Substitution ciphers are probably the most common form of cipher. They work by replacing each letter of the plaintext (and sometimes puntuation marks and spaces) with another letter (or possibly even a random symbol). A monoalphabetic substituti

实现对web漏洞的扫描程序.基于目标的漏洞检测技术。它采用被动的、非破坏性的办法检查系统属性和文件属性，如数据库、注册号等。通过消息文摘算法，对文件的加密数进行检 验。这种技术的实现是运行在一个闭环上，不断地处理文件、系统目标、系统目标属性，然后产生检验数，把这些检验数同原来的检验数相比较。一旦发现改变就通 知管理员。-Implementation of web vulnerability scanner. The leak detection technology based on targe