Internet-Draft EAT Media Types October 2024
Lundblade, et al. Expires 13 April 2025 [Page]
Workgroup:
Remote ATtestation ProcedureS
Internet-Draft:
draft-ietf-rats-eat-media-type-11
Published:
Intended Status:
Standards Track
Expires:
Authors:
L. Lundblade
Security Theory LLC
H. Birkholz
Fraunhofer SIT
T. Fossati
Linaro

EAT Media Types

Abstract

Payloads used in Remote Attestation Procedures may require an associated media type for their conveyance, for example when used in RESTful APIs.

This memo defines media types to be used for Entity Attestation Tokens (EAT).

Discussion Venues

This note is to be removed before publishing as an RFC.

Discussion of this document takes place on the Remote ATtestation ProcedureS Working Group mailing list (rats@ietf.org), which is archived at https://mailarchive.ietf.org/arch/browse/rats/.

Source for this draft and an issue tracker can be found at https://github.com/thomas-fossati/draft-eat-mt.

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 13 April 2025.

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Table of Contents

1. Introduction

Payloads used in Remote Attestation Procedures [RATS-Arch] may require an associated media type for their conveyance, for example when used in RESTful APIs (Figure 1).

Relying Party Attester Verifier POST /verify EAT(Evidence) 200 OK EAT(Attestation Results) POST /auth EAT(Attestation Results) 201 Created
Figure 1: Conveying RATS conceptual messages in REST APIs using EAT

This memo defines media types to be used for Entity Attestation Token (EAT) [EAT] payloads independently of the RATS Conceptual Message in which they manifest themselves. The objective is to give protocol, API and application designers a number of readily available and reusable media types for integrating EAT-based messages in their flows, for example when using HTTP [BUILD-W-HTTP] or CoAP [REST-IoT].

1.1. Requirements Language

This document uses the terms and concepts defined in [RATS-Arch].

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. EAT Types

Figure 2 illustrates the six EAT wire formats and how they relate to each other. [EAT] defines four of them (CWT, JWT and Detached EAT Bundle in its JSON and CBOR flavours), whilst [UCCS] defines UCCS, and we use the abbreviation "UJCS" to refer to unprotected JWT Claims Sets as defined in Section 2 of [JWT].

UJCS UCCS JWT Crypto CWT Claims-Set BUN-J Bundle Digest BUN-C submod Nested-Token Legenda: Process Wire Fmt CDDL
Figure 2: EAT Types

3. A Media Type Parameter for EAT Profiles

EAT is an open and flexible format. To improve interoperability, Section 6 of [EAT] defines the concept of EAT profiles. Profiles are used to constrain the parameters that producers and consumers of a specific EAT profile need to understand in order to interoperate. For example: the number and type of claims, which serialisation format, the supported signature schemes, etc. EATs carry an in-band profile identifier using the eat_profile claim (see Section 4.3.2 of [EAT]). The value of the eat_profile claim is either an OID or a URI.

The media types defined in this document include an optional eat_profile parameter that can be used to mirror the eat_profile claim of the transported EAT. Exposing the EAT profile at the API layer allows API routers to dispatch payloads directly to the profile-specific processor without having to snoop into the request bodies. This design also provides a finer-grained and scalable type system that matches the inherent extensibility of EAT. The expectation being that a certain EAT profile automatically obtains a media type derived from the base (e.g., application/eat+cwt) by populating the eat_profile parameter with the corresponding OID or URL.

When the parameterised version of the EAT media type is used in HTTP (for example, with the "Content-Type" and "Accept" headers), and the value is an absolute URI (Section 4.3 of [URI]), the parameter-value (Appendix A of [HTTP]) MUST use the quoted-string encoding, e.g.:

Instead, when the EAT profile is an OID, the token encoding (i.e., without quotes) can be used, e.g.:

4. Examples

The example in Figure 3 illustrates the usage of EAT media types for transporting attestation evidence as well as negotiating the acceptable format of the attestation result.

