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If these are example addresses, they should be changed. ** The document seems to lack a both a reference to RFC 2119 and the recommended RFC 2119 boilerplate, even if it appears to use RFC 2119 keywords. RFC 2119 keyword, line 115: '... } OPTIONAL,...' RFC 2119 keyword, line 117: '... } OPTIONAL,...' RFC 2119 keyword, line 182: '...certificate that MUST be ignored for t...' RFC 2119 keyword, line 185: '... list of X.509 extensions that MUST be...' RFC 2119 keyword, line 188: '...st of the CA-provided checks that MUST...' (14 more instances...) Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (May 27, 2018) is 2154 days in the past. Is this intentional? Checking references for intended status: Experimental ---------------------------------------------------------------------------- -- Missing reference section? '1' on line 387 looks like a reference -- Missing reference section? '2' on line 390 looks like a reference -- Missing reference section? '3' on line 392 looks like a reference -- Missing reference section? '0' on line 294 looks like a reference Summary: 2 errors (**), 0 flaws (~~), 2 warnings (==), 5 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group 3 Internet-Draft TCI 4 Intended status: Experimental May 27, 2018 5 Expires: November 28, 2018 7 Certificate Limitation Policy 8 draft-belyavskiy-certificate-limitation-policy-06 10 Abstract 12 The document provides a specification of the application-level trust 13 model. Being provided at the application level, the limitations of 14 trust can be distributed separately using cryptographically protected 15 format instead of hardcoding the checks into the application itself. 17 Status of This Memo 19 This Internet-Draft is submitted in full conformance with the 20 provisions of BCP 78 and BCP 79. 22 Internet-Drafts are working documents of the Internet Engineering 23 Task Force (IETF). Note that other groups may also distribute 24 working documents as Internet-Drafts. The list of current Internet- 25 Drafts is at https://datatracker.ietf.org/drafts/current/. 27 Internet-Drafts are draft documents valid for a maximum of six months 28 and may be updated, replaced, or obsoleted by other documents at any 29 time. It is inappropriate to use Internet-Drafts as reference 30 material or to cite them other than as "work in progress." 32 This Internet-Draft will expire on November 28, 2018. 34 Copyright Notice 36 Copyright (c) 2018 IETF Trust and the persons identified as the 37 document authors. All rights reserved. 39 This document is subject to BCP 78 and the IETF Trust's Legal 40 Provisions Relating to IETF Documents 41 (https://trustee.ietf.org/license-info) in effect on the date of 42 publication of this document. Please review these documents 43 carefully, as they describe your rights and restrictions with respect 44 to this document. Code Components extracted from this document must 45 include Simplified BSD License text as described in Section 4.e of 46 the Trust Legal Provisions and are provided without warranty as 47 described in the Simplified BSD License. 49 1. Introduction 51 Binary trust model standardized as a set of trusted anchors and CRLs/ 52 OCSP services does not cover all corner cases in the modern crypto 53 world. There is a need in more differentiated limitations. Some of 54 them are suggested [1] by Google when it limits the usage of 55 Symantec's certificates. The CRL profile does not fit the purpose of 56 such limitations. The CRLs are issued by the same CAs that are 57 subject to be limited. 59 Currently the set of CAs trusted by OS or browsers can be used for 60 the validation purposes. In case when a large enough CA becomes 61 untrusted, it cannot be deleted from the storage of trusted CAs 62 because it may cause error of validation of many certificates. The 63 measures usually taken in such cases usually include application- 64 level limitation of certificates lifetimes, refusing to accept EV- 65 certificates in other way than DV, requirements to use Certificate 66 Transparency, etc. 68 This document suggests a cryptographically signed format dubbed 69 Certificate Limitation Profile (CLP) designed for description of such 70 limitations. This format can be used by applications that use 71 system-wide set of trust anchors for validating purposes or by 72 applications with own wide enough set of trusted anchors in case when 73 the trust anchor for the entity found misbehaving cannot be revoked. 75 Currently the only way to provide such limitations is hard coding 76 them in application itself. Using of CLPs does not allow to 77 completely avoid hard coding but allows to hard code only the minimal 78 set of rarely changing data: 80 the fact that application uses CLP 82 the certificate to verify the signature under the CLP file 84 minimal date of the CLP to be used for the current version of 85 application. 