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Checking references for intended status: Informational ---------------------------------------------------------------------------- == Outdated reference: A later version (-20) exists of draft-young-md-query-13 -- Obsolete informational reference (is this intentional?): RFC 4844 (Obsoleted by RFC 8729)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 January 12, 2021 5 Expires: July 16, 2021 7 SAML Profile for the Metadata Query Protocol 8 draft-young-md-query-saml-14 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.15. 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 July 16, 2021. 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 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 12 99 1. Introduction 101 This document profiles the Metadata Query Protocol 102 [I-D.young-md-query] for use with SAML metadata [SAML2Meta]. 104 The Research and Education Federations group ([REFEDS]) is the voice 105 that articulates the mutual needs of research and education identity 106 federations worldwide. It aims to represent the requirements of 107 research and education in the ever-growing space of access and 108 identity management. 110 From time to time REFEDS will wish to publish a document in the 111 Internet RFC series. Such documents will be published as part of the 112 RFC Independent Submission Stream [RFC4844]; however the REFEDS 113 working group sign-off process will have been followed for these 114 documents, as described in the REFEDS Participant's Agreement 115 [REFEDS.agreement]. 117 This document is a product of the REFEDS Working Group process. 119 1.1. Notation and Conventions 121 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 122 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 123 "OPTIONAL" in this document are to be interpreted as described in 124 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all 125 capitals, as shown here. 127 This document makes use of the Augmented BNF metalanguage defined in 128 [STD68]. 130 2. Request Profile 132 2.1. Content Type 134 Requests compliant with this profile MUST include the following HTTP 135 header to indicate that the metadata returned should be SAML metadata 136 (see Appendix A of [SAML2Meta]): 138 Accept: application/samlmetadata+xml 140 2.2. Identifiers 142 2.2.1. Unique Identifier 144 Each entity known to the responder MUST be associated with the unique 145 identifier of the entity, corresponding to the "entityID" attribute 146 of the entity's "EntityDescriptor" element in SAML metadata. 148 2.2.2. Transformed Identifier 150 SAML 2.0 [SAML2Core] includes profiles based on the transfer of an 151 "artifact" containing the unique identifier of a SAML entity 152 transformed by means of the SHA-1 [RFC3174] hash algorithm (see 153 [SAML2Bind] sections 3.6 and 3.6.4). 155 In order to support use cases in which clients may be in possession 156 of only such a transformed representation of a SAML entity's unique 157 identifier without any way to establish the original entity 158 identifier, a responder compliant with this profile MUST associate 159 each entity with an identifier matching the "sha1id" production in 160 the following ABNF grammar, and treat such an identifier as 161 equivalent to the corresponding untransformed identifier: 163 SHA1 = %x73 %x68 %x61 %x31 ; lower case "sha1" 164 DIGIT = %x30-39 165 HEXDIGIT = DIGIT | %x61-66 ; lower case a-f 166 sha1id = "{" SHA1 "}" sha1hex 167 sha1hex = 40*HEXDIGIT 169 In the above, the "sha1hex" component encodes the 20-octet (160-bit) 170 binary SHA-1 hash value as a sequence of 40 lower case hexadecimal 171 digits. 173 For example, the identifier 175 http://example.org/service 177 transformed by means of SHA-1 hashing would become 179 {sha1}11d72e8cf351eb6c75c721e838f469677ab41bdb 181 Responder implementations MAY detect malformed SHA-1 transformed 182 identifiers (for example where the string of characters following the 183 "}" contains characters other than hexadecimal digits, or is other 184 than exactly 40 characters in length) and return an HTTP status code 185 of 400 ("bad request"). Alternatively, implementations MAY process 186 these as normal identifiers and return an HTTP status code of 404 187 ("not found") if appropriate. 189 2.2.3. Additional Identifiers 191 Entities MAY also be associated with any number of additional 192 responder-defined identifiers naming arbitrary groups of entities. 