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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: April 29, 2018
                                                              S. Erdtman
                                                              Spotify AB
                                                           H. Tschofenig
                                                                ARM Ltd.
                                                        October 26, 2017


                          CBOR Web Token (CWT)
                    draft-ietf-ace-cbor-web-token-09

Abstract

   CBOR Web Token (CWT) is a compact means of representing claims to be
   transferred between two parties.  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.  CWT is derived from JSON Web Token
   (JWT), but uses CBOR rather than JSON.

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 https://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 April 29, 2018.

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
   (https://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
     1.1.  CBOR Related Terminology  . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Claims  . . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Registered Claims . . . . . . . . . . . . . . . . . . . .   5
       3.1.1.  iss (Issuer) Claim  . . . . . . . . . . . . . . . . .   5
       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  . . . . . . . . . . . . . . . . .   6
   4.  Summary of the claim names, keys, and value types . . . . . .   6
   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  . . . . . . . . . .  10
       9.1.1.  Registration Template . . . . . . . . . . . . . . . .  10
       9.1.2.  Initial Registry Contents . . . . . . . . . . . . . .  11
     9.2.  Media Type Registration . . . . . . . . . . . . . . . . .  13
       9.2.1.  Registry Contents . . . . . . . . . . . . . . . . . .  13
     9.3.  CoAP Content-Formats Registration . . . . . . . . . . . .  13
       9.3.1.  Registry Contents . . . . . . . . . . . . . . . . . .  13
     9.4.  CBOR Tag registration . . . . . . . . . . . . . . . . . .  14
       9.4.1.  Registry Contents . . . . . . . . . . . . . . . . . .  14
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  14
     10.2.  Informative References . . . . . . . . . . . . . . . . .  15
   Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . .  15
     A.1.  Example CWT Claims Set  . . . . . . . . . . . . . . . . .  15
     A.2.  Example keys  . . . . . . . . . . . . . . . . . . . . . .  16
       A.2.1.  128-bit Symmetric Key . . . . . . . . . . . . . . . .  16



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       A.2.2.  256-bit Symmetric Key . . . . . . . . . . . . . . . .  16
       A.2.3.  ECDSA P-256 256-bit COSE Key  . . . . . . . . . . . .  17
     A.3.  Example Signed CWT  . . . . . . . . . . . . . . . . . . .  17
     A.4.  Example MACed CWT . . . . . . . . . . . . . . . . . . . .  18
     A.5.  Example Encrypted CWT . . . . . . . . . . . . . . . . . .  19
     A.6.  Example Nested CWT  . . . . . . . . . . . . . . . . . . .  20
     A.7.  Example MACed CWT with a floating-point value . . . . . .  21
   Appendix B.  Acknowledgements . . . . . . . . . . . . . . . . . .  22
   Appendix C.  Document History . . . . . . . . . . . . . . . . . .  22
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  24

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) [RFC8152] specification is used.

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

1.1.  CBOR Related Terminology

   In JSON, maps are called objects and only have one kind of map key: a
   string.  CBOR uses strings, negative integers, and unsigned integers
   as map keys.  The integers are used for compactness of encoding and
   easy comparison.  The inclusion of strings allows for an additional
   range of short encoded values to be used.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and




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   "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
   [RFC8152].

   StringOrURI
      The "StringOrURI" term has the same meaning, syntax, and
      processing rules as the "StringOrUri" term defined in Section 2 of
      JWT [RFC7519], except that it uses a CBOR 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 the CBOR numeric date representation
      (from Section 2.4.1 of [RFC7049]) is used.  The encoding is
      modified so that the leading tag 1 (epoch-based date/time) MUST be
      omitted.

   Claim Name
      The human-readable name used to identify a claim.

   Claim Key
      The CBOR map key used to identify a claim.

   Claim Value
      The CBOR map value representing the value of the claim.

   CWT Claims Set
      The 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 Claim Keys are represented
   using integers or text strings.  Section 4 summarizes all keys used
   to identify the claims defined in this document.







