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Versions: (draft-wahlstroem-ace-cbor-web-token) 00 01 02 03 04 05 06 07 08 09

ACE Working Group                                               M. Jones
Internet-Draft                                                 Microsoft
Intended status: Standards Track                           E. Wahlstroem
Expires: October 15, 2017
                                                              S. Erdtman
                                                              Spotify AB
                                                           H. Tschofenig
                                                                ARM Ltd.
                                                          April 13, 2017


                          CBOR Web Token (CWT)
                    draft-ietf-ace-cbor-web-token-04

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 October 15, 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 . . . . . . . . . . . . . . . . .   5
       3.1.3.  aud (Audience) Claim  . . . . . . . . . . . . . . . .   5
       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.  CBOR Tags and Claim Values  . . . . . . . . . . . . . . . . .   6
   6.  CWT CBOR Tag  . . . . . . . . . . . . . . . . . . . . . . . .   6
   7.  Creating and Validating CWTs  . . . . . . . . . . . . . . . .   7
     7.1.  Creating a CWT  . . . . . . . . . . . . . . . . . . . . .   7
     7.2.  Validating a CWT  . . . . . . . . . . . . . . . . . . . .   8
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
     9.1.  CBOR Web Token (CWT) Claims Registry  . . . . . . . . . .   9
       9.1.1.  Registration Template . . . . . . . . . . . . . . . .  10
       9.1.2.  Initial Registry Contents . . . . . . . . . . . . . .  10
     9.2.  Media Type Registration . . . . . . . . . . . . . . . . .  12
       9.2.1.  Registry Contents . . . . . . . . . . . . . . . . . .  12
     9.3.  CoAP Content-Formats Registration . . . . . . . . . . . .  12
       9.3.1.  Registry Contents . . . . . . . . . . . . . . . . . .  12
     9.4.  CBOR Tag registration . . . . . . . . . . . . . . . . . .  13
       9.4.1.  Registry Contents . . . . . . . . . . . . . . . . . .  13
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  13
     10.2.  Informative References . . . . . . . . . . . . . . . . .  14
   Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . .  14
     A.1.  Example CWT Claims Set  . . . . . . . . . . . . . . . . .  14
     A.2.  Example keys  . . . . . . . . . . . . . . . . . . . . . .  15
       A.2.1.  128-bit Symmetric Key as Hex Encoded String . . . . .  15



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       A.2.2.  256-bit Symmetric Key as Hex Encoded String . . . . .  15
       A.2.3.  ECDSA P-256 256-bit COSE Key  . . . . . . . . . . . .  15
     A.3.  Example Signed CWT  . . . . . . . . . . . . . . . . . . .  16
     A.4.  Example MACed CWT . . . . . . . . . . . . . . . . . . . .  17
     A.5.  Example Encrypted CWT . . . . . . . . . . . . . . . . . .  17
     A.6.  Example Nested CWT  . . . . . . . . . . . . . . . . . . .  18
   Appendix B.  Acknowledgements . . . . . . . . . . . . . . . . . .  19
   Appendix C.  Document History . . . . . . . . . . . . . . . . . .  19
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  20

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 Signature
   (JWS) [RFC7515] and JSON Web Encryption (JWE) [RFC7516] to secure the
   contents of the JWT, which is a set of claims represented in JSON.
   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.

   An alternative encoding of claims is defined in this document.
   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].

   StringOrURI:
      The "StringOrURI" term has the same meaning, syntax, and
      processing rules as the "StringOrUri" term defined in Section 2 of



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      JWT [RFC7519], except that a CWT StringOrURI uses CBOR major type
      3 (text string) instead of a JSON string value.

   NumericDate:
      The "NumericDate" term has the same meaning, syntax, and
      processing rules as the "NumericDate" term defined in Section 2 of
      JWT [RFC7519], except that a CWT NumericDate uses one of the CBOR
      numeric types (0, 1, or 7 with subtypes 25, 26, or 27), instead of
      a numeric JSON value.  The numeric date values that can used for a
      CWT NumericDate are identical to the epoch-based date/time values
      that are specified to follow the tag defined in Section 2.4.1
      (Date and Time) of [RFC7049], except that the tag itself need not
      be present.

