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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 7049 (Obsoleted by RFC 8949) Summary: 1 error (**), 0 flaws (~~), 1 warning (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 ACE Working Group M. Jones 3 Internet-Draft Microsoft 4 Intended status: Standards Track E. Wahlstroem 5 Expires: August 6, 2018 6 S. Erdtman 7 Spotify AB 8 H. Tschofenig 9 ARM Ltd. 10 February 2, 2018 12 CBOR Web Token (CWT) 13 draft-ietf-ace-cbor-web-token-12 15 Abstract 17 CBOR Web Token (CWT) is a compact means of representing claims to be 18 transferred between two parties. The claims in a CWT are encoded in 19 the Concise Binary Object Representation (CBOR) and CBOR Object 20 Signing and Encryption (COSE) is used for added application layer 21 security protection. A claim is a piece of information asserted 22 about a subject and is represented as a name/value pair consisting of 23 a claim name and a claim value. CWT is derived from JSON Web Token 24 (JWT) but uses CBOR rather than JSON. 26 Status of This Memo 28 This Internet-Draft is submitted in full conformance with the 29 provisions of BCP 78 and BCP 79. 31 Internet-Drafts are working documents of the Internet Engineering 32 Task Force (IETF). Note that other groups may also distribute 33 working documents as Internet-Drafts. The list of current Internet- 34 Drafts is at https://datatracker.ietf.org/drafts/current/. 36 Internet-Drafts are draft documents valid for a maximum of six months 37 and may be updated, replaced, or obsoleted by other documents at any 38 time. It is inappropriate to use Internet-Drafts as reference 39 material or to cite them other than as "work in progress." 41 This Internet-Draft will expire on August 6, 2018. 43 Copyright Notice 45 Copyright (c) 2018 IETF Trust and the persons identified as the 46 document authors. All rights reserved. 48 This document is subject to BCP 78 and the IETF Trust's Legal 49 Provisions Relating to IETF Documents 50 (https://trustee.ietf.org/license-info) in effect on the date of 51 publication of this document. Please review these documents 52 carefully, as they describe your rights and restrictions with respect 53 to this document. Code Components extracted from this document must 54 include Simplified BSD License text as described in Section 4.e of 55 the Trust Legal Provisions and are provided without warranty as 56 described in the Simplified BSD License. 58 Table of Contents 60 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 61 1.1. CBOR Related Terminology . . . . . . . . . . . . . . . . 3 62 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 63 3. Claims . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 64 3.1. Registered Claims . . . . . . . . . . . . . . . . . . . . 5 65 3.1.1. iss (Issuer) Claim . . . . . . . . . . . . . . . . . 5 66 3.1.2. sub (Subject) Claim . . . . . . . . . . . . . . . . . 5 67 3.1.3. aud (Audience) Claim . . . . . . . . . . . . . . . . 5 68 3.1.4. exp (Expiration Time) Claim . . . . . . . . . . . . . 5 69 3.1.5. nbf (Not Before) Claim . . . . . . . . . . . . . . . 5 70 3.1.6. iat (Issued At) Claim . . . . . . . . . . . . . . . . 6 71 3.1.7. cti (CWT ID) Claim . . . . . . . . . . . . . . . . . 6 72 4. Summary of the claim names, keys, and value types . . . . . . 6 73 5. CBOR Tags and Claim Values . . . . . . . . . . . . . . . . . 6 74 6. CWT CBOR Tag . . . . . . . . . . . . . . . . . . . . . . . . 6 75 7. Creating and Validating CWTs . . . . . . . . . . . . . . . . 7 76 7.1. Creating a CWT . . . . . . . . . . . . . . . . . . . . . 7 77 7.2. Validating a CWT . . . . . . . . . . . . . . . . . . . . 8 78 8. Security Considerations . . . . . . . . . . . . . . . . . . . 9 79 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 80 9.1. CBOR Web Token (CWT) Claims Registry . . . . . . . . . . 10 81 9.1.1. Registration Template . . . . . . . . . . . . . . . . 10 82 9.1.2. Initial Registry Contents . . . . . . . . . . . . . . 11 83 9.2. Media Type Registration . . . . . . . . . . . . . . . . . 13 84 9.2.1. Registry Contents . . . . . . . . . . . . . . . . . . 13 85 9.3. CoAP Content-Formats Registration . . . . . . . . . . . . 13 86 9.3.1. Registry Contents . . . . . . . . . . . . . . . . . . 14 87 9.4. CBOR Tag registration . . . . . . . . . . . . . . . . . . 14 88 9.4.1. Registry Contents . . . . . . . . . . . . . . . . . . 14 89 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 90 10.1. Normative References . . . . . . . . . . . . . . . . . . 14 91 10.2. Informative References . . . . . . . . . . . . . . . . . 15 92 Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 15 93 A.1. Example CWT Claims Set . . . . . . . . . . . . . . . . . 16 94 A.2. Example keys . . . . . . . . . . . . . . . . . . . . . . 16 95 A.2.1. 128-bit Symmetric Key . . . . . . . . . . . . . . . . 16 96 A.2.2. 256-bit Symmetric Key . . . . . . . . . . . . . . . . 17 97 A.2.3. ECDSA P-256 256-bit COSE Key . . . . . . . . . . . . 17 98 A.3. Example Signed CWT . . . . . . . . . . . . . . . . . . . 17 99 A.4. Example MACed CWT . . . . . . . . . . . . . . . . . . . . 18 100 A.5. Example Encrypted CWT . . . . . . . . . . . . . . . . . . 19 101 A.6. Example Nested CWT . . . . . . . . . . . . . . . . . . . 20 102 A.7. Example MACed CWT with a floating-point value . . . . . . 