EAP Method Update T. Reddy Internet-Draft Nokia Intended status: Standards Track 24 January 2026 Expires: 28 July 2026 Post-Quantum Enhancements to EAP-TLS and EAP-TTLS draft-reddy-emu-pqc-eap-tls-02 Abstract This document proposes enhancements to the Extensible Authentication Protocol with Transport Layer Security (EAP-TLS) and EAP Tunneled TLS (EAP-TTLS) to incorporate post-quantum cryptographic mechanisms. It also addresses challenges related to large certificate sizes and long certificate chains, as identified in [RFC9191], and provides recommendations for integrating PQC algorithms into EAP-TLS and EAP- TTLS deployments. About This Document This note is to be removed before publishing as an RFC. Status information for this document may be found at https://datatracker.ietf.org/doc/draft-reddy-emu-pqc-eap-tls/. Discussion of this document takes place on the EAP Method Update Working Group mailing list (mailto:emu@ietf.org), which is archived at https://mailarchive.ietf.org/arch/browse/emu. Subscribe at https://www.ietf.org/mailman/listinfo/emu/. 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 28 July 2026. Reddy Expires 28 July 2026 [Page 1] Internet-Draft PQC Enhancements to EAP-TLS/TTLS January 2026 Copyright Notice Copyright (c) 2026 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. Data Confidentiality in EAP-TLS . . . . . . . . . . . . . . . 4 4. Post-Quantum Authentication in EAP-TLS . . . . . . . . . . . 5 5. EST Integration . . . . . . . . . . . . . . . . . . . . . . . 6 6. Security Considerations . . . . . . . . . . . . . . . . . . . 7 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 8 References . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Normative References . . . . . . . . . . . . . . . . . . . . . 8 Informative References . . . . . . . . . . . . . . . . . . . . 8 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9 1. Introduction The emergence of a Cryptographically Relevant Quantum Computer (CRQC) would break the mathematical assumptions that underpins widely deployed public-key algorithms, rendering them insecure and obsolete. As a result, there is an urgent need to update protocols and infrastructure with post-quantum cryptographic (PQC) algorithms designed to resist attacks from both quantum and classical adversaries. The cryptographic primitives requiring replacement are discussed in [I-D.ietf-pquip-pqc-engineers], and the NIST PQC Standardization process has initially selected algorithms such as ML- KEM, SLH-DSA, and ML-DSA for usage in security protocols. To mitigate the risks posed by a CRQC, such as the potential compromise of encrypted data and the forging of digital signatures, existing security protocols must be upgraded to support PQC. These risks include "Harvest Now, Decrypt Later" (HNDL) attack, where adversaries capture encrypted traffic today with the intent to decrypt it once CRQCs become available. Protocols such as EAP-TLS Reddy Expires 28 July 2026 [Page 2] Internet-Draft PQC Enhancements to EAP-TLS/TTLS January 2026 and EAP-TTLS are widely used for network access authentication in Enterprise and Wireless environments. To continue providing long- term confidentiality and authentication guarantees, EAP-TLS and EAP- TTLS must evolve to incorporate post-quantum algorithms. However, transitioning these protocols to support PQC introduces practical challenges. [RFC9191] highlights issues related to large certificates and certificate chains in EAP-TLS, which can lead to session failures due to round-trip limitations. PQC certificates and certificate chains tend to be significantly larger than their traditional counterparts, further exacerbating these issues by increasing TLS handshake sizes and the likelihood of session failures. To address these challenges, this draft proposes mitigation strategies that enable the use of PQC within EAP-TLS and EAP-TTLS, ensuring secure and efficient authentication even in constrained network environments. 