## Cryptology ePrint Archive: Report 2022/264

Gradecast in Synchrony and Reliable Broadcast in Asynchrony with Optimal Resilience, Efficiency, and Unconditional Security

Abstract: We revisit Gradecast (Feldman and Micali, STOC’88) in Synchrony and Reliable Broadcast (Bracha, Information and Computation’87) in Asynchrony. For both tasks, we provide new protocols that have three desirable properties: (1) optimal resilience, tolerating $t < n/3$ malicious parties; (2) are communication-efficient, where honest parties send just $O(nL)$ bits for a dealer with a message of $L = \Omega(n)$ bits; (3) and are unconditionally secure, (or statistically secure), without needing to rely on any computational or setup assumptions. To the best of our knowledge, no previous work obtains all three properties simultaneously.