21 103 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 22 104 Appendix C. Document History . . . . . . . . . . . . . . . . . . 22 105 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25 107 1. Introduction 109 The JSON Web Token (JWT) [RFC7519] is a standardized security token 110 format that has found use in OAuth 2.0 and OpenID Connect 111 deployments, among other applications. JWT uses JSON Web Signature 112 (JWS) [RFC7515] and JSON Web Encryption (JWE) [RFC7516] to secure the 113 contents of the JWT, which is a set of claims represented in JSON. 114 The use of JSON for encoding information is popular for Web and 115 native applications, but it is considered inefficient for some 116 Internet of Things (IoT) systems that use low power radio 117 technologies. 119 An alternative encoding of claims is defined in this document. 120 Instead of using JSON, as provided by JWTs, this specification uses 121 CBOR [RFC7049] and calls this new structure "CBOR Web Token (CWT)", 122 which is a compact means of representing secured claims to be 123 transferred between two parties. CWT is closely related to JWT. It 124 references the JWT claims and both its name and pronunciation are 125 derived from JWT. To protect the claims contained in CWTs, the CBOR 126 Object Signing and Encryption (COSE) [RFC8152] specification is used. 128 The suggested pronunciation of CWT is the same as the English word 129 "cot". 131 1.1. CBOR Related Terminology 133 In JSON, maps are called objects and only have one kind of map key: a 134 string. CBOR uses strings, negative integers, and unsigned integers 135 as map keys. The integers are used for compactness of encoding and 136 easy comparison. The inclusion of strings allows for an additional 137 range of short encoded values to be used. 139 2. Terminology 141 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 142 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 143 "OPTIONAL" in this document are to be interpreted as described in BCP 144 14 [RFC2119] [RFC8174] when, and only when, they appear in all 145 capitals, as shown here. 147 This document reuses terminology from JWT [RFC7519] and COSE 148 [RFC8152]. 150 StringOrURI 151 The "StringOrURI" term has the same meaning, syntax, and 152 processing rules as the "StringOrURI" term defined in Section 2 of 153 [RFC7519], except that it uses a CBOR text string instead of a 154 JSON string value. 156 NumericDate 157 The "NumericDate" term has the same meaning, syntax, and 158 processing rules as the "NumericDate" term defined in Section 2 of 159 [RFC7519], except that the CBOR numeric date representation (from 160 Section 2.4.1 of [RFC7049]) is used. The encoding is modified so 161 that the leading tag 1 (epoch-based date/time) MUST be omitted. 163 Claim Name 164 The human-readable name used to identify a claim. 166 Claim Key 167 The CBOR map key used to identify a claim. 169 Claim Value 170 The CBOR map value representing the value of the claim. 172 CWT Claims Set 173 The CBOR map that contains the claims conveyed by the CWT. 175 3. Claims 177 The set of claims that a CWT must contain to be considered valid is 178 context dependent and is outside the scope of this specification. 179 Specific applications of CWTs will require implementations to 180 understand and process some claims in particular ways. However, in 181 the absence of such requirements, all claims that are not understood 182 by implementations MUST be ignored. 184 To keep CWTs as small as possible, the Claim Keys are represented 185 using integers or text strings. Section 4 summarizes all keys used 186 to identify the claims defined in this document. 188 3.1. Registered Claims 190 None of the claims defined below are intended to be mandatory to use 191 or implement. They rather provide a starting point for a set of 192 useful, interoperable claims. Applications using CWTs should define 193 which specific claims they use and when they are required or 194 optional. 196 3.1.1. iss (Issuer) Claim 198 The "iss" (issuer) claim has the same meaning, syntax, and processing 199 rules as the "iss" claim defined in Section 4.1.1 of [RFC7519], 200 except that the value is of type StringOrURI. The Claim Key 1 is 201 used to identify this claim. 203 3.1.2. sub (Subject) Claim 205 The "sub" (subject) claim has the same meaning, syntax, and 206 processing rules as the "sub" claim defined in Section 4.1.2 of 207 [RFC7519], except that the value is of type StringOrURI. The Claim 208 Key 2 is used to identify this claim. 210 3.1.3. aud (Audience) Claim 212 The "aud" (audience) claim has the same meaning, syntax, and 213 processing rules as the "aud" claim defined in Section 4.1.3 of 214 [RFC7519], except that the value of the audience claim is of type 215 StringOrURI when it is not an array or the values of the audience 216 array elements are of type StringOrURI when the audience claim value 217 is an array. The Claim Key 3 is used to identify this claim. 219 3.1.4. exp (Expiration Time) Claim 221 The "exp" (expiration time) claim has the same meaning, syntax, and 222 processing rules as the "exp" claim defined in Section 4.1.4 of 223 [RFC7519], except that the value is of type NumericDate. The Claim 224 Key 4 is used to identify this claim. 