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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: September 6, 2018 6 S. Erdtman 7 Spotify AB 8 H. Tschofenig 9 ARM Ltd. 10 March 5, 2018 12 CBOR Web Token (CWT) 13 draft-ietf-ace-cbor-web-token-13 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 September 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 . . . . . . . . . . . . . . . . 11 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 . . . . . . . . . . . . 14 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 . . . . . . . . . . . . . . . . . . . . . . 16 93 A.1. Example CWT Claims Set . . . . . . . . . . . . . . . . . 16 94 A.2. Example keys . . . . . . . . . . . . . . . . . . . . . . 16 95 A.2.1. 128-bit Symmetric Key . . . . . . . . . . . . . . . . 17 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 . . . . . . . . . . . . . . . . . . . 18 99 A.4. Example MACed CWT . . . . . . . . . . . . . . . . . . . . 19 100 A.5. Example Encrypted CWT . . . . . . . . . . . . . . . . . . 20 101 A.6. Example Nested CWT . . . . . . . . . . . . . . . . . . . 21 102 A.7. Example MACed CWT with a floating-point value . . . . . . 22 103 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 23 104 Appendix C. Document History . . . . . . . . . . . . . . . . . . 23 105 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26 107 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 and processing rules 152 as the "StringOrURI" term defined in Section 2 of [RFC7519], 153 except that it uses a CBOR text string instead of a JSON string 154 value. 156 NumericDate 157 The "NumericDate" term has the same meaning and processing rules 158 as the "NumericDate" term defined in Section 2 of [RFC7519], 159 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 and processing rules as 199 the "iss" claim defined in Section 4.1.1 of [RFC7519], except that 200 the value is of type StringOrURI. The Claim Key 1 is used to 201 identify this claim. 203 3.1.2. sub (Subject) Claim 205 The "sub" (subject) claim has the same meaning and processing rules 206 as the "sub" claim defined in Section 4.1.2 of [RFC7519], except that 207 the value is of type StringOrURI. The Claim Key 2 is used to 208 identify this claim. 210 3.1.3. aud (Audience) Claim 212 The "aud" (audience) claim has the same meaning and processing rules 213 as the "aud" claim defined in Section 4.1.3 of [RFC7519], except that 214 the value of the audience claim is of type StringOrURI when it is not 215 an array or the values of the audience array elements are of type 216 StringOrURI when the audience claim value is an array. The Claim Key 217 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 and processing 222 rules as the "exp" claim defined in Section 4.1.4 of [RFC7519], 223 except that the value is of type NumericDate. The Claim Key 4 is 224 used to identify this claim. 226 3.1.5. nbf (Not Before) Claim 228 The "nbf" (not before) claim has the same meaning and processing 229 rules as the "nbf" claim defined in Section 4.1.5 of [RFC7519], 230 except that the value is of type NumericDate. The Claim Key 5 is 231 used to identify this claim. 233 3.1.6. iat (Issued At) Claim 235 The "iat" (issued at) claim has the same meaning and processing rules 236 as the "iat" claim defined in Section 4.1.6 of [RFC7519], except that 237 the value is of type NumericDate. The Claim Key 6 is used to 238 identify this claim. 