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'JWK' ** 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 2818 (Obsoleted by RFC 9110) ** 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 5246 (Obsoleted by RFC 8446) ** Obsolete normative reference: RFC 5785 (Obsoleted by RFC 8615) ** Obsolete normative reference: RFC 6125 (Obsoleted by RFC 9525) -- Possible downref: Non-RFC (?) normative reference: ref. 'USA15' Summary: 11 errors (**), 0 flaws (~~), 3 warnings (==), 18 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: May 2, 2012 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 October 30, 2011 18 JSON Web Signature (JWS) 19 draft-jones-json-web-signature-03 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 May 2, 2012. 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 . . . . . . . . . . . . . . 10 74 4.3. Private Header Parameter Names . . . . . . . . . . . . . . 10 75 5. Rules for Creating and Validating a JWS . . . . . . . . . . . 10 76 6. Signing JWSs with Cryptographic Algorithms . . . . . . . . . . 12 77 6.1. Creating a JWS with HMAC SHA-256, HMAC SHA-384, or 78 HMAC SHA-512 . . . . . . . . . . . . . . . . . . . . . . . 13 79 6.2. Creating a JWS with RSA SHA-256, RSA SHA-384, or RSA 80 SHA-512 . . . . . . . . . . . . . . . . . . . . . . . . . 14 81 6.3. Creating a JWS with ECDSA P-256 SHA-256, ECDSA P-384 82 SHA-384, or ECDSA P-521 SHA-512 . . . . . . . . . . . . . 15 83 6.4. Additional Algorithms . . . . . . . . . . . . . . . . . . 17 84 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 85 8. Security Considerations . . . . . . . . . . . . . . . . . . . 18 86 8.1. Unicode Comparison Security Issues . . . . . . . . . . . . 18 87 9. Open Issues and Things To Be Done (TBD) . . . . . . . . . . . 19 88 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20 89 10.1. Normative References . . . . . . . . . . . . . . . . . . . 20 90 10.2. Informative References . . . . . . . . . . . . . . . . . . 22 91 Appendix A. JWS Examples . . . . . . . . . . . . . . . . . . . . 22 92 A.1. JWS using HMAC SHA-256 . . . . . . . . . . . . . . . . . . 22 93 A.1.1. Encoding . . . . . . . . . . . . . . . . . . . . . . . 22 94 A.1.2. Decoding . . . . . . . . . . . . . . . . . . . . . . . 24 95 A.1.3. Validating . . . . . . . . . . . . . . . . . . . . . . 24 96 A.2. JWS using RSA SHA-256 . . . . . . . . . . . . . . . . . . 24 97 A.2.1. Encoding . . . . . . . . . . . . . . . . . . . . . . . 25 98 A.2.2. Decoding . . . . . . . . . . . . . . . . . . . . . . . 28 99 A.2.3. Validating . . . . . . . . . . . . . . . . . . . . . . 28 100 A.3. JWS using ECDSA P-256 SHA-256 . . . . . . . . . . . . . . 29 101 A.3.1. Encoding . . . . . . . . . . . . . . . . . . . . . . . 29 102 A.3.2. Decoding . . . . . . . . . . . . . . . . . . . . . . . 30 103 A.3.3. Validating . . . . . . . . . . . . . . . . . . . . . . 31 104 Appendix B. Algorithm Identifier Cross-Reference . . . . . . . . 31 105 Appendix C. Notes on implementing base64url encoding without 106 padding . . . . . . . . . . . . . . . . . . . . . . . 33 107 Appendix D. Acknowledgements . . . . . . . . . . . . . . . . . . 34 108 Appendix E. Document History . . . . . . . . . . . . . . . . . . 35 109 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 36 111 1. Introduction 113 JSON Web Signature (JWS) is a compact signature format intended for 114 space constrained environments such as HTTP Authorization headers and 115 URI query parameters. It represents signed content using JSON 116 [RFC4627] data structures. The JWS signature mechanisms are 117 independent of the type of content being signed, allowing arbitrary 118 content to be signed. A related encryption capability is described 119 in a separate JSON Web Encryption (JWE) [JWE] specification. 121 2. Terminology 123 JSON Web Signature (JWS) A data structure cryptographically securing 124 a JWS Header and a JWS Payload with a JWS Signature. 126 JWS Header A string containing a JSON object that describes the 127 signature applied to the JWS Header and the JWS Payload to create 128 the JWS Signature. 130 JWS Payload The bytes to be signed - a.k.a., the message. 132 JWS Signature A byte array containing the cryptographic material 133 that secures the contents of the JWS Header and the JWS Payload. 135 Encoded JWS Header Base64url encoding of the bytes of the UTF-8 RFC 136 3629 [RFC3629] representation of the JWS Header. 138 Encoded JWS Payload Base64url encoding of the JWS Payload. 140 Encoded JWS Signature Base64url encoding of the JWS Signature. 142 JWS Signing Input The concatenation of the Encoded JWS Header, a 143 period ('.') character, and the Encoded JWS Payload. 145 Header Parameter Names The names of the members within the JSON 146 object represented in a JWS Header. 148 Header Parameter Values The values of the members within the JSON 149 object represented in a JWS Header. 151 Digital Signature For the purposes of this specification, we use 152 this term to encompass both Hash-based Message Authentication 153 Codes (HMACs), which can provide authenticity but not non- 154 repudiation, and digital signatures using public key algorithms, 155 which can provide both. Readers should be aware of this 156 distinction, despite the decision to use a single term for both 157 concepts to improve readability of the specification. 159 Base64url Encoding For the purposes of this specification, this term 160 always refers to the he URL- and filename-safe Base64 encoding 161 described in RFC 4648 [RFC4648], Section 5, with the (non URL- 162 safe) '=' padding characters omitted, as permitted by Section 3.2. 163 (See Appendix C for notes on implementing base64url encoding 164 without padding.) 166 3. JSON Web Signature (JWS) Overview 168 JWS represents signed content using JSON data structures and 169 base64url encoding. The representation consists of three parts: the 170 JWS Header, the JWS Payload, and the JWS Signature. The three parts 171 are base64url-encoded for transmission, and typically represented as 172 the concatenation of the encoded strings in that order, with the 173 three strings being separated by period ('.') characters, as is done 174 when used in JSON Web Tokens (JWTs) [JWT]. 176 A base64url encoded JSON object - the JWS Header - describes the 177 signature method used. A portion of the base64url encoded content 178 that is signed is the Encoded JWS Payload. Finally, JWSs contain a 179 signature that ensures the integrity of the contents of the JWS 180 Header and the JWS Payload. This signature value is base64url 181 encoded to produce the Encoded JWS Signature. 183 The member names within the JWS Header are referred to as Header 184 Parameter Names. These names MUST be unique. The corresponding 185 values are referred to as Header Parameter Values. The JWS Header 186 MUST contain an "alg" parameter, the value of which is a string that 187 unambiguously identifies the algorithm used to sign the JWS Header 188 and the JWS Payload to produce the JWS Signature. 190 3.1. Example JWS 192 The following example JWS Header declares that the encoded object is 193 a JSON Web Token (JWT) [JWT] and the JWS Header and the JWS Payload 194 are signed using the HMAC SHA-256 algorithm: 195 {"typ":"JWT", 196 "alg":"HS256"} 198 Base64url encoding the bytes of the UTF-8 representation of the JWS 199 Header yields this Encoded JWS Header value: 200 eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9 202 The following is an example of a JSON object that can be used as a 203 JWS Payload. (Note that the payload can be any content, and need not 204 be a representation of a JSON object.) 205 {"iss":"joe", 206 "exp":1300819380, 207 "http://example.com/is_root":true} 209 Base64url encoding the bytes of the UTF-8 representation of the JSON 210 object yields the following Encoded JWS Payload. 211 eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ 213 Signing the UTF-8 representation of the JWS Signing Input (the 214 concatenation of the Encoded JWS Header, a period ('.') character, 215 and the Encoded JWS Payload) with the HMAC SHA-256 algorithm and 216 base64url encoding the result, as per Section 6.1, yields this 217 Encoded JWS Signature value: 218 dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk 220 This computation is illustrated in more detail in Appendix A.1. 