Internet DRAFT - draft-ietf-rats-uccs
draft-ietf-rats-uccs
RATS Working Group H. Birkholz
Internet-Draft Fraunhofer SIT
Intended status: Standards Track J. O'Donoghue
Expires: 5 September 2024 Qualcomm Technologies Inc.
N. Cam-Winget
Cisco Systems
C. Bormann
Universität Bremen TZI
4 March 2024
A CBOR Tag for Unprotected CWT Claims Sets
draft-ietf-rats-uccs-09
Abstract
When transported over secure channels, CBOR Web Token (CWT, RFC 8392)
Claims Sets may 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.
About This Document
This note is to be removed before publishing as an RFC.
Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-ietf-rats-uccs/.
Discussion of this document takes place on the Remote ATtestation
procedureS (rats) Working Group mailing list (mailto:rats@ietf.org),
which is archived at https://mailarchive.ietf.org/arch/browse/rats/.
Subscribe at https://www.ietf.org/mailman/listinfo/rats/.
Source for this draft and an issue tracker can be found at
https://github.com/ietf-rats-wg/draft-ietf-rats-uccs.
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/.
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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 September 2024.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
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Please review these documents carefully, as they describe your rights
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Deployment and Usage of UCCS . . . . . . . . . . . . . . . . 4
3. Characteristics of a Secure Channel . . . . . . . . . . . . . 5
4. UCCS in RATS Conceptual Message Conveyance . . . . . . . . . 5
5. Considerations for Using UCCS in Other RATS Contexts . . . . 7
5.1. Delegated Attestation . . . . . . . . . . . . . . . . . . 7
5.2. Privacy Preservation . . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7.1. General Considerations . . . . . . . . . . . . . . . . . 9
7.2. AES-CBC_MAC . . . . . . . . . . . . . . . . . . . . . . . 9
7.3. AES-GCM . . . . . . . . . . . . . . . . . . . . . . . . . 10
7.4. AES-CCM . . . . . . . . . . . . . . . . . . . . . . . . . 10
7.5. ChaCha20 and Poly1305 . . . . . . . . . . . . . . . . . . 10
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.1. Normative References . . . . . . . . . . . . . . . . . . 10
8.2. Informative References . . . . . . . . . . . . . . . . . 11
Appendix A. CDDL . . . . . . . . . . . . . . . . . . . . . . . . 13
Appendix B. Example . . . . . . . . . . . . . . . . . . . . . . 15
Appendix C. JSON Support . . . . . . . . . . . . . . . . . . . . 15
Appendix D. EAT . . . . . . . . . . . . . . . . . . . . . . . . 16
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
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1. Introduction
A CBOR Web Token (CWT) as specified by [RFC8392] is always wrapped in
a CBOR Object Signing and Encryption (COSE, [RFC9052]) envelope.
COSE provides -- amongst other things -- end-to-end data origin
authentication and integrity protection employed by RFC 8392 as well
as optional encryption for CWTs. Under the right circumstances
(Section 3), though, a signature providing proof for authenticity and
integrity can be provided through the transfer protocol and thus
omitted from the information in a CWT without compromising the
intended goal of authenticity and integrity. In other words, if
communicating parties have a pre-existing security association, they
can reuse it to provide authenticity and integrity for their
messages, enabling the basic principle of using resources
parsimoniously. Specifically, if a mutually secured channel is
established between two remote peers, and if that secure channel
provides the required properties (as discussed below), it is possible
to omit the protection provided by COSE, creating a use case for
unprotected CWT Claims Sets. Similarly, if there is one-way
authentication, the party that did not authenticate may be in a
position to send authentication information through this channel that
allows the already authenticated party to authenticate the other
party; this effectively turns the channel into a mutually secured
channel.
This specification allocates a CBOR tag to mark Unprotected CWT
Claims Sets (UCCS) as such and discusses conditions for its proper
use in the scope of Remote Attestation Procedures (RATS [RFC9334])
for the conveyance of RATS Conceptual Messages.
