.1. dNSName 1283 This field MUST contain a fully qualified domain name. If the IKE ID 1284 type is FQDN then the dNSName field MUST match its contents. 1285 Implementations MUST NOT generate names that contain wildcards. 1286 Implementations MAY treat certificates that contain wildcards in this 1287 field as syntactically invalid. 1289 Although this field is in the form of an FQDN, IKE implementations 1290 SHOULD NOT assume that this field contains an FQDN that will resolve 1291 via the DNS, unless this is known by way of some out-of-band 1292 mechanism. Such a mechanism is out of the scope of this document. 1293 Implementations SHOULD NOT treat the failure to resolve as an error. 1295 4.1.3.6.2. iPAddress 1297 If the IKE ID type is IPV4_ADDR or IPV6_ADDR then the iPAddress field 1298 MUST match its contents. Note that although PKIX permits CIDR [14] 1299 notation in the "Name Constraints" extension, PKIX explicitly 1300 prohibits using CIDR notation for conveying identity information. In 1301 other words, the CIDR notation MUST NOT be used in the SubjectAltName 1302 extension. 1304 4.1.3.6.3. rfc822Name 1306 If the IKE ID type is USER_FQDN then the rfc822Name field MUST match 1307 its contents. Although this field is in the form of an Internet mail 1308 address, IKE implementations SHOULD NOT assume that this field 1309 contains a valid email address, unless this is known by way of some 1310 out-of-band mechanism. Such a mechanism is out of the scope of this 1311 document. 1313 4.1.3.7. IssuerAltName 1315 Certification Authority implementations SHOULD NOT assume that other 1316 implementations support the IssuerAltName extension, and especially 1317 should not assume that information contained in this extension will 1318 be displayed to end users. 1320 4.1.3.8. SubjectDirectoryAttributes 1322 The SubjectDirectoryAttributes extension is intended to convey 1323 identification attributes of the subject. IKE implementations MAY 1324 ignore this extension when it is marked non-critical, as PKIX 1325 mandates. 1327 4.1.3.9. BasicConstraints 1329 PKIX mandates that CA certificates contain this extension and that it 1330 be marked critical. IKE implementations SHOULD reject CA 1331 certificates that do not contain this extension. For backwards 1332 compatibility, implementations may accept such certificates if 1333 explicitly configured to do so, but the default for this setting MUST 1334 be to reject such certificates. 1336 4.1.3.10. NameConstraints 1338 Many IKE implementations do not support the NameConstraints 1339 extension. Since PKIX mandates that this extension be marked 1340 critical when present, Certification Authority implementations which 1341 are interested in maximal interoperability for IKE SHOULD NOT 1342 generate certificates which contain this extension. 1344 4.1.3.11. PolicyConstraints 1346 Many IKE implementations do not support the PolicyConstraints 1347 extension. Since PKIX mandates that this extension be marked 1348 critical when present, Certification Authority implementations which 1349 are interested in maximal interoperability for IKE SHOULD NOT 1350 generate certificates which contain this extension. 1352 4.1.3.12. ExtendedKeyUsage 1354 The CA SHOULD NOT include the ExtendedKeyUsage (EKU) extension in 1355 certificates for use with IKE. Note that there were three IPsec 1356 related object identifiers in EKU that were assigned in 1999. The 1357 semantics of these values were never clearly defined. The use of 1358 these three EKU values in IKE/IPsec is obsolete and explicitly 1359 deprecated by this specification. CAs SHOULD NOT issue certificates 1360 for use in IKE with them. (For historical reference only, those 1361 values were id-kp-ipsecEndSystem, id-kp-ipsecTunnel, and id-kp- 1362 ipsecUser.) 1364 The CA SHOULD NOT mark the EKU extension in certificates for use with 1365 IKE and one or more other applications. Nevertheless, this document 1366 defines an ExtendedKeyUsage keyPurposeID that MAY be used to limit a 1367 certificate's use: 1369 id-kp-ipsecIKE OBJECT IDENTIFIER ::= { id-kp 17 } 1371 where id-kp is defined in RFC-3280 [5]. If a certificate is intended 1372 to be used with both IKE and other applications, and one of the other 1373 applications requires use of an EKU value, then such certificates 1374 MUST contain either the keyPurposeID id-kp-ipsecIKE or 1375 anyExtendedKeyUsage [5] as well as the keyPurposeID values associated 1376 with the other applications. Similarly, if a CA issues multiple 1377 otherwise-similar certificates for multiple applications including 1378 IKE, and it is intended that the IKE certificate NOT be used with 1379 another application, the IKE certificate MAY contain an EKU extension 1380 listing a keyPurposeID of id-kp-ipsecIKE to discourage its use with 1381 the other application. Recall however, EKU extensions in 1382 certificates meant for use in IKE are NOT RECOMMENDED. 1384 A summary of the logic flow for peer certificate validation regarding 1385 the EKU extension follows: 1387 o If no EKU extension, continue. 1388 o If EKU present AND contains either id-kp-ipsecIKE or 1389 anyExtendedKeyUsage, continue. 