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. This document adopts terminology defined in [I-D.ietf-pquip-pqt-hybrid-terminology]. For the purposes of this document, it is useful to categorize cryptographic algorithms into three distinct classes: * Traditional Algorithm: An asymmetric cryptographic algorithm based on integer factorization, finite field discrete logarithms, or elliptic curve discrete logarithms. In the context of TLS, an example of a traditional key exchange algorithm is Elliptic Curve Diffie-Hellman (ECDH), which is almost exclusively used in its ephemeral mode, referred to as Elliptic Curve Diffie-Hellman Ephemeral (ECDHE). * Post-Quantum Algorithm: An asymmetric cryptographic algorithm designed to be secure against attacks from both quantum and classical computers. An example of a post-quantum key exchange algorithm is the Module-Lattice Key Encapsulation Mechanism (ML- KEM). * Hybrid Algorithm: We distinguish between key exchanges and signature algorithms: Reddy Expires 28 July 2026 [Page 3] Internet-Draft PQC Enhancements to EAP-TLS/TTLS January 2026 - Hybrid Key Exchange: A key exchange mechanism that combines two component algorithms - one traditional algorithm and one post- quantum algorithm. The resulting shared secret remains secure as long as at least one of the component key exchange algorithms remains unbroken. - PQ/T Hybrid Digital Signature: A multi-algorithm digital signature scheme composed of two or more component signature algorithms, where at least one is a post-quantum algorithm and at least one is a traditional algorithm. Digital signature algorithms play a critical role in X.509 certificates, Certificate Transparency Signed Certificate Timestamps, Online Certificate Status Protocol (OCSP) statements, and any other mechanism that contributes signatures during a TLS handshake or in context of a secure communication establishment. 3. Data Confidentiality in EAP-TLS One of the primary threats to EAP-TLS and EAP-TTLS is the HNDL attack. In this scenario, adversaries can passively capture EAP-TLS handshakes such as those transmitted over the air in Wi-Fi networks and store them for future decryption once CRQCs become available. While EAP-TLS 1.3 [RFC9190] provides forward secrecy through ephemeral key exchange and improves privacy by encrypting client identity and reducing exposure of session metadata, these protections rely on the security of the underlying key exchange algorithm. In the presence of a CRQC, traditional key exchange mechanisms (e.g., ECDHE) would no longer provide long-term confidentiality. In such cases, an adversary could mount a HDNL attack by passively recording EAP-TLS handshakes and decrypting the captured traffic once quantum- capable cryptanalysis becomes feasible. This could retroactively expose information that TLS 1.3 is otherwise designed to protect, including: * The identity of the authenticated client. * Client credentials used in certificate-based authentication (e.g., usernames, device or organization identifiers). To preserve the intended privacy guarantees of TLS 1.3 and to protect against HDNL attacks, EAP-TLS and EAP-TTLS deployments that require long-term confidentiality will need to adopt post-quantum key exchange mechanisms, as outlined in Section 4 of [I-D.ietf-uta-pqc-app]. Reddy Expires 28 July 2026 [Page 4] Internet-Draft PQC Enhancements to EAP-TLS/TTLS January 2026 These mechanisms ensure that even if handshake data is recorded today, it cannot be decrypted in the future, maintaining the confidentiality and privacy of the TLS session. Furthermore, to support hybrid or PQC-only key exchange in bandwidth or latency-constrained EAP deployments, EAP clients and servers should apply the optimizations described in Section 4.1 of [I-D.ietf-uta-pqc-app] to minimize performance overhead. 4. Post-Quantum Authentication in EAP-TLS Although a CRQC would primarily impact the confidentiality of recorded TLS sessions, it could also pose risks to authentication mechanisms that rely on traditional public-key algorithms with long- lived credentials. In particular, if quantum-capable cryptanalysis were to become practical within the validity period of a certificate, an adversary could recover the private key corresponding to a traditionally signed certificate and subsequently impersonate the certificate holder in real time. The feasibility and impact of such attacks depend on several factors, including certificate lifetimes and key management practices. EAP-TLS and