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Versions: (draft-wahlstroem-ace-cbor-web-token) 00 01 02 03 04 05 06 07 08

ACE Working Group                                               M. Jones
Internet-Draft                                                 Microsoft
Intended status: Informational                             E. Wahlstroem
Expires: July 17, 2017
                                                              S. Erdtman
                                                              Spotify AB
                                                           H. Tschofenig
                                                                ARM Ltd.
                                                        January 13, 2017


                          CBOR Web Token (CWT)
                    draft-ietf-ace-cbor-web-token-02

Abstract

   CBOR Web Token (CWT) is a compact means of representing claims to be
   transferred between two parties.  CWT is a profile of the JSON Web
   Token (JWT) that is optimized for constrained devices.  The claims in
   a CWT are encoded in the Concise Binary Object Representation (CBOR)
   and CBOR Object Signing and Encryption (COSE) is used for added
   application layer security protection.  A claim is a piece of
   information asserted about a subject and is represented as a name/
   value pair consisting of a claim name and a claim value.

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 July 17, 2017.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.





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   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
   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.  Claims  . . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Claim Names . . . . . . . . . . . . . . . . . . . . . . .   4
       3.1.1.  iss (Issuer) Claim  . . . . . . . . . . . . . . . . .   4
       3.1.2.  sub (Subject) Claim . . . . . . . . . . . . . . . . .   4
       3.1.3.  aud (Audience) Claim  . . . . . . . . . . . . . . . .   4
       3.1.4.  exp (Expiration Time) Claim . . . . . . . . . . . . .   5
       3.1.5.  nbf (Not Before) Claim  . . . . . . . . . . . . . . .   5
       3.1.6.  iat (Issued At) Claim . . . . . . . . . . . . . . . .   5
       3.1.7.  cti (CWT ID) Claim  . . . . . . . . . . . . . . . . .   5
   4.  Summary of the values, CBOR major types and encoded claim
       keys  . . . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Creating and Validating CWTs  . . . . . . . . . . . . . . . .   6
     5.1.  Creating a CWT  . . . . . . . . . . . . . . . . . . . . .   6
     5.2.  Validating a CWT  . . . . . . . . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
     7.1.  CBOR Web Token (CWT) Claims Registry  . . . . . . . . . .   8
       7.1.1.  Registration Template . . . . . . . . . . . . . . . .   8
       7.1.2.  Initial Registry Contents . . . . . . . . . . . . . .   9
     7.2.  Media Type Registration . . . . . . . . . . . . . . . . .  10
       7.2.1.  Registry Contents . . . . . . . . . . . . . . . . . .  10
     7.3.  CoAP Content-Formats Registration . . . . . . . . . . . .  11
       7.3.1.  Registry Contents . . . . . . . . . . . . . . . . . .  11
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  13
   Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . .  13
     A.1.  CWT with "aud" and symmetric key  . . . . . . . . . . . .  13
     A.2.  CWT with "aud" and EC key . . . . . . . . . . . . . . . .  14
     A.3.  Full CWT  . . . . . . . . . . . . . . . . . . . . . . . .  16
   Appendix B.  Acknowledgements . . . . . . . . . . . . . . . . . .  19
   Appendix C.  Document History . . . . . . . . . . . . . . . . . .  20
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  20




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1.  Introduction

   The JSON Web Token (JWT) [RFC7519] is a standardized security token
   format that has found use in OAuth 2.0 and OpenID Connect
   deployments, among other applications.  JWT uses JSON Web Signatures
   (JWS) [RFC7515] and JSON Web Encryption (JWE) [RFC7516] to secure the
   contents of the JWT, which is a set of claims represented in JSON
   [RFC7519].  The use of JSON for encoding information is popular for
   Web and native applications, but it is considered inefficient for
   some Internet of Things (IoT) systems that use low power radio
   technologies.

