The Istanbul BFT Consensus Algorithm

This paper presents Istanbul BFT (IBFT), a Byzantine fault-tolerant (BFT) consensus algorithm that is used for implementing state-machine replication in the Quorum blockchain, n open source permissioned blockchain platform. IBFT belongs to a class of BFT algorithms that assume a partially synchronous communication model. The IBFT algorithm is deterministic, leader-based, and optimally resilient - tolerating $f$ faulty processes out of $n$, where $n \geq 3f+1$. During periods of good communication, IBFT achieves termination in three message delays. The communication complexity is $O(n^2)$ for normal operation and $O(n)$ for round (or view) changes. We also introduce a variant of IBFT, which achieves $O(n)$ communication complexity during both normal operation and view changes at a small latency penalty compared to IBFT - from 3 to 5 message delays.