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Checking references for intended status: Informational ---------------------------------------------------------------------------- == Outdated reference: A later version (-20) exists of draft-young-md-query-12 -- Obsolete informational reference (is this intentional?): RFC 4844 (Obsoleted by RFC 8729)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 13, 2020 5 Expires: January 14, 2021 7 SAML Profile for the Metadata Query Protocol 8 draft-young-md-query-saml-13 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.14. 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 14, 2021. 45 Copyright Notice 47 Copyright (c) 2020 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 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 12 98 1. Introduction 100 This document profiles the Metadata Query Protocol 101 [I-D.young-md-query] for use with SAML metadata [SAML2Meta]. 103 The Research and Education Federations group ([REFEDS]) is the voice 104 that articulates the mutual needs of research and education identity 105 federations worldwide. It aims to represent the requirements of 106 research and education in the ever-growing space of access and 107 identity management. 109 From time to time REFEDS will wish to publish a document in the 110 Internet RFC series. Such documents will be published as part of the 111 RFC Independent Submission Stream [RFC4844]; however the REFEDS 112 working group sign-off process will have been followed for these 113 documents, as described in the REFEDS Participant's Agreement 114 [REFEDS.agreement]. 116 This document is a product of the REFEDS Working Group process. 118 1.1. Notation and Conventions 120 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 121 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 122 "OPTIONAL" in this document are to be interpreted as described in 123 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all 124 capitals, as shown here. 126 This document makes use of the Augmented BNF metalanguage defined in 127 [STD68]. 129 2. Request Profile 131 2.1. Content Type 133 Requests compliant with this profile MUST include the following HTTP 134 header to indicate that the metadata returned should be SAML metadata 135 (see Appendix A of [SAML2Meta]): 137 Accept: application/samlmetadata+xml 139 2.2. Identifiers 141 2.2.1. Unique Identifier 143 Each entity known to the responder MUST be associated with the unique 144 identifier of the entity, corresponding to the "entityID" attribute 145 of the entity's "EntityDescriptor" element in SAML metadata. 147 2.2.2. Transformed Identifier 149 SAML 2.0 [SAML2Core] includes profiles based on the transfer of an 150 "artifact" containing the unique identifier of a SAML entity 151 transformed by means of the SHA-1 [RFC3174] hash algorithm (see 152 [SAML2Bind] sections 3.6 and 3.6.4). 154 In order to support use cases in which clients may be in possession 155 of only such a transformed representation of a SAML entity's unique 156 identifier without any way to establish the original entity 157 identifier, a responder compliant with this profile MUST associate 158 each entity with an identifier matching the "sha1id" production in 159 the following ABNF grammar, and treat such an identifier as 160 equivalent to the corresponding untransformed identifier: 162 SHA1 = %x73 %x68 %x61 %x31 ; lower case "sha1" 163 DIGIT = %x30-39 164 HEXDIGIT = DIGIT | %x61-66 ; lower case a-f 165 sha1id = "{" SHA1 "}" sha1hex 166 sha1hex = 40*HEXDIGIT 168 In the above, the "sha1hex" component encodes the 20-octet (160-bit) 169 binary SHA-1 hash value as a sequence of 40 lower case hexadecimal 170 digits. 172 For example, the identifier 174 http://example.org/service 176 transformed by means of SHA-1 hashing would become 178 {sha1}11d72e8cf351eb6c75c721e838f469677ab41bdb 180 Responder implementations MAY detect malformed SHA-1 transformed 181 identifiers (for example where the string of characters following the 182 "}" contains characters other than hexadecimal digits, or is other 183 than exactly 40 characters in length) and return an HTTP status code 184 of 400 ("bad request"). Alternatively, implementations MAY process 185 these as normal identifiers and return an HTTP status code of 404 186 ("not found") if appropriate. 188 2.2.3. Additional Identifiers 190 Entities MAY also be associated with any number of additional 191 responder-defined identifiers naming arbitrary groups of entities. 