240 3.1.7. cti (CWT ID) Claim 242 The "cti" (CWT ID) claim has the same meaning and processing rules as 243 the "jti" claim defined in Section 4.1.7 of [RFC7519], except that 244 the value is of type byte string. The Claim Key 7 is used to 245 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 Registration requests are evaluated using the criteria described in 430 the Claim Key instructions in the registration template below after a 431 three-week review period on the cwt-reg-review@ietf.org mailing list, 432 on the advice of one or more Designated Experts. However, to allow 433 for the allocation of values prior to publication, the Designated 434 Experts may approve registration once they are satisfied that such a 435 specification will be published. [[ Note to the RFC Editor: The name 436 of the mailing list should be determined in consultation with the 437 IESG and IANA. Suggested name: cwt-reg-review@ietf.org. ]] 439 Registration requests sent to the mailing list for review should use 440 an appropriate subject (e.g., "Request to register claim: example"). 441 Registration requests that are undetermined for a period longer than 442 21 days can be brought to the IESG's attention (using the 443 iesg@ietf.org mailing list) for resolution. 445 Criteria that should be applied by the Designated Experts includes 446 determining whether the proposed registration duplicates existing 447 functionality, whether it is likely to be of general applicability or 448 whether it is useful only for a single application, and whether the 449 registration description is clear. Registrations for the limited set 450 of values between -256 and 255 and strings of length 1 are to be 451 restricted to claims with general applicability. 453 It is suggested that multiple Designated Experts be appointed who are 454 able to represent the perspectives of different applications using 455 this specification in order to enable broadly informed review of 456 registration decisions. In cases where a registration decision could 457 be perceived as creating a conflict of interest for a particular 458 Expert, that Expert should defer to the judgment of the other 459 Experts. 461 Since a high degree of overlap is expected between the contents of 462 the "CBOR Web Token (CWT) Claims" registry and the "JSON Web Token 463 Claims" registry, overlap in the corresponding pools of Designated 464 Experts would be useful to help ensure that an appropriate level of 465 coordination between the registries is maintained. 467 9.1.1. Registration Template 469 Claim Name: 470 The human-readable name requested (e.g., "iss"). 472 Claim Description: 473 Brief description of the claim (e.g., "Issuer"). 475 JWT Claim Name: 476 Claim Name of the equivalent JWT claim, as registered in 477 [IANA.JWT.Claims]. CWT claims should normally have a 478 corresponding JWT claim. If a corresponding JWT claim would not 479 make sense, the Designated Experts can choose to accept 480 registrations for which the JWT Claim Name is listed as "N/A". 482 Claim Key: 483 CBOR map key for the claim. Different ranges of values use 484 different registration policies [RFC8126]. Integer values between 485 -256 and 255 and strings of length 1 are designated as Standards 486 Action. Integer values from -65536 to 65535 and strings of length 487 2 are designated as Specification Required. Integer values of 488 greater than 65535 and strings of length greater than 2 are 489 designated as Expert Review. Integer values less than -65536 are 490 marked as Private Use. 492 Claim Value Type(s): 493 CBOR types that can be used for the claim value. 