Morph’s Responsive Validity Proof (RVP), a new verification method that combines the strengths of existing approaches while addressing their limitations. Fraud proofs, though effective, are capital-inefficient and lack robust security. No Optimistic Rollup (OP-Rollup) has fully implemented a permissionless fraud-proof challenge mechanism. On the other hand, validity proofs offer high security but are costly and inefficient, limiting Rollup scalability.
What is RVP?
Responsive Validity Proof (RVP) integrates ZK-based validity proofs into optimistic rollups, ensuring sequencers generate ZK proofs when challenged, balancing security and efficiency with combined benefits from both rollup types.
Advantages of RVP Over Interactive Fraud Proofs:
Shorter Challenge Period: RVP shortens the challenge period from 7 days to 1–3, improving efficiency and user experience.
Reduced L2 Submission Costs: It reduces Layer 2 submission costs by eliminating the need to include most transaction bytes through validity proofs.
Improved Challenger Experience: The challenger’s role is simplified to merely initiating challenges, as the sequencer is responsible for generating and verifying the ZK-proof.
Seamless Transition to ZK-Rollup: RVP’s design allows for an easy transition to full ZK-rollups by shifting the sequencer’s ZK-proof submission from responsive to active.
Overall, RVP integrates ZK-proofs into optimistic rollups, enhancing efficiency, security, and cost-effectiveness.
How RVP Shortens the Challenge Period in an Optimistic Rollup:
Purpose of the Challenge Period:
Optimistic rollups use a challenge period to allow time for identifying and contesting any malicious submissions by the sequencer. This ensures only valid state changes are confirmed on Layer 1 (L1).
Factors Influencing Challenge Period Length:
- Completion Time: The time needed for both parties to complete the challenge process.
- Mitigating Malicious Behaviour: Ensuring enough time to counteract any sequencer attempts to block challenger transactions on L1.
RVP’s Impact:
RVP reduces the challenge period by streamlining the process and minimizing opportunities for interference, ensuring faster and secure resolution.
Solutions to Shorten the Challenge Period:
- Streamlined Challenge Process: Traditional multi-round fraud proofs require multiple interactions, each consuming time. RVP simplifies this by needing only one interaction-the sequencer uploads a ZK-proof for verification on L1-significantly reducing the challenge period.
- Protection Against Malicious Behaviour: In RVP, once a challenge is initiated, the sequencer cannot interfere. They must prove correctness via a ZK-proof, preventing DoS attacks and ensuring a smooth challenge process.
Key Benefits of RVP:
- Efficiency: Single interaction shortens resolution time.
- Security: ZK-proofs validate state changes securely.
- Cost-Effectiveness: Fewer interactions lower gas costs.
RVP reduces the challenge period from 7 days to 1–3 days, enhancing efficiency and security.
Why RVP Lowers L2 Operating Costs:
Transaction Compression:
In ZK-rollups, ZK-proofs validate transactions, eliminating the need for extensive transaction details on L1, unlike optimistic rollups that require full transaction replays. This reduces data size and costs.
Efficient Data Submission:
RVP uses ZK-proofs for batch validation, minimizing data volume and submission costs. Sequencers only generate ZK-proofs when challenged, further lowering expenses.
Cost Efficiency:
RVP reduces the need for detailed L1 replays and limits ZK-proof generation to when necessary, making it more cost-effective than both optimistic rollups and traditional ZK-rollups.
Why Sequencers Must Submit ZK-Proofs:
Having challengers submit ZK-proofs to contest sequencer submissions is problematic because challengers would struggle to generate valid ZK-proofs if the sequencer provides invalid transactions. Therefore, it’s more effective for sequencers to submit ZK-proofs to validate their own transactions, ensuring the entity responsible for the data verifies its accuracy, which maintains system integrity.
Why Not Simply Use ZK-Rollups?
Cost and Efficiency:
ZK-rollups, like zkSync and Polygon zkEVM, offer high security but are costly, with transaction fees often higher than optimistic rollups. RVP avoids these costs by using ZK-proofs only when challenged, keeping normal operations efficient and affordable.
Block Finalization Time:
While ZK-rollups aim for quick verification, practical delays mean L2 block finalization can still take 20–24 hours, similar to optimized optimistic rollups.
Seamless Transition:
RVP-based systems can easily transition to full ZK-rollups as technology matures, requiring only minor adjustments to the sequencer’s ZK-proof submission methods.