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Versions: 00 01 02 draft-ietf-oauth-proof-of-possession

OAuth Working Group                                             M. Jones
Internet-Draft                                                 Microsoft
Intended status: Standards Track                              J. Bradley
Expires: October 3, 2014                                   Ping Identity
                                                           H. Tschofenig
                                                           April 1, 2014


        Proof-Of-Possession Semantics for JSON Web Tokens (JWTs)
                draft-jones-oauth-proof-of-possession-00

Abstract

   This specification defines how to express a declaration in a JSON Web
   Token (JWT) that the presenter of the JWT possesses a particular key
   and that the recipient can cryptographically confirm proof-of-
   possession of the key by the presenter.  This property is also
   sometimes described as the presenter being a holder-of-key.

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 October 3, 2014.

Copyright Notice

   Copyright (c) 2014 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



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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . . . 3
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Proof-Of-Possession Representation  . . . . . . . . . . . . . . 3
     2.1.  Proof-of-Possession of a Private Key  . . . . . . . . . . . 4
     2.2.  Proof-of-Possession of a Symmetric Key  . . . . . . . . . . 4
     2.3.  Confirmation  . . . . . . . . . . . . . . . . . . . . . . . 5
     2.4.  Specifics Intentionally Not Specified . . . . . . . . . . . 6
   3.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
     4.1.  JSON Web Token Claims Registration  . . . . . . . . . . . . 7
       4.1.1.  Registry Contents . . . . . . . . . . . . . . . . . . . 7
     4.2.  JWT Confirmation Methods Registry . . . . . . . . . . . . . 7
       4.2.1.  Registration Template . . . . . . . . . . . . . . . . . 8
       4.2.2.  Initial Registry Contents . . . . . . . . . . . . . . . 8
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 8
     5.1.  Normative References  . . . . . . . . . . . . . . . . . . . 8
     5.2.  Informative References  . . . . . . . . . . . . . . . . . . 9
   Appendix A.  Open Issues  . . . . . . . . . . . . . . . . . . . . . 9
   Appendix B.  Document History . . . . . . . . . . . . . . . . . . . 9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 9
























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1.  Introduction

   This specification defines how to express a declaration in a JSON Web
   Token (JWT) [JWT] that the presenter of the JWT possesses a
   particular key and that the recipient can cryptographically confirm
   proof-of-possession of the key by the presenter.  This property is
   also sometimes described as the presenter being a holder-of-key.

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 RFC 2119 [RFC2119].

   Unless otherwise noted, all the protocol parameter names and values
   are case sensitive.

1.2.  Terminology

   This specification uses terms defined in the JSON Web Token (JWT)
   [JWT], JSON Web Key (JWK) [JWK], and JSON Web Encryption (JWE) [JWE]
   specifications.

   These terms are defined for use by this specification:

   Presenter
      Party that possesses the key identified by the JWT.


2.  Proof-Of-Possession Representation

   The presenter of a JWT declares that it possesses a particular key
   and that the recipient can cryptographically confirm proof-of-
   possession of the key by the issuer by including a "cnf"
   (confirmation) claim in the JWT whose value is a JSON object, with
   the JSON object containing a "jwk" (JSON Web Key) member identifying
   the key.

   The presenter can be identified in one of two ways by the JWT,
   depending upon the application requirements.  If the JWT contains a
   "sub" (subject) claim, the presenter is the subject identified by the
   JWT.  (In some applications, the subject identifier will be relative
   to the issuer identified by the "iss" (issuer) claim.)  If the JWT
   contains no "sub" (subject) claim, the presenter is the issuer
   identified by the JWT using the "iss" (issuer) claim.  The case in
   which the presenter is the subject of the JWT is analogous to SAML
   2.0 [OASIS.saml-core-2.0-os] SubjectConfirmation usage.  At least one
   of the "sub" and "iss" claims MUST be present in the JWT, and in some



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   use cases, both MUST be present.

