Internet DRAFT - draft-mahy-mls-xwing
draft-mahy-mls-xwing
MLS R. Mahy
Internet-Draft Unaffiliated
Intended status: Informational 4 March 2024
Expires: 5 September 2024
Messaging Layer Security Ciphersuite using XWing Key Exchange Mechanism
draft-mahy-mls-xwing-00
Abstract
This document registers a new Messaging Layer Security (MLS)
ciphersuite using the X-Wing hybrid post-quantum resistant /
traditional (PQ/T) Key Exchange Mechanism (KEM).
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-mahy-mls-xwing/.
Discussion of this document takes place on the MLS Working Group
mailing list (mailto:mls@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/browse/mls/. Subscribe at
https://www.ietf.org/mailman/listinfo/mls/.
Source for this draft and an issue tracker can be found at
https://github.com/rohanmahy/mahy-mls-xwing/.
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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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 5 September 2024.
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Copyright Notice
Copyright (c) 2024 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
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Security Considerations . . . . . . . . . . . . . . . . . . . 3
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3
4. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Normative References . . . . . . . . . . . . . . . . . . 4
4.2. Informative References . . . . . . . . . . . . . . . . . 4
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 4
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
The potential availability of a cryptographically-relevant quantum
computer has caused concern that well-funded adversaries could
overturn long-held assumptions about the security assurances of
classical Key Exchange Mechanisms (KEMs) and classical cryptographic
signatures, which are fundamental to modern security protocols,
including the MLS protocol [RFC9420].
The MLS Working Group has expressed strong desire to have a handful
of complimentary post-quantum security extensions for use with the
MLS protocol to address the related threats:
1. A straightforward MLS cipher suite that replaces a classical KEM
with a hybrid post-quantum/traditional KEM. Such a cipher suite
could be implemented as a drop-in replacement in many MLS
libraries without changes to any other part of the MLS stack.
The aim is for implementations to have a single KEM which would
be performant and work for the vast majority of implementations.
It addresses the the harvest-now / decrypt-later threat model
using the simplest, and most practicable solution available.
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2. Versions of existing cipher suites that use post-quantum
signatures; and specific guidelines on the construction, use, and
validation of hybrid signatures.
3. One or more mechanisms which reduce the bandwidth or storage
requirements, or improve performance when using post-quantum
algorithms (for example by updating post-quantum keys less
frequently than classical keys, or by sharing portions of post-
quantum keys across a large number of clients or groups.)
This document addresses the first of these work items. It reserves
an MLS cipher suite value based on the MLS default cipher suite, but
replacing the KEM with the X-Wing [I-D.connolly-cfrg-xwing-kem]
hybrid post-quantum / traditional KEM. The IANA Hybrid Public Key
Encryption (HPKE) [RFC9180] Key Exchange Mechanism (KEM) Identifier
value for X-Wing is pending at the time of this writing.
X-Wing is a "concrete, simple choice for [a] post-quantum hybrid KEM,
that should be suitable for the vast majority of use cases". X-Wing
combines the ML-KEM [MLKEM] post-quantum KEM and the X25519 [RFC7748]
traditional KEM. The MLS cipher suite uses the other components of
the default MLS cipher suite
MLS_128_DHKEMX25519_AES128GCM_SHA256_Ed25519.
This document replaces a previous, similar proposal based on the KEM
in [I-D.draft-westerbaan-cfrg-hpke-xyber768d00].
2. Security Considerations
This ciphersuite uses a hybrid post-quantum/traditional KEM and a
traditional signature algorithm. As such, it is designed to provide
confidentiality against quantum and classical attacks, but provides
authenticity against classical attacks only. This is actually very
useful, because an attacker could store MLS-encrypted traffic that
uses any classical KEM today. If years or decades in the future a
quantum attack on classical KEMs becomes feasible, the traffic sent
today (some of which could still be sensitive in the future) will
then be readable. By contrast, an attack on a signature algorithm in
MLS would require an active attack which can extract the private key
during the signature key's lifetime.
The security properties of [I-D.connolly-cfrg-xwing-kem] apply.
3. IANA Considerations
This document registers a new MLS Ciphersuite value.
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Value: new assignment
Name: MLS_128_XWING_AES128GCM_SHA256_Ed25519
Recommended: N
Reference: This document
4. References
4.1. Normative References
[I-D.connolly-cfrg-xwing-kem]
Connolly, D., Schwabe, P., and B. Westerbaan, "X-Wing:
general-purpose hybrid post-quantum KEM", Work in
Progress, Internet-Draft, draft-connolly-cfrg-xwing-kem-
01, 23 January 2024,
<https://datatracker.ietf.org/doc/html/draft-connolly-
cfrg-xwing-kem-01>.
[I-D.draft-westerbaan-cfrg-hpke-xyber768d00]
Westerbaan, B. and C. A. Wood, "X25519Kyber768Draft00
hybrid post-quantum KEM for HPKE", Work in Progress,
Internet-Draft, draft-westerbaan-cfrg-hpke-xyber768d00-02,
4 May 2023, <https://datatracker.ietf.org/doc/html/draft-
westerbaan-cfrg-hpke-xyber768d00-02>.
[RFC9180] 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>.
[RFC9420] Barnes, R., Beurdouche, B., Robert, R., Millican, J.,
Omara, E., and K. Cohn-Gordon, "The Messaging Layer
Security (MLS) Protocol", RFC 9420, DOI 10.17487/RFC9420,
July 2023, <https://www.rfc-editor.org/rfc/rfc9420>.
4.2. Informative References
[MLKEM] National Institute of Standards and Technology, "FIPS 203
(Initial Draft): Module-Lattice-Based Key-Encapsulation
Mechanism Standard", n.d.,
<https://csrc.nist.gov/pubs/fips/203/ipd>.
[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>.
Acknowledgments
Thanks to Joël Alwen, Marta Mularczyk, Britta Hale, and Richard
Barnes.
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Author's Address
Rohan Mahy
Unaffiliated
Email: rohan.ietf@gmail.com
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