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(The document does seem to have the reference to RFC 2119 which the ID-Checklist requires). -- The exact meaning of the all-uppercase expression 'NOT REQUIRED' is not defined in RFC 2119. If it is intended as a requirements expression, it should be rewritten using one of the combinations defined in RFC 2119; otherwise it should not be all-uppercase. == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'MUST not' in this paragraph: If an AC contains attributes apparently encrypted for the AC verifier, then the decryption process MUST not fail. If decryption does fail, then the AC MUST be rejected. -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. 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'CMP') (Obsoleted by RFC 4210) ** Obsolete normative reference: RFC 2630 (ref. 'CMS') (Obsoleted by RFC 3369, RFC 3370) ** Obsolete normative reference: RFC 1510 (ref. 'KRB') (Obsoleted by RFC 4120, RFC 6649) ** Obsolete normative reference: RFC 2251 (ref. 'LDAP') (Obsoleted by RFC 4510, RFC 4511, RFC 4512, RFC 4513) ** Obsolete normative reference: RFC 2560 (ref. 'OCSP') (Obsoleted by RFC 6960) -- No information found for draft-ietf-pkix-pkalgs - is the name correct? -- Possible downref: Normative reference to a draft: ref. 'PKIXALGS' == Outdated reference: draft-ietf-cat-kerberos-pk-init has been published as RFC 4556 == Outdated reference: draft-ietf-pkix-new-part1 has been published as RFC 3280 ** Obsolete normative reference: RFC 1738 (ref. 'URL') (Obsoleted by RFC 4248, RFC 4266) Summary: 12 errors (**), 0 flaws (~~), 10 warnings (==), 8 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 PKIX Working Group S. Farrell 3 INTERNET-DRAFT Baltimore Technologies 4 Expires in six months R. Housley 5 SPYRUS 6 8 August 2000 8 An Internet Attribute Certificate 9 Profile for Authorization 10 12 Status of this Memo 14 This document is an Internet-Draft and is in full conformance with 15 all provisions of Section 10 of [RFC2026]. 17 Internet-Drafts are working documents of the Internet Engineering 18 Task Force (IETF), its areas, and its working groups. Note that 19 other groups may also distribute working documents as Internet- 20 Drafts. Internet-Drafts are draft documents valid for a maximum of 21 six months and may be updated, replaced, or obsoleted by other 22 documents at any time. It is inappropriate to use Internet- Drafts 23 as reference material or to cite them other than as "work in 24 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 Abstract 34 This specification defines a profile for the use of X.509 Attribute 35 Certificates in Internet Protocols. Attribute certificates may be 36 used in a wide range of applications and environments covering a 37 broad spectrum of interoperability goals and a broader spectrum of 38 operational and assurance requirements. The goal of this document is 39 to establish a common baseline for generic applications requiring 40 broad interoperability as well as limited special purpose 41 requirements. The profile places emphasis on attribute certificate 42 support for Internet electronic mail, IPSec, and WWW security 43 applications. 45 Table of Contents 47 Status of this Memo.............................................1 48 Abstract........................................................1 49 Table of Contents...............................................1 50 1. Introduction.................................................3 51 1.1 Delegation and AC chains...............................4 52 1.2 Attribute Certificate Distribution ("push" vs. "pull").4 53 1.3 Document Structure.....................................5 54 2. Terminology..................................................6 55 3. Requirements.................................................7 56 4. Attribute Certificate Profile................................8 57 4.1 X.509 Attribute Certificate Definition.................8 58 4.2 Profile of Standard Fields............................10 59 4.2.1 Version.........................................10 60 4.2.2 Holder..........................................10 61 4.2.3 Issuer..........................................11 62 4.2.4 Signature.......................................12 63 4.2.5 Serial Number...................................12 64 4.2.6 Validity Period.................................12 65 4.2.7 Attributes......................................13 66 4.2.8 Issuer Unique Identifier........................13 67 4.2.9 Extensions......................................13 68 4.3 Extensions............................................14 69 4.3.1 Audit Identity..................................14 70 4.3.2 AC Targeting....................................15 71 4.3.3 Authority Key Identifier........................16 72 4.3.4 Authority Information Access....................16 73 4.3.5 CRL Distribution Points.........................17 74 4.3.6 No Revocation Available.........................17 75 4.4 Attribute Types.......................................17 76 4.4.1 Service Authentication Information..............18 77 4.4.2 Access Identity.................................18 78 4.4.3 Charging Identity...............................19 79 4.4.4 Group...........................................19 80 4.4.5 Role............................................19 81 4.4.6 Clearance.......................................20 82 4.5 Profile of AC issuer's PKC............................21 83 5. Attribute Certificate Validation............................22 84 6. Revocation..................................................23 85 7. Optional Features...........................................24 86 7.1 Attribute Encryption..................................24 87 7.2 Proxying..............................................25 88 7.3 Use of ObjectDigestInfo...............................26 89 7.4 AA Controls...........................................27 90 8. Security Considerations.....................................29 91 9. References..................................................31 92 Author's Addresses.............................................32 93 Full Copyright Statement.......................................32 94 Appendix A: Object Identifiers.................................33 95 Appendix B: ASN.1 Module.......................................34 97 1. Introduction 99 The key words "MUST", "REQUIRED", "SHOULD", "RECOMMENDED", and "MAY" 100 in this document are to be interpreted as described in [RFC2119]. 102 X.509 public key certificates (PKCs) [X.509-1997, X.509-2000, 103 PKIXPROF] bind an identity and a public key. An attribute 104 certificate (AC) is a structure similar to a PKC; the main 105 difference being that the AC contains no public key. An AC may 106 contain attributes that specify group membership, role, security 107 clearance, or other authorization information associated with the AC 108 holder. The syntax for the AC is defined in Recommendation X.509, 109 making the term "X.509 certificate" ambiguous. 111 Some people constantly confuse PKCs and ACs. An analogy may make the 112 distinction clear. A PKC can be considered to be like a passport: it 113 identifies the holder, tends to last for a long time, and should not 114 be trivial to obtain. An AC is more like an entry visa: it is 115 typically issued by a different authority and does not last for as 116 long a time. As acquiring an entry visa typically requires 117 presenting a passport, getting a visa can be a simpler process. 119 Authorization information may be placed in a PKC extension or placed 120 in a separate attribute certificate (AC). The placement of 121 authorization information in PKCs is usually undesirable for two 122 reasons. First, authorization information often does not have the 123 same lifetime as the binding of the identity and the public key. 124 When authorization information is placed in a PKC extension, the 125 general result is the shortening of the PKC useful lifetime. Second, 126 the PKC issuer is not usually authoritative for the authorization 127 information. This results in additional steps for the PKC issuer to 128 obtain authorization information from the authoritative source. 130 For these reasons, it is often better to separate authorization 131 information from the PKC. Yet, authorization information also needs 132 to be bound to an identity. An AC provides this binding; it is 133 simply a digitally signed (or certified) identity and set of 134 attributes. 136 An AC may be used with various security services, including access 137 control, data origin authentication, and non-repudiation. 139 PKCs can provide an identity to access control decision functions. 140 However, in many contexts the identity is not the criterion that is 141 used for access control decisions, rather the role or group- 142 membership of the accessor is the criterion used. Such access 143 control schemes are called role-based access control. 145 When making an access control decision based on an AC, an access 146 control decision function may need to ensure that the appropriate AC 147 holder is the entity that has requested access. One way in which the 148 linkage between the request or identity and the AC can be achieved 149 is the inclusion of a reference to a PKC within the AC and the use 150 of the private key corresponding to the PKC for authentication 151 within the access request. 