193 3. Response Profile 195 3.1. Response Cardinality 197 A request may return information for any number of entities, 198 including none. Responses compliant with this profile MUST use the 199 appropriate representation described below depending on the number of 200 "EntityDescriptor" elements returned. 202 3.1.1. No Entity Descriptors Returned 204 A response which returns no "EntityDescriptor" elements MUST be 205 represented by an HTTP status code of 404 ("not found"). 207 3.1.2. One Entity Descriptor Returned 209 A response which returns a single "EntityDescriptor" element MUST use 210 that element as its document element. The responder MUST NOT make 211 use of a "EntitiesDescriptor" element in this situation (see 212 [SAML2Meta] section 2.3). 214 Such a response MUST include the following HTTP header to indicate 215 that the metadata returned is SAML metadata: 217 Content-Type: application/samlmetadata+xml 219 3.1.3. More Than One Entity Descriptor Returned 221 A response which returns more than one "EntityDescriptor" element 222 MUST consist of a document element which is an "EntitiesDescriptor" 223 element, containing the returned "EntityDescriptor" elements as 224 children. Responses MUST NOT contain nested "EntitiesDescriptor" 225 elements. 227 Such a response MUST include the following HTTP header to indicate 228 that the metadata returned is SAML metadata: 230 Content-Type: application/samlmetadata+xml 232 4. Security Considerations 234 4.1. Integrity 236 As SAML metadata contains information necessary for the secure 237 operation of interacting services it is strongly RECOMMENDED that a 238 mechanism for integrity checking is provided to clients. 240 It is RECOMMENDED that the integrity checking mechanism provided by a 241 responder is a digital signature embedded in the returned metadata 242 document, as defined by [SAML2Meta] section 3. 244 Such digital signatures: 246 o SHOULD use an RSA keypair whose modulus is no less than 2048 bits 247 in length. 249 o MUST NOT use the SHA-1 cryptographic hash algorithm as a digest 250 algorithm. 252 o MUST NOT use the MD5 cryptographic hash algorithm as a digest 253 algorithm. 255 o SHOULD otherwise follow current cryptographic best practices in 256 algorithm selection. 258 4.2. Use of SHA-1 in Transformed Identifiers 260 This profile mandates the availability of an identifier synonym 261 mechanism based on the SHA-1 cryptographic hash algorithm. Although 262 SHA-1 is now regarded as weak enough to exclude it from use in new 263 cryptographic systems, its use in this profile is necessary for full 264 support of the SAML 2.0 standard. 266 The use of SHA-1 in section 3.6.4 of [SAML2Bind], and its resulting 267 use in this protocol, would be vulnerable to an attack in which 268 metadata was introduced into a system by an attacker capable of 269 creating an entity identifier with the same SHA-1 hash as that of an 270 existing entity's identifier. 272 Such an identifier is known as a _second preimage_ of the original, 273 and SHA-1's resistance to discovery of it is referred to as SHA-1's 274 _second-preimage resistance_. 276 As demonstrated by the the [SHAttered] and [Shambles] attacks, the 277 SHA-1 algorithm is known to have weak collision resistance. However, 278 at the time of writing no attacks are known on SHA-1's second- 279 preimage resistance; a result in this area would be required to 280 provide the basis of an attack based on duplicating the SHA-1 hash of 281 an existing identifier. As a result, the use of SHA-1 in SAML and in 282 this protocol is not believed to introduce a security concern. 284 Implementations may guard against the possibility of a future 285 practical attack on the second-preimage resistance of SHA-1 by 286 treating two entities whose "entityID" values have the same SHA-1 287 equivalent as an indicator of malicious intent on the part of the 288 owner of one of the entities. 290 5. IANA Considerations 292 This document has no actions for IANA. 294 6. Acknowledgements 296 The editor would like to acknowledge the following individuals for 297 their contributions to this document: 299 Scott Cantor (The Ohio State University) 301 Leif Johansson (SUNET) 303 Joe St Sauver (University of Oregon) 305 Tom Scavo (Internet2) 307 7. References 309 7.1. Normative References 311 [I-D.young-md-query] 312 Young, I., Ed., "Metadata Query Protocol", draft-young-md- 313 query-12 (work in progress), January 2020. 315 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 316 Requirement Levels", BCP 14, RFC 2119, 317 DOI 10.17487/RFC2119, March 1997, 318 . 