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. Consequently, within the well-
defined scope of a secure channel, it can be acceptable and economic
to use the contents of a CWT without its COSE container and tag it
with a UCCS CBOR tag for further processing within that scope -- or
to use the contents of a UCCS CBOR tag for building a CWT to be
signed by some entity that can vouch for those contents.
1.1. Terminology
The term Claim is used as in [RFC7519].
The terms Claim Key, Claim Value, and CWT Claims Set are used as in
[RFC8392].
The terms Attester, Attesting Environment, Evidence, Relying Party
and Verifier are used as in [RFC9334].
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UCCS: Unprotected CWT Claims Set(s); CBOR map(s) of Claims as
defined by the CWT Claims Registry that are composed of pairs of
Claim Keys and Claim Values.
Secure Channel: [NIST-SP800-90Ar1] defines a Secure Channel as
follows:
| "A path for transferring data between two entities or
| components that ensures confidentiality, integrity and
| replay protection, as well as mutual authentication between
| the entities or components. The secure channel may be
| provided using approved cryptographic, physical or
| procedural methods, or a combination thereof"
For the purposes of the present document, we focus on a protected
communication channel used for conveyance that can ensure the same
qualities as CWT without having the COSE protection available:
mutual authentication, integrity protection, confidentiality.
(Replay protection can be added by including a nonce claim such as
Nonce (claim 10 [IANA.cwt]).) Examples include conveyance via
PCIe (Peripheral Component Interconnect Express) IDE (Integrity
and Data Encryption), or a TLS tunnel.
All terms referenced or defined in this section are capitalized in
the remainder of this document.
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. Deployment and Usage of UCCS
Usage scenarios involving the conveyance of Claims, in particular
RATS, require a standardized data definition and encoding format that
can be transferred and transported using different communication
channels. As these are Claims, the Claims sets defined in [RFC8392]
are a suitable format. However, the way these Claims are secured
depends on the deployment, the security capabilities of the device,
as well as their software stack. For example, a Claim may be
securely stored and conveyed using a device's Trusted Execution
Environment (TEE, see [RFC9397]) or a Trusted Platform Module (TPM,
see [TPM2]). Especially in some resource constrained environments,
the same process that provides the secure communication transport is
also the delegate to compose the Claim to be conveyed. Whether it is
a transfer or transport, a Secure Channel is presumed to be used for
conveying such UCCS. The following sections elaborate on Secure
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Channel characteristics in general and further describe RATS usage
scenarios and corresponding requirements for UCCS deployment.
3. 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. In this regard, UCCS is similar in security considerations to
JWTs [RFC8725] using the algorithm "none". RFC 8725 states:
| [...] if a JWT is cryptographically protected end-to-end by a
| transport layer, such as TLS using cryptographically current
| algorithms, there may be no need to apply another layer of
| cryptographic protections to the JWT. In such cases, the use of
| the "none" algorithm can be perfectly acceptable.
The security considerations discussed, e.g., in Sections 2.1, 3.1,
and 3.2 of [RFC8725] apply in an analogous way to the use of UCCS as
elaborated on in this document.
Secure Channels are often set up in a handshake protocol that
mutually derives a session key, where the handshake protocol
establishes the (identity and thus) authenticity of one or both ends
of the communication. The session key can then be used to provide
confidentiality and integrity of the transfer of information inside
the Secure Channel. (Where the handshake did not provide a mutually
secure channel, further authentication information can be conveyed by
the party not yet authenticated, leading to a mutually secured
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.
As UCCS were initially created for use in RATS Secure Channels, the
following section provides a discussion of their use in these
channels. Where other environments are intended to be used to convey
UCCS, similar considerations need to be documented before UCCS can be
used.
4. UCCS in RATS Conceptual Message Conveyance
This section describes a detailed usage scenario for UCCS in the
context of RATS in conjunction with its attendant security
requirements. The use of UCCS tag CPA601 outside of the RATS context
MUST come with additional instruction leaflets and security
considerations.
For the purposes of this section, any RATS role can be the sender or
the receiver of the UCCS.
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Secure Channels can be transient in nature. For the purposes of this
specification, the mechanisms used to establish a Secure Channel are
out of scope.