226 3.1.5. nbf (Not Before) Claim 228 The "nbf" (not before) claim has the same meaning, syntax, and 229 processing rules as the "nbf" claim defined in Section 4.1.5 of 230 [RFC7519], except that the value is of type NumericDate. The Claim 231 Key 5 is used to identify this claim. 233 3.1.6. iat (Issued At) Claim 235 The "iat" (issued at) claim has the same meaning, syntax, and 236 processing rules as the "iat" claim defined in Section 4.1.6 of 237 [RFC7519], except that the value is of type NumericDate. The Claim 238 Key 6 is used to identify this claim. 240 3.1.7. cti (CWT ID) Claim 242 The "cti" (CWT ID) claim has the same meaning, syntax, and processing 243 rules as the "jti" claim defined in Section 4.1.7 of [RFC7519], 244 except that the value is of type byte string. The Claim Key 7 is 245 used to identify this claim. 247 4. Summary of the claim names, keys, and value types 249 +------+-----+----------------------------------+ 250 | Name | Key | Value type | 251 +------+-----+----------------------------------+ 252 | iss | 1 | text string | 253 | sub | 2 | text string | 254 | aud | 3 | text string | 255 | exp | 4 | integer or floating-point number | 256 | nbf | 5 | integer or floating-point number | 257 | iat | 6 | integer or floating-point number | 258 | cti | 7 | byte string | 259 +------+-----+----------------------------------+ 261 Table 1: Summary of the claim names, keys, and value types 263 5. CBOR Tags and Claim Values 265 The claim values defined in this specification MUST NOT be prefixed 266 with any CBOR tag. For instance, while CBOR tag 1 (epoch-based date/ 267 time) could logically be prefixed to values of the "exp", "nbf", and 268 "iat" claims, this is unnecessary, since the representation of the 269 claim values is already specified by the claim definitions. Tagging 270 claim values would only take up extra space without adding 271 information. However, this does not prohibit future claim 272 definitions from requiring the use of CBOR tags for those specific 273 claims. 275 6. CWT CBOR Tag 277 How to determine that a CBOR data structure is a CWT is application- 278 dependent. In some cases, this information is known from the 279 application context, such as from the position of the CWT in a data 280 structure at which the value must be a CWT. One method of indicating 281 that a CBOR object is a CWT is the use of the "application/cwt" 282 content type by a transport protocol. 284 This section defines the CWT CBOR tag as another means for 285 applications to declare that a CBOR data structure is a CWT. Its use 286 is optional and is intended for use in cases in which this 287 information would not otherwise be known. 289 If present, the CWT tag MUST prefix a tagged object using one of the 290 COSE CBOR tags. In this example, the COSE_Mac0 tag is used. The 291 actual COSE_Mac0 object has been excluded from this example. 293 / CWT CBOR tag / 61( 294 / COSE_Mac0 CBOR tag / 17( 295 / COSE_Mac0 object / 296 ) 297 ) 299 Figure 1: Example of a CWT tag usage 301 7. Creating and Validating CWTs 303 7.1. Creating a CWT 305 To create a CWT, the following steps are performed. The order of the 306 steps is not significant in cases where there are no dependencies 307 between the inputs and outputs of the steps. 309 1. Create a CWT Claims Set containing the desired claims. 311 2. Let the Message be the binary representation of the CWT Claims 312 Set. 314 3. Create a COSE Header containing the desired set of Header 315 Parameters. The COSE Header MUST be valid per the [RFC8152] 316 specification. 318 4. Depending upon whether the CWT is signed, MACed, or encrypted, 319 there are three cases: 321 * If the CWT is signed, create a COSE_Sign/COSE_Sign1 object 322 using the Message as the COSE_Sign/COSE_Sign1 Payload; all 323 steps specified in [RFC8152] for creating a COSE_Sign/ 324 COSE_Sign1 object MUST be followed. 326 * Else, if the CWT is MACed, create a COSE_Mac/COSE_Mac0 object 327 using the Message as the COSE_Mac/COSE_Mac0 Payload; all steps 328 specified in [RFC8152] for creating a COSE_Mac/COSE_Mac0 329 object MUST be followed. 331 * Else, if the CWT is a COSE_Encrypt/COSE_Encrypt0 object, 332 create a COSE_Encrypt/COSE_Encrypt0 using the Message as the 333 plaintext for the COSE_Encrypt/COSE_Encrypt0 object; all steps 334 specified in [RFC8152] for creating a COSE_Encrypt/ 335 COSE_Encrypt0 object MUST be followed. 337 5. If a nested signing, MACing, or encryption operation will be 338 performed, let the Message be the tagged COSE_Sign/COSE_Sign1, 339 COSE_Mac/COSE_Mac0, or COSE_Encrypt/COSE_Encrypt0, and return to 340 Step 3. 342 6. If needed by the application, prepend the COSE object with the 343 appropriate COSE CBOR tag to indicate the type of the COSE 344 object. If needed by the application, prepend the COSE object 345 with the CWT CBOR tag to indicate that the COSE object is a CWT. 347 7.2. Validating a CWT 349 When validating a CWT, the following steps are performed. The order 350 of the steps is not significant in cases where there are no 351 dependencies between the inputs and outputs of the steps. If any of 352 the listed steps fail, then the CWT MUST be rejected -- that is, 353 treated by the application as invalid input. 355 1. Verify that the CWT is a valid CBOR object. 357 2. If the object begins with the CWT CBOR tag, remove it and verify 358 that one of the COSE CBOR tags follows it. 360 3. If the object is tagged with one of the COSE CBOR tags, remove it 361 and use it to determine the type of the CWT, COSE_Sign/ 362 COSE_Sign1, COSE_Mac/COSE_Mac0, or COSE_Encrypt/COSE_Encrypt0. 