Blockchain Hashing Demonstration: A Step-by-Step Guide with Code Examples

As of March 18, 2025, understanding blockchain hashing is key to grasping how this technology ensures data integrity and security. Hashing, a cryptographic cornerstone, transforms variable-length input into fixed-length output, linking blocks in an immutable chain. Authored by cryptostats.xyz, this article provides a hands-on demonstration of blockchain hashing, complete with a step-by-step guide and Python code examples, making it accessible for beginners and enthusiasts alike.

Hashing powers blockchain’s tamper-proof nature—alter one block, and the entire chain’s hashes break, exposing the fraud. Whether you’re exploring Bitcoin’s SHA-256 or Ethereum’s Keccak-256, this guide will walk you through the concept and show you how to simulate it yourself.

What is Blockchain Hashing?

In blockchain, hashing converts data (e.g., transactions) into a unique, fixed-length string called a hash. Each block contains its own hash, the previous block’s hash, and transaction data. This chaining ensures that any change in a block invalidates all subsequent hashes, securing the ledger. Cryptographic hash functions like SHA-256 are fast to compute, irreversible, and collision-resistant—meaning it’s nearly impossible to find two inputs producing the same hash.

Let’s demonstrate this with a simple blockchain of three blocks, then code it in Python to see hashing in action.

Step-by-Step Guide to Blockchain Hashing

1. Create a Block: Define a block with an index, transactions, a timestamp, and the previous block’s hash.
2. Compute the Hash: Use a hash function (e.g., SHA-256) to generate a unique hash from the block’s data.
3. Link Blocks: Include the previous block’s hash in the next block, forming a chain.
4. Test Immutability: Alter a block’s data and observe how subsequent hashes change, breaking the chain.

Code Example: Simulating Blockchain Hashing in Python

Below is a Python script that simulates a basic blockchain with hashing. We’ll use the hashlib library for SHA-256. Copy this code and run it to see how hashes link blocks and detect tampering.

import hashlib
import time
import json

class Block:
    def __init__(self, index, transactions, previous_hash):
        self.index = index
        self.transactions = transactions
        self.timestamp = time.time()
        self.previous_hash = previous_hash
        self.hash = self.calculate_hash()

    def calculate_hash(self):
        # Combine block data into a string and hash it with SHA-256
        block_string = json.dumps({
            "index": self.index,
            "transactions": self.transactions,
            "timestamp": self.timestamp,
            "previous_hash": self.previous_hash
        }, sort_keys=True).encode()
        return hashlib.sha256(block_string).hexdigest()

class Blockchain:
    def __init__(self):
        # Genesis block (first block)
        self.chain = [self.create_genesis_block()]

    def create_genesis_block(self):
        return Block(0, ["Genesis Block"], "0")

    def add_block(self, transactions):
        previous_block = self.chain[-1]
        new_block = Block(len(self.chain), transactions, previous_block.hash)
        self.chain.append(new_block)

    def is_chain_valid(self):
        for i in range(1, len(self.chain)):
            current = self.chain[i]
            previous = self.chain[i - 1]
            # Recalculate hash to verify integrity
            if current.hash != current.calculate_hash():
                return False
            # Check if previous hash matches
            if current.previous_hash != previous.hash:
                return False
        return True

# Demonstration
blockchain = Blockchain()
blockchain.add_block(["Alice pays Bob $50"])
blockchain.add_block(["Bob pays Charlie $20"])

print("Original Blockchain:")
for block in blockchain.chain:
    print(f"Block {block.index}: Hash = {block.hash}, Prev Hash = {block.previous_hash}")

# Tamper with Block 1
blockchain.chain[1].transactions = ["Alice pays Bob $100"]
print("\nAfter Tampering with Block 1:")
for block in blockchain.chain:
    print(f"Block {block.index}: Hash = {block.hash}, Prev Hash = {block.previous_hash}")
print("Is chain valid?", blockchain.is_chain_valid())

        

Output Explanation: The script creates a three-block chain. Initially, all hashes align, and the chain is valid. After tampering with Block 1’s transaction, its hash changes, breaking the link with Block 2—demonstrating blockchain’s immutability.

Why Hashing Matters in Blockchain

Hashing ensures data integrity and security in Web3. In Bitcoin, miners use hashing for Proof-of-Work, solving computational puzzles to validate blocks—a process taking about 10 minutes per block. Ethereum’s Keccak-256 similarly secures transactions. Without hashing, blockchains couldn’t guarantee trustless, tamper-proof records, making it the backbone of decentralized systems.

Conclusion

This demonstration reveals how blockchain hashing creates an unalterable digital ledger—crucial for Web3’s trustless future in 2025. By coding a simple blockchain, you’ve seen firsthand how hashes chain blocks and detect tampering. As cryptostats.xyz continues exploring blockchain tech, try tweaking the code—add more blocks or transactions—and witness hashing’s power yourself.

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