495 Change Controller: 496 For Standards Track RFCs, list the "IESG". For others, give the 497 name of the responsible party. Other details (e.g., postal 498 address, email address, home page URI) may also be included. 500 Specification Document(s): 501 Reference to the document or documents that specify the parameter, 502 preferably including URIs that can be used to retrieve copies of 503 the documents. An indication of the relevant sections may also be 504 included but is not required. 506 9.1.2. Initial Registry Contents 508 o Claim Name: (RESERVED) 509 o Claim Description: This registration reserves the key value 0. 510 o JWT Claim Name: N/A 511 o Claim Key: 0 512 o Claim Value Type(s): N/A 513 o Change Controller: IESG 514 o Specification Document(s): [[ this specification ]] 515 o Claim Name: "iss" 516 o Claim Description: Issuer 517 o JWT Claim Name: "iss" 518 o Claim Key: 1 519 o Claim Value Type(s): text string 520 o Change Controller: IESG 521 o Specification Document(s): Section 3.1.1 of [[ this specification 522 ]] 524 o Claim Name: "sub" 525 o Claim Description: Subject 526 o JWT Claim Name: "sub" 527 o Claim Key: 2 528 o Claim Value Type(s): text string 529 o Change Controller: IESG 530 o Specification Document(s): Section 3.1.2 of [[ this specification 531 ]] 533 o Claim Name: "aud" 534 o Claim Description: Audience 535 o JWT Claim Name: "aud" 536 o Claim Key: 3 537 o Claim Value Type(s): text string 538 o Change Controller: IESG 539 o Specification Document(s): Section 3.1.3 of [[ this specification 540 ]] 542 o Claim Name: "exp" 543 o Claim Description: Expiration Time 544 o JWT Claim Name: "exp" 545 o Claim Key: 4 546 o Claim Value Type(s): integer or floating-point number 547 o Change Controller: IESG 548 o Specification Document(s): Section 3.1.4 of [[ this specification 549 ]] 551 o Claim Name: "nbf" 552 o Claim Description: Not Before 553 o JWT Claim Name: "nbf" 554 o Claim Key: 5 555 o Claim Value Type(s): integer or floating-point number 556 o Change Controller: IESG 557 o Specification Document(s): Section 3.1.5 of [[ this specification 558 ]] 560 o Claim Name: "iat" 561 o Claim Description: Issued At 562 o JWT Claim Name: "iat" 563 o Claim Key: 6 564 o Claim Value Type(s): integer or floating-point number 565 o Change Controller: IESG 566 o Specification Document(s): Section 3.1.6 of [[ this specification 567 ]] 569 o Claim Name: "cti" 570 o Claim Description: CWT ID 571 o JWT Claim Name: "jti" 572 o Claim Key: 7 573 o Claim Value Type(s): byte string 574 o Change Controller: IESG 575 o Specification Document(s): Section 3.1.7 of [[ this specification 576 ]] 578 9.2. Media Type Registration 580 This section registers the "application/cwt" media type in the "Media 581 Types" registry [IANA.MediaTypes] in the manner described in RFC 6838 582 [RFC6838], which can be used to indicate that the content is a CWT. 584 9.2.1. Registry Contents 586 o Type name: application 587 o Subtype name: cwt 588 o Required parameters: N/A 589 o Optional parameters: N/A 590 o Encoding considerations: binary 591 o Security considerations: See the Security Considerations section 592 of [[ this specification ]] 593 o Interoperability considerations: N/A 594 o Published specification: [[ this specification ]] 595 o Applications that use this media type: IoT applications sending 596 security tokens over HTTP(S), CoAP(S), and other transports. 