JSON Web Key (JWK)
draft-jones-json-web-key-03

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 June 13, 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
• 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 Elliptic Curve 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. 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 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 Signature (JWS) [JWS] using the jku (JSON Key URL) header parameter and in JSON Web Encryption (JWE) [JWE] using the jku (JSON Key URL) and epk (Ephemeral Public Key) header parameters.

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. The first specifies that the key is to be used for encryption. Both provide a Key ID for 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":
  [
    {"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 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 Elliptic Curve Keys

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

4.2.2. JWK Key Object Members for RSA Keys

JWKs can represent RSA [RFC3447] keys. In this case, the alg 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 [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:

• Write the Security Considerations section.

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 [MagicSignatures].

Appendix B. Document History

-03

• Use short names since JWK Key Object values are used as JWE Ephemeral Public Keys, and so compactness matters.
• Respect line length restrictions in examples.

-02

• Editorial changes to have this spec better match the JWT, JWS, and JWE specs. No normative changes.

-01

• Changed algorithm member value for Elliptic Curve keys from ECDSA to EC, since Elliptic Curve keys can be used with more algorithms than just the Elliptic Curve Digital Signature Algorithm (ECDSA).
• Added OPTIONAL use member to identify intended key usage, especially since the same Elliptic Curve key should not be used for both signing and encryption operations.

-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