222 4. JWS Header 224 The members of the JSON object represented by the JWS Header describe 225 the signature applied to the Encoded JWS Header and the Encoded JWS 226 Payload and optionally additional properties of the JWS. 227 Implementations MUST understand the entire contents of the header; 228 otherwise, the JWS MUST be rejected for processing. 230 4.1. Reserved Header Parameter Names 232 The following header parameter names are reserved. All the names are 233 short because a core goal of JWSs is for the representations to be 234 compact. 236 +-----------+--------+-------------+--------------------------------+ 237 | Header | JSON | Header | Header Parameter Semantics | 238 | Parameter | Value | Parameter | | 239 | Name | Type | Syntax | | 240 +-----------+--------+-------------+--------------------------------+ 241 | alg | string | StringOrURI | The "alg" (algorithm) header | 242 | | | | parameter identifies the | 243 | | | | cryptographic algorithm used | 244 | | | | to secure the JWS. A list of | 245 | | | | reserved alg values is in | 246 | | | | Table 3. The processing of | 247 | | | | the "alg" (algorithm) header | 248 | | | | parameter, if present, | 249 | | | | requires that the value of the | 250 | | | | "alg" header parameter MUST be | 251 | | | | one that is both supported and | 252 | | | | for which there exists a key | 253 | | | | for use with that algorithm | 254 | | | | associated with the signer of | 255 | | | | the content. The "alg" | 256 | | | | parameter value is case | 257 | | | | sensitive. This header | 258 | | | | parameter is 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 Web Key URL) | 266 | | | | header parameter is an | 267 | | | | absolute URL that refers to a | 268 | | | | resource for a set of | 269 | | | | JSON-encoded public keys, one | 270 | | | | of which corresponds to the | 271 | | | | key that was used to sign the | 272 | | | | JWS. The keys MUST be encoded | 273 | | | | as described in the JSON Web | 274 | | | | Key (JWK) [JWK] specification. | 275 | | | | The protocol used to acquire | 276 | | | | the resource MUST provide | 277 | | | | integrity protection. An HTTP | 278 | | | | GET request to retrieve the | 279 | | | | certificate MUST use TLS RFC | 280 | | | | 2818 [RFC2818] RFC 5246 | 281 | | | | [RFC5246] with server | 282 | | | | authentication RFC 6125 | 283 | | | | [RFC6125]. This header | 284 | | | | parameter is OPTIONAL. | 285 | kid | string | String | The "kid" (key ID) header | 286 | | | | parameter is a hint indicating | 287 | | | | which specific key owned by | 288 | | | | the signer should be used to | 289 | | | | validate the signature. This | 290 | | | | allows signers to explicitly | 291 | | | | signal a change of key to | 292 | | | | recipients. The | 293 | | | | interpretation of the contents | 294 | | | | of the "kid" parameter is | 295 | | | | unspecified. This header | 296 | | | | parameter is OPTIONAL. | 297 | x5u | string | URL | The "x5u" (X.509 URL) header | 298 | | | | parameter is an absolute URL | 299 | | | | that refers to a resource for | 300 | | | | the X.509 public key | 301 | | | | certificate or certificate | 302 | | | | chain corresponding to the key | 303 | | | | used to sign the JWS. The | 304 | | | | identified resource MUST | 305 | | | | provide a representation of | 306 | | | | the certificate or certificate | 307 | | | | chain that conforms to RFC | 308 | | | | 5280 [RFC5280] in PEM encoded | 309 | | | | form RFC 1421 [RFC1421]. The | 310 | | | | protocol used to acquire the | 311 | | | | resource MUST provide | 312 | | | | integrity protection. An HTTP | 313 | | | | GET request to retrieve the | 314 | | | | certificate MUST use TLS RFC | 315 | | | | 2818 [RFC2818] RFC 5246 | 316 | | | | [RFC5246] with server | 317 | | | | authentication RFC 6125 | 318 | | | | [RFC6125]. This header | 319 | | | | parameter is OPTIONAL. | 320 | x5t | string | String | The "x5t" (x.509 certificate | 321 | | | | thumbprint) header parameter | 322 | | | | provides a base64url encoded | 323 | | | | SHA-1 thumbprint (a.k.a. | 324 | | | | digest) of the DER encoding of | 325 | | | | an X.509 certificate that can | 326 | | | | be used to match the | 327 | | | | certificate. This header | 328 | | | | parameter is OPTIONAL. | 329 +-----------+--------+-------------+--------------------------------+ 331 Table 1: Reserved Header Parameter Definitions 333 Additional reserved header parameter names MAY be defined via the 334 IANA JSON Web Signature Header Parameters registry, as per Section 7. 335 The syntax values used above are defined as follows: 337 +-------------+-----------------------------------------------------+ 338 | Syntax Name | Syntax Definition | 339 +-------------+-----------------------------------------------------+ 340 | IntDate | The number of seconds from 1970-01-01T0:0:0Z as | 341 | | measured in UTC until the desired date/time. See | 342 | | RFC 3339 [RFC3339] for details regarding date/times | 343 | | in general and UTC in particular. | 344 | String | Any string value MAY be used. | 345 | StringOrURI | Any string value MAY be used but a value containing | 346 | | a ":" character MUST be a URI as defined in RFC | 347 | | 3986 [RFC3986]. | 348 | URL | A URL as defined in RFC 1738 [RFC1738]. | 349 +-------------+-----------------------------------------------------+ 351 Table 2: Header Parameter Syntax Definitions 353 4.2. Public Header Parameter Names 355 Additional header parameter names can be defined by those using JWSs. 356 However, in order to prevent collisions, any new header parameter 357 name or algorithm value SHOULD either be defined in the IANA JSON Web 358 Signature Header Parameters registry or be defined as a URI that 359 contains a collision resistant namespace. In each case, the definer 360 of the name or value MUST take reasonable precautions to make sure 361 they are in control of the part of the namespace they use to define 362 the header parameter name. 364 New header parameters should be introduced sparingly, as they can 365 result in non-interoperable JWSs. 367 4.3. Private Header Parameter Names 369 A producer and consumer of a JWS may agree to any header parameter 370 name that is not a Reserved Name Section 4.1 or a Public Name 371 Section 4.2. Unlike Public Names, these private names are subject to 372 collision and should be used with caution. 374 New header parameters should be introduced sparingly, as they can 375 result in non-interoperable JWSs. 377 5. Rules for Creating and Validating a JWS 379 To create a JWS, one MUST follow these steps: 381 1. Create the content to be used as the JWS Payload. 383 2. Base64url encode the JWS Payload. This encoding becomes the 384 Encoded JWS Payload. 386 3. Create a JSON object containing a set of desired header 387 parameters. Note that white space is explicitly allowed in the 388 representation and no canonicalization is performed before 389 encoding. 391 4. Translate this JSON object's Unicode code points into UTF-8, as 392 defined in RFC 3629 [RFC3629]. 394 5. Base64url encode the UTF-8 representation of this JSON object as 395 defined in this specification (without padding). This encoding 396 becomes the Encoded JWS Header. 398 6. Compute the JWS Signature in the manner defined for the 399 particular algorithm being used. The JWS Signing Input is always 400 the concatenation of the Encoded JWS Header, a period ('.') 401 character, and the Encoded JWS Payload. The "alg" header 402 parameter MUST be present in the JSON Header, with the algorithm 403 value accurately representing the algorithm used to construct the 404 JWS Signature. 406 7. Base64url encode the representation of the JWS Signature to 407 create the Encoded JWS Signature. 409 When validating a JWS, the following steps MUST be taken. If any of 410 the listed steps fails, then the signed content MUST be rejected. 