# NOTE: '\' line wrapping per RFC 8792

POST /challenge-response/v1/session/1234567890 HTTP/1.1
Host: verifier.example
Accept: application/eat+cwt; eat_profile="tag:ar4si.example,2021"
Content-Type: application/eat+cwt; \
              eat_profile="tag:evidence.example,2022"

[ CBOR-encoded EAT w/ eat_profile="tag:evidence.example,2022" ]
Figure 3: Example REST Verification API (request)

The example in Figure 4 illustrates the usage of EAT media types for transporting attestation results.

# NOTE: '\' line wrapping per RFC 8792

HTTP/1.1 200 OK
Content-Type: application/eat+cwt; \
              eat_profile="tag:ar4si.example,2021"

[ CBOR-encoded EAT w/ eat_profile="tag:ar4si.example,2021" ]
Figure 4: Example REST Verification API (response)

In both cases, a tag URI [TAG] identifying the profile is carried as an explicit parameter.

5. Security Considerations

Media types only provide clues to the processing application. The application must verify that the received data matches the expected format, regardless of the advertised media type. Failing to do so could expose the user to security risks, such as privilege escalation and cross-protocol attacks.

The security consideration of [EAT] and [UCCS] apply in full.

6. IANA Considerations

RFC Editor: please replace RFCthis with this RFC number and remove this note.

6.1. +cwt Structured Syntax Suffix

IANA is requested to register the +cwt structured syntax suffix in the "Structured Syntax Suffixes" registry [IANA.media-type-structured-suffix] in the manner described in [MediaTypes], which can be used to indicate that the media type is encoded as a CWT.

6.1.1. Registry Contents

Name:

CBOR Web Token (CWT)

+suffix:

+cwt

References:

[CWT]

Encoding Considerations:

binary

Interoperability Considerations:

N/A

Fragment Identifier Considerations:

The syntax and semantics of fragment identifiers specified for +cwt SHOULD be as specified for application/cwt. (At publication of this document, there is no fragment identification syntax defined for application/cwt.)

Security Considerations:

See Section 8 of [CWT]

Contact:

RATS WG mailing list (rats@ietf.org), or IETF Security Area (saag@ietf.org)

Author/Change Controller:

Remote ATtestation ProcedureS (RATS) Working Group. The IETF has change control over this registration.

6.2. Media Types

IANA is requested to add the following media types to the "Media Types" registry [IANA.media-types].

Table 1: New Media Types
Name Template Reference
EAT CWT application/eat+cwt RFCthis, Section 6.3
EAT JWT application/eat+jwt RFCthis, Section 6.4
Detached EAT Bundle CBOR application/eat-bun+cbor RFCthis, Section 6.5
Detached EAT Bundle JSON application/eat-bun+json RFCthis, Section 6.6
EAT UCCS application/eat-ucs+cbor RFCthis, Section 6.7
EAT UJCS application/eat-ucs+json RFCthis, Section 6.8

6.3. application/eat+cwt Registration

Type name:

application

Subtype name:

eat+cwt

Required parameters:

n/a

Optional parameters:

"eat_profile" (EAT profile in string format. OIDs MUST use the dotted-decimal notation. The parameter value is case-insensitive.)

Encoding considerations:

binary

Security considerations:

Section 9 of [EAT]

Interoperability considerations:

n/a

Published specification:

RFCthis

Applications that use this media type:

Attesters, Verifiers, Endorsers and Reference-Value providers, Relying Parties that need to transfer EAT payloads over HTTP(S), CoAP(S), and other transports.

Fragment identifier considerations:

n/a

Person & 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

Provisional registration:

no

6.4. application/eat+jwt Registration

Type name:

application

Subtype name:

eat+jwt

Required parameters:

n/a

Optional parameters:

"eat_profile" (EAT profile in string format. OIDs MUST use the dotted-decimal notation. The parameter value is case-insensitive.)

Encoding considerations:

8bit

Security considerations:

Section 9 of [EAT] and [BCP225]

Interoperability considerations:

n/a

Published specification:

RFCthis

Applications that use this media type

Attesters, Verifiers, Endorsers and Reference-Value providers, Relying Parties that need to transfer EAT payloads over HTTP(S), CoAP(S), and other transports.

