What Is Byzantine Fault Tolerance (BFT)?
Also known as: BFT, Byzantine Fault Tolerance, PBFT
In short
Byzantine fault tolerance (BFT) is the ability of a distributed system to keep working correctly and reach a common decision even if some participants fail, give false information or behave maliciously.
The concept is based on the Byzantine Generals Problem. A system being BFT means it can stay safe not only when participants crash, but also when they send conflicting and misleading messages to different parties, which is the hardest type of failure, called a Byzantine fault. Classical BFT algorithms require the condition n ≥ 3f + 1, where n is the total number of nodes and f is the number of faulty nodes; that is, the system works correctly if fewer than one third of the nodes are faulty.
Practical Byzantine Fault Tolerance (PBFT), proposed in 1999 by Miguel Castro and Barbara Liskov, made this idea applicable in real systems. Tendermint (CometBFT), used by the Cosmos ecosystem, IBFT and QBFT supported by Hyperledger Besu, and the finality component of Ethereum's Proof of Stake mechanism are based on BFT principles. These algorithms generally allow blocks to be finalized irreversibly in a short time.
Classical BFT algorithms require nodes to exchange a large number of messages with one another; the communication load grows rapidly as the number of participants increases. This limitation is noticeable in networks where the number of validators is kept relatively small. Bitcoin's Nakamoto consensus, by contrast, adopts a different approach that offers probabilistic rather than absolute finality and can scale to a large number of participants.
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