code: public void close()
      {
          if (forwardEngine != null)
              forwardEngine.close();
          if (reverseEngine != null)
              reverseEngine.close();
  
          forwardEngine = null;
          reverseEngine = null;
      }
docs: Close the transformer engine.
  
  The close functions closes all stored default crypto contexts. This
  deletes key data and forces a cleanup of the crypto contexts.