363 If the object does not have a COSE CBOR tag, the COSE message 364 type is determined from the application context. 366 4. Verify that the resulting COSE Header includes only parameters 367 and values whose syntax and semantics are both understood and 368 supported or that are specified as being ignored when not 369 understood. 371 5. Depending upon whether the CWT is a signed, MACed, or encrypted, 372 there are three cases: 374 * If the CWT is a COSE_Sign/COSE_Sign1, follow the steps 375 specified in [RFC8152] Section 4 (Signing Objects) for 376 validating a COSE_Sign/COSE_Sign1 object. Let the Message be 377 the COSE_Sign/COSE_Sign1 payload. 379 * Else, if the CWT is a COSE_Mac/COSE_Mac0, follow the steps 380 specified in [RFC8152] Section 6 (MAC Objects) for validating 381 a COSE_Mac/COSE_Mac0 object. Let the Message be the COSE_Mac/ 382 COSE_Mac0 payload. 384 * Else, if the CWT is a COSE_Encrypt/COSE_Encrypt0 object, 385 follow the steps specified in [RFC8152] Section 5 (Encryption 386 Objects) for validating a COSE_Encrypt/COSE_Encrypt0 object. 387 Let the Message be the resulting plaintext. 389 6. If the Message begins with a COSE CBOR tag, then the Message is a 390 CWT that was the subject of nested signing, MACing, or encryption 391 operations. In this case, return to Step 1, using the Message as 392 the CWT. 394 7. Verify that the Message is a valid CBOR map; let the CWT Claims 395 Set be this CBOR map. 397 8. Security Considerations 399 The security of the CWT relies upon on the protections offered by 400 COSE. Unless the claims in a CWT are protected, an adversary can 401 modify, add, or remove claims. 403 Since the claims conveyed in a CWT may be used to make authorization 404 decisions, it is not only important to protect the CWT in transit but 405 also to ensure that the recipient can authenticate the party that 406 assembled the claims and created the CWT. Without trust of the 407 recipient in the party that created the CWT, no sensible 408 authorization decision can be made. Furthermore, the creator of the 409 CWT needs to carefully evaluate each claim value prior to including 410 it in the CWT so that the recipient can be assured of the validity of 411 the information provided. 413 While syntactically, the signing and encryption operations for Nested 414 CWTs may be applied in any order, if both signing and encryption are 415 necessary, normally producers should sign the message and then 416 encrypt the result (thus encrypting the signature). This prevents 417 attacks in which the signature is stripped, leaving just an encrypted 418 message, as well as providing privacy for the signer. Furthermore, 419 signatures over encrypted text are not considered valid in many 420 jurisdictions. 422 9. IANA Considerations 424 9.1. CBOR Web Token (CWT) Claims Registry 426 This section establishes the IANA "CBOR Web Token (CWT) Claims" 427 registry. 429 Depending upon the values being requested, registration requests are 430 evaluated on a Standards Track Required, Specification Required, 431 Expert Review, or Private Use basis [RFC8126] after a three-week 432 review period on the cwt-reg-review@ietf.org mailing list, on the 433 advice of one or more Designated Experts. However, to allow for the 434 allocation of values prior to publication, the Designated Experts may 435 approve registration once they are satisfied that such a 436 specification will be published. [[ Note to the RFC Editor: The name 437 of the mailing list should be determined in consultation with the 438 IESG and IANA. Suggested name: cwt-reg-review@ietf.org. ]] 440 Registration requests sent to the mailing list for review should use 441 an appropriate subject (e.g., "Request to register claim: example"). 442 Registration requests that are undetermined for a period longer than 443 21 days can be brought to the IESG's attention (using the 444 iesg@ietf.org mailing list) for resolution. 446 Criteria that should be applied by the Designated Experts includes 447 determining whether the proposed registration duplicates existing 448 functionality, whether it is likely to be of general applicability or 449 whether it is useful only for a single application, and whether the 450 registration description is clear. Registrations for the limited set 451 of values between -256 and 255 and strings of length 1 are to be 452 restricted to claims with general applicability. 454 It is suggested that multiple Designated Experts be appointed who are 455 able to represent the perspectives of different applications using 456 this specification in order to enable broadly informed review of 457 registration decisions. In cases where a registration decision could 458 be perceived as creating a conflict of interest for a particular 459 Expert, that Expert should defer to the judgment of the other 460 Experts. 462 9.1.1. Registration Template 464 Claim Name: 465 The human-readable name requested (e.g., "iss"). 467 Claim Description: 468 Brief description of the claim (e.g., "Issuer"). 470 JWT Claim Name: 471 Claim Name of the equivalent JWT claim, as registered in 472 [IANA.JWT.Claims]. CWT claims should normally have a 473 corresponding JWT claim. If a corresponding JWT claim would not 474 make sense, the Designated Experts can choose to accept 475 registrations for which the JWT Claim Name is listed as "N/A". 