



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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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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