   In this document an alternative encoding of claims is defined.
   Instead of using JSON, as provided by JWTs, this specification uses
   CBOR [RFC7049] and calls this new structure "CBOR Web Token (CWT)",
   which is a compact means of representing secured claims to be
   transferred between two parties.  CWT is closely related to JWT.  It
   references the JWT claims and both its name and pronunciation are
   derived from JWT.  To protect the claims contained in CWTs, the CBOR
   Object Signing and Encryption (COSE) [I-D.ietf-cose-msg]
   specification is used.

   The suggested pronunciation of CWT is the same as the English word
   "cot".

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "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].

   This document reuses terminology from JWT [RFC7519] and COSE
   [I-D.ietf-cose-msg].

   Type3StringOrURI:
      The "Type3StringOrURI" term has the same meaning, syntax, and
      processing rules as the "StringOrUri" term defined in Section 2 of
      JWT [RFC7519], except that Type3StringOrURI uses CBOR major type 3
      instead of a JSON string value.

   Type6NumericDate:
      The "Type6NumericDate" term has the same meaning, syntax, and
      processing rules as the "NumericDate" term defined in Section 2 of
      JWT [RFC7519], except that Type6NumericDate uses CBOR major type
      6, with tag value 1, instead of a numeric JSON value.

   CBOR encoded claim key:



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      The key used to identify a claim value.

   CWT Claims Set
      A CBOR map that contains the claims conveyed by the CWT.

3.  Claims

   The set of claims that a CWT must contain to be considered valid is
   context dependent and is outside the scope of this specification.
   Specific applications of CWTs will require implementations to
   understand and process some claims in particular ways.  However, in
   the absence of such requirements, all claims that are not understood
   by implementations MUST be ignored.

   To keep CWTs as small as possible, the CBOR encoded claim keys are
   represented using CBOR major type 0.  Section 4 summarizes all keys
   used to identify the claims defined in this document.

3.1.  Claim Names

   None of the claims defined below are intended to be mandatory to use
   or implement.  They rather provide a starting point for a set of
   useful, interoperable claims.  Applications using CWTs should define
   which specific claims they use and when they are required or
   optional.

3.1.1.  iss (Issuer) Claim

   The "iss" (issuer) claim has the same meaning, syntax, and processing
   rules as the "iss" claim defined in Section 4.1.1 of JWT [RFC7519],
   except that the format MUST be a Type3StringOrURI.  The CBOR encoded
   claim key 1 MUST be used to identify this claim.

3.1.2.  sub (Subject) Claim

   The "sub" (subject) claim has the same meaning, syntax, and
   processing rules as the "sub" claim defined in Section 4.1.2 of JWT
   [RFC7519], except that the format MUST be a Type3StringOrURI.  The
   CBOR encoded claim key 2 MUST be used to identify this claim.

3.1.3.  aud (Audience) Claim

   The "aud" (audience) claim has the same meaning, syntax, and
   processing rules as the "aud" claim defined in Section 4.1.3 of JWT
   [RFC7519], except that the format MUST be a Type3StringOrURI.  The
   CBOR encoded claim key 3 MUST be used to identify this claim.





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3.1.4.  exp (Expiration Time) Claim

   The "exp" (expiration time) claim has the same meaning, syntax, and
   processing rules as the "exp" claim defined in Section 4.1.4 of JWT
   [RFC7519], except that the format MUST be a Type6NumericDate.  The
   CBOR encoded claim key 4 MUST be used to identify this claim.

3.1.5.  nbf (Not Before) Claim

   The "nbf" (not before) claim has the same meaning, syntax, and
   processing rules as the "nbf" claim defined in Section 4.1.5 of JWT
   [RFC7519], except that the format MUST be a Type6NumericDate.  The
   CBOR encoded claim key 5 MUST be used to identify this claim.

3.1.6.  iat (Issued At) Claim

   The "iat" (issued at) claim has the same meaning, syntax, and
   processing rules as the "iat" claim defined in Section 4.1.6 of JWT
   [RFC7519], except that the format MUST be a Type6NumericDate.  The
   CBOR encoded claim key 6 MUST be used to identify this claim.

