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

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 September 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.  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] (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 Signature (JWS) [JWS] (Jones, M., Bradley, J., and N. Sakimura, “JSON Web Signature (JWS),” March 2012.) using the jku (JSON Key URL) header parameter and in JSON Web Encryption (JWE) [JWE] (Jones, M., Rescorla, E., and J. Hildebrand, “JSON Web Encryption (JWE),” March 2012.) 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 (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),” March 2012.) 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 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

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] (National Institute of Standards and Technology, “Digital Signature Standard (DSS),” June 2009.) 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] (Jonsson, J. and B. Kaliski, “Public-Key Cryptography Standards (PKCS) #1: RSA Cryptography Specifications Version 2.1,” February 2003.) 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 (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., Bradley, J., and N. Sakimura, “JSON Web Signature (JWS),” March 2012.) 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:

• Consider how additional key families would be added.
• 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 (Panzer (editor), J., Laurie, B., and D. Balfanz, “Magic Signatures,” January 2011.) [MagicSignatures].

Appendix B.  Document History

-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