The Istanbul BFT Consensus Algorithm

This paper presents IBFT, a simple and elegant Byzantine fault-tolerant consensus algorithm that is used to implement state machine replication in the Quorum blockchain. IBFT assumes a partially synchronous communication model, where safety does not depend on any timing assumptions and only liveness depends on periods of synchrony. The algorithm is deterministic, leader-based, and optimally resilient - tolerating f faulty processes out of n, where n ≥ 3f+1. During periods of good communication, IBFT achieves termination in three message delays and has O(n2) total communication complexity.