153 ACs may also be used in the context of a data origin authentication 154 service and a non-repudiation service. In these contexts, the 155 attributes contained in the AC provide additional information about 156 the signing entity. This information can be used to make sure that 157 the entity is authorized to sign the data. This kind of checking 158 depends either on the context in which the data is exchanged or on 159 the data that has been digitally signed. 161 1.1 Delegation and AC chains 163 The X.509 standard [X.509-2000] defines authorization as the 164 "conveyance of privilege from one entity that holds such privilege, 165 to another entity". An AC is one authorization mechanism. 167 An ordered sequence of ACs could be used to verify the authenticity 168 of a privilege asserter's privilege. In this way, chains or paths of 169 ACs could be employed to delegate authorization. 171 Since the administration and processing associated with such AC 172 chains is complex and the use of ACs in the Internet today is quite 173 limited, this specification does NOT RECOMMEND the use of AC chains. 174 Other (future) specifications may address the use of AC chains. This 175 specification deals with the simple cases where one authority issues 176 all of the ACs for a particular set of attributes. However, this 177 simplification does not preclude the use of several different 178 authorities, each of which manages a different set of attributes. 179 For example, group membership may be included in one AC issued by 180 one authority, and security clearance may be included in another AC 181 issued by another authority. 183 This means that conformant implementations are only REQUIRED to be 184 able to process a single AC at a time. Processing of more than one 185 AC, one after another, may be necessary. Note however, that 186 validation of an AC MAY require validation of a chain of PKCs, as 187 specified in [PKIXPROF]. 189 1.2 Attribute Certificate Distribution ("push" vs. "pull") 191 As discussed above, ACs provide a mechanism to securely provide 192 authorization information to, for example, access control decision 193 functions. However, there are a number of possible communication 194 paths for ACs. 196 In some environments it is suitable for a client to "push" an AC to 197 a server. This means that no new connections between the client and 198 server are required. It also means that no search burden is imposed 199 on servers, which improves performance and that the AC verifier is 200 only presented with what it "needs to know." In inter-domain cases 201 where the client's rights should be assigned within client's "home" 202 domain, the "push" model is especially suitable. 204 In other cases, it is more suitable for a client simply to 205 authenticate to the server and for the server to request or "pull" 206 the client's AC from an AC issuer or a repository. A major benefit 207 of the "pull" model is that it can be implemented without changes to 208 the client or to the client-server protocol. The "pull" model is 209 especially suitable for inter-domain cases where the client's rights 210 should be assigned within the server's domain, rather than within 211 the client's domain. 213 There are a number of possible exchanges involving three entities: 214 the client, the server, and the AC issuer. In addition, a directory 215 service or other repository for AC retrieval MAY be supported. 217 Figure 1 shows an abstract view of the exchanges that may involve 218 ACs. This profile does not specify a protocol for these exchanges. 220 +--------------+ 221 | | Server Acquisition 222 | AC issuer +----------------------------+ 223 | | | 224 +--+-----------+ | 225 | | 226 | Client | 227 | Acquisition | 228 | | 229 +--+-----------+ +--+------------+ 230 | | AC "push" | | 231 | Client +-------------------------+ Server | 232 | | (part of app. protocol) | | 233 +--+-----------+ +--+------------+ 234 | | 235 | Client | Server 236 | Lookup +--------------+ | Lookup 237 | | | | 238 +---------------+ Repository +---------+ 239 | | 240 +--------------+ 242 Figure 1: AC Exchanges 244 1.3 Document Structure 246 Section 2 defines some terminology. Section 3 specifies the 247 requirements that this profile is intended to meet.; Section 4 248 contains the profile of the X.509 AC. Section 5 specifies rules for 249 AC validation. Section 6 specifies rules for AC revocation checks. 250 Section 7 specifies optional features which MAY be supported; 251 however, support for these features is not required for conformance 252 to this profile. Finally, appendices contain the list of OIDs 253 required to support this specification and an ASN.1 module. 255 2. Terminology 257 For simplicity, we use the terms client and server in this 258 specification. This is not intended to indicate that ACs are only to 259 be used in client-server environments. For example, ACs may be used 260 in the S/MIME v3 context, where the mail user agent would be both a 261 "client" and a "server" in the sense the terms are used here. 263 Term Meaning 265 AA Attribute Authority, the entity that issues the 266 AC, synonymous in this specification with "AC 267 issuer" 268 AC Attribute Certificate 269 AC user any entity that parses or processes an AC 270 AC verifier any entity that checks the validity of an AC and 271 then makes use of the result 272 AC issuer the entity which signs the AC, synonymous in this 273 specification with "AA" 274 AC holder the entity indicated (perhaps indirectly) in the 275 holder field of the AC 276 Client the entity which is requesting the action for 277 which authorization checks are to be made 278 Proxying in this specification, Proxying is used to mean 279 the situation where an application server acts as 280 an application client on behalf of a user. 281 Proxying here does not mean granting of authority. 282 PKC Public Key Certificate - uses the type ASN.1 283 Certificate defined in X.509 and profiled in RFC 284 2459. This (non-standard) acronym is used in order 285 to avoid confusion about the term "X.509 286 certificate". 287 Server the entity which requires that the authorization 288 checks are made 290 3. Requirements 292 This AC profile meets the following requirements. 294 Time/Validity requirements: 296 1. Support for short-lived as well as long-lived ACs. Typical 297 short-lived validity periods might be measured in hours, as 298 opposed to months for PKCs. Short validity periods allow ACs to 299 be useful without a revocation mechanism. 301 Attribute Types: 303 2. Issuers of ACs should be able to define their own attribute 304 types for use within closed domains. 305 3. Some standard attribute types should be defined which can be 306 contained within ACs. Examples include "access identity," 307 "group," "role," "clearance," "audit identity," and "charging 308 identity." 309 4. Standard attribute types should be defined in a manner that 310 permits an AC verifier to distinguish between uses of the same 311 attribute in different domains. For example, the 312 "Administrators group" as defined by Baltimore and the 313 "Administrators group" as defined by SPYRUS should be easily 314 distinguished. 316 Targeting of ACs: 318 5. It should be possible to "target" an AC at one, or a small 319 number of, servers. This means that a trustworthy non-target 320 server will reject the AC for authorization decisions. 322 Push vs. Pull 324 6. ACs should be defined so that they can either be "pushed" by 325 the client to the server, or "pulled" by the server from a 326 repository or other network service, including an online AC 327 issuer. 329 4. Attribute Certificate Profile 331 ACs may be used in a wide range of applications and environments 332 covering a broad spectrum of interoperability goals and a broader 333 spectrum of operational and assurance requirements. The goal of 334 this document is to establish a common baseline for generic 335 applications requiring broad interoperability and limited special 336 purpose requirements. In particular, the emphasis will be on 337 supporting the use of attribute certificates for informal Internet 338 electronic mail, IPSec, and WWW applications. 340 This section presents a profile for ACs that will foster 341 interoperability. This section also defines some private extensions 342 for the Internet community. 344 While the ISO/IEC/ITU documents use the 1993 (or later) version of 345 ASN.1; this document uses the 1988 ASN.1 syntax, as has been done 346 for PKCs [PKIXPROF]. The encoded certificates and extensions from 347 either ASN.1 version are bit-wise identical. 349 Where maximum lengths for fields are specified, these lengths refer 350 to the DER encoding and do not include the ASN.1 tag or length 351 fields. 353 Conforming implementations MUST support the profile specified in 354 this section. 356 4.1 X.509 Attribute Certificate Definition 358 X.509 contains the definition of an AC given below. All types that 359 are not defined in this document can be found in [PKIXPROF]. 