87 It will be possible to move the checks for the limitations to the 88 external cryptographical libraries, such as OpenSSL, instead of 89 checking them at the application level. 91 2. Certificate Limitations Profile 93 A proposed syntax and overall structure of CLP is very similar to the 94 one defined for CRLs [2]. 96 CertificateList ::= SEQUENCE { 97 tbsCertList TBSCertList, 98 signatureAlgorithm AlgorithmIdentifier, 99 signatureValue BIT STRING } 101 TBSCertList ::= SEQUENCE { 102 version Version, 103 signature AlgorithmIdentifier, 104 issuer Name, 105 thisUpdate Time, 106 nextUpdate Time, 107 limitedCertificates SEQUENCE OF SEQUENCE { 108 userCertificate CertificateSerialNumber, 109 certificateIssuer Name, 110 limitationDate Time, 111 limitationPropagation Enum, 112 fingerprint SEQUENCE { 113 fingerprintAlgorithm AlgorithmIdentifier, 114 fingerprintValue OCTET STRING 115 } OPTIONAL, 116 limitations Limitations, 117 } OPTIONAL, 118 }; 120 Limitations ::= SEQUENCE SIZE (1..MAX) OF Limitation 122 Limitation ::= SEQUENCE { 123 limitID OBJECT IDENTIFIER, 124 LimitationValue OCTET STRING 125 -- contains the DER encoding of an ASN.1 value 126 -- corresponding to the limitation type 127 -- identified by limitID 128 } 130 The ASN.1 format of particular limitations is provided in the 131 corresponding sections. Anywhere below the Time in ASN.1 notation is 132 treated according to RFC 5280: 134 Time ::= CHOICE { 135 utcTime UTCTime, 136 generalTime GeneralizedTime } 138 2.1. CLP fields 140 CLP has general structure similar to CRLs. The upper-level fields 141 are: 143 TBSCertList - the sequence of individual certificates to be 144 limited; 146 signatureAlgorithm - the OID of the signature algorithm used for 147 signature; 149 signatureValue - the bit string representing signature of the 150 TBSCertList. 152 2.2. CLP signature 154 The key used for signing the CLP files should have a special Key 155 Usage value and/or an Extended Key Usage value. 157 2.3. CLP entry fields 159 Each entry in list contains the following fields: 161 The issuer of the certificate with limited trust. 163 The serial of the certificate with limited trust. 165 The fingerprint of the certificate with limited trust (optional). 167 limitationPropagation. This field indicates whether limitations 168 are applied to the certificate itself, to all of its descendants 169 in the chain of trust, or both. 171 and a subset of the following limitations: 173 issuedNotAfter - do not trust the certs issued after the specified 174 date 176 trustNotAfter - do not trust the certs after the specified date 178 validityPeriod, days - take minimal value from "native" validity 179 period and specified in the limitation file 181 ignoredX509Extensions - list of X.509 extensions of limited 182 certificate that MUST be ignored for the specified certificate 183 (e.g. EV-indicating extensions) 185 requiredX509extensions - list of X.509 extensions that MUST be 186 present in the certificate to be trusted. 188 requiredNativeChecking - list of the CA-provided checks that MUST 189 be applied 190 applicationNameConstraints - list of domains allowed to be issued 191 by this certificate 193 excludedIssueIntermediatory - disallow issuing of the 194 Intermediatory certificates 196 The limitations are identified by OIDs 198 2.3.1. Limitations 200 2.3.1.1. issuedNotAfter 202 When this limitation is present, any certificate matching the entry 203 and issued after the specified date MUST NOT be trusted 205 The issuedNotAfter limitation is identified by OID TBA. 207 issuedNotAfter ::= SEQUENCE { 208 IssuedNotAfter Time 209 } 211 2.3.1.2. trustNotAfter 213 When this limitation is present, any certificate matching the entry 214 MUST NOT be trusted after the specified date. 216 The trustNotAfter limitation is identified by OID TBA. 218 trustNotAfter ::= SEQUENCE { 219 TrustNotAfter Time 220 } 222 2.3.1.3. validityPeriod 224 When this limitation is present, no certificate matching the entry 225 should be treated as valid after specified period from its validFrom. 227 The validityPeriod is measured in days. 229 The validityPeriod limitation is identified by OID TBA. 231 validityPeriod ::= SEQUENCE { 232 Days INTEGER 233 } 235 2.3.1.4. ignoredX509Extensions 237 When this limitation is present, the extensions listed in this 238 element should be ignored for the matching certificate. 240 The ignoredX509Extensions limitation is identified by OID TBA. 242 ignoredX509Extensions :: = SEQUENCE SIZE (1..MAX) OF ExtenID 243 ExtenID :: = OBJECT IDENTIFIER 245 2.3.1.5. requiredX509extensions 247 When this limitation is present, the extensions listed in this 248 element should be present for the matching certificate. 