JOSE Working Group                                              M. Jones
Internet-Draft                                                 Microsoft
Intended status: Standards Track                          March                            May 12, 2012
Expires: September November 13, 2012

                           JSON Web Key (JWK)
                    draft-ietf-jose-json-web-key-01
                    draft-ietf-jose-json-web-key-02

Abstract

   A JSON Web Key (JWK) is a JSON data structure that represents a
   public key.  This specification also defines a JSON Web Key Set (JWK
   Set) JSON data structure for representing a set of public keys. JWKs.
   Cryptographic algorithms and identifiers used with this specification
   are enumerated in the separate JSON Web Algorithms (JWA)
   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
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   This Internet-Draft will expire on September November 13, 2012.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Example JSON Web Key (JWK) Overview Set  . . . . . . . . . . . . . . . . . . 3
     3.1.  Example JWK . 3
   4.  JSON Web Key (JWK) Format . . . . . . . . . . . . . . . . . . . 4
     4.1.  "alg" (Algorithm Family) Parameter  . . . . 3
   4.  JWK Format . . . . . . . . 4
     4.2.  "use" (Key Use) Parameter . . . . . . . . . . . . . . . . . 5
     4.3.  "kid" (Key ID) Parameter  . 4
     4.1.  JWK Container Object Format . . . . . . . . . . . . . . . . 4
     4.2.  JWK 5
   5.  JSON Web Key Object Set (JWK Set) Format . . . . . . . . . . . . . . . . . . . 5
       4.2.1.  JWK Key Object Members for Elliptic Curve Keys  . . . . 5
       4.2.2.  JWK
     5.1.  "keys" (JSON Web Key Object Members for RSA Keys Set) Parameter . . . . . . . . . . 6
   5.  Base64url encoding as used by JWKs  . . . 5
   6.  IANA Considerations . . . . . . . . . . . 7
   6.  IANA Considerations . . . . . . . . . . . 6
     6.1.  JSON Web Key Set Parameters Registry  . . . . . . . . . . . 7 6
   7.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7 6
   8.  Open Issues and Things To Be Done (TBD) . . . . . . . . . . . . 7 6
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7 6
     9.1.  Normative References  . . . . . . . . . . . . . . . . . . . 7 6
     9.2.  Informative References  . . . . . . . . . . . . . . . . . . 8 7
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . . . 8 7
   Appendix B.  Document History . . . . . . . . . . . . . . . . . . . 8 7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 8

1.  Introduction

   A JSON Web Key (JWK) is a JSON data structure that represents a set
   of
   public keys key as a JSON object [RFC4627].  The JWK format is used to
   represent bare keys;  This specification also
   defines a JSON Web Key Set (JWK Set) JSON data structure for
   representing certificate chains is an explicit
   non-goal a set of JWKs.  Cryptographic algorithms and identifiers
   used with this specification. specification are enumerated in the separate JSON Web Keys
   Algorithms (JWA) [JWA] specification.

   Non-goals for this specification include representing private keys,
   representing symmetric keys, representing certificate chains,
   representing certified keys, and replacing X.509 certificates.

   JWKs are referenced used in the JSON Web Signature (JWS) [JWS] using the "jku" "jwk" (JSON Key URL) Web
   Key) header parameter and in the JSON Web Encryption (JWE) [JWE] using the "jku" "jwk"
   (JSON Key URL) Web Key) and "epk" (Ephemeral Public Key) header parameters.
   The resources referenced by the JWS "jku" (JWK Set URL) and JWE "jku"
   (JWK Set URL) header parameters contain JWK Sets.

2.  Terminology

   JSON Web Key (JWK)  A JSON data structure that represents a set of public keys.  A JWK consists of a single JWK Container Object that
      contains an array of JWK
      key.

   JSON Web Key Objects.

   JWK Container Object Set (JWK Set)  A JSON object that contains an array of JWK Key
      Objects
      JWKs as a member.

   JWK Key Object  A JSON object that represents a single public key.

   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 of [JWS] for notes on implementing base64url
      encoding without padding.)