477 Claim Key: 478 CBOR map key for the claim. Integer values between -256 and 255 479 and strings of length 1 are designated as Standards Track 480 Required. Integer values from -65536 to 65535 and strings of 481 length 2 are designated as Specification Required. Integer values 482 of greater than 65535 and strings of length greater than 2 are 483 designated as Expert Review. Integer values less than -65536 are 484 marked as Private Use. 486 Claim Value Type(s): 487 CBOR types that can be used for the claim value. 489 Change Controller: 490 For Standards Track RFCs, list the "IESG". For others, give the 491 name of the responsible party. Other details (e.g., postal 492 address, email address, home page URI) may also be included. 494 Specification Document(s): 495 Reference to the document or documents that specify the parameter, 496 preferably including URIs that can be used to retrieve copies of 497 the documents. An indication of the relevant sections may also be 498 included but is not required. 500 9.1.2. Initial Registry Contents 502 o Claim Name: (RESERVED) 503 o Claim Description: This registration reserves the key value 0. 504 o JWT Claim Name: N/A 505 o Claim Key: 0 506 o Claim Value Type(s): N/A 507 o Change Controller: IESG 508 o Specification Document(s): [[ this specification ]] 510 o Claim Name: "iss" 511 o Claim Description: Issuer 512 o JWT Claim Name: "iss" 513 o Claim Key: 1 514 o Claim Value Type(s): text string 515 o Change Controller: IESG 516 o Specification Document(s): Section 3.1.1 of [[ this specification 517 ]] 519 o Claim Name: "sub" 520 o Claim Description: Subject 521 o JWT Claim Name: "sub" 522 o Claim Key: 2 523 o Claim Value Type(s): text string 524 o Change Controller: IESG 525 o Specification Document(s): Section 3.1.2 of [[ this specification 526 ]] 528 o Claim Name: "aud" 529 o Claim Description: Audience 530 o JWT Claim Name: "aud" 531 o Claim Key: 3 532 o Claim Value Type(s): text string 533 o Change Controller: IESG 534 o Specification Document(s): Section 3.1.3 of [[ this specification 535 ]] 537 o Claim Name: "exp" 538 o Claim Description: Expiration Time 539 o JWT Claim Name: "exp" 540 o Claim Key: 4 541 o Claim Value Type(s): integer or floating-point number 542 o Change Controller: IESG 543 o Specification Document(s): Section 3.1.4 of [[ this specification 544 ]] 546 o Claim Name: "nbf" 547 o Claim Description: Not Before 548 o JWT Claim Name: "nbf" 549 o Claim Key: 5 550 o Claim Value Type(s): integer or floating-point number 551 o Change Controller: IESG 552 o Specification Document(s): Section 3.1.5 of [[ this specification 553 ]] 555 o Claim Name: "iat" 556 o Claim Description: Issued At 557 o JWT Claim Name: "iat" 558 o Claim Key: 6 559 o Claim Value Type(s): integer or floating-point number 560 o Change Controller: IESG 561 o Specification Document(s): Section 3.1.6 of [[ this specification 562 ]] 564 o Claim Name: "cti" 565 o Claim Description: CWT ID 566 o JWT Claim Name: "jti" 567 o Claim Key: 7 568 o Claim Value Type(s): byte string 569 o Change Controller: IESG 570 o Specification Document(s): Section 3.1.7 of [[ this specification 571 ]] 573 9.2. Media Type Registration 575 This section registers the "application/cwt" media type in the "Media 576 Types" registry [IANA.MediaTypes] in the manner described in RFC 6838 577 [RFC6838], which can be used to indicate that the content is a CWT. 579 9.2.1. Registry Contents 581 o Type name: application 582 o Subtype name: cwt 583 o Required parameters: N/A 584 o Optional parameters: N/A 585 o Encoding considerations: binary 586 o Security considerations: See the Security Considerations section 587 of [[ this specification ]] 588 o Interoperability considerations: N/A 589 o Published specification: [[ this specification ]] 590 o Applications that use this media type: IoT applications sending 591 security tokens over HTTP(S), CoAP(S), and other transports. 592 o Fragment identifier considerations: N/A 593 o Additional information: 595 Magic number(s): N/A 596 File extension(s): N/A 597 Macintosh file type code(s): N/A 599 o Person & email address to contact for further information: 600 IESG, iesg@ietf.org 601 o Intended usage: COMMON 602 o Restrictions on usage: none 603 o Author: Michael B. Jones, mbj@microsoft.com 604 o Change controller: IESG 605 o Provisional registration? No 607 9.3. CoAP Content-Formats Registration 609 This section registers the CoAP Content-Format ID for the 610 "application/cwt" media type in the "CoAP Content-Formats" registry 611 [IANA.CoAP.Content-Formats]. 613 9.3.1. Registry Contents 615 o Media Type: application/cwt 616 o Encoding: - 617 o Id: TBD (maybe 61) 618 o Reference: [[ this specification ]] 620 9.4. CBOR Tag registration 622 This section registers the CWT CBOR tag in the "CBOR Tags" registry 623 [IANA.CBOR.Tags]. 625 9.4.1. Registry Contents 627 o CBOR Tag: TBD (maybe 61 to use the same value as the Content- 628 Format) 629 o Data Item: CBOR Web Token (CWT) 630 o Semantics: CBOR Web Token (CWT), as defined in [[ this 631 specification ]] 632 o Description of Semantics: [[ this specification ]] 633 o Point of Contact: Michael B. Jones, mbj@microsoft.com 635 10. References 637 10.1. Normative References 639 [IANA.CBOR.Tags] 640 IANA, "Concise Binary Object Representation (CBOR) Tags", 641 . 