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.
Status of This Memo
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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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