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'JWK' -- Possible downref: Non-RFC (?) normative reference: ref. 'JWT' ** Downref: Normative reference to an Historic RFC: RFC 1421 ** Obsolete normative reference: RFC 1738 (Obsoleted by RFC 4248, RFC 4266) ** Downref: Normative reference to an Informational RFC: RFC 2104 ** Obsolete normative reference: RFC 3447 (Obsoleted by RFC 8017) ** Obsolete normative reference: RFC 4627 (Obsoleted by RFC 7158, RFC 7159) ** Obsolete normative reference: RFC 5226 (Obsoleted by RFC 8126) ** Obsolete normative reference: RFC 5785 (Obsoleted by RFC 8615) -- Possible downref: Non-RFC (?) normative reference: ref. 'USA15' Summary: 8 errors (**), 0 flaws (~~), 2 warnings (==), 19 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group M. Jones 3 Internet-Draft Microsoft 4 Intended status: Standards Track D. Balfanz 5 Expires: October 31, 2011 Google 6 J. Bradley 7 independent 8 Y. Goland 9 Microsoft 10 J. Panzer 11 Google 12 N. Sakimura 13 Nomura Research Institute 14 P. Tarjan 15 Facebook 16 April 29, 2011 18 JSON Web Signature (JWS) 19 draft-jones-json-web-signature-02 21 Abstract 23 JSON Web Signature (JWS) is a means of representing signed content 24 using JSON data structures. Related encryption capabilities are 25 described in the separate JSON Web Encryption (JWE) specification. 27 Requirements Language 29 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 30 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 31 document are to be interpreted as described in RFC 2119 [RFC2119]. 33 Status of this Memo 35 This Internet-Draft is submitted in full conformance with the 36 provisions of BCP 78 and BCP 79. 38 Internet-Drafts are working documents of the Internet Engineering 39 Task Force (IETF). Note that other groups may also distribute 40 working documents as Internet-Drafts. The list of current Internet- 41 Drafts is at http://datatracker.ietf.org/drafts/current/. 43 Internet-Drafts are draft documents valid for a maximum of six months 44 and may be updated, replaced, or obsoleted by other documents at any 45 time. It is inappropriate to use Internet-Drafts as reference 46 material or to cite them other than as "work in progress." 48 This Internet-Draft will expire on October 31, 2011. 50 Copyright Notice 52 Copyright (c) 2011 IETF Trust and the persons identified as the 53 document authors. All rights reserved. 55 This document is subject to BCP 78 and the IETF Trust's Legal 56 Provisions Relating to IETF Documents 57 (http://trustee.ietf.org/license-info) in effect on the date of 58 publication of this document. Please review these documents 59 carefully, as they describe your rights and restrictions with respect 60 to this document. Code Components extracted from this document must 61 include Simplified BSD License text as described in Section 4.e of 62 the Trust Legal Provisions and are provided without warranty as 63 described in the Simplified BSD License. 65 Table of Contents 67 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 68 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 69 3. JSON Web Signature (JWS) Overview . . . . . . . . . . . . . . 5 70 3.1. Example JWS . . . . . . . . . . . . . . . . . . . . . . . 5 71 4. JWS Header . . . . . . . . . . . . . . . . . . . . . . . . . . 6 72 4.1. Reserved Header Parameter Names . . . . . . . . . . . . . 6 73 4.2. Public Header Parameter Names . . . . . . . . . . . . . . 9 74 4.3. Private Header Parameter Names . . . . . . . . . . . . . . 9 75 5. Rules for Creating and Validating a JWS . . . . . . . . . . . 9 76 6. Base64url encoding as used by JWSs . . . . . . . . . . . . . . 11 77 7. Signing JWSs with Cryptographic Algorithms . . . . . . . . . . 11 78 7.1. Creating a JWS with HMAC SHA-256, HMAC SHA-384, or 79 HMAC SHA-512 . . . . . . . . . . . . . . . . . . . . . . . 12 80 7.2. Creating a JWS with RSA SHA-256, RSA SHA-384, or RSA 81 SHA-512 . . . . . . . . . . . . . . . . . . . . . . . . . 13 82 7.3. Creating a JWS with ECDSA P-256 SHA-256, ECDSA P-384 83 SHA-384, or ECDSA P-521 SHA-512 . . . . . . . . . . . . . 14 84 7.4. Additional Algorithms . . . . . . . . . . . . . . . . . . 16 85 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 86 9. Security Considerations . . . . . . . . . . . . . . . . . . . 16 87 9.1. Unicode Comparison Security Issues . . . . . . . . . . . . 17 88 10. Open Issues and Things To Be Done (TBD) . . . . . . . . . . . 17 89 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18 90 11.1. Normative References . . . . . . . . . . . . . . . . . . . 18 91 11.2. Informative References . . . . . . . . . . . . . . . . . . 20 92 Appendix A. JWS Examples . . . . . . . . . . . . . . . . . . . . 20 93 A.1. JWS using HMAC SHA-256 . . . . . . . . . . . . . . . . . . 20 94 A.1.1. Encoding . . . . . . . . . . . . . . . . . . . . . . . 21 95 A.1.2. Decoding . . . . . . . . . . . . . . . . . . . . . . . 22 96 A.1.3. Validating . . . . . . . . . . . . . . . . . . . . . . 22 97 A.2. JWS using RSA SHA-256 . . . . . . . . . . . . . . . . . . 23 98 A.2.1. Encoding . . . . . . . . . . . . . . . . . . . . . . . 23 99 A.2.2. Decoding . . . . . . . . . . . . . . . . . . . . . . . 26 100 A.2.3. Validating . . . . . . . . . . . . . . . . . . . . . . 26 101 A.3. JWS using ECDSA P-256 SHA-256 . . . . . . . . . . . . . . 27 102 A.3.1. Encoding . . . . . . . . . . . . . . . . . . . . . . . 27 103 A.3.2. Decoding . . . . . . . . . . . . . . . . . . . . . . . 28 104 A.3.3. Validating . . . . . . . . . . . . . . . . . . . . . . 29 105 Appendix B. Algorithm Identifier Cross-Reference . . . . . . . . 29 106 Appendix C. Notes on implementing base64url encoding without 107 padding . . . . . . . . . . . . . . . . . . . . . . . 31 108 Appendix D. Acknowledgements . . . . . . . . . . . . . . . . . . 32 109 Appendix E. Document History . . . . . . . . . . . . . . . . . . 33 110 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 33 112 1. Introduction 114 JSON Web Signature (JWS) is a compact signature format intended for 115 space constrained environments such as HTTP Authorization headers and 116 URI query parameters. It represents signed content using JSON 117 [RFC4627] data structures. The JWS signature mechanisms are 118 independent of the type of content being signed, allowing arbitrary 119 content to be signed. A related encryption capability is described 120 in a separate JSON Web Encryption (JWE) [JWE] specification. 122 2. Terminology 124 JSON Web Signature (JWS) A data structure cryptographically securing 125 a JWS Header Input and a JWS Payload Input with a JWS Crypto 126 Output. 128 JWS Header Input A string containing a base64url encoded JSON object 129 that describes the cryptographic operations applied to the JWS 130 Header Input and the JWS Payload Input. 132 JWS Payload Input A string containing base64url encoded content. 134 JWS Crypto Output A string containing base64url encoded 135 cryptographic material that secures the contents of the JWS Header 136 Input and the JWS Payload Input. 138 Decoded JWS Header Input JWS Header Input that has been base64url 139 decoded back into a JSON object. 141 Decoded JWS Payload Input JWS Payload Input that has been base64url 142 decoded. 144 Decoded JWS Crypto Output JWS Crypto Output that has been base64url 145 decoded back into cryptographic material. 147 JWS Signing Input The concatenation of the JWS Header Input, a 148 period ('.') character, and the JWS Payload Input. 150 Header Parameter Names The names of the members within the JSON 151 object represented in a JWS Header Input. 153 Header Parameter Values The values of the members within the JSON 154 object represented in a JWS Header Input. 156 Digital Signature For the purposes of this specification, we use 157 this term to encompass both Hash-based Message Authentication 158 Codes (HMACs), which can provide authenticity but not non- 159 repudiation, and digital signatures using public key algorithms, 160 which can provide both. Readers should be aware of this 161 distinction, despite the decision to use a single term for both 162 concepts to improve readability of the specification. 