250 The requiredX509extensions limitation is identified by OID TBA. 252 requiredX509extensions :: = SEQUENCE SIZE (1..MAX) OF ExtenID 253 ExtenID :: = OBJECT IDENTIFIER 255 2.3.1.6. requiredNativeChecking 257 When this limitation is present, it specifies that the certificates 258 issued by this CA SHOULD be checked against CRL and/or OCSP, 259 depending on contents of the extension. 261 The requiredNativeChecking limitation is identified by OID TBA. 263 requiredNativeChecking ::= SEQUENCE { 264 RequiredCRLChecking BOOLEAN, 265 RequiredOCSPChecking BOOLEAN 266 } 268 2.3.1.7. applicationNameConstraints 270 This limitation are applied like Name Constraints [3] limitation 271 specified in RFC 5280. 273 This section implies 2 variants of checks: 275 The list of names that are allowed for the CA to issue 276 certificates for 278 The list of names that are forbidden for the CA to issue 279 certificates for 281 The applicationNameConstraints limitation is specified according to 282 RFC 5280, 4.2.1.10 and reuses OID specified in RFC 5280. 284 id-ce-nameConstraints OBJECT IDENTIFIER ::= { id-ce 30 } 286 NameConstraints ::= SEQUENCE { 287 permittedSubtrees [0] GeneralSubtrees OPTIONAL, 288 excludedSubtrees [1] GeneralSubtrees OPTIONAL } 290 GeneralSubtrees ::= SEQUENCE SIZE (1..MAX) OF GeneralSubtree 292 GeneralSubtree ::= SEQUENCE { 293 base GeneralName, 294 minimum [0] BaseDistance DEFAULT 0, 295 maximum [1] BaseDistance OPTIONAL } 297 BaseDistance ::= INTEGER (0..MAX) 299 2.3.1.7.1. excludedIssueIntermediatory 301 When this limitation is present, the intermediate certificates issued 302 by this CA MUST NOT be trusted. 304 The excludedIssueIntermediatory limitation is identified by OID TBA. 306 3. Verification of CLP 308 The verification of CLP SHOULD be performed by the application. The 309 application should check whether the provided CLP matches the 310 internal requirements and is correclty signed by the specified key. 312 4. Verification with CLP 314 In case of using CLP the checks enforced by CLP should be applied 315 after the other checks. 317 The limitation provided by CLP MUST NOT extend the trustworthy of the 318 checked certificate. 320 The limitations are applied after cryptographic validation of the 321 certificate and during building its chain of trust. If the 322 certificate or any of its ascendants in the chain of trust matches 323 any record in the CLP, the limitations are applied from the ascendant 324 to descendants. The issuedNotAfter and trustNotAfter limitations are 325 applied to find out the actual validity periods for the any 326 certificate in the chain of trust. If the CLP prescribes to have a 327 particular extension(s) and the certificate does not have it, the 328 certificate MUST NOT be trusted. 330 Application MAY use more than one CLPs (e.g. app-wide, set of system- 331 wide, user-defined). When multiple CLPs are in use, the limitations 332 are applied simultaneously. 334 In case when more than one chain of trust are valid for a 335 certificate, if any of this chains is valid after applying the 336 limitations, the certificate MUST be treated as valid. 338 5. ASN.1 notation 340 TBD 342 6. Security considerations 344 In case when an application uses CLP, it is recommended to specify 345 the minimal date of issuing of the CLP document somewhere in code. 346 It allows to avoid an attack of CLP rollback when the stale version 347 of CLP is used. 349 It is recommended to distribute CLPs using the channels that are used 350 for distribution of the applications themselves to avoid possible DoS 351 consequences. 353 If application checks for fresh CLPs, it SHOULD check that nextUpdate 354 field in a fresh one is newer than in the current one. The 355 application MAY accept a CLP with nextUpdate in past. If an 356 application is failing to get updates, then it can continue to run 357 with what it has. 359 6.1. Unsigned CLP 361 In case of trusted environment signing CLP can be reluctant. If CLP 362 is delivered via application bundle, it can be verified together with 363 other application data. But it makes sense to separate trust to the 364 source of the content from trust to the content itself. On the other 365 hand it is not a problem to create a local CLP signed by a locally 366 created key. 368 7. IANA considerations 370 TBD 372 8. Acknoledgements 374 Special thanks to Rich Salz, Igor Ustinov, Vasily Dolmatov, Stanislav 375 Smyishlyaev, Patrik Faeltstroem, Alexander Venedioukhin, Artem 376 Chuprina, Viktor Dukhovni. 378 9. References 380 The current version of the document is available on GitHub 381 https://github.com/beldmit/clp 383 10. References 385 10.1. URIs 387 [1] https://groups.google.com/a/chromium.org/forum/#!msg/blink- 388 dev/eUAKwjihhBs/rpxMXjZHCQAJ 390 [2] https://tools.ietf.org/html/rfc5280#section-5 392 [3] https://tools.ietf.org/html/rfc5280#section-4.2.1.10 394 Author's Address 396 Dmitry Belyavskiy 397 Technical Centre of Internet 398 8 Marta str., 1 bld. 12 399 Moscow 127083 400 RU 402 Email: beldmit@gmail.com