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JOSE Working Group                                              M. Jones
Internet-Draft                                                 Microsoft
Intended status: Standards Track                              J. Bradley
Expires: September 13, 2012                                  independent
                                                             N. Sakimura
                                               Nomura Research Institute
                                                          March 12, 2012


                        JSON Web Signature (JWS)
                 draft-ietf-jose-json-web-signature-01

Abstract

   JSON Web Signature (JWS) is a means of representing content secured
   with digital signatures or Hash-based Message Authentication Codes
   (HMACs) using JSON data structures.  Cryptographic algorithms and
   identifiers used with this specification are enumerated in the
   separate JSON Web Algorithms (JWA) specification.  Related encryption
   capabilities are described in the separate JSON Web Encryption (JWE)
   specification.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 13, 2012.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the



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   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.








































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  JSON Web Signature (JWS) Overview  . . . . . . . . . . . . . .  5
     3.1.  Example JWS  . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  JWS Header . . . . . . . . . . . . . . . . . . . . . . . . . .  6
     4.1.  Reserved Header Parameter Names  . . . . . . . . . . . . .  6
     4.2.  Public Header Parameter Names  . . . . . . . . . . . . . . 11
     4.3.  Private Header Parameter Names . . . . . . . . . . . . . . 11
   5.  Rules for Creating and Validating a JWS  . . . . . . . . . . . 11
   6.  Securing JWSs with Cryptographic Algorithms  . . . . . . . . . 13
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 14
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 14
     8.1.  Unicode Comparison Security Issues . . . . . . . . . . . . 15
   9.  Open Issues and Things To Be Done (TBD)  . . . . . . . . . . . 15
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 16
     10.2. Informative References . . . . . . . . . . . . . . . . . . 18
   Appendix A.  JWS Examples  . . . . . . . . . . . . . . . . . . . . 18
     A.1.  JWS using HMAC SHA-256 . . . . . . . . . . . . . . . . . . 18
       A.1.1.  Encoding . . . . . . . . . . . . . . . . . . . . . . . 18
       A.1.2.  Decoding . . . . . . . . . . . . . . . . . . . . . . . 20
       A.1.3.  Validating . . . . . . . . . . . . . . . . . . . . . . 20
     A.2.  JWS using RSA SHA-256  . . . . . . . . . . . . . . . . . . 20
       A.2.1.  Encoding . . . . . . . . . . . . . . . . . . . . . . . 20
       A.2.2.  Decoding . . . . . . . . . . . . . . . . . . . . . . . 24
       A.2.3.  Validating . . . . . . . . . . . . . . . . . . . . . . 24
     A.3.  JWS using ECDSA P-256 SHA-256  . . . . . . . . . . . . . . 25
       A.3.1.  Encoding . . . . . . . . . . . . . . . . . . . . . . . 25
       A.3.2.  Decoding . . . . . . . . . . . . . . . . . . . . . . . 27
       A.3.3.  Validating . . . . . . . . . . . . . . . . . . . . . . 27
     A.4.  Example Plaintext JWS  . . . . . . . . . . . . . . . . . . 27
   Appendix B.  Notes on implementing base64url encoding without
                padding . . . . . . . . . . . . . . . . . . . . . . . 28
   Appendix C.  Acknowledgements  . . . . . . . . . . . . . . . . . . 29
   Appendix D.  Document History  . . . . . . . . . . . . . . . . . . 29
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 30













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1.  Introduction

   JSON Web Signature (JWS) is a compact format for representing content
   secured with digital signatures or Hash-based Message Authentication
   Codes (HMACs) intended for space constrained environments such as
   HTTP Authorization headers and URI query parameters.  It represents
   this content using JSON [RFC4627] data structures.  The JWS digital
   signature and HMAC mechanisms are independent of the type of content
   being secured, allowing arbitrary content to be secured.
   Cryptographic algorithms and identifiers used with this specification
   are enumerated in the separate JSON Web Algorithms (JWA) [JWA]
   specification.  Related encryption capabilities are described in the
   separate JSON Web Encryption (JWE) [JWE] specification.


2.  Terminology

   JSON Web Signature (JWS)  A data structure cryptographically securing
      a JWS Header and a JWS Payload with a JWS Signature value.

   JWS Header  A string representing a JSON object that describes the
      digital signature or HMAC applied to the JWS Header and the JWS
      Payload to create the JWS Signature value.

   JWS Payload  The bytes to be secured - a.k.a., the message.

   JWS Signature  A byte array containing the cryptographic material
      that secures the contents of the JWS Header and the JWS Payload.

   Encoded JWS Header  Base64url encoding of the bytes of the UTF-8 RFC
      3629 [RFC3629] representation of the JWS Header.

   Encoded JWS Payload  Base64url encoding of the JWS Payload.

   Encoded JWS Signature  Base64url encoding of the JWS Signature.

   JWS Secured Input  The concatenation of the Encoded JWS Header, a
      period ('.') character, and the Encoded JWS Payload.

   Header Parameter Names  The names of the members within the JSON
      object represented in a JWS Header.

   Header Parameter Values  The values of the members within the JSON
      object represented in a JWS Header.







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   JWS Compact Serialization  A representation of the JWS as the
      concatenation of the Encoded JWS Header, the Encoded JWS Payload,
      and the Encoded JWS Signature in that order, with the three
      strings being separated by period ('.') characters.

   Base64url Encoding  For the purposes of this specification, this term
      always refers to the URL- and filename-safe Base64 encoding
      described in RFC 4648 [RFC4648], Section 5, with the (non URL-
      safe) '=' padding characters omitted, as permitted by Section 3.2.
      (See Appendix B for notes on implementing base64url encoding
      without padding.)


3.  JSON Web Signature (JWS) Overview

   JWS represents digitally signed or HMACed content using JSON data
   structures and base64url encoding.  The representation consists of
   three parts: the JWS Header, the JWS Payload, and the JWS Signature.
   In the Compact Serialization, the three parts are base64url-encoded
   for transmission, and represented as the concatenation of the encoded
   strings in that order, with the three strings being separated by
   period ('.') characters.  (A JSON Serialization for this information
   is defined in the separate JSON Web Signature JSON Serialization
   (JWS-JS) [JWS-JS] specification.)

   The JWS Header describes the signature or HMAC method and parameters
   employed.  The JWS Payload is the message content to be secured.  The
   JWS Signature ensures the integrity of both the JWS Header and the
   JWS Payload.