164 Base64url Encoding For the purposes of this specification, this term 165 always refers to the he URL- and filename-safe Base64 encoding 166 described in RFC 4648 [RFC4648], Section 5, with the '=' padding 167 characters omitted, as permitted by Section 3.2. 169 3. JSON Web Signature (JWS) Overview 171 JWSs represent content that is base64url encoded and digitally 172 signed, and optionally encrypted, using JSON data structures. A 173 portion of the base64url encoded content that is signed is the JWS 174 Payload Input. An accompanying base64url encoded JSON object - the 175 JWS Header Input - describes the signature method used. 177 The member names within the Decoded JWS Header Input are referred to 178 as Header Parameter Names. These names MUST be unique. The 179 corresponding values are referred to as Header Parameter Values. 181 JWSs contain a signature that ensures the integrity of the contents 182 of the JWS Header Input and the JWS Payload Input. This signature 183 value is the JWS Crypto Output. The JSON Header object MUST contain 184 an "alg" parameter, the value of which is a string that unambiguously 185 identifies the algorithm used to sign the JWS Header Input and the 186 JWS Payload Input to produce the JWS Crypto Output. 188 3.1. Example JWS 190 The following example JSON header object declares that the encoded 191 object is a JSON Web Token (JWT) [JWT] and the JWS Header Input and 192 the JWS Payload Input are signed using the HMAC SHA-256 algorithm: 193 {"typ":"JWT", 194 "alg":"HS256"} 196 Base64url encoding the UTF-8 representation of the JSON header object 197 yields this JWS Header Input value: 198 eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9 200 The following is an example of a JSON object that can be encoded to 201 produce a JWS Payload Input. (Note that the payload can be any 202 base64url encoded content, and need not be a base64url encoded JSON 203 object.) 204 {"iss":"joe", 205 "exp":1300819380, 206 "http://example.com/is_root":true} 208 Base64url encoding the UTF-8 representation of the JSON object yields 209 the following JWS Payload Input. 210 eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ 212 Signing the UTF-8 representation of the JWS Signing Input (the 213 concatenation of the JWS Header Input, a period ('.') character, and 214 the JWS Payload Input) with the HMAC SHA-256 algorithm and base64url 215 encoding the result, as per Section 7.1, yields this JWS Crypto 216 Output value: 217 dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk 219 This computation is illustrated in more detail in Appendix A.1. 221 4. JWS Header 223 The members of the JSON object represented by the Decoded JWS Header 224 Input describe the signature applied to the JWS Header Input and the 225 JWS Payload Input and optionally additional properties of the JWS. 226 Implementations MUST understand the entire contents of the header; 227 otherwise, the JWS MUST be rejected for processing. 229 4.1. Reserved Header Parameter Names 231 The following header parameter names are reserved. All the names are 232 short because a core goal of JWSs is for the representations to be 233 compact. 235 +-----------+--------+--------------+-------------------------------+ 236 | Header | JSON | Header | Header Parameter Semantics | 237 | Parameter | Value | Parameter | | 238 | Name | Type | Syntax | | 239 +-----------+--------+--------------+-------------------------------+ 240 | alg | string | StringAndURI | The "alg" (algorithm) header | 241 | | | | parameter identifies the | 242 | | | | cryptographic algorithm used | 243 | | | | to secure the JWS. A list of | 244 | | | | reserved alg values is in | 245 | | | | Table 3. The processing of | 246 | | | | the "alg" (algorithm) header | 247 | | | | parameter, if present, | 248 | | | | requires that the value of | 249 | | | | the "alg" header parameter | 250 | | | | MUST be one that is both | 251 | | | | supported and for which there | 252 | | | | exists a key for use with | 253 | | | | that algorithm associated | 254 | | | | with the signer of the | 255 | | | | content. The "alg" parameter | 256 | | | | value is case sensitive. | 257 | | | | This header parameter is | 258 | | | | REQUIRED. | 259 | typ | string | String | The "typ" (type) header | 260 | | | | parameter is used to declare | 261 | | | | the type of the signed | 262 | | | | content. The "typ" value is | 263 | | | | case sensitive. This header | 264 | | | | parameter is OPTIONAL. | 265 | jku | string | URL | The "jku" (JSON Key URL) | 266 | | | | header parameter is a URL | 267 | | | | that points to JSON-encoded | 268 | | | | public keys that can be used | 269 | | | | to validate the signature. | 270 | | | | The keys MUST be encoded as | 271 | | | | per the JSON Web Key (JWK) | 272 | | | | [JWK] specification. This | 273 | | | | header parameter is OPTIONAL. | 274 | kid | string | String | The "kid" (key ID) header | 275 | | | | parameter is a hint | 276 | | | | indicating which specific key | 277 | | | | owned by the signer should be | 278 | | | | used to validate the | 279 | | | | signature. This allows | 280 | | | | signers to explicitly signal | 281 | | | | a change of key to | 282 | | | | recipients. Omitting this | 283 | | | | parameter is equivalent to | 284 | | | | setting it to an empty | 285 | | | | string. The interpretation | 286 | | | | of the contents of the "kid" | 287 | | | | parameter is unspecified. | 288 | | | | This header parameter is | 289 | | | | OPTIONAL. | 290 | x5u | string | URL | The "x5u" (X.509 URL) header | 291 | | | | parameter is a URL utilizing | 292 | | | | TLS RFC 5785 [RFC5785] that | 293 | | | | points to an X.509 public key | 294 | | | | certificate or certificate | 295 | | | | chain that can be used to | 296 | | | | validate the signature. This | 297 | | | | certificate or certificate | 298 | | | | chain MUST use the PEM | 299 | | | | encoding RFC 1421 [RFC1421] | 300 | | | | and MUST conform to RFC 5280 | 301 | | | | [RFC5280]. This header | 302 | | | | parameter is OPTIONAL. | 303 | x5t | string | String | The "x5t" (x.509 certificate | 304 | | | | thumbprint) header parameter | 305 | | | | provides a base64url encoded | 306 | | | | SHA-1 thumbprint (a.k.a. | 307 | | | | digest) of the DER encoding | 308 | | | | of an X.509 certificate that | 309 | | | | can be used to match the | 310 | | | | certificate. This header | 311 | | | | parameter is OPTIONAL. | 312 +-----------+--------+--------------+-------------------------------+ 314 Table 1: Reserved Header Parameter Definitions 316 Additional reserved header parameter names MAY be defined via the 317 IANA JSON Web Signature Header Parameters registry, as per Section 8. 318 The syntax values used above are defined as follows: 320 +--------------+----------------------------------------------------+ 321 | Syntax Name | Syntax Definition | 322 +--------------+----------------------------------------------------+ 323 | IntDate | The number of seconds from 1970-01-01T0:0:0Z as | 324 | | measured in UTC until the desired date/time. See | 325 | | RFC 3339 [RFC3339] for details regarding | 326 | | date/times in general and UTC in particular. | 327 | String | Any string value MAY be used. | 328 | StringAndURI | Any string value MAY be used but a value | 329 | | containing a ":" character MUST be a URI as | 330 | | defined in RFC 3986 [RFC3986]. | 331 | URL | A URL as defined in RFC 1738 [RFC1738]. | 332 +--------------+----------------------------------------------------+ 334 Table 2: Header Parameter Syntax Definitions 336 4.2. Public Header Parameter Names 338 Additional header parameter names can be defined by those using JWSs. 339 However, in order to prevent collisions, any new header parameter 340 name or algorithm value SHOULD either be defined in the IANA JSON Web 341 Signature Header Parameters registry or be defined as a URI that 342 contains a collision resistant namespace. In each case, the definer 343 of the name or value MUST take reasonable precautions to make sure 344 they are in control of the part of the namespace they use to define 345 the header parameter name. 347 New header parameters should be introduced sparingly, as they can 348 result in non-interoperable JWSs. 350 4.3. Private Header Parameter Names 352 A producer and consumer of a JWS may agree to any header parameter 353 name that is not a Reserved Name Section 4.1 or a Public Name 354 Section 4.2. Unlike Public Names, these private names are subject to 355 collision and should be used with caution. 