In the scope of RATS Claims, the receiver MUST authenticate the
sender as part of the establishment of the Secure Channel.
Furthermore, the channel MUST provide integrity of the communication
between the communicating RATS roles. For data confidentiality
[RFC4949], the receiving side MUST be authenticated as well; this is
achieved if the sender and receiver mutually authenticate when
establishing the Secure Channel. The quality of the receiver's
authentication and authorization will influence whether the sender
can disclose the UCCS.
The extent to which a Secure Channel can provide assurances that UCCS
originate from a trustworthy Attesting Environment depends on the
characteristics of both the cryptographic mechanisms used to
establish the channel and the characteristics of the Attesting
Environment itself. The assurance provided to a Relying Party
depends on the authenticity and integrity properties of the Secure
Channel used for conveying the UCCS to it.
Ultimately, it is up to the receiver's policy to determine whether to
accept a UCCS from the sender and to the type of Secure Channel it
must negotiate. While the security considerations of the
cryptographic algorithms used are similar to COSE, the considerations
of the Secure Channel should also adhere to the policy configured at
each of end of the Secure Channel. However, the policy controls and
definitions are out of scope for this document.
Where an Attesting Environment serves as an endpoint of a Secure
Channel used to convey a UCCS, the security assurance required of
that Attesting Environment by a Relying Party generally calls for the
Attesting Environment to be implemented using techniques designed to
provide enhanced protection from an attacker wishing to tamper with
or forge UCCS originating from that Attesting Environment. A
possible approach might be to implement the Attesting Environment in
a hardened environment such as a TEE [RFC9397] or a TPM [TPM2].
When UCCS emerge from the Secure Channel and into the receiver, the
security properties of the secure channel no longer protect the UCCS,
which now are subject to the same security properties as any other
unprotected data in the Verifier environment. If the receiver
subsequently forwards UCCS, they are treated as though they
originated within the receiver.
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The Secure Channel context does not govern fully formed CWTs in the
same way it governs UCCS. As with EATs nested in other EATs
(Section 4.2.18.3 (Nested Tokens) of [I-D.ietf-rats-eat]), the Secure
Channel does not endorse fully formed CWTs transferred through it.
Effectively, the COSE envelope of a CWT (or a nested EAT) shields the
CWT Claims Set from the endorsement of the secure channel. (Note
that EAT might add a nested UCCS Claim, and this statement does not
apply to UCCS nested into UCCS, only to fully formed CWTs.)
5. Considerations for Using UCCS in Other RATS Contexts
This section discusses two additional usage scenarios for UCCS in the
context of RATS.
5.1. Delegated Attestation
Another usage scenario is that of a sub-Attester that has no signing
keys (for example, to keep the implementation complexity to a
minimum) and has a Secure Channel, such as local inter-process
communication, to interact with a lead Attester (see Composite
Device, Section 3.3 of [RFC9334]). The sub-Attester produces a UCCS
with the required CWT Claims Set and sends the UCCS through the
Secure Channel to the lead Attester. The lead Attester then computes
a cryptographic hash of the UCCS and protects that hash using its
signing key for Evidence, for example, using a Detached-Submodule-
Digest or Detached EAT Bundle (Section 5 of [I-D.ietf-rats-eat]).
5.2. Privacy Preservation
A Secure Channel which preserves the privacy of the Attester may
provide security properties equivalent to COSE, but only inside the
life-span of the session established. In general, when a privacy
preserving Secure Channel is employed for conveying a conceptual
message the receiver cannot correlate the message with the senders of
other received UCCS messages.
An Attester must consider whether any UCCS it returns over a privacy
preserving Secure Channel compromises the privacy in unacceptable
ways. As an example, the use of the EAT UEID Claim Section 4.2.1 of
[I-D.ietf-rats-eat] in UCCS over a privacy preserving Secure Channel
allows a Verifier to correlate UCCS from a single Attesting
Environment across many Secure Channel sessions. This may be
acceptable in some use-cases (e.g., if the Attesting Environment is a
physical sensor in a factory) and unacceptable in others (e.g., if
the Attesting Environment is a user device belonging to a child).
