📄 Document Hash Verifier

A blockchain-based document verification system built with Next.js and Solana. This application allows you to generate cryptographic hashes of documents and store them immutably on the Solana blockchain for future verification.

🎥 Watch the Build Session

Watch the full coding session where this project was built from scratch:

▶️ Watch on YouTube: Building a Document Verifier on Solana Blockchain

🌟 Features

• 📤 Document Upload: Drag-and-drop or browse to upload documents (PDF, PNG, JPG, DOCX)
• 🔐 SHA-256 Hashing: Generates cryptographically secure hashes of your documents
• ⛓️ Blockchain Storage: Stores document hashes on Solana for immutable record-keeping
• ✅ Document Verification: Verify document authenticity against blockchain records
• 🎨 Modern UI: Beautiful, responsive interface built with Tailwind CSS
• ⚡ Real-time Feedback: Loading states, success/error messages, and visual feedback

🎯 Use Cases

• Educational Credentials: Verify authenticity of degrees and certificates
• Legal Documents: Ensure contracts haven't been tampered with
• Medical Records: Verify integrity of patient records
• Intellectual Property: Timestamp and prove ownership of documents
• Supply Chain: Authenticate product documentation

🚀 Getting Started

Prerequisites

• Node.js (v18 or higher)
• npm or yarn
• Solana CLI (for local development)

Installation

1. Clone the repository

git clone <your-repo-url>
cd document-verifier

2. Install dependencies

npm install

3. Install Solana CLI (if not already installed)

For macOS (using Homebrew):

brew install solana

For Linux/macOS (using official installer):

sh -c "$(curl -sSfL https://release.solana.com/stable/install)"

4. Start the local Solana test validator

solana-test-validator

Keep this running in a separate terminal window.

5. Start the development server

npm run dev

6. Open your browser Navigate to http://localhost:3000

📖 How to Use

Storing a Document Hash

1. Upload Your Document
   • Drag and drop a file or click to browse
   • Supported formats: PDF, PNG, JPG, DOCX (max 10MB)

2. Generate Hash

   • The application automatically generates a SHA-256 hash of your document

3. Store on Blockchain

   • Click "Store on Solana" to save the hash to the blockchain
   • You'll receive an account address and transaction signature

4. Save the Account Address
   • Copy and save the account address - you'll need it to verify the document later

Verifying a Document

1. Navigate to Verification Page
   • Click "Verify a Document" from the home page

2. Upload Document to Verify

   • Upload the document you want to verify

3. Enter Account Address

   • Paste the account address you received when storing the hash

4. Verify

   • Click "Verify Document"
   • The system will compare the document's hash with the blockchain record
   • ✅ Match: Document is authentic and unchanged
   • ❌ Mismatch: Document has been modified or is not the original

🏗️ Architecture

Tech Stack

• Frontend: Next.js 14 (App Router), React, TypeScript
• Styling: Tailwind CSS
• Blockchain: Solana (@solana/web3.js)
• Hashing: Node.js crypto module (SHA-256)
• File Upload: Multer

Project Structure

document-verifier/
├── app/
│   ├── api/
│   │   ├── upload/          # File upload & hash generation
│   │   ├── store/           # Store hash on Solana
│   │   └── verify/          # Verify document against blockchain
│   ├── verify/              # Verification page
│   └── page.tsx             # Home page
├── components/
│   ├── FileUpload.tsx       # Drag-and-drop file upload
│   ├── HashDisplay.tsx      # Display generated hash
│   ├── StoreButton.tsx      # Store hash on blockchain
│   └── VerifyResult.tsx     # Display verification results
├── lib/
│   ├── hash.ts              # SHA-256 hashing utilities
│   └── solana.ts            # Solana blockchain interactions
└── public/
    └── screenshots/         # Application screenshots

🔧 Configuration

Solana Network

By default, the application connects to http://localhost:8899 (local test validator).

To change the network, update the connection in lib/solana.ts:

const SOLANA_RPC_URL =
  process.env.NEXT_PUBLIC_SOLANA_RPC_URL || "http://localhost:8899";

File Upload Limits

• Max file size: 10MB
• Supported formats: PDF, PNG, JPG, DOCX

To modify these limits, update components/FileUpload.tsx and app/api/upload/route.ts.

🛡️ Security Considerations

For Production Use

This demo application uses a keypair for signing transactions. For production, consider:

1. Wallet Integration: Use Solana wallet adapters (Phantom, Solflare, etc.)
2. Network Security: Use Solana mainnet or devnet
3. API Security: Add authentication and rate limiting
4. Input Validation: Enhanced file type and content validation
5. HTTPS: Use secure connections
6. Audit: Security audit of smart contracts

Current Demo Setup

• Uses local Solana test validator
• Keypair-based transaction signing
• File-based hash storage (for demo persistence)
• No authentication or user accounts

🔍 How It Works

1. Hash Generation: When a document is uploaded, the server generates a SHA-256 hash of its contents. This creates a unique "fingerprint" of the document.

2. Blockchain Storage: The hash is stored in a new Solana account. The account address serves as a unique identifier for this document record.

3. Verification: To verify a document, the system:

   • Generates the hash of the uploaded document
   • Retrieves the stored hash from the blockchain using the account address
   • Compares the two hashes
   • Returns whether they match (authentic) or not (tampered/different document)

4. Immutability: Once stored on the blockchain, the hash cannot be modified or deleted, providing a permanent, tamper-proof record.

📝 API Endpoints

POST /api/upload

Upload a file and generate its SHA-256 hash.

Request: multipart/form-data with file

Response:

{
  "hash": "2fd852b8ec18dbb491c38a0ce3cdb0a45311d67d1f7b942db41a85bdb80b6604"
}

POST /api/store

Store a hash on the Solana blockchain.

Request:

{
  "hash": "2fd852b8ec18dbb491c38a0ce3cdb0a45311d67d1f7b942db41a85bdb80b6604"
}

Response:

{
  "account": "9YG6W486MfYBHAYvvCPadp3SamX5LMFPYKRYnKSeqphv",
  "signature": "5az4V6cqyBcUEWaAoKG2AG2PGe3BMeqbeq2ic9E3sqW7..."
}

POST /api/verify

Verify a document against a stored hash.

Request: multipart/form-data with file and accountAddress

Response:

{
  "match": true,
  "message": "Document is authentic",
  "hash": "2fd852b8ec18dbb491c38a0ce3cdb0a45311d67d1f7b942db41a85bdb80b6604",
  "accountAddress": "9YG6W486MfYBHAYvvCPadp3SamX5LMFPYKRYnKSeqphv"
}

🧪 Development

Running Tests

npm test

Building for Production

npm run build
npm start

Linting

npm run lint

🤝 Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

📜 License

This project is open source and available under the MIT License.

🔗 Resources

• Solana Documentation
• Next.js Documentation
• SHA-256 Hash Function
• Web3.js Documentation

💡 Future Enhancements

• Wallet adapter integration (Phantom, Solflare)
• Batch document verification
• Document history tracking
• Email notifications
• API key management
• Advanced analytics dashboard
• Mobile app version
• Multi-language support

🐛 Troubleshooting

Solana validator not starting

# Reset the validator
solana-test-validator --reset

"Failed to generate hash" error

• Ensure file size is under 10MB
• Check file format is supported
• Verify Node.js version is 18+

"Failed to store hash" error

• Ensure Solana test validator is running
• Check connection to localhost:8899
• Verify sufficient SOL in the keypair account

📞 Support

For issues, questions, or suggestions, please open an issue on GitHub.

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Built with ❤️ using Next.js and Solana