What Is a “Chain Reorg” and How Do Checkpoints Prevent It?
A chain reorganisation (reorg) occurs when a node discovers a longer, valid chain that replaces the current chain, causing a rollback of transactions. Reorgs are a natural part of PoW consensus but can be exploited in a 51% attack.
Checkpoints are pre-defined block hashes, often hardcoded into the protocol or released by core developers, that nodes are programmed to never revert past. By establishing a checkpoint, the chain's history up to that point is considered immutable, effectively preventing a malicious chain reorg that extends past the last checkpoint.
Glossar
Chain Reorg
Reorganization ⎊ A chain reorg, within cryptocurrency contexts, represents a sequence of blocks added to a blockchain that are subsequently superseded by a longer, competing chain.
Deep Reorg
Depth ⎊ A deep reorg is a chain reorganization event that affects a significant number of previously confirmed blocks, extending far back into the blockchain's history.
Reorg
Restructuring ⎊ This event signifies a fundamental alteration to the established order of the blockchain's history, typically resulting from a consensus failure or the discovery of a significant vulnerability.
Checkpoints
Checkpoint ⎊ In the Ethereum Proof-of-Stake architecture, checkpoints are specific blocks that mark a point of finality on the Beacon Chain.
Centralization Risks
Control ⎊ Concentration of power within a few validators or large token holders introduces governance risk that can lead to protocol capture or adverse parameter changes.