1390 o Otherwise, reject cert. 1392 4.1.3.13. CRLDistributionPoints 1394 Because this document deprecates the sending of CRLs in-band, the use 1395 of CRLDistributionPoints (CDP) becomes very important if CRLs are 1396 used for revocation checking (as opposed to say Online Certificate 1397 Status Protocol - OCSP [15]). The IPsec peer either needs to have a 1398 URL for a CRL written into its local configuration, or it needs to 1399 learn it from CDP. Therefore, Certification Authority 1400 implementations SHOULD issue certificates with a populated CDP. 1402 Failure to validate the CRLDistributionPoints/ 1403 IssuingDistributionPoint pair can result in CRL substitution where an 1404 entity knowingly substitutes a known good CRL from a different 1405 distribution point for the CRL which is supposed to be used which 1406 would show the entity as revoked. IKE implementations MUST support 1407 validating that the contents of CRLDistributionPoints match those of 1408 the IssuingDistributionPoint to prevent CRL substitution when the 1409 issuing CA is using them. At least one CA is known to default to 1410 this type of CRL use. See Section 4.2.2.5 for more information. 1412 CDPs SHOULD be "resolvable". Several non-compliant Certification 1413 Authority implementations are well known for including unresolvable 1414 CDPs like http://localhost/path_to_CRL and http:///path_to_CRL which 1415 are equivalent to failing to include the CDP extension in the 1416 certificate. 1418 See PKIX docs for CRLDistributionPoints intellectual property rights 1419 (IPR) information. Note that both the CRLDistributionPoints and 1420 IssuingDistributionPoint extensions are RECOMMENDED but not REQUIRED 1421 by PKIX, so there is no requirement to license any IPR. 1423 4.1.3.14. InhibitAnyPolicy 1425 Many IKE implementations do not support the InhibitAnyPolicy 1426 extension. Since PKIX mandates that this extension be marked 1427 critical when present, Certification Authority implementations which 1428 are interested in maximal interoperability for IKE SHOULD NOT 1429 generate certificates which contain this extension. 1431 4.1.3.15. FreshestCRL 1433 IKE implementations MUST NOT assume that the FreshestCRL extension 1434 will exist in peer certificates. Note that most IKE implementations 1435 do not support delta CRLs. 1437 4.1.3.16. AuthorityInfoAccess 1439 PKIX defines the AuthorityInfoAccess extension, which is used to 1440 indicate "how to access CA information and services for the issuer of 1441 the certificate in which the extension appears." Because this 1442 document deprecates the sending of CRLs in band, the use of 1443 AuthorityInfoAccess (AIA) becomes very important if OCSP [15] is to 1444 be used for revocation checking (as opposed to CRLs). The IPsec peer 1445 either needs to have a URI for the OCSP query written into its local 1446 configuration, or it needs to learn it from AIA. Therefore, 1447 implementations SHOULD support this extension, especially if OCSP 1448 will be used. 1450 4.1.3.17. SubjectInfoAccess 1452 PKIX defines the SubjectInfoAccess certificate extension, which is 1453 used to indicate "how to access information and services for the 1454 subject of the certificate in which the extension appears." This 1455 extension has no known use in the context of IPsec. Conformant IKE 1456 implementations SHOULD ignore this extension when present. 1458 4.2. X.509 Certificate Revocation Lists 1460 When validating certificates, IKE implementations MUST make use of 1461 certificate revocation information, and SHOULD support such 1462 revocation information in the form of CRLs, unless non-CRL revocation 1463 information is known to be the only method for transmitting this 1464 information. Deployments that intend to use CRLs for revocation 1465 SHOULD populate the CRLDistributionPoints extension. Therefore 1466 Certification Authority implementations MUST support issuing 1467 certificates with this field populated according to administrator's 1468 needs. IKE implementations MAY provide a configuration option to 1469 disable use of certain types of revocation information, but that 1470 option MUST be off by default. Such an option is often valuable in 1471 lab testing environments. 1473 4.2.1. Multiple Sources of Certificate Revocation Information 1475 IKE implementations which support multiple sources of obtaining 1476 certificate revocation information MUST act conservatively when the 1477 information provided by these sources is inconsistent: when a 1478 certificate is reported as revoked by one trusted source, the 1479 certificate MUST be considered revoked. 1481 4.2.2. X.509 Certificate Revocation List Extensions 1483 4.2.2.1. AuthorityKeyIdentifier 1485 Certification Authority implementations SHOULD NOT assume that IKE 1486 implementations support the AuthorityKeyIdentifier extension, and 1487 thus SHOULD NOT generate certificate hierarchies which are overly 1488 complex to process in the absence of this extension, such as those 1489 that require possibly verifying a signature against a large number of 1490 similarly named CA certificates in order to find the CA certificate 1491 which contains the key that was used to generate the signature. 1493 4.2.2.2. IssuerAltName 1495 Certification Authority implementations SHOULD NOT assume that IKE 1496 implementations support the IssuerAltName extension, and especially 1497 should not assume that information contained in this extension will 1498 be displayed to end users. 