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Checking references for intended status: Informational ---------------------------------------------------------------------------- == Outdated reference: A later version (-20) exists of draft-young-md-query-15 -- Obsolete informational reference (is this intentional?): RFC 4844 (Obsoleted by RFC 8729) Summary: 0 errors (**), 0 flaws (~~), 2 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group I. Young, Ed. 3 Internet-Draft Independent 4 Intended status: Informational July 8, 2021 5 Expires: January 9, 2022 7 SAML Profile for the Metadata Query Protocol 8 draft-young-md-query-saml-15 10 Abstract 12 This document profiles the Metadata Query Protocol for use with SAML 13 metadata. 15 This document is a product of the Research and Education Federations 16 (REFEDS) Working Group process. 18 Editorial Note (To be removed by RFC Editor before publication) 20 Discussion of this draft takes place on the MDX mailing list 21 (mdx@lists.iay.org.uk), which is accessed from [MDX.list]. 23 XML versions, latest edits and the issues list for this document are 24 available from [md-query]. 26 The changes in this draft are summarized in Appendix A.16. 28 Status of This Memo 30 This Internet-Draft is submitted in full conformance with the 31 provisions of BCP 78 and BCP 79. 33 Internet-Drafts are working documents of the Internet Engineering 34 Task Force (IETF). Note that other groups may also distribute 35 working documents as Internet-Drafts. The list of current Internet- 36 Drafts is at https://datatracker.ietf.org/drafts/current/. 38 Internet-Drafts are draft documents valid for a maximum of six months 39 and may be updated, replaced, or obsoleted by other documents at any 40 time. It is inappropriate to use Internet-Drafts as reference 41 material or to cite them other than as "work in progress." 43 This Internet-Draft will expire on January 9, 2022. 45 Copyright Notice 47 Copyright (c) 2021 IETF Trust and the persons identified as the 48 document authors. All rights reserved. 50 This document is subject to BCP 78 and the IETF Trust's Legal 51 Provisions Relating to IETF Documents 52 (https://trustee.ietf.org/license-info) in effect on the date of 53 publication of this document. Please review these documents 54 carefully, as they describe your rights and restrictions with respect 55 to this document. 57 Table of Contents 59 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 60 1.1. Notation and Conventions . . . . . . . . . . . . . . . . 3 61 2. Request Profile . . . . . . . . . . . . . . . . . . . . . . . 3 62 2.1. Content Type . . . . . . . . . . . . . . . . . . . . . . 3 63 2.2. Identifiers . . . . . . . . . . . . . . . . . . . . . . . 4 64 2.2.1. Unique Identifier . . . . . . . . . . . . . . . . . . 4 65 2.2.2. Transformed Identifier . . . . . . . . . . . . . . . 4 66 2.2.3. Additional Identifiers . . . . . . . . . . . . . . . 5 67 3. Response Profile . . . . . . . . . . . . . . . . . . . . . . 5 68 3.1. Response Cardinality . . . . . . . . . . . . . . . . . . 5 69 3.1.1. No Entity Descriptors Returned . . . . . . . . . . . 5 70 3.1.2. One Entity Descriptor Returned . . . . . . . . . . . 5 71 3.1.3. More Than One Entity Descriptor Returned . . . . . . 5 72 4. Security Considerations . . . . . . . . . . . . . . . . . . . 6 73 4.1. Integrity . . . . . . . . . . . . . . . . . . . . . . . . 6 74 4.2. Use of SHA-1 in Transformed Identifiers . . . . . . . . . 6 75 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 76 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 77 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 78 7.1. Normative References . . . . . . . . . . . . . . . . . . 7 79 7.2. Informative References . . . . . . . . . . . . . . . . . 8 80 Appendix A. Change Log (to be removed by RFC Editor before 81 publication) . . . . . . . . . . . . . . . . . . . . 10 82 A.1. draft-young-md-query-saml-00 . . . . . . . . . . . . . . 10 83 A.2. Since draft-young-md-query-saml-00 . . . . . . . . . . . 10 84 A.3. Since draft-young-md-query-saml-01 . . . . . . . . . . . 10 85 A.4. Since draft-young-md-query-saml-02 . . . . . . . . . . . 10 86 A.5. Since draft-young-md-query-saml-03 . . . . . . . . . . . 10 87 A.6. Since draft-young-md-query-saml-04 . . . . . . . . . . . 10 88 A.7. Since draft-young-md-query-saml-05 . . . . . . . . . . . 10 89 A.8. Since draft-young-md-query-saml-06 . . . . . . . . . . . 10 90 A.9. Since draft-young-md-query-saml-07 . . . . . . . . . . . 10 91 A.10. Since draft-young-md-query-saml-08 . . . . . . . . . . . 