412 1. The Encoded JWS Payload MUST be successfully base64url decoded 413 following the restriction given in this specification that no 414 padding characters have been used. 416 2. The Encoded JWS Header MUST be successfully base64url decoded 417 following the restriction given in this specification that no 418 padding characters have been used. 420 3. The JWS Header MUST be completely valid JSON syntax conforming to 421 RFC 4627 [RFC4627]. 423 4. The Encoded JWS Signature MUST be successfully base64url decoded 424 following the restriction given in this specification that no 425 padding characters have been used. 427 5. The JWS Header MUST be validated to only include parameters and 428 values whose syntax and semantics are both understood and 429 supported. 431 6. The JWS Signature MUST be successfully validated against the JWS 432 Header and JWS Payload in the manner defined for the algorithm 433 being used, which MUST be accurately represented by the value of 434 the "alg" header parameter, which MUST be present. 436 Processing a JWS inevitably requires comparing known strings to 437 values in the header. For example, in checking what the algorithm 438 is, the Unicode string encoding "alg" will be checked against the 439 member names in the JWS Header to see if there is a matching header 440 parameter name. A similar process occurs when determining if the 441 value of the "alg" header parameter represents a supported algorithm. 442 Comparing Unicode strings, however, has significant security 443 implications, as per Section 8. 445 Comparisons between JSON strings and other Unicode strings MUST be 446 performed as specified below: 448 1. Remove any JSON applied escaping to produce an array of Unicode 449 code points. 451 2. Unicode Normalization [USA15] MUST NOT be applied at any point to 452 either the JSON string or to the string it is to be compared 453 against. 455 3. Comparisons between the two strings MUST be performed as a 456 Unicode code point to code point equality comparison. 458 6. Signing JWSs with Cryptographic Algorithms 460 JWSs use specific cryptographic algorithms to sign the contents of 461 the JWS Header and the JWS Payload. The use of the following 462 algorithms for producing JWSs is defined in this section. The table 463 below is the list of "alg" header parameter values reserved by this 464 specification, each of which is explained in more detail in the 465 following sections: 467 +--------------------+----------------------------------------------+ 468 | Alg Parameter | Algorithm | 469 | Value | | 470 +--------------------+----------------------------------------------+ 471 | HS256 | HMAC using SHA-256 hash algorithm | 472 | HS384 | HMAC using SHA-384 hash algorithm | 473 | HS512 | HMAC using SHA-512 hash algorithm | 474 | RS256 | RSA using SHA-256 hash algorithm | 475 | RS384 | RSA using SHA-384 hash algorithm | 476 | RS512 | RSA using SHA-512 hash algorithm | 477 | ES256 | ECDSA using P-256 curve and SHA-256 hash | 478 | | algorithm | 479 | ES384 | ECDSA using P-384 curve and SHA-384 hash | 480 | | algorithm | 481 | ES512 | ECDSA using P-521 curve and SHA-512 hash | 482 | | algorithm | 483 +--------------------+----------------------------------------------+ 485 Table 3: JSON Web Signature Reserved Algorithm Values 487 See Appendix B for a table cross-referencing the "alg" values used in 488 this specification with the equivalent identifiers used by other 489 standards and software packages. 491 Of these algorithms, only HMAC SHA-256 MUST be implemented by 492 conforming implementations. It is RECOMMENDED that implementations 493 also support the RSA SHA-256 and ECDSA P-256 SHA-256 algorithms. 494 Support for other algorithms and key sizes is OPTIONAL. 496 The signed content for a JWS is the same for all algorithms: the 497 concatenation of the Encoded JWS Header, a period ('.') character, 498 and the Encoded JWS Payload. This character sequence is referred to 499 as the JWS Signing Input. Note that if the JWS represents a JWT, 500 this corresponds to the portion of the JWT representation preceding 501 the second period character. The UTF-8 representation of the JWS 502 Signing Input is passed to the respective signing algorithms. 504 6.1. Creating a JWS with HMAC SHA-256, HMAC SHA-384, or HMAC SHA-512 506 Hash based Message Authentication Codes (HMACs) enable one to use a 507 secret plus a cryptographic hash function to generate a Message 508 Authentication Code (MAC). This can be used to demonstrate that the 509 MAC matches the hashed content, in this case the JWS Signing Input, 510 which therefore demonstrates that whoever generated the MAC was in 511 possession of the secret. The means of exchanging the shared key is 512 outside the scope of this specification. 514 The algorithm for implementing and validating HMACs is provided in 515 RFC 2104 [RFC2104]. This section defines the use of the HMAC SHA- 516 256, HMAC SHA-384, and HMAC SHA-512 cryptographic hash functions as 517 defined in FIPS 180-3 [FIPS.180-3]. The reserved "alg" header 518 parameter values "HS256", "HS384", and "HS512" are used in the JWS 519 Header to indicate that the Encoded JWS Signature contains a 520 base64url encoded HMAC value using the respective hash function. 522 The HMAC SHA-256 MAC is generated as follows: 524 1. Apply the HMAC SHA-256 algorithm to the UTF-8 representation of 525 the JWS Signing Input using the shared key to produce an HMAC. 527 2. Base64url encode the HMAC, as defined in this specification. 529 The output is the Encoded JWS Signature for that JWS. 531 The HMAC SHA-256 MAC for a JWS is validated as follows: 533 1. Apply the HMAC SHA-256 algorithm to the UTF-8 representation of 534 the JWS Signing Input of the JWS using the shared key. 536 2. Base64url encode the previously generated HMAC, as defined in 537 this specification. 539 3. If the JWS Signature and the previously calculated value exactly 540 match, then one has confirmation that the key was used to 541 generate the HMAC on the JWS and that the contents of the JWS 542 have not be tampered with. 544 4. If the validation fails, the signed content MUST be rejected. 546 Signing with the HMAC SHA-384 and HMAC SHA-512 algorithms is 547 performed identically to the procedure for HMAC SHA-256 - just with 548 correspondingly longer key and result values. 550 6.2. Creating a JWS with RSA SHA-256, RSA SHA-384, or RSA SHA-512 552 This section defines the use of the RSASSA-PKCS1-v1_5 signature 553 algorithm as defined in RFC 3447 [RFC3447], Section 8.2 (commonly 554 known as PKCS#1), using SHA-256, SHA-384, or SHA-512 as the hash 555 function. The RSASSA-PKCS1-v1_5 algorithm is described in FIPS 186-3 556 [FIPS.186-3], Section 5.5, and the SHA-256, SHA-384, and SHA-512 557 cryptographic hash functions are defined in FIPS 180-3 [FIPS.180-3]. 558 The reserved "alg" header parameter values "RS256", "RS384", and 559 "RS512" are used in the JWS Header to indicate that the Encoded JWS 560 Signature contains a base64url encoded RSA signature using the 561 respective hash function. 563 The public keys employed may be retrieved using Header Parameter 564 methods described in Section 4.1 or may be distributed using methods 565 that are outside the scope of this specification. 567 A 2048-bit or longer key length MUST be used with this algorithm. 569 The RSA SHA-256 signature is generated as follows: 571 1. Generate a digital signature of the UTF-8 representation of the 572 JWS Signing Input using RSASSA-PKCS1-V1_5-SIGN and the SHA-256 573 hash function with the desired private key. The output will be a 574 byte array. 576 2. Base64url encode the byte array, as defined in this 577 specification. 579 The output is the Encoded JWS Signature for that JWS. 581 The RSA SHA-256 signature for a JWS is validated as follows: 583 1. Take the Encoded JWS Signature and base64url decode it into a 584 byte array. If decoding fails, the signed content MUST be 585 rejected. 587 2. Submit the UTF-8 representation of the JWS Signing Input and the 588 public key corresponding to the private key used by the signer to 589 the RSASSA-PKCS1-V1_5-VERIFY algorithm using SHA-256 as the hash 590 function. 