JSON Web Key (JWK)
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 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 (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.) [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/.

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

Copyright Notice

Copyright (c) 2012 IETF Trust and the persons identified as the document authors. All rights reserved.

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Table of Contents

1.  Introduction
2.  Terminology
3.  Example JSON Web Key Set
4.  JSON Web Key (JWK) Format
    4.1.  "alg" (Algorithm Family) Parameter
    4.2.  "use" (Key Use) Parameter
    4.3.  "kid" (Key ID) Parameter
5.  JSON Web Key Set (JWK Set) Format
    5.1.  "keys" (JSON Web Key Set) Parameter
6.  IANA Considerations
    6.1.  JSON Web Key Set Parameters Registry
7.  Security Considerations
8.  Open Issues and Things To Be Done (TBD)
9.  References
    9.1.  Normative References
    9.2.  Informative References
Appendix A.  Acknowledgements
Appendix B.  Document History
§  Author's Address

1.  Introduction

A JSON Web Key (JWK) is a JSON data structure that represents a public key as a JSON object [RFC4627] (Crockford, D., “The application/json Media Type for JavaScript Object Notation (JSON),” July 2006.). This specification also defines a JSON Web Key Set (JWK Set) JSON data structure for representing a set of JWKs. Cryptographic algorithms and identifiers used with this specification are enumerated in the separate JSON Web Algorithms (JWA) [JWA] (Jones, M., “JSON Web Algorithms (JWA),” May 2012.) 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 used in the JSON Web Signature (JWS) [JWS] (Jones, M., Bradley, J., and N. Sakimura, “JSON Web Signature (JWS),” May 2012.) jwk (JSON Web Key) header parameter and the JSON Web Encryption (JWE) [JWE] (Jones, M., Rescorla, E., and J. Hildebrand, “JSON Web Encryption (JWE),” May 2012.) jwk (JSON 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 public key.

JSON Web Key Set (JWK Set)

A JSON object that contains an array of JWKs as a member.

Base64url Encoding

For the purposes of this specification, this term always refers to the URL- and filename-safe Base64 encoding described in RFC 4648 (Josefsson, S., “The Base16, Base32, and Base64 Data Encodings,” October 2006.) [RFC4648], Section 5, with the (non URL-safe) '=' padding characters omitted, as permitted by Section 3.2. (See Appendix B of [JWS] (Jones, M., Bradley, J., and N. Sakimura, “JSON Web Signature (JWS),” May 2012.) for notes on implementing base64url encoding without padding.)

3.  Example JSON Web Key Set

The following example JWK Set contains two public 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.)

{"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.  JSON Web Key (JWK) Format

A JSON Web Key (JWK) is a JSON object containing specific 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 Web Algorithms (JWA) [JWA] (Jones, M., “JSON Web Algorithms (JWA),” May 2012.) specification.

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

Additional members MAY be present in the JWK. If present, they MUST be understood by implementations using them. Parameters for representing keys for additional algorithm families or additional key properties SHOULD either be defined in the IANA JSON Web Key Parameters registry [JWA] (Jones, M., “JSON Web Algorithms (JWA),” May 2012.) 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. A list of defined alg values is presented in Section 5.1 of the JSON Web Algorithms (JWA) [JWA] (Jones, M., “JSON Web Algorithms (JWA),” May 2012.) specification. Specific additional members are required to represent the key, depending upon the algorithm family. These members are specified in Section 5 of the JSON Web Algorithms (JWA) [JWA] (Jones, M., “JSON Web Algorithms (JWA),” May 2012.) specification. The alg value is case sensitive. Its value MUST be a string.

alg values SHOULD either be defined in the IANA JSON Web Key Algorithm Families registry [JWA] (Jones, M., “JSON Web Algorithms (JWA),” May 2012.) 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.

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. When used with JWS or JWE, the kid value MAY 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.

5.  JSON Web Key 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 Set. If present, they MUST be understood by implementations using them. Parameters for representing additional properties of JWK Sets SHOULD either be defined in the IANA JSON Web Key Set Parameters registry Section 6.1 (JSON Web Key Set Parameters Registry) or be a URI that contains a collision resistant namespace.

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

The value of the keys (JSON Web Key Set) member is an array of JSON Web Key (JWK) values. This member is REQUIRED.

6.  IANA Considerations

6.1.  JSON Web Key Set Parameters Registry

This specification establishes the IANA JSON Web Key Set Parameters registry for reserved JWK Set parameter names. Inclusion in the registry is RFC Required in the RFC 5226 (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” May 2008.) [RFC5226] sense. The registry records the reserved parameter name and a reference to the RFC that defines it. This specification registers the parameter names defined in Section 5 (JSON Web Key Set (JWK Set) Format).

7.  Security Considerations

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

The security considerations in XML DSIG 2.0 (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,” January 2012.) [W3C.CR‑xmldsig‑core2‑20120124], about public key representations also apply to this specification, other than those that are XML specific.

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

The following items remain to be done in this draft:

• (None at present)

9.  References

9.1. Normative References

9.2. Informative References

Appendix A.  Acknowledgements

A JSON representation for RSA public keys was previously introduced in Magic Signatures (Panzer (editor), J., Laurie, B., and D. Balfanz, “Magic Signatures,” January 2011.) [MagicSignatures].

Appendix B.  Document History

-02

• 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.
• Clarified that values with duplicate member names MUST be rejected.
• Established JSON Web Key Set Parameters registry.
• Explicitly listed non-goals in the introduction.
• Moved algorithm-specific definitions from JWK to JWA.
• Reformatted to give each member definition its own section heading.

-01

• Corrected the Magic Signatures reference.

-00

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

Author's Address