Checkpoint (Consensus)
A specific block that a blockchain's consensus protocol treats as a trusted, agreed-upon reference point, used to anchor finality decisions or help new nodes sync safely.
A checkpoint, in a blockchain consensus context, is a specific block that the protocol or its participants treat as an established, trusted reference point in the chain's history. Proof-of-stake finality mechanisms (see Kaavon's "Finality Gadget" glossary definition) commonly use checkpoints as the specific blocks that validators vote on to achieve finality, rather than voting on every single block individually, which would be considerably less efficient.
Checkpoints also play a practical security role for new or long-offline nodes joining the network: rather than needing to independently validate the chain's entire history purely from its genesis block, a node can start from a recent, widely trusted checkpoint obtained from a reliable source, which is the primary practical defense against a long-range attack (see Kaavon's "Long-Range Attack" glossary definition) exploiting the weak subjectivity (see Kaavon's "Weak Subjectivity" glossary definition) problem facing newly syncing nodes.
Examples
- A proof-of-stake chain's finality gadget has validators vote on specific checkpoint blocks at regular intervals, rather than voting on every individual block in between.
- A new node can sync safely starting from a recent, trusted checkpoint rather than needing to independently validate the chain's entire history back to its genesis block.