置换密码亦称换位密码。置换只不过是一个简单的换位。每个置换都可以用一个置换矩阵 来表示。每个置换都有一个与之对应的逆置换 。置换密码的特点是仅有一个发送方和接收方知道的加密置换（用于加密）和对应的逆置换（用于解密）。它是对明文 长字母组中的字母位置进行重新排列，而每个字母本身并不改变。-Password replacement, also known as transposition cipher. Replacement is just a simple transposition. Each permutation can be represented by a permutation matrix. Each exchange has a corresponding inverse permutation. Replacement of the password feature is only one sender and receiver know the encryption permutation (for encryption) and the corresponding inverse permutation (for decryption). It is a long letter of the plaintext letters in the group re-arranged location, and each letter in itself does not change.