🛡️ P2P ZK Anoxchange

A secure, anonymous, and scalable peer-to-peer token exchange system powered by zkSNARK proofs and on-chain withdrawal rights management.

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🎯 Goal

Build a privacy-preserving P2P exchange (e.g., USDT) that protects users from tracking, using zkSNARK-based zero-knowledge proofs and Merkle tree commitments.

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🧱 Architecture

Component	Purpose
P2PManager.sol	Smart contract managing deposits, withdrawals, and P2P requests
verifier.sol	Verifies zkSNARK proofs generated on the client side
Merkle Tree	Commitments tree (Poseidon hash) stored on-chain
zk-Circuit	Groth16 proof system verifying nullifier, secret, recipient
CLI Tools	Scripts for deposit, requestWithdraw, and withdraw
note.json	Stores note details: nullifier, secret, amount, commitment, root

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🔐 Privacy with zkSNARK

The Groth16 zkSNARK scheme ensures:

• The user knows the nullifier and secret for an existing commitment
• The note has not been used (nullifierHash unused)
• The note belongs to the current Merkle root
• The recipient can be chosen freely

👉 All without revealing the nullifier, secret, amount, or sender.

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🔁 Usage Flow

1. Deposit

• User generates a note {nullifier, secret}
• Creates a commitment: Poseidon(nullifier, secret)
• Calls P2PManager.deposit(commitment, amount)
• Commitment is added to Merkle tree and tokens deposited
• 📝 Note saved in JSON, shareable via private channel

2. P2P Note Transfer

• Send the note to a buyer via Session, QR, or messenger
• Buyer pays in fiat, USDT, or another method

3. Request Withdraw (Optional)

requestWithdraw(commitment, recipientAddress)

• Locks withdrawal rights for a recipient
• Includes expiration (expiresAt) for automatic release if unpaid

4. Withdraw

• Buyer generates Merkle proof + zkSNARK proof

• Calls withdraw() with proof, root, nullifierHash, recipient

• Contract:

  • Verifies proof via verifier.sol
  • Ensures note not spent before
  • Checks reservation (recipient, expiresAt) if set
  • Sends tokens to recipient
  • Marks nullifierHash as spent

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✅ Fraud Protection

Fraud Attempt	Protection
Double-spending a note	nullifierHash valid only once
Linking deposit to withdrawal	zkSNARK hides all details
Seller attempts to withdraw note	requestWithdraw() locks recipient
Buyer reserves note but doesn’t pay	expiresAt auto-expires reservation

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🧪 Deployment (MVP)

Step 1. Compile zk-Circuit

cd circuits/
snarkjs groth16 setup mixer.r1cs pot12_final.ptau mixer.zkey
snarkjs zkey export verificationkey mixer.zkey verification_key.json
snarkjs zkey export solidityverifier mixer.zkey verifier.sol

Step 2. Deploy Contracts

forge script script/Deploy.s.sol --rpc-url http://localhost:8545 --broadcast

Step 3. Generate Note

ts-node cli/deposit.ts

Step 4. Request Withdraw (Optional)

ts-node cli/requestWithdraw.ts note.json recipient_address

Step 5. Withdraw Funds

ts-node cli/withdraw.ts note.json

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📦 Project Structure

p2p-mixer/
├── contracts/
│   ├── P2PManager.sol
│   └── verifier.sol
├── circuits/
│   └── mixer.circom
├── cli/
│   ├── deposit.ts
│   ├── requestWithdraw.ts
│   └── withdraw.ts
├── notes/
│   └── note_<timestamp>.json
├── test/
│   └── P2P.t.sol
└── README.md

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🔜 Upcoming Features

Feature	Status
🧾 Note encryption (PGP/QR)	⏳
⌛ Time-lock (cheque system)	🔜
⚖️ Fee via nominal amount	🔜
📱 React GUI + QR support	🔜
🔄 Batch transfers	🔜
🧩 NFT-based ownership proofs	🔜

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💡 Contributions and ideas are welcome!