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6. IANA Considerations
In the CBOR Tags registry [IANA.cbor-tags] as defined in Section 9.2
of [RFC8949], IANA is requested to allocate the tag in Table 1 from
the Specification Required space (1+2 size), with the present
document as the specification reference.
+========+==========================+======================+
| Tag | Data Item | Semantics |
+========+==========================+======================+
| CPA601 | map (Claims-Set as per | Unprotected CWT |
| | Appendix A of [RFCthis]) | Claims Set [RFCthis] |
+--------+--------------------------+----------------------+
Table 1: Values for Tags
// RFC-Editor: This document uses the CPA (code point allocation)
// convention described in [I-D.bormann-cbor-draft-numbers]. For
// each usage of the term "CPA", please remove the prefix "CPA" from
// the indicated value and replace the residue with the value
// assigned by IANA; perform an analogous substitution for all other
// occurrences of the prefix "CPA" in the document. Finally, please
// remove this note.
7. Security Considerations
The security considerations of [RFC8949] apply. The security
considerations of [RFC8392] need to be applied analogously, replacing
the function of COSE with that of the Secure Channel.
Section 3 discusses security considerations for Secure Channels, in
which UCCS might be used. This document provides the CBOR tag
definition for UCCS and a discussion on security consideration for
the use of UCCS in RATS. Uses of UCCS outside the scope of RATS are
not covered by this document. The UCCS specification -- and the use
of the UCCS CBOR tag, correspondingly -- is not intended for use in a
scope where a scope-specific security consideration discussion has
not been conducted, vetted and approved for that use. In order to be
able to use the UCCS CBOR tag in another such scope, the secure
channel and/or the application protocol (e.g., TLS and the protocol
identified by ALPN) MUST specify the roles of the endpoints in a
fashion that the security properties of conveying UCCS via a Secure
Channel between the roles are well-defined.
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7.1. General Considerations
Implementations of Secure Channels are often separate from the
application logic that has security requirements on them. Similar
security considerations to those described in [RFC9052] for obtaining
the required levels of assurance include:
* Implementations need to provide sufficient protection for private
or secret key material used to establish or protect the Secure
Channel.
* Using a key for more than one algorithm can leak information about
the key and is not recommended.
* An algorithm used to establish or protect the Secure Channel may
have limits on the number of times that a key can be used without
leaking information about the key.
* Evidence in a UCCS conveyed in a Secure Channel generally cannot
be used to support trust in the credentials that were used to
establish that secure channel, as this would create a circular
dependency.
The Verifier needs to ensure that the management of key material used
to establish or protect the Secure Channel is acceptable. This may
include factors such as:
* Ensuring that any permissions associated with key ownership are
respected in the establishment of the Secure Channel.
* Using cryptographic algorithms appropriately.
* Using key material in accordance with any usage restrictions such
as freshness or algorithm restrictions.
* Ensuring that appropriate protections are in place to address
potential traffic analysis attacks.
The remaining subsections of this section highlight some aspects of
specific cryptography choices that are detailed further in [RFC9053].
7.2. AES-CBC_MAC
* A given key should only be used for messages of fixed or known
length.
* Different keys should be used for authentication and encryption
operations.
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* A mechanism to ensure that IV cannot be modified is required.
Section 3.2.1 of [RFC9053] contains a detailed explanation of these
considerations.
7.3. AES-GCM
* The key and nonce pair is unique for every encrypted message.
* The maximum number of messages to be encrypted for a given key is
not exceeded.
Section 4.1.1 of [RFC9053] contains a detailed explanation of these
considerations.
7.4. AES-CCM
* The key and nonce pair is unique for every encrypted message.
* The maximum number of messages to be encrypted for a given block
cipher is not exceeded.
* The number of messages both successfully and unsuccessfully
decrypted is used to determine when rekeying is required.
Section 4.2.1 of [RFC9053] contains a detailed explanation of these
considerations.
7.5. ChaCha20 and Poly1305
* The nonce is unique for every encrypted message.