EAP-TTLS deployments rely on X.509 certificates issued by CAs, and the transition to PQ certificate authentication is constrained by the long lifecycle associated with distributing, deploying, and validating new trust anchors. If CRQCs arrive sooner than anticipated, deployed authentication systems may lack the agility to transition credentials and trust anchors in a timely manner. As a result, deployments that rely on long-lived certificates or that require resistance to future quantum-capable adversaries face an increased risk of authentication compromise. In such scenarios, an on-path attacker that is able to recover a server’s private key within the certificate validity period could impersonate access points (APs) in real time, potentially deceiving users into revealing credentials or connecting to rogue networks. To mitigate these risks, EAP-TLS and EAP-TTLS deployments will need to adopt, over time, either PQ or PQ/T hybrid certificate-based authentication, as described in Section 5 of [I-D.ietf-uta-pqc-app]. The use of PQ or PQ/T hybrid certificates increases the size of individual certificates, certificate chains, and signatures, resulting in significantly larger handshake messages. These larger payloads can lead to packet fragmentation, retransmissions, and handshake delays, issues that are particularly disruptive in constrained or lossy network environments. Reddy Expires 28 July 2026 [Page 5] Internet-Draft PQC Enhancements to EAP-TLS/TTLS January 2026 To address these impacts, EAP-TLS and EAP-TTLS deployments can apply certificate chain optimization techniques outlined in Section 6.1 of [I-D.ietf-uta-pqc-app] to reduce transmission overhead and improve handshake reliability. 5. EST Integration The EAP-client is expected to validate the certificate presented by the EAP-server using a trust anchor that is provisioned out-of-band prior to authentication (e.g., using EST). The Intermediate certificates are provided by the EAP server during the EAP-TLS handshake. The EAP client relies solely on the pre-provisioned trust anchor to build and validate the certificate chain. This model assumes a managed deployment environment with explicitly configured trust relationships between the EAP-client and EAP-server. To further reduce handshake overhead, particularly in deployments using large certificate chains due to post-quantum (PQ) or composite certificates, this draft proposes an optimization that leverages the Enrollment over Secure Transport (EST) protocol [RFC7030], extended by [RFC8295]. Specifically, it allows intermediate certificates to be retrieved in advance by using EST, thereby avoiding the need to transmit them during each EAP-TLS exchange. This section defines extensions to EST to support retrieval of the certificate chain used by a EAP server and EAP clients. The first extension enables clients to obtain access to the complete set of published intermediate certificates of the EAP server. A new path component is defined under the EST well-known URI: GET /.well-known/est/eapservercertchain The '/eapservercertchain' is intended for informational retrieval only and does not require client authentication. It allows clients to retrieve the intermediate certificate chain that the EAP server presents during TLS handshakes. This request is performed using the HTTPS protocol. The EST server MUST support requests without requiring client authentication. The certificate chain provided by the EST server MUST be the same certificate chain EAP server uses in a EAP-TLS or EAP-TTLS session. The second extension enables EAP servers to obtain access to the complete set of published intermediate certificates of the EAP clients. Rather than relying on static configuration, the EAP server can dynamically fetch the client's intermediate certificate chain from a trusted EST server within the same administrative domain. Reddy Expires 28 July 2026 [Page 6] Internet-Draft PQC Enhancements to EAP-TLS/TTLS January 2026 A new path component is defined under the EST well-known URI: GET /.well-known/est/eapclientcertchain The '/eapclientcertchain' is intended for informational retrieval only and does not require client authentication. It allows EAP server to retrieve the intermediate