3.1.  Example JWS

   The following example JWS Header declares that the encoded object is
   a JSON Web Token (JWT) [JWT] and the JWS Header and the JWS Payload
   are secured using the HMAC SHA-256 algorithm:
   {"typ":"JWT",
    "alg":"HS256"}

   Base64url encoding the bytes of the UTF-8 representation of the JWS
   Header yields this Encoded JWS Header value:
   eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9

   The following is an example of a JSON object that can be used as a
   JWS Payload.  (Note that the payload can be any content, and need not
   be a representation of a JSON object.)
   {"iss":"joe",
    "exp":1300819380,
    "http://example.com/is_root":true}



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   Base64url encoding the bytes of the UTF-8 representation of the JSON
   object yields the following Encoded JWS Payload (with line breaks for
   display purposes only):
   eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt
   cGxlLmNvbS9pc19yb290Ijp0cnVlfQ

   Computing the HMAC of the UTF-8 representation of the JWS Secured
   Input (the concatenation of the Encoded JWS Header, a period ('.')
   character, and the Encoded JWS Payload) with the HMAC SHA-256
   algorithm and base64url encoding the result, as per Appendix A.1,
   yields this Encoded JWS Signature value:
   dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk

   Concatenating these parts in the order Header.Payload.Signature with
   period characters between the parts yields this complete JWS
   representation (with line breaks for display purposes only):
   eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9
   .
   eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt
   cGxlLmNvbS9pc19yb290Ijp0cnVlfQ
   .
   dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk

   This computation is illustrated in more detail in Appendix A.1.


4.  JWS Header

   The members of the JSON object represented by the JWS Header describe
   the digital signature or HMAC applied to the Encoded JWS Header and
   the Encoded JWS Payload and optionally additional properties of the
   JWS.  The Header Parameter Names within this object MUST be unique.
   Implementations MUST understand the entire contents of the header;
   otherwise, the JWS MUST be rejected.

   The JWS Header MUST contain an "alg" (algorithm) parameter, the value
   of which is a string that unambiguously identifies the algorithm used
   to secure the JWS Header and the JWS Payload to produce the JWS
   Signature.

   There are three classes of Header Parameter Names: Reserved Header
   Parameter Names, Public Header Parameter Names, and Private Header
   Parameter Names.

4.1.  Reserved Header Parameter Names

   The following header parameter names are reserved.  All the names are
   short because a core goal of JWSs is for the representations to be



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   compact.

   +-----------+--------+----------------+-----------------------------+
   | Header    | JSON   | Header         | Header Parameter Semantics  |
   | Parameter | Value  | Parameter      |                             |
   | Name      | Type   | Syntax         |                             |
   +-----------+--------+----------------+-----------------------------+
   | alg       | string | StringOrURI    | The "alg" (algorithm)       |
   |           |        |                | header parameter identifies |
   |           |        |                | the cryptographic algorithm |
   |           |        |                | used to secure the JWS.  A  |
   |           |        |                | list of defined "alg"       |
   |           |        |                | values is presented in      |
   |           |        |                | Section 3, Table 1 of the   |
   |           |        |                | JSON Web Algorithms (JWA)   |
   |           |        |                | [JWA] specification.  The   |
   |           |        |                | processing of the "alg"     |
   |           |        |                | header parameter requires   |
   |           |        |                | that the value MUST be one  |
   |           |        |                | that is both supported and  |
   |           |        |                | for which there exists a    |
   |           |        |                | key for use with that       |
   |           |        |                | algorithm associated with   |
   |           |        |                | the party that digitally    |
   |           |        |                | signed or HMACed the        |
   |           |        |                | content.  The "alg"         |
   |           |        |                | parameter value is case     |
   |           |        |                | sensitive.  This header     |
   |           |        |                | parameter is REQUIRED.      |






















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   | jku       | string | URL            | The "jku" (JSON Web Key     |
   |           |        |                | URL) header parameter is an |
   |           |        |                | absolute URL that refers to |
   |           |        |                | a resource for a set of     |
   |           |        |                | JSON-encoded public keys,   |
   |           |        |                | one of which corresponds to |
   |           |        |                | the key that was used to    |
   |           |        |                | digitally sign the JWS.     |
   |           |        |                | The keys MUST be encoded as |
   |           |        |                | described in the JSON Web   |
   |           |        |                | Key (JWK) [JWK]             |
   |           |        |                | specification.  The         |
   |           |        |                | protocol used to acquire    |
   |           |        |                | the resource MUST provide   |
   |           |        |                | integrity protection.  An   |
   |           |        |                | HTTP GET request to         |
   |           |        |                | retrieve the certificate    |
   |           |        |                | MUST use TLS RFC 2818       |
   |           |        |                | [RFC2818] RFC 5246          |
   |           |        |                | [RFC5246] with server       |
   |           |        |                | authentication RFC 6125     |
   |           |        |                | [RFC6125].  This header     |
   |           |        |                | parameter is OPTIONAL.      |
   | kid       | string | String         | The "kid" (key ID) header   |
   |           |        |                | parameter is a hint         |
   |           |        |                | indicating which specific   |
   |           |        |                | key owned by the signer     |
   |           |        |                | should be used to validate  |
   |           |        |                | the digital signature.      |
   |           |        |                | This allows signers to      |
   |           |        |                | explicitly signal a change  |
   |           |        |                | of key to recipients.  The  |
   |           |        |                | interpretation of the       |
   |           |        |                | contents of the "kid"       |
   |           |        |                | parameter is unspecified.   |
   |           |        |                | This header parameter is    |
   |           |        |                | OPTIONAL.                   |
   | jpk       | object | JWK Key Object | The "jpk" (JSON Public Key) |
   |           |        |                | header parameter is a       |
   |           |        |                | public key that corresponds |
   |           |        |                | to the key that was used to |
   |           |        |                | digitally sign the JWS.     |
   |           |        |                | This key is represented in  |
   |           |        |                | the same manner as a JSON   |
   |           |        |                | Web Key [JWK] JWK Key       |
   |           |        |                | Object value.  This header  |
   |           |        |                | parameter is OPTIONAL.      |




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   | x5u       | string | URL            | The "x5u" (X.509 URL)       |
   |           |        |                | header parameter is an      |
   |           |        |                | absolute URL that refers to |
   |           |        |                | a resource for the X.509    |
   |           |        |                | public key certificate or   |
   |           |        |                | certificate chain           |
   |           |        |                | corresponding to the key    |
   |           |        |                | used to digitally sign the  |
   |           |        |                | JWS.  The identified        |
   |           |        |                | resource MUST provide a     |
   |           |        |                | representation of the       |
   |           |        |                | certificate or certificate  |
   |           |        |                | chain that conforms to RFC  |
   |           |        |                | 5280 [RFC5280] in PEM       |
   |           |        |                | encoded form RFC 1421       |
   |           |        |                | [RFC1421].  The certificate |
   |           |        |                | containing the public key   |
   |           |        |                | of the entity signing the   |
   |           |        |                | JWS MUST be the first       |
   |           |        |                | certificate.  This MAY be   |
   |           |        |                | followed by additional      |
   |           |        |                | certificates, with each     |
   |           |        |                | subsequent certificate      |
   |           |        |                | being the one used to       |
   |           |        |                | certify the previous one.   |
   |           |        |                | The protocol used to        |
   |           |        |                | acquire the resource MUST   |
   |           |        |                | provide integrity           |
   |           |        |                | protection.  An HTTP GET    |
   |           |        |                | request to retrieve the     |
   |           |        |                | certificate MUST use TLS    |
   |           |        |                | RFC 2818 [RFC2818] RFC 5246 |
   |           |        |                | [RFC5246] with server       |
   |           |        |                | authentication RFC 6125     |
   |           |        |                | [RFC6125].  This header     |
   |           |        |                | parameter is OPTIONAL.      |
   | x5t       | string | String         | The "x5t" (x.509            |
   |           |        |                | certificate thumbprint)     |
   |           |        |                | header parameter provides a |
   |           |        |                | base64url encoded SHA-1     |
   |           |        |                | thumbprint (a.k.a. digest)  |
   |           |        |                | of the DER encoding of an   |
   |           |        |                | X.509 certificate that can  |
   |           |        |                | be used to match the        |
   |           |        |                | certificate.  This header   |
   |           |        |                | parameter is OPTIONAL.      |





