[MLS] Re: New Draft - PQ Combiner

["Hale, Britta (CIV)" <[e-mail]>]

Brendon,

Thank you for the feedback and review/catches. We will take a look at those places and update.

To answer your questions:
On group context extensions: It is certainly good practice to have the context extensions committed to in both groups. Technically, the combined group has a single identifier so it is probably redundant to enforce it across both – I would be interested to hear people’s opinions on whether it is worth doing or not.

The line in section 4.2.2 is to require that a joiner’s first commit is a FULL commit (i.e., one cannot just start the protocol on a PARTIAL commit). We can clarify the text on that.

Cheers,

Britta



From: Brendan McMillion <[e-mail]>
Date: Tuesday, October 28, 2025 at 10:30 AM
To: "Hale, Britta (CIV)" <[e-mail]>
Cc: "[e-mail]" <[e-mail]>
Subject: Re: [MLS] New Draft - PQ Combiner

NPS WARNING: *external sender* verify before acting.

Hi Britta, some minor comments:

- You designate the "pq" group in `pq_session_group_id` but I didn't notice anywhere where you actually verify that the PQ group is PQ.

- Do you have thoughts on whether group context extensions should also be required to be synchronized between the PQ and traditional groups?

- I was confused by the line in section 4.2.2: "After joining, the new member MUST issue a FULL Commit as described in Fig 1b." which I read to mean that after doing an external join, you have to do a second full commit, which I think is probably wrong.

- In this line, I think (signature) is meant to be (symmetric): "More precisely, it provides PQ authenticity against "outsiders", that is, against quantum attackers who do not have access to (signature) secret keys of any group member."

- There are a couple of places where you say "is NOT RECOMMENDED and MUST be rejected". This is duplicative. NOT RECOMMENDED means generally not advisable but may be done if you're smart, and then you follow with "MUST be rejected" which precludes the possibility of "may be done if you're smart".

On Wed, Oct 22, 2025 at 5:56 PM Hale, Britta (CIV) <britta.hale=[e-mail]<mailto:[e-mail]>> wrote:
All,

Thank you to everyone who provided reviews and feedback on the Amortized Post Quantum MLS Combiner Draft (formally Hybrid Post Quantum Combiner Draft), and especially to John Gray for volunteering an extensive read-through since IETF-123. There is now a new version of the draft available integrating feedback:
https://www.ietf.org/archive/id/draft-ietf-mls-combiner-02.txt

We would like to proceed to last call. Any final inputs prior to that are welcome.

Britta

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