def encrypt(self, key, filename):
    chunksize = 128 * 1024
    outFile = os.path.join(os.path.dirname(filename), "(Secured)" + os.path.basename(filename))
    filesize = str(os.path.getsize(filename)).zfill(16)
    IV = Random.new().read(AES.block_size)
    print(IV, len(IV))
    encryptor = AES.new(key, AES.MODE_CBC, IV)

    with open(filename, "rb") as infile:
        with open(outFile, "wb") as outfile:
            outfile.write(filesize.encode('utf-8'))
            outfile.write(IV)
            while True:
                chunk = infile.read(chunksize)
                if len(chunk) == 0:
                    break
                elif len(chunk) % 16 != 0:
                    chunk += b' ' * (16 - (len(chunk) % 16))
                outfile.write(encryptor.encrypt(chunk))
    return outFile