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   | x5c       | array  | ArrayOfStrings | The "x5c" (x.509            |
   |           |        |                | certificate chain) header   |
   |           |        |                | parameter contains the      |
   |           |        |                | X.509 public key            |
   |           |        |                | certificate or certificate  |
   |           |        |                | chain corresponding to the  |
   |           |        |                | key used to digitally sign  |
   |           |        |                | the JWS.  The certificate   |
   |           |        |                | or certificate chain is     |
   |           |        |                | represented as an array of  |
   |           |        |                | certificate values.  Each   |
   |           |        |                | value is a base64-encoded   |
   |           |        |                | (not base64url encoded)     |
   |           |        |                | DER/BER PKIX certificate    |
   |           |        |                | value.  The certificate     |
   |           |        |                | containing the public key   |
   |           |        |                | of the entity signing the   |
   |           |        |                | JWS MUST be the first       |
   |           |        |                | certificate.  This MAY be   |
   |           |        |                | followed by additional      |
   |           |        |                | certificates, with each     |
   |           |        |                | subsequent certificate      |
   |           |        |                | being the one used to       |
   |           |        |                | certify the previous one.   |
   |           |        |                | The recipient MUST verify   |
   |           |        |                | the certificate chain       |
   |           |        |                | according to [RFC5280] and  |
   |           |        |                | reject the JWS if any       |
   |           |        |                | validation failure occurs.  |
   |           |        |                | This header parameter is    |
   |           |        |                | OPTIONAL.                   |
   | typ       | string | String         | The "typ" (type) header     |
   |           |        |                | parameter is used to        |
   |           |        |                | declare the type of the     |
   |           |        |                | secured content.  The "typ" |
   |           |        |                | value is case sensitive.    |
   |           |        |                | This header parameter is    |
   |           |        |                | OPTIONAL.                   |
   +-----------+--------+----------------+-----------------------------+

              Table 1: Reserved Header Parameter Definitions

   Additional reserved header parameter names MAY be defined via the
   IANA JSON Web Signature Header Parameters registry, as per Section 7.
   The syntax values used above are defined as follows:






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   +----------------+--------------------------------------------------+
   | Syntax Name    | Syntax Definition                                |
   +----------------+--------------------------------------------------+
   | IntDate        | The number of seconds from 1970-01-01T0:0:0Z as  |
   |                | measured in UTC until the desired date/time.     |
   |                | See RFC 3339 [RFC3339] for details regarding     |
   |                | date/times in general and UTC in particular.     |
   | String         | Any string value MAY be used.                    |
   | StringOrURI    | Any string value MAY be used but a value         |
   |                | containing a ":" character MUST be a URI as      |
   |                | defined in RFC 3986 [RFC3986].                   |
   | URL            | A URL as defined in RFC 1738 [RFC1738].          |
   | ArrayOfStrings | An array of string values.                       |
   +----------------+--------------------------------------------------+

               Table 2: Header Parameter Syntax Definitions

4.2.  Public Header Parameter Names

   Additional header parameter names can be defined by those using JWSs.
   However, in order to prevent collisions, any new header parameter
   name or algorithm value SHOULD either be defined in the IANA JSON Web
   Signature Header Parameters registry or be defined as a URI that
   contains a collision resistant namespace.  In each case, the definer
   of the name or value needs to take reasonable precautions to make
   sure they are in control of the part of the namespace they use to
   define the header parameter name.

   New header parameters should be introduced sparingly since an
   implementation that does not understand a parameter MUST reject the
   JWS.

4.3.  Private Header Parameter Names

   A producer and consumer of a JWS may agree to any header parameter
   name that is not a Reserved Name Section 4.1 or a Public Name
   Section 4.2.  Unlike Public Names, these private names are subject to
   collision and should be used with caution.

   New header parameters should be introduced sparingly, as they can
   result in non-interoperable JWSs.


5.  Rules for Creating and Validating a JWS

   To create a JWS, one MUST perform these steps.  The order of the
   steps is not significant in cases where there are no dependencies
   between the inputs and outputs of the steps.



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   1.  Create the content to be used as the JWS Payload.

   2.  Base64url encode the bytes of the JWS Payload.  This encoding
       becomes the Encoded JWS Payload.

   3.  Create a JWS Header containing the desired set of header
       parameters.  Note that white space is explicitly allowed in the
       representation and no canonicalization need be performed before
       encoding.

   4.  Base64url encode the bytes of the UTF-8 representation of the JWS
       Header to create the Encoded JWS Header.

   5.  Compute the JWS Signature in the manner defined for the
       particular algorithm being used.  The JWS Secured Input is always
       the concatenation of the Encoded JWS Header, a period ('.')
       character, and the Encoded JWS Payload.  (Note that if the JWS
       represents a JWT, this corresponds to the portion of the JWT
       representation preceding the second period character.)  The "alg"
       (algorithm) header parameter MUST be present in the JSON Header,
       with the algorithm value accurately representing the algorithm
       used to construct the JWS Signature.

   6.  Base64url encode the representation of the JWS Signature to
       create the Encoded JWS Signature.

   7.  The three encoded parts, taken together, are the result.  The
       Compact Serialization of this result is the concatenation of the
       Encoded JWS Header, the Encoded JWS Payload, and the Encoded JWS
       Signature in that order, with the three strings being separated
       by period ('.') characters.

   When validating a JWS, the following steps MUST be taken.  The order
   of the steps is not significant in cases where there are no
   dependencies between the inputs and outputs of the steps.  If any of
   the listed steps fails, then the JWS MUST be rejected.

   1.  Parse the three parts of the input (which are separated by period
       characters when using the JWS Compact Serialization) into the
       Encoded JWS Header, the Encoded JWS Payload, and the Encoded JWS
       Signature.

   2.  The Encoded JWS Header MUST be successfully base64url decoded
       following the restriction given in this specification that no
       padding characters have been used.

   3.  The JWS Header MUST be completely valid JSON syntax conforming to
       RFC 4627 [RFC4627].



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   4.  The JWS Header MUST be validated to only include parameters and
       values whose syntax and semantics are both understood and
       supported.

   5.  The Encoded JWS Payload MUST be successfully base64url decoded
       following the restriction given in this specification that no
       padding characters have been used.

   6.  The Encoded JWS Signature MUST be successfully base64url decoded
       following the restriction given in this specification that no
       padding characters have been used.

   7.  The JWS Signature MUST be successfully validated against the JWS
       Secured Input (the concatenation of the Encoded JWS Header, a
       period ('.') character, and the Encoded JWS Payload) in the
       manner defined for the algorithm being used, which MUST be
       accurately represented by the value of the "alg" (algorithm)
       header parameter, which MUST be present.