357 New header parameters should be introduced sparingly, as they can 358 result in non-interoperable JWSs. 360 5. Rules for Creating and Validating a JWS 362 To create a JWS, one MUST follow these steps: 364 1. Create the payload content to be encoded as the Decoded JWS 365 Payload Input. 367 2. Base64url encode the Decoded JWS Payload Input. This encoding 368 becomes the JWS Payload Input. 370 3. Create a JSON object containing a set of desired header 371 parameters. Note that white space is explicitly allowed in the 372 representation and no canonicalization is performed before 373 encoding. 375 4. Translate this JSON object's Unicode code points into UTF-8, as 376 defined in RFC 3629 [RFC3629]. 378 5. Base64url encode the UTF-8 representation of this JSON object as 379 defined in this specification (without padding). This encoding 380 becomes the JWS Header Input. 382 6. Compute the JWS Crypto Output in the manner defined for the 383 particular algorithm being used. The JWS Signing Input is always 384 the concatenation of the JWS Header Input, a period ('.') 385 character, and the JWS Payload Input. The "alg" header parameter 386 MUST be present in the JSON Header Input, with the algorithm 387 value accurately representing the algorithm used to construct the 388 JWS Crypto Input. 390 When validating a JWS, the following steps MUST be taken. If any of 391 the listed steps fails, then the signed content MUST be rejected. 393 1. The JWS Payload Input MUST be successfully base64url decoded 394 following the restriction given in this specification that no 395 padding characters have been used. 397 2. The JWS Header Input MUST be successfully base64url decoded 398 following the restriction given in this specification that no 399 padding characters have been used. 401 3. The Decoded JWS Header Input MUST be completely valid JSON syntax 402 conforming to RFC 4627 [RFC4627]. 404 4. The JWS Crypto Output MUST be successfully base64url decoded 405 following the restriction given in this specification that no 406 padding characters have been used. 408 5. The JWS Header Input MUST be validated to only include parameters 409 and values whose syntax and semantics are both understood and 410 supported. 412 6. The JWS Crypto Output MUST be successfully validated against the 413 JWS Header Input and JWS Payload Input in the manner defined for 414 the algorithm being used, which MUST be accurately represented by 415 the value of the "alg" header parameter, which MUST be present. 417 Processing a JWS inevitably requires comparing known strings to 418 values in the header. For example, in checking what the algorithm 419 is, the Unicode string encoding "alg" will be checked against the 420 member names in the Decoded JWS Header Input to see if there is a 421 matching header parameter name. A similar process occurs when 422 determining if the value of the "alg" header parameter represents a 423 supported algorithm. Comparing Unicode strings, however, has 424 significant security implications, as per Section 9. 426 Comparisons between JSON strings and other Unicode strings MUST be 427 performed as specified below: 429 1. Remove any JSON applied escaping to produce an array of Unicode 430 code points. 432 2. Unicode Normalization [USA15] MUST NOT be applied at any point to 433 either the JSON string or to the string it is to be compared 434 against. 436 3. Comparisons between the two strings MUST be performed as a 437 Unicode code point to code point equality comparison. 439 6. Base64url encoding as used by JWSs 441 JWSs make use of the base64url encoding as defined in RFC 4648 442 [RFC4648]. As allowed by Section 3.2 of the RFC, this specification 443 mandates that base64url encoding when used with JWSs MUST NOT use 444 padding. The reason for this restriction is that the padding 445 character ('=') is not URL safe. 447 For notes on implementing base64url encoding without padding, see 448 Appendix C. 450 7. Signing JWSs with Cryptographic Algorithms 452 JWSs use specific cryptographic algorithms to sign the contents of 453 the JWS Header Input and the JWS Payload Input. The use of the 454 following algorithms for producing JWSs is defined in this section. 455 The table below is the list of "alg" header parameter values reserved 456 by this specification, each of which is explained in more detail in 457 the following sections: 459 +--------------------+----------------------------------------------+ 460 | Alg Parameter | Algorithm | 461 | Value | | 462 +--------------------+----------------------------------------------+ 463 | HS256 | HMAC using SHA-256 hash algorithm | 464 | HS384 | HMAC using SHA-384 hash algorithm | 465 | HS512 | HMAC using SHA-512 hash algorithm | 466 | RS256 | RSA using SHA-256 hash algorithm | 467 | RS384 | RSA using SHA-384 hash algorithm | 468 | RS512 | RSA using SHA-512 hash algorithm | 469 | ES256 | ECDSA using P-256 curve and SHA-256 hash | 470 | | algorithm | 471 | ES384 | ECDSA using P-384 curve and SHA-384 hash | 472 | | algorithm | 473 | ES512 | ECDSA using P-521 curve and SHA-512 hash | 474 | | algorithm | 475 +--------------------+----------------------------------------------+ 477 Table 3: JSON Web Signature Reserved Algorithm Values 479 See Appendix B for a table cross-referencing the "alg" values used in 480 this specification with the equivalent identifiers used by other 481 standards and software packages. 483 Of these algorithms, only HMAC SHA-256 MUST be implemented by 484 conforming implementations. It is RECOMMENDED that implementations 485 also support the RSA SHA-256 and ECDSA P-256 SHA-256 algorithms. 486 Support for other algorithms is OPTIONAL. 488 The signed content for a JWS is the same for all algorithms: the 489 concatenation of the JWS Header Input, a period ('.') character, and 490 the JWS Payload Input. This character sequence is referred to as the 491 JWS Signing Input. Note that if the JWS represents a JWT, this 492 corresponds to the portion of the JWT representation preceding the 493 second period character. The UTF-8 representation of the JWS Signing 494 Input is passed to the respective signing algorithms. 496 7.1. Creating a JWS with HMAC SHA-256, HMAC SHA-384, or HMAC SHA-512 498 Hash based Message Authentication Codes (HMACs) enable one to use a 499 secret plus a cryptographic hash function to generate a Message 500 Authentication Code (MAC). This can be used to demonstrate that the 501 MAC matches the hashed content, in this case the JWS Signing Input, 502 which therefore demonstrates that whoever generated the MAC was in 503 possession of the secret. The means of exchanging the shared key is 504 outside the scope of this specification. 506 The algorithm for implementing and validating HMACs is provided in 507 RFC 2104 [RFC2104]. This section defines the use of the HMAC SHA- 508 256, HMAC SHA-384, and HMAC SHA-512 cryptographic hash functions as 509 defined in FIPS 180-3 [FIPS.180-3]. The reserved "alg" header 510 parameter values "HS256", "HS384", and "HS512" are used in the JWS 511 Header Input to indicate that the JWS Crypto Output contains a 512 base64url encoded HMAC value using the respective hash function. 514 The HMAC SHA-256 MAC is generated as follows: 516 1. Apply the HMAC SHA-256 algorithm to the UTF-8 representation of 517 the JWS Signing Input using the shared key to produce an HMAC. 519 2. Base64url encode the HMAC, as defined in this specification. 521 The output is the JWS Crypto Output for that JWS. 523 The HMAC SHA-256 MAC for a JWS is validated as follows: 525 1. Apply the HMAC SHA-256 algorithm to the UTF-8 representation of 526 the JWS Signing Input of the JWS using the shared key. 528 2. Base64url encode the previously generated HMAC, as defined in 529 this specification. 