Network Working Group M. Jones Internet-Draft Microsoft Intended status: Standards Track December 13, 2011 Expires: June 15, 2012 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/. 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Code Components extracted from this document must Jones Expires June 15, 2012 [Page 1] Internet-Draft JWK December 2011 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 . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. JSON Web Key (JWK) Overview . . . . . . . . . . . . . . . . . . 3 3.1. Example JWK . . . . . . . . . . . . . . . . . . . . . . . . 3 4. JWK Format . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4.1. JWK Container Object Format . . . . . . . . . . . . . . . . 4 4.2. JWK Key Object Format . . . . . . . . . . . . . . . . . . . 5 4.2.1. JWK Key Object Members for Elliptic Curve Keys . . . . 5 4.2.2. JWK Key Object Members for RSA Keys . . . . . . . . . . 6 5. Base64url encoding as used by JWKs . . . . . . . . . . . . . . 7 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7 7. Security Considerations . . . . . . . . . . . . . . . . . . . . 7 8. Open Issues and Things To Be Done (TBD) . . . . . . . . . . . . 7 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 9.1. Normative References . . . . . . . . . . . . . . . . . . . 7 9.2. Informative References . . . . . . . . . . . . . . . . . . 8 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . . 8 Appendix B. Document History . . . . . . . . . . . . . . . . . . . 8 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 9 Jones Expires June 15, 2012 [Page 2] Internet-Draft JWK December 2011 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.) Jones Expires June 15, 2012 [Page 3] Internet-Draft JWK December 2011 {"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: +--------+----------+-----------------------------------------------+ | Member | JSON | Container Object Member Semantics | | Name | Value | | | | Type | | +--------+----------+-----------------------------------------------+ | jwk | array | The "jwk" member value contains an array of | | | | JWK Key Objects. This member is REQUIRED. | +--------+----------+-----------------------------------------------+ JWK Container Object Member Additional members MAY be present in the JWK Container Object. If present, they MUST be understood by implementations using that JWK. Jones Expires June 15, 2012 [Page 4] Internet-Draft JWK December 2011 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: +--------+--------+-------------------------------------------------+ | Member | JSON | Key Object Member Semantics | | Name | Value | | | | Type | | +--------+--------+-------------------------------------------------+ | alg | string | The "alg" 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 "alg" value. The "alg" 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 "sig" (signature) and "enc" (encryption). | | | | Other values MAY be used. The "use" value is | | | | case sensitive. This member is OPTIONAL. | | kid | string | 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 "kid" value | | | | MAY correspond to a JWS "kid" value. The | | | | interpretation of the "kid" value is | | | | unspecified. This member is OPTIONAL. | +--------+--------+-------------------------------------------------+ JWK Key Object Members 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: Jones Expires June 15, 2012 [Page 5] Internet-Draft JWK December 2011 +--------+--------+-------------------------------------------------+ | Member | JSON | Key Object Member Semantics | | Name | Value | | | | Type | | +--------+--------+-------------------------------------------------+ | crv | string | The "crv" member identifies the cryptographic | | | | curve used with the key. Values defined by | | | | this specification are "P-256", "P-384" and | | | | "P-521". Additional "crv" values MAY be used, | | | | provided they are understood by implementations | | | | using that Elliptic Curve key. The "crv" 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. | +--------+--------+-------------------------------------------------+ Members for Elliptic Curve Keys 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: +--------+--------+-------------------------------------------------+ | Member | JSON | Key Object Member Semantics | | Name | Value | | | | Type | | +--------+--------+-------------------------------------------------+ | mod | string | The "mod" member contains the modulus value for | | | | the RSA public key. It is represented as the | | | | base64url encoding of the value's big endian | | | | representation. | | exp | string | The "exp" member contains the exponent value | | | | for the RSA public key. It is represented as | | | | the base64url encoding of the value's big | | | | endian representation. | +--------+--------+-------------------------------------------------+ Members for RSA Keys Jones Expires June 15, 2012 [Page 6] Internet-Draft JWK December 2011 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: o Write the Security Considerations section. 9. References 9.1. Normative References [FIPS.186-3] National Institute of Standards and Technology, "Digital Signature Standard (DSS)", FIPS PUB 186-3, June 2009. [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. Jones Expires June 15, 2012 [Page 7] Internet-Draft JWK December 2011 9.2. Informative References [JWE] Jones, M., Rescorla, E., and J. Hildebrand, "JSON Web Encryption (JWE)", December 2011. [JWS] Jones, M., Balfanz, D., Bradley, J., Goland, Y., Panzer, J., Sakimura, N., and P. Tarjan, "JSON Web Signature (JWS)", December 2011. [MagicSignatures] Panzer (editor), J., Laurie, B., and D. Balfanz, "Magic Signatures", August 2010. Appendix A. Acknowledgements A JSON representation for RSA public keys was previously introduced in Magic Signatures [MagicSignatures]. Appendix B. Document History -03 o Use short names since JWK Key Object values are used as JWE Ephemeral Public Keys, and so compactness matters. o Respect line length restrictions in examples. -02 o Editorial changes to have this spec better match the JWT, JWS, and JWE specs. No normative changes. -01 o 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). o 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 Jones Expires June 15, 2012 [Page 8] Internet-Draft JWK December 2011 o 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 Michael B. Jones Microsoft Email: mbj@microsoft.com URI: http://self-issued.info/ Jones Expires June 15, 2012 [Page 9]