encrypt_keysector.py

#!/usr/bin/env python3

import os
import sys
from Crypto.Cipher import AES
from Crypto.Hash import SHA256

if len(sys.argv) < 4:
    sys.exit("encrypt_keysector.py <otp> <secret_sector> <output>")

if os.path.getsize(sys.argv[1]) != 256:
    sys.exit("OTP is invalid size (must br 256 bytes)")
if os.path.getsize(sys.argv[2]) != 512:
    sys.exit("secret sector is invalid size (must br 512 bytes)")

def to_bytes(num):
    numstr = b''
    tmp = num
    while len(numstr) < 16:
        numstr += bytes([tmp & 0xFF])
        tmp >>= 8
    return numstr[::-1]

# used from http://www.falatic.com/index.php/108/python-and-bitwise-rotation
rol = lambda val, r_bits, max_bits: \
    (val << r_bits%max_bits) & (2**max_bits-1) | \
    ((val & (2**max_bits-1)) >> (max_bits-(r_bits%max_bits)))

with open(sys.argv[1], "rb") as f:
    otp = f.read(0x90)
with open(sys.argv[2], "rb") as f:
    sector = f.read(512)

otp_hash = SHA256.new(otp).hexdigest()

key_x = int(otp_hash[0:32], 16)
key_y = int(otp_hash[32:64], 16)
normal_key = rol((rol(key_x, 2, 128) ^ key_y) + 0x1FF9E9AAC5FE0408024591DC5D52768A, 87, 128)

cipher = AES.new(to_bytes(normal_key), AES.MODE_ECB)
with open(sys.argv[3], "wb") as f:
    f.write(cipher.encrypt(sector))