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3.1.  Registered Claims

   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 value is of type StringOrURI.  The Claim Key 1 is
   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 value is of type StringOrURI.  The Claim
   Key 2 is 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 value is of type StringOrURI.  The Claim
   Key 3 is 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 value is of type NumericDate.  The Claim
   Key 4 is 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 value is of type NumericDate.  The Claim
   Key 5 is 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




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   [RFC7519], except that the value is of type NumericDate.  The Claim
   Key 6 is 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 value is of type binary string.  The Claim Key 7 is
   used to identify this claim.

4.  Summary of the claim names, keys, and value types

   /---------+-----+----------------------------------\
   | Name    | Key | Value type                       |
   |---------+-----+----------------------------------|
   | iss     | 1   | text string                      |
   | sub     | 2   | text string                      |
   | aud     | 3   | text string                      |
   | exp     | 4   | integer or floating-point number |
   | nbf     | 5   | integer or floating-point number |
   | iat     | 6   | integer or floating-point number |
   | cti     | 7   | binary string                    |
   \---------+-----+----------------------------------/

        Figure 1: Summary of the claim names, keys, and value types

5.  CBOR Tags and Claim Values

   The claim values defined in this specification MUST NOT be prefixed
   with any CBOR tag.  For instance, while CBOR tag 1 (epoch-based date/
   time) 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, this does not prohibit future claim
   definitions from requiring the use of CBOR tags for those specific
   claims.

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.





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   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.

   / 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 [RFC8152]
       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 [RFC8152] 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 [RFC8152] for creating a COSE_Mac/COSE_Mac0
          object MUST be followed.





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       *  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 [RFC8152] 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, add the matching COSE
       CBOR tag, and return to Step 3.

   6.  If needed by the application, add the appropriate COSE CBOR tag
       to the COSE object to indicate the type of the COSE object.  If
       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 use it to determine the type of the CWT, COSE_Sign/
       COSE_Sign1, COSE_Mac/COSE_Mac0, or COSE_Encrypt/COSE_Encrypt0.
       If the object does not have a COSE CBOR tag, the COSE message
       type is determined from the application context.

   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.  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 [RFC8152] Section 4 (Signing Objects) for
          validating a COSE_Sign/COSE_Sign1 object.  Let the Message be
          the COSE_Sign/COSE_Sign1 payload.




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       *  Else, if the CWT is a COSE_Mac/COSE_Mac0, follow the steps
          specified in [RFC8152] 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 [RFC8152] Section 5 (Encryption
          Objects) for validating a COSE_Encrypt/COSE_Encrypt0 object.
          Let the Message be the resulting plaintext.

   6.  If the Message begins with a COSE CBOR tag, then the Message is a
       CWT that was the subject of nested signing, MACing, or encryption
       operations.  In this case, return to Step 1, using the Message as
       the CWT.

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

8.  Security Considerations

   The security of the CWT relies upon 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.

   While syntactically, the signing and encryption operations for Nested
   CWTs may be applied in any order, if both signing and encryption are
   necessary, normally producers should sign the message and then
   encrypt the result (thus encrypting the signature).  This prevents
   attacks in which the signature is stripped, leaving just an encrypted
   message, as well as providing privacy for the signer.  Furthermore,
   signatures over encrypted text are not considered valid in many
   jurisdictions.

9.  IANA Considerations







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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
   after a three-week review period on the cwt-reg-review@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 Experts may approve registration once they are
   satisfied that such a specification will be published.  [[ Note to
   the RFC Editor: The name of the mailing list should be determined in
   consultation with the IESG and IANA.  Suggested name: cwt-reg-
   review@ietf.org. ]]

   Registration requests sent to the mailing list for review should use
   an appropriate subject (e.g., "Request to register claim: example").
   Registration requests that are undetermined for a period longer than
   21 days can be brought to the IESG's attention (using the
   iesg@ietf.org mailing list) for resolution.

   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.

   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
   Experts.

