base24.py

CHARMAP = [bytes([x]) for x in b'BCDFGHJKMPQRTVWXY2346789']

def b24encode(data):
    enc = b''
    for c in data:
        enc += CHARMAP[c >> 4]
        enc += CHARMAP[-(c & 0x0f) - 1]
    return enc

def b24decode(data):
    dec = b''
    hi = -1
    for c in data:
        if hi < 0:
            hi = CHARMAP.index(bytes([c])) << 4
        else:
            dec += bytes([hi | (23 - CHARMAP.index(bytes([c])))])
            hi = -1
    return dec

def b24Keygen(data):
    ''' The actual algorithm used in Windows product key generation. '''
    assert len(data) * 8 >= 114, 'data must be at least 144 bits in length'
    num = int.from_bytes(data, byteorder = 'little')
    enc = b''
    for i in range(29):
        if i % 6 == 5:
            enc += b'-'
        else:
            enc += CHARMAP[num % 24]
            num //= 24
    return enc