ACE: Abstract Consensus Encapsulation for Liveness Boosting of State Machine Replication

TL;DR

ACE introduces a flexible framework that enhances the liveness of state machine replication systems by composing view-based abstractions, effectively improving asynchronous performance and robustness against attacks.

Contribution

It proposes the LBV abstraction and a composition method to boost liveness in existing SMR protocols, applicable to both crash and Byzantine failures.

Findings

ACE outperforms base HotStuff during network asynchrony and attacks.

ACE achieves asynchronous SMR with fewer assumptions, compatible with various consensus protocols.

Implementation demonstrates improved robustness in adversarial scenarios.

Abstract

With the emergence of cross-organization attack-prone byzantine fault-tolerant (BFT) systems, so-called Blockchains, providing asynchronous state machine replication (SMR) solutions is no longer a theoretical concern. This paper introduces ACE: a general framework for the software design of fault-tolerant SMR systems. We first propose a new leader-based-view (LBV) abstraction that encapsulates the core properties provided by each view in a partially synchronous consensus algorithm, designed according to the leader-based view-by-view paradigm (e.g., PBFT and Paxos). Then, we compose several LBV instances in a non-trivial way in order to boost asynchronous liveness of existing SMR solutions. ACE is model agnostic - it abstracts away any model assumptions that consensus protocols may have, e.g., the ratio and types of faulty parties. For example, when the LBV abstraction is instantiated with a partially synchronous consensus algorithm designed to tolerate crash failures, e.g., Paxos or Raft, ACE yields an asynchronous SMR for $n = 2f+1$ parties. However, if the LBV abstraction is instantiated with a byzantine protocol like PBFT or HotStuff, then ACE yields an asynchronous byzantine SMR for $n = 3f+1$ parties. To demonstrate the power of ACE, we implement it in C++, instantiate the LBV abstraction with a view implementation of HotStuff -- a state of the art partially synchronous byzantine agreement protocol -- and compare it with the base HotStuff implementation under different adversarial scenarios. Our evaluation shows that while ACE is outperformed by HotStuff in the optimistic, synchronous, failure-free case, ACE has absolute superiority during network asynchrony and attacks.