JOSE Working Group M.B. Jones
Internet-Draft Microsoft
Intended status: Standards Track April 26, 2013
Expires: October 28, 2013

JSON Web Key (JWK)
draft-ietf-jose-json-web-key-10

Abstract

A JSON Web Key (JWK) is a JavaScript Object Notation (JSON) data structure that represents a cryptographic 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 cryptographic 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 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 object that represents a cryptographic key.
JSON Web Key Set (JWK Set)
A JSON object that contains an array of JWKs as the value of its keys member.
Base64url Encoding
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. 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.

In addition to the common parameters, each JWK will have members that are specific to the kind of key being represented. These members represent the parameters of the key. Section 5 of the JSON Web Algorithms (JWA) [JWA] specification defines multiple kinds of cryptographic keys and their associated members.

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 not understood by implementations encountering them, they MUST be ignored. Member names used for representing key parameters for different kinds of keys need not be distinct. Any new member name SHOULD either be registered in the IANA JSON Web Key Parameters registry Section 6.1 or be a value that contains a Collision Resistant Namespace.

3.1. "kty" (Key Type) Parameter

The kty (key type) member identifies the cryptographic algorithm family used with the key. kty values SHOULD either be registered in the IANA JSON Web Key Types registry [JWA] or be a value that contains a Collision Resistant Namespace. The kty value is a case sensitive string. Use of this member is REQUIRED.

A list of defined kty values can be found in the IANA JSON Web Key Types registry [JWA]; the initial contents of this registry are the values defined in Section 5.1 of the JSON Web Algorithms (JWA) [JWA] specification.

Additional members used with these kty values can be found in the IANA JSON Web Key Parameters registry Section 6.1; the initial contents of this registry are the values defined in Sections 5.2 and 5.3 of the JSON Web Algorithms (JWA) [JWA] specification.

3.2. "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 a case sensitive string. Use of this member is OPTIONAL.

Other values MAY be used. The

3.3. "alg" (Algorithm) Parameter

The alg (algorithm) member identifies the algorithm intended for use with the key. The values used in this field are the same as those used in the JWS [JWS] and JWE [JWE] alg and enc header parameters; these values can be found in the JSON Web Signature and Encryption Algorithms registry [JWA]. Use of this member is OPTIONAL.

3.4. "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 a JWK Set during key rollover. The interpretation of the kid value is unspecified. Key ID values within a JWK Set need not be unique. The kid value is a case sensitive string. Use of this member is OPTIONAL.

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

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 kty or use values. For example, imagine kid values like "Current", "Upcoming", and "Deprecated", used for key rollover guidance. One could apply a label to all keys where the classification fits. If there are multiple "Current" keys, then in this example, they might be differentiated either by having different "kty" or "use" values, or some combination of both. As one example, there might only be one current RSA signing key and one current Elliptic Curve signing key, but both would be "Current".

4. 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 not understood by implementations encountering them, they MUST be ignored. 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 value that contains a Collision Resistant Namespace.

4.1. "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. Use of this member is REQUIRED.

5. String Comparison Rules

Processing a JWK inevitably requires comparing known strings to values in JSON objects. For example, in checking what the key type is, the Unicode string encoding kty will be checked against the member names in the JWK to see if there is a matching name.

Comparisons between JSON strings and other Unicode strings MUST be performed by comparing Unicode code points without normalization as specified in the String Comparison Rules in Section 5.3 of [JWS].

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 3. The same JWK parameter name may be registered multiple times, provided that duplicate parameter registrations are only for algorithm-specific JWK parameters; in this case, the meaning of the duplicate parameter name is disambiguated by the kty value of the JWK containing it.

6.1.1. Registration Template

Parameter Name:

The name requested (e.g., "example"). This name is case sensitive. Names that match other registered names in a case insensitive manner SHOULD NOT be accepted.
Change Controller:

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

Reference to the document(s) that specify the parameter, preferably including URI(s) that can be used to retrieve copies of the document(s). 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 4.

6.2.1. Registration Template

Parameter Name:

The name requested (e.g., "example"). This name is case sensitive. Names that match other registered names in a case insensitive manner SHOULD NOT be accepted.
Change Controller:

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

Reference to the document(s) that specify the parameter, preferably including URI(s) that can be used to retrieve copies of the document(s). 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 and symmetric keys, 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 considerations are listed here.

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

Private and symmetric keys must be protected from disclosure to unintended parties. One recommended means of doing so is to encrypt JWKs or JWK Sets containing them by using the JWK or JWK Set value as the plaintext of a JWE.

The security considerations in RFC 3447 [RFC3447] and RFC 6030 [RFC6030] about protecting private and symmetric keys also apply to this specification.

