import sys
import random
import string
import time
import itertools
import operator
import base64

from Crypto.Hash.HMAC import HMAC

def raw2hex(raw):
    return raw.encode('hex')


def hex2raw(hexstring):
    return base64.b16decode(hexstring)


def slow_foo():
    p = 181
    k = 2
    while k < p:
        if p % k == 0:
            return
        k += 1


def verify(message, tag):
    k = '0123456789ABCDEF'

    # Use MD5 for HMAC
    digest = HMAC(k, message).digest()

    for i in range(16):
        # Artificially extend byte comparison duration
        slow_foo()
        if tag[i] != digest[i]:
            return False

    return True


hexdigits = '0123456789ABCDEF'


def main():
    message = 'Test'

    # Step 1. Iterate through all possible first byte values, and call the
    # Verify oracle for each of them

    # Step 2. Store the byte which caused the longest computation time

    # Step 3. Continue the operation for each byte (except the last)

    # Step 4. Guess the last byte, and query the oracle with the complete tag
    mytag = '???'
    result = verify(message, mytag)
    if result == True:
        print mytag


if __name__ == "__main__":
    main()