1500 4.2.2.3. CRLNumber 1502 As stated in PKIX, all issuers conforming to PKIX MUST include this 1503 extension in all CRLs. 1505 4.2.2.4. DeltaCRLIndicator 1507 4.2.2.4.1. If Delta CRLs Are Unsupported 1509 IKE implementations that do not support delta CRLs MUST reject CRLs 1510 which contain the DeltaCRLIndicator (which MUST be marked critical 1511 according to PKIX) and MUST make use of a base CRL if it is 1512 available. Such implementations MUST ensure that a delta CRL does 1513 not "overwrite" a base CRL, for instance in the keying material 1514 database. 1516 4.2.2.4.2. Delta CRL Recommendations 1518 Since some IKE implementations that do not support delta CRLs may 1519 behave incorrectly or insecurely when presented with delta CRLs, 1520 administrators and deployers should consider whether issuing delta 1521 CRLs increases security before issuing such CRLs. And, if all the 1522 elements in the VPN and PKI systems do not adequately support Delta 1523 CRLs, then their use should be questioned. 1525 The authors are aware of several implementations which behave in an 1526 incorrect or insecure manner when presented with delta CRLs. See 1527 Appendix B for a description of the issue. Therefore, this 1528 specification RECOMMENDS NOT issuing delta CRLs at this time. On the 1529 other hand, failure to issue delta CRLs may expose a larger window of 1530 vulnerability if a full CRL is not issued as often as delta CRLs 1531 would be. See the Security Considerations section of PKIX [5] for 1532 additional discussion. Implementors as well as administrators are 1533 encouraged to consider these issues. 1535 4.2.2.5. IssuingDistributionPoint 1537 A CA that is using CRLDistributionPoints may do so to provide many 1538 "small" CRLs, each only valid for a particular set of certificates 1539 issued by that CA. To associate a CRL with a certificate, the CA 1540 places the CRLDistributionPoints extension in the certificate, and 1541 places the IssuingDistributionPoint in the CRL. The 1542 distributionPointName field in the CRLDistributionPoints extension 1543 MUST be identical to the distributionPoint field in the 1544 IssuingDistributionPoint extension. At least one CA is known to 1545 default to this type of CRL use. See Section 4.1.3.13 for more 1546 information. 1548 4.2.2.6. FreshestCRL 1550 Given the recommendations against Certification Authority 1551 implementations generating delta CRLs, this specification RECOMMENDS 1552 that implementations do not populate CRLs with the FreshestCRL 1553 extension, which is used to obtain delta CRLs. 1555 5. Configuration Data Exchange Conventions 1557 Below we present a common format for exchanging configuration data. 1558 Implementations MUST support these formats, MUST support receiving 1559 arbitrary whitespace at the beginning and end of any line, MUST 1560 support receiving arbitrary line lengths although they SHOULD 1561 generate lines less than 76 characters, and MUST support receiving 1562 the following three line-termination disciplines: LF (US-ASCII 10), 1563 CR (US-ASCII 13), and CRLF. 1565 5.1. Certificates 1567 Certificates MUST be Base64 encoded and appear between the following 1568 delimiters: 1570 -----BEGIN CERTIFICATE----- 1571 -----END CERTIFICATE----- 1573 5.2. CRLs and ARLs 1575 CRLs and ARLs MUST be Base64 encoded and appear between the following 1576 delimiters: 1578 -----BEGIN CRL----- 1579 -----END CRL----- 1581 5.3. Public Keys 1583 IKE implementations MUST support two forms of public keys: 1584 certificates and so-called "raw" keys. Certificates should be 1585 transferred in the same form as above. A raw key is only the 1586 SubjectPublicKeyInfo portion of the certificate, and MUST be Base64 1587 encoded and appear between the following delimiters: 1589 -----BEGIN PUBLIC KEY----- 1590 -----END PUBLIC KEY----- 1592 5.4. PKCS#10 Certificate Signing Requests 1594 A PKCS#10 [9] Certificate Signing Request MUST be Base64 encoded and 1595 appear between the following delimiters: 1597 -----BEGIN CERTIFICATE REQUEST----- 1598 -----END CERTIFICATE REQUEST----- 1600 6. Security Considerations 1602 6.1. Certificate Request Payload 1604 The Contents of CERTREQ are not encrypted in IKE. In some 1605 environments this may leak private information. Administrators in 1606 some environments may wish to use the empty Certification Authority 1607 option to prevent such information from leaking, at the cost of 1608 performance. 1610 6.2. IKEv1 Main Mode 1612 Certificates may be included in any message, and therefore 1613 implementations may wish to respond with CERTs in a message that 1614 offers privacy protection, in Main Mode messages 5 and 6. 1615 Implementations may not wish to respond with CERTs in the second 1616 message, thereby violating the identity protection feature of Main 1617 Mode in IKEv1. 1619 6.3. Disabling Certificate Checks 1621 It is important to note that anywhere this document suggests 1622 implementors provide users with the configuration option to simplify, 1623 modify, or disable a feature or verification step, there may be 1624 security consequences for doing so. Deployment experience has shown 1625 that such flexibility may be required in some environments, but 1626 making use of such flexibility can be inappropriate in others. Such 1627 configuration options MUST default to "enabled" and it is appropriate 1628 to provide warnings to users when disabling such features. 