592 3. If the validation fails, the signed content MUST be rejected. 594 Signing with the RSA SHA-384 and RSA SHA-512 algorithms is performed 595 identically to the procedure for RSA SHA-256 - just with 596 correspondingly longer key and result values. 598 6.3. Creating a JWS with ECDSA P-256 SHA-256, ECDSA P-384 SHA-384, or 599 ECDSA P-521 SHA-512 601 The Elliptic Curve Digital Signature Algorithm (ECDSA) is defined by 602 FIPS 186-3 [FIPS.186-3]. ECDSA provides for the use of Elliptic 603 Curve cryptography, which is able to provide equivalent security to 604 RSA cryptography but using shorter key lengths and with greater 605 processing speed. This means that ECDSA signatures will be 606 substantially smaller in terms of length than equivalently strong RSA 607 Digital Signatures. 609 This specification defines the use of ECDSA with the P-256 curve and 610 the SHA-256 cryptographic hash function, ECDSA with the P-384 curve 611 and the SHA-384 hash function, and ECDSA with the P-521 curve and the 612 SHA-512 hash function. The P-256, P-384, and P-521 curves are also 613 defined in FIPS 186-3. The reserved "alg" header parameter values 614 "ES256", "ES384", and "ES512" are used in the JWS Header to indicate 615 that the Encoded JWS Signature contains a base64url encoded ECDSA 616 P-256 SHA-256, ECDSA P-384 SHA-384, or ECDSA P-521 SHA-512 signature, 617 respectively. 619 The public keys employed may be retrieved using Header Parameter 620 methods described in Section 4.1 or may be distributed using methods 621 that are outside the scope of this specification. 623 A JWS is signed with an ECDSA P-256 SHA-256 signature as follows: 625 1. Generate a digital signature of the UTF-8 representation of the 626 JWS Signing Input using ECDSA P-256 SHA-256 with the desired 627 private key. The output will be the EC point (R, S), where R and 628 S are unsigned integers. 630 2. Turn R and S into byte arrays in big endian order. Each array 631 will be 32 bytes long. 633 3. Concatenate the two byte arrays in the order R and then S. 635 4. Base64url encode the 64 byte array, as defined in this 636 specification. 638 The output is the Encoded JWS Signature for the JWS. 640 The ECDSA P-256 SHA-256 signature for a JWS is validated as follows: 642 1. Take the Encoded JWS Signature and base64url decode it into a 643 byte array. If decoding fails, the signed content MUST be 644 rejected. 646 2. The output of the base64url decoding MUST be a 64 byte array. 648 3. Split the 64 byte array into two 32 byte arrays. The first array 649 will be R and the second S. Remember that the byte arrays are in 650 big endian byte order; please check the ECDSA validator in use to 651 see what byte order it requires. 653 4. Submit the UTF-8 representation of the JWS Signing Input, R, S 654 and the public key (x, y) to the ECDSA P-256 SHA-256 validator. 656 5. If the validation fails, the signed content MUST be rejected. 658 The ECDSA validator will then determine if the digital signature is 659 valid, given the inputs. Note that ECDSA digital signature contains 660 a value referred to as K, which is a random number generated for each 661 digital signature instance. This means that two ECDSA digital 662 signatures using exactly the same input parameters will output 663 different signatures because their K values will be different. The 664 consequence of this is that one must validate an ECDSA signature by 665 submitting the previously specified inputs to an ECDSA validator. 667 Signing with the ECDSA P-384 SHA-384 and ECDSA P-521 SHA-512 668 algorithms is performed identically to the procedure for ECDSA P-256 669 SHA-256 - just with correspondingly longer key and result values. 671 6.4. Additional Algorithms 673 Additional algorithms MAY be used to protect JWSs with corresponding 674 "alg" header parameter values being defined to refer to them. New 675 "alg" header parameter values SHOULD either be defined in the IANA 676 JSON Web Signature Algorithms registry or be a URI that contains a 677 collision resistant namespace. In particular, the use of algorithm 678 identifiers defined in XML DSIG [RFC3275] and related specifications 679 is permitted. 681 7. IANA Considerations 683 This specification calls for: 685 o A new IANA registry entitled "JSON Web Signature Header 686 Parameters" for reserved header parameter names is defined in 687 Section 4.1. Inclusion in the registry is RFC Required in the RFC 688 5226 [RFC5226] sense for reserved JWS header parameter names that 689 are intended to be interoperable between implementations. The 690 registry will just record the reserved header parameter name and a 691 pointer to the RFC that defines it. This specification defines 692 inclusion of the header parameter names defined in Table 1. 694 o A new IANA registry entitled "JSON Web Signature Algorithms" for 695 reserved values used with the "alg" header parameter values is 696 defined in Section 6.4. Inclusion in the registry is RFC Required 697 in the RFC 5226 [RFC5226] sense. The registry will just record 698 the "alg" value and a pointer to the RFC that defines it. This 699 specification defines inclusion of the algorithm values defined in 700 Table 3. 702 8. Security Considerations 704 TBD: Lots of work to do here. We need to remember to look into any 705 issues relating to security and JSON parsing. One wonders just how 706 secure most JSON parsing libraries are. Were they ever hardened for 707 security scenarios? If not, what kind of holes does that open up? 708 Also, we need to walk through the JSON standard and see what kind of 709 issues we have especially around comparison of names. For instance, 710 comparisons of header parameter names and other parameters must occur 711 after they are unescaped. Need to also put in text about: Importance 712 of keeping secrets secret. Rotating keys. Strengths and weaknesses 713 of the different algorithms. 715 TBD: Need to put in text about why strict JSON validation is 716 necessary. Basically, that if malformed JSON is received then the 717 intent of the sender is impossible to reliably discern. One example 718 of malformed JSON that MUST be rejected is an object in which the 719 same member name occurs multiple times. 721 TBD: Write security considerations about the implications of using a 722 SHA-1 hash (for compatibility reasons) for the "x5t" (x.509 723 certificate thumbprint). 725 When utilizing TLS to retrieve information, the authority providing 726 the resource MUST be authenticated and the information retrieved MUST 727 be free from modification. 729 8.1. Unicode Comparison Security Issues 731 Header parameter names in JWSs are Unicode strings. For security 732 reasons, the representations of these names must be compared verbatim 733 after performing any escape processing (as per RFC 4627 [RFC4627], 734 Section 2.5). 736 This means, for instance, that these JSON strings must compare as 737 being equal ("sig", "\u0073ig"), whereas these must all compare as 738 being not equal to the first set or to each other ("SIG", "Sig", 739 "si\u0047"). 741 JSON strings MAY contain characters outside the Unicode Basic 742 Multilingual Plane. For instance, the G clef character (U+1D11E) may 743 be represented in a JSON string as "\uD834\uDD1E". Ideally, JWS 744 implementations SHOULD ensure that characters outside the Basic 745 Multilingual Plane are preserved and compared correctly; 746 alternatively, if this is not possible due to these characters 747 exercising limitations present in the underlying JSON implementation, 748 then input containing them MUST be rejected. 750 9. Open Issues and Things To Be Done (TBD) 752 The following items remain to be done in this draft: 754 o Consider whether there is a better term than "Digital Signature" 755 for the concept that includes both HMACs and digital signatures 756 using public keys. 758 o Consider whether we really want to allow private header parameter 759 names that are not registered with IANA and are not in collision- 760 resistant namespaces. Eventually this could result in interop 761 nightmares where you need to have different code to talk to 762 different endpoints that "knows" about each endpoint's private 763 parameters. 