垃圾邮件过滤技术

电子邮件已经成为人们日常生活中通信、交流的重要手段之一,但垃圾邮件问题也日益严峻,网民平均每天收到的垃圾邮件数量已超过了正常邮件.因此目前反垃圾邮件技术的研究成为了一个热门的话题.文中介绍了基于安全认证、规则匹配和统计学习三类邮件过滤技术及应用情况,分析了过滤技术面临的挑战并指出垃圾邮件过滤的发展趋势.     

垃圾邮件过滤技术研究

电子邮件成为人们相互联系的一种重要方式,同时由于其本身所具有的开放性、低成本等特点使其成为无孔不入的垃圾邮件的一种重要传播途径。为了对抗日益泛滥的垃圾邮件,人们找到了许多方法,在分析了当前主流的反垃圾邮件方法,并比较几种方法优缺点的基础上,设计、实现了反垃圾邮件过滤软件。     

垃圾邮件过滤技术研究

自从互联网普及以来,电子邮件逐渐成为人们生活中便捷的通信手段之一。但随之产生的垃圾邮件泛滥成灾,垃圾邮件过滤技术逐渐成为网络信息安全研究领域的热点。本文首先对垃圾邮件过滤技术研究发展阶段作简要说明,然后从内容过滤、接入过滤、行为过滤等三方面对垃圾邮件过滤技术的研究现状进行综述,最后介绍现有过滤方案,同时讨论目前研究中遇的问题和挑战,并对未来的研究方向进行预测。     

垃圾邮件过滤技术研究

自从互联网普及以来,电子邮件逐渐成为人们生活中便捷的通信手段之一。但随之产生的垃圾邮件泛滥成灾,垃圾邮件过滤技术逐渐成为网络信息安全研究领域的热点。本文首先对垃圾邮件过滤技术研究发展阶段作简要说明,然后从内容过滤、接入过滤、行为过滤等三方面对垃圾邮件过滤技术的研究现状进行综述,最后介绍现有过滤方案,同时讨论目前研究中遇的问题和挑战,并对未来的研究方向进行预测。     

垃圾邮件及其过滤技术概述

电子邮件已成为现代生活通信、交流的重要手段,也是INTERNET服务的主要内容之一,然而垃圾邮件问题日益严重,给用户带来重大损失,如何防范垃圾邮件已成为研究热点。本文主要讨论邮件传递过程的垃圾邮件过滤问题,简单介绍SMTP配置、IP过滤规则设置、用户过滤规则设置以及邮件过滤规则设置等邮件过滤技术。     

垃圾邮件过滤技术发展现状及展望

电子邮件随着Internet的发展给人们带来了方便,但随之而来的垃圾邮件也给人们带来了不少的烦恼。针对垃圾邮件技术的发展与现状,本文对目前的垃圾邮件过滤技术进行了分析,并指出垃圾邮件过滤的发展趋势。     

垃圾邮件过滤技术分析

主要介绍基于邮件的过滤技术,对目前邮件过滤采用的模式———单机模式和将来可能采用的模式———网络模式做了个评估,并重点介绍了在单机模式中的一种基于邮件内容的过滤算法———贝叶斯算法,以及这种算法的不足和改进。     

基于免疫的动态垃圾邮件过滤研究

本文基于生物免疫系统防御机制,探讨了将人工免疫原理应用于垃圾邮件过滤系统(IDSFS),通过动态生成垃圾邮件疫苗,提高系统的检出率.另外,针对传统邮件过滤系统存在的错误肯定率、错误否定率等不足及用户对邮件个性化处理的要求,引入用户反馈机制,使得系统精确率、正确率进一步提高.实验结果表明,该系统具有较强的自学习、自适应能力.     

一种混合型垃圾邮件过滤系统的研究与设计

针对目前互联网垃圾邮件日益泛滥的情况，对目前常用的几种抗击垃圾邮件方法进行了介绍，同时提出一种混合型的垃圾邮件过滤系统，对其进行了详细地阐述。该方法结合贝叶斯理论和基于内容的邮件过滤思想，给出了邮件过滤系统的体系结构，并对其算法进行了分析。     

基于ART神经网络的垃圾邮件过滤技术

本文讨论了自适应谐振理论ART,分析了ART的工作原理,给出了ART的具体算法。以神经网络ART作为分类器来过滤垃圾邮件,ART克服了IBP网络的缺点,可以对垃圾邮价进行更有效地过滤,更好的解决了垃圾邮件特征不断变化而过滤方法相对固定的矛盾。并以实例详述了ART在邮件过滤中的工作过程,获得了很好的结果。     