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

8. References

8.1. 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.
[W3C.CR-xmldsig-core2-20120124] Datta, P., Hirsch, F., Eastlake, D., Cantor, S., Roessler, T., Reagle, J., Yiu, K. and D. Solo, "XML Signature Syntax and Processing Version 2.0", World Wide Web Consortium CR CR-xmldsig-core2-20120124, January 2012.
[JWS] Jones, M.B., Bradley, J. and N. Sakimura, "JSON Web Signature (JWS)", Internet-Draft draft-ietf-jose-json-web-signature, April 2013.
[JWE] Jones, M.B., Rescorla, E. and J. Hildebrand, "JSON Web Encryption (JWE)", Internet-Draft draft-ietf-jose-json-web-encryption, April 2013.
[JWA] Jones, M.B., "JSON Web Algorithms (JWA)", Internet-Draft draft-ietf-jose-json-web-algorithms, April 2013.

8.2. Informative References

[RFC3447] Jonsson, J. and B. Kaliski, "Public-Key Cryptography Standards (PKCS) #1: RSA Cryptography Specifications Version 2.1", RFC 3447, February 2003.
[RFC4122] Leach, P., Mealling, M. and R. Salz, "A Universally Unique IDentifier (UUID) URN Namespace", RFC 4122, July 2005.
[RFC6030] Hoyer, P., Pei, M. and S. Machani, "Portable Symmetric Key Container (PSKC)", RFC 6030, October 2010.
[MagicSignatures] Panzer (editor), J., Laurie, B. and D. Balfanz, "Magic Signatures", January 2011.

Appendix A. Example JSON Web Key Sets

A.1. Example Public Keys

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. The second specifies that the key is to be used with the RS256 algorithm. 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":
    [
      {"kty":"EC",
       "crv":"P-256",
       "x":"MKBCTNIcKUSDii11ySs3526iDZ8AiTo7Tu6KPAqv7D4",
       "y":"4Etl6SRW2YiLUrN5vfvVHuhp7x8PxltmWWlbbM4IFyM",
       "use":"enc",
       "kid":"1"},

      {"kty":"RSA",
       "n": "0vx7agoebGcQSuuPiLJXZptN9nndrQmbXEps2aiAFbWhM78LhWx
  4cbbfAAtVT86zwu1RK7aPFFxuhDR1L6tSoc_BJECPebWKRXjBZCiFV4n3oknjhMs
  tn64tZ_2W-5JsGY4Hc5n9yBXArwl93lqt7_RN5w6Cf0h4QyQ5v-65YGjQR0_FDW2
  QvzqY368QQMicAtaSqzs8KJZgnYb9c7d0zgdAZHzu6qMQvRL5hajrn1n91CbOpbI
  SD08qNLyrdkt-bFTWhAI4vMQFh6WeZu0fM4lFd2NcRwr3XPksINHaQ-G_xBniIqb
  w0Ls1jF44-csFCur-kEgU8awapJzKnqDKgw",
       "e":"AQAB",
       "alg":"RS256",
       "kid":"2011-04-29"}
    ]
  }

A.2. Example Private Keys

The following example JWK Set contains two keys represented as JWKs containing both public and private key values: one using an Elliptic Curve algorithm and a second one using an RSA algorithm. This example extends the example in the previous section, adding private key values. (Line breaks are for display purposes only.)

  {"keys":
    [
      {"kty":"EC",
       "crv":"P-256",
       "x":"MKBCTNIcKUSDii11ySs3526iDZ8AiTo7Tu6KPAqv7D4",
       "y":"4Etl6SRW2YiLUrN5vfvVHuhp7x8PxltmWWlbbM4IFyM",
       "d":"870MB6gfuTJ4HtUnUvYMyJpr5eUZNP4Bk43bVdj3eAE",
       "use":"enc",
       "kid":"1"},