11 92 A.11. Since draft-young-md-query-saml-09 . . . . . . . . . . . 11 93 A.12. Since draft-young-md-query-saml-10 . . . . . . . . . . . 11 94 A.13. Since draft-young-md-query-saml-11 . . . . . . . . . . . 11 95 A.14. Since draft-young-md-query-saml-12 . . . . . . . . . . . 11 96 A.15. Since draft-young-md-query-saml-13 . . . . . . . . . . . 12 97 A.16. Since draft-young-md-query-saml-14 . . . . . . . . . . . 12 98 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 12 100 1. Introduction 102 This document profiles the Metadata Query Protocol 103 [I-D.young-md-query] for use with SAML metadata [SAML2Meta]. 105 The Research and Education Federations group ([REFEDS]) is the voice 106 that articulates the mutual needs of research and education identity 107 federations worldwide. It aims to represent the requirements of 108 research and education in the ever-growing space of access and 109 identity management. 111 From time to time REFEDS will wish to publish a document in the 112 Internet RFC series. Such documents will be published as part of the 113 RFC Independent Submission Stream [RFC4844]; however the REFEDS 114 working group sign-off process will have been followed for these 115 documents, as described in the REFEDS Participant's Agreement 116 [REFEDS.agreement]. 118 This document is a product of the REFEDS Working Group process. 120 1.1. Notation and Conventions 122 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 123 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 124 "OPTIONAL" in this document are to be interpreted as described in 125 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all 126 capitals, as shown here. 128 This document makes use of the Augmented BNF metalanguage defined in 129 [STD68]. 131 2. Request Profile 133 2.1. Content Type 135 Requests compliant with this profile MUST include the following HTTP 136 header to indicate that the metadata returned should be SAML metadata 137 (see Appendix A of [SAML2Meta]): 139 Accept: application/samlmetadata+xml 141 2.2. Identifiers 143 2.2.1. Unique Identifier 145 Each entity known to the responder MUST be associated with the unique 146 identifier of the entity, corresponding to the "entityID" attribute 147 of the entity's "EntityDescriptor" element in SAML metadata. 149 2.2.2. Transformed Identifier 151 SAML 2.0 [SAML2Core] includes profiles based on the transfer of an 152 "artifact" containing the unique identifier of a SAML entity 153 transformed by means of the SHA-1 [RFC3174] hash algorithm (see 154 [SAML2Bind] sections 3.6 and 3.6.4). 156 In order to support use cases in which clients may be in possession 157 of only such a transformed representation of a SAML entity's unique 158 identifier without any way to establish the original entity 159 identifier, a responder compliant with this profile MUST associate 160 each entity with an identifier matching the "sha1id" production in 161 the following ABNF grammar, and treat such an identifier as 162 equivalent to the corresponding untransformed identifier: 164 SHA1 = %x73 %x68 %x61 %x31 ; lower case "sha1" 165 DIGIT = %x30-39 166 HEXDIGIT = DIGIT | %x61-66 ; lower case a-f 167 sha1id = "{" SHA1 "}" sha1hex 168 sha1hex = 40*HEXDIGIT 170 In the above, the "sha1hex" component encodes the 20-octet (160-bit) 171 binary SHA-1 hash value as a sequence of 40 lower case hexadecimal 172 digits. 174 For example, the identifier 176 http://example.org/service 178 transformed by means of SHA-1 hashing would become 180 {sha1}11d72e8cf351eb6c75c721e838f469677ab41bdb 182 Responder implementations MAY detect malformed SHA-1 transformed 183 identifiers (for example where the string of characters following the 184 "}" contains characters other than hexadecimal digits, or is other 185 than exactly 40 characters in length) and return an HTTP status code 186 of 400 ("bad request"). Alternatively, implementations MAY process 187 these as normal identifiers and return an HTTP status code of 404 188 ("not found") if appropriate. 190 2.2.3. Additional Identifiers 192 Entities MAY also be associated with any number of additional 193 responder-defined identifiers naming arbitrary groups of entities. 195 3. Response Profile 197 3.1. Response Cardinality 199 A request may return information for any number of entities, 200 including none. Responses compliant with this profile MUST use the 201 appropriate representation described below depending on the number of 202 "EntityDescriptor" elements returned. 