RATS Working Group M. U. Sardar Internet-Draft TU Dresden Updates: 9334 (if approved) 27 November 2025 Intended status: Informational Expires: 31 May 2026 Guidelines for Security Considerations of RATS draft-sardar-rats-sec-cons-00 Abstract This document aims to provide guidelines and best practices for writing security considerations for technical specifications for RATS targeting the needs of implementers, researchers, and protocol designers. The current version presents an outline of the topics that future versions will cover in more detail. * Corrections in published RATS RFCs * Security concerns in two RATS drafts * General security guidelines, baseline or template for RATS About This Document This note is to be removed before publishing as an RFC. The latest revision of this draft can be found at https://muhammad- usama-sardar.github.io/rats-sec-cons/draft-sardar-rats-sec-cons.html. Status information for this document may be found at https://datatracker.ietf.org/doc/draft-sardar-rats-sec-cons/. Source for this draft and an issue tracker can be found at https://github.com/muhammad-usama-sardar/rats-sec-cons. 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/. Sardar Expires 31 May 2026 [Page 1] Internet-Draft RATS Security Considerations November 2025 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 31 May 2026. Copyright Notice Copyright (c) 2025 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 2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3 3. General Hierarchy of Authentication . . . . . . . . . . . . . 3 4. Threat Modeling . . . . . . . . . . . . . . . . . . . . . . . 4 4.1. System Model . . . . . . . . . . . . . . . . . . . . . . 4 4.2. Actors . . . . . . . . . . . . . . . . . . . . . . . . . 4 4.2.1. Legal perspective . . . . . . . . . . . . . . . . . . 4 4.2.2. Technical perspective . . . . . . . . . . . . . . . . 4 4.3. Threat Model . . . . . . . . . . . . . . . . . . . . . . 4 4.4. Typical Security Goals . . . . . . . . . . . . . . . . . 4 5. Attacks . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 5.1. Replay attacks . . . . . . . . . . . . . . . . . . . . . 5 5.2. Relay attacks . . . . . . . . . . . . . . . . . . . . . . 5 5.3. Diversion attacks . . . . . . . . . . . . . . . . . . . . 5 6. Potential Mitigations . . . . . . . . . . . . . . . . . . . . 5 7. Examples of Specifications That Could Be Improved . . . . . . 5 7.1. RFC9334 . . . . . . . . . . . . . . . . . . . . . . . . . 5 7.1.1. Unprotected Evidence . . . . . . . . . . . . . . . . 5 7.1.2. Missing definitions . . . . . . . . . . . . . . . . . 6 7.1.3. Missing Roles and Conceptual Messages . . . . . . . . 6 7.2. RFC9781 . . . . . . . . . . . . . . . . . . . . . . . . . 6 7.3. RFC9783 . . . . . . . . . . . . . . . . . . . . . . . . . 6 7.4. RFC9711 . . . . . . . . . . . . . . . . . . . . . . . . . 6 7.4.1. Inaccurate opinion . . . . . . . . . . . . . . . . . 6 7.4.2. Inaccurate Privacy Considerations . . . . . . . . . . 7 Sardar Expires 31 May 2026 [Page 2] Internet-Draft RATS Security Considerations November 2025 8. Examples of Parts of Specifications That are Detrimental for Security . . . . . . . . . . . . . . . . . . . . . . . . 7 8.1. Multi-Verifiers . . . . . . . . . . . . . . . . . . . . . 7 8.2. Aggregator-based design . . . . . . . . . . . . . . . . . 8 9. Security Considerations . . . . . . . . . . . . . . . . . . . 8 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 11.1. Normative References . . . . . . . . . . . . . . . . . . 8 11.2. Informative References . . . . . . . . . . . . . . . . . 9 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 11 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11 1. Introduction While excellent guidelines such as [I-D.irtf-cfrg-cryptography-specification] exist, remote attestation [RFC9334] has several distinguishing features which necessitate a separate document. One specific example of such a feature is architectural complexity. The draft presents an outline of three topics that future versions will cover in more detail: * Corrections in published RATS RFCs [RFC9334], [RFC9781], [RFC9783] and [RFC9711] * Security concerns in one currently adopted RATS draft [I-D.ietf-rats-coserv] and one proposed for adoption RATS draft [I-D.deshpande-rats-multi-verifier] * General security guidelines, baseline or template that other drafts can simply point to 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. 3. General Hierarchy of Authentication [Gen-Approach] proposes general hierarchy of one-way authentication, which can help precisely state the intended level of authentication (in decreasing order): * One-way injective agreement Sardar Expires 31 May 2026 [Page 3] Internet-Draft RATS Security Considerations November 2025 * One-way non-injective agreement * Aliveness Recentness can be added to each of these levels of authentication. Details will be added in future versions. 