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Versions: (draft-wahlstroem-oauth-cbor-web-token) 00 draft-ietf-ace-cbor-web-token

ACE Working Group                                          E. Wahlstroem
Internet-Draft                                          Nexus Technology
Intended status: Informational                                  M. Jones
Expires: June 6, 2016                                          Microsoft
                                                           H. Tschofenig
                                                                ARM Ltd.
                                                        December 4, 2015


                          CBOR Web Token (CWT)
                 draft-wahlstroem-ace-cbor-web-token-00

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 June 6, 2016.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of



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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Claims  . . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     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 . . . . . . . . . . . . .   4
       3.1.5.  nbf (Not Before) Claim  . . . . . . . . . . . . . . .   4
       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.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .   6
   Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . .   6
     A.1.  CWT with "aud" and symmetric key  . . . . . . . . . . . .   7
     A.2.  CWT with "aud" and EC key . . . . . . . . . . . . . . . .   8
     A.3.  Full CWT  . . . . . . . . . . . . . . . . . . . . . . . .  10
   Appendix B.  Acknowledgements . . . . . . . . . . . . . . . . . .  12
   Appendix C.  Document History . . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   The JSON Web Token (JWT) [5] 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) [3] and JSON
   Web Encryption (JWE) [4] to secure the contents of the JWT, which is
   a set of claims represented in JSON [5].  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 [6] and calls this new structure "CBOR Web Token (CWT)", which
   is a compact means of representing secured claims to be transferred



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   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) [7] 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" [1].

   This document reuses terminology from JWT [5] and COSE [7].

   Type3StringOrURI:

      The "Type3StringOrURI" term has the same meaning, syntax, and
      processing rules as the "StringOrUri" term defined in Section 2 of
      JWT [5], except that Type3StringOrURI uses CBOR major type 3
      instead of a JSON string value.

      FIXME: Use tag 32 for URIs?

   Type6NumericDate:

      The "Type6NumericDate" term has the same meaning, syntax, and
      processing rules as the "NumericDate" term defined in Section 2 of
      JWT [5], except that Type6NumericDate uses CBOR major type 6, with
      tag value 1, instead of a numeric JSON value.

   CBOR encoded claim key:

      The key used to identify a claim value.

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.






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   To keep CWTs as small as possible, the CBOR encoded claim keys are
   represented using CBOR major type 0.  Section 4 summaries all keys
   used to identity 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 [5], 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
   [5], 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
   [5], except that the format MUST be a Type3StringOrURI.  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
   [5], 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
   [5], except that the format MUST be a Type6NumericDate.  The CBOR
   encoded claim key 5 MUST be used to identify this claim.





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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
   [5], 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 [5], except
   that the format MUST be of major type 3 with a case-sensitive string
   value.  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                      | 3                        |
   \---------+------------------------+--------------------------/

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

   Note: Claims defined by the OpenID Foundation have not yet been
   included in the table above.

5.  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.



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6.  IANA Considerations

   This section will create a registry for CWT claims, possibly relating
   them to the JWT Claims Registry.

7.  Normative References

   [1]        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>.

   [2]        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>.

   [3]        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>.

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

   [5]        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>.

   [6]        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>.

   [7]        Schaad, J., "CBOR Encoded Message Syntax", draft-ietf-
              cose-msg-08 (work in progress), November 2015.

   [8]        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.








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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 [7]
   makes a CWT with "aud" and a symmetric key look like this in CBOR
   diagnostic notation:


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


                 Figure 3: CWT 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)
      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".


{
  "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 [7]
   makes a CWT with "aud" and an EC key look like this in CBOR
   diagnostic notation:






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{
  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.


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.





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A.3.  Full CWT

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


{
   "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 [7]
   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

   A straw man proposal of CWT was written in the draft "Authorization
   for the Internet of Things using OAuth 2.0" [8] with the help of
   Ludwig Seitz, Goeran Selander, and Samuel Erdtman.

Appendix C.  Document History

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

   -00




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   o  Created the initial version based on draft-wahlstroem-oauth-cbor-
      web-token-00.

   o  Now reference the JWT claim definitions, rather than repeating
      them.

Authors' Addresses

   Erik Wahlstroem
   Nexus Technology
   Sweden

   Email: erik.wahlstrom@nexusgroup.com
   URI:   https://www.nexusgroup.com


   Michael B. Jones
   Microsoft

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


   Hannes Tschofenig
   ARM Ltd.
   Hall in Tirol  6060
   Austria

   Email: Hannes.Tschofenig@arm.com






















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