ZK Mixer App

This app allows users to deposit assets and later withdraw them without linking the withdrawal to the deposit. It allows withdrawers to prove ownership of a deposit without revealing which deposit belongs to the withdrawer.

## How it works

• Merkle tree for anonymity set:
  • Each deposit has its own unique commitment: hash of a secret plus public identifier
  • These commitmentsw are stored in a merkle tree (on-chain?)
  • The root of this Merkle tree is updated whenever a new deposit is made
• ZK proofs for withdrawals:
  • The withdrawer proves (using Noir) that they know a valid preimage for a commitment in the Merkle tree (without revealing which commitment they know)
  • The proof should also confirm that the commitment is part of a valid tree root without revealing which specific leaf they control.
  • To prevent double-spending, include a nullifier (a hash of the secret that gets recorded on-chain when withdrawn).

How are ZKPs used in this app

Zero Knowledge Proofs (ZKPs) allow a prover to convince a verifier that a specific computation was correctly executed without requiring the verifier to rerun it. The proof ensures correctness without revealing the inputs used in the computation. The ‘zero-knowledge’ property means that the proof can be structured in a way that leaks no additional information beyond the validity of the computation itself.

Notes

• We have removed paymasters to simplify the code. This means the receiving wallet will need to pay the gas fees therefore, hold native tokens

## Usage

1. Clone the repo

git clone https://github.com/Cyfrin/zk-mixer-cu.git

### 2. Install the dependencies

npm install && cd contracts && forge install

3. Running the tests

forge test

4. (optional) re-creating the verifier

This step is needed if you modify the circuit logic at all.

1. Navigate inside the circuits folder and compile the circuit

nargo compile

2. Generate the verifiaction key

bb write_vk --oracle_hash keccak -b ./target/circuits.json -o ./target

3. Generate the verifier

bb write_solidity_verifier -k ./target/vk -o ./target/Verifier.sol

4. Delete your old Verifier.sol from inside contracts/src and replay with the new one!