一种动态叛徒追踪方案的性能分析

叛徒追踪方案是在共谋密钥攻击和重放攻击中追踪及识别叛徒的有效措施.文中介绍了A.Fiat和T.Tassa提出的3个不同追踪算法,并在系统带宽要求和追踪复杂度方面对算法进行了分析比较,指出算法存在的性能缺陷.理论算法A的系统计算量虽然较低,但是追踪复杂度接近月nρ;算法B,C在系统带宽和追踪复杂度之间进行了均衡,但算法C的追踪复杂度依然很高.较高的复杂度使得方案只能适用于较小用户量系统.     

基于流量序列包标记的IP追踪方法

文章分析了分布式拒绝服务(DDos)攻击的特点和现有的追踪方法,认为对攻击的追踪和辨伪应在网络边界入口和被攻击端进行.根据分布式精确协同较难的特点,提出了一种基于流量序列的包标记法(Flow Sequence Packet Marking,FSPM),用于追踪攻击子网的地址.讨论分析了该方法的算法、有效性、复杂度以及进一步的研究方向.     

一个高效的基于M序列的叛逆者追踪方案

文中提出一种基于M序列的叛逆追踪方案.在该方案中,当发现盗版的解密盒时,能够以黑盒子的追踪方式至少追踪到一个制造盗版解密盒的用户(称为叛徒).该方案的一个非常重要的特点是:当发现盗版的解密盒时,追踪的次数是与用户个数之间成线性关系的.因此,追踪算法的效率非常高.此外,追踪算法的实现不受共谋用户个数的限制.     

基于ICA算法的攻击源研究

近些年来,分布式拒绝攻击DDoS(Distributed Denial of Service)因其实施简单、破坏力及危害性巨大,已经成为目前网络安全中最大的威胁之一,如何有效的防范DDoS攻击、减少DDoS攻击带来的危害已成为当前的研究热点。本文重点分析了基于包标记算法的DDoS攻击源追踪技术,对于各种基于包标记算法的攻击源追踪技术进行了原理研究,并对其各自优缺点分别进行了分析与总结。根据各种基于包标记算法的攻击源追踪技术原理,给出了其算法流程。同时,通过模拟实验,对相关的基于流量模式匹配技术的攻击源追踪技术进行了对比与分析,验证了本文提出的算法的性能。     

对两个基于混沌的序列密码算法的分析

本文指出"混沌非线性反馈密码序列的理论设计和有限精度实现"和"一类新型混沌反馈密码序列的理论设计"两文基于混沌设计的两个序列密码算法产生的乱数序列的前若干值对密钥的变化并不敏感,据此在已知混沌变换的条件下,可以利用已知明文采取先攻击高位密钥再攻击低位密钥的方法对这两个密码算法进行分割攻击.本文还提出了在正确密钥的分布已知条件下使平均计算复杂性达到最小的穷举攻击算法,并将它与分割攻击方法结合,提出了对上述两个密码算法的优化分割攻击方案,并分析了这两个攻击方案的计算复杂性和成功率.     

基于流量强度的DDoS攻击源追踪快速算法

DDoS攻击以其破坏力大、易实施、难检测、难追踪等特点,而成为网络攻击中难处理的问题之一。攻击源追踪技术是阻断攻击源、追踪相关责任、提供法律证据的必要手段。基于网络拓扑理论和路由器流量特性原理以及可编程式路由器的体系结构,提出了一种追踪DDoS攻击源的分布式快速算法,该算法可以准确、协调、高效地判断路由器的数据流量值,受害者可以根据流量强度推断出恶意攻击数据流的来源,从而快速追溯和定位DDoS攻击源。     

基于动态概率包标记的DDOS攻击源追踪技术研究

如何防御分布式拒绝服务(DDoS)攻击是当今最难解决的网络安全问题之一.针对如何追踪DDoS攻击源进行研究,在分析原有动态概率包标记算法的基础上,提出新的算法,并对两种算法的优劣进行分析比较.     

