code: private static function decryptWithPHP71($K, $key_length, $IV, $C, $A, $T)
      {
          $mode = 'aes-'.($key_length).'-gcm';
          $P = openssl_decrypt(null === $C ? '' : $C, $mode, $K, OPENSSL_RAW_DATA, $IV, $T, null === $A ? '' : $A);
          Assertion::true(false !== $P, 'Unable to decrypt or to verify the tag.');
  
          return $P;
      }
docs: @param string      $K          Key encryption key
  @param string      $key_length Key length
  @param string      $IV         Initialization vector
  @param string|null $C          Data to encrypt (null for authentication)
  @param string|null $A          Additional Authentication Data
  @param string      $T          Tag
  
  @return string