Post-quantum hybrid ECDHE-MLKEM Key Agreement for TLSv1.3
draft-kwiatkowski-tls-ecdhe-mlkem-02
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| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Kris Kwiatkowski , Panos Kampanakis , Bas Westerbaan , Douglas Stebila | ||
| Last updated | 2024-09-09 | ||
| RFC stream | (None) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
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draft-kwiatkowski-tls-ecdhe-mlkem-02
Transport Layer Security K. Kwiatkowski
Internet-Draft PQShield
Intended status: Informational P. Kampanakis
Expires: 14 March 2025 AWS
B. E. Westerbaan
Cloudflare
D. Stebila
University of Waterloo
10 September 2024
Post-quantum hybrid ECDHE-MLKEM Key Agreement for TLSv1.3
draft-kwiatkowski-tls-ecdhe-mlkem-02
Abstract
This draft defines two hybrid key agreements for TLS 1.3:
X25519MLKEM768 and SecP256r1MLKEM768, which combine a post-quantum
KEM with an elliptic curve Diffie-Hellman (ECDHE).
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://post-
quantum-cryptography.github.io/draft-kwiatkowski-tls-ecdhe-mlkem/.
Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-kwiatkowski-tls-ecdhe-mlkem/.
Discussion of this document takes place on the Transport Layer
Security Working Group mailing list (mailto:tls@ietf.org), which is
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Source for this draft and an issue tracker can be found at
https://github.com/post-quantum-cryptography/draft-kwiatkowski-tls-
ecdhe-mlkem.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
3. Negotiated Groups . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Construction . . . . . . . . . . . . . . . . . . . . . . 3
3.1.1. Client share . . . . . . . . . . . . . . . . . . . . 4
3.1.2. Server share . . . . . . . . . . . . . . . . . . . . 4
3.1.3. Shared secret . . . . . . . . . . . . . . . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
5.1. SecP256r1MLKEM768 . . . . . . . . . . . . . . . . . . . . 5
5.2. X25519MLKEM768 . . . . . . . . . . . . . . . . . . . . . 5
5.3. Obsoleted Supported Groups . . . . . . . . . . . . . . . 6
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Normative References . . . . . . . . . . . . . . . . . . 6
6.2. Informative References . . . . . . . . . . . . . . . . . 6
Appendix A. Change log . . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
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1.1. Motivation
ML-KEM is a key encapsulation method (KEM) defined in the [FIPS203].
It is designed to withstand cryptanalytic attacks from quantum
computers.
This document introduces two new supported groups for hybrid post-
quantum key agreements in TLS 1.3: X25519MLKEM768 and
SecP256r1MLKEM768. Both combine ML-KEM-768 with ECDH in the manner
of [hybrid].
The first one uses X25519 [rfc7748] and is an update to
X25519Kyber768Draft00 [xyber], the most widely deployed PQ/T hybrid
combiner for TLS v1.3 deployed in 2024.
The second one uses secp256r1 (NIST P-256) [ECDSA] [DSS]. The goal
of this group is to support a use case that requires both shared
secrets to be generated by FIPS-approved mechanisms.
Both constructions aim to provide a FIPS-approved key-establishment
scheme (as per [SP56C]).
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. Negotiated Groups
Both groups enable the derivation of TLS session keys using FIPS-
approved schemes. NIST's special publication 800-56Cr2 [SP56C]
approves the usage of HKDF [HKDF] with two distinct shared secrets,
with the condition that the first one is computed by a FIPS-approved
key-establishment scheme. FIPS also requires a certified
implementation of the scheme, which will remain more ubiqutous for
secp256r1 in the coming years.
For this reason we put the ML-KEM-768 shared secret first in
X25519MLKEM768, and the secp256r1 shared secret first in
SecP256r1MLKEM768.
3.1. Construction
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3.1.1. Client share
When the X25519MLKEM768 group is negotiated, the client's
key_exchange value is the concatenation of the client's ML-KEM-768
encapsulation key and the client's X25519 ephemeral share. The size
of the client share is 1216 bytes (1184 bytes for the ML-KEM part and
32 bytes for X25519).
When the SecP256r1MLKEM768 group is negotiated, the client's
key_exchange value is the concatenation of the secp256r1 ephemeral
share and ML-KEM-768 encapsulation key. The ECDHE share is the
serialized value of the uncompressed ECDH point representation as
defined in Section 4.2.8.2 of [RFC8446]. The size of the client
share is 1249 bytes (65 bytes for the secp256r1 part and 1184 bytes
for ML-KEM).
3.1.2. Server share
When the X25519MLKEM768 group is negotiated, the server's key
exchange value is the concatenation of an ML-KEM ciphertext returned
from encapsulation to the client's encapsulation key, and the
server's ephemeral X25519 share. The size of the server share is
1120 bytes (1088 bytes for the ML-KEM part and 32 bytes for X25519).
When the SecP256r1MLKEM768 group is negotiated, the server's key
exchange value is the concatenation of the server's ephemeral
secp256r1 share encoded in the same way as the client share and an
ML-KEM ciphertext returned from encapsulation to the client's
encapsulation key. The size of the server share is 1153 bytes (1088
bytes for the ML-KEM part and 65 bytes for secp256r1).
