🚩 Challenge #6 : ZKP - Balance Checker

⚠️ Important: Please complete Challenge #5 first if you haven't already, as it contains essential instructions related to all upcoming challenges.

🎫 Build a Balance Checker using Zero-Knowledge Proofs (ZKP) on Arbitrum Stylus:

👷‍♀️ In this challenge, you'll build and deploy a smart contract that utilizes Zero-Knowledge Proofs for private balance verification. You'll work with ZKP circuits, deploy them to an Arbitrum Stylus dev node, and create a frontend that allows users to generate and verify proofs! 🚀

🌟 The final deliverable is a full-stack application featuring balance verification. Deploy your contract to a testnet, then build and upload your app to a public web server.

How ZKP Integration Works

This project leverages Zero-Knowledge Proofs (ZKPs) to enable private verification of balance on Arbitrum Stylus. Here's the workflow:

Circuit Design: The ZKP logic is defined in .circom files (e.g., BalanceChecker.circom) using the Circom language. These circuits encode the rules for verification (e.g., "is balance ≥ 1000 wei?") without revealing the inputs.
Proof System Setup: We use the snarkjs library with the Groth16 proving system to generate proving and verification keys. The trusted setup is simulated using a pre-existing pot12_final.ptau file.
Contract Generation: The verification key is exported to a Solidity contract (e.g., BalanceChecker.sol) that runs on Arbitrum Stylus, allowing on-chain verification of zk-proofs.
Frontend Interaction: The Next.js frontend uses WebAssembly (.wasm) outputs from Circom to generate proofs locally, which are then submitted to the deployed contract for verification.
Arbitrum Stylus Advantage: Stylus' Rust-based environment enables efficient execution of the verifier contract, reducing gas costs compared to traditional EVM-based ZKP verification.

This integration ensures privacy (inputs remain off-chain) and scalability (proof verification is lightweight on-chain).

Checkpoint 0: 📦 Environment Setup 📚

Before starting, ensure you have the following installed:

Clone the Repository

git clone -b stylus-zkp-balance-checker https://github.com/abhi152003/speedrun_stylus.git
cd speedrun_stylus

Install Dependencies

Run the following command to install all necessary dependencies:

yarn install

Checkpoint 1: 🚀 Start Your Dev Environment

Step 1: Start the Nitro Dev Node

Navigate to the cargo-stylus folder:
```
cd packages/cargo-stylus
```
Run the run-dev-node.sh script:
```
bash run-dev-node.sh
```
This script:
- Spins up an Arbitrum Stylus Nitro dev node in Docker.
- Deploys the BalanceChecker.sol contract.
- Generates the ABI for interacting with the contract.

The dev node will be accessible at http://localhost:8547.

Important: After deploying a contract, update the contract address in packages/nextjs/app/balanceChecker/page.tsx:

const CONTRACT_ADDRESS = "<your_new_contract_address>";

Step 2: Start the Frontend

⚠️ Before running the frontend:

Go to the packages/nextjs directory:
cd packages/nextjs
cp .env.example .env
Open the .env file and set:
NEXT_PUBLIC_RPC_URL=http://localhost:8547
NEXT_PUBLIC_PRIVATE_KEY=0xb6b15c8cb491557369f3c7d2c287b053eb229daa9c22138887752191c9520659

Start the development server:

yarn run dev

The app will be available at http://localhost:3000/balanceChecker.

Checkpoint 2: 💫 Explore the Features

Balance Checker

Purpose: Prove that a user's balance exceeds a specified threshold (e.g., ≥ 1000 wei) without revealing the exact balance amount.
Circuit Logic: The BalanceChecker.circom circuit takes a private input (user's balance) and a public input (threshold balance). It performs a comparison to check if balance >= threshold and outputs a proof if the condition is satisfied.
On-Chain Verification: The generated proof is submitted to BalanceChecker.sol deployed on the Arbitrum Stylus dev node. The contract uses the embedded Groth16 verification key to validate the proof against the public threshold, returning true if the user's balance meets or exceeds the threshold, all while keeping the balance private.

Balance Checker Interface Balance verification interface and process flow

Checkpoint 3: 🛠 Modify and Deploy Contracts

You can tinker with circuit logic by modifying files in the packages/circuits folder. After making changes, regenerate contracts using these commands:

circom BalanceChecker.circom --r1cs --wasm --sym
npx snarkjs groth16 setup BalanceChecker.r1cs pot12_final.ptau BalanceChecker_0000.zkey
npx snarkjs zkey contribute BalanceChecker_0000.zkey BalanceChecker_final.zkey --name="Contributor" -v
npx snarkjs zkey export verificationkey BalanceChecker_final.zkey verification_key.json
npx snarkjs zkey export solidityverifier BalanceChecker_final.zkey BalanceChecker.sol

Deploy new contracts by placing them in packages/cargo-stylus/contracts and running:

bash run-dev-node.sh

🛠️ Debugging Tips

Fixing Line Endings for Shell Scripts on Windows (CRLF Issue)

If you encounter errors like Command not found, convert line endings to LF:

sudo apt install dos2unix
dos2unix run-dev-node.sh
chmod +x run-dev-node.sh

Run the script again:

bash run-dev-node.sh

Checkpoint 4: 🚢 Ship your frontend! 🚁

To deploy your app to Vercel:

vercel

Follow Vercel's instructions to get a public URL.

For production deployment:

vercel --prod

Checkpoint 5: 📜 Contract Verification

You can verify your deployed smart contract using:

cargo stylus verify -e http://127.0.0.1:8547 --deployment-tx "$deployment_tx"

Replace $deployment_tx with your deployment transaction hash.

🚀 Deploying to Arbitrum Sepolia

If you want to deploy your Balance Checker contract to the Arbitrum Sepolia testnet, follow these steps:

Add private key to the .env file in the cargo-stylus folder
```
PRIVATE_KEY=your_private_key_of_your_ethereum_wallet
```
Run the Sepolia Deployment Script
```
cd packages/cargo-stylus/
bash run-sepolia-deploy.sh
```
This will deploy your contract to Arbitrum Sepolia and output the contract address and transaction hash.

If you encounter errors like Command not found, convert line endings to LF:
```
sudo apt install dos2unix
dos2unix run-sepolia-deploy.sh
chmod +x run-sepolia-deploy.sh
```
Configure the Frontend for Sepolia
- Go to the packages/nextjs directory:
```
cd packages/nextjs
cp .env.example .env
```
- Open the .env file and set the following variables:
```
NEXT_PUBLIC_RPC_URL=https://sepolia-rollup.arbitrum.io/rpc
NEXT_PUBLIC_PRIVATE_KEY=your_private_key_of_your_ethereum_wallet
```
  Replace your_private_key_of_your_ethereum_wallet with your actual Ethereum wallet private key (never share this key publicly).
Start the Frontend
```
yarn run dev
```
Your frontend will now connect to the Arbitrum Sepolia network and interact with your deployed contract.

🏁 Next Steps

Explore more challenges or contribute to this project!

🏃 Head to your next challenge here.