COSE T. Looker Internet-Draft Mattr Intended status: Standards Track M. Jones Expires: 9 January 2024 independent 8 July 2023 CBOR Web Token (CWT) Claims in COSE Headers draft-ietf-cose-cwt-claims-in-headers-06 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 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 9 January 2024. Copyright Notice Copyright (c) 2023 IETF Trust and the persons identified as the document authors. All rights reserved. Looker & Jones Expires 9 January 2024 [Page 1] Internet-Draft CBOR Web Token (CWT) Claims in COSE Head July 2023 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 Terminology . . . . . . . . . . . . . . . . 3 2. Representation . . . . . . . . . . . . . . . . . . . . . . . 3 3. Privacy Considerations . . . . . . . . . . . . . . . . . . . 4 4. Security Considerations . . . . . . . . . . . . . . . . . . . 4 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 6. Normative References . . . . . . . . . . . . . . . . . . . . 4 7. Informative References . . . . . . . . . . . . . . . . . . . 4 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 5 Appendix B. Document History . . . . . . . . . . . . . . . . . . 5 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 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. Looker & Jones Expires 9 January 2024 [Page 2] Internet-Draft CBOR Web Token (CWT) Claims in COSE Head July 2023 1.1. Requirements 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 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. 2. Representation This document defines the following COSE header parameter: +========+================+=======+=============+===================+ | Name | Label | Value | Value | Description | | | | Type | Registry | | +========+================+=======+=============+===================+ | CWT | TBD (requested | map | [IANA.COSE] | location for | | Claims | assignment 13) | | | CWT Claims in | | | | | | COSE Header | | | | | | Parameters | +--------+----------------+-------+-------------+-------------------+ 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 In cases where CWT claims are present both in the payload and the header of a CWT, an application receiving such a structure MUST verify that their values are identical, unless the application defines other specific processing rules for these claims. 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. The CWT Claims header parameter MAY be used in any COSE object using header parameters, such as COSE_Sign objects. Its use is not restricted to CWTs. Looker & Jones Expires 9 January 2024 [Page 3] Internet-Draft CBOR Web Token (CWT) Claims in COSE Head July 2023 3. 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. 4. Security Considerations Implementers should also review the security considerations for CWT, which are documented in Section 8 of [RFC8392]. 5. IANA Considerations IANA is requested to register the new COSE header parameter "CWT Claims" in the table in Section 2 in the "COSE Header Parameters" registry [IANA.COSE]. 6. Normative References [IANA.COSE] IANA, "COSE Header Parameters", . 7. Informative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8392] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig, "CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392, May 2018, . [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, . Looker & Jones Expires 9 January 2024 [Page 4] Internet-Draft CBOR Web Token (CWT) Claims in COSE Head July 2023 Appendix A. Acknowledgements We would like to thank Daisuke Ajitomi, Laurence Lundblade, Ivaylo Petrov, Orie Steele, and Hannes Tschofenig for their valuable contributions to this specification. Appendix B. Document History -06 * Changed requested IANA COSE Header Parameter assignment number from 11 to 13 due to Countersignature being allocated 11. * Reference correct registry IANA COSE Header Parameters. -05 * Added Acknowledgements section. * Addressed WGLC feedback. Specifically... * Added statement about being able to use the header parameter in any COSE object. * Moved statment about verifing that claim values present in both the header and payload are identical from the Security Considerations to the body of the specification. -04 * Update author affiliation. * Add standard reference to RFC terminology. * Added reference to security considerations from RFC8392. -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. Looker & Jones Expires 9 January 2024 [Page 5] Internet-Draft CBOR Web Token (CWT) Claims in COSE Head July 2023 -00 * 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 independent Email: michael_b_jones@hotmail.com URI: https://self-issued.info/ Looker & Jones Expires 9 January 2024 [Page 6]