标准模型下基于身份的门限签名方案

在标准模型下（不使用随机预言模型）设计可证明安全的门限签名方案具有实际意义。利用L-J方案,设计了一个在标准模型下基于身份的安全的门限签名方案。该方案可容忍[t]小于[n/2+1]个成员被敌手破坏,门限密钥生成算法不需要可信中心,只需成员之间交互协商完成。在计算Diffie-Hellman问题（CDH问题）假设下,该方案是健壮的,且对适应性选择消息攻击是不可伪造的。     

一个无可信中心的(t,n)门限签名方案的安全性分析

一个（t，n）门限签名方案中，任何t个成员的集合能够对任意的消息产生签名而任何少于t个成员的集合都不能发行签名．其中密钥通过可信中心或没有可信中心，通过所有的成员运行交互式协议在n个成员中分配．2003年，下斌等提出了一种基于离散对数问题的无可信中心的（t，n）门限签名方案．该文对王等方案进行了分析．通过广泛性伪造签名，指出这个方案是不安全的，而且指出在合理的假设下，内部攻击者可以伪造签名，即任意恶意的签名者，可以对任何消息进行伪造攻击．     

标准模型下可证安全的基于身份门限环签名

在门限环签名中,任意n个成员组中的t个成员可以代表整个成员组产生(t,n)门限环签名,而对实际的签名者却具有匿名性。目前,基于身份的门限环签名方案大都是在随机预言模型下对其安全性进行证明的,然而在随机预言模型下可证安全的方案却未必是安全的,因此设计标准模型下的门限环签名方案更有意义。利用双线性对技术,提出了一种安全、高效的基于身份门限环签名方案,并在标准模型下基于计算Diffie-Hellman难问题证明方案满足适应性选择消息和身份攻击下的存在不可伪造性;同时,也对方案的无条件匿名性进行了证明。     

一种标准模型下基于身份的有效门限环签名方案

在门限环签名中,任意n个成员组中的t个成员可以代表整个成员组产生(t,n)门限环签名,而对实际的签名者却具有匿名性。为了设计基于身份的门限环签名方案,利用双线性对技术,提出了一种在标准模型下基于身份的有效门限环签名方案,并对方案的安全性进行了分析。最后证明了方案满足无条件匿名性,以及在CDH困难问题的假设下满足适应性选择消息和身份攻击下的存在不可伪造性。     

一个安全的(t,n)门限代理签名

在一个(t,n)门限代理签名方案中,任何t个成员组成的集合可以代表原始签名人进行代理签名,而任何少于t个成员的集合都不能进行代理签名。针对合谋攻击提出了一个安全的(t,n)门限代理签名方案。合谋攻击是指在不知道任何有效的门限代理签名的情况下,恶意代理成员人数大于或等于门限值时,他们能合谋重新构造代理群的秘密参数,从而可以伪造其他代理成员的签名。新方案不仅能满足门限代理签名的性质,而且能抵抗合谋攻击。     

一种可防止合谋攻击的门限签名方案

针对现有门限签名方案在抵抗合谋攻击上的弱点,基于离散对数问题提出了一个（t,n）门限签名方案。在该方案中,t个或t个以上的内部成员合作可以代表群体产生有效的门限签名,但不能获取系统秘密,从而有效地阻止了内部恶意成员的合谋攻击。方案还能够防止伪造攻击,并具有可追踪性。     

签名长度固定的基于身份门限环签名方案

在门限环签名中,任意n个成员组中的t个可以代表整个成员组产生(t,n)门限环签名,而对实际的签名者却具有匿名性。为了设计签名长度是常量的门限环签名方案,通过使用双线性对技术,提出了一种无需随机预言机的基于身份的门限环签名方案。最后,通过对方案的安全性进行分析,指出方案满足无条件匿名性以及在Diffie-Hellman 逆(DHI)困难问题的假设下满足选择消息和身份攻击下的存在不可伪造性。     

