Tornado Hook

A Tornado Cash implementation as a Uniswap v4 hook.

The project implements both the privacy-preserving mechanism of Tornado Cash and the AMM design of Uniswap v4.

It provides three key benefits:

• Privacy: Mixes users' funds to hide their identity.
• Yield: Users earn fees by providing liquidity, while mixing their funds.
• Liquidity: A larger TVL for traders.

This project relies on an updated Circom circuit of Tornado Cash (using Poseidon hashing with some small optimizations) and Noir for zk-verification.

Due to limitations of the PoolManager contract, deposits and withdrawals should be performed through the TornadoHookEntry contract.

Deployment

The contracts can be found in the packages/foundry/ directory. The project is deployed on Unichain and Unichain Sepolia.

Contract	Unichain	Unichain Sepolia
Hook	0xb09470fad3b3b46fe0e8ec598e799664fe0bcd03	0x84Ad671111481c0FcCDDD232df1092C0B1CC4D03
Entry	0x529c072C3C5979886eDb4E8253C11586Cd8f59dE	0x37398add74fE0e5c7007Ea67644723BEfe8818A3

The frontend: https://tornadohook.vercel.app/

How to create a proof

The actual nullifier and secret are computed as keccak256(input) % FIELD_SIZE, where input is a string from the frontend and FIELD_SIZE = 0x30644e72e131a029b85045b68181585d2833e84879b9709143e1f593f0000001.

Circom

To create a proof, first install snarkjs, then follow these steps:

1. Open packages/circuits/circom/main_js/input.json and fill it with your inputs.
2. Go to cd packages/circuits/circom/main_js.
3. Then run node generate_witness.js main.wasm input.json witness.wtns.
4. And run snarkjs groth16 prove main_0001.zkey ./main_js/witness.wtns proof.json public.json.
5. You'll have your proof in proof.json, then abi.encode it to send to the contract.

Check packages/foundry/test/TornadoHook.t.sol for more details.

Noir

To create a proof, first install bb, then follow these steps:

1. Open packages/circuits/noir/Prover.toml and fill it with your inputs.
2. Go to cd packages/circuits/noir.
3. Then run bb prove -b ./target/noir.json -w ./target/noir.gz -o ./target --oracle_hash keccak --output_format bytes_and_fields.
4. You'll have your proof in ./target/proof and ./target/proof_fields.json.

Check packages/foundry/test/TornadoHook.t.sol for more details.

Local testing

To run tests, simply go to cd packages/foundry and run forge test -vvv.

Unfortunately, there are no withdrawal fuzz tests, because for every deposit you need to create a proof, which can't be done in Solidity.

Local setup

To run Tornado Hook locally, follow the steps below:

1. Install dependencies if it was skipped in CLI:

yarn install

2. Run a local network in the first terminal:

yarn chain

This command starts a local Ethereum network using Foundry. The network runs on your local machine and can be used for testing. You can customize the network configuration in packages/foundry/foundry.toml.

3. On a second terminal, deploy the contracts:

yarn deploy

This command deploys the smart contracts to the local network. The contracts are located in packages/foundry/contracts. The yarn deploy command uses the deploy script located in packages/foundry/script to deploy the contract to the network.

4. On a third terminal, start the NextJS app:

yarn start

Visit the app on: http://localhost:3000. You can interact with the smart contracts using the Debug Contracts page. You can tweak the app config in packages/nextjs/scaffold.config.ts.