code: public void zero() {
          ((Buffer) buffer).mark();
          ((Buffer) buffer).position(0);
          buffer.put(ZEROS, 0, buffer.remaining());
          ((Buffer) buffer).reset();
      }
docs: Fill the buffer with zeros. This method does not change the buffer position.
  <p>
  Typically used for security reasons, with buffers that contains
  now-unused plaintext.