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Create simple Blockchain using Python

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  • Difficulty Level : Medium
  • Last Updated : 03 Jun, 2022

A blockchain is a time-stamped decentralized series of fixed records that contains data of any size is controlled by a large network of computers that are scattered around the globe and not owned by a single organization. Every block is secured and connected with each other using hashing technology which protects it from being tampered by an unauthorized person. 

Creating Blockchain using Python, mining new blocks, and displaying the whole blockchain: 

  • The data will be stored in JSON format which is very easy to implement and easy to read. The data is stored in a block and the block contains multiple data. Each and every minute multiple blocks are added and to differentiate one from the other we will use fingerprinting.
  • The fingerprinting is done by using hash and to be particular we will use the SHA256 hashing algorithm. Every block will contain its own hash and also the hash of the previous function so that it cannot get tampered with.
  • This fingerprinting will be used to chain the blocks together. Every block will be attached to the previous block having its hash and to the next block by giving its hash.
  • The mining of the new block is done by giving successfully finding the answer to the proof of work. To make mining hard the proof of work must be hard enough to get exploited.
  • After mining the block successfully the block will then be added to the chain.
  • After mining several blocks the validity of the chain must be checked in order to prevent any kind of tampering with the blockchain.
  • Then the web app will be made by using Flask and deployed locally or publicly as per the need of the user.

Python3




# Python program to create Blockchain
 
# For timestamp
import datetime
 
# Calculating the hash
# in order to add digital
# fingerprints to the blocks
import hashlib
 
# To store data
# in our blockchain
import JSON
 
# Flask is for creating the web
# app and jsonify is for
# displaying the blockchain
from flask import Flask, jsonify
 
 
class Blockchain:
   
    # This function is created
    # to create the very first
    # block and set its hash to "0"
    def __init__(self):
        self.chain = []
        self.create_block(proof=1, previous_hash='0')
 
    # This function is created
    # to add further blocks
    # into the chain
    def create_block(self, proof, previous_hash):
        block = {'index': len(self.chain) + 1,
                 'timestamp': str(datetime.datetime.now()),
                 'proof': proof,
                 'previous_hash': previous_hash}
        self.chain.append(block)
        return block
       
    # This function is created
    # to display the previous block
    def print_previous_block(self):
        return self.chain[-1]
       
    # This is the function for proof of work
    # and used to successfully mine the block
    def proof_of_work(self, previous_proof):
        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[:5] == '00000':
                check_proof = True
            else:
                new_proof += 1
                 
        return new_proof
 
    def hash(self, block):
        encoded_block = json.dumps(block, sort_keys=True).encode()
        return hashlib.sha256(encoded_block).hexdigest()
 
    def chain_valid(self, chain):
        previous_block = chain[0]
        block_index = 1
         
        while block_index < len(chain):
            block = chain[block_index]
            if block['previous_hash'] != self.hash(previous_block):
                return False
               
            previous_proof = previous_block['proof']
            proof = block['proof']
            hash_operation = hashlib.sha256(
                str(proof**2 - previous_proof**2).encode()).hexdigest()
             
            if hash_operation[:5] != '00000':
                return False
            previous_block = block
            block_index += 1
         
        return True
 
 
# Creating the Web
# App using flask
app = Flask(__name__)
 
# Create the object
# of the class blockchain
blockchain = Blockchain()
 
# Mining a new block
@app.route('/mine_block', methods=['GET'])
def mine_block():
    previous_block = blockchain.print_previous_block()
    previous_proof = previous_block['proof']
    proof = blockchain.proof_of_work(previous_proof)
    previous_hash = blockchain.hash(previous_block)
    block = blockchain.create_block(proof, previous_hash)
     
    response = {'message': 'A block is MINED',
                'index': block['index'],
                'timestamp': block['timestamp'],
                'proof': block['proof'],
                'previous_hash': block['previous_hash']}
     
    return jsonify(response), 200
 
# Display blockchain in json format
@app.route('/get_chain', methods=['GET'])
def display_chain():
    response = {'chain': blockchain.chain,
                'length': len(blockchain.chain)}
    return jsonify(response), 200
 
# Check validity of blockchain
@app.route('/valid', methods=['GET'])
def valid():
    valid = blockchain.chain_valid(blockchain.chain)
     
    if valid:
        response = {'message': 'The Blockchain is valid.'}
    else:
        response = {'message': 'The Blockchain is not valid.'}
    return jsonify(response), 200
 
 
# Run the flask server locally
app.run(host='127.0.0.1', port=5000)


Output (mine_block):

{
"index":2,
"message":"A block is MINED",
"previous_hash":"2d83a826f87415edb31b7e12b35949b9dbf702aee7e383cbab119456847b957c",
"proof":533,
"timestamp":"2020-06-01 22:47:59.309000"
}

Output (get_chain):

{
"chain":[{"index":1,
"previous_hash":"0",
"proof":1,
"timestamp":"2020-06-01 22:47:05.915000"},{"index":2,
"previous_hash":"2d83a826f87415edb31b7e12b35949b9dbf702aee7e383cbab119456847b957c",
"proof":533,
"timestamp":"2020-06-01 22:47:59.309000"}],
"length":2
}

Output(valid):

{"message":"The Blockchain is valid."}


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