RATS Working Group
Internet Engineering Task Force (IETF) H. Birkholz
Internet-Draft
Request for Comments: 9781 Fraunhofer SIT
Intended status:
Category: Standards Track J. O'Donoghue
Expires: 7 May 2025
ISSN: 2070-1721 Qualcomm Technologies Inc.
N. Cam-Winget
Cisco Systems
C. Bormann
Universität Bremen TZI
3 November 2024
April 2025
A CBOR Concise Binary Object Representation (CBOR) Tag for Unprotected CWT CBOR
Web Token Claims Sets
draft-ietf-rats-uccs-12 (UCCS)
Abstract
This document defines the Unprotected CWT Claims Set (UCCS), a data
format for representing a CBOR Web Token (CWT) Claims Set without
protecting it by a signature, message authentication code Message Authentication Code (MAC), or
encryption. UCCS enables the use of CWT claims in environments where
protection is provided by other means, such as secure communication
channels or trusted execution environments. This specification
defines a CBOR tag for UCCS and describes the UCCS format, its
encoding, and its processing considerations, and considerations. It also discusses
security implications of using unprotected claims sets.
// (This editors' note will be removed by the RFC editor:) The
// present revision (–12) contains remaining document changes based
// on feedback from the IESG evaluation and has been submitted as
// input to IETF 121.
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
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Internet-Drafts are draft documents valid the IETF community. It has
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This Internet-Draft will expire on 7 May 2025.
https://www.rfc-editor.org/info/rfc9781.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Structure of this document . . . . . . . . . . . . . . . 5 This Document
2. Deployment and Usage of UCCS . . . . . . . . . . . . . . . . 5
3. Characteristics of a Secure Channel . . . . . . . . . . . . . 6
4. UCCS in RATS Conceptual Message Conveyance . . . . . . . . . 7
5. Considerations for Using UCCS in Other RATS Contexts . . . . 8
5.1. Delegated Attestation . . . . . . . . . . . . . . . . . . 8
5.2. Privacy Preservation . . . . . . . . . . . . . . . . . . 9
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
6.1. CBOR Tag registration . . . . . . . . . . . . . . . . . . 9 Registration
6.2. Media-Type application/uccs+cbor Registration . . . . . . 10
6.3. Media-Type application/ujcs+json Registration . . . . . . 10
6.4. Content-Format registration . . . . . . . . . . . . . . . 11 Registration
7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
7.1. General Considerations . . . . . . . . . . . . . . . . . 12
7.2. Algorithm-specific Algorithm-Specific Security Considerations . . . . . . . 13
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
8.1. Normative References . . . . . . . . . . . . . . . . . . 14
8.2. Informative References . . . . . . . . . . . . . . . . . 15
Appendix A. CDDL . . . . . . . . . . . . . . . . . . . . . . . . 16
Appendix B. Example . . . . . . . . . . . . . . . . . . . . . . 18
Appendix C. EAT . . . . . . . . . . . . . . . . . . . . . . . . 19
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction
A CBOR Web Token (CWT) as specified by [RFC8392] is always wrapped in
a CBOR Object Signing and Encryption (COSE, [STD96]) envelope. (COSE) envelope [STD96]. Among
other things, COSE provides -- among other things -- end-to-end data origin authentication and
integrity protection employed by RFC 8392 [RFC8392] 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 preexisting 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]: An actual RFC 8392 A CWT as defined by
[RFC8392] 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].
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 a CWT without having the COSE protection available: available, which
includes mutual authentication, integrity protection, and
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)
Express), IDE (Integrity and Data Encryption) 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
[BCP14] (RFC2119) (RFC8174)
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
1.2. Structure of this document This Document
Section 2 briefly discusses use cases for UCCS. Section 3 addresses
general characteristics of secure channels, followed by a specific
discussion of using them in the context of RATS Conceptual Message
Conveyance in Section 4, and finally some more forward-looking considerations for
using UCCS in other RATS contexts are discussed in Section 5.