361 AttributeCertificate ::= SEQUENCE { 362 acinfo AttributeCertificateInfo, 363 signatureAlgorithm AlgorithmIdentifier, 364 signatureValue BIT STRING 365 } 367 AttributeCertificateInfo ::= SEQUENCE { 368 version AttCertVersion DEFAULT v1, 369 holder Holder, 370 issuer AttCertIssuer, 371 signature AlgorithmIdentifier, 372 serialNumber CertificateSerialNumber, 373 attrCertValidityPeriod AttCertValidityPeriod, 374 attributes SEQUENCE OF Attribute, 375 issuerUniqueID UniqueIdentifier OPTIONAL, 376 extensions Extensions OPTIONAL 377 } 379 AttCertVersion ::= INTEGER { v1(0), v2(1) } 380 Holder ::= SEQUENCE { 381 baseCertificateID [0] IssuerSerial OPTIONAL, 382 -- the issuer and serial number of 383 -- the holder's Public Key Certificate 384 entityName [1] GeneralNames OPTIONAL, 385 -- the name of the claimant or role 386 objectDigestInfo [2] ObjectDigestInfo OPTIONAL 387 -- if present, version must be v2 388 } 390 ObjectDigestInfo ::= SEQUENCE { 391 digestedObjectType ENUMERATED { 392 publicKey (0), 393 publicKeyCert (1), 394 otherObjectTypes (2) }, 395 -- otherObjectTypes MUST NOT 396 -- be used in this profile 397 otherObjectTypeID OBJECT IDENTIFIER OPTIONAL, 398 digestAlgorithm AlgorithmIdentifier, 399 objectDigest BIT STRING 400 } 402 AttCertIssuer ::= CHOICE { 403 v1Form GeneralNames, -- v1 or v2 404 v2Form [0] V2Form -- v2 only 405 } 407 V2Form ::= SEQUENCE { 408 issuerName GeneralNames OPTIONAL, 409 baseCertificateID [0] IssuerSerial OPTIONAL, 410 objectDigestInfo [1] ObjectDigestInfo OPTIONAL 411 -- at least one of issuerName, baseCertificateID 412 -- or objectDigestInfo MUST be present 413 } 415 IssuerSerial ::= SEQUENCE { 416 issuer GeneralNames, 417 serial CertificateSerialNumber, 418 issuerUID UniqueIdentifier OPTIONAL 419 } 421 AttCertValidityPeriod ::= SEQUENCE { 422 notBeforeTime GeneralizedTime, 423 notAfterTime GeneralizedTime 424 } 426 Although the Attribute syntax is defined in [PKIXPROF], we repeat 427 the definition here for convenience. 429 Attribute ::= SEQUENCE { 430 type AttributeType, 431 values SET OF AttributeValue 432 -- at least one value is required 433 } 435 AttributeType ::= OBJECT IDENTIFIER 437 AttributeValue ::= ANY DEFINED BY AttributeType 439 Implementers should note that the DER encoding (see [X.509- 440 1988],[X.208-1988]) of the SET OF values requires ordering of the 441 encodings of the values. Though this issue arises with respect to 442 distinguished names, and has to be handled by [PKIXPROF] 443 implementations, its is much more significant in this context, since 444 the inclusion of multiple values is much more common in ACs. 446 4.2 Profile of Standard Fields 448 For all GeneralName fields in this profile the otherName (except as 449 noted below), x400Address, ediPartyName and registeredID options 450 MUST NOT be used. The use of Kerberos [KRB] principal names, 451 encoded into the otherName, SHOULD however, be supported using the 452 krb5PrincipalName OID and the KerberosName syntax as defined in 453 [PKINIT]. 455 Conforming implementations MUST be able to support the dNSName, 456 directoryName, uniformResourceIdentifier, and iPAddress fields in 457 all cases where GeneralName is used. This is compatible with the 458 GeneralName requirements in [PKIXPROF] (mainly in section 4.2.1.7). 460 4.2.1 Version 462 The version field MUST be the default value of v1. That is, the 463 version field is not present in the DER encoding, except when the 464 holder is identified using the optional objectDigestInfo field, as 465 specified in section 7.3. 467 4.2.2 Holder 469 For any environment where the AC is passed in an authenticated 470 message or session and where the authentication is based on the use 471 of an X.509 PKC, the holder field SHOULD use the baseCertificateID. 473 With the baseCertificateID option, the holder's PKC serialNumber and 474 issuer MUST be identical to the AC holder field. The PKC issuer MUST 475 have a non-empty distinguished name which is to be present as the 476 single value of the holder.baseCertificateID.issuer construct in the 477 directoryName field. The AC holder.baseCertificateID.issuerUID field 478 MUST only be used if the holder's PKC contains an issuerUniqueID 479 field. If both the AC holder.baseCertificateID.issuerUID and the PKC 480 issuerUniqueID fields are present, then the same value MUST be 481 present in both fields. Thus, the baseCertificateID is only usable 482 with PKC profiles (like [PKIXPROF]) which mandate that the PKC 483 issuer field contain a non-empty distinguished name value. 485 Note: An empty distinguished name is a distinguished name where the 486 SEQUENCE OF relative distinguished names is of zero length. In a DER 487 encoding this has the value '3000'H. 489 If the holder field uses the entityName option and the underlying 490 authentication is based on a PKC, then the entityName MUST be the 491 same as the PKC subject field, unless the PKC subject field contains 492 an empty distinguished name. If the PKC subject field contains an 493 empty distinguished name, then the entityName field MUST be 494 identical to one of the values of the PKC subjectAltName field 495 extension. Note that [PKIXPROF] mandates that the subjectAltNames 496 extension be present if the PKC subject is an empty distinguished 497 name. See the security consideration section which mentions some 498 name collision problems that may arise when using the entityName 499 option. 501 In any other case where the holder field uses the entityName option, 502 then only one name SHOULD be present. 504 Implementations conforming to this profile are not required to 505 support the use of the objectDigest field. However, section 7.3 506 specifies how this optional feature MAY be used. 508 Any protocol conforming to this profile SHOULD specify which AC 509 holder option is to be used and how this fits with the supported 510 authentication schemes defined in that protocol. 512 4.2.3 Issuer 514 ACs conforming to this profile MUST use the v1Form choice, which 515 MUST contain one and only one GeneralName, which MUST contain a non- 516 empty distinguished name in the directoryName field. This means that 517 all AC issuers MUST have non-empty distinguished names. 519 Part of the reason for the use of the v1Form field is that it means 520 that the AC issuer does not have to know which PKC the AC verifier 521 will use for it (the AC issuer). Using the baseCertificateID field 522 to reference the AC issuer would mean that the AC verifier would 523 have to trust the PKC that the AC issuer chose (for itself) at AC 524 creation time. 526 4.2.4 Signature 528 Contains the algorithm identifier used to validate the AC signature. 530 This MUST be one of the signing algorithms defined in [PKIXALGS]. 532 id-dsa-with-sha1 MUST be supported by all AC users. The other 533 algorithms MAY be supported. 535 4.2.5 Serial Number 537 For any conforming AC, the issuer/serialNumber pair MUST form a 538 unique combination, even if ACs are very short-lived. 540 AC issuers MUST force the serialNumber to be a positive integer, 541 that is, the sign bit in the DER encoding of the INTEGER value MUST 542 be zero - this can be done by adding a leading (leftmost) '00'H 543 octet if necessary. This removes a potential ambiguity in mapping 544 between a string of octets and an integer value. 546 Given the uniqueness and timing requirements above serial numbers 547 can be expected to contain long integers. AC users MUST be able to 548 handle serialNumber values longer than 4 octets. Conformant ACs MUST 549 NOT contain serialNumber values longer than 20 octets. 551 There is no requirement that the serial numbers used by any AC 552 issuer follow any particular ordering, in particular, they need not 553 be monotonically increasing with time. Each AC issuer MUST ensure 554 that each AC that it issues contain a unique serial number. 556 4.2.6 Validity Period 558 The attrCertValidityPeriod (a.k.a. validity) field specifies the 559 period for which the AC issuer certifies that the binding between 560 the holder and the attributes fields will be valid. 562 The generalized time type, GeneralizedTime, is a standard ASN.1 type 563 for variable precision representation of time. The GeneralizedTime 564 field can optionally include a representation of the time 565 differential between the local time zone and Greenwich Mean Time. 567 For the purposes of this profile, GeneralizedTime values MUST be 568 expressed in Coordinated universal time (UTC) (also known as 569 Greenwich Mean Time or Zulu)) and MUST include seconds (i.e., times 570 are YYYYMMDDHHMMSSZ), even when the number of seconds is zero. 571 GeneralizedTime values MUST NOT include fractional seconds. 572 (Note: this is the same as specified in [PKIXPROF], section 573 4.1.2.5.2.) 575 AC users MUST be able to handle an AC which, at the time of 576 processing, has parts of its validity period or all its validity 577 period in the past or in the future (a post-dated AC). This is valid 578 for some applications, such as backup. 580 4.2.7 Attributes 582 The attributes field gives information about the AC holder. When the 583 AC is used for authorization this will often contain a set of 584 privileges. 586 The attributes field contains a SEQUENCE OF Attribute. Each 587 Attribute MAY contain a SET OF values. For a given AC, each 588 AttributeType OBJECT IDENTIFIER in the sequence MUST be unique. That 589 is, only one instance of each attribute can occur in a single AC, 590 but each instance can be multi-valued. 592 AC users MUST be able to handle multiple values for all attribute 593 types. 595 An AC MUST contain at least one attribute. That is, the SEQUENCE OF 596 Attributes MUST NOT be of zero length. 598 Some standard attribute types are defined in section 4.5. 600 4.2.8 Issuer Unique Identifier 602 This field MUST NOT be used unless it is also used in the AC 603 issuer's PKC, in which case it MUST be used. Note that [PKIXPROF] 604 states that this field SHOULD NOT be used by conforming CAs, but 605 that applications SHOULD be able to parse PKCs containing the field. 607 4.2.9 Extensions 609 The extensions field generally gives information about the AC as 610 opposed to information about the AC holder. 