ACE Seminar: Federated Byzantine Quorum Systems

Speaker: Alvaro Garcia-Perez

Date/Time: 29-Jan-2019, 13:00 UTC

Venue: Robert 3.09



Some of the recent blockchain proposals, such as Stellar and Ripple, use quorum-like structures typical for Byzantine consensus while allowing for open membership. This is achieved by constructing quorums in a decentralised way: each participant independently chooses whom to trust, and quorums arise from these individual decisions. Unfortunately, the theoretical foundations underlying such blockchains have not been thoroughly investigated. To close this gap, in this work we study decentralised quorum construction by means of federated Byzantine quorum systems, used by Stellar. We rigorously prove the correctness of basic broadcast abstractions over federated quorum systems and establish their relationship to the classical Byzantine quorum systems. In particular, we prove correctness in the realistic setting where Byzantine nodes may lie about their trust choices. We show that this setting leads to a novel variant of Byzantine quorum systems where different nodes may have different understanding of what constitutes a quorum.


Alvaro Garcia-Perez is working on algorithms for consensus, and in the past he worked in process algebras, rule formats for structural operational semantics, nominal techniques, lambda calculus, abstract machines and program transformation.

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