Remote ATtestation ProcedureS H. Birkolz Internet-Draft Fraunhofer SIT Intended status: Standards Track N. Smith Expires: 23 April 2023 Intel T. Fossati H. Tschofenig arm 20 October 2022 RATS Conceptual Messages Wrapper draft-ftbs-rats-msg-wrap-01 Abstract This document defines two encapsulation formats for RATS conceptual messages (i.e., evidence, attestation results, endorsements and reference values.) The first format uses a CBOR or JSON array with two members: one for the type, another for the value. The other format wraps the value in a CBOR byte string and prepends a CBOR tag to convey the type information. 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-ftbs-rats-msg-wrap. 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/. Birkolz, et al. Expires 23 April 2023 [Page 1] Internet-Draft RATS CMW October 2022 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 23 April 2023. Copyright Notice Copyright (c) 2022 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 . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3 3. Conceptual Message Wrapper Encodings . . . . . . . . . . . . 3 3.1. CMW Array . . . . . . . . . . . . . . . . . . . . . . . . 4 3.2. CMW CBOR Tags . . . . . . . . . . . . . . . . . . . . . . 6 3.2.1. Use of Pre-existing CBOR Tags . . . . . . . . . . . . 6 4. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5. Security Considerations . . . . . . . . . . . . . . . . . . . 7 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 7.1. Normative References . . . . . . . . . . . . . . . . . . 7 7.2. Informative References . . . . . . . . . . . . . . . . . 8 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 1. Introduction The RATS architecture defines a handful of conceptual messages (see Section 8 of [I-D.ietf-rats-architecture]), such as evidence and attestation results. Each conceptual message can have multiple claims encoding and serialization formats (Section 9 of [I-D.ietf-rats-architecture]). Such serialized message may have to be transported via different protocols - for example, evidence using an EAT [I-D.ietf-rats-eat] encoding serialized as a CBOR payload in a "background check" topological arrangement, or attestation results as Birkolz, et al. Expires 23 April 2023 [Page 2] Internet-Draft RATS CMW October 2022 Attestation Results for Secure Interactions (AR4SI) [I-D.ietf-rats-ar4si] payloads in "passport" mode. In order to minimize the cost associated with registration and maximize interoperability, it is desirable to reuse their typing information across such boundaries. This document defines two encapsulation formats for RATS conceptual messages that aim to achieve the goals stated above. These encapsulation formats are designed to be: * Self-describing - which removes the dependency on the framing provided by the embedding protocol (or the storage system) to convey exact typing information. * Based on media types - which allows amortising their registration cost across many different usage scenarios. A protocol designer could use these formats, for example, to convey evidence, endorsements or reference values in certificates and CRLs extensions ([DICE-arch]), to embed attestation results or evidence as first class authentication credentials in TLS handshake messages [I-D.fossati-tls-attestation], to transport attestation-related payloads in RESTful APIs, or for stable storage of attestation results in form of file system objects. 2. Conventions and Definitions 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. In this document, CDDL [RFC8610] [RFC9165] is used to describe the data formats. The reader is assumed to be familiar with the vocabulary and concepts defined in [I-D.ietf-rats-architecture]. 3. Conceptual Message Wrapper Encodings Two types of RATS Conceptual Message Wrapper (CMW) are specified in this document: 1. a CMW using a CBOR or a JSON array (Section 3.1) Birkolz, et al. Expires 23 April 2023 [Page 3] Internet-Draft RATS CMW October 2022 2. a CMW based on CBOR tags (Section 3.2). 3.1. CMW Array The CMW array illustrated in Figure 1 is composed of two members: * type: either a text string representing a media-type (and optional parameters) [RFC6838] or an unsigned integer corresponding to a CoAP Content-Format [RFC7252] * value: the RATS conceptual message serialized according to the value defined in the type member. A CMW array can be encoded as CBOR [STD94] or JSON [RFC8259]. When using JSON, the value field is encoded as Base64 using the URL and filename safe alphabet (Section 5 of [RFC4648]) without padding. When using CBOR, the value field is encoded as a CBOR byte string. Birkolz, et al. Expires 23 April 2023 [Page 4] Internet-Draft RATS CMW October 2022 cmw = [ type, value ] type = coap-content-format / media-type coap-content-format = uint .size 2 media-type = text .abnf ("media-type" .cat RFC6838) value = cbor-bytes / base64-string cbor-bytes = bytes base64-string = text .regexp "[A-Za-z0-9_-]+" RFC6838 = ' media-type = type-name "/" subtype-name *1("+" suffix) parameters type-name = restricted-name subtype-name = restricted-name ; see https://www.iana.org/assignments/media-type-structured-suffix/ suffix = "xml" / "json" / "ber" / "cbor" / "der" / "fastinfoset" / "wbxml" / "zip" / "tlv" / "json-seq" / "sqlite3" / "jwt" / "gzip" / "cbor-seq" / "zstd" parameters = *(";" parameter-name "=" parameter-value) parameter-name = restricted-name parameter-value = *VCHAR restricted-name = restricted-name-first *126restricted-name-chars restricted-name-first = ALPHA / DIGIT restricted-name-chars = ALPHA / DIGIT / "!" / "#" / "$" / "&" / "-" / "^" / "_" restricted-name-chars =/ "." ; Characters before first dot always ; specify a facet name restricted-name-chars =/ "+" ; Characters after last plus always ; specify a structured syntax suffix VCHAR = %x21-7E ; Visible (printing) characters ALPHA = %x41-5A / %x61-7A ; A-Z / a-z DIGIT = %x30-39 ; 0-9 ' Figure 1: CDDL definition Birkolz, et al. Expires 23 April 2023 [Page 5] Internet-Draft RATS CMW October 2022 3.2. CMW CBOR Tags CBOR Tags used as CMW are derived from CoAP Content Format values. If a CoAP Content Format exists for a RATS conceptual message, the TN() transform defined in Appendix B of [RFC9277] can be used to derive a corresponding CBOR tag in range [1668546817, 1668612095]. The RATS conceptual message is first serialized according to the Content Format associated with the tag and then encoded as a CBOR byte string, to which the tag is prepended. 3.2.1. Use of Pre-existing CBOR Tags If a CBOR tag has been registered in association with a certain RATS conceptual message independently of a CoAP Content Format (i.e., it is not obtained by applying the TN() transform), it can be readily used as an encapsulation without the extra processing described in Section 3.2. A consumer can always distinguish tags that have been derived via TN(), which all fall in the [1668546817, 1668612095] range, from tags that are not, and therefore apply the right decapsulation on receive. 4. Examples The (equivalent) examples below assume the media-type application/ vnd.example.rats-conceptual-msg has been registered alongside a corresponding CoAP content format 30001. The CBOR tag 1668576818 is derived applying the TN transform as described in Section 3.2. [ 30001, h'abcdabcd' ] Figure 2: CBOR encoding [ "application/vnd.example.rats-conceptual-msg", "q82rzQ" ] Figure 3: JSON encoding 1668576818(h'abcdabcd') Figure 4: CBOR tag Birkolz, et al. Expires 23 April 2023 [Page 6] Internet-Draft RATS CMW October 2022 5. Security Considerations This document defines two encapsulation formats for RATS conceptual messages. The messages themselves and their encoding ensure security protection. For this reason there are no further security requirements raised by the introduction of this encapsulation. Changing the encapsulation of a payload by an adversary will result in incorrect processing of the encapsulated messages and this will subsequently lead to a processing error. 6. IANA Considerations When registering a new media type for evidence, in addition to its syntactical description, the author SHOULD provide a public and stable description of the signing and appraisal procedures associated with the data format. 7. References 7.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006, . [RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type Specifications and Registration Procedures", BCP 13, RFC 6838, DOI 10.17487/RFC6838, January 2013, . [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained Application Protocol (CoAP)", RFC 7252, DOI 10.17487/RFC7252, June 2014, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . Birkolz, et al. Expires 23 April 2023 [Page 7] Internet-Draft RATS CMW October 2022 [RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data Interchange Format", STD 90, RFC 8259, DOI 10.17487/RFC8259, December 2017, . [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, . [RFC9165] Bormann, C., "Additional Control Operators for the Concise Data Definition Language (CDDL)", RFC 9165, DOI 10.17487/RFC9165, December 2021, . [RFC9277] Richardson, M. and C. Bormann, "On Stable Storage for Items in Concise Binary Object Representation (CBOR)", RFC 9277, DOI 10.17487/RFC9277, August 2022, . [STD94] Bormann, C. and P. Hoffman, "Concise Binary Object Representation (CBOR)", STD 94, RFC 8949, DOI 10.17487/RFC8949, December 2020, . 7.2. Informative References [DICE-arch] Trusted Computing Group, "DICE Attestation Architecture", March 2021, . [I-D.fossati-tls-attestation] Tschofenig, H., Fossati, T., Howard, P., Mihalcea, I., and Y. Deshpande, "Using Attestation in Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)", Work in Progress, Internet-Draft, draft-fossati- tls-attestation-01, 26 August 2022, . Birkolz, et al. Expires 23 April 2023 [Page 8] Internet-Draft RATS CMW October 2022 [I-D.ietf-rats-ar4si] Voit, E., Birkholz, H., Hardjono, T., Fossati, T., and V. Scarlata, "Attestation Results for Secure Interactions", Work in Progress, Internet-Draft, draft-ietf-rats-ar4si- 03, 6 September 2022, . [I-D.ietf-rats-architecture] Birkholz, H., Thaler, D., Richardson, M., Smith, N., and W. Pan, "Remote Attestation Procedures Architecture", Work in Progress, Internet-Draft, draft-ietf-rats-architecture- 22, 28 September 2022, . [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-16, 9 October 2022, . Acknowledgments TODO acknowledge. Authors' Addresses Henk Birkolz Fraunhofer SIT Email: henk.birkholz@sit.fraunhofer.de Ned Smith Intel Email: ned.smith@intel.com Thomas Fossati arm Email: thomas.fossati@arm.com Hannes Tschofenig arm Email: hannes.tschofenig@arm.com Birkolz, et al. Expires 23 April 2023 [Page 9]