说明：  按照DES加密解密原理采用C语言实现，算法实现中涉及一些位操作，如设置指定位置的位状态，循环左移等位操作，它是算法实现的根基。
(Implement DES algorithm with C according to its encryption and decryption principle, the algorithm involves a number of bit operations, such as setting the bit position of the specified location, rotate the left shift operation, which is the foundation of the algorithm.)