互联网防御DOS/DDOS攻击策略研究

主要介绍DOS/DDOS攻击的原理与种类,并着重介绍防御DOS/DDOS攻击的应对策略,并结合专业防御系统对构建专业防御体系进行了探讨。     

智能电子邮件检测技术的研究

提出了一种智能电子邮件检测模型，该模型主要采用数据挖掘的方法，通过对大量历史邮件信息进行挖掘．提取出有用的规则，应用于邮件的检测。给出了模型的系统结构，提供了必要的示意图，并介绍了各个子模块的功能。分析了该模型的设计思想，针对几个关键技术进行了分析和解释。     

A novel technique for the on-chip tuning of monolithic filters

Monolithic analog filters, with the exception of switched capacitor filters need on-chip tuning. Existing schemes of PLL and master-slave techniques use phase control for tuning. The proposed method uses amplitude detection, where the reference voltage itself is derived from the input. Much work has recently been done on active RC continuous-time filters in VLSI [4]-[8]. The heart of all such systems is an integrator with a voltage-variable time-constant (VVI). To generate the control for the VVI, these schemes use either a self-tuning filter (follow the master technique) [5] or a phase-locked loop [8], locking on to a stable reference frequency. Unlike these techniques which are essentially phase-control schemes, what is proposed here is a gain-control scheme.     

Design of some 2-D filters through the transformation technique

The transformation technique is a powerful tool for designing 2-D FIR filters. However, it is not useful for the design of specially shaped filters with passband/stopband regions not centred around the origin. The authors extend this technique to design two types of filters. A notch filter has a stopband centred about a small region in the 2-D frequency plane. The authors propose an extension to the transformation technique with the windowing concept to achieve the design of notch filters. A directional filter has a passband extending fully along a straight line passing through the origin. The transformation technique is further extended to yield such directional filters. Design and application examples for both these filters are also presented     

基于SIP的IMS安全分析研究

文中首先分析了SIP协议的五个常见漏洞:注册劫持、服务器伪装、消息篡改、会话终止、拒绝服务,然后对IMS安全机制中的接入安全、网络域安全以及安全联盟的建立流程做了分析,并以此为基础分析研究了在IMS中应用SIP协议的漏洞实施攻击的可行性.从分析结果可以看出,IMS的安全机制能够拒绝除了DOS攻击之外的所有基于SIP漏洞的攻击.最后给出了在IMS中实施DOS攻击的流程,并利用Open SERB服务器在100M的局域网中对DOS攻击进行了仿真验证.     

Design of sharp linear-phase FIR bandstop filters using the frequency-response-masking technique

A novel computationally efficient realization of sharp linear-phase finite impulse response (FIR) bandstop filters is proposed. The synthesis scheme for the bandstop filters is derived from variations of the frequency-response-masking technique. Five realization structures are presented in this paper for the synthesis of five different classes of bandstop filters. Approximate expressions for the optimal value of the impulse response up-sampling ratio (M) and the corresponding number of multipliers are derived.     

Activity correlation-based clustering clock-gating technique for digital filters

Clock gating is an effective way to reduce the dynamic power in digital sequential circuits. In this paper, a gate-level activity correlation-based clustering clock-gating (CCG) technique is proposed for digital filters. The CCG technique exploits the correlations between flip-flops, and determines how to group the flip-flops for clock gating. An Activity Correlation Matrix (ACMtx) is introduced to describe the correlations between the flip-flops, and a greedy clustering algorithm is proposed to find an optimised clustering scheme as well. Experiments on ISCAS’89 benchmarks show that the proposed technique can reduce power consumption by 5.08% on average, on top of existing technique. For the circuits with large numbers of flip-flops, our proposed technique can save 15.84% more power on average.     

A Fast FIR filtering technique for multirate filters

This paper presents a technique for applying Fast FIR Algorithms (FFAs) to interpolation and decimation filters. In the event that the prototype filter has a symmetric impulse response, it is shown that the subfilters which result from the application of the FFA will be jointly symmetric. This fact may be exploited in order to further reduce the computational complexity of the system. The effect of transposition upon the proposed structure is discussed, and it is shown that transposition yields a more economical structure in the case of a decimation filter. The computational complexity of the proposed schemes is shown to compare favorably with that of the standard parallel filtering approach.     

Compensation technique for the design of wideband surface-acoustic-wave filters using multistrip couplers

The letter describes a technique which can be used to compensate for losses in amplitude response induced by beam profile reshaping by a multistrip coupler when used with weighted surface-acoustic-wave transducers having large time-band-width products. This is achieved by analytically modifying the conventional weighting of the transducers. Experimental results from two filter designs employing this technique are presented.