204 3.1.1. No Entity Descriptors Returned 206 A response which returns no "EntityDescriptor" elements MUST be 207 represented by an HTTP status code of 404 ("not found"). 209 3.1.2. One Entity Descriptor Returned 211 A response which returns a single "EntityDescriptor" element MUST use 212 that element as its document element. The responder MUST NOT make 213 use of a "EntitiesDescriptor" element in this situation (see 214 [SAML2Meta] section 2.3). 216 Such a response MUST include the following HTTP header to indicate 217 that the metadata returned is SAML metadata: 219 Content-Type: application/samlmetadata+xml 221 3.1.3. More Than One Entity Descriptor Returned 223 A response which returns more than one "EntityDescriptor" element 224 MUST consist of a document element which is an "EntitiesDescriptor" 225 element, containing the returned "EntityDescriptor" elements as 226 children. Responses MUST NOT contain nested "EntitiesDescriptor" 227 elements. 229 Such a response MUST include the following HTTP header to indicate 230 that the metadata returned is SAML metadata: 232 Content-Type: application/samlmetadata+xml 234 4. Security Considerations 236 4.1. Integrity 238 As SAML metadata contains information necessary for the secure 239 operation of interacting services it is strongly RECOMMENDED that a 240 mechanism for integrity checking is provided to clients. 242 It is RECOMMENDED that the integrity checking mechanism provided by a 243 responder is a digital signature embedded in the returned metadata 244 document, as defined by [SAML2Meta] section 3. 246 Such digital signatures: 248 o SHOULD use an RSA keypair whose modulus is no less than 2048 bits 249 in length. 251 o MUST NOT use the SHA-1 cryptographic hash algorithm as a digest 252 algorithm. 254 o MUST NOT use the MD5 cryptographic hash algorithm as a digest 255 algorithm. 257 o SHOULD otherwise follow current cryptographic best practices in 258 algorithm selection. 260 4.2. Use of SHA-1 in Transformed Identifiers 262 This profile mandates the availability of an identifier synonym 263 mechanism based on the SHA-1 cryptographic hash algorithm. Although 264 SHA-1 is now regarded as weak enough to exclude it from use in new 265 cryptographic systems, its use in this profile is necessary for full 266 support of the SAML 2.0 standard. 268 The use of SHA-1 in section 3.6.4 of [SAML2Bind], and its resulting 269 use in this protocol, would be vulnerable to an attack in which 270 metadata was introduced into a system by an attacker capable of 271 creating an entity identifier with the same SHA-1 hash as that of an 272 existing entity's identifier. 274 Such an identifier is known as a _second preimage_ of the original, 275 and SHA-1's resistance to discovery of it is referred to as SHA-1's 276 _second-preimage resistance_. 278 As demonstrated by the the [SHAttered] and [Shambles] attacks, the 279 SHA-1 algorithm is known to have weak collision resistance. However, 280 at the time of writing no attacks are known on SHA-1's second- 281 preimage resistance; a result in this area would be required to 282 provide the basis of an attack based on duplicating the SHA-1 hash of 283 an existing identifier. As a result, the use of SHA-1 in SAML and in 284 this protocol is not believed to introduce a security concern. 286 Implementations may guard against the possibility of a future 287 practical attack on the second-preimage resistance of SHA-1 by 288 treating two entities whose "entityID" values have the same SHA-1 289 equivalent as an indicator of malicious intent on the part of the 290 owner of one of the entities. 292 5. IANA Considerations 294 This document has no actions for IANA. 296 6. Acknowledgements 298 The editor would like to acknowledge the following individuals for 299 their contributions to this document: 301 Scott Cantor (The Ohio State University) 303 Leif Johansson (SUNET) 305 Joe St Sauver (University of Oregon) 307 Tom Scavo (Internet2) 309 7. References 311 7.1. Normative References 313 [I-D.young-md-query] 314 Young, I., Ed., "Metadata Query Protocol", draft-young-md- 315 query-15 (work in progress), Jaly 2021. 317 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 318 Requirement Levels", BCP 14, RFC 2119, 319 DOI 10.17487/RFC2119, March 1997, 320 . 322 [RFC3174] Eastlake 3rd, D. and P. Jones, "US Secure Hash Algorithm 1 323 (SHA1)", RFC 3174, DOI 10.17487/RFC3174, September 2001, 324 . 326 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 327 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 328 May 2017, . 