531 3. If the JWS Crypto Output and the previously calculated value 532 exactly match, then one has confirmation that the key was used to 533 generate the HMAC on the JWS and that the contents of the JWS 534 have not be tampered with. 536 4. If the validation fails, the signed content MUST be rejected. 538 Signing with the HMAC SHA-384 and HMAC SHA-512 algorithms is 539 performed identically to the procedure for HMAC SHA-256 - just with 540 correspondingly longer key and result values. 542 7.2. Creating a JWS with RSA SHA-256, RSA SHA-384, or RSA SHA-512 544 This section defines the use of the RSASSA-PKCS1-v1_5 signature 545 algorithm as defined in RFC 3447 [RFC3447], Section 8.2 (commonly 546 known as PKCS#1), using SHA-256, SHA-384, or SHA-512 as the hash 547 function. The RSASSA-PKCS1-v1_5 algorithm is described in FIPS 186-3 548 [FIPS.186-3], Section 5.5, and the SHA-256, SHA-384, and SHA-512 549 cryptographic hash functions are defined in FIPS 180-3 [FIPS.180-3]. 550 The reserved "alg" header parameter values "RS256", "RS384", and 551 "RS512" are used in the JWS Header Input to indicate that the JWS 552 Crypto Output contains a base64url encoded RSA signature using the 553 respective hash function. 555 The public keys employed may be retrieved using Header Parameter 556 methods described in Section 4.1 or may be distributed using methods 557 that are outside the scope of this specification. 559 A 2048-bit or longer key length MUST be used with this algorithm. 561 The RSA SHA-256 signature is generated as follows: 563 1. Generate a digital signature of the UTF-8 representation of the 564 JWS Signing Input using RSASSA-PKCS1-V1_5-SIGN and the SHA-256 565 hash function with the desired private key. The output will be a 566 byte array. 568 2. Base64url encode the byte array, as defined in this 569 specification. 571 The output is the JWS Crypto Output for that JWS. 573 The RSA SHA-256 signature for a JWS is validated as follows: 575 1. Take the JWS Crypto Output and base64url decode it into a byte 576 array. If decoding fails, the signed content MUST be rejected. 578 2. Submit the UTF-8 representation of the JWS Signing Input and the 579 public key corresponding to the private key used by the signer to 580 the RSASSA-PKCS1-V1_5-VERIFY algorithm using SHA-256 as the hash 581 function. 583 3. If the validation fails, the signed content MUST be rejected. 585 Signing with the RSA SHA-384 and RSA SHA-512 algorithms is performed 586 identically to the procedure for RSA SHA-256 - just with 587 correspondingly longer key and result values. 589 7.3. Creating a JWS with ECDSA P-256 SHA-256, ECDSA P-384 SHA-384, or 590 ECDSA P-521 SHA-512 592 The Elliptic Curve Digital Signature Algorithm (ECDSA) is defined by 593 FIPS 186-3 [FIPS.186-3]. ECDSA provides for the use of Elliptic 594 Curve cryptography, which is able to provide equivalent security to 595 RSA cryptography but using shorter key lengths and with greater 596 processing speed. This means that ECDSA signatures will be 597 substantially smaller in terms of length than equivalently strong RSA 598 Digital Signatures. 600 This specification defines the use of ECDSA with the P-256 curve and 601 the SHA-256 cryptographic hash function, ECDSA with the P-384 curve 602 and the SHA-384 hash function, and ECDSA with the P-521 curve and the 603 SHA-512 hash function. The P-256, P-384, and P-521 curves are also 604 defined in FIPS 186-3. The reserved "alg" header parameter values 605 "ES256", "ES384", and "ES512" are used in the JWS Header Input to 606 indicate that the JWS Crypto Output contains a based64url encoded 607 ECDSA P-256 SHA-256, ECDSA P-384 SHA-384, or ECDSA P-521 SHA-512 608 signature, respectively. 610 The public keys employed may be retrieved using Header Parameter 611 methods described in Section 4.1 or may be distributed using methods 612 that are outside the scope of this specification. 614 A JWS is signed with an ECDSA P-256 SHA-256 signature as follows: 616 1. Generate a digital signature of the UTF-8 representation of the 617 JWS Signing Input using ECDSA P-256 SHA-256 with the desired 618 private key. The output will be the EC point (R, S), where R and 619 S are unsigned integers. 621 2. Turn R and S into byte arrays in big endian order. Each array 622 will be 32 bytes long. 624 3. Concatenate the two byte arrays in the order R and then S. 626 4. Base64url encode the 64 byte array, as defined in this 627 specification. 629 The output is the JWS Crypto Output for the JWS. 631 The ECDSA P-256 SHA-256 signature for a JWS is validated as follows: 633 1. Take the JWS Crypto Output and base64url decode it into a byte 634 array. If decoding fails, the signed content MUST be rejected. 636 2. The output of the base64url decoding MUST be a 64 byte array. 638 3. Split the 64 byte array into two 32 byte arrays. The first array 639 will be R and the second S. Remember that the byte arrays are in 640 big endian byte order; please check the ECDSA validator in use to 641 see what byte order it requires. 643 4. Submit the UTF-8 representation of the JWS Signing Input, R, S 644 and the public key (x, y) to the ECDSA P-256 SHA-256 validator. 646 5. If the validation fails, the signed content MUST be rejected. 648 The ECDSA validator will then determine if the digital signature is 649 valid, given the inputs. Note that ECDSA digital signature contains 650 a value referred to as K, which is a random number generated for each 651 digital signature instance. This means that two ECDSA digital 652 signatures using exactly the same input parameters will output 653 different signatures because their K values will be different. The 654 consequence of this is that one must validate an ECDSA signature by 655 submitting the previously specified inputs to an ECDSA validator. 657 Signing with the ECDSA P-384 SHA-384 and ECDSA P-521 SHA-512 658 algorithms is performed identically to the procedure for ECDSA P-256 659 SHA-256 - just with correspondingly longer key and result values. 661 7.4. Additional Algorithms 663 Additional algorithms MAY be used to protect JWSs with corresponding 664 "alg" header parameter values being defined to refer to them. New 665 "alg" header parameter values SHOULD either be defined in the IANA 666 JSON Web Signature Algorithms registry or be a URI that contains a 667 collision resistant namespace. In particular, the use of algorithm 668 identifiers defined in XML DSIG [RFC3275] and related specifications 669 is permitted. 671 8. IANA Considerations 673 This specification calls for: 675 o A new IANA registry entitled "JSON Web Signature Header 676 Parameters" for reserved header parameter names is defined in 677 Section 4.1. Inclusion in the registry is RFC Required in the RFC 678 5226 [RFC5226] sense for reserved JWS header parameter names that 679 are intended to be interoperable between implementations. The 680 registry will just record the reserved header parameter name and a 681 pointer to the RFC that defines it. This specification defines 682 inclusion of the header parameter names defined in Table 1. 684 o A new IANA registry entitled "JSON Web Signature Algorithms" for 685 reserved values used with the "alg" header parameter values is 686 defined in Section 7.4. Inclusion in the registry is RFC Required 687 in the RFC 5226 [RFC5226] sense. The registry will just record 688 the "alg" value and a pointer to the RFC that defines it. This 689 specification defines inclusion of the algorithm values defined in 690 Table 3. 692 9. Security Considerations 694 TBD: Lots of work to do here. We need to remember to look into any 695 issues relating to security and JSON parsing. One wonders just how 696 secure most JSON parsing libraries are. Were they ever hardened for 697 security scenarios? If not, what kind of holes does that open up? 698 Also, we need to walk through the JSON standard and see what kind of 699 issues we have especially around comparison of names. For instance, 700 comparisons of header parameter names and other parameters must occur 701 after they are unescaped. Need to also put in text about: Importance 702 of keeping secrets secret. Rotating keys. Strengths and weaknesses 703 of the different algorithms. 