3.  Example JSON Web Key (JWK) Overview

   It is sometimes useful to be able to reference public key
   representations, for instance, in order to verify the digital
   signature on content signed with the corresponding private key.  The
   JSON Web Key (JWK) data structure provides a convenient JSON
   representation for sets of public keys utilizing either the Elliptic
   Curve or RSA families of algorithms.

3.1.  Example JWK Set

   The following example JWK Set contains two public keys: keys represented as
   JWKs: one using an Elliptic Curve algorithm and a second one using an
   RSA algorithm.  The first specifies that the key is to be used for
   encryption.  Both provide a Key ID for key matching purposes.  In
   both cases, integers are represented using the base64url encoding of
   their big endian representations.  (Long lines are broken are for
   display purposes only.)
   {"jwk":
   {"keys":
     [
       {"alg":"EC",
        "crv":"P-256",
        "x":"MKBCTNIcKUSDii11ySs3526iDZ8AiTo7Tu6KPAqv7D4",
        "y":"4Etl6SRW2YiLUrN5vfvVHuhp7x8PxltmWWlbbM4IFyM",
        "use":"enc",
        "kid":"1"},

       {"alg":"RSA",
        "mod": "0vx7agoebGcQSuuPiLJXZptN9nndrQmbXEps2aiAFbWhM78LhWx
   4cbbfAAtVT86zwu1RK7aPFFxuhDR1L6tSoc_BJECPebWKRXjBZCiFV4n3oknjhMs
   tn64tZ_2W-5JsGY4Hc5n9yBXArwl93lqt7_RN5w6Cf0h4QyQ5v-65YGjQR0_FDW2
   QvzqY368QQMicAtaSqzs8KJZgnYb9c7d0zgdAZHzu6qMQvRL5hajrn1n91CbOpbI
   SD08qNLyrdkt-bFTWhAI4vMQFh6WeZu0fM4lFd2NcRwr3XPksINHaQ-G_xBniIqb
   w0Ls1jF44-csFCur-kEgU8awapJzKnqDKgw",
        "exp":"AQAB",
        "kid":"2011-04-29"}
     ]
   }

4.  JWK Format

   A JWK consists of a JWK Container Object, which is a  JSON object that
   contains an array of JWK Web Key Objects as a member.  This section
   specifies the format of these objects.

4.1.  JWK Container Object (JWK) Format

   A JWK Container Object JSON Web Key (JWK) is a JSON object containing a specific member.
   This member is:

   +--------+----------+-----------------------------------------------+
   | Member | members, as
   specified below.  Those members that are common to all key types are
   defined below.

   JWKs also require members that are specific to the particular key
   algorithm family to represent the key parameters.  These algorithm
   specific members are defined in Section 5 of the JSON     | Container Object Member Semantics             |
   | Name   | Value    |                                               |
   |        | Type     |                                               |
   +--------+----------+-----------------------------------------------+
   | jwk    | array    | Web Algorithms
   (JWA) [JWA] specification.

   The "jwk" member value contains an array of   |
   |        |          | names within a JWK Key Objects.  This MUST be unique; objects with duplicate
   member is REQUIRED.    |
   +--------+----------+-----------------------------------------------+

                        JWK Container Object Member names MUST be rejected.

   Additional members MAY be present in the JWK Container Object. JWK.  If present, they MUST
   be understood by implementations using that JWK.

4.2.  JWK Key Object Format

   A JWK Key Object is a JSON object containing specific members.  Those
   members that are common to all them.  Parameters for
   representing keys for additional algorithm families or additional key types are as follows:

   +--------+--------+-------------------------------------------------+
   | Member |
   properties SHOULD either be defined in the IANA JSON   | Web Key Object Member Semantics                     |
   | Name   | Value  |                                                 |
   |        | Type   |                                                 |
   +--------+--------+-------------------------------------------------+
   | alg    | string |
   Parameters registry [JWA] or be a URI that contains a collision
   resistant namespace.

