With the 28th session we jumped into the space of byzantine fault tolerant consensus protocols. We covered fault tolerant consensus with various Paxos variants in the past, but this session was the first one looking into how to solve the byzantine generals problem.
Instead of using PBFT  as a first paper we went with Hotstuff  instead. The reasoning behind this choice was (a) Hotstuff presenting a somewhat easy up-to-date consensus algorithm and (b) that it provides a framework enabling one to compare other algorithms (e.g. PBFT) in the space.
For those interested in learning more, I recommend to read the Hotstuff paper  as well as watch the three talks by one of the authors Ittai Abraham.
And finally here are the slides used in the reading group session.
 Castro, Miguel, and Barbara Liskov. “Practical Byzantine fault tolerance.” OSDI. Vol. 99. No. 1999. 1999.
 Yin, Maofan, et al. “Hotstuff: Bft consensus in the lens of blockchain.” arXiv preprint arXiv:1803.05069 (2018).