705 TBD: Need to put in text about why strict JSON validation is 706 necessary. Basically, that if malformed JSON is received then the 707 intent of the sender is impossible to reliably discern. 709 TBD: Write security considerations about the implications of using a 710 SHA-1 hash (for compatibility reasons) for the "x5t" (x.509 711 certificate thumbprint). 713 9.1. Unicode Comparison Security Issues 715 Header parameter names in JWSs are Unicode strings. For security 716 reasons, the representations of these names must be compared verbatim 717 after performing any escape processing (as per RFC 4627 [RFC4627], 718 Section 2.5). 720 This means, for instance, that these JSON strings must compare as 721 being equal ("sig", "\u0073ig"), whereas these must all compare as 722 being not equal to the first set or to each other ("SIG", "Sig", 723 "si\u0047"). 725 JSON strings MAY contain characters outside the Unicode Basic 726 Multilingual Plane. For instance, the G clef character (U+1D11E) may 727 be represented in a JSON string as "\uD834\uDD1E". Ideally, JWS 728 implementations SHOULD ensure that characters outside the Basic 729 Multilingual Plane are preserved and compared correctly; 730 alternatively, if this is not possible due to these characters 731 exercising limitations present in the underlying JSON implementation, 732 then input containing them MUST be rejected. 734 10. Open Issues and Things To Be Done (TBD) 736 The following items remain to be done in this draft (and related 737 drafts): 739 o Consider whether there is a better term than "Digital Signature" 740 for the concept that includes both HMACs and digital signatures 741 using public keys. 743 o Consider whether we really want to allow private header parameter 744 names that are not registered with IANA and are not in collision- 745 resistant namespaces. Eventually this could result in interop 746 nightmares where you need to have different code to talk to 747 different endpoints that "knows" about each endpoint's private 748 parameters. 750 o Clarify the optional ability to provide type information in the 751 JWS header. Specifically, clarify the intended use of the "typ" 752 Header Parameter, whether it conveys syntax or semantics, and 753 indeed, whether this is the right approach. Also clarify the 754 relationship between these type values and MIME [RFC2045] types. 756 o Clarify the semantics of the "kid" (key ID) header parameter. 757 Open issues include: What happens if a "kid" header is received 758 with an unrecognized value? Is that an error? Should it be 759 treated as if it's empty? What happens if the header has a 760 recognized value but the value doesn't match the key associated 761 with that value, but it does match another key that is associated 762 with the issuer? Is that an error? 764 o Consider whether a key type parameter should also be introduced. 766 o Since RFC 3447 Section 8 explicitly calls for people NOT to adopt 767 RSASSA-PKCS1 for new applications and instead requests that people 768 transition to RSASSA-PSS, we probably need some Security 769 Considerations text explaining why RSASSA-PKCS1 is being used 770 (it's what's commonly implemented) and what the potential 771 consequences are. 773 o Add Security Considerations text on timing attacks. 775 o Finish the Security Considerations section. 777 o Sort out what to do with the IANA registries if this is first 778 standardized as an OpenID specification. 780 o Finish the companion encryption specification, per the agreements 781 documented at http://self-issued.info/?p=378. 783 11. References 785 11.1. Normative References 787 [FIPS.180-3] 788 National Institute of Standards and Technology, "Secure 789 Hash Standard (SHS)", FIPS PUB 180-3, October 2008. 791 [FIPS.186-3] 792 National Institute of Standards and Technology, "Digital 793 Signature Standard (DSS)", FIPS PUB 186-3, June 2009. 795 [JWK] Jones, M., "JSON Web Key (JWK)", April 2011. 797 [JWT] Jones, M., Balfanz, D., Bradley, J., Goland, Y., Panzer, 798 J., Sakimura, N., and P. Tarjan, "JSON Web Token (JWT)", 799 March 2011. 801 [RFC1421] Linn, J., "Privacy Enhancement for Internet Electronic 802 Mail: Part I: Message Encryption and Authentication 803 Procedures", RFC 1421, February 1993. 805 [RFC1738] Berners-Lee, T., Masinter, L., and M. McCahill, "Uniform 806 Resource Locators (URL)", RFC 1738, December 1994. 808 [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail 809 Extensions (MIME) Part One: Format of Internet Message 810 Bodies", RFC 2045, November 1996. 812 [RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- 813 Hashing for Message Authentication", RFC 2104, 814 February 1997. 816 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 817 Requirement Levels", BCP 14, RFC 2119, March 1997. 819 [RFC3339] Klyne, G., Ed. and C. Newman, "Date and Time on the 820 Internet: Timestamps", RFC 3339, July 2002. 822 [RFC3447] Jonsson, J. and B. Kaliski, "Public-Key Cryptography 823 Standards (PKCS) #1: RSA Cryptography Specifications 824 Version 2.1", RFC 3447, February 2003. 826 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 827 10646", STD 63, RFC 3629, November 2003. 829 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 830 Resource Identifier (URI): Generic Syntax", STD 66, 831 RFC 3986, January 2005. 833 [RFC4627] Crockford, D., "The application/json Media Type for 834 JavaScript Object Notation (JSON)", RFC 4627, July 2006. 836 [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data 837 Encodings", RFC 4648, October 2006. 839 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 840 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 841 May 2008. 843 [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., 844 Housley, R., and W. Polk, "Internet X.509 Public Key 845 Infrastructure Certificate and Certificate Revocation List 846 (CRL) Profile", RFC 5280, May 2008. 848 [RFC5785] Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known 849 Uniform Resource Identifiers (URIs)", RFC 5785, 850 April 2010. 852 [USA15] Davis, M., Whistler, K., and M. Duerst, "Unicode 853 Normalization Forms", Unicode Standard Annex 15, 09 2009. 855 11.2. Informative References 857 [CanvasApp] 858 Facebook, "Canvas Applications", 2010. 860 [JCA] Oracle, "Java Cryptography Architecture", 2011. 862 [JSS] Bradley, J. and N. Sakimura (editor), "JSON Simple Sign", 863 September 2010. 865 [JWE] Jones, M., Bradley, J., and N. Sakimura, "JSON Web 866 Encryption (JWE)", March 2011. 868 [MagicSignatures] 869 Panzer (editor), J., Laurie, B., and D. Balfanz, "Magic 870 Signatures", August 2010. 872 [RFC3275] Eastlake, D., Reagle, J., and D. Solo, "(Extensible Markup 873 Language) XML-Signature Syntax and Processing", RFC 3275, 874 March 2002. 876 Appendix A. JWS Examples 878 This section provides several examples of JWSs. While these examples 879 all represent JSON Web Tokens (JWTs) [JWT], the payload can be any 880 base64url encoded content. 882 A.1. JWS using HMAC SHA-256 883 A.1.1. Encoding 885 The following example JSON header object declares that the data 886 structure is a JSON Web Token (JWT) [JWT] and the JWS Signing Input 887 is signed using the HMAC SHA-256 algorithm. Note that white space is 888 explicitly allowed in Decoded JWS Header Input strings and no 889 canonicalization is performed before encoding. 890 {"typ":"JWT", 891 "alg":"HS256"} 893 The following byte array contains the UTF-8 characters for the 894 Decoded JWS Header Input: 896 [123, 34, 116, 121, 112, 34, 58, 34, 74, 87, 84, 34, 44, 13, 10, 32, 897 34, 97, 108, 103, 34, 58, 34, 72, 83, 50, 53, 54, 34, 125] 899 Base64url encoding this UTF-8 representation yields this JWS Header 900 Input value: 901 eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9 903 The Decoded JWS Payload Input used in this example follows. (Note 904 that the payload can be any base64url encoded content, and need not 905 be a base64url encoded JSON object.) 