The consensus protocol for the blockchain. The protocol offers high transaction throughput and lower confirmation time because a block can be produced as soon as the previous block has been signed. The protocol proceeds by rounds. In each round, a predetermined leader among the validators should produce a block. The other validators then sign this block, and their collective signatures are aggregated to form a quorum certificate (QC). This quorum certificate is then included in the next block. If the leader fails to produce a block in the round, or not enough signatures were gathered for a QC, then the validators will instead send timeout messages, which are aggregated to form a timeout certificate (TC). Each block always contains a quorum certificate and may contain a timeout certificate for the previous round if and only if the previous round timed out. When blocks on a common chain in two consecutive rounds have quorum certificates, the block in the first of these rounds (together with its ancestors) is considered final. At this point, the protocol ensures that it cannot be rolled back. The two consecutive blocks must also be within the same epoch.
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