凯撒密码（caeser）是用于加密通过信使传递的作战命令。置换加密的优点就在于它易于实施却难于破解。发送方和接收方很容易事先商量好一个密钥，然后通过密钥从明文中生成密文，即使敌人获取密文，通过密文直接猜测其代表的意义，在实践中是不可能的。
在密码学中存在着各种各样的置换方式，但所有不同的置换方式都包含2个相同的元素：密钥和协议(算法)。凯撒密码的密钥是x，算法是将普通字母表中的字母用密钥对应的字母替换。(The Kaiser code (Caeser) is the operational command used to encrypt messages delivered by messenger. The advantage of permutation encryption is that it is easy to implement but difficult to break. The sender and receiver easily beforehand a key, and then through the key generation from the plaintext ciphertext, even if the enemy gets through the ciphertext ciphertext, directly guess the meaning, in practice is not possible.
There are many kinds of permutations in cryptography, but all different permutations have 2 identical elements: key and protocol. The key to the Kaiser code is x. The algorithm replaces the letters in the ordinary alphabet with letters corresponding to the key.)