644 [IANA.CoAP.Content-Formats] 645 IANA, "CoAP Content-Formats", 646 . 649 [IANA.MediaTypes] 650 IANA, "Media Types", 651 . 653 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 654 Requirement Levels", BCP 14, RFC 2119, 655 DOI 10.17487/RFC2119, March 1997, 656 . 658 [RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object 659 Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049, 660 October 2013, . 662 [RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token 663 (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015, 664 . 666 [RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)", 667 RFC 8152, DOI 10.17487/RFC8152, July 2017, 668 . 670 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 671 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 672 May 2017, . 674 10.2. Informative References 676 [IANA.JWT.Claims] 677 IANA, "JSON Web Token Claims", 678 . 680 [RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type 681 Specifications and Registration Procedures", BCP 13, 682 RFC 6838, DOI 10.17487/RFC6838, January 2013, 683 . 685 [RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web 686 Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May 687 2015, . 689 [RFC7516] Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)", 690 RFC 7516, DOI 10.17487/RFC7516, May 2015, 691 . 693 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 694 Writing an IANA Considerations Section in RFCs", BCP 26, 695 RFC 8126, DOI 10.17487/RFC8126, June 2017, 696 . 698 Appendix A. Examples 700 This appendix includes a set of CWT examples that show how the CWT 701 Claims Set can be protected. There are examples that are signed, 702 MACed, encrypted, and that use nested signing and encryption. To 703 make the examples easier to read, they are presented both as hex 704 strings and in the extended CBOR diagnostic notation described in 705 Section 6 of [RFC7049]. 707 Where a byte string is to carry an embedded CBOR-encoded item, the 708 diagnostic notation for this CBOR data item can be enclosed in '<<' 709 and '>>' to notate the byte string resulting from encoding the data 710 item, e.g., h'63666F6F' translates to <<"foo">>. 712 A.1. Example CWT Claims Set 714 The CWT Claims Set used for the different examples displays usage of 715 all the defined claims. For signed and MACed examples, the CWT 716 Claims Set is the CBOR encoding as a byte string. 718 a70175636f61703a2f2f61732e6578616d706c652e636f6d02656572696b7703 719 7818636f61703a2f2f6c696768742e6578616d706c652e636f6d041a5612aeb0 720 051a5610d9f0061a5610d9f007420b71 722 Figure 2: Example CWT Claims Set as hex string 724 { 725 / iss / 1: "coap://as.example.com", 726 / sub / 2: "erikw", 727 / aud / 3: "coap://light.example.com", 728 / exp / 4: 1444064944, 729 / nbf / 5: 1443944944, 730 / iat / 6: 1443944944, 731 / cti / 7: h'0b71' 732 } 734 Figure 3: Example CWT Claims Set in CBOR diagnostic notation 736 A.2. Example keys 738 This section contains the keys used to sign, MAC, and encrypt the 739 messages in this appendix. Line breaks are for display purposes 740 only. 742 A.2.1. 128-bit Symmetric Key 744 a42050231f4c4d4d3051fdc2ec0a3851d5b3830104024c53796d6d6574726963 745 313238030a 747 Figure 4: 128-bit symmetric COSE_Key as hex string 749 { 750 / k / -1: h'231f4c4d4d3051fdc2ec0a3851d5b383' 751 / kty / 1: 4 / Symmetric /, 752 / kid / 2: h'53796d6d6574726963313238' / 'Symmetric128' /, 753 / alg / 3: 10 / AES-CCM-16-64-128 / 754 } 756 Figure 5: 128-bit symmetric COSE_Key in CBOR diagnostic notation 758 A.2.2. 256-bit Symmetric Key 760 a4205820403697de87af64611c1d32a05dab0fe1fcb715a86ab435f1ec99192d 761 795693880104024c53796d6d6574726963323536030a 763 Figure 6: 256-bit symmetric COSE_Key as hex string 765 { 766 / k / -1: h'403697de87af64611c1d32a05dab0fe1fcb715a86ab435f1 767 ec99192d79569388' 768 / kty / 1: 4 / Symmetric /, 769 / kid / 4: h'53796d6d6574726963323536' / 'Symmetric256' /, 770 / alg / 3: 4 / HMAC 256/64 / 771 } 773 Figure 7: 256-bit symmetric COSE_Key in CBOR diagnostic notation 775 A.2.3. ECDSA P-256 256-bit COSE Key 777 a72358206c1382765aec5358f117733d281c1c7bdc39884d04a45a1e6c67c858 778 bc206c1922582060f7f1a780d8a783bfb7a2dd6b2796e8128dbbcef9d3d168db 779 9529971a36e7b9215820143329cce7868e416927599cf65a34f3ce2ffda55a7e 780 ca69ed8919a394d42f0f2001010202524173796d6d6574726963454344534132 781 35360326 783 Figure 8: ECDSA 256-bit COSE Key as hex string 785 { 786 / d / -4: h'6c1382765aec5358f117733d281c1c7bdc39884d04a45a1e 787 6c67c858bc206c19', 788 / y / -3: h'60f7f1a780d8a783bfb7a2dd6b2796e8128dbbcef9d3d168 789 db9529971a36e7b9', 790 / x / -2: h'143329cce7868e416927599cf65a34f3ce2ffda55a7eca69 791 ed8919a394d42f0f', 792 / crv / -1: 1 / P-256 /, 793 / kty / 1: 2 / EC2 /, 794 / kid / 2: h'4173796d6d657472696345434453413 795 23536' / 'AsymmetricECDSA256' /, 796 / alg / 3: -7 / ECDSA 256 / 797 } 799 Figure 9: ECDSA 256-bit COSE Key in CBOR diagnostic notation 801 A.3. Example Signed CWT 803 This section shows a signed CWT with a single recipient and a full 804 CWT Claims Set. 806 The signature is generated using the private key listed in 807 Appendix A.2.3 and it can be validated using the public key from 808 Appendix A.2.3. Line breaks are for