Conventional sections (IANA This
is followed by the IANA Considerations, Security Considerations,
Normative References, and Informative References) follow. References. The normative
Appendix A provides a formal definition of the structure of
UCCS UCCS, as
no formal definition of CWT Claims Sets was provided in [RFC8392].
This employs the Concise Data Definition Language (CDDL) [RFC8610],
using its ability to also describe the structurally similar
Unprotected JWT Claims Sets [RFC7519] (UJCS) [RFC7519] in the same definition.
Appendix B provides an (informative) example for CBOR-
Tagged CBOR-Tagged UCCS.
The normative Appendix C provides CDDL rules that add UCCS-format
tokens to Entity Attestation Tokens (EATs, see
[I-D.ietf-rats-eat]) (EATs) [RFC9711] using its
predefined extension points.
2. Deployment and Usage of UCCS
Usage scenarios involving the conveyance of Claims, Claims (RATS, in particular
RATS,
particular) 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]) (TEE) [RFC9397] or a Trusted Platform Module (TPM,
see [TPM2]).
(TPM) [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
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 [BCP225] using the algorithm "none". Section 3.2 of RFC 8725
[BCP225] 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 RFC 8725 [BCP225] apply in an analogous way to the use of
UCCS as elaborated on in this document. In particular, the need to
"Use Appropriate Algorithms" (Section 3.2 of RFC 8725 [BCP225])
includes choosing appropriate cryptographic algorithms for setting up
and protecting the Secure Channel. For instance, their cryptographic
strength should be at least as strong as any cryptographic keys the
Secure Channel will be used for to protect in transport. Table 5 in
Section 7.2 provides references to some more security considerations
for specific cryptography choices that are discussed in the COSE
initial algorithms specification [RFC9053].
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 601 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.
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 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 determine 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 a UCCS originating from that Attesting Environment. A
possible approach might be to implement the Attesting Environment in
a hardened environment 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.
The Secure Channel context does not govern fully formed CWTs in the
same way it governs UCCS. As with Entity Attestation Tokens (EATs,
see [I-D.ietf-rats-eat]) EATs (see [RFC9711]) nested in
other EATs (Section 4.2.18.3 (Nested Tokens) of [I-D.ietf-rats-eat]), [RFC9711]), 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 an EAT might add a nested UCCS Claim, and this
statement does not apply to UCCS nested into UCCS, UCCS; it only applies 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]). [RFC9711]).
5.2. Privacy Preservation
A Secure Channel which that 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 privacy-
preserving Secure Channel is employed for conveying to convey a conceptual message,
the receiver cannot correlate the message with the senders of other
received UCCS messages beyond the information the Secure Channel
authentication provides.
An Attester must consider whether any UCCS it returns over a privacy 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])
[RFC9711]) in UCCS over a privacy preserving 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 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).
6. IANA Considerations
6.1. CBOR Tag registration Registration
In the CBOR Tags "CBOR Tags" registry [IANA.cbor-tags] as defined in
Section 9.2 of RFC 8949 [STD94], IANA is requested to allocate has allocated 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 601 | map (Claims-Set as per | Unprotected CWT |
| | Appendix A of [RFCthis]) [RFC9781]) | Claims Set [RFCthis] [RFC9781] |
+--------+--------------------------+----------------------+
+-----+--------------------------+----------------------+
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.
6.2. Media-Type application/uccs+cbor Registration
IANA is requested to add has added the following Media-Type to the "Media Types" registry
[IANA.media-types].