906 {"iss":"joe", 907 "exp":1300819380, 908 "http://example.com/is_root":true} 910 The following byte array contains the UTF-8 characters for the 911 Decoded JWS Payload Input: 913 [123, 34, 105, 115, 115, 34, 58, 34, 106, 111, 101, 34, 44, 13, 10, 914 32, 34, 101, 120, 112, 34, 58, 49, 51, 48, 48, 56, 49, 57, 51, 56, 915 48, 44, 13, 10, 32, 34, 104, 116, 116, 112, 58, 47, 47, 101, 120, 97, 916 109, 112, 108, 101, 46, 99, 111, 109, 47, 105, 115, 95, 114, 111, 917 111, 116, 34, 58, 116, 114, 117, 101, 125] 919 Base64url encoding the above yields the JWS Payload Input value: 920 eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ 922 Concatenating the JWS Header Input, a period character, and the JWS 923 Payload Input yields this JWS Signing Input value (with line breaks 924 for display purposes only): 925 eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9 926 . 927 eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ 929 The UTF-8 representation of the JWS Signing Input is the following 930 byte array: 932 [101, 121, 74, 48, 101, 88, 65, 105, 79, 105, 74, 75, 86, 49, 81, 933 105, 76, 65, 48, 75, 73, 67, 74, 104, 98, 71, 99, 105, 79, 105, 74, 934 73, 85, 122, 73, 49, 78, 105, 74, 57, 46, 101, 121, 74, 112, 99, 51, 935 77, 105, 79, 105, 74, 113, 98, 50, 85, 105, 76, 65, 48, 75, 73, 67, 936 74, 108, 101, 72, 65, 105, 79, 106, 69, 122, 77, 68, 65, 52, 77, 84, 937 107, 122, 79, 68, 65, 115, 68, 81, 111, 103, 73, 109, 104, 48, 100, 938 72, 65, 54, 76, 121, 57, 108, 101, 71, 70, 116, 99, 71, 120, 108, 76, 939 109, 78, 118, 98, 83, 57, 112, 99, 49, 57, 121, 98, 50, 57, 48, 73, 940 106, 112, 48, 99, 110, 86, 108, 102, 81] 942 HMACs are generated using keys. This example uses the key 943 represented by the following byte array: 945 [3, 35, 53, 75, 43, 15, 165, 188, 131, 126, 6, 101, 119, 123, 166, 946 143, 90, 179, 40, 230, 240, 84, 201, 40, 169, 15, 132, 178, 210, 80, 947 46, 191, 211, 251, 90, 146, 210, 6, 71, 239, 150, 138, 180, 195, 119, 948 98, 61, 34, 61, 46, 33, 114, 5, 46, 79, 8, 192, 205, 154, 245, 103, 949 208, 128, 163] 951 Running the HMAC SHA-256 algorithm on the UTF-8 representation of the 952 JWS Signing Input with this key yields the following byte array: 954 [116, 24, 223, 180, 151, 153, 224, 37, 79, 250, 96, 125, 216, 173, 955 187, 186, 22, 212, 37, 77, 105, 214, 191, 240, 91, 88, 5, 88, 83, 956 132, 141, 121] 958 Base64url encoding the above HMAC output yields the JWS Crypto Output 959 value: 960 dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk 962 A.1.2. Decoding 964 Decoding the JWS first requires removing the base64url encoding from 965 the JWS Header Input, the JWS Payload Input, and the JWS Crypto 966 Output. We base64url decode the inputs per Section 6 and turn them 967 into the corresponding byte arrays. We translate the header input 968 byte array containing UTF-8 encoded characters into the Decoded JWS 969 Header Input string. 971 A.1.3. Validating 973 Next we validate the decoded results. Since the "alg" parameter in 974 the header is "HS256", we validate the HMAC SHA-256 signature 975 contained in the JWS Crypto Output. If any of the validation steps 976 fail, the signed content MUST be rejected. 978 First, we validate that the decoded JWS Header Input string is legal 979 JSON. 981 To validate the signature, we repeat the previous process of using 982 the correct key and the UTF-8 representation of the JWS Signing Input 983 as input to a SHA-256 HMAC function and then taking the output and 984 determining if it matches the Decoded JWS Crypto Output. If it 985 matches exactly, the signature has been validated. 987 A.2. JWS using RSA SHA-256 989 A.2.1. Encoding 991 The Decoded JWS Header Input in this example is different from the 992 previous example in two ways: First, because a different algorithm is 993 being used, the "alg" value is different. Second, for illustration 994 purposes only, the optional "typ" parameter is not used. (This 995 difference is not related to the signature algorithm employed.) The 996 Decoded JWS Header Input used is: 997 {"alg":"RS256"} 999 The following byte array contains the UTF-8 characters for the 1000 Decoded JWS Header Input: 1002 [123, 34, 97, 108, 103, 34, 58, 34, 82, 83, 50, 53, 54, 34, 125] 1004 Base64url encoding this UTF-8 representation yields this JWS Header 1005 Input value: 1006 eyJhbGciOiJSUzI1NiJ9 1008 The Decoded JWS Payload Input used in this example, which follows, is 1009 the same as in the previous example. Since the JWS Payload Input 1010 will therefore be the same, its computation is not repeated here. 1011 {"iss":"joe", 1012 "exp":1300819380, 1013 "http://example.com/is_root":true} 1015 Concatenating the JWS Header Input, a period character, and the JWS 1016 Payload Input yields this JWS Signing Input value (with line breaks 1017 for display purposes only): 1018 eyJhbGciOiJSUzI1NiJ9 1019 . 1020 eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ 1022 The UTF-8 representation of the JWS Signing Input is the following 1023 byte array: 1025 [101, 121, 74, 104, 98, 71, 99, 105, 79, 105, 74, 83, 85, 122, 73, 1026 49, 78, 105, 74, 57, 46, 101, 121, 74, 112, 99, 51, 77, 105, 79, 105, 1027 74, 113, 98, 50, 85, 105, 76, 65, 48, 75, 73, 67, 74, 108, 101, 72, 1028 65, 105, 79, 106, 69, 122, 77, 68, 65, 52, 77, 84, 107, 122, 79, 68, 1029 65, 115, 68, 81, 111, 103, 73, 109, 104, 48, 100, 72, 65, 54, 76, 1030 121, 57, 108, 101, 71, 70, 116, 99, 71, 120, 108, 76, 109, 78, 118, 1031 98, 83, 57, 112, 99, 49, 57, 121, 98, 50, 57, 48, 73, 106, 112, 48, 1032 99, 110, 86, 108, 102, 81] 1034 The RSA key consists of a public part (n, e), and a private exponent 1035 d. The values of the RSA key used in this example, presented as the 1036 byte arrays representing big endian integers are: 1038 +-----------+-------------------------------------------------------+ 1039 | Parameter | Value | 1040 | Name | | 1041 +-----------+-------------------------------------------------------+ 1042 | n | [161, 248, 22, 10, 226, 227, 201, 180, 101, 206, 141, | 1043 | | 45, 101, 98, 99, 54, 43, 146, 125, 190, 41, 225, 240, | 1044 | | 36, 119, 252, 22, 37, 204, 144, 161, 54, 227, 139, | 1045 | | 217, 52, 151, 197, 182, 234, 99, 221, 119, 17, 230, | 1046 | | 124, 116, 41, 249, 86, 176, 251, 138, 143, 8, 154, | 1047 | | 220, 75, 105, 137, 60, 193, 51, 63, 83, 237, 208, 25, | 1048 | | 184, 119, 132, 37, 47, 236, 145, 79, 228, 133, 119, | 1049 | | 105, 89, 75, 234, 66, 128, 211, 44, 15, 85, 191, 98, | 1050 | | 148, 79, 19, 3, 150, 188, 110, 155, 223, 110, 189, | 1051 | | 210, 189, 163, 103, 142, 236, 160, 198, 104, 247, 1, | 1052 | | 179, 141, 191, 251, 56, 200, 52, 44, 226, 254, 109, | 1053 | | 39, 250, 222, 74, 90, 72, 116, 151, 157, 212, 185, | 1054 | | 207, 154, 222, 196, 199, 91, 5, 133, 44, 44, 15, 94, | 1055 | | 248, 165, 193, 117, 3, 146, 249, 68, 232, 237, 100, | 1056 | | 193, 16, 198, 182, 71, 96, 154, 164, 120, 58, 235, | 1057 | | 156, 108, 154, 215, 85, 49, 48, 80, 99, 139, 131, | 1058 | | 102, 92, 111, 111, 122, 130, 163, 150, 112, 42, 31, | 1059 | | 100, 27, 130, 211, 235, 242, 57, 34, 25, 73, 31, 182, | 1060 | | 134, 135, 44, 87, 22, 245, 10, 248, 53, 141, 154, | 1061 | | 139, 157, 23, 195, 64, 114, 143, 127, 135, 216, 154, | 1062 | | 24, 216, 252, 171, 103, 173, 132, 89, 12, 46, 207, | 1063 | | 117, 147, 57, 54, 60, 7, 3, 77, 111, 96, 111, 158, | 1064 | | 33, 224, 84, 86, 202, 229, 233, 161] | 1065 | e | [1, 0, 1] | 1066 | d | [18, 174, 113, 164, 105, 205, 10, 43, 195, 126, 82, | 1067 | | 108, 69, 0, 87, 31, 29, 97, 117, 29, 100, 233, 73, | 1068 | | 112, 123, 98, 89, 15, 157, 11, 165, 124, 150, 60, 64, | 1069 | | 30, 63, 207, 47, 44, 211, 189, 236, 136, 229, 3, 191, | 1070 | | 198, 67, 155, 11, 40, 200, 47, 125, 55, 151, 103, 31, | 1071 | | 82, 19, 238, 216, 193, 90, 37, 216, 213, 206, 160, 2, | 1072 | | 94, 227, 171, 46, 139, 127, 121, 33, 111, 198, 59, | 1073 | | 234, 86, 39, 83, 180, 6, 68, 198, 161, 81, 39, 217, | 1074 | | 178, 149, 69, 64, 160, 187, 225, 163, 5, 86, 152, 45, | 1075 | | 78, 159, 222, 95, 100, 37, 241, 77, 75, 113, 52, 65, | 1076 | | 181, 93, 199, 59, 155, 74, 237, 204, 146, 172, 227, | 1077 | | 146, 126, 55, 245, 125, 12, 253, 94, 117, 129, 250, | 1078 | | 81, 44, 143, 73, 97, 169, 235, 11, 128, 248, 168, 7, | 1079 | | 70, 114, 138, 85, 255, 70, 71, 31, 52, 37, 6, 59, | 1080 | | 157, 83, 100, 47, 94, 222, 30, 132, 214, 19, 8, 26, | 1081 | | 250, 92, 34, 208, 81, 40, 91, 214, 59, 148, 59, 86, | 1082 | | 93, 137, 138, 5, 104, 84, 19, 229, 60, 60, 108, 101, | 1083 | | 37, 255, 31, 227, 78, 61, 220, 112, 240, 213, 100, | 1084 | | 80, 253, 164, 139, 161, 46, 16, 78, 157, 235, 159, | 1085 | | 184, 24, 129, 225, 196, 189, 242, 93, 146, 71, 244, | 1086 | | 80, 200, 101, 146, 121, 104, 231, 115, 52, 244, 65, | 1087 | | 79, 117, 167, 80, 225, 57, 84, 110, 58, 138, 115, | 1088 | | 157] | 1089 +-----------+-------------------------------------------------------+ 1091 The RSA private key (n, d) is then passed to the RSA signing 1092 function, which also takes the hash type, SHA-256, and the UTF-8 1093 representation of the JWS Signing Input as inputs. The result of the 1094 signature is a byte array S, which represents a big endian integer. 