Byzantine Set-Union Consensus Using Efficient Set Reconciliation

Abstract

Applications of secure multiparty computation such as certain electronic voting or auction protocols require Byzantine agreement on large sets of elements. Implementations proposed in the literature so far have relied on state machine replication, and reach agreement on each individual set element in sequence. We introduce set-union consensus, a specialization of Byzantine consensus that reaches agreement over whole sets. This primitive admits an efficient and simple implementation by the composition of Eppstein's set reconciliation protocol with Ben-Or's ByzConsensus protocol. A free software implementation of this construction is available in GNUnet. Experimental results indicate that our approach results in an efficient protocol for very large sets, especially in the absence of Byzantine faults. We show the versatility of set-union consensus by using it to implement distributed key generation, ballot collection and cooperative decryption for an electronic voting protocol implemented in GNUnet.