597 o Fragment identifier considerations: N/A 598 o Additional information: 600 Magic number(s): N/A 601 File extension(s): N/A 602 Macintosh file type code(s): N/A 604 o Person & email address to contact for further information: 605 IESG, iesg@ietf.org 606 o Intended usage: COMMON 607 o Restrictions on usage: none 608 o Author: Michael B. Jones, mbj@microsoft.com 609 o Change controller: IESG 610 o Provisional registration? No 612 9.3. CoAP Content-Formats Registration 614 This section registers the CoAP Content-Format ID for the 615 "application/cwt" media type in the "CoAP Content-Formats" registry 616 [IANA.CoAP.Content-Formats]. 618 9.3.1. Registry Contents 620 o Media Type: application/cwt 621 o Encoding: - 622 o Id: TBD (maybe 61) 623 o Reference: [[ this specification ]] 625 9.4. CBOR Tag registration 627 This section registers the CWT CBOR tag in the "CBOR Tags" registry 628 [IANA.CBOR.Tags]. 630 9.4.1. Registry Contents 632 o CBOR Tag: TBD (maybe 61 to use the same value as the Content- 633 Format) 634 o Data Item: CBOR Web Token (CWT) 635 o Semantics: CBOR Web Token (CWT), as defined in [[ this 636 specification ]] 637 o Description of Semantics: [[ this specification ]] 638 o Point of Contact: Michael B. Jones, mbj@microsoft.com 640 10. References 642 10.1. Normative References 644 [IANA.CBOR.Tags] 645 IANA, "Concise Binary Object Representation (CBOR) Tags", 646 . 649 [IANA.CoAP.Content-Formats] 650 IANA, "CoAP Content-Formats", 651 . 654 [IANA.MediaTypes] 655 IANA, "Media Types", 656 . 658 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 659 Requirement Levels", BCP 14, RFC 2119, 660 DOI 10.17487/RFC2119, March 1997, 661 . 663 [RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object 664 Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049, 665 October 2013, . 667 [RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token 668 (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015, 669 . 671 [RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)", 672 RFC 8152, DOI 10.17487/RFC8152, July 2017, 673 . 675 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 676 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 677 May 2017, . 679 10.2. Informative References 681 [IANA.JWT.Claims] 682 IANA, "JSON Web Token Claims", 683 . 685 [RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type 686 Specifications and Registration Procedures", BCP 13, 687 RFC 6838, DOI 10.17487/RFC6838, January 2013, 688 . 690 [RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web 691 Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May 692 2015, . 694 [RFC7516] Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)", 695 RFC 7516, DOI 10.17487/RFC7516, May 2015, 696 . 698 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 699 Writing an IANA Considerations Section in RFCs", BCP 26, 700 RFC 8126, DOI 10.17487/RFC8126, June 2017, 701 . 703 Appendix A. Examples 705 This appendix includes a set of CWT examples that show how the CWT 706 Claims Set can be protected. There are examples that are signed, 707 MACed, encrypted, and that use nested signing and encryption. To 708 make the examples easier to read, they are presented both as hex 709 strings and in the extended CBOR diagnostic notation described in 710 Section 6 of [RFC7049]. 712 Where a byte string is to carry an embedded CBOR-encoded item, the 713 diagnostic notation for this CBOR data item can be enclosed in '<<' 714 and '>>' to notate the byte string resulting from encoding the data 715 item, e.g., h'63666F6F' translates to <<"foo">>. 717 A.1. Example CWT Claims Set 719 The CWT Claims Set used for the different examples displays usage of 720 all the defined claims. For signed and MACed examples, the CWT 721 Claims Set is the CBOR encoding as a byte string. 