Blockchain with Python

In this Colab notebook, the intention is to develop a simple Blockchain with Python, to understand how a Block is created, how a chain works and the importance of the hash within the Blockchain. I made comments almost in each line of code to be understandable to everybody.

We're going to use Colab for the development of the code in Python and Postman to get some request we're going to send from Colab with Flask.

• For more information about Postman: https://www.postman.com/
• For more information about Flask: https://flask.palletsprojects.com/en/2.2.x/

The project is divided in 3 steps:

1. Build the Blockchain.
2. Mine the Blockchain to let the new blocks be added.
3. Run the app to recieve the results.

1. Build the Blockchain.

Each Block is going to have the next attributes:

     block = {'index': len(self.chain) + 1,
              'timestamp': str(datetime.datetime.now()), 
              'proof': proof,
              'previous_hash': previous_hash} 

Where:

• Index: The number of the block.
• Time Stamp: The moment of the creation of the block.
• Proof: We're going to use Proof of Work (PoW) to mine the block.
• Previous Hash: The hash of the last block.

IMPORTANT

What is Proof of Work?

Proof of work (PoW) is a decentralized consensus mechanism that requires members of a network to expend effort solving an arbitrary mathematical puzzle to prevent anybody from gaming the system.

What is the SHA-256 Algorithm

SHA-2 (Secure Hash Algorithm 2), of which SHA-256 is a part, is one of the most popular hash algorithms around. A cryptographic hash, also often referred to as a “digest”, “fingerprint” or “signature”, is an almost perfectly unique string of characters that is generated from a separate piece of input text. SHA-256 generates a 256-bit (32-byte) signature.

To generate the hash of each block, we're going to use "hashlib"

     new_proof = 1                                        
     check_proof = False                                   
     while check_proof is False:
         hash_operation = hashlib.sha256(str(new_proof**2 - previous_proof**2).encode()).hexdigest()
         if hash_operation[:4] == '0000':                 
           check_proof = True
         else:
             new_proof +=1
     return new_proof

For more information about haslib for Python: https://docs.python.org/3/library/hashlib.html

2. Mine the Blockchain.

In this part, we're going to assume that a miner is mining a Block to be added to the chain, getting the next result to be received to the miner

response = {'message': 'You just have mined succesfully a block!',   
               'index': block['index'],
               'timestamp': block['timestamp'],
               'proof': block['proof'],
               'previous_hash': block['previous_hash']}

3. Run the app to recieve the results.

We created: @app.route('/mine_block', methods = ['GET'])

To get the response when mining a Block.

@app.route('/get_chain', methods = ['GET'])

To get the response of the chain with the Blocks added previusly.

After mining several Blocks, you will get in Postman a chain like this with all the results:

   "chain": [
       {
           "index": 1,
           "previous_hash": "0",
           "proof": 1,
           "timestamp": "2022-10-18 12:29:09.048680"
       },
       {
           "index": 2,
           "previous_hash": "e85fc637a138b6575be5344322b9d666f2c4a226e2624fe4bc785a1d5e32fdd5",
           "proof": 533,
           "timestamp": "2022-10-18 12:33:57.577925"
       },
       {
           "index": 3,
           "previous_hash": "151701b6081645981c9af67bb26c0e4eb4637aea2cbc3842e22a2455d6e0453b",
           "proof": 45293,
           "timestamp": "2022-10-18 12:36:32.438224"
       },
       {
           "index": 4,
           "previous_hash": "66382bbab5cbe1df77526584a375a2b1f9315682b0ec40219b6964ae2360f0d3",
           "proof": 21391,
           "timestamp": "2022-10-18 12:36:33.290545"
       },
       {
           "index": 5,
           "previous_hash": "018d8254386a167a1b43977014fbae76e00364171faec9c757ce2544034b8a16",
           "proof": 8018,
           "timestamp": "2022-10-18 12:36:34.032219"
       },
       {
           "index": 6,
           "previous_hash": "837e23c14624306641bc4ae3913be55800ca25c0b7569b9ce9c29b9e8c04621c",
           "proof": 48191,
           "timestamp": "2022-10-18 12:36:34.994703"
       },
       {
           "index": 7,
           "previous_hash": "a8859d00f5269bb96af721c66c2fd46cdeef51b693f9025a3ce939ae82d1fbf9",
           "proof": 19865,
           "timestamp": "2022-10-18 12:36:35.658929"
       }
   ],
   "length": 7
}

Hope you enjoy it! 😃