hashbreak.py

#!/usr/bin/env python3
'''Created to answer the question: How does bitcoin mining work? Key
differences between this method and bitcoin's:

  - This method doesn't actually store transactions. :-)

  - This primes the hash function with the previous nonce solution, so solving
    for the nth iteration necessarily requires a solution for the (n-1)
    iteration and all iterations before it. Bitcoin primes the hash function
    with the entire previous block, (which includes its nonce). This method is
    arguably more vulnerable to attacks on SHA-256.

  - Difficulty is in bytes, not bits. It really ought to be in bits but I'm
    lazy and I doubt anyone will ever see this.'''

from itertools import count # iterate infinitely
from hashlib import sha256  # the relevant hash function
from sys import exit        # to exit cleanly with ^C

class Ramp(bytearray):
    def increment(self):

        # LSByte at index zero for efficiency
        for i in range(len(self)):
            if self[i] == 0xff:
                self[i] = 0
            else:
                self[i] += 1
                return

        # if all bytes are zero, add another
        self.append(0)
        print(len(self), "B answers being considered", sep='', end='\r') #DEBUG

    # hacky little-endian nonsense
    def __str__(self):
        return ':'.join([ "{:02x}".format(x) for x in reversed(self) ])

def hash_begins_with_n_zeros(solution: bytes, difficulty: int, primed_hash: sha256):
    h = primed_hash.copy()
    h.update(solution)
    maybe_zeros = h.digest()[:difficulty]
    return all([ x == 0 for x in maybe_zeros ])

def mine():
    primed_hash = sha256()
    for difficulty in count(1):
        solution = Ramp()
        while not hash_begins_with_n_zeros(solution, difficulty, primed_hash):
            solution.increment()
        yield solution
        primed_hash = sha256(solution)

try:
    m = mine()
    last = Ramp()
    d = 1
    for s in m:
        print("Difficulty", d, "solution found!")
        print("When combined with the last result,", s, "SHA256-hashes to", sha256(last + s).hexdigest(), '', sep='\n')
        last = s
        d += 1
except KeyboardInterrupt:
    print()
    exit(0)