fw-pack.py

#!/usr/bin/env python3

import crcmod
import sys

from itertools import cycle
from binascii import hexlify

OBFUSCATION = [
        0x47, 0x22, 0xC0, 0x52, 0x5D, 0x57, 0x48, 0x94, 0xB1, 0x60, 0x60, 0xDB, 0x6F, 0xE3, 0x4C, 0x7C,
        0xD8, 0x4A, 0xD6, 0x8B, 0x30, 0xEC, 0x25, 0xE0, 0x4C, 0xD9, 0x00, 0x7F, 0xBF, 0xE3, 0x54, 0x05,
        0xE9, 0x3A, 0x97, 0x6B, 0xB0, 0x6E, 0x0C, 0xFB, 0xB1, 0x1A, 0xE2, 0xC9, 0xC1, 0x56, 0x47, 0xE9,
        0xBA, 0xF1, 0x42, 0xB6, 0x67, 0x5F, 0x0F, 0x96, 0xF7, 0xC9, 0x3C, 0x84, 0x1B, 0x26, 0xE1, 0x4E,
        0x3B, 0x6F, 0x66, 0xE6, 0xA0, 0x6A, 0xB0, 0xBF, 0xC6, 0xA5, 0x70, 0x3A, 0xBA, 0x18, 0x9E, 0x27,
        0x1A, 0x53, 0x5B, 0x71, 0xB1, 0x94, 0x1E, 0x18, 0xF2, 0xD6, 0x81, 0x02, 0x22, 0xFD, 0x5A, 0x28,
        0x91, 0xDB, 0xBA, 0x5D, 0x64, 0xC6, 0xFE, 0x86, 0x83, 0x9C, 0x50, 0x1C, 0x73, 0x03, 0x11, 0xD6,
        0xAF, 0x30, 0xF4, 0x2C, 0x77, 0xB2, 0x7D, 0xBB, 0x3F, 0x29, 0x28, 0x57, 0x22, 0xD6, 0x92, 0x8B,
    ]

def obfuscate(fw):
    return bytes([a^b for a, b in zip(fw, cycle(OBFUSCATION))])

plain = open(sys.argv[1], 'rb').read()

version = b'*' + bytes(sys.argv[2], 'ascii') + b' ' + bytes(sys.argv[3], 'ascii')
version = version[0:16]

if len(version) < 16:
    version += b'\x00' * (16 - len(version))

packed = obfuscate(plain[:0x2000] + version + plain[0x2000:])

crc = crcmod.predefined.Crc('xmodem')
crc.update(packed)
digest = crc.digest()
digest = bytes([digest[1], digest[0]])

open(sys.argv[4], 'wb').write(packed + digest)