3.1.7.  cti (CWT ID) Claim

   The "cti" (CWT ID) claim has the same meaning, syntax, and processing
   rules as the "jti" claim defined in Section 4.1.7 of JWT [RFC7519],
   except that the format MUST be of major type 2, binary string.  The
   CBOR encoded claim key 7 MUST be used to identify this claim.

4.  Summary of the values, CBOR major types and encoded claim keys

   /---------+------------------------+--------------------------\
   | Claim   | CBOR encoded claim key | CBOR major type of value |
   |---------+------------------------+--------------------------|
   | iss     | 1                      | 3                        |
   | sub     | 2                      | 3                        |
   | aud     | 3                      | 3                        |
   | exp     | 4                      | 6 tag value 1            |
   | nbf     | 5                      | 6 tag value 1            |
   | iat     | 6                      | 6 tag value 1            |
   | cti     | 7                      | 2                        |
   \---------+------------------------+--------------------------/

    Figure 1: Summary of the values, CBOR major types and encoded claim
                                   keys.







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5.  Creating and Validating CWTs

5.1.  Creating a CWT

   To create a CWT, the following steps are performed.  The order of the
   steps is not significant in cases where there are no dependencies
   between the inputs and outputs of the steps.

   1.  Create a CWT Claims Set containing the desired claims.

   2.  Let the Message be the binary representation of the CWT Claims
       Set.

   3.  Create a COSE Header containing the desired set of Header
       Parameters.  The COSE Header MUST be valid according to the
       [I-D.ietf-cose-msg] specification.

   4.  Depending upon whether the CWT is signed, MACed or encrypted,
       there are three cases:

       *  If the CWT is signed, create a COSE_Sign/COSE_Sign1 object
          using the Message as the COSE_Sign/COSE_Sign1 Payload; all
          steps specified in [I-D.ietf-cose-msg] for creating a
          COSE_Sign/COSE_Sign1 object MUST be followed.

       *  Else, if the CWT is MACed, create a COSE_Mac/COSE_Mac0 object
          using the Message as the COSE_Mac/COSE_Mac0 Payload; all steps
          specified in [I-D.ietf-cose-msg] for creating a COSE_Mac/
          COSE_Mac0 object MUST be followed.

       *  Else, if the CWT is a COSE_Encrypt/COSE_Encrypt0 object,
          create a COSE_Encrypt/COSE_Encrypt0 using the Message as the
          plaintext for the COSE_Encrypt/COSE_Encrypt0 object; all steps
          specified in [I-D.ietf-cose-msg] for creating a COSE_Encrypt/
          COSE_Encrypt0 object MUST be followed.

   5.  If a nested signing, MACing or encryption operation will be
       performed, let the Message be the COSE_Sign/COSE_Sign1, COSE_Mac/
       COSE_Mac0 or COSE_Encrypt/COSE_Encrypt0, and return to Step 3,
       using a "content type" header value corresponding to the media
       type "application/cwt" in the new COSE Header created in that
       step.
       Note: If integrity (signing/MACing) and confidentiality
       (encryption) protection are needed, it is recommended to use an
       authenticated encryption algorithm to save space and processing.






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5.2.  Validating a CWT

   When validating a CWT, the following steps are performed.  The order
   of the steps is not significant in cases where there are no
   dependencies between the inputs and outputs of the steps.  If any of
   the listed steps fail, then the CWT MUST be rejected -- that is,
   treated by the application as an invalid input.

   1.  Verify that the CWT is a valid CBOR object.

   2.  Verify that the resulting COSE Header includes only parameters
       and values whose syntax and semantics are both understood and
       supported or that are specified as being ignored when not
       understood.

   3.  Use the CBOR tag to determine the type of the CWT, COSE_Sign/
       COSE_Sign1, COSE_Mac/COSE_Mac0, or COSE_Encrypt/COSE_Encrypt0.

   4.  Depending upon whether the CWT is a COSE_Sign/COSE_Sign1,
       COSE_Mac/COSE_Mac0 or COSE_Encrypt/COSE_Encrypt0, there are three
       cases:

       *  If the CWT is a COSE_Sign/COSE_Sign1, follow the steps
          specified in [I-D.ietf-cose-msg] Section 4 (Signing Objects)
          for validating a COSE_Sign/COSE_Sign1 object.  Let the Message
          be the COSE_Sign/COSE_Sign1 payload.

