说明：  本程序是DES加密系统的c语言源程序，它很可能是使用最广泛的秘钥系统，特别是在保护金融数据的安全中，通常，自动取款机（Automated Teller Machine，ATM）都使用 DES。
(This procedure is the DES encryption system c language source code, it is likely to be the most widely used secret key system, especially in protecting the safety of financial data, usually, ATM (Automated Teller Machine, ATM) are the use of DES.)