612 An AC that has no extensions conforms to the profile; however, 613 section 4.3 defines the extensions that MAY be used with this 614 profile, and whether or not they may be marked critical. If any 615 other critical extension is used, then the AC does not conform to 616 this profile. However, if any other non-critical extension is used, 617 then the AC does conform to this profile. 619 The extensions defined for ACs provide methods for associating 620 additional attributes with holders. This profile also allows 621 communities to define private extensions to carry information unique 622 to those communities. Each extension in an AC may be designated as 623 critical or non-critical. An AC using system MUST reject an AC if 624 it encounters a critical extension it does not recognize; however, a 625 non-critical extension may be ignored if it is not recognized. 626 Section 4.3 presents recommended extensions used within Internet ACs 627 and standard locations for information. Communities may elect to 628 use additional extensions; however, caution should be exercised in 629 adopting any critical extensions in ACs, which might prevent use in 630 a general context. 632 4.3 Extensions 634 4.3.1 Audit Identity 636 In some circumstances it is required (e.g. by data protection/data 637 privacy legislation) that audit trails do not contain records which 638 directly identify individuals. This circumstance may make the use of 639 the AC holder field unsuitable for use in audit trails. 641 To allow for such cases, an AC MAY contain an audit identity 642 extension. Ideally it SHOULD be infeasible to derive the AC holder's 643 identity from the audit identity value without the co-operation of 644 the AC issuer. 646 The value of the audit identity along with the AC issuer/serial 647 SHOULD then be used for audit/logging purposes. If the value of the 648 audit identity is suitably chosen, then a server/service 649 administrator can use audit trails to track the behavior of an AC 650 holder without being able to identify the AC holder. 652 The server/service administrator in combination with the AC issuer 653 MUST be able to identify the AC holder in cases where misbehavior is 654 detected. This means that the AC issuer MUST be able to determine 655 the actual identity of the AC holder from the audit identity. 657 Of course, auditing could be based on the AC issuer/serial pair; 658 however, this method doesn't allow tracking the same AC holder with 659 multiple ACs. Thus, an audit identity is only useful if it lasts for 660 longer than the typical AC lifetime. Auditing could also be based on 661 the AC holder's PKC issuer/serial; however, this will often allow 662 the server/service administrator to identify the AC holder. 664 As the AC verifier might otherwise use the AC holder or some other 665 identifying value for audit purposes, this extension MUST be 666 critical when used. 668 Protocols that use ACs will often expose the identity of the AC 669 holder in the bits on-the-wire. In such cases, an opaque audit 670 identity does not make use of the AC anonymous, it simply ensures 671 that the ensuing audit trails do not contain identifying 672 information. 674 The value of an audit identity MUST be longer than zero octets. The 675 value of an audit identity MUST NOT be longer than 20 octets. 677 name id-pe-ac-auditIdentity 678 OID { id-pe 4 } 679 syntax OCTET STRING 680 criticality MUST be TRUE 682 4.3.2 AC Targeting 684 To target an AC, the target information extension, imported from 685 [X.509-2000], MAY be used to specify a number of servers/services. 686 The intent is that the AC SHOULD only be usable at the specified 687 servers/services. An (honest) AC verifier who is not amongst the 688 named servers/services MUST reject the AC. 690 If this extension is not present, then the AC is not targeted and 691 may be accepted by any server. 693 In this profile, the targeting information simply consists of a list 694 of named targets or groups. 696 The following syntax is used to represent the targeting information: 698 Targets ::= SEQUENCE OF Target 700 Target ::= CHOICE { 701 targetName [0] GeneralName, 702 targetGroup [1] GeneralName, 703 targetCert [2] TargetCert 704 } 706 TargetCert ::= SEQUENCE { 707 targetCertificate IssuerSerial, 708 targetName GeneralName OPTIONAL, 709 certDigestInfo ObjectDigestInfo OPTIONAL 710 } 712 The targetCert CHOICE within the Target structure is only present to 713 allow future compatibility with [X.509-2000] and MUST NOT be used. 715 The targets check passes if the current server (recipient) is one of 716 the targetName fields in the Targets SEQUENCE, or if the current 717 server is a member of one of the targetGroup fields in the Targets 718 SEQUENCE. In this case, the current server is said to "match" the 719 targeting extension. 721 How the membership of a target within a targetGroup is determined is 722 not defined here. It is assumed that any given target "knows" the 723 names of the targetGroups to which it belongs or can otherwise 724 determine its membership. For example, the targetGroup specifies a 725 DNS domain, and the AC verifier knows the DNS domain to which it 726 belongs. For another example, the targetGroup specifies "PRINTERS," 727 and the AC verifier knows whether or not it is a printer or print 728 server. 730 Note: [X.509-2000] defines the extension syntax as a "SEQUENCE OF 731 Targets". Conforming AC issuer implementations MUST only produce one 732 "Targets" element. Confirming AC users MUST be able to accept a 733 "SEQUENCE OF Targets". If more than one Targets element is found in 734 an AC, then the extension MUST be treated as if all Target elements 735 had been found within one Targets element. 737 name id-ce-targetInformation 738 OID { id-ce 55 } 739 syntax SEQUENCE OF Targets 740 criticality MUST be TRUE 742 4.3.3 Authority Key Identifier 744 The authorityKeyIdentifier extension, as profiled in [PKIXPROF], MAY 745 be used to assist the AC verifier in checking the signature of the 746 AC. The [PKIXPROF] description should be read as if "CA" meant "AC 747 issuer." As with PKCs this extension SHOULD be included in ACs. 749 Note: An AC where the issuer field used the baseCertificateID CHOICE 750 would not need an authorityKeyIdentifier extension as it is 751 explicitly linked to the key in the referred certificate. However, 752 as this profile states (in section 4.2.3) that ACs MUST use the 753 v1Form CHOICE, this duplication does not arise. 755 name id-ce-authorityKeyIdentifier 756 OID { id-ce 35 } 757 syntax AuthorityKeyIdentifier 758 criticality MUST be FALSE 760 4.3.4 Authority Information Access 762 The authorityInformationAccess extension, as defined in [PKIXPROF], 763 MAY be used to assist the AC verifier in checking the revocation 764 status of the AC. Support for the id-ad-caIssuers accessMethod is 765 NOT REQUIRED by this profile since AC chains are not expected. 767 The following accessMethod is used to indicate that revocation 768 status checking is provided for this AC, using the OCSP protocol 769 defined in [OCSP]: 771 id-ad-ocsp OBJECT IDENTIFIER ::= { id-ad 1 } 773 The accessLocation MUST contain a URI, and the URI MUST contain an 774 HTTP URL [URL] that specifies the location of an OCSP responder. The 775 AC issuer MUST, of course, maintain an OCSP responder at this 776 location. 778 name id-ce-authorityInfoAccess 779 OID { id-pe 1 } 780 syntax AuthorityInfoAccessSyntax 781 criticality MUST be FALSE 783 4.3.5 CRL Distribution Points 785 The crlDistributionPoints extension, as profiled in [PKIXPROF], MAY 786 be used to assist the AC verifier in checking the revocation status 787 of the AC. See section 6 for details on revocation. 789 If the crlDistributionPoints extension is present, then exactly one 790 distribution point MUST be present. The crlDistributionPoints 791 extension MUST use the DistributionPointName option, which MUST 792 contain a fullName, which MUST contain a single name form. That name 793 MUST contain either a distinguished name or a URI. The URI MUST be 794 either an HTTP URL or an LDAP URL [URL]. 796 name id-ce-cRLDistributionPoints 797 OID { id-ce 31 } 798 syntax CRLDistPointsSyntax 799 criticality MUST be FALSE 801 4.3.6 No Revocation Available 803 The noRevAvail extension, defined in [X.509-2000], allows an AC 804 issuer to indicate that no revocation information will be made 805 available for this AC. 807 This extension MUST be non-critical. An AC verifier that does not 808 understand this extension might be able to find a revocation list 809 from the AC issuer, but the revocation list will never include an 810 entry for the AC. 812 name id-ce-noRevAvail 813 OID { id-ce 56 } 814 syntax NULL (i.e. '0500'H is the DER encoding) 815 criticality MUST be FALSE 817 4.4 Attribute Types 819 Some of the attribute types defined below make use of the 820 IetfAttrSyntax type, also defined below. The reasons for using this 821 type are: 823 1. It allows a separation between the AC issuer and the attribute 824 policy authority. This is useful for situations where a single 825 policy authority (e.g. an organization) allocates attribute 826 values, but where multiple AC issuers are deployed for 827 performance or other reasons. 828 2. The syntaxes allowed for values are restricted to OCTET STRING, 829 OBJECT IDENTIFIER, and UTF8String, which significantly reduces 830 the complexity associated with matching more general syntaxes. 831 All multi-valued attributes using this syntax are restricted so 832 that each value MUST use the same choice of value syntax. For 833 example, AC issuers must not use one value with an oid and a 834 second value with a string. 