2.1.  Proof-of-Possession of a Private Key

   When the key held by the issuer is a private key, the value of the
   "jwk" member is a JSON Web Key (JWK) [JWK] representing the
   corresponding public key.  The following example demonstrates such a
   declaration in the JWT Claims Set of a JWT:

     {
      "iss":"xas.xboxlive.com",
      "aud":"http://auth.xboxlive.com",
      "exp":"1361398824",
      "nbf":"1360189224",
      "cnf":{
        "jwk":{
          "kty":"EC",
          "use":"sig",
          "crv":"P-256",
          "x":"18wHLeIgW9wVN6VD1Txgpqy2LszYkMf6J8njVAibvhM",
          "y":"-V4dS4UaLMgP_4fY4j8ir7cl1TXlFdAgcx55o7TkcSA"
         }
       }
     }

   The JWK MUST contain the REQUIRED key elements for a JWK of that key
   type and MAY contain other JWK elements, including the "kid" (key ID)
   element.

2.2.  Proof-of-Possession of a Symmetric Key

   When the key held by the issuer is a symmetric key, the value of the
   "jwk" member is an encrypted JSON Web Key (JWK) [JWK] encrypted to
   the recipient using the JWE Compact Serialization containing the
   symmetric key.  The rules for encrypting a JWK are found in Section 6
   of the JSON Web Key [JWK] specification.

   The following is an example symmetric key that could be encrypted for
   use in the "jwk" member:

     {
      "kty":"oct",
      "alg":"HS256",
      "k":"ZoRSOrFzN_FzUA5XKMYoVHyzff5oRJxl-IXRtztJ6uE"
     }

   The UTF-8 [RFC3629] encoding of this JWK would be used as the JWE
   Plaintext.



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   The following is an example JWE Header could be used when encrypting
   this key:

     {
      "alg":"RSA1_5",
      "enc":"A128CBC-HS256",
      "cty":"jwk+json"
     }

   The following example JWT Claims Set of a JWT illustrates the use of
   an encrypted symmetric key as the "jwk" claim value:

     {
      "iss": "https://server.example.com",
      "sub": "24400320",
      "aud": "s6BhdRkqt3",
      "nonce": "n-0S6_WzA2Mj",
      "exp": 1311281970,
      "iat": 1311280970,
      "cnf":{
        "jwk":
          "eyJhbGciOiJSU0ExXzUiLCJlbmMiOiJBMTI4Q0JDLUhTMjU2IiwiY3R5Ijoi
           andrK2pzb24ifQ. ... (remainder of JWE omitted for brevity)"
        }
     }

   Note that the case in which the "jwk" claim contains an unencoded JWK
   value and the case in which it contains an encrypted JWK value can be
   distinguished by the type of the member value.  In the first case,
   the value is a JSON object containing the JWK and in the second case,
   the value is a string containing the JWE JSON Serialization of the
   encrypted JWK representation.

2.3.  Confirmation

   The "cnf" (confirmation) claim is used in the JWT to contain the
   "jwk" member because a proof-of-possession key may not be the only
   means of confirming the authenticity of the token.  This is analogous
   to the SAML 2.0 [OASIS.saml-core-2.0-os] SubjectConfirmation element,
   in which a number of different subject confirmation methods can be
   included, including proof-of-possession key information.  When a
   recipient receives a "cnf" claim with a member that it does not
   understand, it MUST ignore that member.

   This specification defines a registry for these elements in
   Section 4.2 and registers the "jwk" member within the registry.





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2.4.  Specifics Intentionally Not Specified

   Proof-of-possession is typically demonstrated by having the issuer
   sign a value determined by the recipient using the key possessed by
   the issuer.  This value is sometimes called a "nonce" or a
   "challenge".

   The means of communicating the nonce and the nature of its contents
   are intentionally not described in this specification, as different
   protocols will communicate this information in different ways.
   Likewise, the means of communicating the signed nonce is also not
   specified, as this is also protocol-specific.

   Note that another means of proving possession of the key when it is a
   symmetric key is to encrypt the key to the recipient.  The means of
   obtaining a key for the recipient is likewise protocol-specific.


3.  Security Considerations

   All of the normal security issues, especially in relationship to
   comparing URIs and dealing with unrecognized values, that are
   discussed in JWT [JWT] also apply here.

   In addition, proof-of-possession introduces its own unique security
   issues.  Possessing the key is only valuable if it is kept secret.
   Appropriate means must be used to ensure that unintended parties do
   not learn the secret or symmetric key value.