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




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      make sense, the Designated Experts can choose to accept
      registrations for which the JWT Claim Name is listed as "N/A".

   Claim Key:
      CBOR map key for the claim.  Integer values between -256 and 255
      and strings of length 1 are designated as Standards Track Document
      required.  Integer values from -65536 to 65535 and strings of
      length 2 are designated as Specification Required.  Integer values
      of greater than 65535 and strings of length greater than 2 are
      designated as expert review.  Integer values less than -65536 are
      marked as private use.

   Claim Value Type(s):
      CBOR types that can be used for the claim value.

   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: (RESERVED)
   o  Claim Description: This registration reserves the key value 0.
   o  JWT Claim Name: N/A
   o  Claim Key: 0
   o  Claim Value Type(s): N/A
   o  Change Controller: IESG
   o  Specification Document(s): [[ this specification ]]

   o  Claim Name: "iss"
   o  Claim Description: Issuer
   o  JWT Claim Name: "iss"
   o  Claim Key: 1
   o  Claim Value Type(s): text string
   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"



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   o  Claim Key: 2
   o  Claim Value Type(s): text string
   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  Claim Key: 3
   o  Claim Value Type(s): text string
   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  Claim Key: 4
   o  Claim Value Type(s): integer or floating-point number
   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  Claim Key: 5
   o  Claim Value Type(s): integer or floating-point number
   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  Claim Key: 6
   o  Claim Value Type(s): integer or floating-point number
   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  Claim Key: 7
   o  Claim Value Type(s): binary string
   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

   [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,
              <https://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, <https://www.rfc-editor.org/info/rfc7049>.

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




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   [RFC8152]  Schaad, J., "CBOR Object Signing and Encryption (COSE)",
              RFC 8152, DOI 10.17487/RFC8152, July 2017,
              <https://www.rfc-editor.org/info/rfc8152>.

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", RFC 5226,
              DOI 10.17487/RFC5226, May 2008,
              <https://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,
              <https://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, <https://www.rfc-editor.org/info/rfc7515>.

   [RFC7516]  Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)",
              RFC 7516, DOI 10.17487/RFC7516, May 2015,
              <https://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].

   Where a byte string is to carry an embedded CBOR-encoded item, the
   diagnostic notation for this CBOR data item can be enclosed in '<<'
   and '>>' to notate the byte string resulting from encoding the data
   item, e.g., h'63666F6F' translates to <<"foo">>.

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.




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   a70175636f61703a2f2f61732e6578616d706c652e636f6d02656572696b7703
   7818636f61703a2f2f6c696768742e6578616d706c652e636f6d041a5612aeb0
   051a5610d9f0061a5610d9f007420b71

              Figure 3: Example CWT Claims Set as hex string

   {
     / 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

   a42050231f4c4d4d3051fdc2ec0a3851d5b3830104024c53796d6d6574726963
   313238030a

            Figure 5: 128-bit symmetric COSE_Key as hex string

   {
     / k /   -1: h'231f4c4d4d3051fdc2ec0a3851d5b383'
     / kty /  1: 4 / Symmetric /,
     / kid /  2: h'53796d6d6574726963313238' / 'Symmetric128' /,
     / alg /  3: 10 / AES-CCM-16-64-128 /
   }

     Figure 6: 128-bit symmetric COSE_Key in CBOR diagnostic notation

A.2.2.  256-bit Symmetric Key

   a4205820403697de87af64611c1d32a05dab0fe1fcb715a86ab435f1ec99192d
   795693880104024c53796d6d6574726963323536030a

            Figure 7: 256-bit symmetric COSE_Key as hex string





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   {
     / k /   -1: h'403697de87af64611c1d32a05dab0fe1fcb715a86ab435f1
                   ec99192d79569388'
     / kty /  1: 4 / Symmetric /,
     / kid /  4: h'53796d6d6574726963323536' / 'Symmetric256' /,
     / alg /  3: 4 / HMAC 256/64 /
   }

