PyChain is a fully functional, decentralized blockchain implementation designed for educational purposes. It features a robust Python backend node, a P2P consensus engine, and a modern Vue.js web wallet.

It demonstrates core blockchain concepts including Proof of Work, RSA Digital Signatures, Distributed Consensus (Longest Chain Rule), and Fault Tolerance.

• Proof of Work (PoW): Dynamic difficulty adjustment to keep block times stable.
• Cryptographic Security: Transactions are signed using RSA-2048 and SHA-256.
• P2P Gossip Protocol: Nodes automatically sync and propagate blocks to peers.
• Deep Validation: Full history replay to prevent "History Rewrite" attacks and double-spending.
• Persistence: The ledger is saved to disk (chain_PORT.json), allowing nodes to survive restarts.

• Modern UI: Built with Vue.js 3 and TailwindCSS (Dark Mode).
• Client-Side Signing: Private keys never leave the browser. Transactions are signed in JS using node-forge.
• Block Explorer: Visual real-time feed of the blockchain state.
• Mining Interface: One-click mining to earn coins directly to your wallet address.

Ensure you have Python 3.8+ installed.

Install the required Python libraries, including Flask, Requests, and Cryptography.

pip install flask requests cryptography flask_cors

To simulate a decentralized network, we will run two separate nodes on the same computer using different ports.

Open a terminal and run:

python chain.py 50000

Open a new terminal window and run:

python chain.py 50001

The nodes will automatically discover each other if you use the provided interact.py or manually register them via the API.

1. Locate the index.html file in your project folder.
2. Open it directly in your browser (Double click) OR serve it via a local server:

   # Optional: Serve via python
   python -m http.server 8000

3. Create Identity: Click "Create New" to generate your Public/Private key pair.
4. Get Coins (Mining):
   • Click the "Mine (Earn)" button.
   • The web client sends a request to the node to mine a block and sets your address as the reward recipient.
   • Wait a few seconds... Balance Updated!
5. Send Coins:
   • Open index.html in a second tab (or Incognito window).
   • Create a second wallet.
   • Copy the second wallet's address.
   • Go back to the first wallet, click "Send", paste the address, and confirm.

You can use the included interact.py script to simulate a full lifecycle (Funding, Transaction, Consensus) automatically.

1. Ensure Node A (50000) and Node B (50001) are running.
2. Run the script:

python interact.py

What happens:

1. Registers Node B with Node A.
2. Generates wallets for Alice and Bob.
3. Mines a block to fund Alice.
4. Alice cryptographically signs a transaction to Bob.
5. Node A mines the block.
6. Node B automatically syncs and validates the transaction.

├── chain.py             # The Core Blockchain Node (Flask API + Logic)
├── index.html           # The Web Wallet & Explorer (Vue.js + Tailwind)
├── interact.py          # Python automation script for testing
├── chain_50000.json     # (Generated) Ledger storage for Node A
└── chain_50001.json     # (Generated) Ledger storage for Node B

"Invalid Reward Amount" Error: If Node B refuses to sync with Node A, it might be due to a strict validation rule on the "Genesis Hack".

• Fix: Ensure you have cleaned up old JSON files (rm chain_*.json) and restarted both nodes simultaneously before testing.

Web Wallet not connecting:

• Fix: Ensure you installed flask_cors and added CORS(app) to your robust_chain.py. Browsers block requests to localhost ports unless CORS is enabled.

This project is open-source and available under the MIT License. Created for educational purposes.