Asymmetric Failure Assumptions for Reliable Distributed Systems

In distributed computing, quorum systems are one way to formalize the kind of failures a system aims to tolerate. These assumptions can be either be global and shared by all processes, or processes can be allowed a degree of freedom in making assumptions based on their personal beliefs. In either case, a quorum system's consistency property provides a foundation for building protocols with provable properties. In this work we extend existing models of asymmetric trust, targeted at systems with Byzantine faults, by introducing a weaker quorum consistency property, aimed for example at systems that are subject to crashes only. We then show that a system which complies with only this weaker consistency property is at most as powerful as one with an easily constructed global failure assumption.