330 [SAML2Bind] 331 Cantor, S., Hirsch, F., Kemp, J., Philpott, R., and E. 332 Maler, "Bindings for the Security Assertion Markup 333 Language (SAML) V2.0", OASIS Standard saml-bindings- 334 2.0-os, March 2005. 336 [SAML2Meta] 337 Cantor, S., Moreh, J., Philpott, R., and E. Maler, 338 "Metadata for the Security Assertion Markup Language 339 (SAML) V2.0", OASIS Standard saml-metadata-2.0-os, March 340 2005. 342 [STD68] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 343 Specifications: ABNF", STD 68, RFC 5234, 344 DOI 10.17487/RFC5234, January 2008, 345 . 347 7.2. Informative References 349 [md-query] 350 Young, I., Ed., "md-query Project", 351 . 353 [MDX.list] 354 Young, I., Ed., "MDX Mailing List", 355 . 357 [REFEDS] Research and Education Federations, "REFEDS Home Page", 358 . 360 [REFEDS.agreement] 361 Research and Education Federations, "REFEDS Participant's 362 Agreement", 363 . 365 [RFC4844] Daigle, L., Ed. and Internet Architecture Board, "The RFC 366 Series and RFC Editor", RFC 4844, DOI 10.17487/RFC4844, 367 July 2007, . 369 [SAML2Core] 370 Cantor, S., Kemp, J., Philpott, R., and E. Maler, 371 "Assertions and Protocol for the OASIS Security Assertion 372 Markup Language (SAML) V2.0", OASIS Standard saml-core- 373 2.0-os, March 2005, . 376 [Shambles] 377 "SHA-1 is a Shambles", January 2020, 378 . 380 [SHAttered] 381 "SHAttered", February 2017, . 383 Appendix A. Change Log (to be removed by RFC Editor before publication) 385 A.1. draft-young-md-query-saml-00 387 Initial version. 389 A.2. Since draft-young-md-query-saml-00 391 Added REFEDS RFC stream boilerplate. 393 A.3. Since draft-young-md-query-saml-01 395 Bump reference to the Metadata Query Protocol [I-D.young-md-query]. 397 Rework Section 2.2 to make the role of transformed identifiers 398 clearer. This changes the semantics slightly (malformed transformed 399 identifiers may now result in a 404 return rather than 400) but this 400 gives implementers more latitude in the way that they handle the 401 feature. 403 A.4. Since draft-young-md-query-saml-02 405 Bump reference to the Metadata Query Protocol [I-D.young-md-query]. 407 A.5. Since draft-young-md-query-saml-03 409 Bump reference to the Metadata Query Protocol [I-D.young-md-query]. 411 Added an Editorial Note to help direct readers back to the 412 discussion. 414 A.6. Since draft-young-md-query-saml-04 416 Fix reference to the Metadata Query Protocol [I-D.young-md-query]. 418 A.7. Since draft-young-md-query-saml-05 420 Bump reference to the Metadata Query Protocol [I-D.young-md-query]. 422 A.8. Since draft-young-md-query-saml-06 424 Bump reference to the Metadata Query Protocol [I-D.young-md-query]. 426 A.9. Since draft-young-md-query-saml-07 428 Bump reference to the Metadata Query Protocol [I-D.young-md-query]. 430 A.10. Since draft-young-md-query-saml-08 432 Bump reference to the Metadata Query Protocol [I-D.young-md-query]. 434 Modernise normative language to include [RFC8174]. 436 Improved references to RFCs. 438 A.11. Since draft-young-md-query-saml-09 440 Bump reference to the Metadata Query Protocol [I-D.young-md-query]. 442 A.12. Since draft-young-md-query-saml-10 444 Bump reference to the Metadata Query Protocol [I-D.young-md-query]. 446 Replace citations in the abstract with straight textual mentions, as 447 required by the ID-NITS checklist. 449 A.13. Since draft-young-md-query-saml-11 451 Bump reference to the Metadata Query Protocol [I-D.young-md-query]. 453 Strengthen Section 4.1 so that SHA-1 now MUST NOT be used in the 454 context of digital signatures. This brings the section in line with 455 current best practice recommendations, particularly in light of the 456 [SHAttered] and [Shambles] attacks. 458 Revised Section 4.2 on the use of SHA-1 in transformed identifiers 459 to: 461 o Make clear that this is a SAML-level issue, not one introduced by 462 the query protocol. 464 o Reference the attacks demonstrating SHA-1's weak collision 465 resistance. 467 o Identify second-preimage resistance as the potential source of the 468 attack we'd be concerned about for the query protocol. 470 o Note that SHA-1's second-preimage resistance is at present 471 uncompromised. 473 A.14. Since draft-young-md-query-saml-12 475 Bump reference to the Metadata Query Protocol [I-D.young-md-query]. 477 A.15. Since draft-young-md-query-saml-13 479 Bump reference to the Metadata Query Protocol [I-D.young-md-query]. 481 A.16. Since draft-young-md-query-saml-14 483 Bump reference to the Metadata Query Protocol [I-D.young-md-query]. 485 Author's Address 487 Ian A. Young (editor) 488 Independent 490 EMail: ian@iay.org.uk