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ML-KEM Post-Quantum Key Agreement for TLS 1.3
ML-KEM Post-Quantum Key Agreement for TLS 1.3
draft-ietf-tls-mlkem-07
| Document | Type | Active Internet-Draft (tls WG) | |
|---|---|---|---|
| Author | Deirdre Connolly | ||
| Last updated | 2026-02-12 | ||
| Replaces | draft-connolly-tls-mlkem-key-agreement | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Informational | ||
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draft-ietf-tls-mlkem-07
Transport Layer Security D. Connolly
Internet-Draft SandboxAQ
Intended status: Informational 12 February 2026
Expires: 16 August 2026
ML-KEM Post-Quantum Key Agreement for TLS 1.3
draft-ietf-tls-mlkem-07
Abstract
This memo defines ML-KEM-512, ML-KEM-768, and ML-KEM-1024 as
NamedGroups and and registers IANA values in the TLS Supported Groups
registry for use in TLS 1.3 to achieve post-quantum (PQ) key
establishment.
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-ietf-tls-mlkem/.
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/tlswg/draft-ietf-tls-mlkem.
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 16 August 2026.
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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
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
3. Key encapsulation mechanisms . . . . . . . . . . . . . . . . 3
4. Construction . . . . . . . . . . . . . . . . . . . . . . . . 3
4.1. Negotiation . . . . . . . . . . . . . . . . . . . . . . . 4
4.2. Transmitting encapsulation keys and ciphertexts . . . . . 4
4.3. Shared secret calculation . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
5.1. Standalone versus hybrid key establishment . . . . . . . 6
5.2. IND-CCA . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.3. Key reuse . . . . . . . . . . . . . . . . . . . . . . . . 7
5.4. Binding properties . . . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
7.1. Normative References . . . . . . . . . . . . . . . . . . 8
7.2. Informative References . . . . . . . . . . . . . . . . . 9
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 10
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
1.1. Motivation
FIPS 203 (ML-KEM) [FIPS203] is a FIPS standard for post-quantum
[RFC9794] key establishment via a lattice-based key encapsulation
mechanism (KEM). This document defines key establishment options for
TLS 1.3 that use solely post-quantum algorithms, without a hybrid
construction that also includes a traditional cryptographic
algorithm. Use cases include regulatory frameworks that require
standalone post-quantum key establishment, targeting smaller key
sizes or less computation, and simplicity.
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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. Key encapsulation mechanisms
This document models key establishment as key encapsulation
mechanisms (KEMs), which consist of three algorithms:
* KeyGen() -> (pk, sk): A probabilistic key generation algorithm,
which generates a public encapsulation key pk and a secret
decapsulation key sk.
* Encaps(pk) -> (ct, shared_secret): A probabilistic encapsulation
algorithm, which takes as input a public encapsulation key pk and
outputs a ciphertext ct and shared secret shared_secret.
* Decaps(sk, ct) -> shared_secret: A decapsulation algorithm, which
takes as input a secret decapsulation key sk and ciphertext ct and
outputs a shared secret shared_secret.
ML-KEM-512, ML-KEM-768 and ML-KEM-1024 conform to this interface:
* ML-KEM-512 has encapsulation keys of size 800 bytes, expanded
decapsulation keys of 1632 bytes, decapsulation key seeds of size
64 bytes, ciphertext size of 768 bytes, and shared secrets of size
32 bytes
* ML-KEM-768 has encapsulation keys of size 1184 bytes, expanded
decapsulation keys of 2400 bytes, decapsulation key seeds of size
64 bytes, ciphertext size of 1088 bytes, and shared secrets of
size 32 bytes
* ML-KEM-1024 has encapsulation keys of size 1568 bytes, expanded
decapsulation keys of 3168 bytes, decapsulation key seeds of size
64 bytes, ciphertext size of 1568 bytes, and shared secrets of
size 32 bytes
4. Construction
The KEMs are defined as NamedGroups, sent in the supported_groups
extension. Section 4.2.7 of [RFC8446]
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4.1. Negotiation
Each parameter set of ML-KEM is assigned an identifier, registered by
IANA in the TLS Supported Groups registry:
enum {
...,
/* ML-KEM Key Establishment Methods */
mlkem512(0x0200),
mlkem768(0x0201),
mlkem1024(0x0202)
...,
} NamedGroup;
4.2. Transmitting encapsulation keys and ciphertexts
The public encapsulation key and ciphertext values are each directly
encoded with fixed lengths as in [FIPS203].
In TLS 1.3 a KEM public encapsulation key pk or ciphertext ct is
represented as a KeyShareEntry Section 4.2.8 of [RFC8446]:
struct {
NamedGroup group;
opaque key_exchange<1..2^16-1>;
} KeyShareEntry;
These are transmitted in the extension_data fields of
KeyShareClientHello and KeyShareServerHello extensions:
struct {
KeyShareEntry client_shares<0..2^16-1>;
} KeyShareClientHello;
struct {
KeyShareEntry server_share;
} KeyShareServerHello;
The client's shares are listed in descending order of client
preference; the server selects one algorithm and sends its
corresponding share.