   CBOR encoded claim key:
      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 StringOrURI.  The CBOR encoded claim
   key 1 MUST be used to identify this claim.




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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 StringOrURI.  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 StringOrURI.  The CBOR
   encoded claim key 3 MUST be used to identify this claim.

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 CWT NumericDate.  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 CWT NumericDate.  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 CWT NumericDate.  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








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   /---------+------------------------+-------------------------------\
   | Claim   | CBOR encoded claim key | CBOR major type of value      |
   |---------+------------------------+-------------------------------|
   | iss     | 1                      | 3                             |
   | sub     | 2                      | 3                             |
   | aud     | 3                      | 3                             |
   | exp     | 4                      | 0, 1, or 7 with float subtype |
   | nbf     | 5                      | 0, 1, or 7 with float subtype |
   | iat     | 6                      | 0, 1, or 7 with float subtype |
   | cti     | 7                      | 2                             |
   \---------+------------------------+-------------------------------/

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

5.  CBOR Tags and Claim Values

   The use of CBOR tags to prefix any of the claim values defined in
   this specification is NOT RECOMMENDED.  For instance, while CBOR tag
   6.1 (seconds-since-the-epoch) could logically be prefixed to values
   of the "exp", "nbf", and "iat" claims, this is unnecessary, since the
   representation of the claim values is already specified by the claim
   definitions.  Tagging claim values would only take up extra space,
   without adding information.  However, other claims defined by other
   specifications can specify that a tag prefix the claim value, when
   appropriate.

6.  CWT CBOR Tag

   How to determine that a CBOR data structure is a CWT is application-
   dependent.  In some cases, this information is known from the
   application context, such as from the position of the CWT in a data
   structure at which the value must be a CWT.  One method of indicating
   that a CBOR object is a CWT is the use of the "application/cwt"
   content type by a transport protocol.

   This section defines the CWT CBOR tag as another means for
   applications to declare that a CBOR data structure is a CWT.  Its use
   is optional, and is intended for use in cases in which this
   information would not otherwise be known.

   If present, the CWT tag MUST prefix a tagged object using one of the
   COSE CBOR tags.  In this example, the COSE_Mac0 tag is used.  The
   actual COSE_Mac0 object has been excluded from this example.







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   / CWT CBOR tag / 61(
     / COSE_Mac0 CBOR tag / 17(
       / COSE_Mac0 object /
     )
   )

                   Figure 2: Example of a CWT tag usage

7.  Creating and Validating CWTs

7.1.  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 per 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



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       type "application/cwt" in the new COSE Header created in that
       step.

   6.  If needed by the application, add the appropriate COSE CBOR tag
       to the COSE object to indicate type of COSE object.  If also
       needed by the application, add the CWT CBOR tag to indicate that
       the COSE object is a CWT.

7.2.  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 invalid input.

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

   2.  If the object begins with the CWT CBOR tag, remove it and verify
       that one of the COSE CBOR tags follows it.

   3.  If the object is tagged with one of the COSE CBOR tags, remove it
       and verify that it corresponds to the structure of the following
       COSE object.

   4.  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.

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

   6.  Depending upon whether the CWT is a signed, MACed, or encrypted,
       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



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          (Encryption Objects) for validating a COSE_Encrypt/
          COSE_Encrypt0 object.  Let the Message be the resulting
          plaintext.

   7.  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.

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

8.  Security Considerations

   The security of the CWT is dependent on the protections offered by
   COSE.  Unless the claims in a CWT are protected, an adversary can
   modify, add, or remove claims.  Since the claims conveyed in a CWT
   may be used to make authorization decisions, it is not only important
   to protect the CWT in transit but also to ensure that the recipient
   can authenticate the party that assembled 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
   of the validity of the information provided.

9.  IANA Considerations

9.1.  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.






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9.1.1.  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".

   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.