Fragment identifier considerations:

n/a

Person & 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

Provisional registration:

no

6.5. application/eat-bun+cbor Registration

Type name:

application

Subtype name:

eat-bun+cbor

Required parameters:

n/a

Optional parameters:

"eat_profile" (EAT profile in string format. OIDs MUST use the dotted-decimal notation. The parameter value is case-insensitive.)

Encoding considerations:

binary

Security considerations:

Section 9 of [EAT]

Interoperability considerations:

n/a

Published specification:

RFCthis

Applications that use this media type:

Attesters, Verifiers, Endorsers and Reference-Value providers, Relying Parties that need to transfer EAT payloads over HTTP(S), CoAP(S), and other transports.

Fragment identifier considerations:

n/a

Person & 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

Provisional registration:

no

6.6. application/eat-bun+json Registration

Type name:

application

Subtype name:

eat-bun+json

Required parameters:

n/a

Optional parameters:

"eat_profile" (EAT profile in string format. OIDs MUST use the dotted-decimal notation. The parameter value is case-insensitive.)

Encoding considerations:

Same as [JSON]

Security considerations:

Section 9 of [EAT]

Interoperability considerations:

n/a

Published specification:

RFCthis

Applications that use this media type

Attesters, Verifiers, Endorsers and Reference-Value providers, Relying Parties that need to transfer EAT payloads over HTTP(S), CoAP(S), and other transports.

Fragment identifier considerations:

n/a

Person & 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

Provisional registration:

no

6.7. application/eat-ucs+cbor Registration

Type name:

application

Subtype name:

eat-ucs+cbor

Required parameters:

n/a

Optional parameters:

"eat_profile" (EAT profile in string format. OIDs MUST use the dotted-decimal notation. The parameter value is case-insensitive.)

Encoding considerations:

binary

Security considerations:

Section 7 of [UCCS]

Interoperability considerations:

n/a

Published specification:

RFCthis

Applications that use this media type:

Attesters, Verifiers, Endorsers and Reference-Value providers, Relying Parties that need to transfer EAT payloads over HTTP(S), CoAP(S), and other transports.

Fragment identifier considerations:

n/a

Person & 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

Provisional registration:

no

6.8. application/eat-ucs+json Registration

Type name:

application

Subtype name:

eat-ucs+json

Required parameters:

n/a

Optional parameters:

"eat_profile" (EAT profile in string format. OIDs MUST use the dotted-decimal notation. The parameter value is case-insensitive.)

Encoding considerations:

Same as [JSON]

Security considerations:

Section 7 of [UCCS]

Interoperability considerations:

n/a

Published specification:

RFCthis

Applications that use this media type

Attesters, Verifiers, Endorsers and Reference-Value providers, Relying Parties that need to transfer EAT payloads over HTTP(S), CoAP(S), and other transports.

Fragment identifier considerations:

n/a

Person & 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

Provisional registration:

no

6.9. CoAP Content-Format Registrations

IANA is requested to register the following Content-Format numbers in the "CoAP Content-Formats" sub-registry, within the "Constrained RESTful Environments (CoRE) Parameters" Registry [IANA.core-parameters]:

Table 2: New Content-Formats
Content-Type Content Coding ID Reference
application/eat+cwt - TBD1 RFCthis
application/eat+jwt - TBD2 RFCthis
application/eat-bun+cbor - TBD3 RFCthis
application/eat-bun+json - TBD4 RFCthis
application/eat-ucs+cbor - TBD5 RFCthis
application/eat-ucs+json - TBD6 RFCthis

TBD1..6 are to be assigned from the space 256..999.

