EAT Media Types
draft-ietf-rats-eat-media-type-12
Document | Type | Active Internet-Draft (rats WG) | |
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Authors | Laurence Lundblade , Henk Birkholz , Thomas Fossati | ||
Last updated | 2024-11-27 (Latest revision 2024-11-03) | ||
RFC stream | Internet Engineering Task Force (IETF) | ||
Intended RFC status | Proposed Standard | ||
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by Jouni Korhonen
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Additional resources | Mailing list discussion | ||
Stream | WG state | Submitted to IESG for Publication | |
Associated WG milestones |
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Document shepherd | Kathleen Moriarty | ||
Shepherd write-up | Show Last changed 2024-05-07 | ||
IESG | IESG state | RFC Ed Queue | |
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Consensus boilerplate | Yes | ||
Telechat date | (None) | ||
Responsible AD | Deb Cooley | ||
Send notices to | Kathleen.Moriarty.ietf@gmail.com | ||
IANA | IANA review state | Version Changed - Review Needed | |
IANA action state | Waiting on RFC Editor | ||
IANA expert review state | Expert Reviews OK | ||
RFC Editor | RFC Editor state | EDIT | |
Details |
draft-ietf-rats-eat-media-type-12
Remote ATtestation ProcedureS L. Lundblade Internet-Draft Security Theory LLC Intended status: Standards Track H. Birkholz Expires: 7 May 2025 Fraunhofer SIT T. Fossati Linaro 3 November 2024 EAT Media Types draft-ietf-rats-eat-media-type-12 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 7 May 2025. Lundblade, et al. Expires 7 May 2025 [Page 1] Internet-Draft EAT Media Types November 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/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 2. EAT Types . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. A Media Type Parameter for EAT Profiles . . . . . . . . . . . 4 4. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 5 5. Security Considerations . . . . . . . . . . . . . . . . . . . 6 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 6.1. +cwt Structured Syntax Suffix . . . . . . . . . . . . . . 6 6.1.1. Registry Contents . . . . . . . . . . . . . . . . . . 6 6.2. Media Types . . . . . . . . . . . . . . . . . . . . . . . 7 6.3. application/eat+cwt Registration . . . . . . . . . . . . 7 6.4. application/eat+jwt Registration . . . . . . . . . . . . 8 6.5. application/eat-bun+cbor Registration . . . . . . . . . . 8 6.6. application/eat-bun+json Registration . . . . . . . . . . 9 6.7. application/eat-ucs+cbor Registration . . . . . . . . . . 9 6.8. application/eat-ucs+json Registration . . . . . . . . . . 10 6.9. CoAP Content-Format Registrations . . . . . . . . . . . . 10 7. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 11 7.1. -04 . . . . . . . . . . . . . . . . . . . . . . . . . . 11 7.2. -03 . . . . . . . . . . . . . . . . . . . . . . . . . . 11 7.3. -02 . . . . . . . . . . . . . . . . . . . . . . . . . . 11 7.4. -01 . . . . . . . . . . . . . . . . . . . . . . . . . . 12 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 8.1. Normative References . . . . . . . . . . . . . . . . . . 12 8.2. Informative References . . . . . . . . . . . . . . . . . 13 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 14 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 Lundblade, et al. Expires 7 May 2025 [Page 2] Internet-Draft EAT Media Types November 2024 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]. 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 UJCS. Lundblade, et al. Expires 7 May 2025 [Page 3] Internet-Draft EAT Media Types November 2024 .-----. .----+ UJCS |<-------------------------. | '-----' | | | | .-----. | +-----+ UCCS |<-----------------------. | | '-----' | | | | | | .------. | | +-----+ JWT |<------. | | | '------' .--+---. | | | | Crypto |<------. | | | .------. '--+---' | | | +-----+ CWT |<------' | | | | '------' .---+-+-+----. | | Claims-Set +--. | .------. '---+---+----' | +-----+ BUN-J |<------. | ^ | v | '------' .--+---. | | | .------. | | Bundle |<------' | | | Digest | | .------. '--+---' | v '--+---' +-----+ BUN-C |<------' ^ .---+----. | | '------' | | submod |<---' | | '--------' v | ^ .--------------. | | | 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. Lundblade, et al. Expires 7 May 2025 [Page 4] Internet-Draft EAT Media Types November 2024 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]) uses the quoted-string encoding, e.g.: application/eat+jwt; eat_profile="tag:evidence.example,2022" Instead, when the EAT profile is an OID, the token encoding (i.e., without quotes) can be used, e.g.: application/eat+cwt; eat_profile=2.999.1. 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. Lundblade, et al. Expires 7 May 2025 [Page 5] Internet-Draft EAT Media Types November 2024 # 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, and stop further processing on failure. 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. In particular, when using application/eat-ucs+json and application/ eat-ucs+cbor the reader should review Section 3 of [UCCS], which contains a detailed discussion about the characteristics of a "Secure Channel" for conveyance of such messages. 