9.1.2.  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



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   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"
   o  Claim Description: Expiration Time
   o  JWT Claim Name: "exp"
   o  CBOR Key Value: 4
   o  CBOR Major Type: 0, 1, or 7 with subtypes 25, 26, or 27
   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: 0, 1, or 7 with subtypes 25, 26, or 27
   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: 0, 1, or 7 with subtypes 25, 26, or 27
   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




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   o  Specification Document(s): Section 3.1.7 of [[ this specification
      ]]

9.2.  Media Type Registration

   This section registers the "application/cwt" media type 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.

9.2.1.  Registry Contents

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

9.3.  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].

9.3.1.  Registry Contents

   o  Media Type: application/cwt
   o  Encoding: -
   o  Id: TBD (maybe 61)



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   o  Reference: [[ this specification ]]

9.4.  CBOR Tag registration

   This section registers the CWT CBOR tag in the "CBOR Tags" registry
   [IANA.CBOR.Tags].

9.4.1.  Registry Contents

   o  CBOR Tag: TBD (maybe 61 to use the same value as the Content-
      Format)
   o  Data Item: CBOR Web Token (CWT)
   o  Semantics: CBOR Web Token (CWT), as defined in [[ this
      specification ]]
   o  Reference: [[ this specification ]]
   o  Point of Contact: Michael B.  Jones, mbj@microsoft.com

10.  References

10.1.  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.CBOR.Tags]
              IANA, "Concise Binary Object Representation (CBOR) Tags",
              <http://www.iana.org/assignments/cbor-tags/
              cbor-tags.xhtml>.

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

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

   [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>.

   [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>.




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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>.

10.2.  Informative References

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

   [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>.

   [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>.

Appendix A.  Examples

   This appendix includes a set of CWT examples that show how the CWT
   Claims Set can be protected.  There are examples that are signed,
   MACed, encrypted, and that use nested signing and encryption.  To
   make the examples easier to read, they are presented both as hex
   strings and in the extended CBOR diagnostic notation described in
   Section 6 of [RFC7049].

A.1.  Example CWT Claims Set

   The CWT Claims Set used for the different examples displays usage of
   all the defined claims.  For signed and MACed examples, the CWT
   Claims Set is the CBOR encoding as a binary string.

   a70175636f61703a2f2f61732e6578616d706c652e636f6d02656572696b7703
   7818636f61703a2f2f6c696768742e6578616d706c652e636f6d041a5612aeb0
   051a5610d9f0061a5610d9f007420b71

              Figure 3: Example CWT Claims Set as hex string



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   {
     / iss / 1: "coap://as.example.com",
     / sub / 2: "erikw",
     / aud / 3: "coap://light.example.com",
     / exp / 4: 1444064944,
     / nbf / 5: 1443944944,
     / iat / 6: 1443944944,
     / cti / 7: h'0b71'
   }

       Figure 4: Example CWT Claims Set in CBOR diagnostic notation

A.2.  Example keys

   This section contains the keys used to sign, MAC, and encrypt the
   messages in this appendix.  Line breaks are for display purposes
   only.

A.2.1.  128-bit Symmetric Key as Hex Encoded String

   8e82e68e61654ecb5a369fe8be7572dd

A.2.2.  256-bit Symmetric Key as Hex Encoded String

   403697de87af64611c1d32a05dab0fe1fcb715a86ab435f1ec99192d79569388

A.2.3.  ECDSA P-256 256-bit COSE Key

   a622582060f7f1a780d8a783bfb7a2dd6b2796e8128dbbcef9d3d168db952997
   1a36e7b92358206c1382765aec5358f117733d281c1c7bdc39884d04a45a1e6c
   67c858bc206c1903260102215820143329cce7868e416927599cf65a34f3ce2f
   fda55a7eca69ed8919a394d42f0f2001

              Figure 5: ECDSA 256-bit COSE Key as hex string

   {
     / d /   -4: h'6c1382765aec5358f117733d281c1c7bdc39884d04a45a1e
                   6c67c858bc206c19',
     / y /   -3: h'60f7f1a780d8a783bfb7a2dd6b2796e8128dbbcef9d3d168
                   db9529971a36e7b9',
     / x /   -2: h'143329cce7868e416927599cf65a34f3ce2ffda55a7eca69
                   ed8919a394d42f0f',
     / crv / -1: 1 / P-256 / ,
     / kty /  1: 2 / EC2 / ,
     / alg /  3: -7 / ECDSA 256 /
   }

       Figure 6: ECDSA 256-bit COSE Key in CBOR diagnostic notation



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A.3.  Example Signed CWT

   This section shows a signed CWT with a single recipient and a full
   CWT Claims Set.