For the client's share, the key_exchange value contains the pk output
of the corresponding ML-KEM parameter set's KeyGen algorithm.
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For the server's share, the key_exchange value contains the ct output
of the corresponding ML-KEM parameter set's Encaps algorithm.
For all parameter sets, the server MUST perform the encapsulation key
check described in Section 7.2 of [FIPS203] on the client's
encapsulation key, and abort with an illegal_parameter alert if it
fails.
For all parameter sets, the client MUST check if the ciphertext
length matches the selected parameter set, and abort with an
illegal_parameter alert if it fails.
If ML-KEM decapsulation fails for any other reason, the connection
MUST be aborted with an internal_error alert.
4.3. Shared secret calculation
The shared secret output from the ML-KEM Encaps and Decaps algorithms
over the appropriate keypair and ciphertext results in the same
shared secret shared_secret as its honest peer, which is inserted
into the TLS 1.3 key schedule in place of the (EC)DHE shared secret,
as shown in Figure 1.
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0
|
v
PSK -> HKDF-Extract = Early Secret
|
+-----> Derive-Secret(...)
+-----> Derive-Secret(...)
+-----> Derive-Secret(...)
|
v
Derive-Secret(., "derived", "")
|
v
shared_secret -> HKDF-Extract = Handshake Secret
^^^^^^^^^^^^^ |
+-----> Derive-Secret(...)
+-----> Derive-Secret(...)
|
v
Derive-Secret(., "derived", "")
|
v
0 -> HKDF-Extract = Master Secret
|
+-----> Derive-Secret(...)
+-----> Derive-Secret(...)
+-----> Derive-Secret(...)
+-----> Derive-Secret(...)
Figure 1: Key schedule for key establishment
5. Security Considerations
5.1. Standalone versus hybrid key establishment
This document defines standalone ML-KEM key establishment for TLS
1.3. Hybrid key establishment mechanisms, which combine a post-
quantum algorithm with a traditional algorithm such as ECDH, are
supported generically via [HYBRID] with some concrete definitions in
[ECDHE-MLKEM]. Hybrid mechanisms provide security as long as at
least one of the component algorithms remains unbroken, combining
quantum-resistant and traditional cryptographic assumptions.
Standalone ML-KEM relies on lattice-based and hash function
cryptographic assumptions for its security.
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5.2. IND-CCA
The main security property for KEMs is indistinguishability under
adaptive chosen ciphertext attack (IND-CCA), which means that shared
secret values should be indistinguishable from random strings even
given the ability to have other arbitrary ciphertexts decapsulated.
IND-CCA corresponds to security against an active attacker, and the
public encapsulation key / secret decapsulation key pair can be
treated as a long-term key or reused. ML-KEM satisfies IND-CCA
security in the random oracle model [KYBERV].
5.3. Key reuse
ML-KEM is explicitly designed to be secure in the event that the
keypair is reused, satisfying IND-CCA security via a variant of the
Fujisaki-Okamoto (FO) transform [FO][HHK].
While it is recommended that implementations avoid reuse of ML-KEM
keypairs to ensure forward secrecy, implementations that do reuse
MUST ensure that the number of reuses abides by bounds in [FIPS203]
or subsequent security analyses of ML-KEM.
Implementations MUST NOT reuse randomness in the generation of ML-KEM
ciphertexts.
[NIST-SP-800-227] includes guidelines and requirements for
implementations on using KEMs securely. Implementers are encouraged
to use implementations resistant to side-channel attacks, especially
those that can be applied by remote attackers.
5.4. Binding properties
TLS 1.3's key schedule commits to the ML-KEM encapsulation key and
the ciphertext as the key_exchange field of the key_share extension
is populated with those values, which are included as part of the
handshake messages. This provides resilience against re-
encapsulation attacks against KEMs used for key establishment
[CDM23].
6. IANA Considerations
This document requests/registers three new entries to the TLS Named
Group (or Supported Group) registry, according to the procedures in
Section 6 of [tlsiana].
Value: 0x0200
Description: MLKEM512
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DTLS-OK: Y
Recommended: N
Reference: This document
Comment: FIPS 203 version of ML-KEM-512
Value: 0x0201
Description: MLKEM768
DTLS-OK: Y
Recommended: N
Reference: This document
Comment: FIPS 203 version of ML-KEM-768
Value: 0x0202
Description: MLKEM1024
DTLS-OK: Y
Recommended: N
Reference: This document
Comment: FIPS 203 version of ML-KEM-1024
7. References
7.1. Normative References
[FIPS203] "Module-lattice-based key-encapsulation mechanism
standard", National Institute of Standards and Technology
(U.S.), DOI 10.6028/nist.fips.203, August 2024,
<https://doi.org/10.6028/nist.fips.203>.
