关于网络通信的密码基础知识及密码学发展。其中包括DES的原理，3重DES的相关介绍。对于网络通信的密码学入门有一定的帮助-Password basic knowledge about the network communication and cryptography development. Including the principle of DES, 3 re-introduction of DES. Have some help for network communication Introduction to Cryptography