836 IetfAttrSyntax ::= SEQUENCE { 837 policyAuthority [0] GeneralNames OPTIONAL, 838 values SEQUENCE OF CHOICE { 839 octets OCTET STRING, 840 oid OBJECT IDENTIFIER, 841 string UTF8String 842 } 843 } 845 In the descriptions below, each attribute type is tagged as either 846 "Multiple Allowed" or "One Attribute value only; multiple values 847 within the IetfAttrSyntax". This refers to the SET OF 848 AttributeValue, the AttributeType still only occurs once, as 849 specified in section 4.2.7. 851 4.4.1 Service Authentication Information 853 The SvceAuthInfo attribute identifies the AC holder to the 854 server/service by a name, and the attribute MAY include optional 855 service specific authentication information. Typically this will 856 contain a username/password pair for a "legacy" application. 858 This attribute provides information that can be presented by the AC 859 verifier to be interpreted and authenticated by a separate 860 application within the target system. Note that this is a different 861 use to that intended for the accessIdentity attribute in 4.4.2 862 below. 864 This attribute type will typically be encrypted when the authInfo 865 field contains sensitive information, such as a password. 867 name id-aca-authenticationInfo 868 OID { id-aca 1 } 869 Syntax SvceAuthInfo 870 values: Multiple allowed 872 SvceAuthInfo ::= SEQUENCE { 873 service GeneralName, 874 ident GeneralName, 875 authInfo OCTET STRING OPTIONAL 876 } 878 4.4.2 Access Identity 880 The accessIdentity attribute identifies the AC holder to the 881 server/service. For this attribute the authInfo field MUST NOT be 882 present. 884 This attribute is intended to be used to provide information about 885 the AC holder, that can be used by the AC verifier (or a larger 886 system of which the AC verifier is a component) to authorize the 887 actions of the AC holder within the AC verifier's system. Note that 888 this is a different use to that intended for the svceAuthInfo 889 attribute described in 4.4.1 above. 891 name id-aca-accessIdentity 892 OID { id-aca 2 } 893 syntax SvceAuthInfo 894 values: Multiple allowed 896 4.4.3 Charging Identity 898 The chargingIdentity attribute identifies the AC holder for charging 899 purposes. In general, the charging identity will be different from 900 other identities of the holder. For example, the holder's company 901 may be charged for service. 903 name id-aca-chargingIdentity 904 OID { id-aca 3 } 905 syntax IetfAttrSyntax 906 values: One Attribute value only; multiple values within the 907 IetfAttrSyntax 909 4.4.4 Group 911 The group attribute carries information about group memberships of 912 the AC holder. 914 name id-aca-group 915 OID { id-aca 4 } 916 syntax IetfAttrSyntax 917 values: One Attribute value only; multiple values within the 918 IetfAttrSyntax 920 4.4.5 Role 922 The role attribute, specified in [X.509-2000], carries information 923 about role allocations of the AC holder. 925 The syntax used for this attribute is: 927 RoleSyntax ::= SEQUENCE { 928 roleAuthority [0] GeneralNames OPTIONAL, 929 roleName [1] GeneralName 930 } 932 The roleAuthority field MAY be used to specify the issuing authority 933 for the role specification certificate. There is no requirement that 934 a role specification certificate necessarily exists for the 935 roleAuthority. This differs from [X.500-2000], where the 936 roleAuthority field is assumed to name the issuer of a role 937 specification certificate. For example, to distinguish the 938 administrator role as defined by "Baltimore" from that defined by 939 "SPYRUS", one could put the value "administrator" in the roleName 940 field and the value "Baltimore" or "SPYRUS" in the roleAuthority 941 field. 943 The roleName field MUST be present, and roleName MUST use the 944 uniformResourceIdentifier CHOICE of the GeneralName. 946 name id-at-role 947 OID { id-at 72 } 948 syntax RoleSyntax 949 values: Multiple allowed 951 4.4.6 Clearance 953 The clearance attribute, specified in [X.501-1993], carries 954 clearance (associated with security labeling) information about the 955 AC holder. 957 The policyId field is used to identify the security policy to which 958 the clearance relates. The policyId indicates the semantics of the 959 classList and securityCategories fields. 961 This specification includes the classList field exactly as is 962 specified in [X.501-1993]. Additional security classification 963 values, and their position in the classification hierarchy, may be 964 defined by a security policy as a local matter or by bilateral 965 agreement. The basic security classification hierarchy is, in 966 ascending order: unmarked, unclassified, restricted, confidential, 967 secret, and top-secret. 969 An organization can develop its own security policy that defines 970 security classification values and their meanings. However, the BIT 971 STRING positions 0 through 5 are reserved for the basic security 972 classification hierarchy. 974 If present, the SecurityCategory field provides further 975 authorization information. The security policy identified by the 976 policyId field indicates the syntaxes that are allowed to be present 977 in the securityCategories SET. An OBJECT IDENTIFIER identifies each 978 of the allowed syntaxes. When one of these syntaxes is present in 979 the securityCategories SET, the OBJECT IDENTIFIER associated with 980 that syntax is carried in the SecurityCategory.type field. 982 Clearance ::= SEQUENCE { 983 policyId OBJECT IDENTIFIER, 984 classList ClassList DEFAULT {unclassified}, 985 securityCategories 986 SET OF SecurityCategory OPTIONAL 987 } 989 ClassList ::= BIT STRING { 990 unmarked (0), 991 unclassified (1), 992 restricted (2) 993 confidential (3), 994 secret (4), 995 topSecret (5) 996 } 998 SecurityCategory ::= SEQUENCE { 999 type [0] IMPLICIT OBJECT IDENTIFIER, 1000 value [1] ANY DEFINED BY type 1001 } 1003 -- This is the same as the original syntax which was defined 1004 -- using the MACRO construct, as follows: 1005 -- SecurityCategory ::= SEQUENCE { 1006 -- type [0] IMPLICIT SECURITY-CATEGORY, 1007 -- value [1] ANY DEFINED BY type 1008 -- } 1009 -- 1010 -- SECURITY-CATEGORY MACRO ::= 1011 -- BEGIN 1012 -- TYPE NOTATION ::= type | empty 1013 -- VALUE NOTATION ::= value (VALUE OBJECT IDENTIFIER) 1014 -- END 1016 name { id-at-clearance } 1017 OID { joint-iso-ccitt(2) ds(5) module(1) 1018 selected-attribute-types(5) clearance (55) } 1019 syntax Clearance - imported from [X.501-1993] 1020 values Multiple allowed 1022 4.5 Profile of AC issuer's PKC 1024 The AC issuer's PKC MUST conform to [PKIXPROF], and the keyUsage 1025 extension in the PKC MUST NOT explicitly indicate that the AC 1026 issuer's public key cannot be used to validate a digital signature. 1027 In order to avoid confusion regarding serial numbers and 1028 revocations, an AC issuer MUST NOT also be a PKC Issuer. That is, 1029 an AC issuer cannot be a CA as well. So, the AC issuer's PKC MUST 1030 NOT have a basicConstraints extension with the cA BOOLEAN set to 1031 TRUE. 1033 5. Attribute Certificate Validation 1035 This section describes a basic set of rules that all valid ACs MUST 1036 satisfy. Some additional checks are also described which AC 1037 verifiers MAY choose to implement. 1039 To be valid an AC MUST satisfy all of the following: 1041 1. The AC signature must be cryptographically correct, and the AC 1042 issuer's entire PKC certification path MUST be verified in 1043 accordance with [PKIXPROF]. 1044 2. The AC issuer's PKC MUST also conform to the profile specified 1045 in section 4.5 above. 1046 3. The AC issuer MUST be directly trusted as an AC issuer (by 1047 configuration or otherwise). 1048 4. The time for which the AC is being evaluated MUST be within the 1049 AC validity. If the evaluation time is equal to either 1050 notBeforeTime or notAfterTime, then the AC is timely and this 1051 check succeeds. Note that in some applications, the evaluation 1052 time MAY not be the same as the current time. 1053 5. The AC targeting check MUST pass as specified in section 4.3.2. 1054 6. If the AC contains an unsupported critical extension, then the 1055 AC MUST be rejected. 1057 Support for an extension in this context means: 1059 1. The AC verifier MUST be able to parse the extension value. 1060 2. Where the extension value SHOULD cause the AC to be rejected, 1061 the AC verifier MUST reject the AC. 1063 Additional Checks: 1065 1. The AC MAY be rejected on the basis of further AC verifier 1066 configuration. For example, an AC verifier may be configured to 1067 reject ACs which contain or lack certain attributes. 1068 2. If the AC verifier provides an interface that allows 1069 applications to query the contents of the AC, then the AC 1070 verifier MAY filter the attributes from the AC on the basis of 1071 configured information. For example, an AC verifier might be 1072 configured not to return certain attributes to certain servers. 1074 6. Revocation 1076 In many environments, the validity period of an AC is less than the 1077 time required to issue and distribute revocation information. 1078 Therefore, short-lived ACs typically do not require revocation 1079 support. However, long-lived ACs and environments where ACs enable 1080 high value transactions MAY require revocation support. 1082 Two revocation schemes are defined, and the AC issuer should elect 1083 the one that is best suited to the environment in which the AC will 1084 be employed. 1086 "Never revoke" scheme: 1088 ACs may be marked so that the relying party understands that no 1089 revocation status information will be made available. The 1090 noRevAvail extension is defined in section 4.3.6, and the 1091 noRevAvail extension MUST be present in the AC to indicate use 1092 of this scheme. 