MLS Challenges & Opportunities Beyond Olm 🔐

https://media.ccc.de/v/matrix-conf-2025-71182-beyond-olm-about-challenges-and-opportunities-in-messaging-layer-security-mls

[matrix] as an end-to-end encrypted communication standard has its flaws. Flaws in privacy, flaws in complexity. With the standard of Messaging Layer Security (MLS), the [matrix] ecosystem has the opportunity to address old flaws, rethink room state and increase interoperability.

In this talk, I will provide a beginner's guide on challenges of [matrix] 3.0.

&gt Messaging Layer Security (RFC 9420, MLS) is a modern layer for end-to-end encrypted group messaging providing Forward Secrecy (PFS) and Post-Compromise Security (PCS). MLS further provides performance that’s logarithmic in the group size, an easy migration to post-quantum security, and is a rigorously analyzed protocol.

This talk will discuss the opportunities and challenges offered by MSC4256 proposing a way to integrate MLS into [matrix] rooms.

As a guidance, I will focus on the following questions :

- Which advantages does MLS feature over Olm ?
- Which tradeoffs can we accept with an interoperable encryption standard ?
- How can we keep a federated ecosystem working with an encryption standard not meant for complete distribution ?
- How can we ensure to keep sync of MLS state and [matrix] room state ?
- How can we incrementally migrate an ecosystem to another encryption standard ?

The entire topic of MLS is obviously too big for a single talk. Many of the open questions may only be discussed briefly. The aim of this talk is not to present outstanding solutions like a miracle but rather to inform about the current state of the specification, the ecosystem and next steps.

The one with the braid (she/her)

https://cfp.2025.matrix.org/matrix-conf-2025/talk/BAKSEA/

#matrixconf2025 #SecurityEncryption

Licensed to the public under https://creativecommons.org/licenses/by-sa/4.0/