企业网站常见攻击及其应对策略

企业网站会经常受到黑客的攻击,主要讨论常见的脚本漏洞、旁注、缓冲区溢出、分布式拒绝服务、解码攻击等五种攻击方式及其应对策略。     

Design Signals: The Role of Software Architecture and Paradigms in Design Thinking and Practice

Does the ontology of design software influence built form? Panagiotis Michalatos , lecturer in architectural technology at Harvard Graduate School of Design and a principal research engineer at Autodesk, Inc, here looks at how the move from drawing typologies to digital modelling since the mid-1990s has affected architectural aesthetics. He goes on to examine two more recent developments that may announce a further paradigm shift: granular tracking of design input, and data organisation practices in biomedics which, transferred to architecture, could allow for a more spatio-temporal approach.     

Modeling and analysis of hierarchical cellular networks with bidirectional overflow and take-back strategies under generally distributed cell residence times

The rapid growth of wireless services and mobile users drives a great interest in cellular networks with a hierarchical structure. Hierarchical cellular networks (HCNs) can provide high system capacity, efficient channel utilization and inherent load-balancing capability. In this paper, we develop an analytical model and a performance analysis method for a two-layer HCN with bidirectional overflow and take-back strategies. Mobile users are divided into two classes. The call requests (including new and handoff calls) of fast and slow users are preferably assigned to the macrolayer and microlayer, respectively. A call from a fast user or slow user can overflow to its non-preferable layer if there is no channel available. The successful overflow call can be taken back to its preferable layer if a channel becomes available. Since the commonly used exponentially distributed assumption for cell residence time and then the channel occupancy time does not hold for emerging mobile networks, we model various cell residence times by general distributions to adapt to more flexible mobility environments. The channel occupancy times are derived in terms of the Laplace transforms of various cell residence times. The handoff rates, overflow rates and take-back rates of each layer are also derived in terms of the new call arrival rates and related probabilities. The stationary probabilities (and then the performance measures) are determined on the basis of the theory of multi-dimensional loss systems.     

嵌入式系统安全中缓冲区溢出防止技术的研究与实现

提出将嵌入式系统下缓冲区溢出分为堆栈溢出攻击和指针攻击两类,并基于该分类提出软硬件结合的防范缓冲区溢出方法,针对两类缓冲区溢出分别采用基于硬件的堆栈保护技术和指针保护技术来防范。与[2]中的软硬件防范技术(HSDefender)相比,本文的方法进一步实现了数据指针的保护。     

数字式自动衰减器设计

文中介绍以数控衰减器ＡＤ７１１８为核心配以衰减控制码电路组成数字式自动衰减器的设计。自动衰减器量根据输入信号电平高低自动调节并具有衰减分贝值的数字显示及数字输出。     

混凝土面板堆石坝坝体过水保护

天生桥一级水电站混凝土面板堆石坝堆石填筑量大，在大坝填筑施工的第一个汛期，坝体内预留底宽１２０ｍ、边坡１：１．４的梯形泄槽，该泄槽与导流隧洞联合运行承担１９９６年汛期泄洪任务。泄槽过流按３０年一遇洪水标准加以保护，选用直径大于２０ｃｍ的干砌块石护坡，其表面覆盖铁网，并用钢筋框格固定，泄槽重要部位采用钢筋铁丝笼充填块石加以保护。泄槽过流后，抽水检查结果表明，过流保护面无任何冲刷破坏，达到了安全渡汛的     

天然气超深井井底压力计算与应用

钻井液喷空后的井底压力可以精确计算,为正确地保证井底压力大于或等于地层压力提供了科学的数据。钻井液喷空后的深井超深井的天然气井,关井后的静气柱压力不是很小。井内有钻井液(或修井液)井底进入天然气时,井底压力在合理地处理井内天然气在井内的运移(体积法放压法)与二次循环法压井循环出进入井内的天然气是相同的,为钻井井控现场为避免压裂套管鞋处或地层压力低的地层提供了可靠的依据。     

基于虚拟仪器的溢流阀动态特性测试技术

在分析溢流阀动态特性测试原理的基础上，设计了溢流阀动态特性测试虚拟仪器系统。此系统应用小波降噪的方法提高测试信号的质量，然后提取信号特征点，得到溢流阀动态特性的各项参数。     

缓冲区溢出攻击与防范

随着计算机和网络技术的发展,计算机和网络的安全正受到日益严重的威胁。各种攻击手段不断出现,造成计算机和网络不能正常运行、数据受到破坏和窃取等。缓冲区溢出攻击是对计算机和网络进行攻击的常见方法之一。它是利用向一个有限的缓冲区中拷贝过长的字符串,导致缓冲区相邻存储单元被覆盖,从而使程序运行失败或跳转到攻击者设计的攻击代码处执行攻击代码。这样攻击者就有机会获取计算机或网络服务器的控制权。介绍了代码植入、参数传递、利用活动记录和函数指针及长跳转缓冲区等攻击方法。同时,介绍了缓冲区溢出攻击的防范措施。     

基于重复平方的重复二倍算法

在重复平方算法的基础上提出了重复二倍算法,极大地降低了乘法模运算溢出的可能性,并给出了具体的实现代码.