7. Changelog

RFC editor: please remove this section

7.1. -04

  • Early IANA review

7.2. -03

  • Update references

7.3. -02

7.4. -01

  • Rename profile to eat_profile for consistency with EAT (Issue#4)

  • The DEB acronym is gone: shorthand is now "bun" from bundle (Issue#8)

  • Incorporate editorial suggestions from Carl and Dave (Issue#7, Issue#9)

8. References

8.1. Normative References

[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, , <https://www.rfc-editor.org/info/rfc8725>.
[CWT]
Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig, "CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392, , <https://www.rfc-editor.org/rfc/rfc8392>.
[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, , <https://datatracker.ietf.org/doc/html/draft-ietf-rats-eat-31>.
[HTTP]
Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, Ed., "HTTP Semantics", STD 97, RFC 9110, DOI 10.17487/RFC9110, , <https://www.rfc-editor.org/rfc/rfc9110>.
[IANA.core-parameters]
IANA, "Constrained RESTful Environments (CoRE) Parameters", <https://www.iana.org/assignments/core-parameters>.
[IANA.media-type-structured-suffix]
IANA, "Structured Syntax Suffixes", <https://www.iana.org/assignments/media-type-structured-suffix>.
[IANA.media-types]
IANA, "Media Types", <https://www.iana.org/assignments/media-types>.
[JSON]
Bray, T., Ed., "The JavaScript Object Notation (JSON) Data Interchange Format", STD 90, RFC 8259, DOI 10.17487/RFC8259, , <https://www.rfc-editor.org/rfc/rfc8259>.
[JWT]
Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token (JWT)", RFC 7519, DOI 10.17487/RFC7519, , <https://www.rfc-editor.org/rfc/rfc7519>.
[MediaTypes]
Freed, N., Klensin, J., and T. Hansen, "Media Type Specifications and Registration Procedures", BCP 13, RFC 6838, DOI 10.17487/RFC6838, , <https://www.rfc-editor.org/rfc/rfc6838>.
[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/rfc/rfc2119>.
[RFC8174]
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <https://www.rfc-editor.org/rfc/rfc8174>.
[UCCS]
Birkholz, H., O'Donoghue, J., Cam-Winget, N., and C. Bormann, "A CBOR Tag for Unprotected CWT Claims Sets", Work in Progress, Internet-Draft, draft-ietf-rats-uccs-10, , <https://datatracker.ietf.org/doc/html/draft-ietf-rats-uccs-10>.
[URI]
Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, DOI 10.17487/RFC3986, , <https://www.rfc-editor.org/rfc/rfc3986>.

8.2. Informative References

[BUILD-W-HTTP]
Best Current Practice 56, <https://www.rfc-editor.org/info/bcp56>.
At the time of writing, this BCP comprises the following:
Nottingham, M., "Building Protocols with HTTP", BCP 56, RFC 9205, DOI 10.17487/RFC9205, , <https://www.rfc-editor.org/info/rfc9205>.
[RATS-Arch]
Birkholz, H., Thaler, D., Richardson, M., Smith, N., and W. Pan, "Remote ATtestation procedureS (RATS) Architecture", RFC 9334, DOI 10.17487/RFC9334, , <https://www.rfc-editor.org/rfc/rfc9334>.
[REST-IoT]
Keränen, A., Kovatsch, M., and K. Hartke, "Guidance on RESTful Design for Internet of Things Systems", Work in Progress, Internet-Draft, draft-irtf-t2trg-rest-iot-14, , <https://datatracker.ietf.org/doc/html/draft-irtf-t2trg-rest-iot-14>.
[TAG]
Kindberg, T. and S. Hawke, "The 'tag' URI Scheme", RFC 4151, DOI 10.17487/RFC4151, , <https://www.rfc-editor.org/rfc/rfc4151>.

Acknowledgments

Thank you Carl Wallace, Carsten Bormann, Dave Thaler, Deb Cooley, Jouni Korhonen, Kathleen Moriarty, Michael Richardson, Paul Howard and Tim Hollebeek for your comments and suggestions.

Authors' Addresses

Laurence Lundblade
Security Theory LLC
Henk Birkholz
Fraunhofer Institute for Secure Information Technology
Rheinstrasse 75
64295 Darmstadt
Germany
Thomas Fossati
Linaro