Lit🔥Tornado🌪

During the hackathon, we utilized Lit Protocol to create a mixer app called "Lit Tornado," similar to Tornado Cash, but without relying on zero-knowledge proofs to enable confidential transactions. Tornado Cash employs zero-knowledge proofs to provide privacy in transactions, but we were able to achieve a similar outcome solely with the features of Lit Protocol. Specifically, Lit Protocol's Lit Actions & PKPs allow for off-chain computation results to be proven on-chain, a property similar to zero-knowledge proofs. While zero-knowledge proofs are indeed a groundbreaking technology, they come with challenges such as high computational and implementation costs. We believe that as more people recognize this fact, there will be an increasing number of cases where Lit Protocol can serve as an alternative to zero-knowledge proofs. With Lit Tornado, we hope to have showcased the vast potential of Lit Protocol.

We rewrote Tornado Cash's smart contract to use Lit PKP signatures for verification instead of zero-knowledge proofs. This change eliminated the need for gas-intensive zk verification and zk-friendly Poseidon Hash, simplifying the code. Due to time constraints, we opted not to use an external server, instead storing the complete Merkle tree state directly within the contract.

Adapting Tornado Cash's zk circuit to a Lit Action was challenging. Although we had a good understanding of the circuit from previous study, implementing the Merkle tree logic proved difficult, as the results often did not meet expectations.

We also found a convenient solution for setting up a relayer by utilizing Lit Protocol. By having Lit PKP sign via Lit Action, it functions as a relayer.

Our technology stack included:

• Lit Actions & PKPs
• NextJs/TypeScript
• daisyUI/Tailwind CSS
• Hardhat
• OpenZeppelin
• wagmi/viem
• ethers
• merkletreejs
• Polygon Mumbai
• Scroll Sepolia