CBOR Web Token (CWT) Claims in COSE Headers
draft-ietf-cose-cwt-claims-in-headers-03

COSE                                                           T. Looker
Internet-Draft                                                     Mattr
Intended status: Standards Track                                M. Jones
Expires: 13 September 2023                                     Microsoft
                                                           12 March 2023

              CBOR Web Token (CWT) Claims in COSE Headers
                draft-ietf-cose-cwt-claims-in-headers-03

Abstract

   This document describes how to include CBOR Web Token (CWT) claims in
   the header parameters of any COSE structure.  This functionality
   helps to facilitate applications that wish to make use of CBOR Web
   Token (CWT) claims in encrypted COSE structures and/or COSE
   structures featuring detached signatures, while having some of those
   claims be available before decryption and/or without inspecting the
   detached payload.

Discussion Venues

   This note is to be removed before publishing as an RFC.

   Source for this draft and an issue tracker can be found at
   https://github.com/tplooker/draft-ietf-cose-cwt-claims-in-headers.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on 13 September 2023.

Copyright Notice

   Copyright (c) 2023 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   Please review these documents carefully, as they describe your rights
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Representation  . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .   3
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
   8.  Informative References  . . . . . . . . . . . . . . . . . . .   4
   Appendix A.  Document History . . . . . . . . . . . . . . . . . .   4
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   In some applications of COSE, it is useful to have a standard
   representation of CWT claims [RFC8392] available in the header
   parameters.  These include encrypted COSE structures, which may or
   may not be an encrypted CWT and/or those featuring a detached
   signature.

   Section 5.3 of the JWT RFC [RFC7519] defined a similar mechanism for
   expressing selected JWT based claims as JOSE header parameters.  This
   JWT feature was motivated by the desire to have certain claims, such
   as the Issuer value, be visible to software processing the JWT, even
   though the JWT is encrypted.  No corresponding feature was
   standardized for CWTs, which was an omission that this specification
   corrects.

   Directly including CWT claim values as COSE header parameter values
   would not work, since there are conflicts between the numeric header
   parameter assignments and the numeric CWT claim assignments.
   Instead, this specification defines a single header parameter
   registered in the IANA "COSE Header Parameters" registry that creates
   a location to store CWT claims in a COSE header parameter.

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2.  Terminology

3.  Representation

   This document defines the following COSE header parameter:

     +========+================+=======+============+===============+
     | Name   | Label          | Value | Value      | Description   |
     |        |                | Type  | Registry   |               |
     +========+================+=======+============+===============+
     | CWT    | TBD (requested | map   | [IANA.CWT] | location for  |
     | claims | assignment 11) |       |            | CWT claims in |
     |        |                |       |            | COSE headers  |
     +--------+----------------+-------+------------+---------------+

                                 Table 1

   The following is a non-normative description for the value type of
   the CWT claim header parameter using CDDL [RFC8610].

   CWT-Claims = {
    * Claim-Label => any
   }

   Claim-Label = int / text

   It is RECOMMENDED that the CWT claims header parameter is used only
   in a protected header to avoid the contents being malleable.  The
   header parameter MUST only occur once in either the protected or
   unprotected header of a COSE structure.

4.  Privacy Considerations

   Some of the registered CWT claims may contain privacy-sensitive
   information.  Therefore care must be taken when expressing CWT claims
   in COSE headers.

5.  Security Considerations

   In cases where CWT claims are both present in the payload and the
   header, an application receiving such as structure MUST verify that
   their values are identical, unless the application defines other
   specific processing rules for these claims.

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6.  IANA Considerations

   IANA is requested to register the new COSE Header parameter in the
   table in Section 3 in the "COSE Header Parameters" registry
   [IANA.COSE].

7.  Normative References

   [IANA.COSE]
              IANA, "COSE Header Parameters",
              <https://www.iana.org/assignments/cose/cose.xhtml#header-
              parameters>.

   [IANA.CWT] IANA, "CBOR Web Token (CWT) Claims",
              <https://www.iana.org/assignments/cwt/cwt.xhtml>.

8.  Informative References

   [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>.

   [RFC8392]  Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig,
              "CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392,
              May 2018, <https://www.rfc-editor.org/info/rfc8392>.

   [RFC8610]  Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
              Definition Language (CDDL): A Notational Convention to
              Express Concise Binary Object Representation (CBOR) and
              JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
              June 2019, <https://www.rfc-editor.org/info/rfc8610>.

Appendix A.  Document History

   -03

   *  Added recommendation around header treatment in protected vs
      unprotected.

   -02

   *  Added CDDL description for CWT claim value.

   -01

   *  Changed example from Key ID to Issuer.

   -00

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   *  Created draft-ietf-cose-cwt-claims-in-headers-00 from draft-
      looker-cose-cwt-claims-in-headers-00 following working group
      adoption.

Authors' Addresses

   Tobias Looker
   Mattr
   Email: tobias.looker@mattr.global

   Michael B. Jones
   Microsoft
   Email: mbj@microsoft.com
   URI:   https://self-issued.info/

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