   Processing a JWS inevitably requires comparing known strings to
   values in the header.  For example, in checking what the algorithm
   is, the Unicode string encoding "alg" will be checked against the
   member names in the JWS Header to see if there is a matching header
   parameter name.  A similar process occurs when determining if the
   value of the "alg" header parameter represents a supported algorithm.

   Comparisons between JSON strings and other Unicode strings MUST be
   performed as specified below:

   1.  Remove any JSON applied escaping to produce an array of Unicode
       code points.

   2.  Unicode Normalization [USA15] MUST NOT be applied at any point to
       either the JSON string or to the string it is to be compared
       against.

   3.  Comparisons between the two strings MUST be performed as a
       Unicode code point to code point equality comparison.


6.  Securing JWSs with Cryptographic Algorithms

   JWS uses cryptographic algorithms to digitally sign or HMAC the
   contents of the JWS Header and the JWS Payload.  The JSON Web
   Algorithms (JWA) [JWA] specification enumerates a set of
   cryptographic algorithms and identifiers to be used with this
   specification.  Specifically, Section 3, Table 1 enumerates a set of
   "alg" (algorithm) header parameter values intended for use this



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   specification.  It also describes the semantics and operations that
   are specific to these algorithms and algorithm families.

   Public keys employed for digital signing can be identified using the
   Header Parameter methods described in Section 4.1 or can be
   distributed using methods that are outside the scope of this
   specification.


7.  IANA Considerations

   This specification calls for:

   o  A new IANA registry entitled "JSON Web Signature Header
      Parameters" for reserved header parameter names is defined in
      Section 4.1.  Inclusion in the registry is RFC Required in the RFC
      5226 [RFC5226] sense for reserved JWS header parameter names that
      are intended to be interoperable between implementations.  The
      registry will just record the reserved header parameter name and a
      pointer to the RFC that defines it.  This specification defines
      inclusion of the header parameter names defined in Table 1.


8.  Security Considerations

   TBD: Lots of work to do here.  We need to remember to look into any
   issues relating to security and JSON parsing.  One wonders just how
   secure most JSON parsing libraries are.  Were they ever hardened for
   security scenarios?  If not, what kind of holes does that open up?
   Also, we need to walk through the JSON standard and see what kind of
   issues we have especially around comparison of names.  For instance,
   comparisons of header parameter names and other parameters must occur
   after they are unescaped.  Need to also put in text about: Importance
   of keeping secrets secret.  Rotating keys.  Strengths and weaknesses
   of the different algorithms.

   TBD: Need to put in text about why strict JSON validation is
   necessary.  Basically, that if malformed JSON is received then the
   intent of the sender is impossible to reliably discern.  One example
   of malformed JSON that MUST be rejected is an object in which the
   same member name occurs multiple times.

   TBD: Write security considerations about the implications of using a
   SHA-1 hash (for compatibility reasons) for the "x5t" (x.509
   certificate thumbprint).

   When utilizing TLS to retrieve information, the authority providing
   the resource MUST be authenticated and the information retrieved MUST



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   be free from modification.

8.1.  Unicode Comparison Security Issues

   Header parameter names in JWSs are Unicode strings.  For security
   reasons, the representations of these names must be compared verbatim
   after performing any escape processing (as per RFC 4627 [RFC4627],
   Section 2.5).

   This means, for instance, that these JSON strings must compare as
   being equal ("sig", "\u0073ig"), whereas these must all compare as
   being not equal to the first set or to each other ("SIG", "Sig",
   "si\u0047").

   JSON strings MAY contain characters outside the Unicode Basic
   Multilingual Plane.  For instance, the G clef character (U+1D11E) may
   be represented in a JSON string as "\uD834\uDD1E".  Ideally, JWS
   implementations SHOULD ensure that characters outside the Basic
   Multilingual Plane are preserved and compared correctly;
   alternatively, if this is not possible due to these characters
   exercising limitations present in the underlying JSON implementation,
   then input containing them MUST be rejected.


9.  Open Issues and Things To Be Done (TBD)

   The following items remain to be done in this draft:

   o  EDITORIAL: Give each header parameter definition its own section.
      This will let them appear in the index, will give space for
      examples when needed, and will get rid of the way-too-cramped
      tables.

   o  Describe the relationship between the JWS, JWE, and JWT header
      parameters.  In particular, point out that the set of "alg" values
      defined by each must be compatible and non-overlapping.

   o  Combine the JWS and JWE "alg" parameter registries and possibly
      also the header parameter registries.

   o  Clarify the intended use of the "typ" Header Parameter across the
      JWS, JWE, and JWT specifications.  Decide whether a registry of
      "typ" values is appropriate.

   o  Add normative text that requires rejecting headers in which member
      names occur multiple times, as apparently this is legal JSON.





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   o  Clarify the semantics of the "kid" (key ID) header parameter.
      Open issues include: What happens if a "kid" header is received
      with an unrecognized value?  Is that an error?  Should it be
      treated as if it's empty?  What happens if the header has a
      recognized value but the value doesn't match the key associated
      with that value, but it does match another key that is associated
      with the issuer?  Is that an error?

   o  Consider whether a key type parameter should also be introduced.

   o  It would be good to have a confirmation method element so it could
      be used with holder-of-key.

   o  EDITORIAL: Think about how to best describe the concept currently
      described as "the bytes of the UTF-8 representation of".  Possible
      terms to use instead of "bytes of" include "byte sequence", "octet
      series", and "octet sequence".  Also consider whether we want to
      add an overall clarifying statement somewhere in each spec
      something like "every place we say 'the UTF-8 representation of
      X', we mean 'the bytes of the UTF-8 representation of X'".  That
      would potentially allow us to omit the "the bytes of" part
      everywhere else.

   o  Write a note in the Security Considerations section about how
      "x5t" (x.509 certificate thumbprint) should be deprecated because
      of known problems with SHA-1.

   o  Add Security Considerations text on timing attacks.

   o  Finish the Security Considerations section.

   o  EDITORIAL: Add an example in which the payload is not a base64url
      encoded JSON object.


10.  References

10.1.  Normative References

   [JWA]      Jones, M., "JSON Web Algorithms (JWA)", March 2012.

   [JWK]      Jones, M., "JSON Web Key (JWK)", March 2012.

   [RFC1421]  Linn, J., "Privacy Enhancement for Internet Electronic
              Mail: Part I: Message Encryption and Authentication
              Procedures", RFC 1421, February 1993.

   [RFC1738]  Berners-Lee, T., Masinter, L., and M. McCahill, "Uniform



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              Resource Locators (URL)", RFC 1738, December 1994.

   [RFC2045]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part One: Format of Internet Message
              Bodies", RFC 2045, November 1996.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.

   [RFC3339]  Klyne, G., Ed. and C. Newman, "Date and Time on the
              Internet: Timestamps", RFC 3339, July 2002.

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, November 2003.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, January 2005.

   [RFC4627]  Crockford, D., "The application/json Media Type for
              JavaScript Object Notation (JSON)", RFC 4627, July 2006.

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, October 2006.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, May 2008.

