Communication complexity of byzantine agreement, revisited

As Byzantine Agreement (BA) protocols find application in large-scale decentralized cryptocurrencies, an increasingly important problem is to design BA with improved communication complexity. A few existing works have shown how achieve subquadratic under adaptive adversary. Intriguingly, they all make a common relaxation about the adaptivity of attacker, that is, if honest node sends message and then gets corrupted some round, adversary cannot erase was already sent—henceforth we say such perform “after-the-fact removal”. By contrast, many (super-)quadratic literature can tolerate after-the-fact removal. In this paper, first prove disallowing removal necessary for achieving subquadratic-communication BA. Next, show new binary constructions (of course, assuming no removal) near-optimal resilience expected constant rounds standard cryptographic assumptions public-key infrastructure (PKI) both synchronous partially settings. comparison, known additional strong as random oracles or ability nodes secrets from memory, even these assumptions, prior work above properties. Lastly, setup assumption multicast-based