Python/blockchain/pow_algorithm.py

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"""
# Title: Proof of Work Algorithm for Blockchain
## Algorithm Statement:
The algorithm implements the Proof of Work (PoW) consensus mechanism used in
blockchain to validate blocks. PoW ensures participants (miners) perform a
computational task to create a valid block and add it to the blockchain. The
difficulty is defined by the number of leading zeros required in the block hash.
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"""
import hashlib
import time
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class Block:
def __init__(self, index, previous_hash, transactions, timestamp, difficulty):
self.index = index
self.previous_hash = previous_hash
self.transactions = transactions
self.timestamp = timestamp
self.nonce = 0 # Start with nonce 0
self.difficulty = difficulty
self.hash = self.compute_hash()
def compute_hash(self):
"""
Generates the hash of the block content.
Combines index, previous hash, transactions, timestamp, and nonce into a string,
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which is then hashed using SHA-256.
"""
block_string = (
f"{self.index}{self.previous_hash}{self.transactions}{self.timestamp}"
f"{self.nonce}"
)
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return hashlib.sha256(block_string.encode()).hexdigest()
def mine_block(self):
"""
Performs Proof of Work by adjusting the nonce until a valid hash is found.
A valid hash has the required number of leading zeros based on the difficulty
level.
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"""
target = (
"0" * self.difficulty
) # Target hash should start with 'difficulty' zeros
while self.hash[: self.difficulty] != target:
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self.nonce += 1
self.hash = self.compute_hash()
print(f"Block mined with nonce {self.nonce}, hash: {self.hash}")
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class Blockchain:
def __init__(self, difficulty):
self.chain = []
self.difficulty = difficulty
self.create_genesis_block()
def create_genesis_block(self):
"""
Creates the first block in the blockchain (the Genesis block).
"""
genesis_block = Block(0, "0", "Genesis Block", time.time(), self.difficulty)
genesis_block.mine_block()
self.chain.append(genesis_block)
def add_block(self, transactions):
"""
Adds a new block to the blockchain after performing Proof of Work.
"""
previous_block = self.chain[-1]
new_block = Block(
len(self.chain),
previous_block.hash,
transactions,
time.time(),
self.difficulty,
)
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new_block.mine_block()
self.chain.append(new_block)
def is_chain_valid(self):
"""
Verifies the integrity of the blockchain by ensuring each block's previous
hash matches and that all blocks meet the Proof of Work requirement.
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"""
for i in range(1, len(self.chain)):
current_block = self.chain[i]
previous_block = self.chain[i - 1]
if current_block.hash != current_block.compute_hash():
print(f"Invalid block at index {i}. Hash mismatch.")
return False
if current_block.previous_hash != previous_block.hash:
print(f"Invalid chain at index {i}. Previous hash mismatch.")
return False
return True
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# Test cases
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def test_blockchain():
"""
Test cases for the Blockchain proof of work algorithm.
"""
# Create blockchain with difficulty level of 4 (hash should start with 4 zeros)
blockchain = Blockchain(difficulty=4)
# Add new blocks
blockchain.add_block("Transaction 1: Alice pays Bob 5 BTC")
blockchain.add_block("Transaction 2: Bob pays Charlie 3 BTC")
# Verify the integrity of the blockchain
assert blockchain.is_chain_valid(), "Blockchain should be valid"
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# Tamper with the blockchain and check validation
blockchain.chain[
1
].transactions = "Transaction 1: Alice pays Bob 50 BTC" # Tampering
assert (
not blockchain.is_chain_valid()
), "Blockchain should be invalid due to tampering"
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print("All test cases passed.")
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if __name__ == "__main__":
test_blockchain()
"""
# Output:
- Block mined with nonce X, hash: 0000abcd...
- Block mined with nonce Y, hash: 0000xyz...
- Block mined with nonce Z, hash: 0000pqrs...
- All test cases passed.
"""