display purposes only. 810 d28443a10126a104524173796d6d657472696345434453413235365850a701756 811 36f61703a2f2f61732e6578616d706c652e636f6d02656572696b77037818636f 812 61703a2f2f6c696768742e6578616d706c652e636f6d041a5612aeb0051a5610d 813 9f0061a5610d9f007420b7158405427c1ff28d23fbad1f29c4c7c6a555e601d6f 814 a29f9179bc3d7438bacaca5acd08c8d4d4f96131680c429a01f85951ecee743a5 815 2b9b63632c57209120e1c9e30 817 Figure 10: Signed CWT as hex string 819 18( 820 [ 821 / protected / << { 822 / alg / 1: -7 / ECDSA 256 / 823 } >>, 824 / unprotected / { 825 / kid / 4: h'4173796d6d657472696345434453413 826 23536' / 'AsymmetricECDSA256' / 827 }, 828 / payload / << { 829 / iss / 1: "coap://as.example.com", 830 / sub / 2: "erikw", 831 / aud / 3: "coap://light.example.com", 832 / exp / 4: 1444064944, 833 / nbf / 5: 1443944944, 834 / iat / 6: 1443944944, 835 / cti / 7: h'0b71' 836 } >>, 837 / signature / h'5427c1ff28d23fbad1f29c4c7c6a555e601d6fa29f 838 9179bc3d7438bacaca5acd08c8d4d4f96131680c42 839 9a01f85951ecee743a52b9b63632c57209120e1c9e 840 30' 841 ] 842 ) 844 Figure 11: Signed CWT in CBOR diagnostic notation 846 A.4. Example MACed CWT 848 This section shows a MACed CWT with a single recipient, a full CWT 849 Claims Set, and a CWT tag. 851 The MAC is generated using the 256-bit symmetric key from 852 Appendix A.2.2 with a 64-bit truncation. Line breaks are for display 853 purposes only. 855 d83dd18443a10104a1044c53796d6d65747269633235365850a70175636f6170 856 3a2f2f61732e6578616d706c652e636f6d02656572696b77037818636f61703a 857 2f2f6c696768742e6578616d706c652e636f6d041a5612aeb0051a5610d9f006 858 1a5610d9f007420b7148093101ef6d789200 860 Figure 12: MACed CWT with CWT tag as hex string 862 61( 863 17( 864 [ 865 / protected / << { 866 / alg / 1: 4 / HMAC-256-64 / 867 } >>, 868 / unprotected / { 869 / kid / 4: h'53796d6d6574726963323536' / 'Symmetric256' / 870 }, 871 / payload / << { 872 / iss / 1: "coap://as.example.com", 873 / sub / 2: "erikw", 874 / aud / 3: "coap://light.example.com", 875 / exp / 4: 1444064944, 876 / nbf / 5: 1443944944, 877 / iat / 6: 1443944944, 878 / cti / 7: h'0b71' 879 } >>, 880 / tag / h'093101ef6d789200' 881 ] 882 ) 883 ) 885 Figure 13: MACed CWT with CWT tag in CBOR diagnostic notation 887 A.5. Example Encrypted CWT 889 This section shows an encrypted CWT with a single recipient and a 890 full CWT Claims Set. 892 The encryption is done with AES-CCM mode using the 128-bit symmetric 893 key from Appendix A.2.1 with a 64-bit tag and 13-byte nonce, i.e., 894 COSE AES-CCM-16-64-128. Line breaks are for display purposes only. 896 d08343a1010aa2044c53796d6d6574726963313238054d99a0d7846e762c49ff 897 e8a63e0b5858b918a11fd81e438b7f973d9e2e119bcb22424ba0f38a80f27562 898 f400ee1d0d6c0fdb559c02421fd384fc2ebe22d7071378b0ea7428fff157444d 899 45f7e6afcda1aae5f6495830c58627087fc5b4974f319a8707a635dd643b 901 Figure 14: Encrypted CWT as hex string 903 16( 904 [ 905 / protected / << { 906 / alg / 1: 10 / AES-CCM-16-64-128 / 907 } >>, 908 / unprotected / { 909 / kid / 4: h'53796d6d6574726963313238' / 'Symmetric128' /, 910 / iv / 5: h'99a0d7846e762c49ffe8a63e0b' 911 }, 912 / ciphertext / h'b918a11fd81e438b7f973d9e2e119bcb22424ba0f38 913 a80f27562f400ee1d0d6c0fdb559c02421fd384fc2e 914 be22d7071378b0ea7428fff157444d45f7e6afcda1a 915 ae5f6495830c58627087fc5b4974f319a8707a635dd 916 643b' 917 ] 918 ) 920 Figure 15: Encrypted CWT in CBOR diagnostic notation 922 A.6. Example Nested CWT 924 This section shows a Nested CWT, signed and then encrypted, with a 925 single recipient and a full CWT Claims Set. 927 The signature is generated using the private ECDSA key from 928 Appendix A.2.3 and it can be validated using the public ECDSA parts 929 from Appendix A.2.3. The encryption is done with AES-CCM mode using 930 the 128-bit symmetric key from Appendix A.2.1 with a 64-bit tag and 931 13-byte nonce, i.e., COSE AES-CCM-16-64-128. The content type is set 932 to CWT to indicate that there are multiple layers of COSE protection 933 before finding the CWT Claims Set. The decrypted ciphertext will be a 934 COSE_sign1 structure. In this example, it is the same one as in 935 Appendix A.3, i.e., a Signed CWT Claims Set. Note that there is no 936 limitation to the number of layers; this is an example with two 937 layers. Line breaks are for display purposes only. 939 d08343a1010aa2044c53796d6d6574726963313238054d4a0694c0e69ee6b595 940 6655c7b258b7f6b0914f993de822cc47e5e57a188d7960b528a747446fe12f0e 941 7de05650dec74724366763f167a29c002dfd15b34d8993391cf49bc91127f545 942 dba8703d66f5b7f1ae91237503d371e6333df9708d78c4fb8a8386c8ff09dc49 943 af768b23179deab78d96490a66d5724fb33900c60799d9872fac6da3bdb89043 944 d67c2a05414ce331b5b8f1ed8ff7138f45905db2c4d5bc8045ab372bff142631 945 610a7e0f677b7e9b0bc73adefdcee16d9d5d284c616abeab5d8c291ce0 947 Figure 16: Signed and Encrypted CWT as hex string 949 16( 950 [ 951 / protected / << { 952 / alg / 1: 10 / AES-CCM-16-64-128 / 953 } >>, 954 / unprotected / { 955 / kid / 4: h'53796d6d6574726963313238' / 'Symmetric128' /, 956 / iv / 5: h'4a0694c0e69ee6b5956655c7b2' 957 }, 958 / ciphertext / h'f6b0914f993de822cc47e5e57a188d7960b528a7474 959 46fe12f0e7de05650dec74724366763f167a29c002d 960 fd15b34d8993391cf49bc91127f545dba8703d66f5b 961 7f1ae91237503d371e6333df9708d78c4fb8a8386c8 962 ff09dc49af768b23179deab78d96490a66d5724fb33 963 900c60799d9872fac6da3bdb89043d67c2a05414ce3 964 31b5b8f1ed8ff7138f45905db2c4d5bc8045ab372bf 965 f142631610a7e0f677b7e9b0bc73adefdcee16d9d5d 966 284c616abeab5d8c291ce0' 967 ] 968 ) 970 Figure 17: Signed and Encrypted CWT in CBOR diagnostic notation 972 A.7. Example MACed CWT with a floating-point value 974 This section shows a MACed CWT with a single recipient and a simple 975 CWT Claims Set. The CWT Claims Set with a floating-point 'iat' value. 