723 a70175636f61703a2f2f61732e6578616d706c652e636f6d02656572696b7703 724 7818636f61703a2f2f6c696768742e6578616d706c652e636f6d041a5612aeb0 725 051a5610d9f0061a5610d9f007420b71 727 Figure 2: Example CWT Claims Set as hex string 729 { 730 / iss / 1: "coap://as.example.com", 731 / sub / 2: "erikw", 732 / aud / 3: "coap://light.example.com", 733 / exp / 4: 1444064944, 734 / nbf / 5: 1443944944, 735 / iat / 6: 1443944944, 736 / cti / 7: h'0b71' 737 } 739 Figure 3: Example CWT Claims Set in CBOR diagnostic notation 741 A.2. Example keys 743 This section contains the keys used to sign, MAC, and encrypt the 744 messages in this appendix. Line breaks are for display purposes 745 only. 747 A.2.1. 128-bit Symmetric Key 749 a42050231f4c4d4d3051fdc2ec0a3851d5b3830104024c53796d6d6574726963 750 313238030a 752 Figure 4: 128-bit symmetric COSE_Key as hex string 754 { 755 / k / -1: h'231f4c4d4d3051fdc2ec0a3851d5b383' 756 / kty / 1: 4 / Symmetric /, 757 / kid / 2: h'53796d6d6574726963313238' / 'Symmetric128' /, 758 / alg / 3: 10 / AES-CCM-16-64-128 / 759 } 761 Figure 5: 128-bit symmetric COSE_Key in CBOR diagnostic notation 763 A.2.2. 256-bit Symmetric Key 765 a4205820403697de87af64611c1d32a05dab0fe1fcb715a86ab435f1ec99192d 766 795693880104024c53796d6d6574726963323536030a 768 Figure 6: 256-bit symmetric COSE_Key as hex string 770 { 771 / k / -1: h'403697de87af64611c1d32a05dab0fe1fcb715a86ab435f1 772 ec99192d79569388' 773 / kty / 1: 4 / Symmetric /, 774 / kid / 4: h'53796d6d6574726963323536' / 'Symmetric256' /, 775 / alg / 3: 4 / HMAC 256/64 / 776 } 778 Figure 7: 256-bit symmetric COSE_Key in CBOR diagnostic notation 780 A.2.3. ECDSA P-256 256-bit COSE Key 782 a72358206c1382765aec5358f117733d281c1c7bdc39884d04a45a1e6c67c858 783 bc206c1922582060f7f1a780d8a783bfb7a2dd6b2796e8128dbbcef9d3d168db 784 9529971a36e7b9215820143329cce7868e416927599cf65a34f3ce2ffda55a7e 785 ca69ed8919a394d42f0f2001010202524173796d6d6574726963454344534132 786 35360326 788 Figure 8: ECDSA 256-bit COSE Key as hex string 790 { 791 / d / -4: h'6c1382765aec5358f117733d281c1c7bdc39884d04a45a1e 792 6c67c858bc206c19', 793 / y / -3: h'60f7f1a780d8a783bfb7a2dd6b2796e8128dbbcef9d3d168 794 db9529971a36e7b9', 795 / x / -2: h'143329cce7868e416927599cf65a34f3ce2ffda55a7eca69 796 ed8919a394d42f0f', 797 / crv / -1: 1 / P-256 /, 798 / kty / 1: 2 / EC2 /, 799 / kid / 2: h'4173796d6d657472696345434453413 800 23536' / 'AsymmetricECDSA256' /, 801 / alg / 3: -7 / ECDSA 256 / 802 } 804 Figure 9: ECDSA 256-bit COSE Key in CBOR diagnostic notation 806 A.3. Example Signed CWT 808 This section shows a signed CWT with a single recipient and a full 809 CWT Claims Set. 811 The signature is generated using the private key listed in 812 Appendix A.2.3 and it can be validated using the public key from 813 Appendix A.2.3. Line breaks are for display purposes only. 815 d28443a10126a104524173796d6d657472696345434453413235365850a701756 816 36f61703a2f2f61732e6578616d706c652e636f6d02656572696b77037818636f 817 61703a2f2f6c696768742e6578616d706c652e636f6d041a5612aeb0051a5610d 818 9f0061a5610d9f007420b7158405427c1ff28d23fbad1f29c4c7c6a555e601d6f 819 a29f9179bc3d7438bacaca5acd08c8d4d4f96131680c429a01f85951ecee743a5 820 2b9b63632c57209120e1c9e30 822 Figure 10: Signed CWT as hex string 824 18( 825 [ 826 / protected / << { 827 / alg / 1: -7 / ECDSA 256 / 828 } >>, 829 / unprotected / { 830 / kid / 4: h'4173796d6d657472696345434453413 831 23536' / 'AsymmetricECDSA256' / 