Transport Layer Security B. E. Westerbaan Internet-Draft Cloudflare Intended status: Standards Track 23 February 2026 Expires: 27 August 2026 Updated recommendations for TLS keyshares draft-westerbaan-tls-keyshare-recommendations-00 Abstract This document updates the recommendations for key shares algorithms (TLS supported groups; previously EC Named Curve Registry) 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 Security Working Group mailing list (mailto:tls@ietf.org), which is archived at https://mailarchive.ietf.org/arch/browse/tls/. Subscribe 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. Westerbaan Expires 27 August 2026 [Page 1] Internet-Draft Updated recommendations for TLS keyshare February 2026 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 27 August 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. Security Considerations . . . . . . . . . . . . . . . . . . . 4 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 4.1. Recommend . . . . . . . . . . . . . . . . . . . . . . . . 4 4.2. Discourage . . . . . . . . . . . . . . . . . . . . . . . 4 5. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 5.1. Normative References . . . . . . . . . . . . . . . . . . 8 5.2. Informative References . . . . . . . . . . . . . . . . . 8 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9 1. Introduction A future cryptographically relevant quantum computer can decrypt TLS handshakes recorded today that do not post-quantum algorithms for their key shares: algorithms designed to be resistant against quantum attack. This threat is known as store-now/decrypt-later (SNDL). Westerbaan Expires 27 August 2026 [Page 2] Internet-Draft Updated recommendations for TLS keyshare February 2026 RFC9847 defines the permitted value of the "Recommended" column of the TLS Supported Groups registry (https://www.iana.org/assignments/ tls-parameters/tls-parameters.xhtml#tls-parameters-8) as: Y: Indicates that the IETF has consensus that the item is RECOMMENDED. This only means that the associated mechanism is fit for the purpose for which it was defined. Careful reading of the documentation for the mechanism is necessary to understand the applicability of that mechanism. The IETF could recommend mechanisms that have limited applicability, but will provide applicability statements that describe any limitations of the mechanism or necessary constraints on its use. N: Indicates that the item has not been evaluated by the IETF and that the IETF has made no statement about the suitability of the associated mechanism. This does not necessarily mean that the mechanism is flawed, only that no consensus exists. The IETF might have consensus to leave an items marked as "N" on the basis of its having limited applicability or usage constraints. D: Indicates that the item is discouraged. This marking could be used to identify mechanisms that might result in problems if they are used, such as a weak cryptographic algorithm or a mechanism that might cause interoperability problems in deployment. When marking a registry entry as “D”, either the References or the Comments Column MUST include sufficient information to determine why the marking has been applied. Implementers and users SHOULD consult the linked references associated with the item to determine the conditions under which the item SHOULD NOT or MUST NOT be used. Given the SNDL threat, the IETF cannot recommend key shares for general use that do not offer post-quantum resistance, and this document updates the TLS Supported Groups registry (https://www.iana.org/assignments/tls-parameters/tls- parameters.xhtml#tls-parameters-8) accordingly. Among the currently registered post-quantum key share algorithms, IETF recommends X25519MLKEM768 for its 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. Westerbaan Expires 27 August 2026 [Page 3] Internet-Draft Updated recommendations for TLS keyshare February 2026 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. 4.1. Recommend +=======+================+=============+ | Value | Description | Recommended | +=======+================+=============+ | 4588 | X25519MLKEM768 | Y | +-------+----------------+-------------+ Table 1 4.2. Discourage +=======+======================+=============+======================+ | Value | Description | Recommended | Comment | +=======+======================+=============+======================+ | 9 | sect283k1 | D | Vulnerable to | | | | | store-now/decrypt- | | | | | later quantum | | | | | attack, see | | | | | TBA:this-document | +-------+----------------------+-------------+----------------------+ | 10 | sect283r1 | D | Vulnerable to | | | | | store-now/decrypt- | | | | | later quantum | | | | | attack, see | | | | | TBA:this-document | +-------+----------------------+-------------+----------------------+ | 11 | sect409k1 | D | Vulnerable to | | | | | store-now/decrypt- | | | | | later quantum | | | | | attack, see | Westerbaan Expires 27 August 2026 [Page 4] Internet-Draft Updated recommendations for TLS keyshare February 2026 | | | | TBA:this-document | +-------+----------------------+-------------+----------------------+ | 12 | sect409r1 | D | Vulnerable to | | | | | store-now/decrypt- | | | | | later quantum | | | | | attack, see | | | | | TBA:this-document | +-------+----------------------+-------------+----------------------+ | 13 | sect571k1 | D | Vulnerable to | | | | | store-now/decrypt- | | | | | later quantum | | | | | attack, see | | | | | TBA:this-document | +-------+----------------------+-------------+----------------------+ | 14 | sect571r1 | D | Vulnerable to | | | | | store-now/decrypt- | | | | | later quantum | | | | | attack, see | | | | | TBA:this-document | +-------+----------------------+-------------+----------------------+ | 22 | secp256k1 | D | Vulnerable to | | | | | store-now/decrypt- | | | | | later quantum | | | | | attack, see | | | | | TBA:this-document | +-------+----------------------+-------------+----------------------+ | 23 | secp256r1 | D | Vulnerable to | | | | | store-now/decrypt- | | | | | later quantum | | | | | attack, see | | | | | TBA:this-document | +-------+----------------------+-------------+----------------------+ | 24 | secp384r1 | D | Vulnerable to | | | | | store-now/decrypt- | | | | | later quantum | | | | | attack, see | | | | | TBA:this-document | +-------+----------------------+-------------+----------------------+ | 25 | secp521r1 | D | Vulnerable to | | | | | store-now/decrypt- | | | | | later quantum | | | | | attack, see | | | | | TBA:this-document | +-------+----------------------+-------------+----------------------+ | 26 | brainpoolP256r1 | D | Vulnerable to | | | | | store-now/decrypt- | | | | | later quantum | | | | | attack, see | Westerbaan Expires 27 August 2026 [Page 5] Internet-Draft Updated recommendations for TLS keyshare February 2026 | | | | TBA:this-document | +-------+----------------------+-------------+----------------------+ | 27 | brainpoolP384r1 | D | Vulnerable to | | | | | store-now/decrypt- | | | | | later quantum | | | | | attack, see | | | | | TBA:this-document | +-------+----------------------+-------------+----------------------+ | 28 | brainpoolP512r1 | D | Vulnerable to | | | | | store-now/decrypt- | | | | | later quantum | | | | | attack, see | | | | | TBA:this-document | +-------+----------------------+-------------+----------------------+ | 29 | x25519 | D | Vulnerable to | | | | | store-now/decrypt- | | | | | later quantum | | | | | attack, see | | | | | TBA:this-document | +-------+----------------------+-------------+----------------------+ | 30 | x448 | D | Vulnerable to | | | | | store-now/decrypt- | | | | | later quantum | | | | | attack, see | | | | | TBA:this-document | +-------+----------------------+-------------+----------------------+ | 31 | brainpoolP256r1tls13 | D | Vulnerable to | | | | | store-now/decrypt- | | | | | later quantum | | | | | attack, see | | | | | TBA:this-document | +-------+----------------------+-------------+----------------------+ | 32 | brainpoolP384r1tls13 | D | Vulnerable to | | | | | store-now/decrypt- | | | | | later quantum | | | | | attack, see | | | | | TBA:this-document | +-------+----------------------+-------------+----------------------+ | 33 | brainpoolP512r1tls13 | D | Vulnerable to | | | | | store-now/decrypt- | | | | | later quantum | | | | | attack, see | | | | | TBA:this-document | +-------+----------------------+-------------+----------------------+ | 34 | GC256A | D | Vulnerable to | | | | | store-now/decrypt- | | | | | later quantum | | | | | attack, see | Westerbaan Expires 27 August 2026 [Page 6] Internet-Draft Updated recommendations for TLS keyshare February 2026 | | | | TBA:this-document | +-------+----------------------+-------------+----------------------+ | 35 | GC256B | D | Vulnerable to | | | | | store-now/decrypt- | | | | | later quantum | | | | | attack, see | | | | | TBA:this-document | +-------+----------------------+-------------+----------------------+ | 36 | GC256C | D | Vulnerable to | | | | | store-now/decrypt- | | | | | later quantum | | | | | attack, see | | | | | TBA:this-document | +-------+----------------------+-------------+----------------------+ | 37 | GC256D | D | Vulnerable to | | | | | store-now/decrypt- | | | | | later quantum | | | | | attack, see | | | | | TBA:this-document | +-------+----------------------+-------------+----------------------+ | 38 | GC512A | D | Vulnerable to | | | | | store-now/decrypt- | | | | | later quantum | | | | | attack, see | | | | | TBA:this-document | +-------+----------------------+-------------+----------------------+ | 39 | GC512B | D | Vulnerable to | | | | | store-now/decrypt- | | | | | later quantum | | | | | attack, see | | | | | TBA:this-document | +-------+----------------------+-------------+----------------------+ | 40 | GC512C | D | Vulnerable to | | | | | store-now/decrypt- | | | | | later quantum | | | | | attack, see | | | | | TBA:this-document | +-------+----------------------+-------------+----------------------+ | 41 | curveSM2 | D | Vulnerable to | | | | | store-now/decrypt- | | | | | later quantum | | | | | attack, see | | | | | TBA:this-document | +-------+----------------------+-------------+----------------------+ | 256 | ffdhe2048 | D | Vulnerable to | | | | | store-now/decrypt- | | | | | later quantum | | | | | attack, see | Westerbaan Expires 27 August 2026 [Page 7] Internet-Draft Updated recommendations for TLS keyshare February 2026 | | | | TBA:this-document | +-------+----------------------+-------------+----------------------+ | 257 | ffdhe3072 | D | Vulnerable to | | | | | store-now/decrypt- | | | | | later quantum | | | | | attack, see | | | | | TBA:this-document | +-------+----------------------+-------------+----------------------+ | 258 | ffdhe4096 | D | Vulnerable to | | | | | store-now/decrypt- | | | | | later quantum | | | | | attack, see | | | | | TBA:this-document | +-------+----------------------+-------------+----------------------+ | 259 | ffdhe6144 | D | Vulnerable to | | | | | store-now/decrypt- | | | | | later quantum | | | | | attack, see | | | | | TBA:this-document | +-------+----------------------+-------------+----------------------+ | 260 | ffdhe8192 | D | Vulnerable to | | | | | store-now/decrypt- | | | | | later quantum | | | | | attack, see | | | | | TBA:this-document | +-------+----------------------+-------------+----------------------+ Table 2 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, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . 5.2. Informative References [RFC9847] Salowey, J. and S. Turner, "IANA Registry Updates for TLS and DTLS", RFC 9847, DOI 10.17487/RFC9847, December 2025, . Westerbaan Expires 27 August 2026 [Page 8] Internet-Draft Updated recommendations for TLS keyshare February 2026 Author's Address Bas Westerbaan Cloudflare Email: bas@cloudflare.com Westerbaan Expires 27 August 2026 [Page 9]