977 The MAC is generated using the 256-bit symmetric key from 978 Appendix A.2.2 with a 64-bit truncation. Line breaks are for display 979 purposes only. 981 d18443a10104a1044c53796d6d65747269633235364ba106fb41d584367c2000 982 0048b8816f34c0542892 984 Figure 18: MACed CWT with a floating-point value as hex string 986 17( 987 [ 988 / protected / << { 989 / alg / 1: 4 / HMAC-256-64 / 990 } >>, 991 / unprotected / { 992 / kid / 4: h'53796d6d6574726963323536' / 'Symmetric256' /, 993 }, 994 / payload / << { 995 / iat / 6: 1443944944.5 996 } >>, 997 / tag / h'b8816f34c0542892' 998 ] 999 ) 1001 Figure 19: MACed CWT with a floating-point value in CBOR diagnostic 1002 notation 1004 Appendix B. Acknowledgements 1006 This specification is based on JSON Web Token (JWT) [RFC7519], the 1007 authors of which also include Nat Sakimura and John Bradley. It also 1008 incorporates suggestions made by many people, including Carsten 1009 Bormann, Esko Dijk, Benjamin Kaduk, Jim Schaad, Ludwig Seitz, and 1010 Goeran Selander. 1012 [[ RFC Editor: Is it possible to preserve the non-ASCII spellings of 1013 the names Erik Wahlstroem and Goeran Selander in the final 1014 specification? ]] 1016 Appendix C. Document History 1018 [[ to be removed by the RFC Editor before publication as an RFC ]] 1020 -12 1022 o Updated the RFC 5226 reference to RFC 8126. 1024 o Made the IANA registration criteria consistent across sections. 1026 o Stated that registrations for the limited set of values between 1027 -256 and 255 and strings of length 1 are to be restricted to 1028 claims with general applicability. 1030 o Changed the "Reference" field name to "Description of Semantics" 1031 in the CBOR Tag registration request. 1033 o Asked the RFC Editor whether it is possible to preserve the non- 1034 ASCII spellings of the names Erik Wahlstroem and Goeran Selander 1035 in the final specification. 1037 -11 1039 o Corrected the "iv" value in the signed and encrypted CWT example. 1041 o Mention CoAP in the "application/cwt" media type registration. 1043 o Changed references of the form "Section 4.1.1 of JWT " to "Section 4.1.1 of " 1045 so that rfcmarkup will generate correct external section reference 1046 links. 1048 o Updated Acknowledgements. 1050 -10 1052 o Clarified that the audience claim value can be a single audience 1053 value or an array of audience values, just as is the case for the 1054 JWT "aud" claim. 1056 o Clarified the nested CWT description. 1058 o Changed uses of "binary string" to "byte string". 1060 -09 1062 o Added key ID values to the examples. 1064 o Key values for the examples are now represented in COSE_Key format 1065 using CBOR diagnostic notation. 1067 -08 1069 o Updated the diagnostic notation for embedded objects in the 1070 examples, addressing feedback by Carsten Bormann. 1072 -07 1074 o Updated examples for signing and encryption. Signatures are now 1075 deterministic as recommended by COSE specification. 1077 -06 1079 o Addressed review comments by Carsten Bormann and Jim Schaad. All 1080 changes were editorial in nature. 1082 -05 1084 o Addressed working group last call comments with the following 1085 changes: 1087 o Say that CWT is derived from JWT, rather than CWT is a profile of 1088 JWT. 1090 o Used CBOR type names in descriptions, rather than major/minor type 1091 numbers. 1093 o Clarified the NumericDate and StringOrURI descriptions. 1095 o Changed to allow CWT claim names to use values of any legal CBOR 1096 map key type. 1098 o Changed to use the CWT tag to identify nested CWTs instead of the 1099 CWT content type. 1101 o Added an example using a floating-point date value. 1103 o Acknowledged reviewers. 1105 -04 1107 o Specified that the use of CBOR tags to prefix any of the claim 1108 values defined in this specification is NOT RECOMMENDED. 1110 -03 1112 o Reworked the examples to include signed, MACed, encrypted, and 1113 nested CWTs. 1115 o Defined the CWT CBOR tag and explained its usage. 1117 -02 1119 o Added IANA registration for the application/cwt media type. 1121 o Clarified the nested CWT language. 1123 o Corrected nits identified by Ludwig Seitz. 1125 -01 1127 o Added IANA registration for CWT Claims. 1129 o Added IANA registration for the application/cwt CoAP content- 1130 format type. 1132 o Added Samuel Erdtman as an editor. 1134 o Changed Erik's e-mail address. 1136 -00 1138 o Created the initial working group version based on draft- 1139 wahlstroem-ace-cbor-web-token-00. 1141 Authors' Addresses 1143 Michael B. Jones 1144 Microsoft 1146 Email: mbj@microsoft.com 1147 URI: http://self-issued.info/ 1149 Erik Wahlstroem 1150 Sweden 1152 Email: erik@wahlstromstekniska.se 1154 Samuel Erdtman 1155 Spotify AB 1156 Birger Jarlsgatan 61, 4tr 1157 Stockholm 113 56 1158 Sweden 1160 Phone: +46702691499 1161 Email: erdtman@spotify.com 1163 Hannes Tschofenig 1164 ARM Ltd. 1165 Hall in Tirol 6060 1166 Austria 1168 Email: Hannes.Tschofenig@arm.com