1630 7. Intellectual Property Rights 1632 No new intellectual property rights are introduced by this document. 1634 8. IANA Considerations 1636 There are no known numbers which IANA will need to manage. 1638 9. References 1640 9.1. Normative References 1642 [1] Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)", 1643 RFC 2409, November 1998. 1645 [2] Maughan, D., Schneider, M., and M. Schertler, "Internet Security 1646 Association and Key Management Protocol (ISAKMP)", RFC 2408, 1647 November 1998. 1649 [3] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", 1650 draft-ietf-ipsec-ikev2-15 (work in progress), August 2004. 1652 [4] Kent, S. and R. Atkinson, "Security Architecture for the 1653 Internet Protocol", RFC 2401, November 1998. 1655 [5] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet X.509 1656 Public Key Infrastructure Certificate and Certificate Revocation 1657 List (CRL) Profile", RFC 3280, April 2002. 1659 [6] Piper, D., "The Internet IP Security Domain of Interpretation 1660 for ISAKMP", RFC 2407, November 1998. 1662 [7] Bradner, S., "Key words for use in RFCs to Indicate Requirement 1663 Levels", BCP 14, RFC 2119, March 1997. 1665 [8] Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981. 1667 [9] Kaliski, B., "PKCS #10: Certification Request Syntax Version 1668 1.5", RFC 2314, March 1998. 1670 9.2. Informative References 1672 [10] Kent, S. and K. Seo, "Security Architecture for the Internet 1673 Protocol", draft-ietf-ipsec-rfc2401bis-06 (work in progress), 1674 March 2005. 1676 [11] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) 1677 Specification", RFC 1883, December 1995. 1679 [12] Eastlake, D., "Domain Name System Security Extensions", 1680 RFC 2535, March 1999. 1682 [13] Lynn, C., "X.509 Extensions for IP Addresses and AS 1683 Identifiers", draft-ietf-pkix-x509-ipaddr-as-extn-03 (work in 1684 progress), September 2003. 1686 [14] Fuller, V., Li, T., Yu, J., and K. Varadhan, "Classless Inter- 1687 Domain Routing (CIDR): an Address Assignment and Aggregation 1688 Strategy", RFC 1519, September 1993. 1690 [15] Myers, M., Ankney, R., Malpani, A., Galperin, S., and C. Adams, 1691 "X.509 Internet Public Key Infrastructure Online Certificate 1692 Status Protocol - OCSP", RFC 2560, June 1999. 1694 [16] Arsenault, A. and S. Turner, "Internet X.509 Public Key 1695 Infrastructure: Roadmap", draft-ietf-pkix-roadmap-09 (work in 1696 progress), July 2002. 1698 Appendix A. Change History 1700 November 2005 (-07) 1702 * 3.1 - renumbered table notes to avoid confusion with references 1703 (9 Nov 2005 pki4ipsec email from Jim Schaad) 1704 * 3.2.2 - changed "signing certificate" to "a certificate used 1705 for signing" (9 Nov 2005 pki4ipsec email from Jim Schaad) 1706 * 4.1 - added text re: implications of disabling checks ("escape 1707 clause") (8 Nov 2005 pki4ipsec email from Bill Sommerfeld, 10 1708 Nov 2005 pki4ipsec email from Gregory M Lebovitz) 1709 * 4.1.3.2 - removed text from pseudocode: "If told (by 1710 configuration) to ignore KeyUsage (KU), accept cert regardless 1711 of its markings." 1712 * 4.1.3.12 - replaced text with clearer text (8 Nov 2005 1713 pki4ipsec email from Bill Sommerfeld) 1714 * 4.1.3.12 - removed text from pseudocode: "If told (by 1715 configuration) to ignore ExtendedKeyUsage (EKU), accept cert 1716 regardless of the presence or absence of the extension." 1717 * 4.1.3.17 - removed gratuitous "private" modifier from 1718 SubjectInfoAccess section (9 Nov 2005 pki4ipsec email from Jim 1719 Schaad) 1720 * 4.2.2.4.2 - clarified delta CRL text so that it no longer could 1721 be read as implying that full CRLs can't be issued at the time 1722 a certificate is revoked. (9 Nov 2005 pki4ipsec email from Jim 1723 Schaad) 1724 * Security Considerations - added "Disabling Certificate Checks" 1725 section 1727 October 2005 (-06) 1728 * 4.1.3.12 - added text re: id-kp-ipsecIKE 1730 July 2005 (-05) 1732 * 3.1 - added "See 2401bis [10], section 4.4.3.2 for more 1733 details." to resolve issue #561. 1734 * 3.1.10 - added text pointing to PAD in 2401bis [10] to 1735 discussion of binding identity to policy. 1737 December 2004 (-04) 1739 * Added Paul Hoffman's text from issue #708 1740 * Added text explaining that it's possible for a recipient to 1741 receive CERT payloads containing certs that the recipient 1742 considers a trust anchor (15 Nov 2004 pki4ipsec email from 1743 Peter Williams) 1744 * Replaced text in 4.1.3 with Kent's text (issue #655) (22 Nov 1745 2004 pki4ipsec email from Stephen Kent, Paul Hoffman) 1747 September 2004 (-03) 1749 * Minor editorial changes in abstract and introduction clarifing 1750 when something is from IPsec, IKE, etc 1751 * Minor editorial changes throughout 1752 * Fixed "Certification Authority" instead of "Certificate 1753 Authority" 1754 * Cleaned up initiator/responder when really referred to sender/ 1755 recipient 1756 * Fixed inconsistancy in text by making sure that all text on the 1757 topic of sending CERTREQs follow