Recover a XP product key from the registry

xpproductkey.py

import math


# HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\DigitalProductId
# offset from 28 (0x1c) to 43 (0x2b) 
b = [0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00]
digits = "BCDFGHJKMPQRTVWXY2346789"

def base24(b):
    v = sum((256 ** i) * c for i, c in enumerate(b))
    for _ in range(int(math.ceil(math.log(256) * len(b) / math.log(24)))):
        yield digits[v % 24]
        v //= 24

print(''.join(('-' if i % 5 == 0 else '') + c for i, c in enumerate(reversed(list(base24(b))[:25])))[1:])