   [RFC6125]  Saint-Andre, P. and J. Hodges, "Representation and
              Verification of Domain-Based Application Service Identity
              within Internet Public Key Infrastructure Using X.509
              (PKIX) Certificates in the Context of Transport Layer
              Security (TLS)", RFC 6125, March 2011.

   [USA15]    Davis, M., Whistler, K., and M. Duerst, "Unicode
              Normalization Forms", Unicode Standard Annex 15, 09 2009.




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10.2.  Informative References

   [CanvasApp]
              Facebook, "Canvas Applications", 2010.

   [JSS]      Bradley, J. and N. Sakimura (editor), "JSON Simple Sign",
              September 2010.

   [JWE]      Jones, M., Rescorla, E., and J. Hildebrand, "JSON Web
              Encryption (JWE)", March 2012.

   [JWS-JS]   Jones, M., Bradley, J., and N. Sakimura, "JSON Web
              Signature JSON Serialization (JWS-JS)", March 2012.

   [JWT]      Jones, M., Balfanz, D., Bradley, J., Goland, Y., Panzer,
              J., Sakimura, N., and P. Tarjan, "JSON Web Token (JWT)",
              March 2012.

   [MagicSignatures]
              Panzer (editor), J., Laurie, B., and D. Balfanz, "Magic
              Signatures", January 2011.


Appendix A.  JWS Examples

   This section provides several examples of JWSs.  While these examples
   all represent JSON Web Tokens (JWTs) [JWT], the payload can be any
   base64url encoded content.

A.1.  JWS using HMAC SHA-256

A.1.1.  Encoding

   The following example JWS Header declares that the data structure is
   a JSON Web Token (JWT) [JWT] and the JWS Secured Input is secured
   using the HMAC SHA-256 algorithm.
   {"typ":"JWT",
    "alg":"HS256"}

   The following byte array contains the UTF-8 characters for the JWS
   Header:

   [123, 34, 116, 121, 112, 34, 58, 34, 74, 87, 84, 34, 44, 13, 10, 32,
   34, 97, 108, 103, 34, 58, 34, 72, 83, 50, 53, 54, 34, 125]

   Base64url encoding this UTF-8 representation yields this Encoded JWS
   Header value:
   eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9



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   The JWS Payload used in this example follows.  (Note that the payload
   can be any base64url encoded content, and need not be a base64url
   encoded JSON object.)
   {"iss":"joe",
    "exp":1300819380,
    "http://example.com/is_root":true}

   The following byte array contains the UTF-8 characters for the JWS
   Payload:

   [123, 34, 105, 115, 115, 34, 58, 34, 106, 111, 101, 34, 44, 13, 10,
   32, 34, 101, 120, 112, 34, 58, 49, 51, 48, 48, 56, 49, 57, 51, 56,
   48, 44, 13, 10, 32, 34, 104, 116, 116, 112, 58, 47, 47, 101, 120, 97,
   109, 112, 108, 101, 46, 99, 111, 109, 47, 105, 115, 95, 114, 111,
   111, 116, 34, 58, 116, 114, 117, 101, 125]

   Base64url encoding the above yields the Encoded JWS Payload value
   (with line breaks for display purposes only):
   eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt
   cGxlLmNvbS9pc19yb290Ijp0cnVlfQ

   Concatenating the Encoded JWS Header, a period character, and the
   Encoded JWS Payload yields this JWS Secured Input value (with line
   breaks for display purposes only):
   eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9
   .
   eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt
   cGxlLmNvbS9pc19yb290Ijp0cnVlfQ

   The UTF-8 representation of the JWS Secured Input is the following
   byte array:

   [101, 121, 74, 48, 101, 88, 65, 105, 79, 105, 74, 75, 86, 49, 81,
   105, 76, 65, 48, 75, 73, 67, 74, 104, 98, 71, 99, 105, 79, 105, 74,
   73, 85, 122, 73, 49, 78, 105, 74, 57, 46, 101, 121, 74, 112, 99, 51,
   77, 105, 79, 105, 74, 113, 98, 50, 85, 105, 76, 65, 48, 75, 73, 67,
   74, 108, 101, 72, 65, 105, 79, 106, 69, 122, 77, 68, 65, 52, 77, 84,
   107, 122, 79, 68, 65, 115, 68, 81, 111, 103, 73, 109, 104, 48, 100,
   72, 65, 54, 76, 121, 57, 108, 101, 71, 70, 116, 99, 71, 120, 108, 76,
   109, 78, 118, 98, 83, 57, 112, 99, 49, 57, 121, 98, 50, 57, 48, 73,
   106, 112, 48, 99, 110, 86, 108, 102, 81]

   HMACs are generated using keys.  This example uses the key
   represented by the following byte array:

   [3, 35, 53, 75, 43, 15, 165, 188, 131, 126, 6, 101, 119, 123, 166,
   143, 90, 179, 40, 230, 240, 84, 201, 40, 169, 15, 132, 178, 210, 80,
   46, 191, 211, 251, 90, 146, 210, 6, 71, 239, 150, 138, 180, 195, 119,



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   98, 61, 34, 61, 46, 33, 114, 5, 46, 79, 8, 192, 205, 154, 245, 103,
   208, 128, 163]

   Running the HMAC SHA-256 algorithm on the UTF-8 representation of the
   JWS Secured Input with this key yields the following byte array:

   [116, 24, 223, 180, 151, 153, 224, 37, 79, 250, 96, 125, 216, 173,
   187, 186, 22, 212, 37, 77, 105, 214, 191, 240, 91, 88, 5, 88, 83,
   132, 141, 121]

   Base64url encoding the above HMAC output yields the Encoded JWS
   Signature value:
   dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk

A.1.2.  Decoding

   Decoding the JWS first requires removing the base64url encoding from
   the Encoded JWS Header, the Encoded JWS Payload, and the Encoded JWS
   Signature.  We base64url decode the inputs and turn them into the
   corresponding byte arrays.  We translate the header input byte array
   containing UTF-8 encoded characters into the JWS Header string.

A.1.3.  Validating

   Next we validate the decoded results.  Since the "alg" parameter in
   the header is "HS256", we validate the HMAC SHA-256 value contained
   in the JWS Signature.  If any of the validation steps fail, the JWS
   MUST be rejected.

   First, we validate that the JWS Header string is legal JSON.

   To validate the HMAC value, we repeat the previous process of using
   the correct key and the UTF-8 representation of the JWS Secured Input
   as input to a SHA-256 HMAC function and then taking the output and
   determining if it matches the JWS Signature.  If it matches exactly,
   the HMAC has been validated.