Gregory Lebovitz's proposal 1758 for CERT payloads: "should deal with all the CRL, Intermediat 1759 Certs, Trust Anchors, etc OOB of IKE; MUST be able to send and 1760 receive EE cert payload; only real exception is Intermediate 1761 Cets which MAY be sent and SHOULD be able to be receivable (but 1762 in reality there are very few hierarchies in operation, so 1763 really it's a corner case); SHOULD NOT send the other stuff 1764 (CRL, Trust Anchors, etc) in cert payloads in IKE; SHOULD be 1765 able to accept the other stuff if by chance it gets sent, 1766 though we hope they don't get sent" 1767 * 3.1 - removed text suggesting that it would be reasonable to 1768 terminate IKEv2 processing if the initiator were to receive a 1769 responder-generated IDr 1770 * 3.1.1 - noted that certificates may contain multiple IP 1771 addresses 1773 * 3.1.9 - removed (temporarily?) confusing text stating that 1774 overlapping policies was prohibited, text which was 1775 inconsistent with text right above it 1776 * 3.2.7.2 - SHOULD changed to MUST terminate if peer's 1777 certificate chain violates local policy 1778 * 3.3 - removed text implying that pausing in the middle of an 1779 IKE exchange in order to obtain revocation status information 1780 via http or OCSP would reduce latency in IKE 1781 * 4.2 - allow deployments that don't wish to populate CDP (for 1782 instance if a source of revocation information is configured 1783 via some other means) to skip populating CDP, making consistent 1784 with 4.1.3.13 and the issues IPR spelled out in PKIX 1785 * Somehow a CRL out-of-band configuration format had been 1786 omitted. 1787 * #555: Kent-1.0 Introduction - document now references IKEv2 1788 * #559: Kent-Profile Document 3.1.0 - use sender/recipient 1789 instead of agent 1790 * #564: Kent-Profile Document 3.1.1 - specified that support for 1791 ID_IPV4_ADDR and/or ID_IPV6_ADDR are contingent on device 1792 support for IPv4 and/or IPv6 1793 * #568: Kent-Profile document 3.1.4 - specified that there wasn't 1794 a standard and besides no one has implemented it 1795 * #571: Kent-Profile document 3.1.8 - tried to be even more 1796 clearer than was asked for by spelling things out in detail 1797 * #572: Kent-Profile document 3.1.8 Formerly issue #18 - now 1798 specifies that it's only a local matter if that information is 1799 not coordinated with other administrators 1800 * #573: Kent-Profile document 3.2.3/Myers - revocation 1801 information no longer exchanged in-band, plus Mike Myers has 1802 submitted an OCSP w/IKE draft, which is references by this 1803 document. 1804 * #578 Kent-Profile document 4.0.0 - went through entire PKIX 1805 profile section and prefaced "implementation" with "IKE" or 1806 "Certification Authority" wherever it was sure to be one or the 1807 other 1808 * #581: Kent-Profile document 4.1.3.9 - replaced description with 1809 text from RFC 2459 1810 * #584: Maillist-Lebovitz PKI Life Cycle-Revocation - fixed 1811 * #586: Maillist-Allison Empty CertReq - there is now lots of 1812 text dealing with when empty certreqs are permitted 1813 * 3.2.7.1 - CERTREQ only mandatory if in-band exchange of keymat 1814 is desired (28 Jul 2004 pki4ipsec email from jknowles@ 1815 SonicWALL.com) 1816 * 3.3.6 - clarified that "non-compliant" means not sending a 1817 CERTREQ (28 Jul 2004 pki4ipsec email from jknowles@ 1818 SonicWALL.com) 1820 * 3.2.7.1 - fixed contradition: mandatory to respond to CERTREQ 1821 UNLESS configured not to (28 Jul 2004 pki4ipsec email from 1822 jknowles@SonicWALL.com) 1823 * 3.2.9.2 and 3.2.9.3 - CERTREQ contains an issuer name only for 1824 IKEv2 (19 Sep 2004 email from Charlie Kaufman) 1825 * Answered 'Section 3.1.9 para 2: "The initiator MUST know by 1826 policy..." is a difficult to interpret requirement. It could 1827 mean that it must be possible to configure in policy which ID 1828 is to be sent. Did you mean "the initiator must decide...", 1829 where the decision might be wired into a particular 1830 implementation?' by changing it to be merely descriptive, and 1831 to refer to policy configuration (19 Sep 2004 email from 1832 Charlie Kaufman) 1833 * IPSEC -> IPsec (19 Sep 2004 email from Charlie Kaufman) 1834 * 3.1.1 para 1: "MUST be stored" changed to "MUST be encoded" (19 1835 Sep 2004 email from Charlie Kaufman) 1836 * 3.1.5 para 2 - made it clear that empty SubjectNames are 1837 permitted by PKIX in certificates, but this document doesn't 1838 permit them in ID (19 Sep 2004 email from Charlie Kaufman) 1839 * 3.2.7.1 - clarified by specifying that it's a trust anchor 1840 that's being chosen, not end-entity certificate (19 Sep 2004 1841 email from Charlie Kaufman) 1842 * 3.3.9.5 - fixed confusing last paragraph (19 Sep 2004 email 1843 from Charlie Kaufman) 1844 * 3.3.10.3 - made it more clear that this section is really 1845 talking about duplicate certificate payloads (19 Sep 2004 email 1846 from Charlie Kaufman) 1847 * 4.1.2.2 para 2 and 3 - moved to 3.1.x section where is belongs 1848 (19 Sep 2004 email from Charlie Kaufman) 1849 * 4.1.3.5 - the last sentence of 4.1.3.4 copied here (19 Sep 2004 1850 email from Charlie Kaufman) 1851 * 4.2.2.4.2 - SHOULD -> should (19 Sep 2004 email from Charlie 1852 Kaufman) 1853 * 3.2.5 and 3.3.4 - added description of URL scheme support (16 1854 Aug 2004 pki4ipsec email from Tero Kivinen) 1855 * Removed 6.1 and 6.3 because they were either incorrect or 1856 didn't add any new security considerations above and beyond the 1857 IKE documents. 