3. Secure Computation without Agreement

Abstract

AbstractIn the previous chapter, we have shown that authenticated Byzantine Agreement protocols cannot be composed concurrently (or even in parallel) when a third or more of the parties are corrupted. An immediate and important ramification of this result relates to the composition of secure multi-party computation. All known protocols for general secure multi-party computation strongly rely on the extensive use of a broadcast primitive. When a third or more of the parties are corrupted, this broadcast is implemented using authenticated Byzantine Agreement. Essentially, this use of Byzantine Agreement cannot be eliminated since the standard definition of secure computation (for the case of an honest majority) actually implies Byzantine Agreement. Moreover, it is accepted folklore that the use of a broadcast channel is essential for achieving secure multiparty computation, even when there is no honest majority. Due to the above state of affairs, all known protocols for secure multi-party computation in the point-to-point network model do not remain secure under concurrent or even parallel composition.KeywordsSecure ComputationBroadcast ChannelAuxiliary InputHonest PartyByzantine AgreementThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.