   Proof-of-possession via encrypted symmetric secrets is subject to
   replay attacks.  This attack can be avoided when a signed nonce or
   challenge is used, since the recipient can use a distinct nonce or
   challenged for each interaction.


4.  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



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   for review and comment, with an appropriate subject (e.g., "Request
   for access token type: example"). [[ Note to the RFC Editor: The name
   of the mailing list should be determined in consultation with the
   IESG and IANA.  Suggested name: jwt-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.  Registration requests that are undetermined for a period
   longer than 21 days can be brought to the IESG's attention (using the
   iesg@iesg.org mailing list) for resolution.

   Criteria that should be applied by the Designated Expert(s) includes
   determining whether the proposed registration duplicates existing
   functionality, determining whether it is likely to be of general
   applicability or whether it is useful only for a single application,
   and whether the registration makes sense.

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

   It is suggested that multiple Designated Experts be appointed who are
   able to represent the perspectives of different applications using
   this specification, in order to enable broadly-informed review of
   registration decisions.  In cases where a registration decision could
   be perceived as creating a conflict of interest for a particular
   Expert, that Expert should defer to the judgment of the other
   Expert(s).

4.1.  JSON Web Token Claims Registration

   This specification registers the "cnf" claim in the IANA JSON Web
   Token Claims registry defined in [JWT].

4.1.1.  Registry Contents

   o  Claim Name: "cnf"
   o  Claim Description: Confirmation
   o  Change Controller: IESG
   o  Specification Document(s): Section 2.3 of this document

4.2.  JWT Confirmation Methods Registry

   This specification establishes the IANA JWT Confirmation Methods
   registry for JWT "cnf" member values.  The registry records the
   confirmation method member and a reference to the specification that



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   defines it.

4.2.1.  Registration Template

   Confirmation Method Value:
      The name requested (e.g., "example").  Because a core goal of this
      specification is for the resulting representations to be compact,
      it is RECOMMENDED that the name be short -- not to exceed 8
      characters without a compelling reason to do so.  This name is
      case-sensitive.  Names may not match other registered names in a
      case-insensitive manner unless the Designated Expert(s) state that
      there is a compelling reason to allow an exception in this
      particular case.

   Confirmation Method Description:
      Brief description of the confirmation method (e.g., "Example
      description").

   Change Controller:
      For Standards Track RFCs, state "IESG".  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.

4.2.2.  Initial Registry Contents

   o  Confirmation Method Value: "jwk"
   o  Confirmation Method Description: JSON Web Key or Encrypted JSON
      Web Key
   o  Change Controller: IESG
   o  Specification Document(s): Section 2 of [[ this document ]]


5.  References

5.1.  Normative References

   [JWE]      Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)",
              draft-ietf-jose-json-web-encryption (work in progress),
              March 2014.

   [JWK]      Jones, M., "JSON Web Key (JWK)",
              draft-ietf-jose-json-web-key (work in progress),



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              March 2014.

   [JWT]      Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
              (JWT)", draft-ietf-oauth-json-web-token (work in
              progress), March 2014.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, November 2003.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

5.2.  Informative References

   [OASIS.saml-core-2.0-os]
              Cantor, S., Kemp, J., Philpott, R., and E. Maler,
              "Assertions and Protocol for the OASIS Security Assertion
              Markup Language (SAML) V2.0", OASIS Standard saml-core-
              2.0-os, March 2005.


Appendix A.  Open Issues

   In some conversations, we have said that it is the issuer of the JWT
   that possesses the key, and in some conversations, we have said that
   it is the presenter of the JWT that possesses the key.  Which
   description should we use?


Appendix B.  Document History

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

   -00

   o  Wrote the first draft.











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Authors' Addresses

   Michael B. Jones
   Microsoft

   Email: mbj@microsoft.com
   URI:   http://self-issued.info/


   John Bradley
   Ping Identity

   Email: ve7jtb@ve7jtb.com
   URI:   http://www.thread-safe.com/


   Hannes Tschofenig

   Email: Hannes.Tschofenig@gmx.net
   URI:   http://www.tschofenig.priv.at































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