一种高效群签名方案的密码学分析

2005年,张键红等提出了一种基于RSA的高效群签名方案,签名与验证的计算量只需要9次模幂乘运算。该文提出了一种伪造攻击方案指出张等的方案是不安全的,任一群成员在撤消中心的帮助下可以不利用自己的秘密参数对任何消息生成有效的群签名。同时,指出了群成员的识别算法是错误的,身份追踪式是与具体签名无关的常量,即身份追踪算法无法追踪到真实的签名者。最后,指出了他们的方案具有关联性。     

基于代数方法的概率报文标注算法研究

网络攻击的追踪是对网络攻击做出正确响应的重要前提,采用代数方法,利用IP报文中的选项字段,以概率将流经路由器的地址标注报文,使得受攻击主机端能够利用被标注报文内的地址信息重构攻击路径,从而追踪到攻击源点.重点讨论了如何运用代数方法记录报文流经路由器的地址,以及利用报文中记录的信息重构路径使ISP部署相关策略对这些范围的主机加以防范.可以预见,网络攻击的追踪和路径重构技术仍将是目前网络安全一个重要的研究热点,而且随着IPv6的应用,攻击源追踪问题将取得实质性突破.同时指出了该方法存在的问题,并进行了进一步展望.     

对拒绝服务网络攻击路由的反向追踪算法

针对拒绝服务攻击 ,介绍几种常用的发现拒绝服务攻击路径的反向追踪算法 ,提出两种基于IP选项的数据包标记算法 ,并给出了相应的算法实现。最后对这些算法的有关性能进行了比较。     

Median-based robust algorithms for tracing neurons from noisy confocal microscope images

This paper presents a method to exploit rank statistics to improve fully automatic tracing of neurons from noisy digital confocal microscope images. Previously proposed exploratory tracing (vectorization) algorithms work by recursively following the neuronal topology, guided by responses of multiple directional correlation kernels. These algorithms were found to fail when the data was of lower quality (noisier, less contrast, weak signal, or more discontinuous structures). This type of data is commonly encountered in the study of neuronal growth on microfabricated surfaces. We show that by partitioning the correlation kernels in the tracing algorithm into multiple subkernels, and using the median of their responses as the guiding criterion improves the tracing precision from 41% to 89% for low-quality data, with a 5% improvement in recall. Improved handling was observed for artifacts such as discontinuities and/or hollowness of structures. The new algorithms require slightly higher amounts of computation, but are still acceptably fast, typically consuming less than 2 seconds on a personal computer (Pentium III, 500 MHz, 128 MB). They produce labeling for all somas present in the field, and a graph-theoretic representation of all dendritic/axonal structures that can be edited. Topological and size measurements such as area, length, and tortuosity are derived readily. The efficiency, accuracy, and fully-automated nature of the proposed method makes it attractive for large-scale applications such as high-throughput assays in the pharmaceutical industry, and study of neuron growth on nano/micro-fabricated structures. A careful quantitative validation of the proposed algorithms is provided against manually derived tracing, using a performance measure that combines the precision and recall metrics.     

激光飞行标刻运动跟踪技术

研究了在线激光飞行标刻运动跟踪的原理,提出运动的工件坐标系和静止的振镜扫描坐标系定义,通过分析两坐标系的映射关系得到激光飞行标刻图形数据的运动补偿公式。针对生产线匀速和变速运动的不同特点,基于计算机平台设计并实现了开环恒速计算跟踪和闭环位移检测跟踪两种运动跟踪算法模型。实验结果表明,开环恒速计算跟踪模型采用纯软件计算实现运动跟踪,不需增加额外硬件,适合恒速工作环境。闭环位移检测跟踪模型通过旋转编码器采集生产线位移反馈信号来实现运动跟踪补偿,避免了开环模型下因速度波动容易导致的计算跟踪误差,具有速度自适应的优点,在变速情况下也能得到良好的标刻效果。     

Local tracing of curvilinear structures in volumetric color images: Application to the Brainbow analysis

In this study, we compare two vectorial tracing methods for 3D color images: (i) a conventional piecewise linear generalized cylinder algorithm that uses color and edge information and (ii) a principal curve tracing algorithm that uses the gradient and Hessian of a given density estimate. We tested the algorithms on synthetic and Brainbow dataset to show the effectiveness of the proposed algorithms. Results indicate that the proposed methods can successfully trace multiple axons in dense neighborhoods.     

