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COSE "typ" (type) Header Parameter
draft-ietf-cose-typ-header-parameter-05

Document Type Active Internet-Draft (cose WG)
Authors Michael B. Jones , Orie Steele
Last updated 2024-04-10 (Latest revision 2024-04-03)
Replaces draft-jones-cose-typ-header-parameter
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draft-ietf-cose-typ-header-parameter-05
COSE Working Group                                            M.B. Jones
Internet-Draft                                    Self-Issued Consulting
Intended status: Standards Track                               O. Steele
Expires: 5 October 2024                                        Transmute
                                                            3 April 2024

                   COSE "typ" (type) Header Parameter
                draft-ietf-cose-typ-header-parameter-05

Abstract

   This specification adds the equivalent of the JSON Object Signing and
   Encryption (JOSE) typ (type) header parameter to CBOR Object Signing
   and Encryption (COSE).  This enables the benefits of explicit typing,
   as defined in the JSON Web Token Best Current Practices BCP, to be
   brought to COSE objects.  The syntax of the COSE type header
   parameter value is the same as the existing COSE content type header
   parameter.

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 5 October 2024.

Copyright Notice

   Copyright (c) 2024 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 Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Notation and Conventions . . . . . . . . . .   3
   2.  COSE "typ" (type) header parameter  . . . . . . . . . . . . .   3
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  COSE Header Parameter Registrations . . . . . . . . . . .   4
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     5.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Appendix A.  Document History . . . . . . . . . . . . . . . . . .   5
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   CBOR Object Signing and Encryption (COSE) [RFC9052] defines header
   parameters that parallel many of those defined by the JSON Object
   Signing and Encryption (JOSE) [RFC7515] [RFC7516] specifications.
   However, one way in which COSE does not provide equivalent
   functionality to JOSE is that it does not define an equivalent of the
   typ (type) header parameter, which is used for declaring the type of
   the entire JOSE data structure.  The security benefits of having typ
   (type) are described in Section 3.11 of the JSON Web Token Best
   Current Practices [RFC8725], which recommends its use for "explicit
   typing" -- using typ values to distinguish between different kinds of
   JSON Web Tokens (JWTs) [RFC7519].

   This specification adds the equivalent of the JOSE typ (type) header
   parameter to COSE so that the benefits of explicit typing can be
   brought to COSE objects.  The syntax of the COSE type header
   parameter value is the same as the existing COSE content type header
   parameter, allowing both unsigned integer CoAP Content-Formats
   [IANA.CoAP.ContentFormats] values and string Media Type
   [IANA.MediaTypes] values to be used.

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   The term "COSE object" is used as defined in [RFC9052].  An example
   of a COSE object is a COSE_Sign1 structure, as described in
   Section 4.2 of [RFC9052].

1.1.  Requirements Notation and Conventions

   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 BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  COSE "typ" (type) header parameter

   The typ (type) header parameter is used by COSE applications to
   declare the type of this complete COSE object, as compared to the
   content type header parameter, which declares the type of the COSE
   object payload.  This is intended for use by the application when
   more than one kind of COSE object could be present in an application
   data structure that can contain a COSE object; the application can
   use this value to disambiguate among the different kinds of COSE
   objects that might be present.  It will typically not be used by
   applications when the kind of COSE object is already known.  Use of
   this header parameter is OPTIONAL.

   The syntax of this header parameter value is the same as the content
   type header parameter defined in Section 3.1 of [RFC9052]; it is
   either an unsigned integer CoAP Content-Formats
   [IANA.CoAP.ContentFormats] value or a string Content Type value.
   Content Type values have a Media Type name [IANA.MediaTypes] and MAY
   include Media Type parameters.

   This parameter is ignored by COSE implementations (libraries
   implementing [RFC9052] and this specification), other than being
   passed through to applications using those implementations.  Any
   processing of this parameter is performed by the COSE application
   using application-specific processing rules.  For instance, an
   application might verify that the typ value is a particular
   application-chosen media type and reject the data structure if it is
   not.

   The typ parameter MUST NOT be present in unprotected headers.

   The typ parameter does not describe the content of unprotected
   headers.  Changes to unprotected headers do not change the type of
   the COSE object.

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3.  Security Considerations

   The case for explicit typing of COSE objects is equivalent to the
   case made for explicit typing in Section 3.11 of JSON Web Token Best
   Current Practices [RFC8725]: Explicit typing can prevent confusion
   between different kinds of COSE objects.

   COSE applications employing explicit typing should reject COSE
   objects with a type header parameter value different than values that
   they expect in that application context.  They should also reject
   COSE objects without a type header parameter when one is expected.

4.  IANA Considerations

4.1.  COSE Header Parameter Registrations

   This section registers the following value in the IANA "COSE Header
   Parameters" registry [IANA.COSE.HeaderParameters].

   *  Name: typ (type)
   *  Label: TBD (requested assignment 16)
   *  Value Type: uint / tstr
   *  Value Registry: [IANA.CoAP.ContentFormats] or [IANA.MediaTypes]
   *  Description: Type of the complete COSE object
   *  Reference: Section 2 of this specification

5.  References

5.1.  Normative References

   [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>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8725]  Sheffer, Y., Hardt, D., and M. Jones, "JSON Web Token Best
              Current Practices", BCP 225, RFC 8725,
              DOI 10.17487/RFC8725, February 2020,
              <https://www.rfc-editor.org/info/rfc8725>.

   [RFC9052]  Schaad, J., "CBOR Object Signing and Encryption (COSE):
              Structures and Process", STD 96, RFC 9052,
              DOI 10.17487/RFC9052, August 2022,
              <https://www.rfc-editor.org/info/rfc9052>.

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5.2.  Informative References

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

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

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

   [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>.

   [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>.

Appendix A.  Document History

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

   -05

   *  Addressed Area Director review comments.

   -04

   *  Addressed SECDIR review comments.

   -03

   *  Addressed GENART and OPSDIR review comments.

   -02

   *  Addressed working group last call comments.

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   *  Changed requested assignment from 14 to 16 due to conflict a with
      new assignment.

   -01

   *  Added language about media type parameters.

   -00

   *  Initial working group version based on draft-jones-cose-typ-
      header-parameter-01.

Acknowledgements

   We would like to thank Henk Birkholz, Carsten Bormann, Susan Hares,
   Dan Harkins, Murray Kucherawy, Marco Tiloca, Gunter Van de Velde,
   √Čric Vyncke, and Dale Worley for their valuable contributions to this
   specification.

Authors' Addresses

   Michael B. Jones
   Self-Issued Consulting
   Email: michael_b_jones@hotmail.com
   URI:   https://self-issued.info/

   Orie Steele
   Transmute
   Email: orie@transmute.industries

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