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arXiv 2107.11331cs.DC
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如何信任陌生人:拜占庭法定人数系统的组成

How to Trust Strangers: Composition of Byzantine Quorum Systems

Orestis Alpos, Christian Cachin, Luca Zanolini

摘要:

信任是任何分布式、容错或安全系统的基础。信任假设指定了系统(如区块链网络)可以容忍的故障,并确定了它正确运行的条件。在易受拜占庭故障影响的系统中,信任假设通常通过可能一起失败的进程集来指定。信任在传统上是对称的,因此系统中的所有进程都遵守关于潜在故障的相同全局假设。最近,人们也考虑了非对称信任模型,特别是在区块链的背景下,每个参与者都可以自由选择信任谁。在这两种情况下,如何构建信任假设是一个悬而未决的问题。考虑两个或多个系统,由不同的、可能不相交的参与者运行,对故障有不同的假设:它们如何协同工作?这项工作回答了这个问题的第一次,并提供了对称和非对称的法定人数系统的组成规则。这些规则是静态的,不需要参与者之间的交互或对新的信任假设的协议。此外,它们确保如果原始系统允许运行特定的协议(保证一致性和可用性),那么联合系统也将如此。同时,组合系统可以容忍尽可能多的错误,这取决于底层的一致性和可用性属性。在个人拜占庭法定人数系统模型中以不对称信任达成共识(Losa等人,DISC 2019)被证明是不可能的,如果过程的信任假设彼此偏离。与不对称的法定人数系统,并通过应用我们的组成规则,我们展示了如何共识实际上是可能的,即使与不相交的进程集的组合。

英文摘要:

Trust is the basis of any distributed, fault-tolerant, or secure system. A trust assumption specifies the failures that a system, such as a blockchain network, can tolerate and determines the conditions under which it operates correctly. In systems subject to Byzantine faults, the trust assumption is usually specified through sets of processes that may fail together. Trust has traditionally been symmetric, such that all processes in the system adhere to the same, global assumption about potential faults. Recently, asymmetric trust models have also been considered, especially in the context of blockchains, where every participant is free to choose who to trust. In both cases, it is an open question how to compose trust assumptions. Consider two or more systems, run by different and possibly disjoint sets of participants, with different assumptions about faults: how can they work together? This work answers this question for the first time and offers composition rules for symmetric and for asymmetric quorum systems. These rules are static and do not require interaction or agreement on the new trust assumption among the participants. Moreover, they ensure that if the original systems allow for running a particular protocol (guaranteeing consistency and availability), then so will the joint system. At the same time, the composed system tolerates as many faults as possible, subject to the underlying consistency and availability properties. Reaching consensus with asymmetric trust in the model of personal Byzantine quorum systems (Losa et al., DISC 2019) was shown to be impossible, if the trust assumptions of the processes diverge from each other. With asymmetric quorum systems, and by applying our composition rule, we show how consensus is actually possible, even with the combination of disjoint sets of processes.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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