[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>.
7.2. Informative References
[AVIRAM] Nimrod Aviram, Benjamin Dowling, Ilan Komargodski, Kenny
Paterson, Eyal Ronen, and Eylon Yogev, "[TLS] Combining
Secrets in Hybrid Key Exchange in TLS 1.3", 1 September
2021, <https://mailarchive.ietf.org/arch/msg/tls/
F4SVeL2xbGPaPB2GW_GkBbD_a5M/>.
[CDM23] Cremers, C., Dax, A., and N. Medinger, "Keeping Up with
the KEMs: Stronger Security Notions for KEMs and automated
analysis of KEM-based protocols", 2023,
<https://eprint.iacr.org/2023/1933.pdf>.
[DOWLING] Dowling, B., Fischlin, M., Günther, F., and D. Stebila, "A
Cryptographic Analysis of the TLS 1.3 Handshake Protocol",
Springer Science and Business Media LLC, Journal of
Cryptology vol. 34, no. 4, DOI 10.1007/s00145-021-09384-1,
July 2021, <https://doi.org/10.1007/s00145-021-09384-1>.
[ECDHE-MLKEM]
Kwiatkowski, K., Kampanakis, P., Westerbaan, B., and D.
Stebila, "Post-quantum hybrid ECDHE-MLKEM Key Agreement
for TLSv1.3", Work in Progress, Internet-Draft, draft-
ietf-tls-ecdhe-mlkem-04, 8 February 2026,
<https://datatracker.ietf.org/doc/html/draft-ietf-tls-
ecdhe-mlkem-04>.
[FO] Fujisaki, E. and T. Okamoto, "Secure Integration of
Asymmetric and Symmetric Encryption Schemes", Springer
Science and Business Media LLC, Journal of Cryptology vol.
26, no. 1, pp. 80-101, DOI 10.1007/s00145-011-9114-1,
December 2011,
<https://doi.org/10.1007/s00145-011-9114-1>.
[HHK] Hofheinz, D., Hövelmanns, K., and E. Kiltz, "A Modular
Analysis of the Fujisaki-Okamoto Transformation", Springer
International Publishing, Lecture Notes in Computer
Science pp. 341-371, DOI 10.1007/978-3-319-70500-2_12,
ISBN ["9783319704999", "9783319705002"], 2017,
<https://doi.org/10.1007/978-3-319-70500-2_12>.
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[HPKE] Barnes, R., Bhargavan, K., Lipp, B., and C. Wood, "Hybrid
Public Key Encryption", RFC 9180, DOI 10.17487/RFC9180,
February 2022, <https://www.rfc-editor.org/rfc/rfc9180>.
[HYBRID] Stebila, D., Fluhrer, S., and S. Gueron, "Hybrid key
exchange in TLS 1.3", Work in Progress, Internet-Draft,
draft-ietf-tls-hybrid-design-16, 7 September 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-tls-
hybrid-design-16>.
[KYBERV] "Formally verifying Kyber Episode V: Machine-checked IND-
CCA security and correctness of ML-KEM in EasyCrypt",
n.d., <https://eprint.iacr.org/2024/843.pdf>.
[LUCKY13] Al Fardan, N. J. and K. G. Paterson, "Lucky Thirteen:
Breaking the TLS and DTLS record protocols", n.d.,
<https://ieeexplore.ieee.org/
iel7/6547086/6547088/06547131.pdf>.
[NIST-SP-800-227]
Alagic, G., Barker, E., Chen, L., Moody, D., Robinson, A.,
Silberg, H., and N. Waller, "Recommendations for key-
encapsulation mechanisms", National Institute of Standards
and Technology (U.S.), DOI 10.6028/nist.sp.800-227,
September 2025, <https://doi.org/10.6028/nist.sp.800-227>.
[RACCOON] Merget, R., Brinkmann, M., Aviram, N., Somorovsky, J.,
Mittmann, J., and J. Schwenk, "Raccoon Attack: Finding and
Exploiting Most-Significant-Bit-Oracles in TLS-DH(E)",
September 2020, <https://raccoon-attack.com/>.
[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>.
[tlsiana] Salowey, J. A. and S. Turner, "IANA Registry Updates for
TLS and DTLS", Work in Progress, Internet-Draft, draft-
ietf-tls-rfc8447bis-15, 21 July 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-tls-
rfc8447bis-15>.
Acknowledgments
Thanks to Douglas Stebila for consultation on the draft-ietf-tls-
hybrid-design design, and to Scott Fluhrer, Eric Rescorla, and
Rebecca Guthrie for reviews.
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Author's Address
Deirdre Connolly
SandboxAQ
Email: durumcrustulum@gmail.com
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