基于SHA-1算法邮件过滤系统的研究与实现

【作者】 杨启华；

【导师】 卢显良；

【作者基本信息】 电子科技大学 ， 计算机系统结构， 2005， 硕士

【摘要】 近年来,一些公司或个人为了个人或商业利益,在未经收件人同意的情况下,利用电子邮件发送大量商业广告及各种不良信息,形成影响极坏、后果严重的垃圾邮件。本文主要是针对现今垃圾邮件大量泛滥的现状,综合分析了国内外各种流行的垃圾邮件过滤方法,比较各种方法的利弊,设计并实现了一套行之有效的垃圾邮件过滤系统。本文首先分析了当今邮件过滤领域的现状,讨论了当今主要的垃圾邮件过滤方法和垃圾邮件发送者惯用的方法,可以说,现在的邮件过滤方法大部分是基于文本方式,比如基于神经网络,贝叶斯等,或者简单的对邮件地址进行黑白名单的分类。这些方法优点明显,但是缺点也很突出,本文针对这些方法固有的缺点,综合它们的优点,设计实现一种新型的过滤系统。在设计之初,本文重点讨论了邮件系统的基本知识,只有对邮件发送机制有深入的了解,才可能对过滤技术的实施有全面的掌握。本文还主要针对邮件头结构进行了分析,这是本文邮件过滤的关键之一,因为邮件格式,编码方式等必要信息都存在于头结构中。哈希算法因为其固有的特点,可以大大简化邮件内容,使过滤效率得到很大提高。为了将SHA-1 算法应用到邮件过滤系统中,改善邮件过滤的效率,本文简要分析了一下哈希算法的原理机制,比较了多种主流算法的优劣。接下来本文综合各种过滤方法的特点,概要设计了基于SHA-1 算法的邮件过滤系统,针对过滤点选择,hash 算法选择,过滤流程等问题进行了详细讨论,本文针对垃圾邮件的特点,适当的运用了hash 算法的优势,结合了各种过滤方法,使过滤系统行之有效。概要设计后,本文将过滤系统划分为各个模块,对各个模块进行了详细设计,初步完成了预想的过滤功能。主要模块大体分为头结构的分析,正文的分析,hash 模块实现,存储结构的设计等。最后,我们通过大量的试验来验证过滤的效果,实践证明,过滤系统工作良好,基本达到了预期的目标,同时也发现了一些问题,需要进一步完善。更多还原

【Abstract】 Recently, In order to win the maximum interest, some companies and personssend a large numbers of commercial advertisements and bad information toconsumers using E-mail unobtain the content of the user. These actions bring to theappearance of the spam that has abominable impact to the society. Aiming at thisstatement, this paper design and achieve an effective system of filtering to damp theflooding of spam after synthetically analyzing all kinds of the methods of spam filterand comparing the advantage and disadvantage of these methods.The paper analyzes the acturality of the filter field, and discusses the majormethods of the filter system and the general methods that the spam sender used. Itcan be said that nowadays most of the methods are based on the text checking such asthe method based on the NN, the method based on the Bayes and so on. Thesemethods have distinct flaws. Aim at these flaws and integrate the merits, the paperdesign and achieve a fire new system.At first, this paper focus on the basic knowledge of mail system because only wehave deeply familiar with the mechanism of mail system, can we roundly grasp theimplement of the mail filter technology. The paper also has analyzed the mail headstructure in that it is the key in the process of the mail filter. Much importantinformation is picked up from the head structure. In order to apply the SHA-1arithmetic to the system of mail filter and consequently improve the efficiency of themail filter, the paper briefly analyze the theory and mechanism of the encryptarithmetic and compare the several major arithmetic.Secondly, synthetizing all kinds of mail filters’characteristic, the paper outlinethe frame of the mail filter based on the SHA-1 arithmetic, and discuss some keypoints such as the choice of the filter point, the choice of the hash arithmetic, the flowof the filter and so on. Aiming at the characteristic of the spam and rationally utilizethe predominance of the hash arithmetic, the paper combine many other methods offilter so as to make the system effective.After the general design, the paper partitions the system to several modules andmakes detailed design and implement. The major modules include head structureanalyse module, text analyse module, hash module, storage module and so on.In the end, we carry a huge number of tests in order to validate the effect of thefilter. The result shows that the system can work in gear and reach the anticipative更多还原