     Figure 8: 256-bit symmetric COSE_Key in CBOR diagnostic notation

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

   a72358206c1382765aec5358f117733d281c1c7bdc39884d04a45a1e6c67c858
   bc206c1922582060f7f1a780d8a783bfb7a2dd6b2796e8128dbbcef9d3d168db
   9529971a36e7b9215820143329cce7868e416927599cf65a34f3ce2ffda55a7e
   ca69ed8919a394d42f0f2001010202524173796d6d6574726963454344534132
   35360326

              Figure 9: 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 /,
     / kid /  2: h'4173796d6d657472696345434453413
                   23536' / 'AsymmetricECDSA256' /,
     / alg /  3: -7 / ECDSA 256 /
   }

       Figure 10: ECDSA 256-bit COSE Key in CBOR diagnostic notation

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.







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   d28443a10126a104524173796d6d657472696345434453413235365850a701756
   36f61703a2f2f61732e6578616d706c652e636f6d02656572696b77037818636f
   61703a2f2f6c696768742e6578616d706c652e636f6d041a5612aeb0051a5610d
   9f0061a5610d9f007420b7158405427c1ff28d23fbad1f29c4c7c6a555e601d6f
   a29f9179bc3d7438bacaca5acd08c8d4d4f96131680c429a01f85951ecee743a5
   2b9b63632c57209120e1c9e30

                    Figure 11: Signed CWT as hex string

   18(
     [
       / protected / << {
         / alg / 1: -7 / ECDSA 256 /
       } >>,
       / unprotected / {
         / kid / 4: h'4173796d6d657472696345434453413
                      23536' / 'AsymmetricECDSA256' /
       },
       / payload / << {
         / 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'5427c1ff28d23fbad1f29c4c7c6a555e601d6fa29f
                       9179bc3d7438bacaca5acd08c8d4d4f96131680c42
                       9a01f85951ecee743a52b9b63632c57209120e1c9e
                       30'
     ]
   )

             Figure 12: Signed CWT in CBOR diagnostic notation

A.4.  Example MACed CWT

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

   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.







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   d83dd18443a10104a1044c53796d6d65747269633235365850a70175636f6170
   3a2f2f61732e6578616d706c652e636f6d02656572696b77037818636f61703a
   2f2f6c696768742e6578616d706c652e636f6d041a5612aeb0051a5610d9f006
   1a5610d9f007420b7148093101ef6d789200

              Figure 13: MACed CWT with CWT tag as hex string

   61(
     17(
       [
         / protected / << {
           / alg / 1: 4 / HMAC-256-64 /
         } >>,
         / unprotected / {
           / kid / 4: h'53796d6d6574726963323536' / 'Symmetric256' /
         },
         / payload / << {
           / 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 14: 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.

   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.

   d08343a1010aa2044c53796d6d6574726963313238054d99a0d7846e762c49ff
   e8a63e0b5858b918a11fd81e438b7f973d9e2e119bcb22424ba0f38a80f27562
   f400ee1d0d6c0fdb559c02421fd384fc2ebe22d7071378b0ea7428fff157444d
   45f7e6afcda1aae5f6495830c58627087fc5b4974f319a8707a635dd643b

                  Figure 15: Encrypted CWT as hex string




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   16(
     [
       / protected / << {
         / alg / 1: 10 / AES-CCM-16-64-128 /
       } >>,
       / unprotected / {
         / kid / 4: h'53796d6d6574726963313238' / 'Symmetric128' /,
         / iv /  5: h'99a0d7846e762c49ffe8a63e0b'
       },
       / ciphertext / h'b918a11fd81e438b7f973d9e2e119bcb22424ba0f38
                        a80f27562f400ee1d0d6c0fdb559c02421fd384fc2e
                        be22d7071378b0ea7428fff157444d45f7e6afcda1a
                        ae5f6495830c58627087fc5b4974f319a8707a635dd
                        643b'
     ]
   )

           Figure 16: 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.

