PKI-X.509公钥证书及其CA的研究进展

CA及公钥证书是目前Internet上各类安全应用系统的主要密钥管理方式。本文首先描述了用于在Internet分布式网络环境下管理公钥的PKIX.509证书管理模型及其研究进展,全面分析了构造PKI的主要协议,X.500目录协议和X.509基于证书的认证协议,并对证书存取协议及其最新发展进行了描述。     

32位技术引领信息安全新时代

现代社会是网络社会,计算机网络已经并将深刻地影响人类生活的各个方面,特别是自二十世纪九十年代以来随着Internet的迅猛发展,使得网络上信息安全问题日益凸现。为解决Internet的安全问题, 世界各国对其进行了多年的研究, 初步形成了一套完整的Internet安全解决方案,即目前被广泛采用的公钥基础设施(Pubic Key Infrastructure,PKI)。     

因特网密钥交换协议的远程用户认证技术

在Internet密钥交换协议的基础上引入扩展IKE协议和混合认证方式,解决了IPsec协议中远程用户认证的问题,同时根据公钥基础设施PKI部署的不同情况提出了远程用户接入基于IPsec协议的VPN网络的解决方案。     

SESAME认证协议的研究与分析

分布式文件系统的安全性问题越来越突出,随着Internet的广泛应用,跨越大型网络的文件系统的使用容易受到来自网络的攻击,认证问题日益重要。目前使用较多的是基于对称密钥密码体制的Kerberos认证系统。本文对基于公钥密码体制的SESAME认证和访问控制协议进行了研究和分析,指出了由了采用了公钥密码体制,SESAME技术能够实现单点登录、强用户认证、用户和系统间的交互认证、基于角色的访问控制和用户的授权等功能。     

RSA公钥密码系统算法结构及其安全性

随着Internet的广泛使用,信息的安全与保密显得越来越重要,日益激增的电子商务和因特网应用需求使公钥密码系统得以普及。文章在简要介绍了RSA公钥密码系统的产生背景之后,详细介绍了RSA公钥密码算法的数论理论基础及密码算法结构,最后分析了RSA公钥密码系统的安全性。     

安全电子邮件协议

一、PGP PGP(Pretty Good Privacy)是针对电子邮件在Internet上通信的安全问题而设计的一种公钥加密系统.PGP包含4个密码单元:单钥密码(IDEA)、双钥密码(RSA)、单向杂凑算法(MD-5)和一个随机数生成算法.PGP的用户拥有一张公钥列表(key ring),列出了所需要通信的用户及其公钥.PGP最初被设计为一个独立于邮件客户端的程序,邮件在发送前被作为附件进行加密.图l是利用PGP在Internet上通信的示意图.     

无线传感器网络中一种基于公钥的密钥分配方案

针对基于对称密钥的密钥分配技术无法彻底解决无线传感器网络中密钥分配的安全问题,提出了一种基于公钥的密钥预分配方案,基站利用一系列原始公钥和单向散列函数产生公钥集合,并为每个节点随机分配公私钥对和公钥集合的子集。由于私钥的唯一性,采用该方案不仅能够提高网络的安全性能,而且可以改善网络的存储开销。利用随机图论的相关原理证明,该方案与传统的密钥预分配方案相比,既保证了网络的安全,又兼顾了网络和节点资源有限的实际,在连通性不变的前提下,其网络安全性和网络的扩展性大幅度提高。     

移动Adhoc网络中的密钥管理

文章首先介绍了移动Adhoc网络面临的主要安全威胁,并由此得到在Adhoc网络中应用PKI的重要意义。并介绍了目前现有的Adhoc网络密钥管理最基本的两个方案：分布式公钥管理方案和自组织公钥管理方案,分别论述了其基本原理以及不足之处。     

浅谈Internet网络维护与防火墙

随着Internet网络技术的不断发展,网络已经发展成为人们生活中必不可少的一部分。但是,Internet网络安全问题一直很严重,人们现在越来越关注Internet网络维护与防火墙,因此,研究Internet网络维护与防火墙具有非常重大的意义。本文介绍了Internet网络安全的重要意义和内涵,提出了Internet网络的维护的一些措施。     

