BlockChain Java Implementation

A comprehensive blockchain implementation written in Java, featuring a complete cryptocurrency system with mining, transactions, and network functionality.

🚀 Features

• Complete Blockchain Architecture: Implements a full blockchain with blocks, transactions, and proof-of-work mining
• Cryptocurrency System: Digital currency with wallet management and transaction processing
• Mining Algorithm: Proof-of-work consensus mechanism with adjustable difficulty
• Network Simulation: Multi-user network environment with concurrent mining
• Cryptographic Security: RSA encryption for transaction signatures and SHA-256 for block hashing
• Transaction Validation: Comprehensive validation system to prevent fraud and double-spending
• User Management: Multi-user support with unique key pairs and wallets

📁 Project Structure

BlockChain_Java/
├── Main.java                 # Entry point and simulation runner
├── blockpack/
│   └── Block.java            # Block structure and implementation
├── transactionspack/
│   ├── Transaction.java      # Transaction class with digital signatures
│   └── TransactionData.java  # Transaction data structure
├── userpack/
│   └── User.java            # User class with wallet and mining functionality
├── cryptographypack/
│   └── CRYPTO.java          # Cryptographic utilities (RSA, SHA-256)
└── net/
    └── Network.java         # Network management and blockchain consensus

🛠️ Core Components

Block (blockpack/Block.java)

• Contains transaction data, previous block hash, and nonce
• Immutable structure ensuring blockchain integrity
• Support for genesis block creation

Transaction (transactionspack/)

• Transaction.java: Digital signatures using RSA encryption
• TransactionData.java: Core transaction information (sender, receiver, amount)
• Reference-based system for tracking coin ownership

User (userpack/User.java)

• Wallet Management: Tracks coin ownership through transaction references
• Mining Capability: Built-in miner with proof-of-work algorithm
• Transaction Creation: Send coins to other users with miner rewards
• Key Management: RSA key pair generation and management

Cryptography (cryptographypack/CRYPTO.java)

• RSA Encryption: For transaction signatures and verification
• SHA-256 Hashing: For block hash generation and proof-of-work
• Key Generation: Secure key pair creation for users

Network (net/Network.java)

• Blockchain Management: Maintains the complete blockchain
• Transaction Pool: Manages pending transactions
• Consensus: Validates and adds new blocks to the chain
• Multi-user Support: Handles multiple concurrent users and miners

🚀 Getting Started

Prerequisites

• Java 8 or higher
• No external dependencies required (uses only Java standard library)

Running the Application

1. Clone the repository:

   git clone <repository-url>
   cd BlockChain_Java

2. Compile the project:

   javac *.java */*.java

3. Run the simulation:

   java Main

Example Usage

The Main.java file contains a comprehensive simulation that demonstrates:

• Creating multiple users (PEPPE, MARCO, COLA, etc.)
• Mining new blocks
• Performing transactions between users
• Demonstrating fraud detection (BadUser example)
• Network consensus and validation

💡 Key Features Demonstrated

Mining System

• Users can start/stop mining at any time
• Proof-of-work algorithm with adjustable difficulty
• Miners receive rewards for successfully mining blocks
• Concurrent mining support

Transaction System

• Send coins between users with transaction fees
• Reference-based coin tracking (no double-spending)
• Digital signature verification
• Automatic change calculation

Security Features

• Fraud Detection: Invalid transactions are rejected
• Digital Signatures: All transactions are cryptographically signed
• Chain Validation: Each block references the previous block's hash
• Double-spending Prevention: Reference-based transaction validation

🔧 Technical Details

Mining Algorithm

• Uses SHA-256 proof-of-work
• Difficulty adjustable via leading zeros requirement
• Nonce-based mining with incremental search

Transaction Validation

1. Verify digital signature
2. Check transaction references
3. Validate sufficient funds
4. Prevent double-spending

Network Consensus

• First valid block wins
• Invalid transactions are rejected
• Automatic network synchronization

🎯 Use Cases

This implementation serves as:

• Educational Tool: Learn blockchain and cryptocurrency concepts
• Research Platform: Experiment with consensus algorithms
• Proof of Concept: Demonstrate blockchain functionality
• Development Base: Foundation for more complex blockchain projects

🐛 Known Limitations

• Single-threaded validation (could be optimized)
• In-memory storage only (no persistence)
• Simple network simulation (not real P2P networking)
• Fixed block size and transaction limits

🤝 Contributing

Feel free to submit issues, feature requests, or pull requests to improve this blockchain implementation.

📄 License

This project is open source. Please check the repository for specific license information.

👥 Authors

• Fausto Zamparelli

🔗 Additional Notes

This implementation focuses on educational value and demonstrates core blockchain concepts including:

• Cryptographic hashing and digital signatures
• Proof-of-work consensus
• Transaction validation and wallet management
• Network simulation and multi-user interaction

For production use, consider additional features like:

• Persistent storage
• Real network protocols
• Advanced consensus mechanisms
• Enhanced security measures