Advanced

Rollups: Optimistic vs ZK Internals — Key concepts

Understand scaling choices.

Developer Advanced

4/8 — Rollups: Optimistic vs ZK Internals — Key concepts

Fraud vs validityOptimistic rollups rely on fault proofs within a window; ZK rollups publish validity proofs.

Challenge window

t_final = t_publish + challengePeriod

Funds are safe after the challenge period if no valid fraud proof is posted.

Data availabilityUsers can only exit if they can reconstruct state. DA layers or calldata provide this.

Exit data need

exitable if stateDataAvailable == true

No DA, no trustless exits.

BridgingL1 contracts escrow assets; L2 withdrawals prove state transitions back to L1.

Key points

Challenge periods:Withdrawals finalize after fraud-proof window.
Validity proofs:Immediate finality once proof verified on L1.
Sequencer role:Ordering + batching; censorship risk mitigated by escape hatches.
Canonical bridge:Escrow on L1, proofs/receipts from L2 trigger releases.
DA:Calldata vs external DA layers; if data missing, exits may halt.