* @param $fp_src file path to the file to decrypt.
* @param $fp_dst file path to the file to write decrypted file (could be the same).
* @param $k string composed of the key and the iv separated by a point ('.')
* @param $fp_src file path to the file to decrypt.
* @param $fp_dst file path to the file to write decrypted file (could be the same).
* @param $k string composed of the key and the iv separated by a point ('.')