Visible to the public The Round Complexity of Perfect MPC with Active Security and Optimal Resiliency

TitleThe Round Complexity of Perfect MPC with Active Security and Optimal Resiliency
Publication TypeConference Paper
Year of Publication2020
AuthorsApplebaum, Benny, Kachlon, Eliran, Patra, Arpita
Conference Name2020 IEEE 61st Annual Symposium on Foundations of Computer Science (FOCS)
Date PublishedNov. 2020
ISBN Number978-1-7281-9621-3
KeywordsComplexity theory, Computational modeling, control theory, cryptographic protocols, cryptography, Human Behavior, Information-Theoretic Cryptography, Protocols, pubcrawl, resilience, Resiliency, Round Complexity, Scalability, secure computation, security, Task Analysis
AbstractIn STOC 1988, Ben-Or, Goldwasser, and Wigderson (BGW) established an important milestone in the fields of cryptography and distributed computing by showing that every functionality can be computed with perfect (information-theoretic and error-free) security at the presence of an active (aka Byzantine) rushing adversary that controls up to n/3 of the parties. We study the round complexity of general secure multiparty computation in the BGW model. Our main result shows that every functionality can be realized in only four rounds of interaction, and that some functionalities cannot be computed in three rounds. This completely settles the round-complexity of perfect actively-secure optimally-resilient MPC, resolving a long line of research. Our lower-bound is based on a novel round-reduction technique that allows us to lift existing three-round lower-bounds for verifiable secret sharing to four-round lower-bounds for general MPC. To prove the upper-bound, we develop new round-efficient protocols for computing degree-2 functionalities over large fields, and establish the completeness of such functionalities. The latter result extends the recent completeness theorem of Applebaum, Brakerski and Tsabary (TCC 2018, Eurocrypt 2019) that was limited to the binary field.
Citation Keyapplebaum_round_2020