A CBOR Tag for Unprotected CWT Claims Sets
draft-birkholz-rats-uccs-00

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Authors Henk Birkholz  , Nancy Cam-Winget  , Carsten Bormann 
Last updated 2020-03-09
Replaced by draft-ietf-rats-uccs, draft-ietf-rats-uccs
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RATS Working Group                                           H. Birkholz
Internet-Draft                                            Fraunhofer SIT
Intended status: Standards Track                           N. Cam-Winget
Expires: September 10, 2020                                Cisco Systems
                                                              C. Bormann
                                                 Universitaet Bremen TZI
                                                          March 09, 2020

               A CBOR Tag for Unprotected CWT Claims Sets
                      draft-birkholz-rats-uccs-00

Abstract

   CBOR Web Token (CWT, RFC 8392) Claims Sets sometimes do not need the
   protection afforded by wrapping them into COSE, as is required for a
   true CWT.  This specification defines a CBOR tag for such unprotected
   CWT claims sets (UCCS) and discusses conditions for its proper use.

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   Copyright (c) 2020 IETF Trust and the persons identified as the
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Characteristics of a Secure Channel . . . . . . . . . . . . .   3
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     5.2.  Informative References  . . . . . . . . . . . . . . . . .   4
   Appendix A.  Example  . . . . . . . . . . . . . . . . . . . . . .   4
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   A CBOR Web Token (CWT) as specified by [RFC8392] is always wrapped in
   a CBOR Object Signing and Encryption (COSE, [RFC8152]) envelope.
   COSE provides - amongst other things - the integrity protection
   mandated by RFC 8392 and optional encryption for CWTs.  Under the
   right circumstances, though, a signature providing proof for
   authenticity and integrity can be omitted from the information in a
   CWT without compromising the intended goal of authenticity and
   integrity.  If a secure channel is established in an appropriate
   fashion between two remote peers, and if that secure channel provides
   the correct properties, it is possible to omit the protection
   provided by COSE, creating a use case for unprotected CWT Claims
   Sets.

   This specification allocates a CBOR tag to mark Unprotected CWT
   Claims Sets (UCCS) as such and discusses conditions for its proper
   use.

   This specification does not change [RFC8392]: A true CWT does not
   make use of the tag allocated here; the UCCS tag is an alternative to
   using COSE protection and a CWT tag.

1.1.  Terminology

   The terms Claim and Claims Set are used as in [RFC8392].

   UCCS:  Unprotected CWT Claims Set

   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

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

2.  Characteristics of a Secure Channel

   A Secure Channel for the conveyance of UCCS needs to provide the
   security properties that would otherwise be provided by COSE for a
   CWT.

   Secure Channels are often set up in a handshake protocol that agrees
   a session key, where the handshake protocol establishes the
   authenticity of one of both ends of the communication as well as
   confidentiality.  The session key can then be used to protect
   confidentiality and integrity of the transfer of information inside
   the secure channel.  A well-known example of a such a secure channel
   setup protocol is the TLS [RFC8446] handshake; the TLS record
   protocol can then be used for secure conveyance.

   If only authenticity/integrity is required, the secure channel needs
   to be set up with authentication of the side that is providing the
   UCCS.  If confidentiality is also required, the receiving side also
   needs to be authenticated.

3.  IANA Considerations

   In the registry [IANA.cbor-tags], IANA is requested to allocate the
   tag in Table 1 from the FCFS space, with the present document as the
   specification reference.

       +--------+-----------+--------------------------------------+
       |    Tag | Data Item | Semantics                            |
       +--------+-----------+--------------------------------------+
       | TBD601 | map       | Unprotected CWT Claims Set [RFCthis] |
       +--------+-----------+--------------------------------------+

                         Table 1: Values for Tags

4.  Security Considerations

   The security considerations of [RFC7049] and [RFC8392] apply.

   {#secchan} discusses security considerations for secure channels, in
   which UCCS might be used.

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5.  References

5.1.  Normative References

   [IANA.cbor-tags]
              IANA, "Concise Binary Object Representation (CBOR) Tags",
              <http://www.iana.org/assignments/cbor-tags>.

   [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>.

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

   [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>.

   [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>.

5.2.  Informative References

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

Appendix A.  Example

   The example CWT Claims Set from Appendix A.1 of [RFC8392] can be
   turned into an UCCS by enclosing it with a tag number TBD601:

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    <TBD601>(
      {
        / 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'
      }
    )

Authors' Addresses

   Henk Birkholz
   Fraunhofer SIT
   Rheinstrasse 75
   Darmstadt  64295
   Germany

   Email: henk.birkholz@sit.fraunhofer.de

   Nancy Cam-Winget
   Cisco Systems
   3550 Cisco Way
   San Jose, CA  95134
   USA

   Email: ncamwing@cisco.com

   Carsten Bormann
   Universitaet Bremen TZI
   Bibliothekstrasse 1
   Bremen  28369
   Germany

   Phone: +49-421-218-63921
   Email: cabo@tzi.de

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