1858 August 2004 (-02) (Edited by Gregory Lebovitz, with XML formatting 1859 and cross-referencing by Paul Knight) 1861 * 3.1.1 the text between the **s was added to paragraph, per the 1862 question that arose in IETF60 WG session: Implementations MUST 1863 be capable of verifying that the address contained in the ID is 1864 the same as the peer source address **contained in the outer 1865 most IP header**. 1867 * 3.2.7 - added HTTP_CERT_LOOKUP_SUPPORTED to this section and 1868 described its use - #38 1869 * 3.3 - changed back sending of intermediate CA certificates from 1870 SHOULD NOT to MAY (for backward compatibility). Added text to 1871 explain further why we want to stay away from actually doing it 1872 though. 1873 * 3.3.8 - changed text per Knowles/Korver 2004.07.28. 1874 * 3.3.9.5 - Change discard of Irrelevant Certificates from may to 1875 SHOULD - #23(Kent 2004.04.26) 1876 * 4.1.3.2 KU - re-worked to reflect discussion on list and in 1877 IETF60 - #36 1878 * 4.1.3.12 EKU - re-worked to reflect discussion on list and in 1879 IETF60 - #36 1880 * [IKEv2] update the reference to the -14 draft of May 29, 2004 1882 July 2004 (-01) (Edited by Gregory Lebovitz) 1884 * Changed ISAKMP references in Abstract and Intro to IKE. 1885 * Editorial changes to make the text conform with the summary 1886 table in 3.1, especially in the text following the table in 1887 3.1. Particular note should be paid to changes in section 1888 3.5.1. 1889 * Sect 3.1.1 - editorial changes to aid in clarification. Added 1890 text on when deployers might consider using IP addr, but 1891 strongly encouraged not to. 1892 * Sect 3.1.8 removed IP address from list of practically used ID 1893 types. 1894 * 3.1.9 overhauled (per Kivinen, July 18) 1895 * 3.2 - added IKEv2's Hash and URL of x.509 to list of those 1896 profiled and gave it its own section, now 3.2.5 1897 * added note in CRL/ARL section about revocation occurring OOB of 1898 IKE 1899 * deleted ARL as its own section and collapsed it into Revocation 1900 Lists (CRL and ARL) for consciseness. Renumbered accordingly. 1901 * Sect 3.2.7.2 - Changed from MUST not send empty certreqs to 1902 SHOULD send CERTREQs which contain CA fields with direction on 1903 how, but MAY send empty CERTREQs in certain case. Use case 1904 added, and specifics of both initiator and responder behavior 1905 listed. 1906 * APPENDIX C added to fill out the explanation (mostly discussion 1907 from list). 1908 * 3.3 - clarified that sending CRLs and chaining certs is 1909 deprecated. 1910 * added IKEv2's Hash and URL of x.509 to list of those profiled 1911 and gave it its own section. Condensed ARL into CRL and 1912 renumbered accordingly. 1914 * duplicate section was removed, renumbered accordingly 1915 * 3.3.10.2 - title changed. sending chaining becomes SHOULD NOT. 1916 * 4.1.2 added text to explicity call out support for CN, C, O, OU 1917 * collapsed 4.1.2.3 into 4.1.2.2 and renumbered accordingly. 1918 * Collapsed 4.1.3.2 into 4.1.3.1 and renumbered accordingly 1919 * Edited 4.1.3.2 Key Usage and 4.1.3.12 ExtKey Usage according to 1920 Hoffman, July18 1921 * 4.1.3.3 if receive cert w/ PKUP, ignore it. 1922 * 4.1.3.13 - CDP changed text to represent SHOULD issue, and how 1923 important CDP becomes when we do not send CRLs in-band. Added 1924 SHOULD for CDPs actually being resolvable (reilly email). 1925 * Reordered 6.4 for better clarity. 1926 * Added Rescorla to Acknowledgements section, as he is no longer 1927 listed as an editor, since -00. 1929 May 2004 (renamed draft-ietf-pki4ipsec-ikecert-profile-00.txt) 1930 (edited by Brian Korver) 1932 * Made it clearer that the format of the ID_IPV4_ADDR payload 1933 comes from RFC791 and is nothing new. (Tero Kivinen Feb 29) 1934 * Permit implementations to skip verifying that the peer source 1935 address matches the contents of ID_IPV{4,6}_ADDR. (Tero 1936 Kivinen Feb 29, Gregory Lebovitz Feb 29) 1937 * Removed paragraph suggesting that implementations favor 1938 unauthenticated peer source addresses over an unauthenticated 1939 ID for initial policy lookup. (Tero Kivinen Feb 29, Gregory 1940 Lebovitz Feb 29) 1941 * Removed some text implying RSA encryption mode was in scope. 1942 (Tero Kivinen Feb 29) 1943 * Relaxed deprecation of PKCS#7 CERT payloads. (Tero Kivinen Feb 1944 29) 1945 * Made it clearer that out-of-scope local heuristics should be 1946 used for picking an EE cert to use when generating CERTREQ, not 1947 when receiving CERTREQ. (Tero Kivinen Feb 29) 1948 * Made it clearer that CERT processing can be skipped when the 1949 contents of a CERT are already known. (Tero Kivinen Feb 29) 1950 * Implementations SHOULD generate BASE64 lines less than 76 1951 characters. (Tero Kivinen Feb 29) 1952 * Added "Except where specifically stated in this document, 1953 implementations MUST conform to the requirements of PKIX" 1954 (Steve Hanna Oct 7, 2003) 1955 * RECOMMENDS against populating the ID payload with IP addresses 1956 due to interoperability issues such as problem with NAT 1957 traversal. (Gregory Lebovitz May 14) 1958 * Changed "as revoked by one source" to "as revoked by one 1959 trusted source". (Michael Myers, May 15) 1961 * Specifying Certificate Authorities section needed to be 1962 regularized with Gregory Lebovitz's CERT proposal from -04. 