With our talk “Eventually Consistent Access Control: Practical Insights on Matrix from Decentralized Systems Theory”, we were at the @matrix conference 2025 in Strasbourg: https://media.ccc.de/v/matrix-conf-2025-72768-eventually-consistent-access-control-practical-insights-on-matrix-from-decentralized-systems-theory [m]@🇫🇷🥳 The talk covers scientific foundations as well as 6 years of our own research on Matrix. #MatrixConf2025

Our paper, “To the Best of Knowledge and Belief: On Eventually Consistent Access Control”, is now available as CC-BY: https://dl.acm.org/doi/10.1145/3714393.3726520 At the example of @matrix.org, we showed traditional conceptualizations of access control as insufficient, and present eventual consistency as alternative.

Wouldn't it be nice if your #Matrix homeserver could garbage-collect all this ancient room history and just keep a small cryptographic proof that everything was alright?
Our newest paper, “Proof-Carrying CRDTs allow Succinct Non-Interactive Byzantine Update Validation” https://dl.acm.org/doi/10.1145/3721473.3722142.
Byzantine-fault tolerant #CRDT ("Conflict-Free Replicated Data Types") are the scientific basis for Matrix, and in this work, CRDTs are combined first-time with non-interactive cryptographic proofs, as they are known from the zero-knowledge field. At the example of Matrix, we evaluate whether that combination is futile. There is still a lot of research to be done to make this a reality in Matrix, but the results were better than we expected:
While making every event carry a proof of authorization is not practical yet, one could add a proof to more seldom things like room upgrades. The article is freely available as Open Acces under CC-BY, and our implementation is licensed MIT. https://github.com/kit-dsn/proof-carrying-crdts

Our paper “ReP2P Matrix: Decentralized Relays to Improve Reliability and Performance of Peer-to-Peer Matrix”, is now available under CC-BY: https://dl.acm.org/doi/abs/10.1145/3694809.3700741 Code and data based on the existing peer-to-peer @matrix prototypes available as well: https://gitlab.kit.edu/kit/tm/telematics/rep2p-matrix

My research group hosts this year's ROBUST 2025 workshop on Byzantine fault tolerance and state-machine replication, and seeks your participation and contributions! We look for 25min presentations, including preliminary results and open question. See you on March 17/18! https://gi-robust.github.io/robust25/

The #MatrixConf has left Berlin 🇩🇪, for now. I love to scroll through the photos in the Matrix guest book everyone created together at the closing event, the conference had such a nice vibe. 📸 See you all again in France, October 2025! 🇫🇷👋

The first ever #MatrixConf is going great, so many people, ranging from researchers to practitioners, companies to government organizations. 😄 First time I heard from the Matrix efforts of the Swiss post for a nationwide communication system, especially for B2C https://cfp.matrix.org/matrixconf2024/talk/FUXFHY/ 🇨🇭