765 o Clarify the optional ability to provide type information in the 766 JWS header. Specifically, clarify the intended use of the "typ" 767 Header Parameter, whether it conveys syntax or semantics, and 768 indeed, whether this is the right approach. Also clarify the 769 relationship between these type values and MIME [RFC2045] types. 771 o Clarify the semantics of the "kid" (key ID) header parameter. 772 Open issues include: What happens if a "kid" header is received 773 with an unrecognized value? Is that an error? Should it be 774 treated as if it's empty? What happens if the header has a 775 recognized value but the value doesn't match the key associated 776 with that value, but it does match another key that is associated 777 with the issuer? Is that an error? 779 o Consider whether a key type parameter should also be introduced. 781 o Since RFC 3447 Section 8 explicitly calls for people NOT to adopt 782 RSASSA-PKCS1 for new applications and instead requests that people 783 transition to RSASSA-PSS, we probably need some Security 784 Considerations text explaining why RSASSA-PKCS1 is being used 785 (it's what's commonly implemented) and what the potential 786 consequences are. 788 o Add Security Considerations text on timing attacks. 790 o It would be good to have a confirmation method element so it could 791 be used with holder-of-key. 793 o Think about how to best describe the concept currently described 794 as "the bytes of the UTF-8 representation of". Possible terms to 795 use instead of "bytes of" include "byte sequence", "octet series", 796 and "octet sequence". Also consider whether we want to add an 797 overall clarifying statement somewhere in each spec something like 798 "every place we say 'the UTF-8 representation of X', we mean 'the 799 bytes of the UTF-8 representation of X'". That would potentially 800 allow us to omit the "the bytes of" part everywhere else. 802 o Consider whether a media type should be proposed, such as 803 "application/jws". 805 o Finish the Security Considerations section. 807 o Add an example in which the payload is not a base64url encoded 808 JSON object. 810 o Consider having an algorithm that is a MAC using SHA-256 that 811 provides content integrity but for which there is no associated 812 secret. This would be like the JWT "alg":"none", in that no 813 validation of the authenticity content is provided, but with a 814 checksum provided. 816 o Consider whether to define the JWT "alg":"none" here, rather than 817 in the JWT spec. 819 10. References 821 10.1. Normative References 823 [FIPS.180-3] 824 National Institute of Standards and Technology, "Secure 825 Hash Standard (SHS)", FIPS PUB 180-3, October 2008. 827 [FIPS.186-3] 828 National Institute of Standards and Technology, "Digital 829 Signature Standard (DSS)", FIPS PUB 186-3, June 2009. 831 [JWK] Jones, M., "JSON Web Key (JWK)", October 2011. 833 [RFC1421] Linn, J., "Privacy Enhancement for Internet Electronic 834 Mail: Part I: Message Encryption and Authentication 835 Procedures", RFC 1421, February 1993. 837 [RFC1738] Berners-Lee, T., Masinter, L., and M. McCahill, "Uniform 838 Resource Locators (URL)", RFC 1738, December 1994. 840 [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail 841 Extensions (MIME) Part One: Format of Internet Message 842 Bodies", RFC 2045, November 1996. 844 [RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- 845 Hashing for Message Authentication", RFC 2104, 846 February 1997. 848 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 849 Requirement Levels", BCP 14, RFC 2119, March 1997. 851 [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. 853 [RFC3339] Klyne, G., Ed. and C. Newman, "Date and Time on the 854 Internet: Timestamps", RFC 3339, July 2002. 856 [RFC3447] Jonsson, J. and B. Kaliski, "Public-Key Cryptography 857 Standards (PKCS) #1: RSA Cryptography Specifications 858 Version 2.1", RFC 3447, February 2003. 860 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 861 10646", STD 63, RFC 3629, November 2003. 863 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 864 Resource Identifier (URI): Generic Syntax", STD 66, 865 RFC 3986, January 2005. 867 [RFC4627] Crockford, D., "The application/json Media Type for 868 JavaScript Object Notation (JSON)", RFC 4627, July 2006. 870 [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data 871 Encodings", RFC 4648, October 2006. 873 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 874 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 875 May 2008. 877 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 878 (TLS) Protocol Version 1.2", RFC 5246, August 2008. 880 [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., 881 Housley, R., and W. Polk, "Internet X.509 Public Key 882 Infrastructure Certificate and Certificate Revocation List 883 (CRL) Profile", RFC 5280, May 2008. 885 [RFC5785] Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known 886 Uniform Resource Identifiers (URIs)", RFC 5785, 887 April 2010. 889 [RFC6125] Saint-Andre, P. and J. Hodges, "Representation and 890 Verification of Domain-Based Application Service Identity 891 within Internet Public Key Infrastructure Using X.509 892 (PKIX) Certificates in the Context of Transport Layer 893 Security (TLS)", RFC 6125, March 2011. 895 [USA15] Davis, M., Whistler, K., and M. Duerst, "Unicode 896 Normalization Forms", Unicode Standard Annex 15, 09 2009. 898 10.2. Informative References 900 [CanvasApp] 901 Facebook, "Canvas Applications", 2010. 903 [JCA] Oracle, "Java Cryptography Architecture", 2011. 905 [JSS] Bradley, J. and N. Sakimura (editor), "JSON Simple Sign", 906 September 2010. 908 [JWE] Jones, M., Bradley, J., and N. Sakimura, "JSON Web 909 Encryption (JWE)", October 2011. 911 [JWT] Jones, M., Balfanz, D., Bradley, J., Goland, Y., Panzer, 912 J., Sakimura, N., and P. Tarjan, "JSON Web Token (JWT)", 913 October 2011. 915 [MagicSignatures] 916 Panzer (editor), J., Laurie, B., and D. Balfanz, "Magic 917 Signatures", August 2010. 919 [RFC3275] Eastlake, D., Reagle, J., and D. Solo, "(Extensible Markup 920 Language) XML-Signature Syntax and Processing", RFC 3275, 921 March 2002. 923 Appendix A. JWS Examples 925 This section provides several examples of JWSs. While these examples 926 all represent JSON Web Tokens (JWTs) [JWT], the payload can be any 927 base64url encoded content. 929 A.1. JWS using HMAC SHA-256 931 A.1.1. Encoding 933 The following example JWS Header declares that the data structure is 934 a JSON Web Token (JWT) [JWT] and the JWS Signing Input is signed 935 using the HMAC SHA-256 algorithm. Note that white space is 936 explicitly allowed in JWS Header strings and no canonicalization is 937 performed before encoding. 938 {"typ":"JWT", 939 "alg":"HS256"} 941 The following byte array contains the UTF-8 characters for the JWS 942 Header: 944 [123, 34, 116, 121, 112, 34, 58, 34, 74, 87, 84, 34, 44, 13, 10, 32, 945 34, 97, 108, 103, 34, 58, 34, 72, 83, 50, 53, 54, 34, 125] 947 Base64url encoding this UTF-8 representation yields this Encoded JWS 948 Header value: 949 eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9 951 The JWS Payload used in this example follows. (Note that the payload 952 can be any base64url encoded content, and need not be a base64url 953 encoded JSON object.) 954 {"iss":"joe", 955 "exp":1300819380, 956 "http://example.com/is_root":true} 958 The following byte array contains the UTF-8 characters for the JWS 959 Payload: 961 [123, 34, 105, 115, 115, 34, 58, 34, 106, 111, 101, 34, 44, 13, 10, 962 32, 34, 101, 120, 112, 34, 58, 49, 51, 48, 48, 56, 49, 57, 51, 56, 963 48, 44, 13, 10, 32, 34, 104, 116, 116, 112, 58, 47, 47, 101, 120, 97, 964 109, 112, 108, 101, 46, 99, 111, 109, 47, 105, 115, 95, 114, 111, 965 111, 116, 34, 58, 116, 114, 117, 101, 125] 967 Base64url encoding the above yields the Encoded JWS Payload value: 968 eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ 970 Concatenating the Encoded JWS Header, a period character, and the 971 Encoded JWS Payload yields this JWS Signing Input value (with line 972 breaks for display purposes only): 973 eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9 974 . 