Rollups (Optimistic vs ZK) in Blockchain / Solidity - Quick Revision & Key Differences

Recall & Review

beginner

What is a rollup in blockchain?

A rollup is a technology that bundles many transactions together off the main blockchain to make processing faster and cheaper, then submits a summary back to the main chain.

intermediate

How do Optimistic Rollups verify transactions?

Optimistic Rollups assume transactions are valid by default and only check them if someone challenges with proof of fraud.

intermediate

What is the main difference between Optimistic and ZK Rollups?

Optimistic Rollups trust transactions unless challenged, while ZK Rollups use cryptographic proofs to verify transactions instantly.

beginner

What does ZK stand for in ZK Rollups?

ZK stands for Zero-Knowledge, which means the rollup uses zero-knowledge proofs to prove transactions are correct without revealing all details.

advanced

Why might someone choose Optimistic Rollups over ZK Rollups?

Optimistic Rollups are often easier to build and support more complex smart contracts, but they have longer withdrawal times due to challenge periods.

What do Optimistic Rollups assume about transactions?

A They are valid unless proven otherwise

B They are invalid until verified

C They require zero-knowledge proofs

D They are processed only on the main chain

Optimistic Rollups assume transactions are valid by default and only check if challenged.

What technology do ZK Rollups use to verify transactions?

A Fraud proofs

B Zero-knowledge proofs

C Proof of work

D Proof of stake

ZK Rollups use zero-knowledge proofs to instantly verify transactions.

Which rollup type usually has faster withdrawal times?

A ZK Rollups

B Optimistic Rollups

C Both are the same

D Neither supports withdrawals

ZK Rollups verify transactions instantly, so withdrawals are faster than Optimistic Rollups which have challenge periods.

Why might Optimistic Rollups be preferred for complex smart contracts?

A They run only on Layer 1

B They use zero-knowledge proofs

C They have no challenge periods

D They are easier to build and support more complex logic

Optimistic Rollups are often easier to develop for complex contracts compared to ZK Rollups.

What is a key risk with Optimistic Rollups?

A They require heavy computation on Layer 1

B They cannot bundle transactions

C Fraud proofs might be missed causing invalid transactions

D They do not support smart contracts

If no one challenges a fraudulent transaction in Optimistic Rollups, it may remain accepted.

Explain how Optimistic Rollups and ZK Rollups differ in verifying transactions.

Think about trust assumptions and proof methods.

Describe the advantages and disadvantages of using Optimistic Rollups.

Consider speed, security, and complexity.