Updated recommendations for TLS keyshares
draft-westerbaan-tls-keyshare-recommendations-02
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| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Bas Westerbaan , Muhammad Usama Sardar | ||
| Last updated | 2026-04-14 | ||
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| Intended RFC status | (None) | ||
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| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
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draft-westerbaan-tls-keyshare-recommendations-02
Transport Layer Security B. E. Westerbaan
Internet-Draft Cloudflare
Updates: 8446, 9325 (if approved) M. Usama Sardar
Intended status: Standards Track TU Dresden
Expires: 16 October 2026 14 April 2026
Updated recommendations for TLS keyshares
draft-westerbaan-tls-keyshare-recommendations-02
Abstract
This document recommends X25519MLKEM768 for use in TLS by updating
its entry in the TLS Supported Groups registry (previously EC Named
Curve Registry) to Recommended in the light of the future arrival of
cryptographically relevant quantum computers.
[[ NOTE I use key share in the title and here as it's more accurate
than "group" and perhaps more well known in the context TLS than key
agreement or key exchange. ]]
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://bwesterb.github.io/draft-westerbaan-tls-keyshare-
recommendations/draft-westerbaan-tls-keyshare-recommendations.html.
Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-westerbaan-tls-keyshare-
recommendations/.
Discussion of this document takes place on the Transport Layer
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at https://www.ietf.org/mailman/listinfo/tls/.
Source for this draft and an issue tracker can be found at
https://github.com/bwesterb/draft-westerbaan-tls-keyshare-
recommendations.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
3. Security Considerations . . . . . . . . . . . . . . . . . . . 3
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 3
5.1. Normative References . . . . . . . . . . . . . . . . . . 3
5.2. Informative References . . . . . . . . . . . . . . . . . 4
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 4
1. Introduction
A future cryptographically relevant quantum computer (CRQC) [RFC9794]
can decrypt TLS handshakes recorded today that do not use post-
quantum algorithms for their key shares: algorithms designed to be
resistant against quantum attack. This threat is known as "harvest
now, decrypt later" (HNDL) [I-D.ietf-pquip-pqc-engineers].
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To address this threat, this document updates the TLS Supported
Groups registry (https://www.iana.org/assignments/tls-parameters/tls-
parameters.xhtml#tls-parameters-8) to mark X25519MLKEM768 as
Recommended (Y) as defined in Section 6 of [RFC9847], as it is a
post-quantum key share with widespread support.
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. Security Considerations
Before the arrival of a cryptographically relevant quantum computer
(CRQC), a TLS connection that negotiated a non-post quantum key share
can be recorded decrypted in the future.
After the arrival of a CRQC, allowing a non-post quantum key share to
be negotiated allows for an active quantum attack that achieves MITM,
even if the server certificate is post quantum.
4. IANA Considerations
This document updates the TLS Supported Groups registry
(https://www.iana.org/assignments/tls-parameters/tls-
parameters.xhtml#tls-parameters-8), according to the procedures in
Section 6 of [RFC9847] as follows.
+=======+================+=============+
| Value | Description | Recommended |
+=======+================+=============+
| 4588 | X25519MLKEM768 | Y |
+-------+----------------+-------------+
Table 1
5. References
5.1. 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>.
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[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>.
[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>.
[RFC9325] Sheffer, Y., Saint-Andre, P., and T. Fossati,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 9325, DOI 10.17487/RFC9325, November
2022, <https://www.rfc-editor.org/rfc/rfc9325>.
[RFC9847] Salowey, J. and S. Turner, "IANA Registry Updates for TLS
and DTLS", RFC 9847, DOI 10.17487/RFC9847, December 2025,
<https://www.rfc-editor.org/rfc/rfc9847>.
5.2. Informative References
[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,
<https://datatracker.ietf.org/doc/html/draft-ietf-pquip-
pqc-engineers-14>.
[RFC9794] Driscoll, F., Parsons, M., and B. Hale, "Terminology for
Post-Quantum Traditional Hybrid Schemes", RFC 9794,
DOI 10.17487/RFC9794, June 2025,
<https://www.rfc-editor.org/rfc/rfc9794>.
Authors' Addresses
Bas Westerbaan
Cloudflare
Email: bas@cloudflare.com
Muhammad Usama Sardar
TU Dresden
Email: muhammad_usama.sardar@tu-dresden.de
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