975 eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ 977 The UTF-8 representation of the JWS Signing Input is the following 978 byte array: 980 [101, 121, 74, 48, 101, 88, 65, 105, 79, 105, 74, 75, 86, 49, 81, 981 105, 76, 65, 48, 75, 73, 67, 74, 104, 98, 71, 99, 105, 79, 105, 74, 982 73, 85, 122, 73, 49, 78, 105, 74, 57, 46, 101, 121, 74, 112, 99, 51, 983 77, 105, 79, 105, 74, 113, 98, 50, 85, 105, 76, 65, 48, 75, 73, 67, 984 74, 108, 101, 72, 65, 105, 79, 106, 69, 122, 77, 68, 65, 52, 77, 84, 985 107, 122, 79, 68, 65, 115, 68, 81, 111, 103, 73, 109, 104, 48, 100, 986 72, 65, 54, 76, 121, 57, 108, 101, 71, 70, 116, 99, 71, 120, 108, 76, 987 109, 78, 118, 98, 83, 57, 112, 99, 49, 57, 121, 98, 50, 57, 48, 73, 988 106, 112, 48, 99, 110, 86, 108, 102, 81] 989 HMACs are generated using keys. This example uses the key 990 represented by the following byte array: 992 [3, 35, 53, 75, 43, 15, 165, 188, 131, 126, 6, 101, 119, 123, 166, 993 143, 90, 179, 40, 230, 240, 84, 201, 40, 169, 15, 132, 178, 210, 80, 994 46, 191, 211, 251, 90, 146, 210, 6, 71, 239, 150, 138, 180, 195, 119, 995 98, 61, 34, 61, 46, 33, 114, 5, 46, 79, 8, 192, 205, 154, 245, 103, 996 208, 128, 163] 998 Running the HMAC SHA-256 algorithm on the UTF-8 representation of the 999 JWS Signing Input with this key yields the following byte array: 1001 [116, 24, 223, 180, 151, 153, 224, 37, 79, 250, 96, 125, 216, 173, 1002 187, 186, 22, 212, 37, 77, 105, 214, 191, 240, 91, 88, 5, 88, 83, 1003 132, 141, 121] 1005 Base64url encoding the above HMAC output yields the Encoded JWS 1006 Signature value: 1007 dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk 1009 A.1.2. Decoding 1011 Decoding the JWS first requires removing the base64url encoding from 1012 the Encoded JWS Header, the Encoded JWS Payload, and the Encoded JWS 1013 Signature. We base64url decode the inputs and turn them into the 1014 corresponding byte arrays. We translate the header input byte array 1015 containing UTF-8 encoded characters into the JWS Header string. 1017 A.1.3. Validating 1019 Next we validate the decoded results. Since the "alg" parameter in 1020 the header is "HS256", we validate the HMAC SHA-256 signature 1021 contained in the JWS Signature. If any of the validation steps fail, 1022 the signed content MUST be rejected. 1024 First, we validate that the JWS Header string is legal JSON. 1026 To validate the signature, we repeat the previous process of using 1027 the correct key and the UTF-8 representation of the JWS Signing Input 1028 as input to a SHA-256 HMAC function and then taking the output and 1029 determining if it matches the JWS Signature. If it matches exactly, 1030 the signature has been validated. 1032 A.2. JWS using RSA SHA-256 1033 A.2.1. Encoding 1035 The JWS Header in this example is different from the previous example 1036 in two ways: First, because a different algorithm is being used, the 1037 "alg" value is different. Second, for illustration purposes only, 1038 the optional "typ" parameter is not used. (This difference is not 1039 related to the signature algorithm employed.) The JWS Header used 1040 is: 1041 {"alg":"RS256"} 1043 The following byte array contains the UTF-8 characters for the JWS 1044 Header: 1046 [123, 34, 97, 108, 103, 34, 58, 34, 82, 83, 50, 53, 54, 34, 125] 1048 Base64url encoding this UTF-8 representation yields this Encoded JWS 1049 Header value: 1050 eyJhbGciOiJSUzI1NiJ9 1052 The JWS Payload used in this example, which follows, is the same as 1053 in the previous example. Since the Encoded JWS Payload will 1054 therefore be the same, its computation is not repeated here. 1055 {"iss":"joe", 1056 "exp":1300819380, 1057 "http://example.com/is_root":true} 1059 Concatenating the Encoded JWS Header, a period character, and the 1060 Encoded JWS Payload yields this JWS Signing Input value (with line 1061 breaks for display purposes only): 1062 eyJhbGciOiJSUzI1NiJ9 1063 . 1064 eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ 1066 The UTF-8 representation of the JWS Signing Input is the following 1067 byte array: 1069 [101, 121, 74, 104, 98, 71, 99, 105, 79, 105, 74, 83, 85, 122, 73, 1070 49, 78, 105, 74, 57, 46, 101, 121, 74, 112, 99, 51, 77, 105, 79, 105, 1071 74, 113, 98, 50, 85, 105, 76, 65, 48, 75, 73, 67, 74, 108, 101, 72, 1072 65, 105, 79, 106, 69, 122, 77, 68, 65, 52, 77, 84, 107, 122, 79, 68, 1073 65, 115, 68, 81, 111, 103, 73, 109, 104, 48, 100, 72, 65, 54, 76, 1074 121, 57, 108, 101, 71, 70, 116, 99, 71, 120, 108, 76, 109, 78, 118, 1075 98, 83, 57, 112, 99, 49, 57, 121, 98, 50, 57, 48, 73, 106, 112, 48, 1076 99, 110, 86, 108, 102, 81] 1078 The RSA key consists of a public part (n, e), and a private exponent 1079 d. The values of the RSA key used in this example, presented as the 1080 byte arrays representing big endian integers are: 1082 +-----------+-------------------------------------------------------+ 1083 | Parameter | Value | 1084 | Name | | 1085 +-----------+-------------------------------------------------------+ 1086 | n | [161, 248, 22, 10, 226, 227, 201, 180, 101, 206, 141, | 1087 | | 45, 101, 98, 99, 54, 43, 146, 125, 190, 41, 225, 240, | 1088 | | 36, 119, 252, 22, 37, 204, 144, 161, 54, 227, 139, | 1089 | | 217, 52, 151, 197, 182, 234, 99, 221, 119, 17, 230, | 1090 | | 124, 116, 41, 249, 86, 176, 251, 138, 143, 8, 154, | 1091 | | 220, 75, 105, 137, 60, 193, 51, 63, 83, 237, 208, 25, | 1092 | | 184, 119, 132, 37, 47, 236, 145, 79, 228, 133, 119, | 1093 | | 105, 89, 75, 234, 66, 128, 211, 44, 15, 85, 191, 98, | 1094 | | 148, 79, 19, 3, 150, 188, 110, 155, 223, 110, 189, | 1095 | | 210, 189, 163, 103, 142, 236, 160, 198, 104, 247, 1, | 1096 | | 179, 141, 191, 251, 56, 200, 52, 44, 226, 254, 109, | 1097 | | 39, 250, 222, 74, 90, 72, 116, 151, 157, 212, 185, | 1098 | | 207, 154, 222, 196, 199, 91, 5, 133, 44, 44, 15, 94, | 1099 | | 248, 165, 193, 117, 3, 146, 249, 68, 232, 237, 100, | 1100 | | 193, 16, 198, 182, 71, 96, 154, 164, 120, 58, 235, | 1101 | | 156, 108, 154, 215, 85, 49, 48, 80, 99, 139, 131, | 1102 | | 102, 92, 111, 111, 122, 130, 163, 150, 112, 42, 31, | 1103 | | 100, 27, 130, 211, 235, 242, 57, 34, 25, 73, 31, 182, | 1104 | | 134, 135, 44, 87, 22, 245, 10, 248, 53, 141, 154, | 1105 | | 139, 157, 23, 195, 64, 114, 143, 127, 135, 216, 154, | 1106 | | 24, 216, 252, 171, 103, 173, 132, 89, 12, 46, 207, | 1107 | | 117, 147, 57, 54, 60, 7, 3, 77, 111, 96, 111, 158, | 1108 | | 33, 224, 84, 86, 202, 229, 233, 161] | 1109 | e | [1, 0, 1] | 1110 | d | [18, 174, 113, 164, 105, 205, 10, 43, 195, 126, 82, | 1111 | | 108, 69, 0, 87, 31, 29, 97, 117, 29, 100, 233, 73, | 1112 | | 112, 123, 98, 89, 15, 157, 11, 165, 124, 150, 60, 64, | 1113 | | 30, 63, 207, 47, 44, 211, 189, 236, 136, 229, 3, 191, | 1114 | | 198, 67, 155, 11, 40, 200, 47, 125, 55, 151, 103, 31, | 1115 | | 82, 19, 238, 216, 193, 90, 37, 216, 213, 206, 160, 2, | 1116 | | 94, 227, 171, 46, 139, 127, 121, 33, 111, 198, 59, | 1117 | | 234, 86, 39, 83, 180, 6, 68, 198, 161, 81, 39, 217, | 1118 | | 178, 149, 69, 64, 160, 187, 225, 163, 5, 86, 152, 45, | 1119 | | 78, 159, 222, 95, 100, 37, 241, 77, 75, 113, 52, 65, | 1120 | | 181, 93, 199, 59, 155, 74, 237, 204, 146, 172, 227, | 1121 | | 146, 126, 55, 245, 125, 12, 253, 94, 117, 129, 250, | 1122 | | 81, 44, 143, 73, 97, 169, 235, 11, 128, 248, 168, 7, | 1123 | | 70, 114, 138, 85, 255, 70, 71, 31, 52, 37, 6, 59, | 1124 | | 157, 83, 100, 47, 94, 222, 30, 132, 214, 19, 8, 26, | 1125 | | 250, 92, 34, 208, 81, 40, 91, 214, 59, 148, 59, 86, | 1126 | | 93, 137, 138, 5, 104, 84, 19, 229, 60, 60, 108, 101, | 1127 | | 37, 255, 31, 227, 78, 61, 220, 112, 240, 213, 100, | 1128 | | 80, 253, 164, 139, 161, 46, 16, 78, 157, 235, 159, | 1129 | | 184, 24, 129, 225, 196, 189, 242, 93, 146, 71, 244, | 1130 | | 80, 200, 101, 146, 121, 104, 231, 115, 52, 244, 65, | 1131 | | 79, 117, 167, 80, 225, 57, 84, 110, 58, 138, 115, | 1132 | | 157] | 1133 +-----------+-------------------------------------------------------+ 1135 The RSA private key (n, d) is then passed to the RSA signing 1136 function, which also takes the hash type, SHA-256, and the UTF-8 1137 representation of the JWS Signing Input as inputs. The result of the 1138 signature is a byte array S, which represents a big endian integer. 