Proof of Work based throttling

pow.py

# Playing around with Proof of Work
import random, binascii, md5

# random byte string generator
# k byte random string is output
def rand_bytes(k):
    num = random.getrandbits(8*k)
    s = hex(num)[2:]
    if(s[-1]=='L'):
        s = s[:-1]
    return binascii.a2b_hex(s.zfill(2*k))



# Work to find a k byte string with first l bits of md5 hash zero
def work(l, k):
    while True:
        cand = rand_bytes(k)
        m = md5.new()
        m.update(cand)
        h = m.digest()
        h_bin = bin(int(binascii.b2a_hex(h), 16))[2:]
        h_bin = h_bin.zfill(16*8)
        if(h_bin[:l] == '0'*l):
            print 'Found Solution'