194 3. Response Profile 196 3.1. Response Cardinality 198 A request may return information for any number of entities, 199 including none. Responses compliant with this profile MUST use the 200 appropriate representation described below depending on the number of 201 "EntityDescriptor" elements returned. 203 3.1.1. No Entity Descriptors Returned 205 A response which returns no "EntityDescriptor" elements MUST be 206 represented by an HTTP status code of 404 ("not found"). 208 3.1.2. One Entity Descriptor Returned 210 A response which returns a single "EntityDescriptor" element MUST use 211 that element as its document element. The responder MUST NOT make 212 use of a "EntitiesDescriptor" element in this situation (see 213 [SAML2Meta] section 2.3). 215 Such a response MUST include the following HTTP header to indicate 216 that the metadata returned is SAML metadata: 218 Content-Type: application/samlmetadata+xml 220 3.1.3. More Than One Entity Descriptor Returned 222 A response which returns more than one "EntityDescriptor" element 223 MUST consist of a document element which is an "EntitiesDescriptor" 224 element, containing the returned "EntityDescriptor" elements as 225 children. Responses MUST NOT contain nested "EntitiesDescriptor" 226 elements. 228 Such a response MUST include the following HTTP header to indicate 229 that the metadata returned is SAML metadata: 231 Content-Type: application/samlmetadata+xml 233 4. Security Considerations 235 4.1. Integrity 237 As SAML metadata contains information necessary for the secure 238 operation of interacting services it is strongly RECOMMENDED that a 239 mechanism for integrity checking is provided to clients. 241 It is RECOMMENDED that the integrity checking mechanism provided by a 242 responder is a digital signature embedded in the returned metadata 243 document, as defined by [SAML2Meta] section 3. 245 Such digital signatures: 247 o SHOULD use an RSA keypair whose modulus is no less than 2048 bits 248 in length. 250 o MUST NOT use the SHA-1 cryptographic hash algorithm as a digest 251 algorithm. 253 o MUST NOT use the MD5 cryptographic hash algorithm as a digest 254 algorithm. 256 o SHOULD otherwise follow current cryptographic best practices in 257 algorithm selection. 259 4.2. Use of SHA-1 in Transformed Identifiers 261 This profile mandates the availability of an identifier synonym 262 mechanism based on the SHA-1 cryptographic hash algorithm. Although 263 SHA-1 is now regarded as weak enough to exclude it from use in new 264 cryptographic systems, its use in this profile is necessary for full 265 support of the SAML 2.0 standard. 267 The use of SHA-1 in section 3.6.4 of [SAML2Bind], and its resulting 268 use in this protocol, would be vulnerable to an attack in which 269 metadata was introduced into a system by an attacker capable of 270 creating an entity identifier with the same SHA-1 hash as that of an 271 existing entity's identifier. 273 Such an identifier is known as a _second preimage_ of the original, 274 and SHA-1's resistance to discovery of it is referred to as SHA-1's 275 _second-preimage resistance_. 277 As demonstrated by the the [SHAttered] and [Shambles] attacks, the 278 SHA-1 algorithm is known to have weak collision resistance. However, 279 at the time of writing no attacks are known on SHA-1's second- 280 preimage resistance; a result in this area would be required to 281 provide the basis of an attack based on duplicating the SHA-1 hash of 282 an existing identifier. As a result, the use of SHA-1 in SAML and in 283 this protocol is not believed to introduce a security concern. 285 Implementations may guard against the possibility of a future 286 practical attack on the second-preimage resistance of SHA-1 by 287 treating two entities whose "entityID" values have the same SHA-1 288 equivalent as an indicator of malicious intent on the part of the 289 owner of one of the entities. 291 5. IANA Considerations 293 This document has no actions for IANA. 295 6. Acknowledgements 297 The editor would like to acknowledge the following individuals for 298 their contributions to this document: 300 Scott Cantor (The Ohio State University) 302 Leif Johansson (SUNET) 304 Joe St Sauver (University of Oregon) 306 Tom Scavo (Internet2) 308 7. References 310 7.1. Normative References 312 [I-D.young-md-query] 313 Young, I., Ed., "Metadata Query Protocol", draft-young-md- 314 query-13 (work in progress), January 2021. 316 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 317 Requirement Levels", BCP 14, RFC 2119, 318 DOI 10.17487/RFC2119, March 1997, 319 . 321 [RFC3174] Eastlake 3rd, D. and P. Jones, "US Secure Hash Algorithm 1 322 (SHA1)", RFC 3174, DOI 10.17487/RFC3174, September 2001, 323 . 