https://blog.gongquiz.com/2023/11/23/feistel-%ec%95%94%ed%98%b8-%eb%b0%a9%ec%8b%9d%ec%97%90-%eb%8c%80%ed%95%9c-%ec%84%a4%eb%aa%85%ec%9c%bc%eb%a1%9c-%ea%b0%80%ec%9e%a5-%ec%98%b3%ec%a7%80-%ec%95%8a%ec%9d%80-%ea%b2%83%ec%9d%80-9%ea%b8%89/