无可信中心的(t,n)门限签名方案

在基于离散对数的安全机制的前提下讨论了(t，n)门限群签名方案．目前流行的门限签名方案一般可分为需要可信中心和不需要可信中心两类．由于在许多特定的应用环境下，一个可被所有成员信任的可信中心并不存在，所以不需要可信中心的门限群签名方案就显得很有吸引力．但已有的方案中使用了秘密共享技术，超过门限值的小组成员利用他们所掌握的秘密份额就能够恢复某个成员的私钥．为了解决这个问题，在新的方案中，利用联合秘密共享技术(joint secret sharing)解决了传统的秘密共享技术造成的成员的私钥泄露问题．     

基于分组秘密共享的(t,n)门限群签名体制

已有的门限群签名体制无法抵抗合谋攻击的原因,是群中任意t或更多个成员共享的秘密就是群密钥,所以群中任何一组成员合谋可以恢复群密钥,从而可以假冒其他小组生成有效的群签名,所以设计性能良好的门限签名被认为是open问题．该文给出了一种新的适用于(t,n)门限群签名的秘密共享方案称为分组秘密共享方案,群中任意t个成员共享一个秘密,而群秘密是所有组共享秘密的和．基于分组秘密共享方案设计了一类安全的可追查签名者身份的(t,n)门限群签名体制,部分成员合谋无法获得任何系统秘密参数,从而可以抵抗合谋攻击。     

有效的门限签名算法

门限签名是一种特殊的数字签名,它在现实生活中具有广泛的用途。一个(t,n)门限签名方案是指n个成员组成的群中,群中任何不少于t个成员合作就能产生签名,然而任何少于t个成员合作都无法伪造签名。但是,现有的许多签名算法都存在一个普遍的缺陷,即不能抵抗合谋攻击,换句话说,任意t个成员合谋就可以恢复出秘密系统参数,从而就可以伪造其他签名小组签名。针对较小的n和t以及较大n和t分别提出两种有效的抗合谋攻击的门限签名方案,当n和t较小时,给出了一种基于分组秘密共享的RSA门限签名算法;当n和t比较大时,提供了一种具有指定签名者的方案来解决合谋攻击问题。     

Only connect: teaching, technology and telesis

Abstract This paper describes an approach to the design of interactive multimedia materials being developed in a European Community project. The developmental process is seen as a dialogue between technologists and teachers. This dialogue is often problematic because of the differences in training, experience and culture between them. Conditions needed for fruitful dialogue are described and the generic model for learning design used in the project is explained.     

European Community policy and the market

Abstract This paper starts with some reflections on the policy considerations and priorities which are shaping European Commission (EC) research programmes. Then it attempts to position the current projects which seek to capitalise on information and communications technologies for learning in relation to these priorities and the apparent realities of the marketplace. It concludes that while there are grounds to be optimistic about the contribution EC programmes can make to the efficiency and standard of education and training, they are still too technology driven.     

一种自适应子融合集成多分类器方法

融合集成方法已经广泛应用在模式识别领域,然而一些基分类器实时性能稳定性较差,导致多分类器融合性能差,针对上述问题本文提出了一种新的基于多分类器的子融合集成分类器系统。该方法考虑在度量层融合层次之上通过对各类基多分类器进行动态选择,票数最多的类别作为融合系统中对特征向量识别的类别,构成一种新的自适应子融合集成分类器方法。实验表明,该方法比传统的分类器以及分类融合方法识别准确率明显更高,具有更好的鲁棒性。     

Avoiding semantic and temporal gaps in developing software intensive systems

Development of software intensive systems (systems) in practice involves a series of self-contained phases for the lifecycle of a system. Semantic and temporal gaps, which occur among phases and among developer disciplines within and across phases, hinder the ongoing development of a system because of the interdependencies among phases and among disciplines. Such gaps are magnified among systems that are developed at different times by different development teams, which may limit reuse of artifacts of systems development and interoperability among the systems. This article discusses such gaps and a systems development process for avoiding them.     

