#! /usr/bin/env python

# hg658c.wordpress.com
# Version 3

import sys
import os
from binascii import hexlify, unhexlify
from Crypto.Cipher import AES
from Crypto.Hash import SHA256
from Crypto.Util import number


RSA_D = "2345ADB2C06E54D7373E2A233A50150A" \
        "4044E417FBF76FB1AC8A444E72A345AA" \
        "14B7C349A4824C96DF9ECF7D8CC50425" \
        "32930DBD40D86FDCD892398702E3EA51" \
        "41C90F10494BB91440E89B104626CCCB" \
        "E45A5133362359732954BD63FCA58929" \
        "E3D890014FDF83847E6B19F0D9E1117E" \
        "9706984EAA57E114934B273366C4DBD1"

RSA_N = "C206CF93A9E6EE1CE17984DD54422AC4" \
        "561A4EEB969D1BA81432626D6409FA03" \
        "3B3738F8BBA046ACEF3BAC35094B70AF" \
        "231D9DC43C1D68EDBEBE983E267B72FD" \
        "3C2A7614D60FA7457B92B6A45C49F307" \
        "EA23DE51E7E0C36D6440FC4F62C44CCB" \
        "4169914E43DBFDAE536F002B2D670CE0" \
        "A2A11FD1AF4C484C1A6FED9C228199A3"

RSA_E = "010001"

SIG_TEMPLATE = "0001FFFFFFFFFFFFFFFFFFFFFFFFFFFF" \
               "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF" \
               "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF" \
               "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF" \
               "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF" \
               "003021300906052B0E03021A05000420"

AES128CBC_KEY = "48EE9D8621739F26C215C49071e2438A"
AES128CBC_IV  = "A68FBBCA44BB1F5364A530608BCDEAAB"

XML_VERSION_STRING = b'<?xml version="1.0" ?>'

def print_usage():
	print("Usage : " + sys.argv[0] + " {encrypt | decrypt} input_file output_file")
	sys.exit(1)

def load_config(config_file):
	if os.path.isfile(config_file):
		cf = open(config_file, "rb")
		config = cf.read()
		cf.close()
	else:
		print("Config file not found..exiting")
		sys.exit(1)
	return config

def save_to_file(dest_file, data):
	wfile = open(dest_file,"wb")
	wfile.write(data)
	wfile.close()

def get_sha256_hash_from_sig(sig):
	sig_int = int(hexlify(sig),16)
	rsa_n = int(RSA_N,16)
	dec_sig_as_int = pow(sig_int, 0x10001, rsa_n );
	decrypted_sig = number.long_to_bytes(dec_sig_as_int, 128)
	target_sha256 = hexlify(decrypted_sig)[-64:]
	return target_sha256

def calc_actual_sha256_hash(enc_config_body):
	sha256 = SHA256.new()
	sha256.update(enc_config_body)
	actual_sha256_sig = sha256.hexdigest()
	actual_sha256_sig = str.encode(actual_sha256_sig)
	return actual_sha256_sig

def decrypt_body(enc_config_body):
	iv = unhexlify(AES128CBC_IV)
	key= unhexlify(AES128CBC_KEY)
	cipher = AES.new(key, AES.MODE_CBC, iv)
	decrypted_data = cipher.decrypt(enc_config_body)
	# Strip block padding
	decrypted_data=decrypted_data.rstrip(b'\0')
	return decrypted_data


def decrypt_config(input_file, output_file):
	enc_config=load_config(input_file)
	sig = enc_config[:0x80]
	enc_config_body=enc_config[0x80:]

	print("verifying signature...")
	target_sha256_hash = get_sha256_hash_from_sig(sig)
	actual_sha256_hash = calc_actual_sha256_hash(enc_config_body)

	if (actual_sha256_hash == target_sha256_hash):
		print("Signature ok...")
	else:
		print("Signature not ok...exiting")
		sys.exit(1)

	print("Decrypting...")
	decrypted_data = decrypt_body(enc_config_body)

	check_config(decrypted_data)

	print("Saving decrypted config to " + output_file + "...")
	save_to_file(output_file, decrypted_data)

def check_config(new_config_file):
	head = new_config_file[0:len(XML_VERSION_STRING)]
	if head != XML_VERSION_STRING:
		print("Not a valid config file...exiting")
		sys.exit(1)

def encrypt_config(input_file, output_file):
	new_config_file=load_config(input_file)

	check_config(new_config_file)

	padding_amount = len(new_config_file) % 32
	print("" + str(padding_amount) + " bytes padding needed")
	print("Adding padding...")
	new_config_file=new_config_file + b'\0'*(32-padding_amount)

	print("Encrypting config...")
	iv = unhexlify(AES128CBC_IV)
	key= unhexlify(AES128CBC_KEY)
	aes = AES.new(key, AES.MODE_CBC, iv)
	enc_new_config = aes.encrypt(new_config_file)

	print("Calculating SHA256 hash...")
	h = SHA256.new()
	h.update(enc_new_config)
	actual_sha256_sig = h.hexdigest()

	sig = SIG_TEMPLATE+actual_sha256_sig;

	print("Encrypting Signature...")
	sig_int = int(sig,16)
	rsa_d = int(RSA_D,16)
	rsa_n = int(RSA_N,16)
	enc_sig_int = pow(sig_int, rsa_d, rsa_n);

	encrypted_sig = number.long_to_bytes(enc_sig_int, 128)
	enc_config = encrypted_sig + enc_new_config

	print("Saving encrypted config to " + output_file + "...")
	save_to_file(output_file, enc_config)

def main():

	if len(sys.argv) < 4:
		print_usage()

	input_file = sys.argv[2]
	output_file = sys.argv[3]
	command = sys.argv[1]

	if (command == "encrypt"):
		encrypt_config(input_file, output_file)
	elif (command == "decrypt"):
		decrypt_config(input_file, output_file)
	else:
		print_usage()



if __name__ == "__main__":
	main()