4.1.  "alg" (Algorithm Family) Parameter

   The "alg" (algorithm family) member identifies the cryptographic   |
   |        |        |
   algorithm family used with the key.  Values     |
   |        |        |  A list of defined by this specification are "EC" and      |
   |        |        | "RSA". "alg" values
   is presented in Section 5.1 of the JSON Web Algorithms (JWA) [JWA]
   specification.  Specific additional members are         |
   |        |        | required to represent
   the key, depending upon   |
   |        |        | the "alg" value. algorithm family.  These members are
   specified in Section 5 of the JSON Web Algorithms (JWA) [JWA]
   specification.  The "alg" value is case       |
   |        |        | sensitive.  This member is REQUIRED.            |
   | use    | string |  Its value MUST be
   a string.

   "alg" values SHOULD either be defined in the IANA JSON Web Key
   Algorithm Families registry [JWA] or be a URI that contains a
   collision resistant namespace.

4.2.  "use" (Key Use) Parameter

   The "use" (key use) member identifies the intended use of |
   |        |        | the key.
   Values defined by this specification  |
   |        |        | are "sig" (signature) and "enc"
   (encryption).   |
   |        |        |  Other values MAY be used.  The "use" value is   |
   |        |        | case
   sensitive.  Its value MUST be a string.  This member is OPTIONAL.       |
   | kid    | string | The

4.3.  "kid" (Key ID) Parameter

   The "kid" (key ID) member can be used to match  |
   |        |        | a specific key.  This
   can be used, for          |
   |        |        | instance, to choose among a set of keys within  |
   |        |        | the
   JWK during key rollover.  The  When used with JWS or JWE, the "kid" value   |
   |        |        |
   MAY correspond be used to match a JWS or JWE "kid" header parameter value.  The       |
   |        |        |
   interpretation of the "kid" value is            |
   |        |        | unspecified.  Its value MUST be
   a string.  This member is OPTIONAL.          |
   +--------+--------+-------------------------------------------------+

                          JWK

5.  JSON Web Key Object Members Set (JWK Set) Format

   A JSON Web Key Set (JWK Set) is a JSON object that contains an array
   of JSON Web Key values as the value of its "keys" member.

   The member names within a JWK Set MUST be unique; objects with
   duplicate member names MUST be rejected.

   Additional members MAY be present in the JWK Key Object. Set. If present, they
   MUST be understood by implementations using that key.

4.2.1.  JWK Key Object Members them.  Parameters for Elliptic Curve Keys

   JWKs can represent Elliptic Curve [FIPS.186-3] keys.  In this case,
   the "alg" member value MUST be "EC".  Furthermore, these
   representing additional
   members MUST properties of JWK Sets SHOULD either be present:

   +--------+--------+-------------------------------------------------+
   | Member |
   defined in the IANA JSON   | Web Key Object Member Semantics                     |
   | Name   | Value  |                                                 |
   |        | Type   |                                                 |
   +--------+--------+-------------------------------------------------+
   | crv    | string | The "crv" member identifies the cryptographic   |
   |        |        | curve used with the key.  Values defined by     |
   |        |        | this specification are "P-256", "P-384" and     |
   |        |        | "P-521".  Additional "crv" values MAY Set Parameters registry Section 6.1
   or be used,  |
   |        |        | provided they are understood by implementations |
   |        |        | using a URI that Elliptic Curve key. contains a collision resistant namespace.

5.1.  "keys" (JSON Web Key Set) Parameter

   The "crv" value |
   |        |        | is case sensitive.                              |
   | x      | string | The "x" member contains the x coordinate for    |
   |        |        | the elliptic curve point.  It is represented as |
   |        |        | the base64url encoding of the coordinate's big  |
   |        |        | endian representation.                          |
   | y      | string | The "y" "keys" (JSON Web Key Set) member contains the y coordinate for    |
   |        |        | the elliptic curve point.  It is represented as |
   |        |        | the base64url encoding an array of the coordinate's big  |
   |        |        | endian representation.                          |
   +--------+--------+-------------------------------------------------+

                      Members for Elliptic Curve Keys

4.2.2.  JWK JSON
   Web Key Object Members for RSA Keys

   JWKs can represent RSA [RFC3447] keys.  In this case, the "alg" (JWK) values.  This member value MUST be "RSA".  Furthermore, these additional members
   MUST be present:

   +--------+--------+-------------------------------------------------+
   | Member | is REQUIRED.

