Small Byzantine Quorum Systems

In this paper we present two protocols for asynchronous Byzantine Quorum Systems (BQS) built on top of reliable channels—one for self-verifying data and the other for any data. Our protocols tolerate f Byzantine failures with f fewer servers than existing solutions by eliminating nonessential work in the write protocol and by using read and write quorums of different sizes. In practice, however, engineering asynchronous reliable channels is difficult in many environments. To address this concern, we modify the original asynchronous BQS protocol of Malkhi and Reiter to work on unreliable channels and discuss how our two new asynchronous protocols can be used to derive an efficient protocol for synchronous Byzantine systems.