       *  Else, if the CWT is a COSE_Mac/COSE_Mac0, follow the steps
          specified in [I-D.ietf-cose-msg] Section 6 (MAC Objects) for
          validating a COSE_Mac/COSE_Mac0 object.  Let the Message be
          the COSE_Mac/COSE_Mac0 payload.

       *  Else, if the CWT is a COSE_Encrypt/COSE_Encrypt0 object,
          follow the steps specified in [I-D.ietf-cose-msg] Section 5
          (Encryption Objects) for validating a COSE_Encrypt/
          COSE_Encrypt0 object.  Let the Message be the resulting
          plaintext.

   5.  If the COSE Header contains a "content type" header value
       corresponding to the media type "application/cwt", then the
       Message is a CWT that was the subject of nested signing or
       encryption operations.  In this case, return to Step 1, using the
       Message as the CWT.

   6.  Verify that the Message is a valid CBOR object; let the CWT
       Claims Set be this CBOR object.





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6.  Security Considerations

   The security of the CWT is dependent on the protection offered by
   COSE.  Without protecting the claims contained in a CWT an adversary
   is able to modify, add or remove claims.  Since the claims conveyed
   in a CWT are used to make authorization decisions it is not only
   important to protect the CWT in transit but also to ensure that the
   recipient is able to authenticate the party that collected the claims
   and created the CWT.  Without trust of the recipient in the party
   that created the CWT no sensible authorization decision can be made.
   Furthermore, the creator of the CWT needs to carefully evaluate each
   claim value prior to including it in the CWT so that the recipient
   can be assured about the correctness of the provided information.

7.  IANA Considerations

7.1.  CBOR Web Token (CWT) Claims Registry

   This section establishes the IANA "CBOR Web Token (CWT) Claims"
   registry.

   Values are registered on a Specification Required [RFC5226] basis, on
   the advice of one or more Designated Experts.  However, to allow for
   the allocation of values prior to publication, the Designated Experts
   may approve registration once they are satisfied that such a
   specification will be published.

   Criteria that should be applied by the Designated Experts includes
   determining whether the proposed registration duplicates existing
   functionality, whether it is likely to be of general applicability or
   whether it is useful only for a single application, and whether the
   registration description is clear.

7.1.1.  Registration Template

   Claim Name:
      The human-readable name requested (e.g., "iss").

   Claim Description:
      Brief description of the claim (e.g., "Issuer").

   JWT Claim Name:
      Claim Name of the equivalent JWT claim as registered in
      [IANA.JWT.Claims].  CWT claims should normally have a
      corresponding JWT claim.  If a corresponding JWT claim would not
      make sense, the Designated Experts can choose to accept
      registrations for which the JWT Claim Name is listed as "N/A".




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   CBOR Key Value:
      Key value for the claim.  The key value MUST be an integer in the
      range of 1 to 65536.

   CBOR Major Type:
      CBOR major type and optional tag for the claim.

   Change Controller:
      For Standards Track RFCs, list the "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 or documents that specify the parameter,
      preferably including URIs that can be used to retrieve copies of
      the documents.  An indication of the relevant sections may also be
      included but is not required.

7.1.2.  Initial Registry Contents

   o  Claim Name: "iss"
   o  Claim Description: Issuer
   o  JWT Claim Name: "iss"
   o  CBOR Key Value: 1
   o  CBOR Major Type: 3
   o  Change Controller: IESG
   o  Specification Document(s): Section 3.1.1 of [[ this specification
      ]]

   o  Claim Name: "sub"
   o  Claim Description: Subject
   o  JWT Claim Name: "sub"
   o  CBOR Key Value: 2
   o  CBOR Major Type: 3
   o  Change Controller: IESG
   o  Specification Document(s): Section 3.1.2 of [[ this specification
      ]]

   o  Claim Name: "aud"
   o  Claim Description: Audience
   o  JWT Claim Name: "aud"
   o  CBOR Key Value: 3
   o  CBOR Major Type: 3
   o  Change Controller: IESG
   o  Specification Document(s): Section 3.1.3 of [[ this specification
      ]]

   o  Claim Name: "exp"