A.2.  JWS using RSA SHA-256

A.2.1.  Encoding

   The JWS Header in this example is different from the previous example
   in two ways: First, because a different algorithm is being used, the
   "alg" value is different.  Second, for illustration purposes only,
   the optional "typ" parameter is not used.  (This difference is not
   related to the algorithm employed.)  The JWS Header used is:
   {"alg":"RS256"}




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   The following byte array contains the UTF-8 characters for the JWS
   Header:

   [123, 34, 97, 108, 103, 34, 58, 34, 82, 83, 50, 53, 54, 34, 125]

   Base64url encoding this UTF-8 representation yields this Encoded JWS
   Header value:
   eyJhbGciOiJSUzI1NiJ9

   The JWS Payload used in this example, which follows, is the same as
   in the previous example.  Since the Encoded JWS Payload will
   therefore be the same, its computation is not repeated here.
   {"iss":"joe",
    "exp":1300819380,
    "http://example.com/is_root":true}

   Concatenating the Encoded JWS Header, a period character, and the
   Encoded JWS Payload yields this JWS Secured Input value (with line
   breaks for display purposes only):
   eyJhbGciOiJSUzI1NiJ9
   .
   eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt
   cGxlLmNvbS9pc19yb290Ijp0cnVlfQ

   The UTF-8 representation of the JWS Secured Input is the following
   byte array:

   [101, 121, 74, 104, 98, 71, 99, 105, 79, 105, 74, 83, 85, 122, 73,
   49, 78, 105, 74, 57, 46, 101, 121, 74, 112, 99, 51, 77, 105, 79, 105,
   74, 113, 98, 50, 85, 105, 76, 65, 48, 75, 73, 67, 74, 108, 101, 72,
   65, 105, 79, 106, 69, 122, 77, 68, 65, 52, 77, 84, 107, 122, 79, 68,
   65, 115, 68, 81, 111, 103, 73, 109, 104, 48, 100, 72, 65, 54, 76,
   121, 57, 108, 101, 71, 70, 116, 99, 71, 120, 108, 76, 109, 78, 118,
   98, 83, 57, 112, 99, 49, 57, 121, 98, 50, 57, 48, 73, 106, 112, 48,
   99, 110, 86, 108, 102, 81]

   The RSA key consists of a public part (n, e), and a private exponent
   d.  The values of the RSA key used in this example, presented as the
   byte arrays representing big endian integers are:












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   +-----------+-------------------------------------------------------+
   | Parameter | Value                                                 |
   | Name      |                                                       |
   +-----------+-------------------------------------------------------+
   | n         | [161, 248, 22, 10, 226, 227, 201, 180, 101, 206, 141, |
   |           | 45, 101, 98, 99, 54, 43, 146, 125, 190, 41, 225, 240, |
   |           | 36, 119, 252, 22, 37, 204, 144, 161, 54, 227, 139,    |
   |           | 217, 52, 151, 197, 182, 234, 99, 221, 119, 17, 230,   |
   |           | 124, 116, 41, 249, 86, 176, 251, 138, 143, 8, 154,    |
   |           | 220, 75, 105, 137, 60, 193, 51, 63, 83, 237, 208, 25, |
   |           | 184, 119, 132, 37, 47, 236, 145, 79, 228, 133, 119,   |
   |           | 105, 89, 75, 234, 66, 128, 211, 44, 15, 85, 191, 98,  |
   |           | 148, 79, 19, 3, 150, 188, 110, 155, 223, 110, 189,    |
   |           | 210, 189, 163, 103, 142, 236, 160, 198, 104, 247, 1,  |
   |           | 179, 141, 191, 251, 56, 200, 52, 44, 226, 254, 109,   |
   |           | 39, 250, 222, 74, 90, 72, 116, 151, 157, 212, 185,    |
   |           | 207, 154, 222, 196, 199, 91, 5, 133, 44, 44, 15, 94,  |
   |           | 248, 165, 193, 117, 3, 146, 249, 68, 232, 237, 100,   |
   |           | 193, 16, 198, 182, 71, 96, 154, 164, 120, 58, 235,    |
   |           | 156, 108, 154, 215, 85, 49, 48, 80, 99, 139, 131,     |
   |           | 102, 92, 111, 111, 122, 130, 163, 150, 112, 42, 31,   |
   |           | 100, 27, 130, 211, 235, 242, 57, 34, 25, 73, 31, 182, |
   |           | 134, 135, 44, 87, 22, 245, 10, 248, 53, 141, 154,     |
   |           | 139, 157, 23, 195, 64, 114, 143, 127, 135, 216, 154,  |
   |           | 24, 216, 252, 171, 103, 173, 132, 89, 12, 46, 207,    |
   |           | 117, 147, 57, 54, 60, 7, 3, 77, 111, 96, 111, 158,    |
   |           | 33, 224, 84, 86, 202, 229, 233, 161]                  |
   | e         | [1, 0, 1]                                             |























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   | d         | [18, 174, 113, 164, 105, 205, 10, 43, 195, 126, 82,   |
   |           | 108, 69, 0, 87, 31, 29, 97, 117, 29, 100, 233, 73,    |
   |           | 112, 123, 98, 89, 15, 157, 11, 165, 124, 150, 60, 64, |
   |           | 30, 63, 207, 47, 44, 211, 189, 236, 136, 229, 3, 191, |
   |           | 198, 67, 155, 11, 40, 200, 47, 125, 55, 151, 103, 31, |
   |           | 82, 19, 238, 216, 193, 90, 37, 216, 213, 206, 160, 2, |
   |           | 94, 227, 171, 46, 139, 127, 121, 33, 111, 198, 59,    |
   |           | 234, 86, 39, 83, 180, 6, 68, 198, 161, 81, 39, 217,   |
   |           | 178, 149, 69, 64, 160, 187, 225, 163, 5, 86, 152, 45, |
   |           | 78, 159, 222, 95, 100, 37, 241, 77, 75, 113, 52, 65,  |
   |           | 181, 93, 199, 59, 155, 74, 237, 204, 146, 172, 227,   |
   |           | 146, 126, 55, 245, 125, 12, 253, 94, 117, 129, 250,   |
   |           | 81, 44, 143, 73, 97, 169, 235, 11, 128, 248, 168, 7,  |
   |           | 70, 114, 138, 85, 255, 70, 71, 31, 52, 37, 6, 59,     |
   |           | 157, 83, 100, 47, 94, 222, 30, 132, 214, 19, 8, 26,   |
   |           | 250, 92, 34, 208, 81, 40, 91, 214, 59, 148, 59, 86,   |
   |           | 93, 137, 138, 5, 104, 84, 19, 229, 60, 60, 108, 101,  |
   |           | 37, 255, 31, 227, 78, 61, 220, 112, 240, 213, 100,    |
   |           | 80, 253, 164, 139, 161, 46, 16, 78, 157, 235, 159,    |
   |           | 184, 24, 129, 225, 196, 189, 242, 93, 146, 71, 244,   |
   |           | 80, 200, 101, 146, 121, 104, 231, 115, 52, 244, 65,   |
   |           | 79, 117, 167, 80, 225, 57, 84, 110, 58, 138, 115,     |
   |           | 157]                                                  |
   +-----------+-------------------------------------------------------+

   The RSA private key (n, d) is then passed to the RSA signing
   function, which also takes the hash type, SHA-256, and the UTF-8
   representation of the JWS Secured Input as inputs.  The result of the
   digital signature is a byte array S, which represents a big endian
   integer.  In this example, S is:





