   d08343a1010aa2044c53796d6d6574726963313238054d4a0694c0e69ee6b595
   6655c7b258b7f6b0914f993de822cc47e5e57a188d7960b528a747446fe12f0e
   7de05650dec74724366763f167a29c002dfd15b34d8993391cf49bc91127f545
   dba8703d66f5b7f1ae91237503d371e6333df9708d78c4fb8a8386c8ff09dc49
   af768b23179deab78d96490a66d5724fb33900c60799d9872fac6da3bdb89043
   d67c2a05414ce331b5b8f1ed8ff7138f45905db2c4d5bc8045ab372bff142631
   610a7e0f677b7e9b0bc73adefdcee16d9d5d284c616abeab5d8c291ce0

             Figure 17: Signed and Encrypted CWT as hex string






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   16(
     [
       / protected / << {
         / alg / 1: 10 / AES-CCM-16-64-128 /
       } >>,
       / unprotected / {
         / kid / 4: h'53796d6d6574726963313238' / 'Symmetric128' /,
         / iv /  5: h'86bbd41cc32604396324b7f380'
       },
       / ciphertext / h'f6b0914f993de822cc47e5e57a188d7960b528a7474
                        46fe12f0e7de05650dec74724366763f167a29c002d
                        fd15b34d8993391cf49bc91127f545dba8703d66f5b
                        7f1ae91237503d371e6333df9708d78c4fb8a8386c8
                        ff09dc49af768b23179deab78d96490a66d5724fb33
                        900c60799d9872fac6da3bdb89043d67c2a05414ce3
                        31b5b8f1ed8ff7138f45905db2c4d5bc8045ab372bf
                        f142631610a7e0f677b7e9b0bc73adefdcee16d9d5d
                        284c616abeab5d8c291ce0'
     ]
   )

      Figure 18: Signed and Encrypted CWT in CBOR diagnostic notation

A.7.  Example MACed CWT with a floating-point value

   This section shows a MACed CWT with a single recipient and a simple
   CWT Claims Set. The CWT Claims Set with a floating-point 'iat' value.

   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.

   d18443a10104a1044c53796d6d65747269633235364ba106fb41d584367c2000
   0048b8816f34c0542892

      Figure 19: MACed CWT with a floating-point value as hex string















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   17(
     [
       / protected / << {
         / alg / 1: 4 / HMAC-256-64 /
       } >>,
       / unprotected / {
         / kid / 4: h'53796d6d6574726963323536' / 'Symmetric256' /,
       },
       / payload / << {
         / iat / 6: 1443944944.5
       } >>,
       / tag / h'b8816f34c0542892'
     ]
   )

    Figure 20: MACed CWT with a floating-point value 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.  It also
   incorporates suggestions made by many people, notably Carsten
   Bormann, Jim Schaad, Ludwig Seitz, and Goeran Selander.

Appendix C.  Document History

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

   -09

   o  Added key ID values to the examples.

   o  Key values for the examples are now represented in COSE_Key format
      using CBOR diagnostic notation.

   -08

   o  Updated the diagnostic notation for embedded objects in the
      examples, addressing feedback by Carsten Bormann.

   -07

   o  Updated examples for signing and encryption.  Signatures are now
      deterministic as recommended by COSE specification.

   -06




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   o  Addressed review comments by Carsten Bormann and Jim Schaad.  All
      changes were editorial in nature.

   -05

   o  Addressed working group last call comments with the following
      changes:

   o  Say that CWT is derived from JWT, rather than CWT is a profile of
      JWT.

   o  Used CBOR type names in descriptions, rather than major/minor type
      numbers.

   o  Clarified the NumericDate and StringOrURI descriptions.

   o  Changed to allow CWT claim names to use values of any legal CBOR
      map key type.

   o  Changed to use the CWT tag to identify nested CWTs instead of the
      CWT content type.

   o  Added an example using a floating-point date value.

   o  Acknowledged reviewers.

   -04

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

   -03

   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




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   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


   Hannes Tschofenig
   ARM Ltd.
   Hall in Tirol  6060
   Austria

   Email: Hannes.Tschofenig@arm.com






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