Network Working Group M.B. Jones
Internet-Draft Microsoft
Intended status: Standards Track October 31, 2011
Expires: May 03, 2012

JSON Web Key (JWK)
draft-jones-json-web-key-02

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 [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 May 03, 2012.

Copyright Notice

Copyright (c) 2011 IETF Trust and the persons identified as the 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.


Table of Contents

1. Introduction

A JSON Web Key (JWK) is a JSON data structure that represents a set of public keys as a JSON object [RFC4627]. 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] 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 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 C of [JWS] for notes on implementing base64url encoding without padding.)

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 Elliptic Curve or RSA families of algorithms.

3.1. Example JWK

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

{"keyvalues":
   [
     {"algorithm":"EC",
      "curve":"P-256",
      "x":"MKBCTNIcKUSDii11ySs3526iDZ8AiTo7Tu6KPAqv7D4",
      "y":"4Etl6SRW2YiLUrN5vfvVHuhp7x8PxltmWWlbbM4IFyM",
      "use":"encryption",
      "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:

JWK Container Object Member
Member Name JSON Value Type Container Object Member Semantics
keyvalues array The keyvalues member value contains an array of JWK Key Objects. This member is REQUIRED.

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:

JWK Key Object Members
Member Name JSON Value Type Key Object Member Semantics
algorithm string The algorithm member identifies the cryptographic algorithm family used with the key. Values defined by this specification are EC and RSA. Specific additional members are required to represent the key, depending upon the algorithm value. The algorithm value is case sensitive. This member is REQUIRED.
use string The use member identifies the intended use of the key. Values defined by this specification are signature and encryption. Other values MAY be used. The use value is case sensitive. This member is OPTIONAL.
keyid string The keyid (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 keyid value MAY correspond to a JWS kid value. The interpretation of the keyid value is unspecified. This member is OPTIONAL.

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 Elliptic Curve Keys

JWKs can represent Elliptic Curve [FIPS.186-3] keys. In this case, the algorithm member value MUST be EC. Furthermore, these additional members MUST be present:

Members for Elliptic Curve Keys
Member Name JSON Value Type Key Object Member Semantics
curve string The curve member identifies the cryptographic curve used with the key. Values defined by this specification are P-256, P-384 and P-521. Additional curve values MAY be used, provided they are understood by implementations using that Elliptic Curve key. The curve 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 member contains the y coordinate for the elliptic curve point. It is represented as the base64url encoding of the coordinate's big endian representation.

4.2.2. JWK Key Object Members for RSA Keys

JWKs can represent RSA [RFC3447] keys. In this case, the algorithm member value MUST be RSA. Furthermore, these additional members MUST be present:

Members for RSA Keys
Member Name JSON Value Type Key Object Member Semantics
modulus string The modulus member contains the modulus value for the RSA public key. It is represented as the base64url encoding of the value's big endian representation.
exponent string The exponent member contains the exponent value for the RSA public key. It is represented as the base64url encoding of the value's big endian representation.

5. Base64url encoding as used by JWKs

JWKs make use of the base64url encoding as defined in RFC 4648 [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] specification.

6. IANA Considerations

No IANA actions are required by this specification.

7. Security Considerations

TBD

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

The following items remain to be done in this draft:

9. References

9.1. Normative References

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

9.2. Informative References

[MagicSignatures] Panzer (editor), J., Laurie, B. and D. Balfanz, "Magic Signatures", August 2010.
[JWS] Jones, M.B., Balfanz, D., Bradley, J., Goland, Y.Y., Panzer, J., Sakimura, N. and P. Tarjan, "JSON Web Signature (JWS)", October 2011.

Appendix A. Acknowledgements

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

Appendix B. Document History

-02

-01

-00

Author's Address

Michael B. Jones Microsoft EMail: mbj@microsoft.com URI: http://self-issued.info/