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   +--------+----------------------------------------------------------+
   | Result | Value                                                    |
   | Name   |                                                          |
   +--------+----------------------------------------------------------+
   | S      | [112, 46, 33, 137, 67, 232, 143, 209, 30, 181, 216, 45,  |
   |        | 191, 120, 69, 243, 65, 6, 174, 27, 129, 255, 247, 115,   |
   |        | 17, 22, 173, 209, 113, 125, 131, 101, 109, 66, 10, 253,  |
   |        | 60, 150, 238, 221, 115, 162, 102, 62, 81, 102, 104, 123, |
   |        | 0, 11, 135, 34, 110, 1, 135, 237, 16, 115, 249, 69, 229, |
   |        | 130, 173, 252, 239, 22, 216, 90, 121, 142, 232, 198,     |
   |        | 109, 219, 61, 184, 151, 91, 23, 208, 148, 2, 190, 237,   |
   |        | 213, 217, 217, 112, 7, 16, 141, 178, 129, 96, 213, 248,  |
   |        | 4, 12, 167, 68, 87, 98, 184, 31, 190, 127, 249, 217, 46, |
   |        | 10, 231, 111, 36, 242, 91, 51, 187, 230, 244, 74, 230,   |
   |        | 30, 177, 4, 10, 203, 32, 4, 77, 62, 249, 18, 142, 212,   |
   |        | 1, 48, 121, 91, 212, 189, 59, 65, 238, 202, 208, 102,    |
   |        | 171, 101, 25, 129, 253, 228, 141, 247, 127, 55, 45, 195, |
   |        | 139, 159, 175, 221, 59, 239, 177, 139, 93, 163, 204, 60, |
   |        | 46, 176, 47, 158, 58, 65, 214, 18, 202, 173, 21, 145,    |
   |        | 18, 115, 160, 95, 35, 185, 232, 56, 250, 175, 132, 157,  |
   |        | 105, 132, 41, 239, 90, 30, 136, 121, 130, 54, 195, 212,  |
   |        | 14, 96, 69, 34, 165, 68, 200, 242, 122, 122, 45, 184, 6, |
   |        | 99, 209, 108, 247, 202, 234, 86, 222, 64, 92, 178, 33,   |
   |        | 90, 69, 178, 194, 85, 102, 181, 90, 193, 167, 72, 160,   |
   |        | 112, 223, 200, 163, 42, 70, 149, 67, 208, 25, 238, 251,  |
   |        | 71]                                                      |
   +--------+----------------------------------------------------------+

   Base64url encoding the digital signature produces this value for the
   Encoded JWS Signature (with line breaks for display purposes only):
   cC4hiUPoj9Eetdgtv3hF80EGrhuB__dzERat0XF9g2VtQgr9PJbu3XOiZj5RZmh7
   AAuHIm4Bh-0Qc_lF5YKt_O8W2Fp5jujGbds9uJdbF9CUAr7t1dnZcAcQjbKBYNX4
   BAynRFdiuB--f_nZLgrnbyTyWzO75vRK5h6xBArLIARNPvkSjtQBMHlb1L07Qe7K
   0GarZRmB_eSN9383LcOLn6_dO--xi12jzDwusC-eOkHWEsqtFZESc6BfI7noOPqv
   hJ1phCnvWh6IeYI2w9QOYEUipUTI8np6LbgGY9Fs98rqVt5AXLIhWkWywlVmtVrB
   p0igcN_IoypGlUPQGe77Rw

A.2.2.  Decoding

   Decoding the JWS from this example requires processing the Encoded
   JWS Header and Encoded JWS Payload exactly as done in the first
   example.

A.2.3.  Validating

   Since the "alg" parameter in the header is "RS256", we validate the
   RSA SHA-256 digital signature contained in the JWS Signature.  If any
   of the validation steps fail, the JWS MUST be rejected.



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   First, we validate that the JWS Header string is legal JSON.

   Validating the JWS Signature is a little different from the previous
   example.  First, we base64url decode the Encoded JWS Signature to
   produce a digital signature S to check.  We then pass (n, e), S and
   the UTF-8 representation of the JWS Secured Input to an RSA signature
   verifier that has been configured to use the SHA-256 hash function.

A.3.  JWS using ECDSA P-256 SHA-256

A.3.1.  Encoding

   The JWS Header for this example differs from the previous example
   because a different algorithm is being used.  The JWS Header used is:
   {"alg":"ES256"}

   The following byte array contains the UTF-8 characters for the JWS
   Header:

   [123, 34, 97, 108, 103, 34, 58, 34, 69, 83, 50, 53, 54, 34, 125]

   Base64url encoding this UTF-8 representation yields this Encoded JWS
   Header value:
   eyJhbGciOiJFUzI1NiJ9

   The JWS Payload used in this example, which follows, is the same as
   in the previous examples.  Since the Encoded JWS Payload will
   therefore be the same, its computation is not repeated here.
   {"iss":"joe",
    "exp":1300819380,
    "http://example.com/is_root":true}

   Concatenating the Encoded JWS Header, a period character, and the
   Encoded JWS Payload yields this JWS Secured Input value (with line
   breaks for display purposes only):
   eyJhbGciOiJFUzI1NiJ9
   .
   eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt
   cGxlLmNvbS9pc19yb290Ijp0cnVlfQ

   The UTF-8 representation of the JWS Secured Input is the following
   byte array:

   [101, 121, 74, 104, 98, 71, 99, 105, 79, 105, 74, 70, 85, 122, 73,
   49, 78, 105, 74, 57, 46, 101, 121, 74, 112, 99, 51, 77, 105, 79, 105,
   74, 113, 98, 50, 85, 105, 76, 65, 48, 75, 73, 67, 74, 108, 101, 72,
   65, 105, 79, 106, 69, 122, 77, 68, 65, 52, 77, 84, 107, 122, 79, 68,
   65, 115, 68, 81, 111, 103, 73, 109, 104, 48, 100, 72, 65, 54, 76,



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   121, 57, 108, 101, 71, 70, 116, 99, 71, 120, 108, 76, 109, 78, 118,
   98, 83, 57, 112, 99, 49, 57, 121, 98, 50, 57, 48, 73, 106, 112, 48,
   99, 110, 86, 108, 102, 81]

   The ECDSA key consists of a public part, the EC point (x, y), and a
   private part d.  The values of the ECDSA key used in this example,
   presented as the byte arrays representing big endian integers are:

   +-----------+-------------------------------------------------------+
   | Parameter | Value                                                 |
   | Name      |                                                       |
   +-----------+-------------------------------------------------------+
   | x         | [127, 205, 206, 39, 112, 246, 196, 93, 65, 131, 203,  |
   |           | 238, 111, 219, 75, 123, 88, 7, 51, 53, 123, 233, 239, |
   |           | 19, 186, 207, 110, 60, 123, 209, 84, 69]              |
   | y         | [199, 241, 68, 205, 27, 189, 155, 126, 135, 44, 223,  |
   |           | 237, 185, 238, 185, 244, 179, 105, 93, 110, 169, 11,  |
   |           | 36, 173, 138, 70, 35, 40, 133, 136, 229, 173]         |
   | d         | [142, 155, 16, 158, 113, 144, 152, 191, 152, 4, 135,  |
   |           | 223, 31, 93, 119, 233, 203, 41, 96, 110, 190, 210,    |
   |           | 38, 59, 95, 87, 194, 19, 223, 132, 244, 178]          |
   +-----------+-------------------------------------------------------+

