https://blog.faceutil.com/2017/03/25/%eb%82%98%eb%a7%8c%ec%9d%98-%ec%84%9c%eb%aa%85%ed%8c%8c%ec%9d%bcsign-key%eb%a7%8c%eb%93%a4%ea%b8%b0-%e3%8e%b4/