理解对称加密算法的原理，熟悉常用的对称加密算法：DES,TripleDES,Blowfish

以DES加密算法为例，掌握分组加密算法加，解密过程的实现。

-Understand the principles of symmetric encryption algorithm, familiar with the commonly used symmetric encryption algorithms: DES, TripleDES, Blowfish　DES encryption algorithm as an example in order to master the block cipher encryption and decryption process is achieved.