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] Lundblade, et al. Expires 7 May 2025 [Page 6] Internet-Draft EAT Media Types November 2024 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]. +==============+=====================+======================+ | Name | Template | Reference | +==============+=====================+======================+ | EAT CWT | application/eat+cwt | RFCthis, Section 6.3 | +--------------+---------------------+----------------------+ | EAT JWT | application/eat+jwt | RFCthis, Section 6.4 | +--------------+---------------------+----------------------+ | Detached EAT | application/eat- | RFCthis, Section 6.5 | | Bundle CBOR | bun+cbor | | +--------------+---------------------+----------------------+ | Detached EAT | application/eat- | RFCthis, Section 6.6 | | Bundle JSON | bun+json | | +--------------+---------------------+----------------------+ | EAT UCCS | application/eat- | RFCthis, Section 6.7 | | | ucs+cbor | | +--------------+---------------------+----------------------+ | EAT UJCS | application/eat- | RFCthis, Section 6.8 | | | ucs+json | | +--------------+---------------------+----------------------+ Table 1: New Media Types 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.) Lundblade, et al. Expires 7 May 2025 [Page 7] Internet-Draft EAT Media Types November 2024 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.) Lundblade, et al. Expires 7 May 2025 [Page 8] Internet-Draft EAT Media Types November 2024 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.) Lundblade, et al. Expires 7 May 2025 [Page 9] Internet-Draft EAT Media Types November 2024 Encoding considerations: binary Security considerations: Sections 3 and 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: Sections 3 and 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]: Lundblade, et al. Expires 7 May 2025 [Page 10] Internet-Draft EAT Media Types November 2024 +==========================+================+======+===========+ | 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 | +--------------------------+----------------+------+-----------+ Table 2: New Content-Formats TBD1..6 are to be assigned from the space 256..9999. 7. Changelog // RFC editor: please remove this section 7.1. -04 * Early IANA review 7.2. -03 * Update references 7.3. -02 * Update references * Register +cwt SSS (Issue#14 (https://github.com/ietf-rats-wg/ draft-eat-mt/issues/14)) * Move from eat-jwt to eat+jwt (Issue#14 (https://github.com/ietf- rats-wg/draft-eat-mt/issues/14)) * Move from eat-cwt to eat+cwt (Issue#14 (https://github.com/ietf- rats-wg/draft-eat-mt/issues/14)) Lundblade, et al. Expires 7 May 2025 [Page 11] Internet-Draft EAT Media Types November 2024 7.4. -01 * Rename profile to eat_profile for consistency with EAT (Issue#4 (https://github.com/ietf-rats-wg/draft-eat-mt/issues/4)) * The DEB acronym is gone: shorthand is now "bun" from bundle (Issue#8 (https://github.com/ietf-rats-wg/draft-eat-mt/issues/8)) * Incorporate editorial suggestions from Carl and Dave (Issue#7 (https://github.com/ietf-rats-wg/draft-eat-mt/issues/7), Issue#9 (https://github.com/ietf-rats-wg/draft-eat-mt/issues/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, February 2020, <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, May 2018, <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, 6 September 2024, <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, June 2022, <https://www.rfc-editor.org/rfc/rfc9110>. [IANA.core-parameters] IANA, "Constrained RESTful Environments (CoRE) Parameters", <https://www.iana.org/assignments/core-parameters>. Lundblade, et al. Expires 7 May 2025 [Page 12] Internet-Draft EAT Media Types November 2024 [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, December 2017, <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, May 2015, <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, January 2013, <https://www.rfc-editor.org/rfc/rfc6838>. [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-12, 3 November 2024, <https://datatracker.ietf.org/doc/html/ draft-ietf-rats-uccs-12>. [URI] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, DOI 10.17487/RFC3986, January 2005, <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, June 2022, <https://www.rfc-editor.org/info/rfc9205>. Lundblade, et al. Expires 7 May 2025 [Page 13] Internet-Draft EAT Media Types November 2024 [RATS-Arch] 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>. [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-15, 21 October 2024, <https://datatracker.ietf.org/doc/html/ draft-irtf-t2trg-rest-iot-15>. [TAG] Kindberg, T. and S. Hawke, "The 'tag' URI Scheme", RFC 4151, DOI 10.17487/RFC4151, October 2005, <https://www.rfc-editor.org/rfc/rfc4151>. Acknowledgments Thank you Carl Wallace, Carsten Bormann, Dave Thaler, Deb Cooley, Éric Vyncke, Francesca Palombini, Jouni Korhonen, Kathleen Moriarty, Michael Richardson, Murray Kucherawy, Orie Steele, Paul Howard, Roman Danyliw and Tim Hollebeek for your comments and suggestions. Authors' Addresses Laurence Lundblade Security Theory LLC Email: lgl@securitytheory.com Henk Birkholz Fraunhofer Institute for Secure Information Technology Rheinstrasse 75 64295 Darmstadt Germany Email: henk.birkholz@ietf.contact Thomas Fossati Linaro Email: thomas.fossati@linaro.org Lundblade, et al. Expires 7 May 2025 [Page 14]