6.  IANA Considerations

6.1.  JSON   | Web Key Object Member Semantics                     |
   | Name   | Value  |                                                 |
   |        | Type   |                                                 |
   +--------+--------+-------------------------------------------------+
   | mod    | string | The "mod" member contains Set Parameters Registry

   This specification establishes the modulus value IANA JSON Web Key Set Parameters
   registry for |
   |        |        | reserved JWK Set parameter names.  Inclusion in the RSA public key.  It
   registry is represented as the   |
   |        |        | base64url encoding of RFC Required in the value's big endian    |
   |        |        | representation.                                 |
   | exp    | string | RFC 5226 [RFC5226] sense.  The "exp" member contains the exponent value    |
   |        |        | for the RSA public key.  It is represented as   |
   |        |        |
   registry records the base64url encoding of reserved parameter name and a reference to the value's big       |
   |        |        | endian representation.                          |
   +--------+--------+-------------------------------------------------+

                           Members for RSA Keys

5.  Base64url encoding as used by JWKs

   JWKs make use of
   RFC that defines it.  This specification registers the base64url encoding as parameter
   names defined in RFC 4648
   [RFC4648].  As allowed by Section 3.2 of 5.

7.  Security Considerations

   A key is no more trustworthy than the RFC, method by which it was
   received.

   The security considerations in XML DSIG 2.0
   [W3C.CR-xmldsig-core2-20120124], about public key representations
   also apply to this specification
   mandates specification, other than those that base64url encoding when used with JWKs MUST NOT use
   padding.  Notes on implementing base64url encoding can be found in
   the JWS [JWS] specification.

6.  IANA Considerations

   No IANA actions are required by this specification.

7.  Security Considerations

   TBD XML
   specific.

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

   The following items remain to be done in this draft:

   o  Consider how additional key families would be added.

   o  Write the Security Considerations section.  (None at present)

9.  References

9.1.  Normative References

   [FIPS.186-3]
              National Institute of Standards and Technology, "Digital
              Signature Standard (DSS)", FIPS PUB 186-3, June 2009.

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

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

   [RFC3447]  Jonsson, J. and B. Kaliski, "Public-Key Cryptography
              Standards (PKCS) #1: RSA Cryptography Specifications
              Version 2.1", RFC 3447, February 2003.

   [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.

9.2.  Informative References

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

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

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

   [W3C.CR-xmldsig-core2-20120124]
              Eastlake, D., Reagle, J., Yiu, K., Solo, D., Datta, P.,
              Hirsch, F., Cantor, S., and T. Roessler, "XML Signature
              Syntax and Processing Version 2.0", World Wide Web
              Consortium CR CR-xmldsig-core2-20120124, January 2012,
              <http://www.w3.org/TR/2012/CR-xmldsig-core2-20120124>.

Appendix A.  Acknowledgements

   A JSON representation for RSA public keys was previously introduced
   in Magic Signatures [MagicSignatures].

Appendix B.  Document History

   -02

   o  Simplified JWK terminology to get replace the "JWK Key Object" and
      "JWK Container Object" terms with simply "JSON Web Key (JWK)" and
      "JSON Web Key Set (JWK Set)" and to eliminate potential confusion
      between single keys and sets of keys.  As part of this change, the
      top-level member name for a set of keys was changed from "jwk" to
      "keys".

   o  Clarified that values with duplicate member names MUST be
      rejected.

   o  Established JSON Web Key Set Parameters registry.

   o  Explicitly listed non-goals in the introduction.

   o  Moved algorithm-specific definitions from JWK to JWA.

   o  Reformatted to give each member definition its own section
      heading.

   -01

   o  Corrected the Magic Signatures reference.

   -00

   o  Created the initial IETF draft based upon
      draft-jones-json-web-key-03 with no normative changes.

Author's Address

   Michael B. Jones
   Microsoft

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