Fraud Proof
A challenge that lets anyone prove a rollup posted an invalid state update, triggering a rollback on the base chain.
Optimistic rollups assume submitted transactions are valid by default. A fraud proof is the check on that assumption. During a challenge window, usually about seven days on Ethereum, any watcher can submit evidence that a batch was computed wrong. If the proof holds, the bad state is reverted and the proposer loses their bond.
The model is cheap because most batches are never challenged. The cost is delay: withdrawals to the base layer wait out the full window. It also assumes at least one honest, watchful party exists to catch fraud and bother to submit the proof.
Related terms
A rollup that assumes transaction batches are valid and lets anyone challenge fraud within a set dispute window.
Validity ProofA cryptographic proof submitted with every rollup batch that mathematically guarantees the new state was computed correctly.
RollupA scaling method that batches many transactions off-chain and posts a compressed proof or record to the base layer.
SequencerThe rollup component that decides the order of incoming transactions and posts them as compressed batches to the base chain.