1094 Where no noRevAvail is not present, then the AC issuer is 1095 implicitly stating that revocation status checks are supported, 1096 and some revocation method MUST be provided to allow AC 1097 verifiers to establish the revocation status of the AC. 1099 "Pointer in AC" scheme: 1101 ACs may "point" to sources of revocation status information, 1102 using either an authorityInfoAccess extension or a 1103 crlDistributionPoints extension within the AC. 1105 For AC users, the "never revoke" scheme MUST be supported, and the 1106 "pointer in AC" scheme SHOULD be supported. If only the "never 1107 revoke" scheme is supported, then all ACs that do not contain a 1108 noRevAvail extension, MUST be rejected. 1110 For AC issuers, the "never revoke" scheme MUST be supported. If all 1111 ACs that will ever be issued by that AC issuer, will contain a 1112 noRevAvail extension, then the "pointer in AC" scheme need not be 1113 supported. If any AC can be issued that does not contain the 1114 noRevAvail extension, then the "pointer in AC" scheme MUST be 1115 supported. 1117 An AC verifier MAY use any source for AC revocation status 1118 information. 1120 7. Optional Features 1122 This section specifies features that MAY be implemented. Conformance 1123 to this profile does NOT require support for these features; 1124 however, if these features are offered, they MUST be offered as 1125 described below. 1127 7.1 Attribute Encryption 1129 Where an AC will be carried in clear within an application protocol 1130 or where an AC contains some sensitive information like a legacy 1131 application username/password, then encryption of AC attributes MAY 1132 be needed. 1134 When a set of attributes are to be encrypted within an AC, the 1135 Cryptographic Message Syntax, EnvelopedData structure [CMS] is used 1136 to carry the ciphertext and associated per-recipient keying 1137 information. 1139 This type of attribute encryption is targeted. Before the AC is 1140 signed, the attributes are encrypted for a set of predetermined 1141 recipients. 1143 The AC then contains the ciphertext inside its signed data. The 1144 EenvelopedData (id-envelopedData) ContentType is used, and the 1145 content field will contain the EnvelopedData type. 1147 The ciphertext is included in the AC as the value of an encAttrs 1148 attribute. Only one encAttrs attribute can be present in an AC; 1149 however, the encAttrs attribute MAY be multi-valued, and each of its 1150 values will contain an independent EnvelopedData. 1152 Each value can contain a set of attributes (each possibly a multi- 1153 valued attribute) encrypted for a set of predetermined recipients. 1155 The cleartext that is encrypted has the type: 1157 ACClearAttrs ::= SEQUENCE { 1158 acIssuer GeneralName, 1159 acSerial INTEGER, 1160 attrs SEQUENCE OF Attribute 1161 } 1163 The DER encoding of the ACClearAttrs structure is used as the 1164 encryptedContent field of the EnvelopedData. The DER encoding MUST 1165 be embedded in an OCTET STRING. 1167 The acIssuer and acSerial fields are present to prevent ciphertext 1168 stealing. When an AC verifier has successfully decrypted an 1169 encrypted attribute it MUST then check that the AC issuer and 1170 serialNumber fields contain the same values. This prevents a 1171 malicious AC issuer from copying ciphertext from another AC (without 1172 knowing its corresponding plaintext). 1174 The procedure for an AC issuer when encrypting attributes is 1175 illustrated by the following (any other procedure that gives the 1176 same result MAY be used): 1178 1. Identify the sets of attributes that are to be encrypted for 1179 each set of recipients. 1180 2. For each attribute set which is to be encrypted: 1181 2.1. Create an EnvelopedData structure for the data for this 1182 set of recipients. 1183 2.2. Encode the ContentInfo containing the EnvelopedData as a 1184 value of the encAttrs attribute 1185 2.3. Ensure the cleartext attributes are not present in the 1186 to-be-signed AC 1187 3. Add the encAttrs (with its multiple values) to the AC 1189 Note that there may be more than one attribute of the same type (the 1190 same OBJECT IDENTIFIER) after decryption. That is, an AC MAY contain 1191 the same attribute type both in clear and in encrypted form (and 1192 indeed several times if the same recipient is associated with more 1193 than one EnvelopedData). One approach implementers may choose, would 1194 be to merge attributes values following decryption in order to re- 1195 establish the "once only" constraint. 1197 name id-aca-encAttrs 1198 OID { id-aca 6} 1199 Syntax ContentInfo 1200 values Multiple Allowed 1202 If an AC contains attributes apparently encrypted for the AC 1203 verifier, then the decryption process MUST not fail. If decryption 1204 does fail, then the AC MUST be rejected. 1206 7.2 Proxying 1208 When a server acts as a client for another server on behalf of the 1209 AC holder, the server MAY need to proxy an AC. Such proxying MAY 1210 have to be done under the AC issuer's control, so that not every AC 1211 is proxiable and so that a given proxiable AC can be proxied in a 1212 targeted fashion. Support for chains of proxies (with more than one 1213 intermediate server) MAY also be required. Note that this does not 1214 involve a chain of ACs. 1216 In order to meet this requirement we define another extension, 1217 ProxyInfo, similar to the targeting extension. 1219 When this extension is present, the AC verifier must check that the 1220 entity from which the AC was received was allowed to send it and 1221 that the AC is allowed to be used by this verifier. 1223 The proxying information consists of a set of proxy information, 1224 each of which is a set of targeting information. If the verifier and 1225 the sender of the AC are both named in the same proxy set then the 1226 AC can be accepted (the exact rule is given below). 1228 The effect is that the AC holder can send the AC to any valid target 1229 which can then only proxy to targets which are in one of the same 1230 proxy sets as itself. 1232 The following data structure is used to represent the 1233 targeting/proxying information. 1235 ProxyInfo ::= SEQUENCE OF Targets 1237 As in the case of targeting, the targetCert CHOICE MUST NOT be used. 1239 A proxy check succeeds if either one of the conditions below is met: 1241 1. The identity of the sender as established by the underlying 1242 authentication service matches the holder field of the AC, and the 1243 current server "matches" any one of the proxy sets. Recall that 1244 "matches" is as defined section 4.3.2. 1246 2. The identity of the sender as established by the underlying 1247 authentication service "matches" one of the proxy sets (call it 1248 set "A"), and the current server is one of the targetName fields 1249 in the set "A", or the current server is a member of one of the 1250 targetGroup fields in set "A". 1252 When an AC is proxied more than once, a number of targets will be on 1253 the path from the original client, which is normally, but not 1254 always, the AC holder. In such cases, prevention of AC "stealing" 1255 requires that the AC verifier MUST check that all targets on the 1256 path are members of the same proxy set. It is the responsibility of 1257 the AC using protocol to ensure that a trustworthy list of targets 1258 on the path is available to the AC verifier. 1260 name id-pe-ac-proxying 1261 OID { id-pe 10 } 1262 syntax ProxyInfo 1263 criticality MUST be TRUE 1265 7.3 Use of ObjectDigestInfo 1267 In some environments, it may be required that the AC is not linked 1268 either to an identity (via entityName) or to a PKC (via 1269 baseCertificateID). The objectDigestInfo CHOICE in the holder field 1270 allows support for this requirement. 1272 If the holder is identified with the objectDigestInfo field, then 1273 the AC version field MUST contain v2 (the integer 1). 1275 The idea is to link the AC to an object by placing a hash of that 1276 object into the holder field of the AC. For example, this allows 1277 production of ACs that are linked to public keys rather than names. 1279 It also allows production of ACs which contain privileges associated 1280 with an executable object such as a Java class. However, this 1281 profile only specifies how to use a hash over a public key or PKC. 1282 That is, conformant ACs MUST NOT use the otherObjectTypes value for 1283 the digestedObjectType. 1285 To link an AC to a public key, the hash must be calculated over the 1286 representation of that public key which would be present in a PKC, 1287 specifically, the input for the hash algorithm MUST be the DER 1288 encoding of a SubjectPublicKeyInfo representation of the key. Note: 1289 This includes the AlgorithmIdentifier as well as the BIT STRING. The 1290 rules given in [PKIXPROF] for encoding keys MUST be followed. In 1291 this case the digestedObjectType MUST be publicKey and the 1292 otherObjectTypeID field MUST NOT be present. 1294 Note that if the public key value used as input to the hash function 1295 has been extracted from a PKC, then it is possible that the 1296 SubjectPublicKeyInfo from that PKC is NOT the value which should be 1297 hashed. This can occur if DSA Dss-parms are inherited as described 1298 in section 7.3.3 of [PKIXPROF]. The correct input for hashing in 1299 this context will include the value of the parameters inherited from 1300 the CA's PKC, and thus may differ from the SubjectPublicKeyInfo 1301 present in the PKC. 1303 Implementations which support this feature MUST be able to handle 1304 the representations of public keys for the algorithms specified in 1305 section 7.3 of [PKIXPROF]. In this case the digestedObjectType MUST 1306 be publicKey and the otherObjectTypeID field MUST NOT be present. 