+===========+=======================+========================+
+===========+=======================+=========================+
| Name | Template | Reference |
+===========+=======================+========================+
+===========+=======================+=========================+
| uccs+cbor | application/uccs+cbor | Section 6.2 of RFCthis RFC 9781 |
+-----------+-----------------------+------------------------+
+-----------+-----------------------+-------------------------+
Table 2: Media Type Registration
Type name: application
Subtype name: uccs+cbor
Required parameters: n/a
Optional parameters: n/a
Encoding considerations: binary (CBOR data item)
Security considerations: Section 7 of RFCthis RFC 9781
Interoperability considerations: none
Published specification: RFCthis RFC 9781
Applications that use this media type: Applications that transfer
Unprotected CWT Claims Set(s) (UCCS) over Secure Channels
Fragment identifier considerations: The syntax and semantics of
fragment identifiers is as specified for "application/cbor". (At
publication of this document, there is no fragment identification
syntax defined for "application/cbor".)
Additional information:
Deprecated alias names for this type: N/A
Magic number(s): N/A
File extension(s): .uccs
Macintosh file type code(s): N/A
Person and email address to contact for further information: RATS WG
mailing list (rats@ietf.org)
Intended usage: COMMON
Restrictions on usage: none
Author/Change controller: IETF
6.3. Media-Type application/ujcs+json Registration
IANA is requested to add has added the following Media-Type to the "Media Types" registry
[IANA.media-types].
+===========+=======================+========================+
+===========+=======================+=========================+
| Name | Template | Reference |
+===========+=======================+========================+
+===========+=======================+=========================+
| ujcs+json | application/ujcs+json | Section 6.3 of RFCthis RFC 9781 |
+-----------+-----------------------+------------------------+
+-----------+-----------------------+-------------------------+
Table 3: JSON Media Type Registration
Type name: application
Subtype name: ujcs+json
Required parameters: n/a
Optional parameters: n/a
Encoding considerations: binary (UTF-8)
Security considerations: Section 7 of RFCthis RFC 9781
Interoperability considerations: none
Published specification: RFCthis RFC 9781
Applications that use this media type: Applications that transfer
Unprotected JWT Claims Set(s) (UJCS) over Secure Channels
Fragment identifier considerations: The syntax and semantics of
fragment identifiers is as specified for "application/json". (At
publication of this document, there is no fragment identification
syntax defined for "application/json".)
Additional information:
Deprecated alias names for this type: N/A
Magic number(s): N/A
File extension(s): .ujcs
Macintosh file type code(s): N/A
Person and email address to contact for further information: RATS WG
mailing list (rats@ietf.org)
Intended usage: COMMON
Restrictions on usage: none
Author/Change controller: IETF
6.4. Content-Format registration Registration
IANA is requested to register a Content-Format number has registered the following in the "CoAP Content-Formats" subregistry,
registry within the "Constrained RESTful Environments (CoRE)
Parameters" registry [IANA.core-parameters], as
follows:
+=======================+================+========+=============+ group [IANA.core-parameters].
+=======================+================+=====+=============+
| Content Type | Content Coding | ID | Reference |
+=======================+================+========+=============+
+=======================+================+=====+=============+
| application/uccs+cbor | - | TBD601 601 | Section 6.4 |
| | | | of RFCthis RFC 9781 |
+-----------------------+----------------+--------+-------------+
+-----------------------+----------------+-----+-------------+
Table 4: Content-Format Registration
// RFC editor: please replace TBD601 by the number actually assigned
// by IANA (601 is suggested).
7. Security Considerations
The security considerations of [STD94] apply. The security
considerations of [RFC8392] need to be applied analogously, replacing
the function of COSE with that of the Secure Channel; in particular particular,
"it is not only important to protect the CWT in transit but also to
ensure that the recipient can authenticate the party that assembled
the claims and created the CWT".
Section 3 discusses security considerations for Secure Channels, 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 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.
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 [STD96] 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.
7.2. Algorithm-specific Algorithm-Specific Security Considerations
Table 5 provides references to some security considerations of
specific cryptography choices that are discussed in [RFC9053].
