Publish or Perish: Defending Withholding Attack in Dfinity Consensus

Synchronous Byzantine consensus has regained its popularity with the rise of permissioned blockchains due to its significantly better fault tolerance (up to minority faults) than its partially synchronous counterpart (less than one third). Dfinity Consensus is a state-of-the-art synchronous Byzantine consensus protocol. However, Dfinity is vulnerable to the withholding attack. For example, adversaries can strategically withhold blocks, resulting in an increase in latency and unbounded message complexity. Motivated by this observation, we present Dfinity++, which can effectively defend such an attack. The key idea behind Dfinity++ is simple. Since honest replicas would timely publish their blocks, one can detect delayed blocks and then trigger a fast switch to the next iteration, leading to better resource usage. Our results show that against a static/mildly adversary, Dfinity++ is able to reduce the latency (of committing a new block) by 10.7%, and at the same time enjoys a message complexity of O(n2).