public function decrypt($fullpath, $key, $ciphertext = false)
 {
     $this->ensure_phpseclib('Crypt_Rijndael', 'Crypt/Rijndael');
     $rijndael = new Crypt_Rijndael();
     if (defined('UPDRAFTPLUS_DECRYPTION_ENGINE')) {
         if ('openssl' == UPDRAFTPLUS_DECRYPTION_ENGINE) {
             $rijndael->setPreferredEngine(CRYPT_ENGINE_OPENSSL);
         } elseif ('mcrypt' == UPDRAFTPLUS_DECRYPTION_ENGINE) {
             $rijndael->setPreferredEngine(CRYPT_ENGINE_MCRYPT);
         } elseif ('internal' == UPDRAFTPLUS_DECRYPTION_ENGINE) {
             $rijndael->setPreferredEngine(CRYPT_ENGINE_INTERNAL);
         }
     }
     $rijndael->setKey($key);
     return false == $ciphertext ? $rijndael->decrypt(file_get_contents($fullpath)) : $rijndael->decrypt($ciphertext);
 }