4. Threat Modeling This section describes "What can go wrong?" TODO. 4.1. System Model TODO. 4.2. Actors TODO. 4.2.1. Legal perspective * Data subject is an identifiable natural person (as defined in Article 4 (1) of GDPR [GDPR]). * (Data) Controller (as defined in Article 4 (7) of GDPR [GDPR]) manages and controls what happens with personal data of data subject. * (Data) Processor (as defined in Article 4 (8) of GDPR [GDPR]) performs data processing on behalf of the data controller. TODO. 4.2.2. Technical perspective * Infrastucture Provider is a role which refers to the Processor in GDPR. An example of this role is a cloud service provider (CSP). TODO. 4.3. Threat Model TODO. 4.4. Typical Security Goals TODO. Sardar Expires 31 May 2026 [Page 4] Internet-Draft RATS Security Considerations November 2025 5. Attacks Security considerations in RATS specifications need to clarify how the following attacks are avoided or mitigated: 5.1. Replay attacks See [Meeting-124-RATS-Slides]. TODO. 5.2. Relay attacks See [Meeting-124-RATS-Slides]. TODO. 5.3. Diversion attacks In this attack, a network adversary -- with Dolev-Yao capabilities [Dolev-Yao] and access (e.g., via Foreshadow [Foreshadow]) to attestation key of any machine in the world -- can redirect a connection intended for a specific Infrastructure Provider to the compromised machine, potentially resulting in exposure of confidential data [Meeting-122-TLS-Slides]. TODO. 6. Potential Mitigations This section will describe the countermeasures and their evaluation. See [Meeting-124-RATS-Slides]. TODO. 7. Examples of Specifications That Could Be Improved 7.1. RFC9334 7.1.1. Unprotected Evidence Section 7.4 of [RFC9334] has: | A conveyance protocol that provides authentication and integrity | protection can be used to convey Evidence that is otherwise | unprotected (e.g., not signed). Sardar Expires 31 May 2026 [Page 5] Internet-Draft RATS Security Considerations November 2025 Using a conveyance protocol that provides authentication and integrity protection, such as TLS 1.3 [RFC8446], to convey Evidence that is otherwise unprotected (e.g., not signed) undermines all security of remote attestation. Essentially, this breaks the chain up to the trust anchor (such as hardware manufacturer) for remote attestation. Hence, remote attestation effectively provides no protection in this case and the security guarantees are limited to those of the conveyance protocol only. In order to benefit from remote attestation, Evidence MUST be protected using dedicated keys chaining back to the trust anchor for remote attestation. 7.1.2. Missing definitions [RFC9334] uses the term Conceptual Messages in capitalization without proper definition. 7.1.3. Missing Roles and Conceptual Messages * Identity Supplier and its corresponding conceptual message Identity are missing and need to be added to the architecture [Tech-Concepts]. * Attestation Challenge as conceptual message needs to be added to the architecture [Tech-Concepts]. 7.2. RFC9781 As argued above for RFC9334, security considerations in [RFC9781] are essentially insufficient. 7.3. RFC9783 [RFC9783] uses: * 3x epoch handle (with reference to Section 10.2 of [RFC9334] and Section 10.3 of [RFC9334]) whereas RFC9334 never uses epoch handle at all! * 1x epoch ID with no reference and no explanation of how it is different from epoch handle 7.4. RFC9711 7.4.1. Inaccurate opinion Section 7.4 of [RFC9711] has: Sardar Expires 31 May 2026 [Page 6] Internet-Draft RATS Security Considerations November 2025 | For attestation, the keys are associated with specific devices and | are configured by device manufacturers. The quoted text is inaccurate and just an opinion of the editors. It should preferably be removed from the RFC. For example, in SGX, the keys are not configured by the manufacturer alone. The platform owner can provide a random value called OWNER_EPOCH. For technical details and proposed text, see [Clarifications-EAT]. 7.4.2. Inaccurate Privacy Considerations Section 8.4 of [RFC9711] has: | The nonce claim is based on a value usually derived remotely | (outside of the entity). Attester-generated nonce does not provide any replay protection since the Attester can pre-generate an Evidence that might not reflect the actual system state, but a past one. See the attack trace for Attester-generated nonce at [Sec-Cons-RATS]. For replay protection, nonce should _always_ be derived remotely (for example, by the Relying Party). 