Checkpoint Block

Overview

Meaning and scope

A checkpoint block is a block designated by a protocol, validator vote, client rule, or operator policy as a reference point for finality, synchronization, or trusted history. Some proof-of-stake systems vote on periodic checkpoint blocks to justify and finalize chain segments. Other checkpoints are hardcoded or socially selected.

Mechanism and operation

Checkpoints reduce the amount of history a participant must reconsider or use as anchors for consensus decisions. In Ethereum proof-of-stake, the first block in an epoch acts as a checkpoint, and validators cast a Consensus Vote on checkpoint pairs. Sufficient voting weight can justify and then finalize checkpoints. Once finalized under protocol assumptions, earlier history receives much stronger protection against reorganization than a recently proposed block. Client software can ship a known block hash to speed initial synchronization or protect against long-range attacks. An operator can define a payment checkpoint after a chosen confirmation depth.

Practical payment example

A sync client trusts a known checkpoint only after checking the authority and method by which that checkpoint was established.

Operational checks

Governance can select a recovery checkpoint during an exceptional incident. A checkpoint should be identified by Block ID, network, block number or epoch, and the authority or votes that support it. Relying only on a number allows a competing block at the same position to be substituted.

Distinctions and limits

These uses may provide trust or convenience, but they do not all have the same automatic consensus status. A Checkpoint Block does not make later descendants final automatically. Light clients also need to verify the validator set, signatures, and transition from a trusted checkpoint according to the protocol. An outdated checkpoint can leave a client unable to follow legitimate upgrades or validator changes.

Related reading

Related definitions: Consensus Vote, Block ID.