code: final public static Key makeSystem(String s) {
      byte[] kb= decodeKeyName(s);
      byte[] kb2 = new byte[kb.length+1];
      System.arraycopy(kb,0,kb2,1,kb.length);
      kb2[0] = Key.BUILT_IN_KEY;
      return Key.make(kb2);
    }
docs: Hide a user key by turning it into a system key of type HIDDEN_USER_KEY