Optimistic Rollups

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Pronunciation

[op-tuh-mis-tik rohl-uhps]

Analogy

Imagine a system where a trusted courier (the rollup operator) brings a batch of signed documents (transactions) to the main office (Layer 1) and declares they are all correct. The office 'optimistically' accepts them but posts them publicly for a week (the dispute period). During this week, anyone (verifiers) can inspect the documents. If they find a fraudulent one, they can sound an alarm (submit a ), and the office will then carefully check that specific document and penalize the courier if fraud is confirmed.

Definition

A type of rollup that 'optimistically' assumes transactions are valid and posts them to without immediate proof. They use a fraud-proving system where anyone can challenge suspicious transactions during a dispute period, forcing a verification on .

Key Points Intro

Optimistic Rollups improve by assuming transactions are valid by default, relying on fraud proofs for security.

Key Points

Operators bundle transactions and post them to Layer 1, asserting their validity.

A challenge period allows verifiers to submit fraud proofs if they detect an invalid state transition.

If a fraud proof is successful, the incorrect transaction is reverted, and the malicious operator is penalized.

Generally easier to implement and more EVM-compatible than ZK-Rollups initially.

Withdrawals from Optimistic Rollups typically have a delay (the challenge period) to allow for fraud proofs.

Example

and are prominent Optimistic Rollups on . Users can transact on these L2s with lower , but withdrawing funds back to involves a waiting period of about a week.

Technical Deep Dive

Optimistic Rollups data (or roots) to the . The contract maintains the rollup's . When a new batch of transactions is submitted, it's considered pending until the challenge period (e.g., 7 days) elapses. During this time, anyone can execute a by re-executing the disputed (s) on to demonstrate invalidity. This mechanism requires at least one honest verifier to be watching the rollup. The economic incentives are designed to encourage verifiers (e.g., by rewarding successful fraud proofs) and discourage malicious operators (e.g., by their staked bond).

Caveat

The main drawback is the potentially long withdrawal time due to the challenge period. They also rely on the assumption that at least one honest and active verifier will detect and prove fraud if it occurs.

Related Terms

Blockchain & Cryptocurrency Glossary

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