JOSE Working Group M.B. Jones
Internet-Draft Microsoft
Intended status: Standards Track July 6, 2012
Expires: January 05, 2013

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

Abstract

A JSON Web Key (JWK) is a JavaScript Object Notation (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 for use with this specification are described in the separate JSON Web Algorithms (JWA) specification.

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Table of Contents

1. Introduction

A JSON Web Key (JWK) is a JavaScript Object Notation (JSON) [RFC4627] 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 for use with this specification are described in the separate JSON Web Algorithms (JWA) [JWA] specification.

Goals for this specification do not include representing private keys, representing symmetric keys, representing certificate chains, representing certified keys, and replacing X.509 certificates.

JWKs and JWK Sets are used in the JSON Web Signature (JWS) [JWS] and JSON Web Encryption (JWE) [JWE] specifications.

1.1. Notational Conventions

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 Key words for use in RFCs to Indicate Requirement Levels [RFC2119].

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 [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.)
Collision Resistant Namespace
A namespace that allows names to be allocated in a manner such that they are highly unlikely to collide with other names. For instance, collision resistance can be achieved through administrative delegation of portions of the namespace or through use of collision-resistant name allocation functions. Examples of Collision Resistant Namespaces include: Domain Names, Object Identifiers (OIDs) as defined in the ITU-T X.660 and X.670 Recommendation series, and Universally Unique IDentifiers (UUIDs) [RFC4122]. When using an administratively delegated namespace, the definer of a name needs to take reasonable precautions to ensure they are in control of the portion of the namespace they use to define the name.

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.

A JWK also requires members that are specific to the particular kind of key to represent the key parameters. See Section 5 of the JSON Web Algorithms (JWA) [JWA] specification for definitions of the members specific to the kinds of keys defined there.

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. Member names for representing specific kinds of keys SHOULD either be registered in the IANA JSON Web Key Parameters registry Section 6.1 or be URIs that contain a Collision Resistant Namespace.

4.1. "alg" (Algorithm Family) Parameter

The alg (algorithm family) member identifies the cryptographic algorithm family used with the key. The alg value is case sensitive. Its value MUST be a string.

A list of defined alg values is presented in Section 5.1 of the JSON Web Algorithms (JWA) [JWA] specification. Additional members used with these alg values are defined in Sections 5.2 and 5.3 of the JSON Web Algorithms (JWA) [JWA] specification. alg values SHOULD either be registered in the IANA JSON Web Key Algorithm Families registry [JWA] 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: use value is case sensitive. Its value MUST be a string. This member is OPTIONAL.

Other values MAY be used. The

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. The interpretation of the kid value is unspecified. Key ID values within a JWK Set need not be unique; for instance, in some contexts different keys using the same Key ID value might be present, with the keys being disambiguated using other information, such as the alg or use values. The kid value is case sensitive. Its value MUST be a string. This member is OPTIONAL.

When used with JWS or JWE, the kid value MAY be used to match a JWS or JWE kid header parameter value.

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 registered in the IANA JSON Web Key Set Parameters registry Section 6.2 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

The following registration procedure is used for all the registries established by this specification.

Values are registered with a Specification Required [RFC5226] after a two week review period on the [TBD]@ietf.org mailing list, on the advice of one or more Designated Experts. However, to allow for the allocation of values prior to publication, the Designated Expert(s) may approve registration once they are satisfied that such a specification will be published.

Registration requests must be sent to the [TBD]@ietf.org mailing list for review and comment, with an appropriate subject (e.g., "Request for access token type: example"). [[ Note to RFC-EDITOR: The name of the mailing list should be determined in consultation with the IESG and IANA. Suggested name: jose-reg-review. ]]

Within the review period, the Designated Expert(s) will either approve or deny the registration request, communicating this decision to the review list and IANA. Denials should include an explanation and, if applicable, suggestions as to how to make the request successful.

IANA must only accept registry updates from the Designated Expert(s), and should direct all requests for registration to the review mailing list.

6.1. JSON Web Key Parameters Registry

This specification establishes the IANA JSON Web Key Parameters registry for reserved JWK parameter names. The registry records the reserved parameter name and a reference to the specification that defines it. This specification registers the parameter names defined in Section 4.

6.1.1. Registration Template

Parameter Name:

The name requested (e.g., "example").
Change Controller:

For standards-track RFCs, state "IETF". For others, give the name of the responsible party. Other details (e.g., postal address, e-mail address, home page URI) may also be included.
Specification Document(s):

Reference to the document that specifies the parameter, preferably including a URI that can be used to retrieve a copy of the document. An indication of the relevant sections may also be included, but is not required.

6.1.2. Initial Registry Contents

6.2. JSON Web Key Set Parameters Registry

This specification establishes the IANA JSON Web Key Set Parameters registry for reserved JWK Set parameter names. The registry records the reserved parameter name and a reference to the specification that defines it. This specification registers the parameter names defined in Section 5.

6.2.1. Registration Template

Parameter Name:

The name requested (e.g., "example").
Change Controller:

For standards-track RFCs, state "IETF". For others, give the name of the responsible party. Other details (e.g., postal address, e-mail address, home page URI) may also be included.
Specification Document(s):

Reference to the document that specifies the parameter, preferably including a URI that can be used to retrieve a copy of the document. An indication of the relevant sections may also be included, but is not required.

6.2.2. Initial Registry Contents

7. Security Considerations

All of the security issues faced by any cryptographic application must be faced by a JWS/JWE/JWK agent. Among these issues are protecting the user's private key, preventing various attacks, and helping the user avoid mistakes such as inadvertently encrypting a message for the wrong recipient. The entire list of security considerations is beyond the scope of this document, but some significant concerns are listed here.

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

Per Section 4.3, applications should not assume that kid values are unique within a JWK Set.

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

8. Open Issues

[[ to be removed by the RFC editor before publication as an RFC ]]

The following items remain to be considered or 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.
[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.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, May 2008.
[JWA] Jones, M.B., "JSON Web Algorithms (JWA)", July 2012.

9.2. Informative References

[RFC4122] Leach, P., Mealling, M. and R. Salz, "A Universally Unique IDentifier (UUID) URN Namespace", RFC 4122, July 2005.
[W3C.CR-xmldsig-core2-20120124] Reagle, J., Solo, D., Datta, P., Hirsch, F., Eastlake, D., Roessler, T., Cantor, S. and K. Yiu, "XML Signature Syntax and Processing Version 2.0", World Wide Web Consortium CR CR-xmldsig-core2-20120124, January 2012.
[MagicSignatures] Panzer (editor), J., Laurie, B. and D. Balfanz, "Magic Signatures", January 2011.
[JWS] Jones, M.B., Bradley, J. and N. Sakimura, "JSON Web Signature (JWS)", July 2012.
[JWE] Jones, M.B., Rescorla, E. and J. Hildebrand, "JSON Web Encryption (JWE)", July 2012.

Appendix A. Acknowledgements

A JSON representation for RSA public keys was previously introduced by John Panzer, Ben Laurie, and Dirk Balfanz in Magic Signatures [MagicSignatures].

Appendix B. Document History

[[ to be removed by the RFC editor before publication as an RFC ]]

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Author's Address

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