无线传感器网络的安全问题

网络安全是无线传感器网络应用的前提和基础。考虑到主要的网络威胁,公钥加密和基于公钥的密钥管理对于WSN来说是最为安全也是最有效地安全措施。随后对一些典型算法进行了分析,并指出了无线传感器网络的下一步发展方向。     

Virtual impedance control for a regional dynamic voltage restorer

A dynamic voltage restorer (DVR) can be installed in a middle-voltage (MV) power grid, to concurrently protect a cluster of sensitive loads from voltage sags. To further improve its efficiency and reduce the difficulty in its implementation, a novel control strategy for operating such a DVR as a virtual impedance in series with sensitive loads is proposed in this paper. In addition to its usual function of compensating for voltage sags, such a DVR can also operate as a virtual inductance, to function as a fault current limiter (FCL) during a downstream fault, or a virtual capacitance, to function as a series compensator (SC) to compensate the voltage loss along the feeder line during heavy load. Based on a dual-loop control design, strategies for operating a DVR as a series virtual inductance and a virtual capacitance are proposed, and methods for tuning the parameter values and a stability analysis of the whole system are presented. The feasibility and effectiveness of the proposed method are verified by simulations using the PSCAD software, and experimental results obtained using a prototype DVR are presented.     

温度控制装置中的InSb-In磁敏电阻

研究了InSb-In共晶体薄膜磁敏电阻(MR)的温度特性,并把这种磁敏电阻应用到温度控制领域,设计了一种基于InSb-In磁敏电阻的温度控制器,由InSb-In磁敏电阻温度采集电路、信号处理电路和控制执行电路三部分组成。实验结果表明,InSb-In磁敏电阻材料同其他温敏元件材料一样,具有很好的温度特性,其温度特性与热敏电阻NTC极为相近;用InSb-In磁敏电阻材料制作的温控器具有灵敏度高、控温范围宽的优点,在低温区其灵敏度可以高于30mV/℃,常温下也可达到23mV/℃左右。同时它还具有稳定性强、可靠性好、受环境因素影响小、结构简单紧凑、价格低廉、对材料要求低等诸多优点,是一种值得推广应用的新型材料温度开关。     

New formulation of GNSS acquisition with CFAR detection

This paper deals with the analysis of the acquisition process performed by a global navigation satellite system (GNSS) receiver with a pilot and data channel or in case of GNSS hybrid receiver. Signal acquisition decides the presence or absence of GNSS signal by comparing signal under test with a fixed threshold and provides a code delay and a Doppler frequency estimation, but in low signal conditions or in a noisy environment; acquisition systems are vulnerable and can give a high false alarm and low detection probability. Firstly, we introduce a cell‐averaging‐constant false alarm rate (CFAR) then a data‐pilot cell‐averaging‐CFAR detector fusion based to deal with these situations. In this context, we use a new mathematical derivation to develop a closed‐form analytic expressions for the probabilities of detection and false alarm. The performances of the proposed detector are evaluated and compared with a non‐CFAR case through an analytical and numerical results validated by Mont Carlo simulations. Copyright © 2016 John Wiley & Sons, Ltd.     

A precision low-power analog front end in 180 nm CMOS for wireless implantable capacitive pressure sensors

This paper presents a new capacitance to voltage analog-front end (AFE) designed in 180 nm CMOS technology for wireless implantable applications. This AFE consists of a Low-dropout regulator (LDO), bandgap reference (BGR), switched-capacitor (SC) sampler, SC op-amp and oscillator. The LDO regulates the wireless power supply coming from an off-chip rectifier and provides a stable and accurate DC voltage. Capacitance is converted to a discrete voltage by a SC sampling circuit and then amplified by a SC op-amp. Both of SC sampling and SC op amp circuits form a correlated double sampling scheme. This AFE is designed to sense a capacitance range from 6 pF to 7 pF (300–1000 mmHg) corresponding to a 0.68 V–1.07 V discrete output voltage with a sampling frequency of 1.63 KHz. This AFE has a sensitivity of 0.39 mV/fF, average power consumption of 201 μW and 3.25% accuracy operating over a 2.1 V–3.3 V rectified wireless supply voltage and −40 °C ~125 °C temperature range.     

