On-Chain Document Timestamp

A decentralized application (dApp) that allows users to timestamp documents on the Ethereum blockchain (Sepolia Testnet).

• Client-Side Hashing: Files are hashed in the browser using the Web Crypto API. The file itself never leaves your device.
• Immutable Proof: The SHA-256 hash is registered on-chain with the owner's address and timestamp.
• Verification: Anyone can verify a document's existence and registration details by re-uploading the file or providing its hash.

• Node.js (v18 or later)
• MetaMask browser extension

1. Clone & Install

   git clone <repo-url>
   cd onchain-doc-proof
   npm install
   cd web
   npm install
   cd ..

2. Configure Environment

   • Copy .env.example to .env in the root directory.
   • Fill in your RPC_URL (e.g., from Infura or Alchemy) and PRIVATE_KEY (account to deploy contract).

   cp .env.example .env

3. Deploy Smart Contract

   npx hardhat run scripts/deploy.ts --network sepolia

   Copy the deployed contract address from the output.

4. Configure Frontend

   • Copy web/.env.local.example to web/.env.local.
   • Paste the contract address.

   cd web
   cp .env.local.example .env.local
   # Edit .env.local and set NEXT_PUBLIC_CONTRACT_ADDRESS

5. Run the App

   npm run dev

   Open http://localhost:3000.

1. Open App: Show the "Connect MetaMask" button. Click it and connect your wallet (Sepolia network).
2. Upload: Select a file (e.g., an image or PDF). Show the computed SHA-256 hash appearing instantly.
3. Register: Click "Register On-Chain". Confirm the transaction in MetaMask.
4. Wait: While waiting, explain that only the hash is sent to the chain, preserving privacy.
5. Success: Point out the transaction hash link (or toaster notification).
6. Verify: Refresh the page or go to the "Verify" section.
   • Upload the same file again.
   • Click "Verify".
   • Show the "✅ Document Found" method with your address and timestamp.
   • (Optional) Modify the file slightly, upload, and show it returns "❌ Not Found".

• Privacy: We only store the bytes32 SHA-256 hash. The original file contents are NOT stored on-chain or sent to any server.
• Collisions: We assume SHA-256 creates unique hashes for distinct documents.
• Identity: The "owner" is simply the wallet that sent the transaction. It proves possession of the file at that time, but not necessarily authorship.