A complete blockchain implementation in Java featuring cryptocurrency transactions, digital wallets, and proof-of-work mining. This project demonstrates fundamental blockchain concepts including transaction validation, UTXO (Unspent Transaction Output) management, digital signatures, and Merkle trees.

• Blockchain Architecture: Complete blockchain with linked blocks and hash validation
• Cryptocurrency Transactions: Send and receive digital currency between wallets
• Digital Wallets: Secure wallet generation with ECDSA public/private key pairs
• Proof of Work Mining: Configurable difficulty mining with nonce calculation
• Transaction Validation: Digital signature verification and transaction integrity checks
• UTXO Management: Unspent Transaction Output tracking for accurate balance calculation
• Merkle Trees: Transaction hashing for block integrity
• Genesis Block: Initial block with pre-funded wallet for testing

Javachain/
├── src/javachain/
│   ├── javachain.java        # Main class and blockchain logic
│   ├── Block.java            # Block structure and mining
│   ├── Transaction.java      # Transaction processing and validation
│   ├── Wallet.java           # Wallet management and key generation
│   ├── TransactionInput.java # Transaction input handling
│   ├── TransactionOutput.java# Transaction output management
│   └── StringUtil.java       # Cryptographic utilities
├── lib/
│   ├── bcprov-jdk18on-1.81.jar # Bouncy Castle cryptography library
│   └── gson-2.6.2.jar        # JSON serialization library
└── README.md
� README.md

1. Block Class:

   • Contains transaction list, previous block hash, timestamp, and nonce
   • Implements proof-of-work mining algorithm
   • Calculates Merkle root for transaction verification

2. Transaction Class:

   • ECDSA digital signature generation and verification
   • Input/output value validation
   • Transaction processing with UTXO management

3. Wallet Class:

   • ECDSA key pair generation (prime192v1 curve)
   • Balance calculation from UTXOs
   • Transaction creation and signing

4. StringUtil Class:

   • SHA-256 hashing utilities
   • ECDSA signature operations
   • Merkle tree root calculation
   • Base64 encoding for key serialization

• ECDSA Cryptography: Elliptic Curve Digital Signature Algorithm for secure transactions
• SHA-256 Hashing: Cryptographic hashing for block and transaction integrity
• Bouncy Castle Provider: Industry-standard cryptographic library
• Transaction Validation: Multi-layer validation including signature verification and balance checks

• Java Development Kit (JDK) 8 or higher
• Command Line Interface (PowerShell, Command Prompt, or Terminal)

git clone https://github.com/ryukgod26/Javachain.git

cd Javachain

The project includes required JAR files in the lib/ directory:

• bcprov-jdk18on-1.81.jar - Bouncy Castle Cryptography Provider
• gson-2.6.2.jar - Google JSON library

javac -cp "lib/*" src/javachain/*.java

java -cp ".;lib/*" src.javachain.javachain

For Linux/Mac users, use colon separator:

java -cp ".:lib/*" src.javachain.javachain

The main class demonstrates:

1. Creating wallets with cryptographic key pairs
2. Genesis transaction with initial funding
3. Mining blocks with proof-of-work
4. Transaction processing between wallets
5. Blockchain validation

Creating and Mining genesis Block...
Transaction Successfully added to the Block.
Block Mined ....000a1b2c3d4e5f6789abcdef...
The Balance of Wallet1 is: 100.0
Wallet1 is Sending 10 coins to Wallet2.
Transaction Successfully added to the Block.
Block Mined ....000f1e2d3c4b5a6978563412...
The Balance of Wallet1 is: 90.0
The Balance of Wallet2 is: 10.0
Blockchain is Valid.
The Blockchain is Correct and Working Perfectly.
erfectly.

Mining Difficulty: Adjust in javachain.java

public static int difficulty = 3; // Number of leading zeros required

Minimum Transaction Value:

public static float minimumTransactionValue = 0.1f;

The project includes comprehensive validation:

• Hash Integrity: Verifies block hash calculations
• Chain Validation: Ensures proper block linking
• Transaction Verification: Validates digital signatures
• UTXO Consistency: Checks input/output balance
• Mining Validation: Confirms proof-of-work compliance

1. Blockchain Structure: Linked list of blocks with cryptographic hashes
2. Mining Process: Proof-of-work algorithm finding hash with leading zeros
3. Digital Signatures: ECDSA signing/verification for transaction authenticity
4. UTXO Model: Bitcoin-style unspent transaction output tracking
5. Merkle Trees: Efficient transaction verification structure

• Elliptic Curve: prime192v1 curve for key generation
• Hash Function: SHA-256 for all hashing operations
• Signature Algorithm: ECDSA with Bouncy Castle provider
• Encoding: Base64 for key serialization

• Modify transaction fees in Transaction.java
• Implement different mining algorithms in Block.java
• Add transaction types in the main blockchain logic
• Extend wallet functionality for multi-signature support

• Create multiple blockchain instances
• Implement consensus mechanisms
• Add peer-to-peer communication

This project demonstrates:

• Blockchain fundamentals and cryptocurrency mechanics
• Cryptographic implementations in Java
• Object-oriented design for complex systems
• Security considerations in distributed systems
• Data structures and algorithms in blockchain context

1. Fork the repository
2. Create a feature branch
3. Implement your changes
4. Add comprehensive tests
5. Submit a pull request

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

• Bitcoin Whitepaper
• Bouncy Castle Cryptography
• ECDSA Algorithm
• Merkle Trees

ryukgod26

• GitHub: @ryukgod26

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