   The signature is generated using the private key listed in
   Appendix A.2.3 and it can be validated using the public key from
   Appendix A.2.3.  Line breaks are for display purposes only.

   d28443a10126a05850a70175636f61703a2f2f61732e6578616d706c652e636f6
   d02656572696b77037818636f61703a2f2f6c696768742e6578616d706c652e63
   6f6d041a5612aeb0051a5610d9f0061a5610d9f007420b7158401fe410abce650
   effed497f05d7f9462de67d571384097de0d96f1e2514d284cdd85634f269af6c
   36c64f22e7691abb464bed2ff23176cdba9fd9e213f637d082

                    Figure 7: Signed CWT as hex string

   18(
     [
       / protected / h'a10126' / {
         / alg / 1: -7 / ECDSA 256 /
       } / ,
       / unprotected / {},
       / payload / h'a70175636f61703a2f2f61732e6578616d706c652e63
                     6f6d02656572696b77037818636f61703a2f2f6c6967
                     68742e6578616d706c652e636f6d041a5612aeb0051a
                     5610d9f0061a5610d9f007420b71' / {
           / iss / 1: "coap://as.example.com",
           / sub / 2: "erikw",
           / aud / 3: "coap://light.example.com",
           / exp / 4: 1444064944,
           / nbf / 5: 1443944944,
           / iat / 6: 1443944944,
           / cti / 7: h'0b71'
         } / ,
       / signature / h'1fe410abce650effed497f05d7f9462de67d571384
                       097de0d96f1e2514d284cdd85634f269af6c36c64f
                       22e7691abb464bed2ff23176cdba9fd9e213f637d0
                       82'
     ]
   )

             Figure 8: Signed CWT in CBOR diagnostic notation








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A.4.  Example MACed CWT

   This section shows a MACed CWT with a single recipient and a full CWT
   Claims Set.

   The MAC is generated using the 256-bit symmetric key from
   Appendix A.2.2 with a 64-bit truncation.  Line breaks are for display
   purposes only.

   d83dd18443a10104a05850a70175636f61703a2f2f61732e6578616d706c652e
   636f6d02656572696b77037818636f61703a2f2f6c696768742e6578616d706c
   652e636f6d041a5612aeb0051a5610d9f0061a5610d9f007420b7148093101ef
   6d789200

              Figure 9: MACed CWT with CWT tag as hex string

   61(
     17(
       [
         / protected / h'a10104' / {
           / alg / 1: 4 / HMAC 256/64 /
         } / ,
         / unprotected / {},
         / payload / h'a70175636f61703a2f2f61732e6578616d706c652e636f
                       6d02656572696b77037818636f61703a2f2f6c69676874
                       2e6578616d706c652e636f6d041a5612aeb0051a5610d9
                       f0061a5610d9f007420b71' / {
             / iss / 1: "coap://as.example.com",
             / sub / 2: "erikw",
             / aud / 3: "coap://light.example.com",
             / exp / 4: 1444064944,
             / nbf / 5: 1443944944,
             / iat / 6: 1443944944,
             / cti / 7: h'0b71'
           } / ,
         / tag / h'093101ef6d789200'
       ]
     )
   )

       Figure 10: MACed CWT with CWT tag in CBOR diagnostic notation

A.5.  Example Encrypted CWT

   This section shows an encrypted CWT with a single recipient and a
   full CWT Claims Set.