1095 In this example, S is: 1097 +--------+----------------------------------------------------------+ 1098 | Result | Value | 1099 | Name | | 1100 +--------+----------------------------------------------------------+ 1101 | S | [112, 46, 33, 137, 67, 232, 143, 209, 30, 181, 216, 45, | 1102 | | 191, 120, 69, 243, 65, 6, 174, 27, 129, 255, 247, 115, | 1103 | | 17, 22, 173, 209, 113, 125, 131, 101, 109, 66, 10, 253, | 1104 | | 60, 150, 238, 221, 115, 162, 102, 62, 81, 102, 104, 123, | 1105 | | 0, 11, 135, 34, 110, 1, 135, 237, 16, 115, 249, 69, 229, | 1106 | | 130, 173, 252, 239, 22, 216, 90, 121, 142, 232, 198, | 1107 | | 109, 219, 61, 184, 151, 91, 23, 208, 148, 2, 190, 237, | 1108 | | 213, 217, 217, 112, 7, 16, 141, 178, 129, 96, 213, 248, | 1109 | | 4, 12, 167, 68, 87, 98, 184, 31, 190, 127, 249, 217, 46, | 1110 | | 10, 231, 111, 36, 242, 91, 51, 187, 230, 244, 74, 230, | 1111 | | 30, 177, 4, 10, 203, 32, 4, 77, 62, 249, 18, 142, 212, | 1112 | | 1, 48, 121, 91, 212, 189, 59, 65, 238, 202, 208, 102, | 1113 | | 171, 101, 25, 129, 253, 228, 141, 247, 127, 55, 45, 195, | 1114 | | 139, 159, 175, 221, 59, 239, 177, 139, 93, 163, 204, 60, | 1115 | | 46, 176, 47, 158, 58, 65, 214, 18, 202, 173, 21, 145, | 1116 | | 18, 115, 160, 95, 35, 185, 232, 56, 250, 175, 132, 157, | 1117 | | 105, 132, 41, 239, 90, 30, 136, 121, 130, 54, 195, 212, | 1118 | | 14, 96, 69, 34, 165, 68, 200, 242, 122, 122, 45, 184, 6, | 1119 | | 99, 209, 108, 247, 202, 234, 86, 222, 64, 92, 178, 33, | 1120 | | 90, 69, 178, 194, 85, 102, 181, 90, 193, 167, 72, 160, | 1121 | | 112, 223, 200, 163, 42, 70, 149, 67, 208, 25, 238, 251, | 1122 | | 71] | 1123 +--------+----------------------------------------------------------+ 1125 Base64url encoding the signature produces this value for the JWS 1126 Crypto Output: 1127 cC4hiUPoj9Eetdgtv3hF80EGrhuB__dzERat0XF9g2VtQgr9PJbu3XOiZj5RZmh7AAuHIm4Bh-0Qc_lF5YKt_O8W2Fp5jujGbds9uJdbF9CUAr7t1dnZcAcQjbKBYNX4BAynRFdiuB--f_nZLgrnbyTyWzO75vRK5h6xBArLIARNPvkSjtQBMHlb1L07Qe7K0GarZRmB_eSN9383LcOLn6_dO--xi12jzDwusC-eOkHWEsqtFZESc6BfI7noOPqvhJ1phCnvWh6IeYI2w9QOYEUipUTI8np6LbgGY9Fs98rqVt5AXLIhWkWywlVmtVrBp0igcN_IoypGlUPQGe77Rw 1129 A.2.2. Decoding 1131 Decoding the JWS from this example requires processing the JWS Header 1132 Input and JWS Payload Input exactly as done in the first example. 1134 A.2.3. Validating 1136 Since the "alg" parameter in the header is "RS256", we validate the 1137 RSA SHA-256 signature contained in the JWS Crypto Output. If any of 1138 the validation steps fail, the signed content MUST be rejected. 1140 First, we validate that the decoded JWS Header Input string is legal 1141 JSON. 1143 Validating the JWS Crypto Output is a little different from the 1144 previous example. First, we base64url decode the JWS Crypto Output 1145 to produce a signature S to check. We then pass (n, e), S and the 1146 UTF-8 representation of the JWS Signing Input to an RSA signature 1147 verifier that has been configured to use the SHA-256 hash function. 1149 A.3. JWS using ECDSA P-256 SHA-256 1151 A.3.1. Encoding 1153 The Decoded JWS Header Input for this example differs from the 1154 previous example because a different algorithm is being used. The 1155 Decoded JWS Header Input used is: 1156 {"alg":"ES256"} 1158 The following byte array contains the UTF-8 characters for the 1159 Decoded JWS Header Input: 1161 [123, 34, 97, 108, 103, 34, 58, 34, 69, 83, 50, 53, 54, 34, 125] 1163 Base64url encoding this UTF-8 representation yields this JWS Header 1164 Input value: 1165 eyJhbGciOiJFUzI1NiJ9 1167 The Decoded JWS Payload Input used in this example, which follows, is 1168 the same as in the previous examples. Since the JWS Payload Input 1169 will therefore be the same, its computation is not repeated here. 1170 {"iss":"joe", 1171 "exp":1300819380, 1172 "http://example.com/is_root":true} 1174 Concatenating the JWS Header Input, a period character, and the JWS 1175 Payload Input yields this JWS Signing Input value (with line breaks 1176 for display purposes only): 1177 eyJhbGciOiJFUzI1NiJ9 1178 . 1179 eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ 1181 The UTF-8 representation of the JWS Signing Input is the following 1182 byte array: 1184 [101, 121, 74, 104, 98, 71, 99, 105, 79, 105, 74, 70, 85, 122, 73, 1185 49, 78, 105, 74, 57, 46, 101, 121, 74, 112, 99, 51, 77, 105, 79, 105, 1186 74, 113, 98, 50, 85, 105, 76, 65, 48, 75, 73, 67, 74, 108, 101, 72, 1187 65, 105, 79, 106, 69, 122, 77, 68, 65, 52, 77, 84, 107, 122, 79, 68, 1188 65, 115, 68, 81, 111, 103, 73, 109, 104, 48, 100, 72, 65, 54, 76, 1189 121, 57, 108, 101, 71, 70, 116, 99, 71, 120, 108, 76, 109, 78, 118, 1190 98, 83, 57, 112, 99, 49, 57, 121, 98, 50, 57, 48, 73, 106, 112, 48, 1191 99, 110, 86, 108, 102, 81] 1192 The ECDSA key consists of a public part, the EC point (x, y), and a 1193 private part d. The values of the ECDSA key used in this example, 1194 presented as the byte arrays representing big endian integers are: 1196 +-----------+-------------------------------------------------------+ 1197 | Parameter | Value | 1198 | Name | | 1199 +-----------+-------------------------------------------------------+ 1200 | x | [127, 205, 206, 39, 112, 246, 196, 93, 65, 131, 203, | 1201 | | 238, 111, 219, 75, 123, 88, 7, 51, 53, 123, 233, 239, | 1202 | | 19, 186, 207, 110, 60, 123, 209, 84, 69] | 1203 | y | [199, 241, 68, 205, 27, 189, 155, 126, 135, 44, 223, | 1204 | | 237, 185, 238, 185, 244, 179, 105, 93, 110, 169, 11, | 1205 | | 36, 173, 138, 70, 35, 40, 133, 136, 229, 173] | 1206 | d | [142, 155, 16, 158, 113, 144, 152, 191, 152, 4, 135, | 1207 | | 223, 31, 93, 119, 233, 203, 41, 96, 110, 190, 210, | 1208 | | 38, 59, 95, 87, 194, 19, 223, 132, 244, 178] | 1209 +-----------+-------------------------------------------------------+ 1211 The ECDSA private part d is then passed to an ECDSA signing function, 1212 which also takes the curve type, P-256, the hash type, SHA-256, and 1213 the UTF-8 representation of the JWS Signing Input as inputs. The 1214 result of the signature is the EC point (R, S), where R and S are 1215 unsigned integers. In this example, the R and S values, given as 1216 byte arrays representing big endian integers are: 1218 +--------+----------------------------------------------------------+ 1219 | Result | Value | 1220 | Name | | 1221 +--------+----------------------------------------------------------+ 1222 | R | [14, 209, 33, 83, 121, 99, 108, 72, 60, 47, 127, 21, 88, | 1223 | | 7, 212, 2, 163, 178, 40, 3, 58, 249, 124, 126, 23, 129, | 1224 | | 154, 195, 22, 158, 166, 101] | 1225 | S | [197, 10, 7, 211, 140, 60, 112, 229, 216, 241, 45, 175, | 1226 | | 8, 74, 84, 128, 166, 101, 144, 197, 242, 147, 80, 154, | 1227 | | 143, 63, 127, 138, 131, 163, 84, 213] | 1228 +--------+----------------------------------------------------------+ 1230 Concatenating the S array to the end of the R array and base64url 1231 encoding the result produces this value for the JWS Crypto Output: 1232 DtEhU3ljbEg8L38VWAfUAqOyKAM6-Xx-F4GawxaepmXFCgfTjDxw5djxLa8ISlSApmWQxfKTUJqPP3-Kg6NU1Q 1234 A.3.2. Decoding 1236 Decoding the JWS from this example requires processing the JWS Header 1237 Input and JWS Payload Input exactly as done in the first example. 