JSON Web Key (JWK)
draft-jones-json-web-key-00

Abstract

A JSON Web Key (JWK) is a JSON data structure that represents a set of public keys.

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.

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This Internet-Draft will expire on October 31, 2011.

Copyright Notice

Copyright (c) 2011 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.  JSON Web Key (JWK) Overview
    3.1.  Example JWK
4.  JWK Format
    4.1.  JWK Container Object Format
    4.2.  JWK Key Object Format
        4.2.1.  JWK Key Object Members for ECDSA Keys
        4.2.2.  JWK Key Object Members for RSA Keys
5.  Base64url encoding as used by JWKs
6.  IANA Considerations
7.  Security Considerations
8.  References
    8.1.  Normative References
    8.2.  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 set of public keys as a JSON object [RFC4627] (Crockford, D., “The application/json Media Type for JavaScript Object Notation (JSON),” July 2006.). The JWK format is used to represent bare keys; representing certificate chains is an explicit non-goal of this specification. JSON Web Keys are referenced in JSON Web Signatures (JWSs) [JWS] (Jones, M., Balfanz, D., Bradley, J., Goland, Y., Panzer, J., Sakimura, N., and P. Tarjan, “JSON Web Signature (JWS),” April 2011.) using the jku (JSON Key URL) header parameter.

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 Objects.

JWK Container Object

A JSON object that contains an array of JWK Key Objects 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 he 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 '=' padding characters omitted, as permitted by Section 3.2.

3.  JSON Web Key (JWK) Overview

It is sometimes useful to be able to reference public key representations, for instance, in order to verify the 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 ECDSA or RSA families of algorithms.

3.1.  Example JWK

The following example JWK contains two public keys: one using the ECDSA algorithm and a second one using the RSA algorithm. In both cases, integers are represented using the base64url encoding of their big endian representations.

{"keyvalues":
   [
     {"algorithm":"ECDSA",
      "curve":"P-256",
      "x":"MKBCTNIcKUSDii11ySs3526iDZ8AiTo7Tu6KPAqv7D4",
      "y":"4Etl6SRW2YiLUrN5vfvVHuhp7x8PxltmWWlbbM4IFyM",
      "keyid":"1"},

    {"algorithm":"RSA",
      "modulus": "0vx7agoebGcQSuuPiLJXZptN9nndrQmbXEps2aiAFbWhM78LhWx4cbbfAAtVT86zwu1RK7aPFFxuhDR1L6tSoc_BJECPebWKRXjBZCiFV4n3oknjhMstn64tZ_2W-5JsGY4Hc5n9yBXArwl93lqt7_RN5w6Cf0h4QyQ5v-65YGjQR0_FDW2QvzqY368QQMicAtaSqzs8KJZgnYb9c7d0zgdAZHzu6qMQvRL5hajrn1n91CbOpbISD08qNLyrdkt-bFTWhAI4vMQFh6WeZu0fM4lFd2NcRwr3XPksINHaQ-G_xBniIqbw0Ls1jF44-csFCur-kEgU8awapJzKnqDKgw",
      "exponent":"AQAB",
      "keyid":"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 Key Objects as a member. This section specifies the format of these objects.

4.1.  JWK Container Object Format

A JWK Container Object is a JSON object containing a specific member. This member is:

Additional members MAY be present in the JWK Container Object. 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 key types are as follows:

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

4.2.1.  JWK Key Object Members for ECDSA Keys

JWKs can represent Elliptic Curve Digital Signature Algorithm (ECDSA) [FIPS.186‑3] (National Institute of Standards and Technology, “Digital Signature Standard (DSS),” June 2009.) keys. In this case, the algorithm member value MUST be ECDSA. Furthermore, these additional members MUST be present:

4.2.2.  JWK Key Object Members for RSA Keys

JWKs can represent RSA [RFC3447] (Jonsson, J. and B. Kaliski, “Public-Key Cryptography Standards (PKCS) #1: RSA Cryptography Specifications Version 2.1,” February 2003.) keys. In this case, the algorithm member value MUST be RSA. Furthermore, these additional members MUST be present:

5.  Base64url encoding as used by JWKs

JWKs make use of the base64url encoding as defined in RFC 4648 (Josefsson, S., “The Base16, Base32, and Base64 Data Encodings,” October 2006.) [RFC4648]. As allowed by Section 3.2 of the RFC, this specification mandates that base64url encoding when used with JWKs MUST NOT use padding. Notes on implementing base64url encoding can be found in the JWS [JWS] (Jones, M., Balfanz, D., Bradley, J., Goland, Y., Panzer, J., Sakimura, N., and P. Tarjan, “JSON Web Signature (JWS),” April 2011.) specification.

6.  IANA Considerations

No IANA actions are required by this specification.

7.  Security Considerations

TBD

8.  References

8.1. Normative References

8.2. 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,” August 2010.) [MagicSignatures].

Appendix B.  Document History

-00

• Created first version based upon decisions made at the Internet Identity Workshop (IIW), as documented at http://self-issued.info/?p=390.

Author's Address