1963 (Tylor Allison, May 15) 1964 * Added text specifying how recipients SHOULD NOT be expected to 1965 iterate over multiple end-entity certs. (Tylor Allison, May 1966 15) 1967 * Modified text to refer to IKEv2 as well as IKEv1/ISAKMP where 1968 relevant. 1969 * IKEv2: Explained that IDr sent by responder doesn't have to 1970 match the [IDr] sent initiator in second exchange. 1971 * IKEv2: Noted that "The identity ... does not necessarily have 1972 to match anything in the CERT payload" (S3.5) is not 1973 contradicted by SHOULD in this document. 1974 * IKEv2: Noted that ID_USER_FQDN renamed to ID_RFC822_ADDR, and 1975 ID_USER_FQDN would be used exclusively in this document. 1976 * IKEv2: Declared that 3 new CERTREQ and CERT types are not 1977 profiled in this document (well, at least not yet, pending WG 1978 discussion of what to do -- note that they are only SHOULDs in 1979 IKEv2). 1980 * IKEv2: Noted that CERTREQ payload changed from DN to SHA-1 of 1981 SubjectPublicKeyInfo. 1982 * IKEv2: Noted new requirement that specifies that the first 1983 certificate sent MUST be the EE cert (section 3.6). 1985 February 2004 (-04) 1987 * Minor editorial changes to clean up language 1988 * Deprecate in-band exchange of CRLs 1989 * Incorporated Gregory Lebovitz's proposal for CERT payloads: 1990 "should deal with all the CRL, Intermediat Certs, Trust 1991 Anchors, etc OOB of IKE; MUST be able to send and receive EE 1992 cert payload; only real exception is Intermediate Cets which 1993 MAY be sent and SHOULD be able to be receivable (but in reality 1994 there are very few hierarchies in operation, so really it's a 1995 corner case); SHOULD NOT send the other stuff (CRL, Trust 1996 Anchors, etc) in cert payloads in IKE; SHOULD be able to accept 1997 the other stuff if by chance it gets sent, though we hope they 1998 don't get sent" 1999 * Incorporated comments contained in Oct 7, 2003 email from 2000 steve.hanna@sun.com to ipsec@lists.tislabs.com 2001 * Moved text from "Profile of ISAKMP" Background section to each 2002 payload section (removing duplication of these sections) 2003 * Removed "Certificate-Related Playloads in ISAKMP" section since 2004 it was not specific to IKE. 2005 * Incorporated Gregory Lebovitz's table in the "Identification 2006 Payload" section 2008 * Moved text from "binding identity to policy" sections to each 2009 payload section 2010 * Moved text from "IKE" section into now-combined "IKE/ISAKMP" 2011 section 2012 * ID_USER_FQDN and ID_FQDN promoted to MUST from MAY 2013 * Promoted sending ID_DER_ASN1_DN to MAY from SHOULD NOT, and 2014 receiving from MUST from MAY 2015 * Demoted ID_DER_ASN1_GN to MUST NOT 2016 * Demoted populating SubjectName in place of populating the 2017 dNSName from SHOULD NOT to MUST NOT and removed the text 2018 regarding domainComponent 2019 * Revocation information checking MAY now be disabled, although 2020 not by default 2021 * Aggressive Mode removed from this profile 2023 June 2003 (-03) 2025 * Minor editorial changes to clean up language 2026 * Minor additional clarifying text 2027 * Removed hyphenation 2028 * Added requirement that implementations support configuration 2029 data exchange having arbitrary line lengths 2031 February 2003 (-02) 2033 * Word choice: move from use of "root" to "trust anchor", in 2034 accordance with PKIX 2035 * SBGP note and reference for placing address subnet and range 2036 information into certificates 2037 * Clarification of text regarding placing names of hosts into the 2038 Name commonName attribute of SubjectName 2039 * Added table to clarify text regarding processing of the 2040 certificate extension criticality bit 2041 * Added text underscoring processing requirements for 2042 CRLDistributionPoints and IssuingDistributionPoint 2044 October 2002, Reorganization (-01) 2046 June 2002, Initial Draft (-00) 2048 Appendix B. The Possible Dangers of Delta CRLs 2050 The problem is that the CRL processing algorithm is sometimes written 2051 incorrectly with the assumption that all CRLs are base CRLs and it is 2052 assumed that CRLs will pass content validity tests. Specifically, 2053 such implementations fail to check the certificate against all 2054 possible CRLs: if the first CRL that is obtained from the keying 2055 material database fails to decode, no further revocation checks are 2056 performed for the relevant certificate. This problem is compounded 2057 by the fact that implementations which do not understand delta CRLs 2058 may fail to decode such CRLs due to the critical DeltaCRLIndicator 2059 extension. The algorithm that is implemented in this case is 2060 approximately: 2062 o fetch newest CRL 2063 o check validity of CRL signature 2064 o if CRL signature is valid then 2065 o if CRL does not contain unrecognized critical extensions 2066 o and certificate is on CRL then 2067 o set certificate status to revoked 2069 The authors note that a number of PKI toolkits do not even provide a 2070 method for obtaining anything but the newest CRL, which in the 2071 presence of delta CRLs may in fact be a delta CRL, not a base CRL. 2073 Note that the above algorithm is dangerous in many ways. See PKIX 2074 [5] for the correct algorithm. 