1308 In order to link an AC to a PKC via a digest, the digest MUST be 1309 calculated over the DER encoding of the entire PKC, including the 1310 signature value. In this case the digestedObjectType MUST be 1311 publicKeyCert and the otherObjectTypeID field MUST NOT be present. 1313 7.4 AA Controls 1315 During AC validation a relying party has to answer the question: is 1316 this AC issuer trusted to issue ACs containing this attribute? The 1317 AAControls PKC extension MAY be used to help answer the question. 1318 The AAControls extension is intended to be used in CA and AC issuer 1319 PKCs. 1321 id-pe-aaControls OBJECT IDENTIFIER ::= { id-pe 6 } 1323 AAControls ::= SEQUENCE { 1324 pathLenConstraint INTEGER (0..MAX) OPTIONAL, 1325 permittedAttrs [0] AttrSpec OPTIONAL, 1326 excludedAttrs [1] AttrSpec OPTIONAL, 1327 permitUnSpecified BOOLEAN DEFAULT TRUE 1328 } 1330 AttrSpec::= SEQUENCE OF OBJECT IDENTIFIER 1332 The AAControls extension is used as follows: 1334 The pathLenConstraint, if present, is interpreted as in [PKIXPROF]. 1335 It restricts the allowed distance between the AA CA, (a CA directly 1336 trusted to include AAControls in its PKCs), and the AC issuer. 1338 The permittedAttrs field specifies a set of attribute types that any 1339 AC issuer below this AA CA is allowed to include in ACs. If this 1340 field is not present, it means that no attribute types are 1341 explicitly allowed. 1343 The excludedAttrs field specifies a set of attribute types that no 1344 AC issuer is allowed to include in ACs. If this field is not 1345 present, it means that no attribute types are explicitly disallowed. 1347 The permitUnSpecified field specifies how to handle attribute types 1348 which are not present in either the permittedAttrs or excludedAttrs 1349 fields. TRUE (the default) means that any unspecified attribute type 1350 is allowed in ACs; FALSE means that no unspecified attribute type is 1351 allowed. 1353 When AAControls are used, the following additional checks on an AA's 1354 PKC chain MUST all succeed for the AC to be valid: 1356 1. Some CA on the ACs certificate path MUST be directly trusted to 1357 issue PKCs which precede the AC issuer in the certification 1358 path, call this CA the "AA CA". 1359 2. All PKCs on the path from the AA CA down to and including the 1360 AC issuer's PKC MUST contain an AAControls extension; however, 1361 the AA CA's PKC need not contain this extension. 1362 3. Only those attributes in the AC which are allowed according to 1363 all of the AAControls extension values in all of the PKCs from 1364 the AA CA to the AC issuer, may be used for authorization 1365 decisions, all other attributes MUST be ignored. This check 1366 MUST be applied to the set of attributes following attribute 1367 decryption, and the id-aca-encAttrs type MUST also be checked. 1369 name id-pe-aaControls 1370 OID { id-pe 6 } 1371 syntax AAControls 1372 criticality MAY be TRUE 1374 8. Security Considerations 1376 The protection afforded for private keys is a critical factor in 1377 maintaining security. Failure of AC issuers to protect their 1378 private keys will permit an attacker to masquerade as them, 1379 potentially generating false ACs or revocation status. Existence of 1380 bogus ACs and revocation status will undermine confidence in the 1381 system. If the compromise is detected, all ACs issued by the AC 1382 issuer MUST be revoked. Rebuilding after such a compromise will be 1383 problematic, so AC issuers are advised to implement a combination of 1384 strong technical measures (e.g., tamper-resistant cryptographic 1385 modules) and appropriate management procedures (e.g., separation of 1386 duties) to avoid such an incident. 1388 Loss of an AC issuer's private signing key may also be problematic. 1389 The AC issuer would not be able to produce revocation status or 1390 perform AC renewal. AC issuers are advised to maintain secure backup 1391 for signing keys. The security of the key backup procedures is a 1392 critical factor in avoiding key compromise. 1394 The availability and freshness of revocation status will affect the 1395 degree of assurance that should be placed in a long-lived AC. While 1396 long-lived ACs expire naturally, events may occur during its natural 1397 lifetime which negate the binding between the AC holder and the 1398 attributes. If revocation status is untimely or unavailable, the 1399 assurance associated with the binding is clearly reduced. 1401 The binding between an AC holder and attributes cannot be stronger 1402 than the cryptographic module implementation and algorithms used to 1403 generate the signature. Short key lengths or weak hash algorithms 1404 will limit the utility of an AC. AC issuers are encouraged to note 1405 advances in cryptology so they can employ strong cryptographic 1406 techniques. 1408 Inconsistent application of name comparison rules may result in 1409 acceptance of invalid targeted or proxied ACs, or rejection of valid 1410 ones. The X.500 series of specifications defines rules for 1411 comparing distinguished names. These rules require comparison of 1412 strings without regard to case, character set, multi-character white 1413 space substrings, or leading and trailing white space. This 1414 specification and [PKIXPROF] relaxes these requirements, requiring 1415 support for binary comparison at a minimum. 1417 AC issuers MUST encode the distinguished name in the AC 1418 holder.entityName field identically to the distinguished name in the 1419 holder's PKC. If different encodings are used, implementations of 1420 this specification may fail to recognize that the AC and PKC belong 1421 to the same entity. 1423 Implementers MUST ensure that following validation of an AC, only 1424 attributes that the issuer is trusted to issue are used in 1425 authorization decisions. Other attributes, which MAY be present MUST 1426 be ignored. Given that the AA controls PKC extension is optional to 1427 implement, AC verifiers MUST be provided with this information by 1428 other means. Configuration information is a likely alternative 1429 means. This becomes very important if an AC verifier trusts more 1430 than one AC issuer. 1432 There is often a requirement to map between the authentication 1433 supplied by a particular security protocol (e.g. TLS, S/MIME) and 1434 the AC holder's identity. If the authentication uses PKCs, then this 1435 mapping is straightforward. However, it is envisaged that ACs will 1436 also be used in environments where the holder may be authenticated 1437 using other means. Implementers SHOULD be very careful in mapping 1438 the authenticated identity to the AC holder. 1440 9. References 1442 [CMC] Myers, M., et al. "Certificate Management Messages over 1443 CMS", RFC2797. 1444 [CMP] Adams, C., Farrell, S., "Internet X.509 Public Key 1445 Infrastructure - Certificate Management Protocols", 1446 RFC2510. 1447 [CMS] Housley, R., "Cryptographic Message Syntax", RFC 2630. 1448 [ESS] Hoffman, P., "Enhanced Security Services for S/MIME", 1449 RFC2634. 1450 [KRB] Kohl, J., Neuman, C., "The Kerberos Network 1451 Authentication Service (V5)", RFC 1510. 1452 [LDAP] Wahl, M., et al., "Lightweight Directory Access Protocol 1453 (v3)", RFC 2251. 1454 [OCSP] Myers, M., et al., " X.509 Internet Public Key 1455 Infrastructure - Online Certificate Status Protocol - 1456 OCSP", RFC 2560. 1457 [PKIXALGS] Polk, T., Bassham, L., "Internet X.509 Public Key 1458 Infrastructure Representation of Public Keys and Digital 1459 Signatures in Internet X.509 Public Key Infrastructure 1460 Certificates", draft-ietf-pkix-pkalgs-00.txt, work-in- 1461 progress. 1462 [PKINIT] Tung, B., et al., "Public Key Cryptography for Initial 1463 Authentication in Kerberos", draft-ietf-cat-kerberos-pk- 1464 init-11.txt, work-in-progress. 1465 [PKIXPROF] Housley, R., Ford, W., Polk, T, & Solo, D., "Internet 1466 Public Key Infrastructure - X.509 Certificate and CRL 1467 Profile", draft-ietf-pkix-new-part1-02.txt, work-in- 1468 progress. 1469 [RFC2026] Bradner, S., "The Internet Standards Process -- Revision 1470 3", RFC 2026, BCP 9, October 1996. 1471 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1472 Requirement Levels", RFC 2119. 1473 [URL] Berners-Lee, T., Masinter L., and M. McCahill., "Uniform 1474 Resource Locators (URL)", RFC 1738. 1475 [X.208-1988]CCITT Recommendation X.208: Specification of Abstract 1476 Syntax Notation One (ASN.1). 1988. 1477 [X.209-88] CCITT Recommendation X.209: Specification of Basic 1478 Encoding Rules for Abstract Syntax Notation One (ASN.1). 1479 1988. 1480 [X.501-88] CCITT Recommendation X.501: The Directory - Models. 1481 1988. 1482 [X.501-1993]ITU-T Recommendation X.501 : Information Technology - 1483 Open Systems Interconnection - The Directory: Models, 1484 1993. 1485 [X.509-1988]CCITT Recommendation X.509: The Directory - 1486 Authentication Framework. 1988. 1487 [X.509-1997]ITU-T Recommendation X.509: The Directory - 1488 Authentication Framework. 1997. 1489 [X.509-2000]ITU-T Recommendation X.509: The Directory - Public-Key 1490 and Attribute Certificate Frameworks. 2000 1492 Author's Addresses 1494 Stephen Farrell 1495 Baltimore Technologies 1496 61/62 Fitzwilliam Lane 1497 Dublin 2 1498 IRELAND 1500 tel: +353-1-647-3000 1501 email: stephen.farrell@baltimore.ie 1503 Russell Housley 1504 SPYRUS 1505 381 Elden Street 1506 Suite 1120 1507 Herndon, VA 20170 1508 USA 1510 tel: +1-703-707-0696 1511 email: housley@spyrus.com 1513 Full Copyright Statement 1515 Copyright (C) The Internet Society (date). All Rights Reserved. 