Robust model-based vasculature detection in noisy biomedical images

This paper presents a set of algorithms for robust detection of vasculature in noisy retinal video images. Three methods are studied for effective handling of outliers. The first method is based on Huber's censored likelihood ratio test. The second is based on the use of a alpha-trimmed test statistic. The third is based on robust model selection algorithms. All of these algorithms rely on a mathematical model for the vasculature that accounts for the expected variations in intensity/texture profile, width, orientation, scale, and imaging noise. These unknown parameters are estimated implicitly within a robust detection and estimation framework. The proposed algorithms are also useful as nonlinear vessel enhancement filters. The proposed algorithms were evaluated over carefully constructed phantom images, where the ground truth is known a priori, as well as clinically recorded images for which the ground truth was manually compiled. A comparative evaluation of the proposed approaches is presented. Collectively, these methods outperformed prior approaches based on Chaudhuri et al. (1989) matched filtering, as well as the verification methods used by prior exploratory tracing algorithms, such as the work of Can et aL (1999). The Huber censored likelihood test yielded the best overall improvement, with a 145.7% improvement over the exploratory tracing algorithm, and a 43.7% improvement in detection rates over the matched filter.     

基于三维射线跟踪的城市微小区电波传播预测算法

射线跟踪算法是用于城市微小区电波传播预测的一种有效算法,但大多文献只对其正向算法进行了详细的探讨,而对于比较精确的反向算法却少有提及.本文对基于三维模型的射线跟踪反向算法进行了详细的讨论,并建立了城市微小区的三维的反向射线跟踪模型.     

室内可见光LED信道特性研究

为了研究室内多个白光LED构成的室内无线信道的特性,首先分析了多LED通信系统的基本构成,然后分析了光线追迹法求脉冲响应的基本原理和基本方法,提出了用简化的光线追迹法计算信道的脉冲响应,这种方法仅仅考虑三次以下的反射情况.最后,用数值仿真方法对室内信道的脉冲响应进行了研究.仿真结果表明,系统的脉冲响应以直接响应和一阶响应为主,并随接收器和发射装置的位置不同而发生变化.     

Review of information hiding on Chinese text

Text information hiding is an important technology to protect the security and integrity of text content.The research progress of Chinese text information hiding was reviewed.According to the clue of Chinese text information hiding,the existing algorithms were divided into three categories,algorithms based on text images,algorithms based on text format and algorithms based on text content.The implementation process of each type of algorithm was elaborated and the advantages and disadvantages of the algorithm were analyzed.At the same time,their principles,embedded capacity and anti-attack capability was compared and analyzed.In addition,the problems existing in Chinese text information hiding technology was summarized,and the research trends were discussed in the future.It is expected to provide reference for research in this field.     

二维谱估计算法的空间探测性能分析及验证

针对二维谱估计算法的空间探测性能分析的需求,从计算速度、计算量、顽健性、计算精度以及实际工程应用的角度出发,对基于L型阵列的二维MUSIC、二维干涉仪、二维增广矩阵束的谱估计算法进行了简要介绍,并对上述二维谱估计算法的性能进行了仿真分析,得到了3种算法的角度RMSE的对比分析,可知在同样仿真条件下,二维增广矩阵束算法最优,二维MUSIC算法次之,二维干涉算法最差。同时,构建了相应的试验场景,通过试验分析上述二维谱估计算法的空间探测性能,得到的试验结论与仿真结论一致。在此基础上,提出了二维增广矩阵束算法可扩展应用到雷达测控一体化系统的思路。     

Deep knowledge tracking algorithm based on forgetting law

Knowledge tracking(KT) algorithm, which can model the cognitive level of learners, is a fundamental artificial intelligence approach to solve the personalized learning problem in the field of education. The recently presented separated self-attentive neural knowledge tracing(SAINT) algorithm has got a great improvement on predictingthe accuracy of students’ answers in comparison with the present other methods.However there is still potential to enhance its performance for it fails to effectively...