FHE Rock Paper Scissors Demo

A demonstration of Zama's Fully Homomorphic Encryption (FHEVM) using a simple Rock Paper Scissors game. Watch your moves get encrypted, computed on-chain while still encrypted, and then decrypted to reveal the winner.

What This Demonstrates

This project shows the complete FHE lifecycle:

1. Client-side encryption - Your move is encrypted in the browser before touching the blockchain
2. On-chain encrypted computation - The smart contract determines the winner without ever seeing the actual moves
3. Async decryption - Results are decrypted only after both players commit
4. Live process tracking - The Game Process Monitor shows every FHE operation in real-time

The game is simple on purpose - Rock Paper Scissors is just a vehicle to demonstrate how FHE works.

Game Process Monitor

The most important feature is the live activity monitor at the bottom of the screen. It shows you:

• When moves are being encrypted
• When zero-knowledge proofs are generated
• When encrypted data is submitted to the blockchain
• When the contract requests decryption
• When results are revealed

This lets you see exactly what's happening with your encrypted data at each step.

How FHE Works Here

Encryption Phase:

• You pick rock, paper, or scissors
• The move is encrypted in your browser using FHEVM
• A zero-knowledge proof is generated to verify the encrypted input is valid
• Both encrypted move and proof are sent to the smart contract

Computation Phase:

• Smart contract receives both encrypted moves
• Contract logic runs: if (move1 beats move2) - but on encrypted data
• Winner is determined without decrypting the moves
• Everything stays encrypted on-chain

Decryption Phase:

• Player requests game resolution
• Contract sends encrypted result to FHEVM oracle
• Oracle decrypts and returns result via callback
• Winner is revealed

The blockchain never sees your actual move until the decryption phase. That's FHE in action.

Try It Yourself

git clone https://github.com/GoJackzi/RockPaperScissors.git
cd RockPaperScissors
npm install --legacy-peer-deps
npm run dev

You'll need:

• Node.js 18+
• MetaMask
• Sepolia testnet ETH

Create .env.local:

NEXT_PUBLIC_FHEVM_RELAYER_URL=https://relayer.testnet.zama.cloud
NEXT_PUBLIC_SEPOLIA_RPC_URL=https://eth-sepolia.g.alchemy.com/v2/YOUR_ALCHEMY_KEY
NEXT_PUBLIC_CONTRACT_ADDRESS=0x19AC891d6d1c91fb835d87Aef919C2F199c0E469
NEXT_PUBLIC_CHAIN_ID=11155111

Play a game and watch the Game Process Monitor to see FHE in action.

Contract Details

• Network: Sepolia Testnet
• Address: 0x19AC891d6d1c91fb835d87Aef919C2F199c0E469
• View on Etherscan: Contract Link

The contract uses Zama's FHEVM library to perform computations on encrypted data (euint8 types for moves, ebool for comparisons).

Tech Stack

• Frontend: Next.js 15, React 19, TypeScript
• Smart Contract: Solidity 0.8.24 with FHEVM
• Encryption: Zama FHEVM v0.8
• Network: Sepolia testnet
• Deployment: Vercel

Learn More

• Zama FHEVM Documentation
• What is Fully Homomorphic Encryption?

License

MIT

---

Built to demonstrate Zama's FHEVM technology