凯撒密码作为一种最为古老的对称加密体制，在古罗马的时候都已经很流行，他的基本思想是：通过把字母移动一定的位数来实现加密和解密。- As one of the most ancient Caesar cipher symmetric encryption system, when in Rome have been very popular, his basic idea is: by moving letters to achieve a certain number of bits enc