1517 This document and translations of it may be copied and furnished to 1518 others, and derivative works that comment on or otherwise explain it 1519 or assist in its implementation may be prepared, copied, published 1520 and distributed, in whole or in part, without restriction of any 1521 kind, provided that the above copyright notice and this paragraph 1522 are included on all such copies and derivative works. In addition, 1523 the ASN.1 module presented in Appendix B may be used in whole or in 1524 part without inclusion of the copyright notice. However, this 1525 document itself may not be modified in any way, such as by removing 1526 the copyright notice or references to the Internet Society or other 1527 Internet organizations, except as needed for the purpose of 1528 developing Internet standards in which case the procedures for 1529 copyrights defined in the Internet Standards process shall be 1530 followed, or as required to translate it into languages other than 1531 English. 1533 The limited permissions granted above are perpetual and will not be 1534 revoked by the Internet Society or its successors or assigns. This 1535 document and the information contained herein is provided on an "AS 1536 IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK 1537 FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT 1538 NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN 1539 WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF 1540 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 1542 Appendix A: Object Identifiers 1544 This (normative) appendix lists the new object identifiers which are 1545 defined in this specification. Some of these are required only for 1546 support of optional features and are not required for conformance to 1547 this profile. This specification mandates support for OIDs which 1548 have arc elements with values that are less than 2^32, (i.e. they 1549 MUST be between 0 and 4,294,967,295 inclusive) and SHOULD be less 1550 than 2^31 (i.e. less than or equal to 2,147,483,647). This allows 1551 each arc element to be represented within a single 32 bit word. 1552 Implementations MUST also support OIDs where the length of the 1553 dotted decimal (see [LDAP], section 4.1.2) string representation can 1554 be up to 100 bytes (inclusive). Implementations MUST be able to 1555 handle OIDs with up to 20 elements (inclusive). AA's SHOULD NOT 1556 issue ACs which contain OIDs that breach these requirements. 1558 The following OIDs are imported from [PKIXPROF]: 1560 id-pkix OBJECT IDENTIFIER ::= { iso(1) identified-organization(3) 1561 dod(6) internet(1) security(5) mechanisms(5) pkix(7) } 1562 id-mod OBJECT IDENTIFIER ::= { id-pkix 0 } 1563 id-pe OBJECT IDENTIFIER ::= { id-pkix 1 } 1564 id-ad OBJECT IDENTIFIER ::= { id-pkix 48 } 1565 id-at OBJECT IDENTIFIER ::= { joint-iso-ccitt(2) ds(5) 4 } 1566 id-ce OBJECT IDENTIFIER ::= { joint-iso-ccitt(2) ds(5) 29 } 1568 The following new ASN.1 module OID is defined: 1570 id-mod-attribute-cert OBJECT IDENTIFIER ::= { id-mod 12 } 1572 The following AC extension OIDs are defined: 1574 id-pe-ac-auditIdentity OBJECT IDENTIFIER ::= { id-pe 4 } 1575 id-pe-ac-proxying OBJECT IDENTIFIER ::= { id-pe 10 } 1576 id-ce-targetInformation OBJECT IDENTIFIER ::= { id-ce 55 } 1578 The following PKC extension OIDs are defined: 1580 id-pe-aaControls OBJECT IDENTIFIER ::= { id-pe 6 } 1582 The following attribute OIDs are defined: 1584 id-aca OBJECT IDENTIFIER ::= { id-pkix 10 } 1585 id-aca-authenticationInfo OBJECT IDENTIFIER ::= { id-aca 1 } 1586 id-aca-accessIdentity OBJECT IDENTIFIER ::= { id-aca 2 } 1587 id-aca-chargingIdentity OBJECT IDENTIFIER ::= { id-aca 3 } 1588 id-aca-group OBJECT IDENTIFIER ::= { id-aca 4 } 1589 id-aca-encAttrs OBJECT IDENTIFIER ::= { id-aca 6 } 1590 id-at-role OBJECT IDENTIFIER ::= { id-at 72 } 1591 id-at-clearance OBJECT IDENTIFIER ::= 1592 { joint-iso-ccitt(2) ds(5) module(1) 1593 selected-attribute-types(5) clearance (55) } 1595 Appendix B: ASN.1 Module 1597 PKIXAttributeCertificate {iso(1) identified-organization(3) dod(6) 1598 internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) 1599 id-mod-attribute-cert(12)} 1601 DEFINITIONS EXPLICIT TAGS ::= 1603 BEGIN 1605 -- EXPORTS ALL -- 1607 IMPORTS 1609 -- IMPORTed module OIDs MAY change if [PKIXPROF] changes 1610 -- PKIX Certificate Extensions 1611 Attribute, AlgorithmIdentifier, CertificateSerialNumber, 1612 Extensions, UniqueIdentifier, 1613 id-pkix, id-pe, id-kp, id-ad, id-at 1614 FROM PKIX1Explicit88 {iso(1) identified-organization(3) 1615 dod(6) internet(1) security(5) mechanisms(5) 1616 pkix(7) id-mod(0) id-pkix1-explicit-88(1)} 1618 GeneralName, GeneralNames, id-ce 1619 FROM PKIX1Implicit88 {iso(1) identified-organization(3) 1620 dod(6) internet(1) security(5) mechanisms(5) 1621 pkix(7) id-mod(0) id-pkix1-implicit-88(2)} ; 1623 id-pe-ac-auditIdentity OBJECT IDENTIFIER ::= { id-pe 4 } 1624 id-pe-aaControls OBJECT IDENTIFIER ::= { id-pe 6 } 1625 id-pe-ac-proxying OBJECT IDENTIFIER ::= { id-pe 10 } 1626 id-ce-targetInformation OBJECT IDENTIFIER ::= { id-ce 55 } 1628 id-aca OBJECT IDENTIFIER ::= { id-pkix 10 } 1630 id-aca-authenticationInfo OBJECT IDENTIFIER ::= { id-aca 1 } 1631 id-aca-accessIdentity OBJECT IDENTIFIER ::= { id-aca 2 } 1632 id-aca-chargingIdentity OBJECT IDENTIFIER ::= { id-aca 3 } 1633 id-aca-group OBJECT IDENTIFIER ::= { id-aca 4 } 1634 -- { id-aca 5 } is reserved 1635 id-aca-encAttrs OBJECT IDENTIFIER ::= { id-aca 6 } 1637 id-at-role OBJECT IDENTIFIER ::= { id-at 72} 1638 id-at-clearance OBJECT IDENTIFIER ::= 1639 { joint-iso-ccitt(2) ds(5) module(1) 1640 selected-attribute-types(5) clearance (55) } 1642 -- Uncomment this if using a 1988 level ASN.1 compiler 1643 -- UTF8String ::= [UNIVERSAL 12] IMPLICIT OCTET STRING 1645 AttributeCertificate ::= SEQUENCE { 1646 acinfo AttributeCertificateInfo, 1647 signatureAlgorithm AlgorithmIdentifier, 1648 signatureValue BIT STRING 1649 } 1651 AttributeCertificateInfo ::= SEQUENCE { 1652 version AttCertVersion DEFAULT v1, 1653 holder Holder, 1654 issuer AttCertIssuer, 1655 signature AlgorithmIdentifier, 1656 serialNumber CertificateSerialNumber, 1657 attrCertValidityPeriod AttCertValidityPeriod, 1658 attributes SEQUENCE OF Attribute, 1659 issuerUniqueID UniqueIdentifier OPTIONAL, 1660 extensions Extensions OPTIONAL 1661 } 1663 AttCertVersion ::= INTEGER {v1(0), v2(1) } 1665 Holder ::= SEQUENCE { 1666 baseCertificateID [0] IssuerSerial OPTIONAL, 1667 -- the issuer and serial number of 1668 -- the holder's Public Key Certificate 1669 entityName [1] GeneralNames OPTIONAL, 1670 -- the name of the claimant or role 1671 objectDigestInfo [2] ObjectDigestInfo OPTIONAL 1672 -- if present, version must be v2 1673 } 1675 ObjectDigestInfo ::= SEQUENCE { 1676 digestedObjectType ENUMERATED { 1677 publicKey (0), 1678 publicKeyCert (1), 1679 otherObjectTypes (2) }, 1680 -- otherObjectTypes MUST NOT 1681 -- MUST NOT be used in this profile 1682 otherObjectTypeID OBJECT IDENTIFIER OPTIONAL, 1683 digestAlgorithm AlgorithmIdentifier, 1684 objectDigest BIT STRING 1685 } 1687 AttCertIssuer ::= CHOICE { 1688 v1Form GeneralNames, -- v1 or v2 1689 v2Form [0] V2Form -- v2 only 1690 } 1692 V2Form ::= SEQUENCE { 1693 issuerName GeneralNames OPTIONAL, 1694 baseCertificateID [0] IssuerSerial OPTIONAL, 1695 objectDigestInfo [1] ObjectDigestInfo OPTIONAL 1696 -- at least one of issuerName, baseCertificateID 1697 -- or objectDigestInfo must be present 1698 } 1699 IssuerSerial ::= SEQUENCE { 1700 issuer GeneralNames, 1701 serial CertificateSerialNumber, 1702 issuerUID UniqueIdentifier OPTIONAL 1703 } 1705 AttCertValidityPeriod ::= SEQUENCE { 1706 notBeforeTime GeneralizedTime, 1707 notAfterTime GeneralizedTime 1708 } 1710 Targets ::= SEQUENCE OF Target 1712 Target ::= CHOICE { 1713 targetName [0] GeneralName, 1714 targetGroup [1] GeneralName, 1715 targetCert [2] TargetCert 1716 } 1718 TargetCert ::= SEQUENCE { 1719 targetCertificate IssuerSerial, 1720 targetName GeneralName OPTIONAL, 1721 certDigestInfo ObjectDigestInfo OPTIONAL 1722 } 1724 IetfAttrSyntax ::= SEQUENCE { 1725 policyAuthority[0] GeneralNames OPTIONAL, 1726 values SEQUENCE OF CHOICE { 1727 octets OCTET STRING, 1728 oid OBJECT IDENTIFIER, 1729 string UTF8String 1730 } 1731 } 1733 SvceAuthInfo ::= SEQUENCE { 1734 service GeneralName, 1735 ident GeneralName, 1736 authInfo OCTET STRING OPTIONAL 1737 } 1739 RoleSyntax ::= SEQUENCE { 1740 roleAuthority [0] GeneralNames OPTIONAL, 1741 roleName [1] GeneralName 1742 } 1744 Clearance ::= SEQUENCE { 1745 policyId OBJECT IDENTIFIER, 1746 classList ClassList DEFAULT {unclassified}, 1747 securityCategories 1748 SET OF SecurityCategory OPTIONAL 1749 } 1751 ClassList ::= BIT STRING { 1752 unmarked (0), 1753 unclassified (1), 1754 restricted (2), 1755 confidential (3), 1756 secret (4), 1757 topSecret (5) 1758 } 1760 SecurityCategory ::= SEQUENCE { 1761 type [0] IMPLICIT OBJECT IDENTIFIER, 1762 value [1] ANY DEFINED BY type 1763 } 1765 AAControls ::= SEQUENCE { 1766 pathLenConstraint INTEGER (0..MAX) OPTIONAL, 1767 permittedAttrs [0] AttrSpec OPTIONAL, 1768 excludedAttrs [1] AttrSpec OPTIONAL, 1769 permitUnSpecified BOOLEAN DEFAULT TRUE 1770 } 1772 AttrSpec::= SEQUENCE OF OBJECT IDENTIFIER 1774 ACClearAttrs ::= SEQUENCE { 1775 acIssuer GeneralName, 1776 acSerial INTEGER, 1777 attrs SEQUENCE OF Attribute 1778 } 1780 ProxyInfo ::= SEQUENCE OF Targets 1782 END