Denial of service attacks and defenses in decentralized trust management

Trust management is an approach to scalable and flexible access control in decentralized systems. In trust management, a server often needs to evaluate a chain of credentials submitted by a client; this requires the server to perform multiple expensive digital signature verifications. In this paper, we study low-bandwidth Denial-of-Service (DoS) attacks that exploit the existence of trust management systems to deplete server resources. Although the threat of DoS attacks has been studied for some application-level protocols such as authentication protocols, we show that it is especially destructive for trust management systems. Exploiting the delegation feature in trust management languages, an attacker can forge a long credential chain to force a server to consume a large amount of computing resource. Using game theory as an analytic tool, we demonstrate that unprotected trust management servers will easily fall prey to a witty attacker who moves smartly. We report our empirical study of existing trust management systems, which manifests the gravity of this threat. We also propose a defense technique using credential caching, and show that it is effective in the presence of intelligent attackers. A preliminary version of this paper was presented at the Second IEEE International Conference on Security and Privacy in Communication Networks, Baltimore, MD, USA, August 2006.     

IP地址的安全机制研究

针对网络安全问题,对IP地址的安全性进行了系统化研究,提出了接入路由器的概念,在此基础上提出了在接入路由器中的IP验证和对其管辖局域网IP验证的思路和方法,从而从根本上解决了IP地址不可信的问题,可有效防御IP地址欺骗、DoS攻击等网络安全问题,为相关管理机关管理虚拟空间和侦查办案提供了良好的机制。     

标志图形符号化表现特征的分析

论述了标志图形符号化表现形式,并且运用符号能指和所指的基本原理将标志图形的视觉符号进行解构和分析,以此凸显符号在标志图形设计中的重要性,旨在更准确地运用其相关原理进行标志设计。     

艺术设计专业背景下广告理论课程教学方法改革研究

文章本着以学生为主体,以教师为主导的教育理念,针对艺术设计类学生的认知特点,研究如何有效开展广告学理论课程的教学方法。通过教学改革的研究与实践,总结出了艺术设计专业背景下广告学理论课程四个有效的教学方法:形象化、案例化、网络化、实践化。     

Bayes理论在机器人信息融合中的应用

移动机器人的自动能力中实时避障和导航是一个很关键的技术,研究的主要问题是：机器人在运动时需要充分的环境信息,而且处理这些信息的速度要快,同时也要满足实时性的要求。文章介绍了将Bayes经典推理理论应用于机器人对未知环境的探索、感知过程,确定了具体的实验方案和实现步骤,完成了一个简化的仿真算例,并通过仿真结果对该方法的有效性和性能进行了验证和评估。     

论中国传统造型观念在图形设计中的传承

传统造型观念是中国传统艺术的一个重要组成部分,它作为一种民族文化和视觉美感的研究形式,是不容被忽视的。本文通过对传统造型观念在造型手法与特点等方面的分析,找出它在艺术形式和表现手法上对现代图形设计的影响。并进一步论述中国传统造型观念对于图形设计的现实意义.从而说明传承与发扬我们的传统文化,把其精神元素融入图形设计中,必定会使图形设计与国际化视觉语言进行有机结合,这是中国现代设计的必由之路。     

D-S证据理论在移动机器人信息融合中的应用

移动机器人的自动能力中实时避障和导航是一个很关键的技术,研究中主要的问题是：机器人在运动时需要充分的环境信息,而且处理这些信息的速度要快,同时也要满足实时性的要求。详细介绍了将D-S证据理论应用于移动机器人对未知环境的探索、感知过程,并通过仿真结果对D-S证据融合方法的性能进行研究与改进,确定了D-S证据融合方案的具体实现步骤,并完成了一个简化的仿真算例,得出了相关结论。     

Controller synthesis with guaranteed closed-loop phase constraints

In this paper, we present an analysis and synthesis approach for guaranteeing that the phase of a single-input, single-output closed-loop transfer function is contained in the interval [−α,α] for a given α>0 at all frequencies. Specifically, we first derive a sufficient condition involving a frequency domain inequality for guaranteeing a given phase constraint. Next, we use the Kalman–Yakubovich–Popov theorem to derive an equivalent time domain condition. In the case where , we show that frequency and time domain sufficient conditions specialize to the positivity theorem. Furthermore, using linear matrix inequalities, we develop a controller synthesis approach for guaranteeing a phase constraint on the closed-loop transfer function. Finally, we extend this synthesis approach to address mixed gain and phase constraints on the closed-loop transfer function.     

A -based optimal finite-word-length controller design

A novel optimal Finite Word Length (FWL) controller design is proposed in the framework of μ theory. A computationally tractable close-loop stability measure with FWL implementation considerations of the controller is derived based on the μ theory, and the optimal FWL controller realizations are obtained by solving the resulting optimal FWL realization problem using linear matrix inequality techniques.     

基于OWL的本体集成

提出一种新的本体集成方法。分析了本体集成的原因,阐述了本体集成时应遵循的4条基本原则,并给出了集成的分类,提出了一种基于OWL DL图闭包的本体集成方法。该方法将OWL DL本体抽象为RDFS图模型,根据给定的OWL DL推理规则生成OWL DL本体的图闭包,在此基础上进行本体集成,同时提出了几种计算实体相似度的方法,将本方法与COMA++和FCA-merge进行实验对比,本方法在准确率和召回率上占优势。