2076 Appendix C. More on Empty CERTREQs 2078 Sending empty certificate requests is commonly used in 2079 implementations, and in the IPsec interop meetings, vendors have 2080 generally agreed that it means that send all/any end-entity 2081 certificates you have (if multiple end-entity certificates are sent, 2082 they must have same public key, as otherwise the other end does not 2083 know which key was used). For 99% of cases the client have exactly 2084 one certificate and public key, so it really doesn't matter, but the 2085 server might have multiple, thus it simply needs to say to the 2086 client, use any certificate you have. If we are talking about 2087 corporate vpns etc, even if the client have multiple certificates or 2088 keys, all of them would be usable when authenticating to the server, 2089 so client can simply pick one. 2091 If there is some real difference on which cert to use (like ones 2092 giving different permissions), then the client must be configured 2093 anyways, or it might even ask the user which one to use (the user is 2094 the only one who knows whether he needs admin privileges, thus needs 2095 to use admin cert, or is the normal email privileges ok, thus using 2096 email only cert). 2098 99% of the cases the client have exactly one certificate, so it will 2099 send it. In 90% of the rest of the cases, any of the certificates is 2100 ok, as they are simply different certificates from same CA, or 2101 different CAs for the same corporate VPN, thus any of them is ok. 2103 Sending empty certificate requests has been agreed there to mean 2104 "give me your cert; any cert". 2106 Justification: 2108 o Responder first does all it can to send a certreq with a CA, check 2109 for IP match in SPD, have a default set of CAs to use in ambiguous 2110 cases, etc. 2111 o sending empty certreq's is fairly common in implementations today, 2112 and is generally accepted to mean "send me a cert, any cert that 2113 works for you" 2114 o saves responder sending potentially 100's of certs, the 2115 fragmentation problems that follow, etc. 2116 o in +90% of use cases, Initiators have exactly 1 cert 2117 o in +90% of the remaining use cases, the multiple certs it has are 2118 issued by the same CA 2119 o in the remaining use case(s) -- if not all the others above -- the 2120 Initiator will be configured explicitly with which cert to send, 2121 so responding to an empty certreq is easy. 2123 The following example shows why initiators need to have sufficient 2124 policy definition to know which certificate to use for a given 2125 connection it initiates. 2127 EXAMPLE: Your client (initiator) is configured with VPN policies for 2128 gateways A and B (representing perhaps corporate partners). 2130 The policies for the two gateways look something like: 2132 Acme Company policy (gateway A) 2133 Engineering can access 10.1.1.0 2134 Trusted CA: CA-A, Trusted Users: OU=Engineering 2135 Partners can access 20.1.1.0 2136 Trusted CA: CA-B, Trusted Users: OU=AcmePartners 2138 Bizco Company policy (gateway B) 2139 sales can access 30.1.1.0 2140 Trusted CA: CA-C, Trusted Users: OU=Sales 2141 Partners can access 40.1.1.0 2142 Trusted CA: CA-B, Trusted Users: OU=BizcoPartners 2144 You are an employee of Acme and you are issued the following 2145 certificates: 2147 o From CA-A: CN=JoeUser,OU=Engineering 2148 o From CA-B: CN=JoePartner,OU=BizcoPartners 2150 The client MUST be configured locally to know which CA to use when 2151 connecting to either gateway. If your client is not configured to 2152 know the local credential to use for the remote gateway, this 2153 scenario will not work either. If you attempt to connect to Bizco, 2154 everything will work... as you are presented with responding with a 2155 certificate signed by CA-B or CA-C... as you only have a certificate 2156 from CA-B you are OK. If you attempt to connect to Acme, you have an 2157 issue because you are presented with an ambiguous policy selection. 2158 As the initiator, you will be presented with certificate requests 2159 from both CA A and CA B. You have certificates issued by both CAs, 2160 but only one of the certificates will be usable. How does the client 2161 know which certificate it should present? It must have sufficiently 2162 clear local policy specifying which one credential to present for the 2163 connection it initiates. 2165 Appendix D. Acknowledgements 2167 The authors would like to acknowledge the expired draft-ietf-ipsec- 2168 pki-req-05.txt for providing valuable materials for this document. 2170 The authors would like to especially thank Eric Rescorla, one of its 2171 original authors, in addition to Greg Carter, Steve Hanna, Russ 2172 Housley, Charlie Kaufman, Tero Kivinen, and Gregory Lebovitz for 2173 their valuable comments, some of which have been incorporated 2174 verbatim into this document. Paul Knight performed the arduous tasks 2175 of coverting the text to XML format. 2177 Author's Address 2179 Brian Korver 2180 Network Resonance, Inc. 2181 2483 E. 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