hbkdf

#!/usr/bin/env python3

# Brief:
# A basic key-derivation-function with a Hashcash-like PoW.
# The Hashcash method employed here uses the following pseudocode:
#
# curr_hash=hash(input)
# token=init_value
# loop until curr_hash has n trailing zeroes
#   curr_hash=hash(curr_hash+token)
#   token=increment(token)
#
# The ordered iteration ensures the algorithm cannot be sped up using multithreading.
#
# Usage:
# ./hashcash <text> <number of trailing zeroes in hex representation of target hash>
#
# Adapted from https://gist.github.com/i3visio/388ef5154052ed8173df4b7b9eda541b


import hashlib, math, itertools, sys

def trailing_zeros(n):
    """Number of trailing 0s in binary representation of integer n."""
    if n <= 0: return 0
    for i in itertools.count(0):
        if n & (1<<i): return i

def irange(n):
    """Implementation of xrange(n) that does not overflow."""
    i = 0
    while i < n:
        yield i; i += 1

def all_strings(charset='0123456789ABCDEF'):
    """Yields all strings in given character set, sorted by length."""
    m = len(charset)
    for n in itertools.count(0):
        for i in irange(m**n):
            yield ''.join([charset[(i//(m**j))%m] for j in range(n)])

def make_token(s, n, charset='0123456789ABCDEF'):
    """Makes hashcash token of value 'n' against basestring 's'."""
    h = hashlib.sha512(s.encode()).hexdigest()
    for token in all_strings(charset):
        h=hashlib.sha512(h.encode()+token.encode()).hexdigest()
        if trailing_zeros(int(h,16)) >= n: return [token,h]

key=sys.argv[1]
nzeroes=sys.argv[2]

output=make_token(key,4*int(nzeroes))
print("Key: ",output[0])
print("Final SHA512: ",output[1])