DES密码系统

摘要
    随着计算机被广泛应用的信息时代，信息本身就是时间，就是财富。大量信息用数据形式存放在计算机系统里。信息的传输则通过公共信道。这些计算机系统和公共信道是不设防的，是很脆弱的，容易受到攻击和破坏，信息的丢失不容易被发现，而后果是极其严重的。如何保护信息的安全已不仅仅是军事和政府部门感兴趣的问题，各企事业单位也愈感迫切。密码是有效而且可行的保护信息安全的办法，有效是指密码能够做到使信息不被非法窃取，不被篡改或破坏，可行是说它需要付出的代价是可以接受的。
本文主要是对DES数据加密标准原理和流程的描述，DES是1种国际上通用的分组密码。DES是1个分组加密算法（Feistel加密网络算法），它以64-位为分组对数据加密。 64-位1组的明文从算法的1端输入， 64-位的密文从算法的另1端输出。DES是1个对称算法：加密与解密使用同1种算法。DES是加密的两个基本技术—混乱和扩散的组合（先代替后置换），并使用16轮相同的组合技术达到对数据的加密与解密，在加密与解密过程中主要采用ECB模式和MFC制作界面来实现的，最后通过运行测试，程序正确。

关键词: 数据加密标准；DES；密钥；数据加密；数据解密；S盒等.

Abstract
  Along with the development of information ages，calculators are being extensively applied in our daily life.
Information in itself is time, is wealth.A great deal of information has been deposited in the calculator system with the data form and it is delivered through public letter way.These calculator systems and the public letter ways which are non-defence,
are too fragile to be attacked and destroyed, the lost information are not easy to be found and then the concequence becomes 本文来自中国科教评价网
very serious.How to protect the safety of information is not only an interesting problem to the military and government sections, but also the urgent pressure to each enterprise. Password is the most available and feasible way to protecte the safety
of information, avalibility means that the password can effectively attain information from illegal pilferage, and being tempered and destroyed, feasibility is to say that the price of paying is acceptable.
This text is mainly description that encrypts the standard principle and process to the data of DESthe DES is a kind of
grouping password in international general use, and it is a set of grouping encrypt calculating way (the Feistel encrypt calculating way) with 64-bit grouping for data encrypt. A set of original text should be input as inlet condition of the     calculating way, be output as outlet parameters. The DES is a symmetry calculating way: Encrypt and decrypt are using the
same calculating way and it is also the combinition of two encrypt basic techniques--confusion and pervation (instead of
postpose permutation first), in the usage of 16-round similar combination technique. Use 16 same combination techniques to attain the logarithms also according to of encrypt and decrypt, the main adoption  ECB mode and MFCs manufacture the interface in encrypt and decrypt process to carry out of, Pass to circulate the test finally, procedure exactitude.

Keywords: the standard of the data encrypts;DES;key; the data encrypt;the data decrypt;s box etc.