1139 In this example, S is: 1141 +--------+----------------------------------------------------------+ 1142 | Result | Value | 1143 | Name | | 1144 +--------+----------------------------------------------------------+ 1145 | S | [112, 46, 33, 137, 67, 232, 143, 209, 30, 181, 216, 45, | 1146 | | 191, 120, 69, 243, 65, 6, 174, 27, 129, 255, 247, 115, | 1147 | | 17, 22, 173, 209, 113, 125, 131, 101, 109, 66, 10, 253, | 1148 | | 60, 150, 238, 221, 115, 162, 102, 62, 81, 102, 104, 123, | 1149 | | 0, 11, 135, 34, 110, 1, 135, 237, 16, 115, 249, 69, 229, | 1150 | | 130, 173, 252, 239, 22, 216, 90, 121, 142, 232, 198, | 1151 | | 109, 219, 61, 184, 151, 91, 23, 208, 148, 2, 190, 237, | 1152 | | 213, 217, 217, 112, 7, 16, 141, 178, 129, 96, 213, 248, | 1153 | | 4, 12, 167, 68, 87, 98, 184, 31, 190, 127, 249, 217, 46, | 1154 | | 10, 231, 111, 36, 242, 91, 51, 187, 230, 244, 74, 230, | 1155 | | 30, 177, 4, 10, 203, 32, 4, 77, 62, 249, 18, 142, 212, | 1156 | | 1, 48, 121, 91, 212, 189, 59, 65, 238, 202, 208, 102, | 1157 | | 171, 101, 25, 129, 253, 228, 141, 247, 127, 55, 45, 195, | 1158 | | 139, 159, 175, 221, 59, 239, 177, 139, 93, 163, 204, 60, | 1159 | | 46, 176, 47, 158, 58, 65, 214, 18, 202, 173, 21, 145, | 1160 | | 18, 115, 160, 95, 35, 185, 232, 56, 250, 175, 132, 157, | 1161 | | 105, 132, 41, 239, 90, 30, 136, 121, 130, 54, 195, 212, | 1162 | | 14, 96, 69, 34, 165, 68, 200, 242, 122, 122, 45, 184, 6, | 1163 | | 99, 209, 108, 247, 202, 234, 86, 222, 64, 92, 178, 33, | 1164 | | 90, 69, 178, 194, 85, 102, 181, 90, 193, 167, 72, 160, | 1165 | | 112, 223, 200, 163, 42, 70, 149, 67, 208, 25, 238, 251, | 1166 | | 71] | 1167 +--------+----------------------------------------------------------+ 1169 Base64url encoding the signature produces this value for the Encoded 1170 JWS Signature: 1171 cC4hiUPoj9Eetdgtv3hF80EGrhuB__dzERat0XF9g2VtQgr9PJbu3XOiZj5RZmh7AAuHIm4Bh-0Qc_lF5YKt_O8W2Fp5jujGbds9uJdbF9CUAr7t1dnZcAcQjbKBYNX4BAynRFdiuB--f_nZLgrnbyTyWzO75vRK5h6xBArLIARNPvkSjtQBMHlb1L07Qe7K0GarZRmB_eSN9383LcOLn6_dO--xi12jzDwusC-eOkHWEsqtFZESc6BfI7noOPqvhJ1phCnvWh6IeYI2w9QOYEUipUTI8np6LbgGY9Fs98rqVt5AXLIhWkWywlVmtVrBp0igcN_IoypGlUPQGe77Rw 1173 A.2.2. Decoding 1175 Decoding the JWS from this example requires processing the Encoded 1176 JWS Header and Encoded JWS Payload exactly as done in the first 1177 example. 1179 A.2.3. Validating 1181 Since the "alg" parameter in the header is "RS256", we validate the 1182 RSA SHA-256 signature contained in the JWS Signature. If any of the 1183 validation steps fail, the signed content MUST be rejected. 1185 First, we validate that the JWS Header string is legal JSON. 1187 Validating the JWS Signature is a little different from the previous 1188 example. First, we base64url decode the Encoded JWS Signature to 1189 produce a signature S to check. We then pass (n, e), S and the UTF-8 1190 representation of the JWS Signing Input to an RSA signature verifier 1191 that has been configured to use the SHA-256 hash function. 1193 A.3. JWS using ECDSA P-256 SHA-256 1195 A.3.1. Encoding 1197 The JWS Header for this example differs from the previous example 1198 because a different algorithm is being used. The JWS Header used is: 1199 {"alg":"ES256"} 1201 The following byte array contains the UTF-8 characters for the JWS 1202 Header: 1204 [123, 34, 97, 108, 103, 34, 58, 34, 69, 83, 50, 53, 54, 34, 125] 1206 Base64url encoding this UTF-8 representation yields this Encoded JWS 1207 Header value: 1208 eyJhbGciOiJFUzI1NiJ9 1210 The JWS Payload used in this example, which follows, is the same as 1211 in the previous examples. Since the Encoded JWS Payload will 1212 therefore be the same, its computation is not repeated here. 1213 {"iss":"joe", 1214 "exp":1300819380, 1215 "http://example.com/is_root":true} 1217 Concatenating the Encoded JWS Header, a period character, and the 1218 Encoded JWS Payload yields this JWS Signing Input value (with line 1219 breaks for display purposes only): 1220 eyJhbGciOiJFUzI1NiJ9 1221 . 1222 eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ 1224 The UTF-8 representation of the JWS Signing Input is the following 1225 byte array: 1227 [101, 121, 74, 104, 98, 71, 99, 105, 79, 105, 74, 70, 85, 122, 73, 1228 49, 78, 105, 74, 57, 46, 101, 121, 74, 112, 99, 51, 77, 105, 79, 105, 1229 74, 113, 98, 50, 85, 105, 76, 65, 48, 75, 73, 67, 74, 108, 101, 72, 1230 65, 105, 79, 106, 69, 122, 77, 68, 65, 52, 77, 84, 107, 122, 79, 68, 1231 65, 115, 68, 81, 111, 103, 73, 109, 104, 48, 100, 72, 65, 54, 76, 1232 121, 57, 108, 101, 71, 70, 116, 99, 71, 120, 108, 76, 109, 78, 118, 1233 98, 83, 57, 112, 99, 49, 57, 121, 98, 50, 57, 48, 73, 106, 112, 48, 1234 99, 110, 86, 108, 102, 81] 1236 The ECDSA key consists of a public part, the EC point (x, y), and a 1237 private part d. The values of the ECDSA key used in this example, 1238 presented as the byte arrays representing big endian integers are: 1240 +-----------+-------------------------------------------------------+ 1241 | Parameter | Value | 1242 | Name | | 1243 +-----------+-------------------------------------------------------+ 1244 | x | [127, 205, 206, 39, 112, 246, 196, 93, 65, 131, 203, | 1245 | | 238, 111, 219, 75, 123, 88, 7, 51, 53, 123, 233, 239, | 1246 | | 19, 186, 207, 110, 60, 123, 209, 84, 69] | 1247 | y | [199, 241, 68, 205, 27, 189, 155, 126, 135, 44, 223, | 1248 | | 237, 185, 238, 185, 244, 179, 105, 93, 110, 169, 11, | 1249 | | 36, 173, 138, 70, 35, 40, 133, 136, 229, 173] | 1250 | d | [142, 155, 16, 158, 113, 144, 152, 191, 152, 4, 135, | 1251 | | 223, 31, 93, 119, 233, 203, 41, 96, 110, 190, 210, | 1252 | | 38, 59, 95, 87, 194, 19, 223, 132, 244, 178] | 1253 +-----------+-------------------------------------------------------+ 1255 The ECDSA private part d is then passed to an ECDSA signing function, 1256 which also takes the curve type, P-256, the hash type, SHA-256, and 1257 the UTF-8 representation of the JWS Signing Input as inputs. The 1258 result of the signature is the EC point (R, S), where R and S are 1259 unsigned integers. In this example, the R and S values, given as 1260 byte arrays representing big endian integers are: 1262 +--------+----------------------------------------------------------+ 1263 | Result | Value | 1264 | Name | | 1265 +--------+----------------------------------------------------------+ 1266 | R | [14, 209, 33, 83, 121, 99, 108, 72, 60, 47, 127, 21, 88, | 1267 | | 7, 212, 2, 163, 178, 40, 3, 58, 249, 124, 126, 23, 129, | 1268 | | 154, 195, 22, 158, 166, 101] | 1269 | S | [197, 10, 7, 211, 140, 60, 112, 229, 216, 241, 45, 175, | 1270 | | 8, 74, 84, 128, 166, 101, 144, 197, 242, 147, 80, 154, | 1271 | | 143, 63, 127, 138, 131, 163, 84, 213] | 1272 +--------+----------------------------------------------------------+ 1274 Concatenating the S array to the end of the R array and base64url 1275 encoding the result produces this value for the Encoded JWS 1276 Signature: 1277 DtEhU3ljbEg8L38VWAfUAqOyKAM6-Xx-F4GawxaepmXFCgfTjDxw5djxLa8ISlSApmWQxfKTUJqPP3-Kg6NU1Q 1279 A.3.2. Decoding 1281 Decoding the JWS from this example requires processing the Encoded 1282 JWS Header and Encoded JWS Payload exactly as done in the first 1283 example. 1285 A.3.3. Validating 1287 Since the "alg" parameter in the header is "ES256", we validate the 1288 ECDSA P-256 SHA-256 signature contained in the JWS Signature. If any 1289 of the validation steps fail, the signed content MUST be rejected. 1291 First, we validate that the JWS Header string is legal JSON. 1293 Validating the JWS Signature is a little different from the first 1294 example. First, we base64url decode the Encoded JWS Signature as in 1295 the previous examples but we then need to split the 64 member byte 1296 array that must result into two 32 byte arrays, the first R and the 1297 second S. We then pass (x, y), (R, S) and the UTF-8 representation of 1298 the JWS Signing Input to an ECDSA signature verifier that has been 1299 configured to use the P-256 curve with the SHA-256 hash function. 