1239 A.3.3. Validating 1241 Since the "alg" parameter in the header is "ES256", we validate the 1242 ECDSA P-256 SHA-256 signature contained in the JWS Crypto Output. If 1243 any of the validation steps fail, the signed content MUST be 1244 rejected. 1246 First, we validate that the decoded JWS Header Input string is legal 1247 JSON. 1249 Validating the JWS Crypto Output is a little different from the first 1250 example. First, we base64url decode the JWS Crypto Output as in the 1251 previous examples but we then need to split the 64 member byte array 1252 that must result into two 32 byte arrays, the first R and the second 1253 S. We then pass (x, y), (R, S) and the UTF-8 representation of the 1254 JWS Signing Input to an ECDSA signature verifier that has been 1255 configured to use the P-256 curve with the SHA-256 hash function. 1257 As explained in Section 7.3, the use of the k value in ECDSA means 1258 that we cannot validate the correctness of the signature in the same 1259 way we validated the correctness of the HMAC. Instead, 1260 implementations MUST use an ECDSA validator to validate the 1261 signature. 1263 Appendix B. Algorithm Identifier Cross-Reference 1265 This appendix contains a table cross-referencing the "alg" values 1266 used in this specification with the equivalent identifiers used by 1267 other standards and software packages. See XML DSIG [RFC3275] and 1268 Java Cryptography Architecture [JCA] for more information about the 1269 names defined by those documents. 1271 +-------+-----+----------------------------+----------+-------------+ 1272 | Algor | JWS | XML DSIG | JCA | OID | 1273 | ithm | | | | | 1274 +-------+-----+----------------------------+----------+-------------+ 1275 | HMAC | HS2 | http://www.w3.org/2001/04/ | HmacSHA2 | 1.2.840.113 | 1276 | using | 56 | xmldsig-more#hmac-sha256 | 56 | 549.2.9 | 1277 | SHA-2 | | | | | 1278 | 56 | | | | | 1279 | hash | | | | | 1280 | algo | | | | | 1281 | rithm | | | | | 1282 | HMAC | HS3 | http://www.w3.org/2001/04/ | HmacSHA3 | 1.2.840.113 | 1283 | using | 84 | xmldsig-more#hmac-sha384 | 84 | 549.2.10 | 1284 | SHA-3 | | | | | 1285 | 84 | | | | | 1286 | hash | | | | | 1287 | algo | | | | | 1288 | rithm | | | | | 1289 | HMAC | HS5 | http://www.w3.org/2001/04/ | HmacSHA5 | 1.2.840.113 | 1290 | using | 12 | xmldsig-more#hmac-sha512 | 12 | 549.2.11 | 1291 | SHA-5 | | | | | 1292 | 12 | | | | | 1293 | hash | | | | | 1294 | algo | | | | | 1295 | rithm | | | | | 1296 | RSA | RS2 | http://www.w3.org/2001/04/ | SHA256wi | 1.2.840.113 | 1297 | using | 56 | xmldsig-more#rsa-sha256 | thRSA | 549.1.1.11 | 1298 | SHA-2 | | | | | 1299 | 56 | | | | | 1300 | hash | | | | | 1301 | algo | | | | | 1302 | rithm | | | | | 1303 | RSA | RS3 | http://www.w3.org/2001/04/ | SHA384wi | 1.2.840.113 | 1304 | using | 84 | xmldsig-more#rsa-sha384 | thRSA | 549.1.1.12 | 1305 | SHA-3 | | | | | 1306 | 84 | | | | | 1307 | hash | | | | | 1308 | algo | | | | | 1309 | rithm | | | | | 1310 | RSA | RS5 | http://www.w3.org/2001/04/ | SHA512wi | 1.2.840.113 | 1311 | using | 12 | xmldsig-more#rsa-sha512 | thRSA | 549.1.1.13 | 1312 | SHA-5 | | | | | 1313 | 12 | | | | | 1314 | hash | | | | | 1315 | algo | | | | | 1316 | rithm | | | | | 1317 | ECDSA | ES2 | http://www.w3.org/2001/04/ | SHA256wi | 1.2.840.100 | 1318 | using | 56 | xmldsig-more#ecdsa-sha256 | thECDSA | 45.3.1.7 | 1319 | P-256 | | | | | 1320 | curve | | | | | 1321 | and | | | | | 1322 | SHA-2 | | | | | 1323 | 56 | | | | | 1324 | hash | | | | | 1325 | algo | | | | | 1326 | rithm | | | | | 1327 | ECDSA | ES3 | http://www.w3.org/2001/04/ | SHA384wi | 1.3.132.0.3 | 1328 | using | 84 | xmldsig-more#ecdsa-sha384 | thECDSA | 4 | 1329 | P-384 | | | | | 1330 | curve | | | | | 1331 | and | | | | | 1332 | SHA-3 | | | | | 1333 | 84 | | | | | 1334 | hash | | | | | 1335 | algo | | | | | 1336 | rithm | | | | | 1337 | ECDSA | ES5 | http://www.w3.org/2001/04/ | SHA512wi | 1.3.132.0.3 | 1338 | using | 12 | xmldsig-more#ecdsa-sha512 | thECDSA | 5 | 1339 | P-521 | | | | | 1340 | curve | | | | | 1341 | and | | | | | 1342 | SHA-5 | | | | | 1343 | 12 | | | | | 1344 | hash | | | | | 1345 | algo | | | | | 1346 | rithm | | | | | 1347 +-------+-----+----------------------------+----------+-------------+ 1349 Table 4: Algorithm Identifier Cross-Reference 1351 Appendix C. Notes on implementing base64url encoding without padding 1353 This appendix describes how to implement base64url encoding and 1354 decoding functions without padding based upon standard base64 1355 encoding and decoding functions that do use padding. 1357 To be concrete, example C# code implementing these functions is shown 1358 below. Similar code could be used in other languages. 1360 static string base64urlencode(byte [] arg) 1361 { 1362 string s = Convert.ToBase64String(arg); // Standard base64 encoder 1363 s = s.Split('=')[0]; // Remove any trailing '='s 1364 s = s.Replace('+', '-'); // 62nd char of encoding 1365 s = s.Replace('/', '_'); // 63rd char of encoding 1366 return s; 1367 } 1369 static byte [] base64urldecode(string arg) 1370 { 1371 string s = arg; 1372 s = s.Replace('-', '+'); // 62nd char of encoding 1373 s = s.Replace('_', '/'); // 63rd char of encoding 1374 switch (s.Length % 4) // Pad with trailing '='s 1375 { 1376 case 0: break; // No pad chars in this case 1377 case 2: s += "=="; break; // Two pad chars 1378 case 3: s += "="; break; // One pad char 1379 default: throw new System.Exception( 1380 "Illegal base64url string!"); 1381 } 1382 return Convert.FromBase64String(s); // Standard base64 decoder 1383 } 1385 As per the example code above, the number of '=' padding characters 1386 that needs to be added to the end of a base64url encoded string 1387 without padding to turn it into one with padding is a deterministic 1388 function of the length of the encoded string. Specifically, if the 1389 length mod 4 is 0, no padding is added; if the length mod 4 is 2, two 1390 '=' padding characters are added; if the length mod 4 is 3, one '=' 1391 padding character is added; if the length mod 4 is 1, the input is 1392 malformed. 1394 An example correspondence between unencoded and encoded values 1395 follows. The byte sequence below encodes into the string below, 1396 which when decoded, reproduces the byte sequence. 1397 3 236 255 224 193 1398 A-z_4ME 1400 Appendix D. Acknowledgements 1402 Solutions for signing JSON content were previously explored by Magic 1403 Signatures [MagicSignatures], JSON Simple Sign [JSS], and Canvas 1404 Applications [CanvasApp], all of which influenced this draft. 1406 Appendix E. Document History 1408 -02 1410 o Reference the JSON Web Key (JWK) specification from the "jku" 1411 header parameter. 1413 -01 1415 o Changed RSA SHA-256 from MUST be supported to RECOMMENDED that it 1416 be supported. Rationale: Several people have objected to the 1417 requirement for implementing RSA SHA-256, some because they will 1418 only be using HMACs and symmetric keys, and others because they 1419 only want to use ECDSA when using asymmetric keys, either for 1420 security or key length reasons, or both. 1422 o Clarified that "x5u" is an HTTPS URL referencing a PEM-encoded 1423 certificate or certificate chain. 1425 o Clarified that the "alg" parameter value is case sensitive. 1427 o Changed "x5t" (x.509 certificate thumbprint) to use a SHA-1 hash, 1428 rather than a SHA-256 hash, for compatibility reasons. 1430 -00 1432 o Created first signature draft using content split from 1433 draft-jones-json-web-token-01. This split introduced no semantic 1434 changes. 1436 Authors' Addresses 1438 Michael B. Jones 1439 Microsoft 1441 Email: mbj@microsoft.com 1442 URI: http://self-issued.info/ 1444 Dirk Balfanz 1445 Google 1447 Email: balfanz@google.com 1448 John Bradley 1449 independent 1451 Email: ve7jtb@ve7jtb.com 1453 Yaron Y. Goland 1454 Microsoft 1456 Email: yarong@microsoft.com 1458 John Panzer 1459 Google 1461 Email: jpanzer@google.com 1463 Nat Sakimura 1464 Nomura Research Institute 1466 Email: n-sakimura@nri.co.jp 1468 Paul Tarjan 1469 Facebook 1471 Email: pt@fb.com