A quad-rotor system for driving and flying missions by tilting mechanism of rotors: From design to control

This article presents the hybrid design and control of a quad-rotor system called Flymobile. Flymobile is a combined system of a mobile robot and a quad-rotor system aimed to perform both flying and driving tasks. Flymobile performs flying tasks in the same way as conventional quad-rotor systems while the tilting mechanism of each rotor allows Flymobile to navigate in its terrain for a driving task. The body frame with rotors is implemented by a calibration process through a test-bed equipped with a force sensor. The triangular wheel frame is designed to mimic motions of a mobile robot with three passive wheels. Sensor data of a gyro and an accelerometer are filtered and used for controlling the attitude of the system. Focusing on a practical approach of implementing a hybrid system, a non model-based approach is applied to control Flymobile. Experimental studies are demonstrated to show the feasibility of performing both driving and flying missions.     

Optical and electrical characteristics of GaN vertical light emitting diode with current block layer

A GaN vertical light emitting diode(LED)with a current block layer(CBL)was investigated.Vertical LEDs without a CBL,with a non-ohmic contact CBL and with a silicon dioxide CBL were fabricated.Optical and electrical tests were carried out.The results show that the light output power of vertical LEDs with a non-ohmic contact CBL and with a silicon dioxide CBL are 40.6%and 60.7%higher than that of vertical LEDs without a CBL at 350 mA,respectively.The efficiencies of vertical LEDs without a CBL,with a non-ohmic contact CBL and with a silicon dioxide CBL drop to 72%,78%and 85.5%of their maximum efficiency at 350 mA,respectively. Moreover,vertical LEDs with a non-ohmic contact CBL have relatively superior anti-electrostatic ability.     

多路径环境下电信流量模型研究

在下一代通信网络中,一个终端可同时拥有多个网络接口,在一对源、目的终端间存在多条可用路径。这为网络通信提供了一种全新的思路,即利用多条路径并发进行数据传输。针对多路径传输出现的问题,文章为多路径传输建立了流量模型,分析了多路径传输流媒体的优势,提出了＂流体带宽＂和＂流体调度＂的概念,并引入网络流理论计算了多路径环境下的目标流量。     

Design and application of a depletion-mode NJFET in a high-voltage BiCMOS process

A novel depletion-mode NJFET compatible high-voltage BiCMOS process is proposed and experimentally demonstrated with a four-branch 12-bit DAC(digital-to-analog converter).With this process,an NJFET with a pinch-off voltage ofabout-1.5 V and a breakdown voltage of about 16 V,an NLDDMOS(N-type lightly-dosed-drain in MOS) with a turn-on voltage of about 1.0 V and a breakdown voltage of about 35 V,and a Zener diode with a reverse voltage of about 5.6 V were obtained.Measurement results showed that the conver...     

Integrated Sliding‐Mode Sensorless Driver with Pre‐driver and Current Sensing Circuit for Accurate Speed Control of PMSM

This paper proposes a fully sensorless driver for a permanent magnet synchronous motor (PMSM) integrated with a digital motor controller and an analog pre‐driver, including sensing circuits and estimators. In the motor controller, a position estimator estimates the back electromotive force and rotor position using a sliding‐mode observer. In the pre‐driver, drivers for the power devices are designed with a level shifter and isolation technique. In addition, a current sensing circuit measures a three‐phase current. All of these circuits are integrated in a single chip such that the driver achieves control of the speed with high accuracy. Using an IC fabricated using a 0.18 μm BCDMOS process, the performance was verified experimentally. The driver showed stable operation in spite of the variation in speed and load, a similar efficiency near 1% compared to a commercial driver, a low speed error of about 0.1%, and therefore good performance for the PMSM drive.     

Longitudinally Excited CO<Subscript>2</Subscript> Laser with Short Laser Pulse like TEA CO<Subscript>2</Subscript> Laser

We have developed a longitudinally excited CO₂ laser with a short laser pulse similar to that of TEA and Q-switched CO₂ lasers. A capacitor transfer circuit with a low shunt resistance provided rapid discharge and a sharp spike pulse with a short pulse tail. Specifically, a circuit with a resistance of 10 M Ω provided a spike pulse width of 103.3 ns and a pulse tail length of 61.9 μs, whereas a circuit with a shunt resistance of 100 Ω provided a laser pulse with a spike pulse width of 96.3 ns and a pulse tail length of 17.2 μs. The laser pulses from this longitudinally excited CO₂ laser were used for processing a human tooth without carbonization and for glass marking without cracks.