https://blog.faceutil.com/2017/03/30/%ec%9b%8c3%ec%8b%9c%eb%94%94%ed%82%a4%ec%b2%b4%ec%9d%b8%ec%a7%80-%eb%8b%a4%ec%9a%b4-%ec%9b%8c%ed%81%ac%eb%9e%98%ed%94%84%ed%8a%b83-cdkey-%ec%84%a4%ec%b9%98-%ec%82%ac%ec%9a%a9%eb%b2%95-%cf%89/