DARX — ZK Dark Pool

Private trading powered by zero-knowledge proofs.

Trade at midpoint prices with encrypted order data. Orders are matched off-chain and settled on-chain via a Groth16 ZK proof; only you and the relayer see your order details (relayer privacy).

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Features

• Private order book — Side, size, price, value, and filled amount are AES-256-GCM encrypted in the database.
• ZK-settled trades — Matched trades are proven in-circuit (midpoint tolerance) and settled on Arbitrum Sepolia with a single settleTrade call.
• Midpoint pricing — BBO feeds from Binance (with CoinGecko fallback); trades clear at the midpoint.
• Modern stack — Next.js 16, React 19, Wagmi, RainbowKit, Supabase, Circom, snarkjs, Foundry.

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How it works

┌─────────────┐     submit order      ┌─────────────┐     match / encrypt     ┌──────────────┐
│   Frontend  │ ───────────────────► │   Backend    │ ──────────────────────► │   Supabase   │
│ (Next.js)   │                       │ (Express)    │                          │   (orders)   │
└──────┬──────┘                       └──────┬───────┘                          └──────────────┘
       │                                    │
       │  if matched:                        │  fullProve (snarkjs in-process)
       │  approve + settleTrade()            │  → proof + publicInputs
       ▼                                    ▼
┌─────────────┐                       ┌─────────────┐
│  DarkPool   │ ◄── verify proof ──── │  Groth16    │
│  (Arbitrum  │      + transfer       │  Verifier   │
│   Sepolia)  │                       │  (Solidity) │
└─────────────┘                       └─────────────┘

1. User connects wallet, enters amount (token or USDC), submits BUY/SELL.
2. Backend stores the order (encrypted), tries to match with an open opposite order.
3. Matched: Backend generates a ZK proof with snarkjs.groth16.fullProve; frontend approves tokens and calls DarkPool.settleTrade(proof, buyer, seller, ...); backend marks both orders filled.
4. Unmatched: Order stays open; when a counterparty matches later, they run settlement and the first user’s UI can poll until filled.

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Tech stack

Layer	Technologies
Frontend	Next.js 16, React 19, Wagmi, RainbowKit, Tailwind, Shadcn UI, TanStack Query & Table
Backend	Node.js, Express, Supabase, snarkjs (in-process proof)
Contracts	Solidity 0.8, Foundry, OpenZeppelin
ZK	Circom, Groth16 (snarkjs), Verifier.sol
Chain	Arbitrum Sepolia

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Project structure

zk-darkpool/
├── backend/                    # API, matching, ZK proof generation
│   ├── index.js                # Express app, orders + /match-and-settle
│   ├── api/index.js            # Vercel serverless entry (exports app)
│   ├── build/                  # Circuit artifacts (copy from root build/)
│   │   ├── trade_check_js/     # wasm + generate_witness.js
│   │   └── circuit_final.zkey
│   ├── lib/
│   │   ├── crypto.js           # AES-256-GCM for order encryption
│   │   └── supabase.js
│   └── database/               # SQL schema & migrations (optional, see .gitignore)
├── contracts/                  # Solidity
│   ├── DarkPool.sol
│   ├── Verifier.sol            # Groth16 verifier
│   └── MockERC20.sol
├── interface/frontend/         # Next.js app
│   ├── app/                    # Trade, orders, layout
│   ├── components/
│   ├── hooks/
│   └── constants/
├── circuits/                  # Circom source (compile → root build/, then copy to backend/build/)
├── lib/openzeppelin-contracts/
└── deploy.txt                 # Deploy commands & addresses (Arbitrum Sepolia)

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Getting started

Prerequisites

• Node.js 18+
• pnpm (or npm)
• Foundry (for contracts)
• Circom + snarkjs (for circuit build)
• Supabase project
• Wallet on Arbitrum Sepolia

1. Backend

cd backend
cp .env.example .env   # or create .env
# Set: PORT, SUPABASE_URL, SUPABASE_ANON_KEY, RELAYER_SECRET
pnpm install
pnpm dev

• Create the orders table (see backend/database/orders.sql; if migrating to encryption, run migrate_encrypted.sql).
• Proof generation uses backend/build/: copy the contents of the root build/ (after compiling the circuit) into backend/build/ so that trade_check_js/ and circuit_final.zkey are present.

2. Frontend

cd interface/frontend
pnpm install
pnpm dev

Set NEXT_PUBLIC_API_URL (e.g. http://localhost:3001). Configure chain and contract addresses (Wagmi + Darkpool contract) for Arbitrum Sepolia.

3. Contracts (Arbitrum Sepolia)

See deploy.txt for RPC and commands. Deploy in order: Verifier → MockERC20 (base + quote) → DarkPool(verifier, base, quote). Update frontend config and token constants with the deployed addresses.

4. Circuit

Compile the Circom circuit and run the trusted setup to produce build/trade_check_js/ and circuit_final.zkey. Copy the entire build/ output into backend/build/ so the backend can generate proofs (in-process via snarkjs, no CLI).

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Environment

Variable	Where	Description
PORT	Backend	Server port (e.g. 3001)
SUPABASE_URL	Backend	Supabase project URL
SUPABASE_ANON_KEY	Backend	Supabase anon key
RELAYER_SECRET	Backend	Secret for order encryption (relayer privacy)
NEXT_PUBLIC_API_URL	Frontend	Backend API base URL

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API overview

Method	Path	Description
POST	/api/orders/submit	Submit order; returns order + optional match
POST	/match-and-settle	Generate ZK proof (used by frontend when matched)
GET	/api/orders/:id?user_address=0x...	Get order (decrypted for owner)
GET	/api/users/:address/orders	List orders for address (decrypted)
PATCH	/api/orders/:id	Update order (e.g. cancel)
GET	/api/binance/prices, /api/binance/bookTicker	Price proxy (Binance + fallback)

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Deployment

• Backend: Deploy the backend/ folder (e.g. Vercel with api/index.js). Ensure backend/build/ is included (circuit wasm + zkey). Proof is generated in-process with snarkjs.groth16.fullProve (no npx/CLI).
• Frontend: Set NEXT_PUBLIC_API_URL to the deployed backend URL. Deploy to Vercel or any static/Node host.

See backend/README-SETUP.md for EACCES, temp dir, and circuit copy details.

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License

MIT