certificate chain that the EAP clients present during TLS handshakes. This request is performed using the HTTPS protocol. The EST server MUST support requests without requiring client authentication. The certificate chain provided by the EST server MUST be the same certificate chain EAP clients use in the EAP-TLS or EAP-TTLS session. EAP servers and clients are RECOMMENDED to cache retrieved certificate chains to reduce latency and network overhead. However, they SHOULD implement mechanisms to detect changes or expiration. These include periodic re-fetching, honoring HTTP cache control headers (e.g., Cache-Control, ETag), and verifying the validity period of intermediate certificates. As an alternative, a device MAY attempt to retrieve the certificate chain from the EST server (e.g., /eapservercertchain or /eapclientcertchain) only when certificate validation fails during an EAP-TLS or EAP-TTLS handshake. While this on-demand retrieval can serve as a fallback to recover from outdated intermediate certificate, it has the drawback of delaying authentication. After retrieving intermediate certificates via EST, a EAP client that believes it has a complete set of intermediate certificates to authenticate the EAP server sends the tls_flags extension as defined in [I-D.kampanakis-tls-scas-latest] with the 0xTBD1 flag set to 1 in its ClientHello message. Similarly, a EAP server that believes it has a complete set of intermediate certificates to authenticate the EAP client sends the same tls_flags extension with 0xTBD1 set to 1 in its CertificateRequest message. In both cases, only the end-entity certificates will be provided by the EAP client and server during the TLS handshake, relying on the recipient to possess or retrieve the necessary intermediate certificates for certificate chain validation. 6. Security Considerations The security considerations outlined in [I-D.ietf-uta-pqc-app] and [I-D.ietf-pquip-pqc-engineers] must be carefully evaluated and taken into account for both EAP-TLS and EAP-TTLS deployments. Reddy Expires 28 July 2026 [Page 7] Internet-Draft PQC Enhancements to EAP-TLS/TTLS January 2026 7. IANA Considerations This document does not request the creation of a new IANA registry nor the registration of the two URI path components defined in Section 5. Acknowledgements TBA. References Normative References [I-D.ietf-uta-pqc-app] Reddy.K, T. and H. Tschofenig, "Post-Quantum Cryptography Recommendations for TLS-based Applications", Work in Progress, Internet-Draft, draft-ietf-uta-pqc-app-00, 18 September 2025, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC7030] Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed., "Enrollment over Secure Transport", RFC 7030, DOI 10.17487/RFC7030, October 2013, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8295] Turner, S., "EST (Enrollment over Secure Transport) Extensions", RFC 8295, DOI 10.17487/RFC8295, January 2018, . [RFC9190] Preuß Mattsson, J. and M. Sethi, "EAP-TLS 1.3: Using the Extensible Authentication Protocol with TLS 1.3", RFC 9190, DOI 10.17487/RFC9190, February 2022, . Informative References Reddy Expires 28 July 2026 [Page 8] Internet-Draft PQC Enhancements to EAP-TLS/TTLS January 2026 [I-D.ietf-pquip-pqc-engineers] Banerjee, A., Reddy.K, T., Schoinianakis, D., Hollebeek, T., and M. Ounsworth, "Post-Quantum Cryptography for Engineers", Work in Progress, Internet-Draft, draft-ietf- pquip-pqc-engineers-14, 25 August 2025, . [I-D.ietf-pquip-pqt-hybrid-terminology] D, F., P, M., and B. Hale, "Terminology for Post-Quantum Traditional Hybrid Schemes", Work in Progress, Internet- Draft, draft-ietf-pquip-pqt-hybrid-terminology-06, 10 January 2025, . [I-D.kampanakis-tls-scas-latest] Kampanakis, P., Bytheway, C., Westerbaan, B., and M. Thomson, "Suppressing CA Certificates in TLS 1.3", Work in Progress, Internet-Draft, draft-kampanakis-tls-scas- latest-03, 5 January 2023, . [RFC9191] Sethi, M., Preuß Mattsson, J., and S. Turner, "Handling Large Certificates and Long Certificate Chains in TLS- Based EAP Methods", RFC 9191, DOI 10.17487/RFC9191, February 2022, . Author's Address Tirumaleswar Reddy Nokia Bangalore Karnataka India Email: k.tirumaleswar_reddy@nokia.com Reddy Expires 28 July 2026 [Page 9]