🌀 ZK-ETH-Mixer : A Private ETH Mixer Using Poseidon Commitments

A zero-knowledge mixer protocol inspired by Tornado Cash enabling anonymous on-chain transfers using zk-SNARKs and Poseidon-based commitments.

---

📌 Overview

ZK-ETH-Mixer is a privacy-focused smart contract protocol that allows users to deposit and withdraw cryptocurrency in a completely anonymous way. It uses zero-knowledge proofs to unlink the sender and recipient addresses, making on-chain analysis ineffective.

This implementation uses:

• Poseidon Hash for zk-friendly Merkle commitments.
• Noir for building custom zk-SNARK circuits.
• Hardhat and Ethers.js for Ethereum development and interaction.
• zk-SNARK verifier deployed on-chain to validate anonymous proofs.

---

🎯 Key Features

• ✅ Anonymous deposits and withdrawals
• 🔒 Poseidon hash-based commitments
• 🌳 Merkle tree structure for anonymity set
• ✨ Zero-knowledge proof verification
• 💸 Fixed denomination ETH transfers
• 🧾 Nullifier system to prevent double-spending

---

🧠 How It Works

📥 Deposit Phase

1. User generates a (secret, nullifier) pair.
2. Computes commitment = PoseidonHash(secret, nullifier).
3. Sends a fixed amount (e.g., 0.1 ETH) with the commitment to the contract.
4. The contract inserts the commitment into a Merkle tree and stores it on-chain.

📤 Withdraw Phase

1. User generates a zk-SNARK proof showing:
   • They know a secret pair (secret, nullifier) that hashes to a commitment in the tree.
   • The nullifier hasn’t been used before.
2. User submits the proof and nullifierHash to the contract.
3. If valid, the contract:
   • Verifies the proof on-chain
   • Transfers ETH to the specified recipient
   • Marks the nullifierHash as spent

---

🛠 Tech Stack

Component	Tech
Smart Contracts	Solidity
ZK Circuits	Noir + SnarkJS
Hashing	Poseidon
Testing	Hardhat + Mocha
Interaction	Ethers.js
Frontend (opt)	React + Tailwind

---

🧪 Local Development Setup

✅ Prerequisites

• Node.js (v18+)
• Yarn or NPM
• Hardhat
• Noir
• SnarkJS

📦 Install

git clone https://github.com/your-username/ZK-ETH-Mixer.git
cd tornado-clone

# Install dependencies
yarn install
# or
npm install

🛠 Build ZK Circuit

cd circuits/
Noir mixer.nr --r1cs --wasm --sym
cd mixer_js/
node generate_witness.js mixer.wasm input.json witness.wtns
snarkjs groth16 setup mixer.r1cs pot12_final.ptau mixer_0000.zkey
snarkjs zkey contribute mixer_0000.zkey mixer_final.zkey
snarkjs zkey export verificationkey mixer_final.zkey verification_key.json

🧪 Test Smart Contracts

cd ..
npx hardhat test

---

💡 Architecture

├── contracts/
│   ├── ZK-ETH-Mixer.sol        # Main mixer contract
│   └── Verifier.sol            # zk-SNARK proof verifier
├── circuits/
│   └── mixer.nr            # ZK circuit (Poseidon hash, Merkle inclusion)
├── scripts/
│   └── deploy.js               # Deployment scripts
├── test/
│   └── mixer.test.js           # Unit tests (deposit/withdraw/proof)
├── frontend/ (optional)
│   └── React UI (connect wallet, deposit, withdraw)

---

📤 Usage Flow

1. User generates: secret, nullifier → computes commitment.
2. Deposits ETH via deposit(commitment) function.
3. Waits for more users (anonymity set grows).
4. Generates proof off-chain (using witness data + zk key).
5. Calls withdraw(proof, root, nullifierHash, recipient) on-chain.
6. Receives ETH privately at recipient address.

---

📈 Future Enhancements

• 🪙 ERC20 support
• 🪂 Relayer integration (for true privacy)
• 🧾 Better UI/UX with React
• 🌍 IPFS or off-chain state syncing
• 🔁 Cross-chain mixer (L2, zkSync, Polygon)

---

👨‍💻 Contributing

Contributions are welcome! Please open issues or pull requests.

# Run linter and tests before submitting PR
npx hardhat test
npm run lint

---

📜 License

MIT License © 2025 YourName

⚠️ For educational and research purposes only. This repository is not intended for production use. Always consult legal experts before deploying any privacy-preserving application to a public blockchain.

---

🧠 Credits & Resources

• Tornado Cash
• Poseidon Hash
• Noir Docs
• ZK Learning
• ZK Hack YOLO change