The Istanbul BFT Consensus Algorithm
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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 ≥ 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.
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