832 }, 833 / payload / << { 834 / iss / 1: "coap://as.example.com", 835 / sub / 2: "erikw", 836 / aud / 3: "coap://light.example.com", 837 / exp / 4: 1444064944, 838 / nbf / 5: 1443944944, 839 / iat / 6: 1443944944, 840 / cti / 7: h'0b71' 841 } >>, 842 / signature / h'5427c1ff28d23fbad1f29c4c7c6a555e601d6fa29f 843 9179bc3d7438bacaca5acd08c8d4d4f96131680c42 844 9a01f85951ecee743a52b9b63632c57209120e1c9e 845 30' 846 ] 847 ) 849 Figure 11: Signed CWT in CBOR diagnostic notation 851 A.4. Example MACed CWT 853 This section shows a MACed CWT with a single recipient, a full CWT 854 Claims Set, and a CWT tag. 856 The MAC is generated using the 256-bit symmetric key from 857 Appendix A.2.2 with a 64-bit truncation. Line breaks are for display 858 purposes only. 860 d83dd18443a10104a1044c53796d6d65747269633235365850a70175636f6170 861 3a2f2f61732e6578616d706c652e636f6d02656572696b77037818636f61703a 862 2f2f6c696768742e6578616d706c652e636f6d041a5612aeb0051a5610d9f006 863 1a5610d9f007420b7148093101ef6d789200 865 Figure 12: MACed CWT with CWT tag as hex string 867 61( 868 17( 869 [ 870 / protected / << { 871 / alg / 1: 4 / HMAC-256-64 / 872 } >>, 873 / unprotected / { 874 / kid / 4: h'53796d6d6574726963323536' / 'Symmetric256' / 875 }, 876 / payload / << { 877 / iss / 1: "coap://as.example.com", 878 / sub / 2: "erikw", 879 / aud / 3: "coap://light.example.com", 880 / exp / 4: 1444064944, 881 / nbf / 5: 1443944944, 882 / iat / 6: 1443944944, 883 / cti / 7: h'0b71' 884 } >>, 885 / tag / h'093101ef6d789200' 886 ] 887 ) 888 ) 890 Figure 13: MACed CWT with CWT tag in CBOR diagnostic notation 892 A.5. Example Encrypted CWT 894 This section shows an encrypted CWT with a single recipient and a 895 full CWT Claims Set. 897 The encryption is done with AES-CCM mode using the 128-bit symmetric 898 key from Appendix A.2.1 with a 64-bit tag and 13-byte nonce, i.e., 899 COSE AES-CCM-16-64-128. Line breaks are for display purposes only. 901 d08343a1010aa2044c53796d6d6574726963313238054d99a0d7846e762c49ff 902 e8a63e0b5858b918a11fd81e438b7f973d9e2e119bcb22424ba0f38a80f27562 903 f400ee1d0d6c0fdb559c02421fd384fc2ebe22d7071378b0ea7428fff157444d 904 45f7e6afcda1aae5f6495830c58627087fc5b4974f319a8707a635dd643b 906 Figure 14: Encrypted CWT as hex string 908 16( 909 [ 910 / protected / << { 911 / alg / 1: 10 / AES-CCM-16-64-128 / 912 } >>, 913 / unprotected / { 914 / kid / 4: h'53796d6d6574726963313238' / 'Symmetric128' /, 915 / iv / 5: h'99a0d7846e762c49ffe8a63e0b' 916 }, 917 / ciphertext / h'b918a11fd81e438b7f973d9e2e119bcb22424ba0f38 918 a80f27562f400ee1d0d6c0fdb559c02421fd384fc2e 919 be22d7071378b0ea7428fff157444d45f7e6afcda1a 920 ae5f6495830c58627087fc5b4974f319a8707a635dd 921 643b' 922 ] 923 ) 925 Figure 15: Encrypted CWT in CBOR diagnostic notation 927 A.6. Example Nested CWT 929 This section shows a Nested CWT, signed and then encrypted, with a 930 single recipient and a full CWT Claims Set. 932 The signature is generated using the private ECDSA key from 933 Appendix A.2.3 and it can be validated using the public ECDSA parts 934 from Appendix A.2.3. The encryption is done with AES-CCM mode using 935 the 128-bit symmetric key from Appendix A.2.1 with a 64-bit tag and 936 13-byte nonce, i.e., COSE AES-CCM-16-64-128. The content type is set 937 to CWT to indicate that there are multiple layers of COSE protection 938 before finding the CWT Claims Set. The decrypted ciphertext will be a 939 COSE_sign1 structure. In this example, it is the same one as in 940 Appendix A.3, i.e., a Signed CWT Claims