+===================+============================+
| Algorithm | Reference |
+===================+============================+
| AES-CBC-MAC | Section 3.2.1 of [RFC9053] |
+-------------------+----------------------------+
| AES-GCM | Section 4.1.1 of [RFC9053] |
+-------------------+----------------------------+
| AES-CCM | Section 4.2.1 of [RFC9053] |
+-------------------+----------------------------+
| ChaCha20/Poly1305 | Section 4.3.1 of [RFC9053] |
+-------------------+----------------------------+
Table 5: Algorithm-specific Algorithm-Specific Security
Considerations
8. References
8.1. Normative References
[BCP14] Best Current Practice 14,
<https://www.rfc-editor.org/info/bcp14>.
At the time of writing, this BCP comprises the following:
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>.
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>.
[BCP225] Best Current Practice 225,
<https://www.rfc-editor.org/info/bcp225>.
At the time of writing, this BCP comprises the following:
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>.
[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>.
[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>.
[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>.
<https://www.rfc-editor.org/info/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/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/rfc/rfc8392>. <https://www.rfc-editor.org/info/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>. <https://www.rfc-editor.org/info/rfc8610>.
[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>.
<https://www.rfc-editor.org/info/rfc9165>.
[STD94] Internet Standard 94,
<https://www.rfc-editor.org/info/std94>.
At the time of writing, this STD comprises the following:
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/info/rfc8949>.
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-31, 6
September 2024, <https://datatracker.ietf.org/doc/html/
draft-ietf-rats-eat-31>.
[IANA.core-parameters]
IANA, "Constrained RESTful Environments (CoRE)
Parameters",
<https://www.iana.org/assignments/core-parameters>.
[IANA.media-types]
IANA, "Media Types",
<https://www.iana.org/assignments/media-types>.
[NIST-SP800-90Ar1]
Barker, E. and J. Kelsey, "Recommendation for Random
Number Generation Using Deterministic Random Bit
Generators", National Institute of Standards and
Technology, NIST SP 800-90Ar1,
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>.
<https://www.rfc-editor.org/info/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>.
<https://www.rfc-editor.org/info/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>. <https://www.rfc-editor.org/info/rfc8747>.
[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>. <https://www.rfc-editor.org/info/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>. <https://www.rfc-editor.org/info/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>.
<https://www.rfc-editor.org/info/rfc9397>.
[RFC9711] Lundblade, L., Mandyam, G., O'Donoghue, J., and C.
Wallace, "The Entity Attestation Token (EAT)", RFC 9711,
DOI 10.17487/RFC9711, April 2025,
<https://www.rfc-editor.org/info/rfc9711>.
[STD96] Internet Standard 96,
<https://www.rfc-editor.org/info/std96>.
At the time of writing, this STD comprises the following:
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>.
Schaad, J., "CBOR Object Signing and Encryption (COSE):
Countersignatures", STD 96, RFC 9338,
DOI 10.17487/RFC9338, December 2022,
<https://www.rfc-editor.org/info/rfc9338>.
[TPM2] Trusted Computing Group, "Trusted Platform Module Library Specification,
Specification", Family
“2.0”, "2.0", Level 00, Revision 01.59 ed., Trusted Computing
Group", 01.59,
2019.
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.
The CDDL model in Figure 1 shows how to use CDDL for defining the CWT
Claims Set defined in [RFC8392]. These CDDL rules have been built
such that they also can describe [RFC7519] Claims sets by disabling
feature "cbor" and enabling feature "json".
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 $$Claims-Set-Claims socket, e.g.:
; [RFC8747]
$$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
The above definitions, concepts concepts, and security considerations also
define a JSON-encoded Claims-Set as encapsulated in a JWT. Such an
unsigned Claims-Set can be referred to as a "Unprotected JWT Claims
Set", or a "UJCS". The CDDL definition of Claims-Set in Figure 1 can
be used for a "UJCS": UJCS:
UJCS = Claims-Set
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:
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. EAT
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]). [RFC9711]).
$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@ietf.contact
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
Carsten Bormann
Universität Bremen TZI
Postfach 330440
D-28359 Bremen
Germany
Phone: +49-421-218-63921
Email: cabo@tzi.org