* The number of messages both successfully and unsuccessfully
decrypted is used to determine when rekeying is required.
Section 4.3.1 of [RFC9053] contains a detailed explanation of these
considerations.
8. References
8.1. Normative References
[IANA.cbor-tags]
IANA, "Concise Binary Object Representation (CBOR) Tags",
<https://www.iana.org/assignments/cbor-tags>.
[IANA.cwt] IANA, "CBOR Web Token (CWT) Claims",
<https://www.iana.org/assignments/cwt>.
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[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/rfc/rfc2119>.
[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/rfc/rfc7519>.
[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/rfc/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/rfc/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/rfc/rfc8610>.
[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/rfc/rfc8725>.
[RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", STD 94, RFC 8949,
DOI 10.17487/RFC8949, December 2020,
<https://www.rfc-editor.org/rfc/rfc8949>.
[RFC9165] Bormann, C., "Additional Control Operators for the Concise
Data Definition Language (CDDL)", RFC 9165,
DOI 10.17487/RFC9165, December 2021,
<https://www.rfc-editor.org/rfc/rfc9165>.
8.2. Informative References
[I-D.ietf-rats-eat]
Lundblade, L., Mandyam, G., O'Donoghue, J., and C.
Wallace, "The Entity Attestation Token (EAT)", Work in
Progress, Internet-Draft, draft-ietf-rats-eat-25, 15
January 2024, <https://datatracker.ietf.org/doc/html/
draft-ietf-rats-eat-25>.
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[NIST-SP800-90Ar1]
Barker, E. and J. Kelsey, "Recommendation for Random
Number Generation Using Deterministic Random Bit
Generators", National Institute of Standards and
Technology, DOI 10.6028/nist.sp.800-90ar1, June 2015,
<https://doi.org/10.6028/nist.sp.800-90ar1>.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2",
FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
<https://www.rfc-editor.org/rfc/rfc4949>.
[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/rfc/rfc8446>.
[RFC8747] Jones, M., Seitz, L., Selander, G., Erdtman, S., and H.
Tschofenig, "Proof-of-Possession Key Semantics for CBOR
Web Tokens (CWTs)", RFC 8747, DOI 10.17487/RFC8747, March
2020, <https://www.rfc-editor.org/rfc/rfc8747>.
[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/rfc/rfc9052>.
[RFC9053] Schaad, J., "CBOR Object Signing and Encryption (COSE):
Initial Algorithms", RFC 9053, DOI 10.17487/RFC9053,
August 2022, <https://www.rfc-editor.org/rfc/rfc9053>.
[RFC9334] Birkholz, H., Thaler, D., Richardson, M., Smith, N., and
W. Pan, "Remote ATtestation procedureS (RATS)
Architecture", RFC 9334, DOI 10.17487/RFC9334, January
2023, <https://www.rfc-editor.org/rfc/rfc9334>.
[RFC9397] Pei, M., Tschofenig, H., Thaler, D., and D. Wheeler,
"Trusted Execution Environment Provisioning (TEEP)
Architecture", RFC 9397, DOI 10.17487/RFC9397, July 2023,
<https://www.rfc-editor.org/rfc/rfc9397>.
[TPM2] "Trusted Platform Module Library Specification, Family
“2.0”, Level 00, Revision 01.59 ed., Trusted Computing
Group", 2019.
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Appendix A. CDDL
The Concise Data Definition Language (CDDL), as defined in [RFC8610]
and [RFC9165], provides an easy and unambiguous way to express
structures for protocol messages and data formats that use CBOR or
JSON.
[RFC8392] does not define CDDL for CWT Claims Sets.
// RFC-Editor: This document uses the CPA (code point allocation)
// convention described in [I-D.bormann-cbor-draft-numbers]. Please
// replace the number 601 in the code blocks below by the value that
// has been assigned for CPA601 and remove this note.
This specification proposes using the definitions in Figure 1 for the
CWT Claims Set defined in [RFC8392]. Note that these definitions
have been built such that they also can describe [RFC7519] Claims
sets by disabling feature "cbor" and enabling feature "json", but
this flexibility is not the subject of the present specification.