Set. Note that there is no 941 limitation to the number of layers; this is an example with two 942 layers. Line breaks are for display purposes only. 944 d08343a1010aa2044c53796d6d6574726963313238054d4a0694c0e69ee6b595 945 6655c7b258b7f6b0914f993de822cc47e5e57a188d7960b528a747446fe12f0e 946 7de05650dec74724366763f167a29c002dfd15b34d8993391cf49bc91127f545 947 dba8703d66f5b7f1ae91237503d371e6333df9708d78c4fb8a8386c8ff09dc49 948 af768b23179deab78d96490a66d5724fb33900c60799d9872fac6da3bdb89043 949 d67c2a05414ce331b5b8f1ed8ff7138f45905db2c4d5bc8045ab372bff142631 950 610a7e0f677b7e9b0bc73adefdcee16d9d5d284c616abeab5d8c291ce0 952 Figure 16: Signed and Encrypted CWT as hex string 954 16( 955 [ 956 / protected / << { 957 / alg / 1: 10 / AES-CCM-16-64-128 / 958 } >>, 959 / unprotected / { 960 / kid / 4: h'53796d6d6574726963313238' / 'Symmetric128' /, 961 / iv / 5: h'4a0694c0e69ee6b5956655c7b2' 962 }, 963 / ciphertext / h'f6b0914f993de822cc47e5e57a188d7960b528a7474 964 46fe12f0e7de05650dec74724366763f167a29c002d 965 fd15b34d8993391cf49bc91127f545dba8703d66f5b 966 7f1ae91237503d371e6333df9708d78c4fb8a8386c8 967 ff09dc49af768b23179deab78d96490a66d5724fb33 968 900c60799d9872fac6da3bdb89043d67c2a05414ce3 969 31b5b8f1ed8ff7138f45905db2c4d5bc8045ab372bf 970 f142631610a7e0f677b7e9b0bc73adefdcee16d9d5d 971 284c616abeab5d8c291ce0' 972 ] 973 ) 975 Figure 17: Signed and Encrypted CWT in CBOR diagnostic notation 977 A.7. Example MACed CWT with a floating-point value 979 This section shows a MACed CWT with a single recipient and a simple 980 CWT Claims Set. The CWT Claims Set with a floating-point 'iat' value. 982 The MAC is generated using the 256-bit symmetric key from 983 Appendix A.2.2 with a 64-bit truncation. Line breaks are for display 984 purposes only. 986 d18443a10104a1044c53796d6d65747269633235364ba106fb41d584367c2000 987 0048b8816f34c0542892 989 Figure 18: MACed CWT with a floating-point value as hex string 991 17( 992 [ 993 / protected / << { 994 / alg / 1: 4 / HMAC-256-64 / 995 } >>, 996 / unprotected / { 997 / kid / 4: h'53796d6d6574726963323536' / 'Symmetric256' /, 998 }, 999 / payload / << { 1000 / iat / 6: 1443944944.5 1001 } >>, 1002 / tag / h'b8816f34c0542892' 1003 ] 1004 ) 1006 Figure 19: MACed CWT with a floating-point value in CBOR diagnostic 1007 notation 1009 Appendix B. Acknowledgements 1011 This specification is based on JSON Web Token (JWT) [RFC7519], the 1012 authors of which also include Nat Sakimura and John Bradley. It also 1013 incorporates suggestions made by many people, including Carsten 1014 Bormann, Esko Dijk, Benjamin Kaduk, Carlos Martinez, Kathleen 1015 Moriarty, Dan Romascanu, Kyle Rose, Jim Schaad, Ludwig Seitz, and 1016 Goeran Selander. 1018 [[ RFC Editor: Is it possible to preserve the non-ASCII spellings of 1019 the names Erik Wahlstroem and Goeran Selander in the final 1020 specification? ]] 1022 Appendix C. Document History 1024 [[ to be removed by the RFC Editor before publication as an RFC ]] 1026 -13 1028 o Clarified the registration criteria applied to different ranges of 1029 Claim Key values, as suggested by Kathleen Moriarty and Dan 1030 Romascanu. 1032 o No longer describe the syntax of CWT claims as being the same as 1033 that of the corresponding JWT claims, as suggested by Kyle Rose. 1035 o Added guidance about the selection of the Designated Experts, as 1036 suggested by Benjamin Kaduk. 1038 o Acknowledged additional reviewers. 1040 -12 1042 o Updated the RFC 5226 reference to RFC 8126. 1044 o Made the IANA registration criteria consistent across sections. 