Optimistically tuning synchronous byzantine consensus: another win for null messages

Modular methods that transform Byzantine consensus protocols for the synchronous model into ones that are fast and communication efficient in failure-free executions are presented. Small and short protocol segments called layers are custom designed to act as a highly efficient preliminary stage that solves Consensus if no failures occur. When composed with a Byzantine consensus protocol of choice, they allow considerable control over the tradeoff in the combined protocol’s behavior in the presence of failures and its performance in their absence. In failure-free executions, they are more efficient than all existing Byzantine consensus protocols. In the presence of failures, they incur a small cost over the complexity of the original consensus protocol being transformed. A key ingredient underlying the efficiency of the new layers is the judicious use of null messages for broadcasting information in failure-free runs. In particular, the notion of a silent validation round, which implements such a broadcast, is defined and used in several ways.