Making Byzantine Fault Tolerant Systems Tolerate Byzantine Faults

This paper argues for a new approach to building Byzantine fault tolerant systems. We observe that although recently developed BFT state machine replication protocols are quite fast, they don’t actually tolerate Byzantine faults very well: a single faulty client or server is capable of rendering PBFT, Q/U, HQ, and Zyzzyva virtually unusable. In this paper, we (1) demonstrate that existing protocols are dangerously fragile, (2) define a set of principles for constructing BFT services that remain useful even when Byzantine faults occur, and (3) apply these new principles to construct a new protocol, Aardvark, which can achieve peak performance within 25% of that of the best existing protocol in our tests and which provides a significant fraction of that performance when the network is well behaved and up to f servers and any number of clients are faulty. We observe useful throughputs between 11706 and 38667 for a broad range of injected faults.