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UCCS-Untagged = Claims-Set
UCCS-Tagged = #6.601(UCCS-Untagged)
Claims-Set = {
* $$Claims-Set-Claims
* Claim-Label .feature "extended-claims-label" => any
}
Claim-Label = CBOR-ONLY<int> / text
string-or-uri = text
$$Claims-Set-Claims //= ( iss-claim-label => string-or-uri )
$$Claims-Set-Claims //= ( sub-claim-label => string-or-uri )
$$Claims-Set-Claims //= ( aud-claim-label => string-or-uri )
$$Claims-Set-Claims //= ( exp-claim-label => ~time )
$$Claims-Set-Claims //= ( nbf-claim-label => ~time )
$$Claims-Set-Claims //= ( iat-claim-label => ~time )
$$Claims-Set-Claims //= ( cti-claim-label => bytes )
iss-claim-label = JC<"iss", 1>
sub-claim-label = JC<"sub", 2>
aud-claim-label = JC<"aud", 3>
exp-claim-label = JC<"exp", 4>
nbf-claim-label = JC<"nbf", 5>
iat-claim-label = JC<"iat", 6>
cti-claim-label = CBOR-ONLY<7> ; jti in JWT: different name and text
JSON-ONLY<J> = J .feature "json"
CBOR-ONLY<C> = C .feature "cbor"
JC<J,C> = JSON-ONLY<J> / CBOR-ONLY<C>
Figure 1: CDDL definition for Claims-Set
Specifications that define additional Claims should also supply
additions to the $$Claims-Set-Claims socket, e.g.:
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; [RFC8747]
$$Claims-Set-Claims //= ( 8: CWT-cnf ) ; cnf
CWT-cnf = {
(1: CWT-COSE-Key) //
(2: CWT-Encrypted_COSE_Key) //
(3: CWT-kid)
}
CWT-COSE-Key = COSE_Key
CWT-Encrypted_COSE_Key = COSE_Encrypt / COSE_Encrypt0
CWT-kid = bytes
;;; Insert the required CDDL from RFC 9052 to complete these
;;; definitions. This can be done manually or automated by a
;;; tool that implements an import directive such as:
;# import rfc9052
Appendix B. Example
This appendix is informative.
The example CWT Claims Set from Appendix A.1 of [RFC8392] can be
turned into a UCCS by enclosing it with a tag number CPA601:
601(
{
/ 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'
}
)
Appendix C. JSON Support
This appendix is informative.
The above definitions, concepts and security considerations all may
be applied to define a JSON-encoded Claims-Set. Such an unsigned
Claims-Set can be referred to as a "UJCS", an "Unprotected JWT Claims
Set". The CDDL definition in Figure 1 can be used for a "UJCS".
UJCS = Claims-Set
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Appendix D. EAT
This appendix is informative.
The following CDDL adds UCCS-format and UJCS-format tokens to EAT
using its predefined extension points (see Section 4.2.18 (submods)
of [I-D.ietf-rats-eat]).
$EAT-CBOR-Tagged-Token /= UCCS-Tagged
$EAT-CBOR-Untagged-Token /= UCCS-Untagged
$JSON-Selector /= [type: "UJCS", nested-token: UJCS]
Acknowledgements
Laurence Lundblade suggested some improvements to the CDDL. Carl
Wallace provided a very useful review.
Authors' Addresses
Henk Birkholz
Fraunhofer SIT
Rheinstrasse 75
64295 Darmstadt
Germany
Email: henk.birkholz@sit.fraunhofer.de
Jeremy O'Donoghue
Qualcomm Technologies Inc.
279 Farnborough Road
Farnborough
GU14 7LS
United Kingdom
Email: jodonogh@qti.qualcomm.com
Nancy Cam-Winget
Cisco Systems
3550 Cisco Way
San Jose, CA 95134
United States of America
Email: ncamwing@cisco.com
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Carsten Bormann
Universität Bremen TZI
Postfach 330440
D-28359 Bremen
Germany
Phone: +49-421-218-63921
Email: cabo@tzi.org
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