Revisiting Fast Practical Byzantine Fault Tolerance

TL;DR

This paper identifies safety and liveness issues in existing Byzantine Fault Tolerance protocols Zyzzyva and FaB through simple scenarios, highlighting critical flaws in their practical implementations.

Contribution

It provides a detailed analysis revealing safety and liveness violations in Zyzzyva and FaB, emphasizing the need for revisiting and improving these protocols.

Findings

Safety violation in Zyzzyva demonstrated with four replicas.

Liveness violation in FaB shown with minimal view changes.

Issues manifest early in protocol execution, in the first log slot.

Abstract

In this note, we observe a safety violation in Zyzzyva and a liveness violation in FaB. To demonstrate these issues, we require relatively simple scenarios, involving only four replicas, and one or two view changes. In all of them, the problem is manifested already in the first log slot.