Create a Simple Blockchain Using Python

Blockchain is a decentralized, time-stamped series of immutable records that store data of any size. Controlled by a global network of computers—rather than a single entity—each block is secured and linked via cryptographic hashing, preventing unauthorized tampering.

Building a Blockchain with Python

Here’s how to create a blockchain in Python, mine new blocks, and display the entire chain:

Key Components

1. Data Storage

   • Data is stored in JSON format for readability and ease of implementation.
   • Each block contains multiple data points, differentiated by unique fingerprints (hashes).

2. Hashing Algorithm

   • The SHA256 algorithm generates fingerprints (hashes) for each block.

   • Every block stores:

     • Its own hash.
     • The hash of the previous block (ensuring tamper-proof chaining).

3. Blockchain Structure

   • Blocks are "chained" by referencing the previous block’s hash.

   • Example block structure:

     {
       "index": 2,
       "previous_hash": "734dd03fe5...",
       "proof": 632238,
       "timestamp": "2020-06-01 22:47:59.309000"
     }

4. Mining New Blocks

   • Mining involves solving a proof-of-work puzzle (computationally difficult problem).
   • Successfully mined blocks are added to the chain after validation.

5. Chain Validation

   • Regular checks ensure no tampering occurs (e.g., validating hashes and proof-of-work).

6. Web App Deployment

   • Use Flask to deploy the blockchain locally or publicly.

Example Outputs

• Mined Block:

  {
    "index": 2,
    "message": "A block is MINED",
    "previous_hash": "734dd03fe5...",
    "proof": 632238,
    "timestamp": "2020-06-01 22:47:59.309000"
  }

• Full Chain:

  {
    "chain": [
      {"index": 1, "previous_hash": "0", "proof": 1, "timestamp": "2020-06-01 22:47:05.915000"},
      {"index": 2, "previous_hash": "734dd03fe5...", "proof": 632238, "timestamp": "2020-06-01 22:47:59.309000"}
    ],
    "length": 2
  }

• Validation:

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

Step-by-Step Implementation

1. Import Libraries:

   • Use hashlib for cryptographic hashing and Flask for the web interface.

2. Blockchain Class:

   • Initialize the chain and genesis block (first block).

3. Mining:

   • Solve proof-of-work to add new blocks.

   • Example mining function:

     def mine_block(self):
         previous_block = self.chain[-1]
         previous_proof = previous_block['proof']
         proof = self.proof_of_work(previous_proof)
         previous_hash = self.hash(previous_block)
         block = self.create_block(proof, previous_hash)
         return block

4. Proof of Work:

   • Adjust difficulty to control mining speed (e.g., find a hash starting with 0000).

5. Validation:

   • Check block hashes and proof-of-work consistency.

6. Web App (Flask):

   • Endpoints to:

     • Mine blocks (/mine_block).
     • Display the full chain (/get_chain).
     • Validate the chain (/valid).

👉 Learn more about blockchain technology

FAQs

Q1: Why use SHA256 for hashing?
A1: SHA256 is cryptographically secure, ensuring block integrity and tamper resistance.

Q2: What’s the role of proof-of-work?
A2: It prevents spam and ensures blocks are added at a controlled rate.

Q3: Can I deploy this on a live network?
A3: Yes! Use Flask’s public deployment options (e.g., ngrok or cloud hosting).

Final Notes

• Expand the chain by increasing proof-of-work difficulty.
• Integrate smart contracts for advanced use cases.

👉 Explore blockchain development further