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• Repudiable E2EE Messages

  In a discussion [1] started by @bengo@mastodon.social, the topic of direct message repudiation was brought up as a security/privacy concern. Currently, unencrypted Mastodon/ActivityPub DMs have repudiation (plausible deniability), because the activities are signed by the instance actor key, not tied to individual user actors. If we would like to preserve this feature in E2EE DMs, we need to consider how activities are signed (tied to our work on limiting metadata exposure [2]), and how messa...

• Protocol for Updating KEM used for E2EE

  At today's meeting we briefly discussed how we would go about updating the KEM algorithm used to establish MLS keys. I mentioned the BeeKEM (https://eprint.iacr.org/2026/1434, https://github.com/swicg/activitypub-e2ee/issues/95) protocol as an example, though I have concerns about this particular protocol. The lead authors are currently PhD students, and this is potentially part of their program (no issue there). My main problems are that there is a non-trivial amount of LLM use in their r...