For both groups, 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.
3.1.3. Shared secret
For X25519MLKEM768, the shared secret is the concatenation of the ML-
KEM shared secret and the X25519 shared secret. The shared secret is
64 bytes (32 bytes for each part).
For SecP256r1MLKEM768, the shared secret is the concatenation of the
ECDHE and ML-KEM shared secret. The ECDHE shared secret is the
x-coordinate of the ECDH shared secret elliptic curve point
represented as an octet string as defined in Section 7.4.2 of
[RFC8446]. The size of the shared secret is 64 bytes (32 bytes for
each part).
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4. Security Considerations
The same security considerations as those described in [hybrid] apply
to the approach used by this document. The security analysis relies
crucially on the TLS 1.3 message transcript, and one cannot assume a
similar hybridisation is secure in other protocols.
Implementers are encouraged to use implementations resistant to side-
channel attacks, especially those that can be applied by remote
attackers.
5. IANA Considerations
This document requests/registers two new entries to the TLS Supported
Groups registry, according to the procedures in Section 6 of
[tlsiana]. These identifiers are to be used with the final, ratified
by NIST, version of ML-KEM which is specified in [FIPS203].
5.1. SecP256r1MLKEM768
Value: 4587 (0x11EB)
Description: SecP256r1MLKEM768
DTLS-OK: Y
Recommended: N
Reference: This document
Comment: Combining secp256r1 ECDH with ML-KEM-768
5.2. X25519MLKEM768
Value: 4588 (0x11EC)
Description: X25519MLKEM768
DTLS-OK: Y
Recommended: N
Reference: This document
Comment: Combining X25519 ECDH with ML-KEM-768
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5.3. Obsoleted Supported Groups
This document obsoletes 25497 and 25498 in the TLS Supported Groups
registry.
6. References
6.1. Normative References
[FIPS203] "Module-Lattice-Based Key-Encapsulation Mechanism
Standard", National Institute of Standards and Technology,
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>.
[rfc7748] Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves
for Security", RFC 7748, DOI 10.17487/RFC7748, January
2016, <https://www.rfc-editor.org/rfc/rfc7748>.
[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>.
[SP56C] Barker, E., Chen, L., and R. Davis, "Recommendation for
Key-Derivation Methods in Key-Establishment Schemes",
National Institute of Standards and Technology,
DOI 10.6028/nist.sp.800-56cr2, August 2020,
<https://doi.org/10.6028/nist.sp.800-56cr2>.
6.2. Informative References
[DSS] Chen, L., Moody, D., Regenscheid, A., Robinson, A., and K.
Randall, "Recommendations for Discrete Logarithm-based
Cryptography:: Elliptic Curve Domain Parameters", National
Institute of Standards and Technology,
DOI 10.6028/nist.sp.800-186, February 2023,
<https://doi.org/10.6028/nist.sp.800-186>.
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[ECDSA] American National Standards Institute, "Public Key
Cryptography for the Financial Services Industry: The
Elliptic Curve Digital Signature Algorithm (ECDSA)",
ANSI ANS X9.62-2005, November 2005.
[HKDF] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand
Key Derivation Function (HKDF)", RFC Editor,
DOI 10.17487/rfc5869, May 2010,
<https://doi.org/10.17487/rfc5869>.
[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-10, 5 April 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-tls-
hybrid-design-10>.
[tlsiana] Salowey, J. A. and S. Turner, "IANA Registry Updates for
TLS and DTLS", Work in Progress, Internet-Draft, draft-
ietf-tls-rfc8447bis-09, 30 April 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-tls-
rfc8447bis-09>.
[xyber] Westerbaan, B. and D. Stebila, "X25519Kyber768Draft00
hybrid post-quantum key agreement", Work in Progress,
Internet-Draft, draft-tls-westerbaan-xyber768d00-03, 24
September 2023, <https://datatracker.ietf.org/doc/html/
draft-tls-westerbaan-xyber768d00-03>.
Appendix A. Change log
* draft-kwiatkowski-tls-ecdhe-mlkem-02:
- Adds section that mentions supported groups that this document
obsoletes.
- Fix a reference to encapsulation in the FIPS 203.
* draft-kwiatkowski-tls-ecdhe-mlkem-01:
- Add X25519MLKEM768
* draft-kwiatkowski-tls-ecdhe-mlkem-00:
- Change Kyber name to ML-KEM
- Swap reference to I-D.cfrg-schwabe-kyber with FIPS-203
- Change codepoint. New value is equal to old value + 1.
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* draft-kwiatkowski-tls-ecdhe-kyber-01: Fix size of key shares
generated by the client and the server
* draft-kwiatkowski-tls-ecdhe-kyber-00: updates following IANA
review
Authors' Addresses
Kris Kwiatkowski
PQShield
Email: kris@amongbytes.com
Panos Kampanakis
AWS
Email: kpanos@amazon.com
Bas Westerbaan
Cloudflare
Email: bas@cloudflare.com
Douglas Stebila
University of Waterloo
Email: dstebila@waterloo.ca
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