In August last year we released Zeth, the first Type-1 zkEVM built using the RISC Zero zkVM, which allowed developers to enshrine EVM execution in ZK. Then this year in May we upgraded Zeth to support Optimistic rollups as part of the Optimism Foundation’s RFP, empowering developers to generate validity proofs that consecrate rollup derivation in zero-knowledge.

Today, we’re announcing Kailua, a software suite for upgrading optimistic rollups to Hybrid ZK rollups, with its first implementation backed by Optimism’s Kona rollup state transition engine. Kailua not only transparently executes Kona unmodified in the zkVM, but introduces its own novel fault proof game that advances the current state-of-the-art in dispute resolution by reducing collateral requirements and finality delays!

Kailua

Not to be confused with the town in the Hawaiian district of Kona, Kailua is a suite of tools and contracts to migrate rollups from long interactive fault proving systems to short non-interactive ZK fault proofs generated using the RISC Zero zkVM. Its main components are:

1. A set of contracts for disputes in ZK, currently compatible only with OP Stack rollups.
2. A CLI tool to automatically migrate rollups to ZK fault proofs.
3. A state proposer agent that advances the rollup state under the rules of the ZK game.
4. A rollup validator agent that challenges and proves any state transition faults in ZK.

Note: The minimum OP stack version required to use Kailua is V1.4 because it leverages the DisputeGameFactory contract instead of the deprecated L2OutputOracle contract.

Kailua Solves Core Rollup Problems

Kailua’s dispute game combines zero-knowledge proving with the optimistic rollup paradigm in a novel hybrid system that improves security and performance while reducing operational costs and finality delays! This is summarized in the table below:

• D is max comp. depth | N/A | 3 transactions K block proofs | | Minimum Finality Delay for an N block proposal | D + log(N) timeouts
• D is max comp. depth | N proof times | 1 timeout K block proof times |

It saves on proving costs

Unlike ZK Rollups, Kailua’s hybrid paradigm permits rollups not only to operate normally without worrying about constant proving costs and times, but also to relieve their users of any added costs for proving, which add up and become non-negligible in cases where:

• Rollups which subsidize transaction fees for their users might not want the added cost.
• Rollups which experience frequent empty blocks might find the added proving burden unsustainable.
• Rollups with very low block times would exacerbate both of the above issues.
• Rollups with custom precompile contracts require extra specialized engineering efforts for accelerated proving.

In Kailua’s novel design, the costs to resolve a dispute using ZK are fully borne by the dishonest parties, whether they are a faulty proposer or validator!

It lowers the participation requirements