1301 As explained in Section 6.3, the use of the k value in ECDSA means 1302 that we cannot validate the correctness of the signature in the same 1303 way we validated the correctness of the HMAC. Instead, 1304 implementations MUST use an ECDSA validator to validate the 1305 signature. 1307 Appendix B. Algorithm Identifier Cross-Reference 1309 This appendix contains a table cross-referencing the "alg" values 1310 used in this specification with the equivalent identifiers used by 1311 other standards and software packages. See XML DSIG [RFC3275] and 1312 Java Cryptography Architecture [JCA] for more information about the 1313 names defined by those documents. 1315 +-------+-----+----------------------------+----------+-------------+ 1316 | Algor | JWS | XML DSIG | JCA | OID | 1317 | ithm | | | | | 1318 +-------+-----+----------------------------+----------+-------------+ 1319 | HMAC | HS2 | http://www.w3.org/2001/04/ | HmacSHA2 | 1.2.840.113 | 1320 | using | 56 | xmldsig-more#hmac-sha256 | 56 | 549.2.9 | 1321 | SHA-2 | | | | | 1322 | 56 | | | | | 1323 | hash | | | | | 1324 | algo | | | | | 1325 | rithm | | | | | 1326 | HMAC | HS3 | http://www.w3.org/2001/04/ | HmacSHA3 | 1.2.840.113 | 1327 | using | 84 | xmldsig-more#hmac-sha384 | 84 | 549.2.10 | 1328 | SHA-3 | | | | | 1329 | 84 | | | | | 1330 | hash | | | | | 1331 | algo | | | | | 1332 | rithm | | | | | 1333 | HMAC | HS5 | http://www.w3.org/2001/04/ | HmacSHA5 | 1.2.840.113 | 1334 | using | 12 | xmldsig-more#hmac-sha512 | 12 | 549.2.11 | 1335 | SHA-5 | | | | | 1336 | 12 | | | | | 1337 | hash | | | | | 1338 | algo | | | | | 1339 | rithm | | | | | 1340 | RSA | RS2 | http://www.w3.org/2001/04/ | SHA256wi | 1.2.840.113 | 1341 | using | 56 | xmldsig-more#rsa-sha256 | thRSA | 549.1.1.11 | 1342 | SHA-2 | | | | | 1343 | 56 | | | | | 1344 | hash | | | | | 1345 | algo | | | | | 1346 | rithm | | | | | 1347 | RSA | RS3 | http://www.w3.org/2001/04/ | SHA384wi | 1.2.840.113 | 1348 | using | 84 | xmldsig-more#rsa-sha384 | thRSA | 549.1.1.12 | 1349 | SHA-3 | | | | | 1350 | 84 | | | | | 1351 | hash | | | | | 1352 | algo | | | | | 1353 | rithm | | | | | 1354 | RSA | RS5 | http://www.w3.org/2001/04/ | SHA512wi | 1.2.840.113 | 1355 | using | 12 | xmldsig-more#rsa-sha512 | thRSA | 549.1.1.13 | 1356 | SHA-5 | | | | | 1357 | 12 | | | | | 1358 | hash | | | | | 1359 | algo | | | | | 1360 | rithm | | | | | 1361 | ECDSA | ES2 | http://www.w3.org/2001/04/ | SHA256wi | 1.2.840.100 | 1362 | using | 56 | xmldsig-more#ecdsa-sha256 | thECDSA | 45.3.1.7 | 1363 | P-256 | | | | | 1364 | curve | | | | | 1365 | and | | | | | 1366 | SHA-2 | | | | | 1367 | 56 | | | | | 1368 | hash | | | | | 1369 | algo | | | | | 1370 | rithm | | | | | 1371 | ECDSA | ES3 | http://www.w3.org/2001/04/ | SHA384wi | 1.3.132.0.3 | 1372 | using | 84 | xmldsig-more#ecdsa-sha384 | thECDSA | 4 | 1373 | P-384 | | | | | 1374 | curve | | | | | 1375 | and | | | | | 1376 | SHA-3 | | | | | 1377 | 84 | | | | | 1378 | hash | | | | | 1379 | algo | | | | | 1380 | rithm | | | | | 1381 | ECDSA | ES5 | http://www.w3.org/2001/04/ | SHA512wi | 1.3.132.0.3 | 1382 | using | 12 | xmldsig-more#ecdsa-sha512 | thECDSA | 5 | 1383 | P-521 | | | | | 1384 | curve | | | | | 1385 | and | | | | | 1386 | SHA-5 | | | | | 1387 | 12 | | | | | 1388 | hash | | | | | 1389 | algo | | | | | 1390 | rithm | | | | | 1391 +-------+-----+----------------------------+----------+-------------+ 1393 Table 4: Algorithm Identifier Cross-Reference 1395 Appendix C. Notes on implementing base64url encoding without padding 1397 This appendix describes how to implement base64url encoding and 1398 decoding functions without padding based upon standard base64 1399 encoding and decoding functions that do use padding. 1401 To be concrete, example C# code implementing these functions is shown 1402 below. Similar code could be used in other languages. 1404 static string base64urlencode(byte [] arg) 1405 { 1406 string s = Convert.ToBase64String(arg); // Standard base64 encoder 1407 s = s.Split('=')[0]; // Remove any trailing '='s 1408 s = s.Replace('+', '-'); // 62nd char of encoding 1409 s = s.Replace('/', '_'); // 63rd char of encoding 1410 return s; 1411 } 1413 static byte [] base64urldecode(string arg) 1414 { 1415 string s = arg; 1416 s = s.Replace('-', '+'); // 62nd char of encoding 1417 s = s.Replace('_', '/'); // 63rd char of encoding 1418 switch (s.Length % 4) // Pad with trailing '='s 1419 { 1420 case 0: break; // No pad chars in this case 1421 case 2: s += "=="; break; // Two pad chars 1422 case 3: s += "="; break; // One pad char 1423 default: throw new System.Exception( 1424 "Illegal base64url string!"); 1425 } 1426 return Convert.FromBase64String(s); // Standard base64 decoder 1427 } 1429 As per the example code above, the number of '=' padding characters 1430 that needs to be added to the end of a base64url encoded string 1431 without padding to turn it into one with padding is a deterministic 1432 function of the length of the encoded string. Specifically, if the 1433 length mod 4 is 0, no padding is added; if the length mod 4 is 2, two 1434 '=' padding characters are added; if the length mod 4 is 3, one '=' 1435 padding character is added; if the length mod 4 is 1, the input is 1436 malformed. 1438 An example correspondence between unencoded and encoded values 1439 follows. The byte sequence below encodes into the string below, 1440 which when decoded, reproduces the byte sequence. 1441 3 236 255 224 193 1442 A-z_4ME 1444 Appendix D. Acknowledgements 1446 Solutions for signing JSON content were previously explored by Magic 1447 Signatures [MagicSignatures], JSON Simple Sign [JSS], and Canvas 1448 Applications [CanvasApp], all of which influenced this draft. 1450 Appendix E. Document History 1452 -03 1454 o Simplified terminology to better match JWE, where the terms "JWS 1455 Header" and "Encoded JWS Header", are now used, for instance, 1456 rather than the previous terms "Decoded JWS Header Input" and "JWS 1457 Header Input". Likewise the terms "JWS Payload" and "JWS 1458 Signature" are now used, rather than "JWS Payload Input" and "JWS 1459 Crypto Output". 1461 o The "jku" and "x5u" URLs are now required to be absolute URLs. 1463 o Removed this unnecessary language from the "kid" description: 1464 "Omitting this parameter is equivalent to setting it to an empty 1465 string". 1467 o Changed StringAndURI to StringOrURI. 1469 -02 1471 o Reference the JSON Web Key (JWK) specification from the "jku" 1472 header parameter. 1474 -01 1476 o Changed RSA SHA-256 from MUST be supported to RECOMMENDED that it 1477 be supported. Rationale: Several people have objected to the 1478 requirement for implementing RSA SHA-256, some because they will 1479 only be using HMACs and symmetric keys, and others because they 1480 only want to use ECDSA when using asymmetric keys, either for 1481 security or key length reasons, or both. 1483 o Clarified that "x5u" is an HTTPS URL referencing a PEM-encoded 1484 certificate or certificate chain. 1486 o Clarified that the "alg" parameter value is case sensitive. 1488 o Changed "x5t" (x.509 certificate thumbprint) to use a SHA-1 hash, 1489 rather than a SHA-256 hash, for compatibility reasons. 1491 -00 1493 o Created first signature draft using content split from 1494 draft-jones-json-web-token-01. This split introduced no semantic 1495 changes. 1497 Authors' Addresses 1499 Michael B. Jones 1500 Microsoft 1502 Email: mbj@microsoft.com 1503 URI: http://self-issued.info/ 1505 Dirk Balfanz 1506 Google 1508 Email: balfanz@google.com 1510 John Bradley 1511 independent 1513 Email: ve7jtb@ve7jtb.com 1515 Yaron Y. Goland 1516 Microsoft 1518 Email: yarong@microsoft.com 1520 John Panzer 1521 Google 1523 Email: jpanzer@google.com 1525 Nat Sakimura 1526 Nomura Research Institute 1528 Email: n-sakimura@nri.co.jp 1530 Paul Tarjan 1531 Facebook 1533 Email: pt@fb.com