Optimally Efficient Multi-party Fair Exchange and Fair Secure Multi-party Computation

Multi-party fair exchange (MFE) and secure multi-party computation (fair SMPC) are under-studied fields of research, with practical importance. In particular, we consider MFE scenarios where at the end protocol, either every participant receives other participant’s item, or no anything. We analyze case a trusted third party (TTP) is optimistically available, although emphasize that trust put on TTP only regarding fairness , our protocols preserve privacy exchanged items against TTP. SMPC case, prove malicious can harm fairness, but not security . construct an asymptotically optimal protocol requires constant number rounds (in comparison to linear) O(n 2 ) messages cubic), n participating parties. enable parties efficiently any item be into verifiable encryption (e.g., signatures contract). show how apply this top achieve very little overhead (independent circuit size). then generalize handle topology (participants arbitrary participants). Our guarantees in its strongest sense: even if all n-1 participants colluding each other, still guaranteed.