Asymmetric Byzantine Consensus
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Byzantine quorum systems provide a widely used abstraction for realizing consensus in a distributed system prone to Byzantine faults, in which every process has the same failure assumption. Motivated by the requirements of more flexible trust models in the context of blockchain consensus, Cachin and Tackmann (OPODIS 2019) introduced asymmetric quorum systems as a generalization of Byzantine quorum systems, where every process is free to choose which other processes to trust and which not; this results in a subjective, asymmetric trust assumption. Consensus is arguably one of the most important notions in distributed computing and also relevant for practical systems. This work shows how to realize consensus protocols with asymmetric trust. A first protocol works in partially synchronous systems; it generalizes the consensus algorithm underlying PBFT and uses digital signatures. A second protocol is asynchronous, uses no cryptographic signatures, and achieves optimal resilience. Randomization is provided through a common coin primitive with asymmetric trust. The resulting protocols can find application also in other domains.
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