pow.py

import hashlib
import binascii

"""
Simplified implementation of HashCash proof-of-work algorithm. 
"""

difficulty = 3

def hash_msg(message, hex=False):
    """
    Return sha-256 hash from any binary message
    :param message: binary string
    :type message: bytes
    :param hex: flag, that signals to encode result in hex
    :return: sha-256 hash
    :rtype: bytes|str
    """
    hash_algo = hashlib.sha256()
    hash_algo.update(message)
    digest = hash_algo.digest()
    if not hex:
        return digest
    return binascii.hexlify(digest).decode()

def check_difficulty(pow_hash):
    """
    Checks whether proof-of-work hash has {difficulty} number of leading zeroes.
    :param pow_hash: proof-of-work hash
    :type pow_hash: str
    :return: true if check succeeds, otherwise - false
    :rtype: bool
    """
    n = len(pow_hash)
    cnt = 0
    for i in range(n):
        if pow_hash[i] != '0':
            break
        cnt += 1
    return cnt >= difficulty

def proof_of_work(mining_hash):
    """
    Simplified hashimoto proof-of-work.
    :param mining_hash: mining hash
    :type mining_hash: str
    :return: tuple of nonce and proof-of-work hash
    :rtype: tuple[int, str]
    """
    pow_hash, nonce = None, -1
    while True:
        byte_msg = ("%s%s" % (nonce + 1, mining_hash)).encode()
        # Prepare proof-of-work sha256 hash with candidate nonce
        pow_hash = hash_msg(byte_msg, hex=True)
        # Check if the resulting hash is valid pow hash
        isvalid = check_difficulty(pow_hash)
        nonce += 1
        if isvalid:
            break
    if isvalid:
        return nonce, pow_hash
    return None, None