320 [RFC3174] Eastlake 3rd, D. and P. Jones, "US Secure Hash Algorithm 1 321 (SHA1)", RFC 3174, DOI 10.17487/RFC3174, September 2001, 322 . 324 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 325 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 326 May 2017, . 328 [SAML2Bind] 329 Cantor, S., Hirsch, F., Kemp, J., Philpott, R., and E. 330 Maler, "Bindings for the Security Assertion Markup 331 Language (SAML) V2.0", OASIS Standard saml-bindings- 332 2.0-os, March 2005. 334 [SAML2Meta] 335 Cantor, S., Moreh, J., Philpott, R., and E. Maler, 336 "Metadata for the Security Assertion Markup Language 337 (SAML) V2.0", OASIS Standard saml-metadata-2.0-os, March 338 2005. 340 [STD68] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 341 Specifications: ABNF", STD 68, RFC 5234, 342 DOI 10.17487/RFC5234, January 2008, 343 . 345 7.2. Informative References 347 [md-query] 348 Young, I., Ed., "md-query Project", 349 . 351 [MDX.list] 352 Young, I., Ed., "MDX Mailing List", 353 . 355 [REFEDS] Research and Education Federations, "REFEDS Home Page", 356 . 358 [REFEDS.agreement] 359 Research and Education Federations, "REFEDS Participant's 360 Agreement", 361 . 363 [RFC4844] Daigle, L., Ed. and Internet Architecture Board, "The RFC 364 Series and RFC Editor", RFC 4844, DOI 10.17487/RFC4844, 365 July 2007, . 367 [SAML2Core] 368 Cantor, S., Kemp, J., Philpott, R., and E. Maler, 369 "Assertions and Protocol for the OASIS Security Assertion 370 Markup Language (SAML) V2.0", OASIS Standard saml-core- 371 2.0-os, March 2005, . 374 [Shambles] 375 "SHA-1 is a Shambles", January 2020, 376 . 378 [SHAttered] 379 "SHAttered", February 2017, . 381 Appendix A. Change Log (to be removed by RFC Editor before publication) 383 A.1. draft-young-md-query-saml-00 385 Initial version. 387 A.2. Since draft-young-md-query-saml-00 389 Added REFEDS RFC stream boilerplate. 391 A.3. Since draft-young-md-query-saml-01 393 Bump reference to the Metadata Query Protocol [I-D.young-md-query]. 395 Rework Section 2.2 to make the role of transformed identifiers 396 clearer. This changes the semantics slightly (malformed transformed 397 identifiers may now result in a 404 return rather than 400) but this 398 gives implementers more latitude in the way that they handle the 399 feature. 401 A.4. Since draft-young-md-query-saml-02 403 Bump reference to the Metadata Query Protocol [I-D.young-md-query]. 405 A.5. Since draft-young-md-query-saml-03 407 Bump reference to the Metadata Query Protocol [I-D.young-md-query]. 409 Added an Editorial Note to help direct readers back to the 410 discussion. 412 A.6. Since draft-young-md-query-saml-04 414 Fix reference to the Metadata Query Protocol [I-D.young-md-query]. 416 A.7. Since draft-young-md-query-saml-05 418 Bump reference to the Metadata Query Protocol [I-D.young-md-query]. 420 A.8. Since draft-young-md-query-saml-06 422 Bump reference to the Metadata Query Protocol [I-D.young-md-query]. 424 A.9. Since draft-young-md-query-saml-07 426 Bump reference to the Metadata Query Protocol [I-D.young-md-query]. 428 A.10. Since draft-young-md-query-saml-08 430 Bump reference to the Metadata Query Protocol [I-D.young-md-query]. 432 Modernise normative language to include [RFC8174]. 434 Improved references to RFCs. 436 A.11. Since draft-young-md-query-saml-09 438 Bump reference to the Metadata Query Protocol [I-D.young-md-query]. 440 A.12. Since draft-young-md-query-saml-10 442 Bump reference to the Metadata Query Protocol [I-D.young-md-query]. 444 Replace citations in the abstract with straight textual mentions, as 445 required by the ID-NITS checklist. 447 A.13. Since draft-young-md-query-saml-11 449 Bump reference to the Metadata Query Protocol [I-D.young-md-query]. 451 Strengthen Section 4.1 so that SHA-1 now MUST NOT be used in the 452 context of digital signatures. This brings the section in line with 453 current best practice recommendations, particularly in light of the 454 [SHAttered] and [Shambles] attacks. 456 Revised Section 4.2 on the use of SHA-1 in transformed identifiers 457 to: 459 o Make clear that this is a SAML-level issue, not one introduced by 460 the query protocol. 462 o Reference the attacks demonstrating SHA-1's weak collision 463 resistance. 465 o Identify second-preimage resistance as the potential source of the 466 attack we'd be concerned about for the query protocol. 468 o Note that SHA-1's second-preimage resistance is at present 469 uncompromised. 471 A.14. Since draft-young-md-query-saml-12 473 Bump reference to the Metadata Query Protocol [I-D.young-md-query]. 475 Author's Address 477 Ian A. Young (editor) 478 Independent 480 EMail: ian@iay.org.uk