1046 o Stated that registrations for the limited set of values between 1047 -256 and 255 and strings of length 1 are to be restricted to 1048 claims with general applicability. 1050 o Changed the "Reference" field name to "Description of Semantics" 1051 in the CBOR Tag registration request. 1053 o Asked the RFC Editor whether it is possible to preserve the non- 1054 ASCII spellings of the names Erik Wahlstroem and Goeran Selander 1055 in the final specification. 1057 -11 1059 o Corrected the "iv" value in the signed and encrypted CWT example. 1061 o Mention CoAP in the "application/cwt" media type registration. 1063 o Changed references of the form "Section 4.1.1 of JWT " to "Section 4.1.1 of " 1065 so that rfcmarkup will generate correct external section reference 1066 links. 1068 o Updated Acknowledgements. 1070 -10 1072 o Clarified that the audience claim value can be a single audience 1073 value or an array of audience values, just as is the case for the 1074 JWT "aud" claim. 1076 o Clarified the nested CWT description. 1078 o Changed uses of "binary string" to "byte string". 1080 -09 1082 o Added key ID values to the examples. 1084 o Key values for the examples are now represented in COSE_Key format 1085 using CBOR diagnostic notation. 1087 -08 1088 o Updated the diagnostic notation for embedded objects in the 1089 examples, addressing feedback by Carsten Bormann. 1091 -07 1093 o Updated examples for signing and encryption. Signatures are now 1094 deterministic as recommended by COSE specification. 1096 -06 1098 o Addressed review comments by Carsten Bormann and Jim Schaad. All 1099 changes were editorial in nature. 1101 -05 1103 o Addressed working group last call comments with the following 1104 changes: 1106 o Say that CWT is derived from JWT, rather than CWT is a profile of 1107 JWT. 1109 o Used CBOR type names in descriptions, rather than major/minor type 1110 numbers. 1112 o Clarified the NumericDate and StringOrURI descriptions. 1114 o Changed to allow CWT claim names to use values of any legal CBOR 1115 map key type. 1117 o Changed to use the CWT tag to identify nested CWTs instead of the 1118 CWT content type. 1120 o Added an example using a floating-point date value. 1122 o Acknowledged reviewers. 1124 -04 1126 o Specified that the use of CBOR tags to prefix any of the claim 1127 values defined in this specification is NOT RECOMMENDED. 1129 -03 1131 o Reworked the examples to include signed, MACed, encrypted, and 1132 nested CWTs. 1134 o Defined the CWT CBOR tag and explained its usage. 1136 -02 1138 o Added IANA registration for the application/cwt media type. 1140 o Clarified the nested CWT language. 1142 o Corrected nits identified by Ludwig Seitz. 1144 -01 1146 o Added IANA registration for CWT Claims. 1148 o Added IANA registration for the application/cwt CoAP content- 1149 format type. 1151 o Added Samuel Erdtman as an editor. 1153 o Changed Erik's e-mail address. 1155 -00 1157 o Created the initial working group version based on draft- 1158 wahlstroem-ace-cbor-web-token-00. 1160 Authors' Addresses 1162 Michael B. Jones 1163 Microsoft 1165 Email: mbj@microsoft.com 1166 URI: http://self-issued.info/ 1168 Erik Wahlstroem 1169 Sweden 1171 Email: erik@wahlstromstekniska.se 1173 Samuel Erdtman 1174 Spotify AB 1175 Birger Jarlsgatan 61, 4tr 1176 Stockholm 113 56 1177 Sweden 1179 Phone: +46702691499 1180 Email: erdtman@spotify.com 1181 Hannes Tschofenig 1182 ARM Ltd. 1183 Hall in Tirol 6060 1184 Austria 1186 Email: Hannes.Tschofenig@arm.com