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   o  Claim Description: Expiration Time
   o  JWT Claim Name: "exp"
   o  CBOR Key Value: 4
   o  CBOR Major Type: 6, tag value 1
   o  Change Controller: IESG
   o  Specification Document(s): Section 3.1.4 of [[ this specification
      ]]

   o  Claim Name: "nbf"
   o  Claim Description: Not Before
   o  JWT Claim Name: "nbf"
   o  CBOR Key Value: 5
   o  CBOR Major Type: 6, tag value 1
   o  Change Controller: IESG
   o  Specification Document(s): Section 3.1.5 of [[ this specification
      ]]

   o  Claim Name: "iat"
   o  Claim Description: Issued At
   o  JWT Claim Name: "iat"
   o  CBOR Key Value: 6
   o  CBOR Major Type: 6, tag value 1
   o  Change Controller: IESG
   o  Specification Document(s): Section 3.1.6 of [[ this specification
      ]]

   o  Claim Name: "cti"
   o  Claim Description: CWT ID
   o  JWT Claim Name: "jti"
   o  CBOR Key Value: 7
   o  CBOR Major Type: 2
   o  Change Controller: IESG
   o  Specification Document(s): Section 3.1.7 of [[ this specification
      ]]

7.2.  Media Type Registration

   This section registers the "application/cwt" media type [RFC2046] in
   the "Media Types" registry [IANA.MediaTypes] in the manner described
   in RFC 6838 [RFC6838], which can be used to indicate that the content
   is a CWT.

7.2.1.  Registry Contents

   o  Type name: application
   o  Subtype name: cwt
   o  Required parameters: N/A
   o  Optional parameters: N/A



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   o  Encoding considerations: binary
   o  Security considerations: See the Security Considerations section
      of [[ this specification ]]
   o  Interoperability considerations: N/A
   o  Published specification: [[ this specification ]]
   o  Applications that use this media type: IoT applications sending
      security tokens over HTTP(S) and other transports.
   o  Fragment identifier considerations: N/A
   o  Additional information:

         Magic number(s): N/A
         File extension(s): N/A
         Macintosh file type code(s): N/A

   o  Person & email address to contact for further information:
      IESG, iesg@ietf.org
   o  Intended usage: COMMON
   o  Restrictions on usage: none
   o  Author: Michael B. Jones, mbj@microsoft.com
   o  Change controller: IESG
   o  Provisional registration?  No

7.3.  CoAP Content-Formats Registration

   This section registers the CoAP Content-Format ID for the
   "application/cwt" media type in the "CoAP Content-Formats" registry
   [IANA.CoAP.Content-Formats] established by [RFC7252].

7.3.1.  Registry Contents

   o  Media Type: application/cwt
   o  Encoding: -
   o  Id: TBD (maybe 61)
   o  Reference: [[ this specification ]]

8.  References

8.1.  Normative References

   [I-D.ietf-cose-msg]
              Schaad, J., "CBOR Object Signing and Encryption (COSE)",
              draft-ietf-cose-msg-24 (work in progress), November 2016.

   [IANA.CoAP.Content-Formats]
              IANA, "CoAP Content-Formats",
              <http://www.iana.org/assignments/core-parameters/
              core-parameters.xhtml#content-formats>.




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   [IANA.JWT.Claims]
              IANA, "JSON Web Token Claims",
              <http://www.iana.org/assignments/jwt>.

   [IANA.MediaTypes]
              IANA, "Media Types",
              <http://www.iana.org/assignments/media-types>.

   [RFC2046]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part Two: Media Types", RFC 2046,
              DOI 10.17487/RFC2046, November 1996,
              <http://www.rfc-editor.org/info/rfc2046>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              DOI 10.17487/RFC5226, May 2008,
              <http://www.rfc-editor.org/info/rfc5226>.

