#! /usr/bin/env python

# hg658c.wordpress.com
# This is for the Huawei HG633
"""
To decrypt encrypted values in the config, use
echo -n "RvldRxOemFEAL+AInOj90g==" | base64 -d | openssl enc -d -aes-128-cbc
-K BBB1182E7453BD73B8ECC4465FA402F9 -iv 6C76E0304A94A2B711C6BE8884F4D06C -nopad ; echo
"""

import sys
import os
from binascii import hexlify, unhexlify
from Crypto.Cipher import AES
from Crypto.Hash import MD5
from Crypto.Util import number
import zlib

#30003/100020
RSA_D = (
    "1A9FCE09FD5B6FAA0CEC5C9841B4105D"
    "0AD9D1DD0324817413EEF77267C56DBE"
    "E76C135B63160F759FD5333B060AFC08"
    "71C813D0FDDFA3AA3CA5DD4C0430940D"
    "B14A9DF8A31B4B38B4690BE84E9A38D0"
    "FBB405244648CED3A8EAFE7F5451752E"
    "F201B94A13C1DF915012302F12C6946B"
    "230474034A665B2CAAD23794BF7B6381")

#30003/40010
RSA_N = (
    "B1AAE240AE798C9051E97745519F737A"
    "4F5E82902CAA630420EC5B0F6FE64926"
    "CA9D766811C354C951E58B4796037159"
    "45F344DEA71A72106E1BA10FF72721DF"
    "C7C5273A808ADF2F8A39BEB2D03370A8"
    "7749E778F2135A1625FFFBBFB17631A3"
    "207C9E129105F3E7DCE0AFA654321597"
    "F9B2026BD197AEABF2F03B1EB8137F1D")

RSA_E = "010001"

SIG_TEMPLATE = ("0001ffffffffffffffffffffffffffff"
                "ffffffffffffffffffffffffffffffff"
                "ffffffffffffffffffffffffffffffff"
                "ffffffffffffffffffffffffffffffff"
                "ffffffffffffffffffffffffffffffff"
                "ffffffffffffffffffffffffff003020"
                "300c06082a864886f70d020505000410")

#30000/10040
AES256CBC_KEY = "BBB1182E7453BD73B8ECC4465FA402F9FB399D941A15360B230C9FBEEA6832A4"
#30000/20040
AES256CBC_IV  = "6C76E0304A94A2B711C6BE8884F4D06C"

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_md5_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_md5 = hexlify(decrypted_sig)[-64:]
    return target_md5

def calc_actual_md5_hash(enc_config_body):
    md5 = MD5.new()
    md5.update(enc_config_body)
    actual_md5_sig = md5.hexdigest()
    actual_md5_sig = str.encode(actual_md5_sig)
    return actual_md5_sig

def decrypt_config(input_file, output_file):
    enc_config=load_config(input_file)

    print("Decrypting...")
    iv = unhexlify(AES256CBC_IV)
    key= unhexlify(AES256CBC_KEY)
    cipher = AES.new(key, AES.MODE_CBC, iv)
    try:
        decrypted_data = cipher.decrypt(enc_config)
        decompressed_data=""

        decompressed_data = zlib.decompress(decrypted_data)
    except:
        print("Bad config file...exiting")
        sys.exit(1)

    config_text = decompressed_data[:-0x80]
    actual_md5_hash = calc_actual_md5_hash(config_text)

    print("Verifying signature...")
    sig = decompressed_data [-0x80:]
    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_md5_hash = hexlify(decrypted_sig)[-32:]

    if (actual_md5_hash == target_md5_hash):
        print("Signature ok...")
    else:
        print("Signature not ok...exiting")
        sys.exit(1)

    config_text = config_text[:-1]
    check_config(config_text)

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

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_data=load_config(input_file)
    check_config(new_config_data)
    new_config_data += '\0'.encode()

    print("Calculating MD5 hash...")
    h = MD5.new()
    h.update(new_config_data)
    actual_md5_sig = h.hexdigest()

    sig = SIG_TEMPLATE + actual_md5_sig;

    print("Adding 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)
    new_config_data = new_config_data + encrypted_sig

    print("Compressing config...")
    compressed_data = zlib.compress(new_config_data, 9)

    padding_amount = len(compressed_data) % 16
    print("" + str(padding_amount) + " bytes padding needed")
    print("Adding padding...")
    compressed_data=compressed_data + b'\0'*(16-padding_amount)

    print("Encrypting config...")
    iv = unhexlify(AES256CBC_IV)
    key= unhexlify(AES256CBC_KEY)
    aes = AES.new(key, AES.MODE_CBC, iv)
    enc_new_config = aes.encrypt(compressed_data)

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