Designing economic np control charts: A programmed simulation approach

This paper presents control charts models and the necessary simulation software for the location of economic values of the control parameters. The simulation program is written in FORTRAN, requires only 10K of main storage, and can run on most mini and micro computers. Two models are presented - one describes the process when it is operating at full capacity and the other when the process is operating under capacity. The models allow the product quality to deteriorate to a further level before an existing out-of-control state is detected, and they can also be used in situations where no prior knowledge exists of the out-of-control causes and the resulting proportion defectives.     

The development of robot art

Going through a few examples of robot artists who are recognized worldwide, we try to analyze the deepest meaning of what is called “robot art” and the related art field definition. We also try to highlight its well-marked borders, such as kinetic sculptures, kinetic art, cyber art, and cyberpunk. A brief excursion into the importance of the context, the message, and its semiotics is also provided, case by case, together with a few hints on the history of this discipline in the light of an artistic perspective. Therefore, the aim of this article is to try to summarize the main characteristics that might classify robot art as a unique and innovative discipline, and to track down some of the principles by which a robotic artifact can or cannot be considered an art piece in terms of social, cultural, and strictly artistic interest. This work was presented in part at the 13th International Symposium on Artificial Life and Robotics, Oita, Japan, January 31–February 2, 2008     

Explanation and prediction: an architecture for default and abductive reasoning

Although there are many arguments that logic is an appropriate tool for artificial intelligence, there has been a perceived problem with the monotonicity of classical logic. This paper elaborates on the idea that reasoning should be viewed as theory formation where logic tells us the consequences of our assumptions. The two activities of predicting what is expected to be true and explaining observations are considered in a simple theory formation framework. Properties of each activity are discussed, along with a number of proposals as to what should be predicted or accepted as reasonable explanations. An architecture is proposed to combine explanation and prediction into one coherent framework. Algorithms used to implement the system as well as examples from a running implementation are given.     

Three Process Perspectives: Organizations, Teams, and People

This paper provides the author's personal views and perspectives on software process improvement. Starting with his first work on technology assessment in IBM over 20 years ago, Watts Humphrey describes the process improvement work he has been directly involved in. This includes the development of the early process assessment methods, the original design of the CMM, and the introduction of the Personal Software Process (PSP)^SM and Team Software Process (TSP){^SM}. In addition to describing the original motivation for this work, the author also reviews many of the problems he and his associates encountered and why they solved them the way they did. He also comments on the outstanding issues and likely directions for future work. Finally, this work has built on the experiences and contributions of many people. Mr. Humphrey only describes work that he was personally involved in and he names many of the key contributors. However, so many people have been involved in this work that a full list of the important participants would be impractical.     

基于复小波噪声方差显著修正的SAR图像去噪

提出了一种基于复小波域统计建模与噪声方差估计显著性修正相结合的合成孔径雷达(Synthetic Aperture Radar,SAR)图像斑点噪声滤波方法。该方法首先通过对数变换将乘性噪声模型转化为加性噪声模型,然后对变换后的图像进行双树复小波变换(Dualtree Complex Wavelet Transform,DCWT),并对复数小波系数的统计分布进行建模。在此先验分布的基础上,通过运用贝叶斯估计方法从含噪系数中恢复原始系数,达到滤除噪声的目的。实验结果表明该方法在去除噪声的同时保留了图像的细节信息,取得了很好的降噪效果。     

How do children do mathematics with LOGO?

Abstract  This paper considers some results of a study designed to investigate the kinds of mathematical activity undertaken by children (aged between 8 and 11) as they learned to program in LOGO. A model of learning modes is proposed, which attempts to describe the ways in which children used and acquired understanding of the programming/mathematical concepts involved. The remainder of the paper is concerned with discussing the validity and limitations of the model, and its implications for further research and curriculum development.