8. Examples of Parts of Specifications That are Detrimental for Security We believe that the following parts of designs are detrimental for the RATS ecosystem: 8.1. Multi-Verifiers The design of multi-verifiers [I-D.deshpande-rats-multi-verifier] not only increases security risks in terms of increasing the Trusted Computing Base (TCB), but also increases the privacy risks, as potentially sensitive information is sent to multiple verifiers. Besides, the rationale presented by the authors -- appraisal policy being the intellectual property of the vendors -- breaks the open- source nature of RATS ecosystem. This requires blindly trusting the vendors and increases the attack surface. Sardar Expires 31 May 2026 [Page 7] Internet-Draft RATS Security Considerations November 2025 8.2. Aggregator-based design Aggregator in [I-D.ietf-rats-coserv] is an explicit trust anchor and the addition of new trust anchor needs to have a strong justification. Having a malicious Aggregator in the design trivially breaks all the guarantees. It should be clarified how trust is established between Aggregator and Verifier in the context of Confidential Computing threat model. The fact that Aggregator has collective information of Reference Values Provider and Endorsers makes it a special target of attack, and thus a single point of failure. It increases security risks because Aggregator can be compromised independent of the Reference Values Provider and Endorsers. That is, even if Reference Values Provider and Endorsers are secure, the compromise of Aggregator breaks the security of the system. Moreover, if Aggregator is not running inside a TEE, it is relatively easy to compromise the secrets. 9. Security Considerations All of this document is about security considerations. 10. IANA Considerations This document has no IANA actions. 11. References 11.1. 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, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [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, . Sardar Expires 31 May 2026 [Page 8] Internet-Draft RATS Security Considerations November 2025 [RFC9711] Lundblade, L., Mandyam, G., O'Donoghue, J., and C. Wallace, "The Entity Attestation Token (EAT)", RFC 9711, DOI 10.17487/RFC9711, April 2025, . [RFC9781] Birkholz, H., O'Donoghue, J., Cam-Winget, N., and C. Bormann, "A Concise Binary Object Representation (CBOR) Tag for Unprotected CBOR Web Token Claims Sets (UCCS)", RFC 9781, DOI 10.17487/RFC9781, May 2025, . [RFC9783] Tschofenig, H., Frost, S., Brossard, M., Shaw, A., and T. Fossati, "Arm's Platform Security Architecture (PSA) Attestation Token", RFC 9783, DOI 10.17487/RFC9783, June 2025, . 11.2. Informative References [Clarifications-EAT] Sardar, M. U., "Clarifications in draft-ietf-rats-eat", April 2025, . [Dolev-Yao] Dolev, D. and A. Yao, "On the security of public key protocols", March 1983. [Foreshadow] Jo Van Bulck, Marina Minkin, Ofir Weisse, Daniel Genkin, Baris Kasikci, Frank Piessens, Mark Silberstein, Thomas F Wenisch, Yuval Yarom, and Raoul Strackx, "Foreshadow", October 2025, . [GDPR] European Commission, "Regulation (EU) 2016/679 of the European Parliament and of the Council of 27 April 2016 on the protection of natural persons with regard to the pro- cessing of personal data and on the free movement of such data, and repealing Direc- tive 95/46/EC (General Data Protection Regulation) (Text with EEA relevance)", May 2016, . [Gen-Approach] Sardar, M. U., "Perspicuity of Attestation Mechanisms in Confidential Computing: General Approach", October 2025, . Sardar Expires 31 May 2026 [Page 9] Internet-Draft RATS Security Considerations November 2025 [I-D.deshpande-rats-multi-verifier] Deshpande, Y., jun, Z., Labiod, H., and H. Birkholz, "Remote Attestation with Multiple Verifiers", Work in Progress, Internet-Draft, draft-deshpande-rats-multi- verifier-03, 20 October 2025, . [I-D.ietf-rats-coserv] Howard, P., Fossati, T., Birkholz, H., Kamal, S., Mandyam, G., and D. Ma, "Concise Selector for Endorsements and Reference Values", Work in Progress, Internet-Draft, draft-ietf-rats-coserv-02, 20 October 2025, . [I-D.irtf-cfrg-cryptography-specification] Sullivan, N. and C. A. Wood, "Guidelines for Writing Cryptography Specifications", Work in Progress, Internet- Draft, draft-irtf-cfrg-cryptography-specification-02, 7 July 2025, . [Meeting-122-TLS-Slides] Sardar, M. U., Moustafa, M., and T. Aura, "Identity Crisis in Attested TLS for Confidential Computing", March 2025, . [Meeting-124-RATS-Slides] Sardar, M. U., "Guidelines for Security Considerations of RATS", November 2025, . [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, . [Sec-Cons-RATS] Sardar, M. U., "Security considerations of remote attestation (RFC9334)", November 2024, . Sardar Expires 31 May 2026 [Page 10] Internet-Draft RATS Security Considerations November 2025 [Tech-Concepts] Sardar, M. U., "Perspicuity of Attestation Mechanisms in Confidential Computing: Technical Concepts", October 2025, . Acknowledgments The author wishes to thank Ira McDonald and Ivan Gudymenko for insightful discussions. The author also wishes to thank the authors of [I-D.ietf-rats-coserv] (in particular Thomas Fossati and Paul Howard) for several discussions, which unfortunately could not resolve the above concerns, and hence led to this draft. The author also gratefully acknowledges the authors of [I-D.irtf-cfrg-cryptography-specification], which serves as the inspiration of this work. Author's Address Muhammad Usama Sardar TU Dresden Email: muhammad_usama.sardar@tu-dresden.de Sardar Expires 31 May 2026 [Page 11]