325 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 326 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 327 May 2017, . 329 [SAML2Bind] 330 Cantor, S., Hirsch, F., Kemp, J., Philpott, R., and E. 331 Maler, "Bindings for the Security Assertion Markup 332 Language (SAML) V2.0", OASIS Standard saml-bindings- 333 2.0-os, March 2005. 335 [SAML2Meta] 336 Cantor, S., Moreh, J., Philpott, R., and E. Maler, 337 "Metadata for the Security Assertion Markup Language 338 (SAML) V2.0", OASIS Standard saml-metadata-2.0-os, March 339 2005. 341 [STD68] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 342 Specifications: ABNF", STD 68, RFC 5234, 343 DOI 10.17487/RFC5234, January 2008, 344 . 346 7.2. Informative References 348 [md-query] 349 Young, I., Ed., "md-query Project", 350 . 352 [MDX.list] 353 Young, I., Ed., "MDX Mailing List", 354 . 356 [REFEDS] Research and Education Federations, "REFEDS Home Page", 357 . 359 [REFEDS.agreement] 360 Research and Education Federations, "REFEDS Participant's 361 Agreement", 362 . 364 [RFC4844] Daigle, L., Ed. and Internet Architecture Board, "The RFC 365 Series and RFC Editor", RFC 4844, DOI 10.17487/RFC4844, 366 July 2007, . 368 [SAML2Core] 369 Cantor, S., Kemp, J., Philpott, R., and E. Maler, 370 "Assertions and Protocol for the OASIS Security Assertion 371 Markup Language (SAML) V2.0", OASIS Standard saml-core- 372 2.0-os, March 2005, . 375 [Shambles] 376 "SHA-1 is a Shambles", January 2020, 377 . 379 [SHAttered] 380 "SHAttered", February 2017, . 382 Appendix A. Change Log (to be removed by RFC Editor before publication) 384 A.1. draft-young-md-query-saml-00 386 Initial version. 388 A.2. Since draft-young-md-query-saml-00 390 Added REFEDS RFC stream boilerplate. 392 A.3. Since draft-young-md-query-saml-01 394 Bump reference to the Metadata Query Protocol [I-D.young-md-query]. 396 Rework Section 2.2 to make the role of transformed identifiers 397 clearer. This changes the semantics slightly (malformed transformed 398 identifiers may now result in a 404 return rather than 400) but this 399 gives implementers more latitude in the way that they handle the 400 feature. 402 A.4. Since draft-young-md-query-saml-02 404 Bump reference to the Metadata Query Protocol [I-D.young-md-query]. 406 A.5. Since draft-young-md-query-saml-03 408 Bump reference to the Metadata Query Protocol [I-D.young-md-query]. 410 Added an Editorial Note to help direct readers back to the 411 discussion. 413 A.6. Since draft-young-md-query-saml-04 415 Fix reference to the Metadata Query Protocol [I-D.young-md-query]. 417 A.7. Since draft-young-md-query-saml-05 419 Bump reference to the Metadata Query Protocol [I-D.young-md-query]. 421 A.8. Since draft-young-md-query-saml-06 423 Bump reference to the Metadata Query Protocol [I-D.young-md-query]. 425 A.9. Since draft-young-md-query-saml-07 427 Bump reference to the Metadata Query Protocol [I-D.young-md-query]. 429 A.10. Since draft-young-md-query-saml-08 431 Bump reference to the Metadata Query Protocol [I-D.young-md-query]. 433 Modernise normative language to include [RFC8174]. 435 Improved references to RFCs. 437 A.11. Since draft-young-md-query-saml-09 439 Bump reference to the Metadata Query Protocol [I-D.young-md-query]. 441 A.12. Since draft-young-md-query-saml-10 443 Bump reference to the Metadata Query Protocol [I-D.young-md-query]. 445 Replace citations in the abstract with straight textual mentions, as 446 required by the ID-NITS checklist. 448 A.13. Since draft-young-md-query-saml-11 450 Bump reference to the Metadata Query Protocol [I-D.young-md-query]. 452 Strengthen Section 4.1 so that SHA-1 now MUST NOT be used in the 453 context of digital signatures. This brings the section in line with 454 current best practice recommendations, particularly in light of the 455 [SHAttered] and [Shambles] attacks. 457 Revised Section 4.2 on the use of SHA-1 in transformed identifiers 458 to: 460 o Make clear that this is a SAML-level issue, not one introduced by 461 the query protocol. 463 o Reference the attacks demonstrating SHA-1's weak collision 464 resistance. 466 o Identify second-preimage resistance as the potential source of the 467 attack we'd be concerned about for the query protocol. 469 o Note that SHA-1's second-preimage resistance is at present 470 uncompromised. 472 A.14. Since draft-young-md-query-saml-12 474 Bump reference to the Metadata Query Protocol [I-D.young-md-query]. 476 A.15. Since draft-young-md-query-saml-13 478 Bump reference to the Metadata Query Protocol [I-D.young-md-query]. 480 Author's Address 482 Ian A. Young (editor) 483 Independent 485 EMail: ian@iay.org.uk