blockchain: implement simple_proof_of_work.py

Author: mapaba79

blockchain/simple_proof_of_work.py

@@ -0,0 +1,62 @@
+"""
+Proof of Work (PoW) implementation.
+This algorithm is used in blockchain technology
+to reach consensus and secure the network
+"""
+
+import hashlib
+
+
+def proof_of_work(
+    block_number: int, transactions: str, previous_hash: str, difficulty: int
+) -> tuple[int, str]:
+    """
+    Finds a nonce such that the SHA-256 hash of the block starts with
+    a specific number of zeros (difficulty).
+
+    >>> proof_of_work(1, "test", "abc", 1)[1].startswith("0")
+    True
+    >>> # Consistency check: same input must produce same output
+    >>> res1 = proof_of_work(1, "data", "hash", 2)
+    >>> res2 = proof_of_work(1, "data", "hash", 2)
+    >>> res1 == res2
+    True
+    >>> # Difficulty 0 should return nonce 0 immediately
+    >>> proof_of_work(1, "data", "hash", 0)[0]
+    0
+    """
+    if difficulty < 0:
+        raise ValueError("difficulty must be a non-negative integer")
+
+    prefix = "0" * difficulty
+    nonce = 0
+
+    while True:
+        # Create a single string representing all block data
+        text = f"{block_number}{transactions}{previous_hash}{nonce}"
+
+        # Calculate the SHA-256 hash
+        current_hash = hashlib.sha256(text.encode()).hexdigest()
+
+        # Check if the hash meets the difficulty requirement
+        if current_hash.startswith(prefix):
+            return nonce, current_hash
+
+        nonce += 1
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()
+
+    # Example usage:
+    example_tx = "Alice sends 1 BTC to Bob"
+    prev_h = "00000abcdef1234567890"
+    diff = 4
+
+    print(f"Mining block... (Difficulty: {diff})")
+    nonce, hash_found = proof_of_work(1, example_tx, prev_h, diff)
+
+    print(f"Success! Nonce: {nonce}")
+    print(f"Hash: {hash_found}")