Blockchain FastAPI & UTXO Blockchain Implementation

Overview

This project demonstrates two blockchain implementations:

1. Blockchain FastAPI Implementation - A simple blockchain with FastAPI endpoints for mining blocks, accepting transactions, adding blocks, and fetching the blockchain.
2. UTXO Blockchain Implementation - A blockchain using the Unspent Transaction Output (UTXO) model to handle transactions, including UTXO generation, signing, verification, and processing.

Blockchain FastAPI Implementation

Objective

The goal is to implement FastAPI endpoints to manage blockchain functionalities:

• Mining a new block.
• Accepting new transactions.
• Adding received blocks to the chain.
• Fetching the current blockchain.

Requirements

• Python 3.x
• FastAPI and Uvicorn for serving the application.

Endpoints:

/mine_block

• Method: POST
• Response: Success or error message with mined block data.

/new_transaction

• Accepts transaction data (sender, receiver, amount, input UTXOs, output UTXOs, signature) and adds it to a list of pending transactions.
• Method: POST
• Body:

  {
    "sender": "sender_address",
    "receiver": "receiver_address",
    "amount": 10,
    "input_utxos": ["utxo1", "utxo2"],
    "output_utxos": ["utxo3", "utxo4"],
    "signature": "transaction_signature"
  }

• Response: Success message.

/add_block

• Accepts a block and validates it before appending it to the chain.
• Method: POST
• Body:

  {
    "index": 1,
    "transactions": [{"sender": "sender_address", "receiver": "receiver_address", "amount": 10}],
    "previous_hash": "previous_hash_value",
    "proof": 123456,
    "timestamp": 1638246823
  }

• Response: Success or error message.

/chain

• Returns the current blockchain.
• Method: GET
• Response: List of all blocks in the blockchain.

Blockchain Functions:

• Mining: Mines new blocks via a proof-of-work algorithm.
• Transactions: Adds pending transactions to a mined block.
• Block Validation: Ensures blocks are valid before adding them to the chain.

How to Run:

Install dependencies:

pip install -r requirements.txt
Run the FastAPI app:

uvicorn fastapi:app --reload
Open the browser and go to http://127.0.0.1:8000/docs to interact with the API using Swagger UI.

Example Usage:

• Mine a Block:
  POST /mine_block

• Add a New Transaction:
  POST /new_transaction with transaction data.

• Add a Block:
  POST /add_block with block data.

• Get the Blockchain:
  GET /chain to retrieve the current blockchain.

Code Explanation:

• blockchain.py: Contains the blockchain logic (block creation, mining, transactions).
• fastapi.py: Defines FastAPI endpoints for interacting with the blockchain.

Features and Enhancements:

• Proof-of-Work: Simple proof-of-work where the hash of the proof must start with a "0".
• Transaction Handling: Transactions are added to the chain once mined.
• Block Validation: Ensures blocks are properly linked.

Future Enhancements:

• Consensus Mechanism: Implement a more advanced algorithm for block validation across multiple nodes.
• Blockchain UI: Create an interface to visualize the blockchain.
• Transaction Pool: Manage pending transactions with a more complex system.

UTXO Blockchain Implementation

Objective

The goal of this section is to demonstrate how a blockchain using the Unspent Transaction Output (UTXO) model can be implemented for handling transactions. It provides functionality for creating UTXOs, signing and verifying transactions, and processing transactions between users.

Requirements

• Python 3.8 or higher
• cryptography package for cryptographic operations (can be installed via pip install cryptography)

Features

• UTXO Management

  • Generates UTXOs (Unspent Transaction Outputs) for recipients.
  • Tracks UTXOs in a dictionary (utxo_set).

• Transaction Signing and Verification

  • Creates and signs transactions using elliptic curve cryptography (ECC).
  • Verifies transaction signatures to ensure integrity and authenticity.

• Blockchain Transaction Processing

  • Transfers funds between users, updates the UTXO set, and manages balances.
  • Supports basic transaction flow (spending UTXOs and generating new ones).

• Logging

  • Provides logging for key operations such as UTXO creation, transaction processing, and errors.

How to Use

1. Clone or download the repository.
2. Install the required dependencies using pip install cryptography.
3. Run the main.py script to simulate a blockchain environment with transactions between Alice, Bob, and Charlie.

Example Workflow

1. Alice generates a UTXO with 100 coins and sends 30 coins to Bob.
2. Bob then sends 20 coins to Charlie.
3. The system ensures that Alice and Bob have sufficient funds and creates new UTXOs accordingly.

Code Explanation

utxo.py

• Blockchain Class:
  • Manages the UTXO set and ledger of transactions.
  • Supports methods to generate private/public key pairs (generate_keys), create new UTXOs (create_utxo), sign transactions (sign_transaction), and verify transactions (verify_transaction).
  • The process_transaction method handles the logic for transferring funds, verifying the transaction, and updating the UTXO set.

main.py

• Main Functionality:
  • Demonstrates how the Blockchain class can be used to simulate transactions between Alice, Bob, and Charlie.
  • It first creates an initial UTXO for Alice, then processes transactions between users, printing the UTXO set at each stage.

Sample Output:

Created UTXO: 98e9e6f9e2d47dffed9b77c13ec4fcb48fd8f4ea8f1d40e4b8c5a8273952ba76 for Alice with amount 100
Current UTXO Set:
UTXO: 98e9e6f9e2d47dffed9b77c13ec4fcb48fd8f4ea8f1d40e4b8c5a8273952ba76, Amount: 100, Recipient: Alice

Transaction processed: Alice sent 30 to Bob
Current UTXO Set:
UTXO: 98e9e6f9e2d47dffed9b77c13ec4fcb48fd8f4ea8f1d40e4b8c5a8273952ba76, Amount: 70, Recipient: Alice
UTXO: 1284c11c42380f29f9cde543a2e31f2e3a98842a4a2633d66b4b70f94d6b0f52, Amount: 30, Recipient: Bob

Transaction processed: Bob sent 20 to Charlie
Current UTXO Set:
UTXO: 98e9e6f9e2d47dffed9b77c13ec4fcb48fd8f4ea8f1d40e4b8c5a8273952ba76, Amount: 70, Recipient: Alice
UTXO: 1284c11c42380f29f9cde543a2e31f2e3a98842a4a2633d66b4b70f94d6b0f52, Amount: 10, Recipient: Bob
UTXO: b3f3ac98fca1a50dbf9cf1e0cf30be51b25f62a7b923d1be328c82a6c498e7a9, Amount: 20, Recipient: Charlie

Running the Project

Clone the repository (if you haven’t already):

git clone https://github.com/your-username/utxo-blockchain.git
cd utxo-blockchain
Install dependencies:

pip install -r requirements.txt
Run the script:

python main.py

Future Enhancements

Implement additional blockchain features like block mining, proof-of-work, and block validation. Integrate a peer-to-peer network for decentralized transaction processing. Implement a more complex UTXO management system (e.g., handling change and more granular transaction outputs).