   [RFC6838]  Freed, N., Klensin, J., and T. Hansen, "Media Type
              Specifications and Registration Procedures", BCP 13,
              RFC 6838, DOI 10.17487/RFC6838, January 2013,
              <http://www.rfc-editor.org/info/rfc6838>.

   [RFC7049]  Bormann, C. and P. Hoffman, "Concise Binary Object
              Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
              October 2013, <http://www.rfc-editor.org/info/rfc7049>.

   [RFC7159]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
              2014, <http://www.rfc-editor.org/info/rfc7159>.

   [RFC7252]  Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
              Application Protocol (CoAP)", RFC 7252,
              DOI 10.17487/RFC7252, June 2014,
              <http://www.rfc-editor.org/info/rfc7252>.

   [RFC7515]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web
              Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
              2015, <http://www.rfc-editor.org/info/rfc7515>.

   [RFC7516]  Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)",
              RFC 7516, DOI 10.17487/RFC7516, May 2015,
              <http://www.rfc-editor.org/info/rfc7516>.



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   [RFC7519]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
              (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
              <http://www.rfc-editor.org/info/rfc7519>.

8.2.  Informative References

   [I-D.seitz-ace-oauth-authz]
              Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and
              H. Tschofenig, "Authorization for the Internet of Things
              using OAuth 2.0", draft-seitz-ace-oauth-authz-00 (work in
              progress), October 2015.

Appendix A.  Examples

   Three examples of CWTs follow.

A.1.  CWT with "aud" and symmetric key

   A CWT used in the context of ACE requires at least the "aud" and a
   "cks" claim (defined elsewhere).  This means that "iss", "alg",
   "key_ops" and others are pre-established and assumed.  This would
   look like this non-normative JSON.


{
  "aud":"coap://light.example.com",
  "cks":
    [                       // COSE_Key is a CBOR map with an array of keys
      {
        "kty":4,            // symmetric key is indicated using kty 4
        "k": "loremipsum"   // the symmetric key
      }
    ]
}


       Figure 2: "aud" claim and symmetric key in non-normative JSON

   Using the CBOR encoded claim keys according to Section 4 and COSE
   [I-D.ietf-cose-msg] makes a CWT with "aud" and a symmetric key look
   like this in CBOR diagnostic notation:










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   {
     3: "coap://light.example.com",
     8:
     [
       {
         1: 4,
         -1: "loremipsum"
       }
     ]
   }


                 Figure 3: CWT in CBOR diagnostic notation

   Defined in CBOR.


a2                                      # map(2)
   03                                   # unsigned(3)
   78 18                                # text(24)
      636f61703a2f2f6c696768742e6578616d706c652e636f6d # "coap://light.example.com"
   08                                   # unsigned(8)
   81                                   # array(1)
      a2                                # map(2)
         01                             # unsigned(1)
         04                             # unsigned(4)
         20                             # negative(0)
         6a                             # text(10)
            6c6f72656d697073756d        # "loremipsum"


            Figure 4: CWT with "aud" and symmetric key in CBOR

   Size of the CWT with a symmetric key of 10 bytes is 45 bytes.  This
   is then packaged signed and encrypted using COSE.

A.2.  CWT with "aud" and EC key

   Token with "aud" set to "coap://light.example.com" and an EC key with
   "kid" set to "11".











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{
  "aud": "coap://light.example.com",
  "cks":
    [                       // COSE_Key is a CBOR map with an array of keys
      {
        "kty": "EC",
        "kid": "11",
        "crv": 1, // using P-384
        "x": h'bac5b11cad8f99f9c72b05cf4b9e26d244dc189f745228255a219a86d6a09eff',
        "y": h'20138bf82dc1b6d562be0fa54ab7804a3a64b6d72ccfed6b6fb6ed28bbfc117e'
      }
    ]
}


          Figure 5: "aud" claim and EC key in non-normative JSON

   Using the CBOR encoded claim keys according to Section 4 and COSE
   [I-D.ietf-cose-msg] makes a CWT with "aud" and an EC key look like
   this in CBOR diagnostic notation:


{
  3: "coap://light.example.com",
  8:
  [
    {
      1: 2,
      2: "11",
      -1: 1,
      -2: h'bac5b11cad8f99f9c72b05cf4b9e26d244dc189f745228255a219a86d6a09eff',
      -3: h'20138bf82dc1b6d562be0fa54ab7804a3a64b6d72ccfed6b6fb6ed28bbfc117e'
    }
  ]
}


           Figure 6: CWT with EC key in CBOR diagnostic notation

   Defined in CBOR.