   The ECDSA private part d is then passed to an ECDSA signing function,
   which also takes the curve type, P-256, the hash type, SHA-256, and
   the UTF-8 representation of the JWS Secured Input as inputs.  The
   result of the digital signature is the EC point (R, S), where R and S
   are unsigned integers.  In this example, the R and S values, given as
   byte arrays representing big endian integers are:

   +--------+----------------------------------------------------------+
   | Result | Value                                                    |
   | Name   |                                                          |
   +--------+----------------------------------------------------------+
   | R      | [14, 209, 33, 83, 121, 99, 108, 72, 60, 47, 127, 21, 88, |
   |        | 7, 212, 2, 163, 178, 40, 3, 58, 249, 124, 126, 23, 129,  |
   |        | 154, 195, 22, 158, 166, 101]                             |
   | S      | [197, 10, 7, 211, 140, 60, 112, 229, 216, 241, 45, 175,  |
   |        | 8, 74, 84, 128, 166, 101, 144, 197, 242, 147, 80, 154,   |
   |        | 143, 63, 127, 138, 131, 163, 84, 213]                    |
   +--------+----------------------------------------------------------+

   Concatenating the S array to the end of the R array and base64url
   encoding the result produces this value for the Encoded JWS Signature
   (with line breaks for display purposes only):
   DtEhU3ljbEg8L38VWAfUAqOyKAM6-Xx-F4GawxaepmXFCgfTjDxw5djxLa8ISlSA
   pmWQxfKTUJqPP3-Kg6NU1Q




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A.3.2.  Decoding

   Decoding the JWS from this example requires processing the Encoded
   JWS Header and Encoded JWS Payload exactly as done in the first
   example.

A.3.3.  Validating

   Since the "alg" parameter in the header is "ES256", we validate the
   ECDSA P-256 SHA-256 digital signature contained in the JWS Signature.
   If any of the validation steps fail, the JWS MUST be rejected.

   First, we validate that the JWS Header string is legal JSON.

   Validating the JWS Signature is a little different from the first
   example.  First, we base64url decode the Encoded JWS Signature as in
   the previous examples but we then need to split the 64 member byte
   array that must result into two 32 byte arrays, the first R and the
   second S. We then pass (x, y), (R, S) and the UTF-8 representation of
   the JWS Secured Input to an ECDSA signature verifier that has been
   configured to use the P-256 curve with the SHA-256 hash function.

   As explained in Section 3.3 of the JSON Web Algorithms (JWA) [JWA]
   specification, the use of the k value in ECDSA means that we cannot
   validate the correctness of the digital signature in the same way we
   validated the correctness of the HMAC.  Instead, implementations MUST
   use an ECDSA validator to validate the digital signature.

A.4.  Example Plaintext JWS

   The following example JWS Header declares that the encoded object is
   a Plaintext JWS:
   {"alg":"none"}

   Base64url encoding the bytes of the UTF-8 representation of the JWS
   Header yields this Encoded JWS Header:
   eyJhbGciOiJub25lIn0

   The JWS Payload used in this example, which follows, is the same as
   in the previous examples.  Since the Encoded JWS Payload will
   therefore be the same, its computation is not repeated here.
   {"iss":"joe",
    "exp":1300819380,
    "http://example.com/is_root":true}

   The Encoded JWS Signature is the empty string.

   Concatenating these parts in the order Header.Payload.Signature with



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   period characters between the parts yields this complete JWS (with
   line breaks for display purposes only):
   eyJhbGciOiJub25lIn0
   .
   eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt
   cGxlLmNvbS9pc19yb290Ijp0cnVlfQ
   .


Appendix B.  Notes on implementing base64url encoding without padding

   This appendix describes how to implement base64url encoding and
   decoding functions without padding based upon standard base64
   encoding and decoding functions that do use padding.

   To be concrete, example C# code implementing these functions is shown
   below.  Similar code could be used in other languages.
   static string base64urlencode(byte [] arg)
   {
     string s = Convert.ToBase64String(arg); // Standard base64 encoder
     s = s.Split('=')[0]; // Remove any trailing '='s
     s = s.Replace('+', '-'); // 62nd char of encoding
     s = s.Replace('/', '_'); // 63rd char of encoding
     return s;
   }

   static byte [] base64urldecode(string arg)
   {
     string s = arg;
     s = s.Replace('-', '+'); // 62nd char of encoding
     s = s.Replace('_', '/'); // 63rd char of encoding
     switch (s.Length % 4) // Pad with trailing '='s
     {
       case 0: break; // No pad chars in this case
       case 2: s += "=="; break; // Two pad chars
       case 3: s += "="; break; // One pad char
       default: throw new System.Exception(
         "Illegal base64url string!");
     }
     return Convert.FromBase64String(s); // Standard base64 decoder
   }

   As per the example code above, the number of '=' padding characters
   that needs to be added to the end of a base64url encoded string
   without padding to turn it into one with padding is a deterministic
   function of the length of the encoded string.  Specifically, if the
   length mod 4 is 0, no padding is added; if the length mod 4 is 2, two
   '=' padding characters are added; if the length mod 4 is 3, one '='



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   padding character is added; if the length mod 4 is 1, the input is
   malformed.

   An example correspondence between unencoded and encoded values
   follows.  The byte sequence below encodes into the string below,
   which when decoded, reproduces the byte sequence.
   3 236 255 224 193
   A-z_4ME


Appendix C.  Acknowledgements

   Solutions for signing JSON content were previously explored by Magic
   Signatures [MagicSignatures], JSON Simple Sign [JSS], and Canvas
   Applications [CanvasApp], all of which influenced this draft.  Dirk
   Balfanz, Yaron Y. Goland, John Panzer, and Paul Tarjan all made
   significant contributions to the design of this specification.


Appendix D.  Document History

   -01

   o  Moved definition of Plaintext JWSs (using "alg":"none") here from
      the JWT specification since this functionality is likely to be
      useful in more contexts that just for JWTs.

   o  Added "jpk" and "x5c" header parameters for including JWK public
      keys and X.509 certificate chains directly in the header.

   o  Clarified that this specification is defining the JWS Compact
      Serialization.  Referenced the new JWS-JS spec, which defines the
      JWS JSON Serialization.

   o  Added text "New header parameters should be introduced sparingly
      since an implementation that does not understand a parameter MUST
      reject the JWS".

   o  Clarified that the order of the creation and validation steps is
      not significant in cases where there are no dependencies between
      the inputs and outputs of the steps.

   o  Changed "no canonicalization is performed" to "no canonicalization
      need be performed".

   o  Corrected the Magic Signatures reference.





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   o  Made other editorial improvements suggested by JOSE working group
      participants.

   -00

   o  Created the initial IETF draft based upon
      draft-jones-json-web-signature-04 with no normative changes.

   o  Changed terminology to no longer call both digital signatures and
      HMACs "signatures".


Authors' Addresses

   Michael B. Jones
   Microsoft

   Email: mbj@microsoft.com
   URI:   http://self-issued.info/


   John Bradley
   independent

   Email: ve7jtb@ve7jtb.com


   Nat Sakimura
   Nomura Research Institute

   Email: n-sakimura@nri.co.jp




















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