#!/usr/bin/env python
# Decrypts the Tom-Skype 5.0.x - 5.1.x era keyfiles and outputs them in UTF-8
# Jeffrey Knockel jeffk <at> cs <dot> unm <dot> edu
# Usage: python decrypt.py < keyfile > plainfile

import binascii
import struct
import sys
from Crypto.Cipher import AES as Cipher

KEY = '0sr TM#RWFD,a43 '.encode('utf-16le')

def decrypt(key, hexcrypt):
    crypt = binascii.a2b_hex(hexcrypt.encode('ascii'))
    crypt = b''.join(crypt[i + 1:i + 2] for i in range(0, len(crypt), 2))
    n, = struct.unpack('<I', crypt[:4])
    cipher = Cipher.new(key, Cipher.MODE_ECB)
    return cipher.decrypt(crypt[4:])[:n]

def main():
    if hasattr(sys.stdout, 'buffer'):
        sys.stdout = sys.stdout.buffer
    for lineno, line in enumerate(sys.stdin):
        stripped = line.strip('\0\t\n\x0b\x0c\r ')
        if stripped:
            try:
                plain = decrypt(KEY, stripped).decode('gbk').encode('utf-8')
            except Exception:
                sys.stderr.write('Error decrypting line %d\n' % (lineno + 1))
            else:
                sys.stdout.write(plain + b'\n')

if __name__ == '__main__':
    main()