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a2                                      # map(2)
   03                                   # unsigned(3)
   78 18                                # text(24)
      636f61703a2f2f6c696768742e6578616d706c652e636f6d # "coap://light.example.com"
   08                                   # unsigned(8)
   81                                   # array(1)
      a5                                # map(5)
         01                             # unsigned(1)
         02                             # unsigned(2)
         02                             # unsigned(2)
         62                             # text(2)
            3131                        # "11"
         20                             # negative(0)
         01                             # unsigned(1)
         21                             # negative(1)
         58 20                          # bytes(32)
            bac5b11cad8f99f9c72b05cf4b9e26d244dc189f745228255a219a86d6a09eff # "\xBA\xC5\xB1\x1C\xAD\x8F\x99\xF9\xC7+\x05\xCFK\x9E&\xD2D\xDC\x18\x9FtR(%Z!\x9A\x86\xD6\xA0\x9E\xFF"
         22                             # negative(2)
         58 20                          # bytes(32)
            20138bf82dc1b6d562be0fa54ab7804a3a64b6d72ccfed6b6fb6ed28bbfc117e # "\x13\x8B\xF8-\xC1\xB6\xD5b\xBE\x0F\xA5J\xB7\x80J:d\xB6\xD7,\xCF\xEDko\xB6\xED(\xBB\xFC\x11~"


                       Figure 7: CWT with EC in CBOR

   Size of the CWT with an EC key is 109 bytes.  This is then packaged
   signed and encrypted using COSE.

A.3.  Full CWT

   CWT using all claims defined by this specification, plus extensions
   for AIF and an EC key.




















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{
   "iss": "coap://as.example.com",
   "aud": "coap://light.example.com",
   "sub": "erikw",
   "exp": 1444064944,
   "nbf": 1443944944,
   "iat": 1443944944,
   "cti": 2929,
   "cks":
     [                       // COSE_Key is a CBOR map with an array of keys
       {
         "kty": "EC",
         "kid": "11",
         "crv": 1, // using P-384
         "x": h'bac5b11cad8f99f9c72b05cf4b9e26d244dc189f745228255a219a86d6a09eff',
         "y": h'20138bf82dc1b6d562be0fa54ab7804a3a64b6d72ccfed6b6fb6ed28bbfc117e'
       }
     ],
   "aif": [["/s/light", 1], ["/a/led", 5], ["/dtls", 2]]
 }


       Figure 8: All claims, "aif" and EC key in non-normative JSON

   Using the CBOR encoded claim keys according to Section 4 and COSE
   [I-D.ietf-cose-msg] makes a full CWT look like this in CBOR
   diagnostic notation:
























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{
  1: "coap://as.example.com",
  3: "coap://light.example.com",
  2: "erikw",
  4: 1(1444064944),
  5: 1(1443944944),
  6: 1(1443944944),
  7: 2929,
  8: [
    {
      1: 2,
      2: "11",
      -1: 1,
      -2: h'bac5b11cad8f99f9c72b05cf4b9e26d244dc189f745228255a219a86d6a09eff',
      -3: h'20138bf82dc1b6d562be0fa54ab7804a3a64b6d72ccfed6b6fb6ed28bbfc117e'
    }
    ],
  9: [["/s/light", 1], ["/a/led", 5], ["/dtls", 2]]
}


        Figure 9: Full CWT with EC key in CBOR diagnostic notation

   Defined in CBOR.