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   The encryption is done with AES-CCM mode using the 128-bit symmetric
   key from Appendix A.2.1 with a 64-bit tag and 13-byte nonce, i.e.,
   COSE AES-CCM-16-64-128.  Line breaks are for display purposes only.

   d08343a1010aa1054d3a869e378e72b77d077c29be025858d275ad9cd7df1b10
   ba8cde785c74b1e1e6ada287e2baf1451b06862529b784d230b0111773b6c369
   1319aec4dcc379fe47115a5d62632727c05f4567fc84dd79554db86676a14978
   42de805d8be93180af4d6ff3043886a0

                  Figure 11: Encrypted CWT as hex string

   16(
     [
       / protected / h'a1010a' / {
         / alg / 1: 10 / AES-CCM-16-64-128 /
       } /,
       / unprotected / {
         / iv / 5: h'3a869e378e72b77d077c29be02'
       },
       / ciphertext / h'd275ad9cd7df1b10ba8cde785c74b1e1e6ada287e2b
                        af1451b06862529b784d230b0111773b6c3691319ae
                        c4dcc379fe47115a5d62632727c05f4567fc84dd795
                        54db86676a1497842de805d8be93180af4d6ff30438
                        86a0'
     ]
   )

           Figure 12: Encrypted CWT in CBOR diagnostic notation

A.6.  Example Nested CWT

   This section shows a Nested CWT, signed and then encrypted, with a
   single recipient and a full CWT Claims Set.

   The signature is generated using the private ECDSA key from
   Appendix A.2.3 and it can be validated using the public ECDSA parts
   from Appendix A.2.3.  The encryption is done with AES-CCM mode using
   the 128-bit symmetric key from Appendix A.2.1 with a 64-bit tag and
   13-byte nonce, i.e., COSE AES-CCM-16-64-128.  The content type is set
   to CWT to indicate that there are multiple layers of COSE protection
   before finding the CWT Claims Set. The decrypted ciphertext will be a
   COSE_sign1 structure.  In this example, it is the same one as in
   Appendix A.3, i.e., a Signed CWT Claims Set.  Note that there is no
   limitation to the number of layers; this is an example with two
   layers.  Line breaks are for display purposes only.






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   d08346a203183d010aa1054d9120e5dc42c9f9aec05ebe8a4858a538be026c02
   4a40b19d6dbea3ddb18b31021f874a097a05ff3cdaa4665bafc8e46a3d7f37ad
   f002fe57eee267f8f62a9c1621af75e1ecd742a3d801c2cc82358cf104a8d902
   4d38a599ea6027d482dc2948a88fe83f9734804299c832401029e2d32a984789
   c8e9563e8d2a751323bb7e4462b549e0fa89ef93f78bf6425635fba76b4aa804
   7908e89b3b7c3d59d8a80e22f70a1b6ee8c162c564341c2f15cec252d3da038c

             Figure 13: Signed and Encrypted CWT as hex string

   16(
     [
       / protected / h'a203183d010a' / {
         / content type / 3: 61, / CWT /
         / alg / 1: 10 / AES-CCM-16-64-128 /
       } / ,
       / unprotected / {
         / iv / 5: h'9120e5dc42c9f9aec05ebe8a48'
       },
       / ciphertext / h'38be026c024a40b19d6dbea3ddb18b31021f874a097
                        a05ff3cdaa4665bafc8e46a3d7f37adf002fe57eee2
                        67f8f62a9c1621af75e1ecd742a3d801c2cc82358cf
                        104a8d9024d38a599ea6027d482dc2948a88fe83f97
                        34804299c832401029e2d32a984789c8e9563e8d2a7
                        51323bb7e4462b549e0fa89ef93f78bf6425635fba7
                        6b4aa8047908e89b3b7c3d59d8a80e22f70a1b6ee8c
                        162c564341c2f15cec252d3da038c'
     ]
   )

      Figure 14: Signed and Encrypted CWT in CBOR diagnostic notation

Appendix B.  Acknowledgements

   This specification is based on JSON Web Token (JWT) [RFC7519], the
   authors of which also include Nat Sakimura and John Bradley.  Ludwig
   Seitz and Goeran Selander have made contributions the specification.

Appendix C.  Document History

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

   -04

   o  Specified that the use of CBOR tags to prefix any of the claim
      values defined in this specification is NOT RECOMMENDED.

   -03




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   o  Reworked the examples to include signed, MACed, encrypted, and
      nested CWTs.
   o  Defined the CWT CBOR tag and explained its usage.

   -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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