**Session Date/Time:** 04 Nov 2024 09:30

# mls

## Summary

The MLS working group meeting focused on extensions to the MLS protocol, aiming to prioritize and triage them effectively. Discussions covered various topics, including extension frameworks, post-quantum combiners, light clients, split commits, associated parties, semi-private messaging, and alternative AAD handling. Several proposals were presented, and feedback was solicited from the group regarding adoption and further development.

## Key Discussion Points

*   **Extension Prioritization:** The main goal is to determine which extensions to focus on and how to prioritize them.
*   **Extension Definitions:** Clarifying the definition of "extension" in MLS to avoid ambiguity (IANA registry vs. any non-main spec draft vs. a component being extended).
*   **Safe Extensions Framework:** Concerns about the complexity and potential issues with the Safe Extensions framework, particularly regarding security boundaries and multiple extensions. Alternative approaches were discussed.
*   **Post-Quantum Combiners (PQ Combiners):**  Discussion of a hybrid approach combining post-quantum and traditional cryptography, offering flexibility in ratcheting and trading off between confidentiality and authenticity.
*   **Light Clients:** Presenting the concept of light clients, which join MLS groups faster by downloading only a portion of the tree, with tradeoffs in authentication. Security concerns and potential misinterpretations were emphasized.
*   **Split Commits:** Presenting split commits to reduce commit sizes for individual clients, involving a third party that personalizes the commit message, removing the need to broadcast the entire update path.
*   **Associated Parties:** Extension for sharing key material with external parties. Concerns about complexity were raised and discussion of the possibility of simplification.
*   **Semi-Private Messaging:** Key discussion regarding the use of associated parties for semi-private messages.
*   **Additional Authenticated Data (AAD):** Discussing ways to authenticate data that is not part of the message, including stripping the AAD field.

## Decisions and Action Items

*   **Action Item (Richard Barnes):** File an issue elaborating on concerns regarding the Safe Extensions framework and propose an alternative.
*   **Action Item (Chairs):** Schedule virtual interims to discuss extension frameworks and associated parties, and adoption consideration for semi-private messaging, ideally with a side-by-side comparison of associated parties use vs standalone.
*   **Decision:** Schedule a working group adoption call for PQ combiners.
*   **Action Item (Joelle):** Update terminology in the split commits draft to reflect "split commits" instead of earlier terms, and for Marta Mularchic and Joelle Alwen to re-read private messaging draft with associated parties, and update slides accordingly.
*   **Action Item (Richard Barnes):** Flesh out the security considerations section for the light clients draft, adding warning labels and examples of appropriate and inappropriate use cases, include this with a light MLS red light emoji to highlight its dangers
*    **Action Item (Raphael):** Look at the issue if need separate secret trees

## Next Steps

*   Schedule virtual interims to discuss extension frameworks, light clients, associated parties, and semi-private messaging.
*   Review and refine the light clients draft based on feedback, focusing on security considerations and appropriate use cases.
*   Prepare for the working group adoption call for PQ combiners.
*    Working group adoption call for PQ combiners