a9                                      # map(9)
   01                                   # unsigned(1)
   75                                   # text(21)
      636f61703a2f2f61732e6578616d706c652e636f6d # "coap://as.example.com"
   03                                   # unsigned(3)
   78 18                                # text(24)
      636f61703a2f2f6c696768742e6578616d706c652e636f6d # "coap://light.example.com"
   02                                   # unsigned(2)
   65                                   # text(5)
      6572696b77                        # "erikw"
   04                                   # unsigned(4)
   c1                                   # tag(1)
      1a 5612aeb0                       # unsigned(1444064944)
   05                                   # unsigned(5)
   c1                                   # tag(1)
      1a 5610d9f0                       # unsigned(1443944944)
   06                                   # unsigned(6)
   c1                                   # tag(1)
      1a 5610d9f0                       # unsigned(1443944944)
   07                                   # unsigned(7)
   19 0b71                              # unsigned(2929)
   08                                   # unsigned(8)



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   81                                   # array(1)
      a5                                # map(5)
         01                             # unsigned(1)
         02                             # unsigned(2)
         02                             # unsigned(2)
         62                             # text(2)
            3131                        # "11"
         20                             # negative(0)
         01                             # unsigned(1)
         21                             # negative(1)
         58 20                          # bytes(32)
            bac5b11cad8f99f9c72b05cf4b9e26d244dc189f745228255a219a86d6a09eff # "\xBA\xC5\xB1\x1C\xAD\x8F\x99\xF9\xC7+\x05\xCFK\x9E&\xD2D\xDC\x18\x9FtR(%Z!\x9A\x86\xD6\xA0\x9E\xFF"
         22                             # negative(2)
         58 20                          # bytes(32)
            20138bf82dc1b6d562be0fa54ab7804a3a64b6d72ccfed6b6fb6ed28bbfc117e # "\x13\x8B\xF8-\xC1\xB6\xD5b\xBE\x0F\xA5J\xB7\x80J:d\xB6\xD7,\xCF\xEDko\xB6\xED(\xBB\xFC\x11~"
   09                                   # unsigned(9)
   83                                   # array(3)
      82                                # array(2)
         68                             # text(8)
            2f732f6c69676874            # "/s/light"
         01                             # unsigned(1)
      82                                # array(2)
         66                             # text(6)
            2f612f6c6564                # "/a/led"
         05                             # unsigned(5)
      82                                # array(2)
         65                             # text(5)
            2f64746c73                  # "/dtls"
         02                             # unsigned(2)


                    Figure 10: Full CWT with EC in CBOR

   Size of the CWT with an EC key is 194 bytes.  This is then packaged
   signed and encrypted using COSE.

Appendix B.  Acknowledgements

   This specification is based on JSON Web Token (JWT) [RFC7519], the
   authors of which also include Nat Sakimura and John Bradley.  A straw
   man proposal of CWT was written in the draft "Authorization for the
   Internet of Things using OAuth 2.0" [I-D.seitz-ace-oauth-authz] with
   the help of Ludwig Seitz and Goeran Selander.








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Appendix C.  Document History

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

   -02

   o  Added IANA registration for the application/cwt media type.
   o  Clarified the nested CWT language.
   o  Corrected nits identified by Ludwig Seitz.

   -01

   o  Added IANA registration for CWT Claims.
   o  Added IANA registration for the application/cwt CoAP content-
      format type.
   o  Added Samuel Erdtman as an editor.
   o  Changed Erik's e-mail address.

   -00

   o  Created the initial working group version based on draft-
      wahlstroem-ace-cbor-web-token-00.

Authors' Addresses

   Michael B. Jones
   Microsoft

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


   Erik Wahlstroem
   Sweden

   Email: erik@wahlstromstekniska.se


   Samuel Erdtman
   Spotify AB
   Birger Jarlsgatan 61, 4tr
   Stockholm  113 56
   Sweden

   Phone: +46702691499
   Email: erdtman@spotify.com





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   Hannes Tschofenig
   ARM Ltd.
   Hall in Tirol  6060
   Austria

   Email: Hannes.Tschofenig@arm.com













































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