Guidelines for Security Considerations of RATS
draft-sardar-rats-sec-cons-00

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/.
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 material or to cite them other than as "work in progress."
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 document authors. All rights reserved.
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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
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 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
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 * 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.
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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).
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 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:
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 | 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.
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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,
 <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,
 May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
 [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>.
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 [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/rfc/rfc9711>.
 [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,
 <https://www.rfc-editor.org/rfc/rfc9781>.
 [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, <https://www.rfc-editor.org/rfc/rfc9783>.
11.2. Informative References
 [Clarifications-EAT]
 Sardar, M. U., "Clarifications in draft-ietf-rats-eat",
 April 2025, <https://mailarchive.ietf.org/arch/msg/
 rats/4V2zZHhk5IuxwcUMNWpPBpnzpaM/>.
 [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, <https://foreshadowattack.eu/>.
 [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, <https://eur-lex.europa.eu/eli/reg/2016/679/oj>.
 [Gen-Approach]
 Sardar, M. U., "Perspicuity of Attestation Mechanisms in
 Confidential Computing: General Approach", October 2025,
 <https://www.researchgate.net/publication/396593308_Perspi
 cuity_of_Attestation_Mechanisms_in_Confidential_Computing_
 General_Approach>.
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 [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,
 <https://datatracker.ietf.org/doc/html/draft-deshpande-
 rats-multi-verifier-03>.
 [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,
 <https://datatracker.ietf.org/doc/html/draft-ietf-rats-
 coserv-02>.
 [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, <https://datatracker.ietf.org/doc/html/draft-
 irtf-cfrg-cryptography-specification-02>.
 [Meeting-122-TLS-Slides]
 Sardar, M. U., Moustafa, M., and T. Aura, "Identity Crisis
 in Attested TLS for Confidential Computing", March 2025,
 <https://datatracker.ietf.org/meeting/122/materials/
 slides-122-tls-identity-crisis-00>.
 [Meeting-124-RATS-Slides]
 Sardar, M. U., "Guidelines for Security Considerations of
 RATS", November 2025,
 <https://datatracker.ietf.org/meeting/124/materials/
 slides-124-rats-sessb-guideline-for-security-
 consideration-of-rats-00>.
 [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>.
 [Sec-Cons-RATS]
 Sardar, M. U., "Security considerations of remote
 attestation (RFC9334)", November 2024,
 <https://mailarchive.ietf.org/arch/msg/rats/
 jcAv9FKbYSIVtUNQ8ggEHL8lrmM/>.
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 [Tech-Concepts]
 Sardar, M. U., "Perspicuity of Attestation Mechanisms in
 Confidential Computing: Technical Concepts", October 2025,
 <https://www.researchgate.net/publication/396199290_Perspi
 cuity_of_Attestation_Mechanisms_in_Confidential_Computing_
 Technical_Concepts>.
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
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