Attestation-Based Challenger

What is an Ecosystem Project Idea?

An Ecosystem Project Idea is an idea for a project that someone could build within the Optimism ecosystem. As opposed to an Ecosystem Concept or an Ecosystem Idea, an Ecosystem Project is generally more fleshed out and corresponds to a relatively clear product to be built.

Summary

Originally, Optimism considered introducing an attestation-based challenger module as a pathway towards decentralization. Though focus has shifted towards fault proofs, the attestation-based module remains a fascinating and worthwhile concept. Instead of a multisig, this module would utilize a smart contract that verifies EIP-712 signatures. Any participant could call the smart contract with an array of signatures and a proposed output hash for a given L2 block number. If a threshold of signatures approves that output hash for that block number— and if the existing proposed output hash in the L2OutputOracle contract differs from the signed-off proposal—then the original proposed output hash is discarded.

Possible Features

• Develop a slim server with a simple API route such as /signature/block/N that returns a signature over the correct proposal hash for block N.
• Design the API to be callable by anyone.
• If an incorrect proposal on L1 is detected, the API would be called on various known machines to obtain a threshold of signatures.
• Incorporate a smart contract that accepts a proposed output hash for an L2 block number and a threshold of signatures.
• If the threshold is met, and the proposed hash differs from the existing one in the L2OutputOracle, the existing proposal is removed.

Impact

• Offer a novel approach towards securing the integrity of L2 block proposals.
• Contribute to the broader ecosystem's understanding of decentralization mechanisms.
• Help test the potential effectiveness of attestation-based challenger modules in a blockchain context.
• Better than multisigs, easier than fault proofs.