      {"kty":"RSA",
       "n":"0vx7agoebGcQSuuPiLJXZptN9nndrQmbXEps2aiAFbWhM78LhWx4
  cbbfAAtVT86zwu1RK7aPFFxuhDR1L6tSoc_BJECPebWKRXjBZCiFV4n3oknjhMst
  n64tZ_2W-5JsGY4Hc5n9yBXArwl93lqt7_RN5w6Cf0h4QyQ5v-65YGjQR0_FDW2Q
  vzqY368QQMicAtaSqzs8KJZgnYb9c7d0zgdAZHzu6qMQvRL5hajrn1n91CbOpbIS
  D08qNLyrdkt-bFTWhAI4vMQFh6WeZu0fM4lFd2NcRwr3XPksINHaQ-G_xBniIqbw
  0Ls1jF44-csFCur-kEgU8awapJzKnqDKgw",
       "e":"AQAB",
       "d":"X4cTteJY_gn4FYPsXB8rdXix5vwsg1FLN5E3EaG6RJoVH-HLLKD9
  M7dx5oo7GURknchnrRweUkC7hT5fJLM0WbFAKNLWY2vv7B6NqXSzUvxT0_YSfqij
  wp3RTzlBaCxWp4doFk5N2o8Gy_nHNKroADIkJ46pRUohsXywbReAdYaMwFs9tv8d
  _cPVY3i07a3t8MN6TNwm0dSawm9v47UiCl3Sk5ZiG7xojPLu4sbg1U2jx4IBTNBz
  nbJSzFHK66jT8bgkuqsk0GjskDJk19Z4qwjwbsnn4j2WBii3RL-Us2lGVkY8fkFz
  me1z0HbIkfz0Y6mqnOYtqc0X4jfcKoAC8Q",
       "p":"83i-7IvMGXoMXCskv73TKr8637FiO7Z27zv8oj6pbWUQyLPQBQxtPV
  nwD20R-60eTDmD2ujnMt5PoqMrm8RfmNhVWDtjjMmCMjOpSXicFHj7XOuVIYQyqV
  WlWEh6dN36GVZYk93N8Bc9vY41xy8B9RzzOGVQzXvNEvn7O0nVbfs",
       "q":"3dfOR9cuYq-0S-mkFLzgItgMEfFzB2q3hWehMuG0oCuqnb3vobLyum
  qjVZQO1dIrdwgTnCdpYzBcOfW5r370AFXjiWft_NGEiovonizhKpo9VVS78TzFgx
  kIdrecRezsZ-1kYd_s1qDbxtkDEgfAITAG9LUnADun4vIcb6yelxk",
       "dp":"G4sPXkc6Ya9y8oJW9_ILj4xuppu0lzi_H7VTkS8xj5SdX3coE0oim
  YwxIi2emTAue0UOa5dpgFGyBJ4c8tQ2VF402XRugKDTP8akYhFo5tAA77Qe_Nmtu
  YZc3C3m3I24G2GvR5sSDxUyAN2zq8Lfn9EUms6rY3Ob8YeiKkTiBj0",
       "dq":"s9lAH9fggBsoFR8Oac2R_E2gw282rT2kGOAhvIllETE1efrA6huUU
  vMfBcMpn8lqeW6vzznYY5SSQF7pMdC_agI3nG8Ibp1BUb0JUiraRNqUfLhcQb_d9
  GF4Dh7e74WbRsobRonujTYN1xCaP6TO61jvWrX-L18txXw494Q_cgk",
       "qi":"GyM_p6JrXySiz1toFgKbWV-JdI3jQ4ypu9rbMWx3rQJBfmt0FoYzg
  UIZEVFEcOqwemRN81zoDAaa-Bk0KWNGDjJHZDdDmFhW3AN7lI-puxk_mHZGJ11rx
  yR8O55XLSe3SPmRfKwZI6yU24ZxvQKFYItdldUKGzO6Ia6zTKhAVRU",
       "alg":"RS256",
       "kid":"2011-04-29"}
    ]
  }

A.3. Example Symmetric Keys

The following example JWK Set contains two symmetric keys represented as JWKs: one designated as being for use with the AES Key Wrap algorithm and a second one that is an HMAC key. (Line breaks are for display purposes only.)

  {"keys":
    [
      {"kty":"oct",
       "alg":"A128KW",
       "k":"GawgguFyGrWKav7AX4VKUg"},

      {"kty":"oct",
       "k":"AyM1SysPpbyDfgZld3umj1qzKObwVMkoqQ-EstJQLr_T-1qS0gZH75
  aKtMN3Yj0iPS4hcgUuTwjAzZr1Z9CAow",
       "kid":"HMAC key used in JWS A.1 example"}
    ]
  }

Appendix B. Acknowledgements

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

This specification is the work of the JOSE Working Group, which includes dozens of active and dedicated participants. In particular, the following individuals contributed ideas, feedback, and wording that influenced this specification:

Dirk Balfanz, Richard Barnes, John Bradley, Brian Campbell, Breno de Medeiros, Joe Hildebrand, Edmund Jay, Ben Laurie, James Manger, Tony Nadalin, Axel Nennker, John Panzer, Eric Rescorla, Nat Sakimura, Jim Schaad, Paul Tarjan, Hannes Tschofenig, and Sean Turner.

Jim Schaad and Karen O'Donoghue chaired the JOSE working group and Sean Turner and Stephen Farrell served as Security area directors during the creation of this specification.

Appendix C. 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/