替代密码包括多种类型，如单表替代密码，多表替代密码，多字母替代密码等。试编程实现一种典型的单表替代密码—凯撒（Caesar）密码。它的加密方法是将明文中的每个字母用此字符在字母表中后面的第k个字母替代。-Alternative password includes many types, such as single-table alternative password, multi-table alternative to passwords, and more letters, such as alternatives to passwords. Try programming a typical single-table alternative password- Caesar (Caesar) password. Its encryption method is to express each letter in the alphabet with this character in the back of the first k letters alternative.