论文标题
从对称到不对称的异步拜占庭共识
From Symmetric to Asymmetric Asynchronous Byzantine Consensus
论文作者
论文摘要
共识可以说是分布式计算中最重要的概念之一。在异步,随机和无签名的实现中,Moveréfaoui等人的协议。 (PODC 2014和JACM 2015)代表了一个具有里程碑意义的结果,该结果已延长,并在实用系统中进行了。这些协议具有最佳的弹性,并在预期的是,仅预期的二次消息复杂性数量恒定。随机化是通过普通胶原始的。在传统的共识协议中,所有涉及的过程都遵循一个全局的对称故障模型,通常仅由故障过程数量的界限定义。然而,由于对区块链的应用,最近考虑了更灵活的信任假设。特别是,凭借不对称的信任,一个过程可以自由选择它信任的其他过程以及哪些过程可能会碰撞。本文重新审查了Mostéfaoui等人的最佳异步方案。并显示如何通过不对称信任实现它。本文首先要详细指出为什么该协议的某些版本可能会违反livesice。然后,它提出了一个不影响其属性的协议的修复程序,但让它恢复了其原始版本的简单性(PODC 2014)。同时,本文展示了如何实现与非对称法定人数的随机无签名异步拜占庭共识。这会产生具有主观,不对称信任和恒定预期运行时间的最佳共识协议。例如,它适用于区块链的应用。
Consensus is arguably one of the most important notions in distributed computing. Among asynchronous, randomized, and signature-free implementations, the protocols of Mostéfaoui et al. (PODC 2014 and JACM 2015) represent a landmark result, which has been extended later and taken up in practical systems. The protocols achieve optimal resilience and takes, in expectation, only a constant expected number of rounds of quadratic message complexity. Randomization is provided through a common-coin primitive. In traditional consensus protocols, all involved processes adhere to a global, symmetric failure model, typically only defined by bounds on the number of faulty processes. Motivated by applications to blockchains, however, more flexible trust assumptions have recently been considered. In particular, with asymmetric trust, a process is free to choose which other processes it trusts and which ones might collude against it. This paper revisits the optimal asynchronous protocol of Mostéfaoui et al. and shows how to realize it with asymmetric trust. The paper starts by pointing out in detail why some versions of this protocol may violate liveness. Then it proposes a fix for the protocol that does not affect its properties, but lets it regain the simplicity of its original version (PODC 2014). At the same time, the paper shows how to realize randomized signature-free asynchronous Byzantine consensus with asymmetric quorums. This results in an optimal consensus protocol with subjective, asymmetric trust and constant expected running time. It is suitable for applications to blockchains, for instance.