RFC 9851: TLS 1.2 is in Feature Freeze

Abstract

Use of TLS 1.3, which fixes some known deficiencies in TLS 1.2, is
growing. This document specifies that no changes will be approved
for TLS 1.2 outside of urgent security fixes (as determined by
TLS Working Group consensus), new TLS Exporter Labels, and
new Application-Layer Protocol Negotiation (ALPN) Protocol IDs.
This applies to TLS only; it does not apply to DTLS (in
any DTLS version).¶

Status of This Memo

This is an Internet Standards Track document.¶

This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by
the Internet Engineering Steering Group (IESG). Further
information on Internet Standards is available in Section 2 of
RFC 7841.¶

Information about the current status of this document, any
errata, and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9851.¶

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.¶

1. Introduction

TLS 1.3 [TLS13] fixes most known deficiencies with TLS 1.2 [TLS12] and its use is growing. Some examples of the fixes include
encrypting more of the traffic so that it is not readable by outsiders and
removing most cryptographic primitives that are now considered weak. Importantly, TLS
1.3 enjoys robust security proofs.¶

Both versions have several extension points. Items like new cryptographic
algorithms, new supported groups (formerly “named curves”), etc., can be
added without defining a new protocol. This document specifies that no changes will be approved for TLS 1.2 outside of
urgent security fixes (as determined by TLS Working Group consensus) and the exceptions listed in Section 4.¶

This applies to TLS only. As such, it does not apply to
DTLS, in any DTLS version.¶

2. Implications for Post-Quantum Cryptography (PQC)

Cryptographically relevant quantum computers, once available, are likely to
greatly lessen the time and effort needed to break
RSA, finite-field-based Diffie-Hellman (FFDH), or Elliptic Curve Cryptography (ECC) which are currently used in TLS.
In 2016, the US National Institute of Standards and Technology (NIST) started a
multi-year effort to standardize algorithms that will be “safe”
once quantum computers are feasible [PQC]. Initial discussions in
the IETF community happened
around the same time [CFRGSLIDES].¶

In 2024, NIST released standards for [ML-KEM], [ML-DSA], and [SLH-DSA].
Many other countries and organizations are publishing their roadmaps,
including the multi-national standards organization ETSI [ETSI].¶

While the industry was waiting for NIST to finish standardization, the
IETF has had several efforts underway.
A working group was formed in early 2023 to work on the use of Post-Quantum Cryptography (PQC) in IETF protocols
[PQUIPWG].
Several other working groups, including TLS [TLSWG],
are working on
specifications to support hybrid algorithms and identifiers, for use during a
transition from classic to a post-quantum world.¶

It is important to note that effort within the TLS Working Group is focused exclusively on TLS 1.3 or later.
Put bluntly, PQC for
TLS 1.2 will not be specified (see Section 4) at any time; anyone wishing
to deploy PQC should expect to use TLS 1.3.¶

3. Security Considerations

This entire document is about security and provides post-quantum security concerns
as an additional reason to upgrade to TLS 1.3.¶

4. IANA Considerations

No TLS registries [TLS13REG] are being closed by this document.
Rather, this document modifies the instructions to IANA and the TLS
Designated Experts to constrain the type of entries that can be added to existing
registries.¶

This document does not introduce any new limitations on the registrations for either of
the following two registries:¶

• TLS Application-Layer Protocol Negotiation (ALPN) Protocol IDs¶

• TLS Exporter Labels¶

The following note has been added to the other TLS registries:¶

Any TLS entry added after the IESG approves publication of RFC 9851
is intended for TLS 1.3 or later, and makes no similar requirement on
DTLS. Such entries should have an informal indication like “For TLS 1.3
or later” in that entry, such as the “Comment” column.¶

At the time of publication, the note has been added to the following TLS registries:¶

• TLS Alerts¶

• TLS Authorization Data Formats¶

• TLS CachedInformationType Values¶

• TLS Certificate Compression Algorithm IDs¶

• TLS Certificate Status Types¶

• TLS Certificate Types¶

• TLS Cipher Suites¶

• TLS ClientCertificateType Identifiers¶

• TLS ContentType¶

• TLS EC Curve Types¶

• TLS EC Point Formats¶

• TLS ExtensionType Values¶

• TLS HandshakeType¶

• TLS HashAlgorithm¶

• TLS Heartbeat Message Types¶

• TLS Heartbeat Modes¶

• TLS KDF Identifiers¶

• TLS PskKeyExchangeMode¶

• TLS SignatureAlgorithm¶

• TLS SignatureScheme¶

• TLS Supplemental Data Formats (SupplementalDataType)¶

• TLS Supported Groups¶

• TLS UserMappingType Values¶

Any TLS registry created after this document is approved for publication
should indicate whether the actions defined here are applicable.¶

5. References

Acknowledgments

We gratefully acknowledge Amanda Baber, David Dong, and Sabrina Tanamal
of IANA for their help in revising and clarifying Section 4.¶

Authors’ Addresses