Greetings Deirdre and TLS,
I read through draft-connolly-tls-mlkem-key-agreement-00 (and https://github.com/dconnolly/draft-connolly-tls-mlkem-key-agreement/blob/main/draft-connolly-tls-mlkem-key-agreement.md) and I have a few comments. First, though, I want to say thank you for writing this draft. I'll echo some of what has already been voiced on this thread and say that, while some plan to use composite key establishment, it makes sense to also specify the use of standalone ML-KEM in TLS 1.3 as another option. Other WGs (lamps and ipsecme) have already begun to specify the use of standalone FIPS 203, 204, and 205 in various protocols. With respect to this draft, there is certainly interest from National Security System vendors in using standalone ML-KEM-1024 in TLS 1.3 for CNSA 2.0 compliance (as CNSA 2.0 does not require nor recommend hybrid solutions for security). A few specific comments: 1. In Section 1.1 (or Introduction - Motivation in the github version), I would suggest that the second sentence ("Having a fully post-quantum...") is not needed, i.e. that there need not be a justification for why it is necessary to specify how to use ML-KEM in TLS 1.3 (vs. hybrid). It could be appropriate to contextualize the specification of ML-KEM w.r.t the advent of a CRQC, though I also don't think that is necessary. As an example, we can compare to the Introduction in draft-ietf-lamps-cms-kyber-03. 2. Section 3 (Construction on github) currently reads, "We align with [hybrid] except that instead of joining ECDH options with a KEM, we just have the KEM as a NamedGroup." I think it is a more useful framing to base this specification (for the use of a standalone algorithm) off of RFC 8446 instead of the draft spec for a hybrid solution. I understand wanting to align the approach with the approach taken for the hybrid solution, but I don't think that fact needs to be explicitly documented in this draft. When this draft is standardized, I think it's important that it is able to be read, understood, and implemented without needing to refer to the hybrid draft. It could be stated (how it is in the hybrid draft), "ML-KEM-512 (if included), ML-KEM-768, and ML-KEM-1024 are represented as a NamedGroup and sent in the supported_groups extension." 3. On a related note, the hybrid draft says, "Note that TLS 1.3 uses the phrase "groups" to refer to key exchange algorithms -- for example, the supported_groups extension -- since all key exchange algorithms in TLS 1.3 are Diffie-Hellman-based. As a result, some parts of this document will refer to data structures or messages with the term "group" in them despite using a key exchange algorithm that is not Diffie-Hellman-based nor a group." This seems okay, but on the IANA registry for TLS Supported Groups, it indicates 0-255 and 512-65535 are for elliptic curve groups, and 256-511 are for FFDH groups. Where does ML-KEM fit in? Do ranges need to be re-evaluated? As an example, for IKEv2, RFC 9370 changes the name of Transform Type 4 from Diffie-Hellman Group to Key Exchange Method in order to accommodate QR KEMs. 4. In the Discussion section (on github), does the portion on failures need to contain more information about how a failure should be handled in TLS? Should a decrypt_error alert be sent? 5. In Section 4 (or Security Considerations on github), this may be a silly question, but is the definition of "commits" well-understood (in the first sentence on datatracker; in the first sentence of Binding properties on github)? It is not used in RFC 8446 so it might be worth explaining the meaning or using different phrasing in this sentence. Also, what are the WG's thoughts on including standalone PQC signatures in the same draft? Thanks in advance! Rebecca Rebecca Guthrie she/her Center for Cybersecurity Standards (CCSS) Cybersecurity Collaboration Center (CCC) National Security Agency (NSA) From: TLS <tls-boun...@ietf.org> On Behalf Of Deirdre Connolly Sent: Tuesday, March 5, 2024 9:15 PM To: TLS@ietf.org Subject: [TLS] ML-KEM key agreement for TLS 1.3 I have uploaded a preliminary version of ML-KEM for TLS 1.3<https://datatracker.ietf.org/doc/draft-connolly-tls-mlkem-key-agreement/> and have a more fleshed out<https://github.com/dconnolly/draft-tls-mlkem-key-agreement> version to be uploaded when datatracker opens. It is a straightforward new `NamedGroup` to support key agreement via ML-KEM-768 or ML-KEM-1024, in a very similar style to -hybrid-design<https://datatracker.ietf.org/doc/draft-ietf-tls-hybrid-design/>. It will be nice to have pure-PQ options (that are FIPS / CNSA 2.0 compatible) ready to go when users are ready to use them. Cheers, Deirdre
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