二次调频-伪码调相复合信号的伪码盲估计

针对二次调频-伪码调相复合信号的伪码盲估计难题,提出一种基于三次相位函数和频谱搬移的伪码盲估计算法。首先利用平方法消去伪码和信息码的相位突变,针对平方法带来的噪声恶化问题,采用对三次相位函数累加平均的方法估计二、三阶系数,利用估计的高精度系数重构指数项,对原复合信号进行降阶,再对降阶后的信号取实部可得正弦载波与伪码调相的复合信号,最后采用频谱搬移的方法可恢复出原伪码序列。仿真结果表明,该算法具有可行性,当信噪比大于等于1 dB时,伪码估计的正确率大于0.9,表现出较好的性能。     

Coding behavior of authentication code on the internet

With the rapid growth of Internet services, virtual world has witnessed an increasingly large number of online users who have a variety of needs such as accessing various websites to gather information, easing business transactions, and sharing updates. As a result, information security has become a major concern among online users, and the verification of access codes is now the main practice used to keep information systems safe. However, some issues arise as the result of coding and managing behavior, and this research seeks to address these issues. After following the Focus Group method and interviewing 13 college students, this research finds that forgetting the access code is one of the biggest challenges to most online users simply because of the longer duration and the time when the users have a need to access the websites again, their memory will eclipse. In addition, online users usually develop self-constructed rules to cope with elusive code. These rules include: creating some sets of code that may not be meaningful to outsiders; taking different degrees of complex measures to register authentication codes, dependent upon the importance of the websites to the online users; writing the authentication codes on a scratchpad and sticking it on the computer screen; and keeping the codes in a notebook or computer file. The above practices nevertheless run the risk of being usurped by hackers, and it is found that hacking frequently takes place among closest friends, as they are quite familiar with the coding behavior of the victims. While assisting coding management does not help in this regard, as it is generally too expensive, online users troubled by the forgetting of access codes often end up with re-applying for a new set of authentication codes after unsuccessfully trying to login. All these self-constructed rules, nevertheless, constitute threat to information security. The research, in conclusion, calls for an education campaign to promote healthy coding behavior and effective coding management. The obtained findings provide valuable references for both academicians and practitioners to understand the online users’ coding behaviors and to effectively manage them accordingly to improve the resulting information security.     

面向隐私保护的两层传感网Top-k查询处理方法

无线传感器网络中的隐私保护技术已经成为研究热点,其中具有隐私保护能力的Top-k查询已经成为富有挑战性的研究问题.提出了一种基于前缀编码验证(PMV)机制的两层传感器网络隐私保护Top-k查询处理方法.通过引入PMV机制,并利用加密和Hash消息身份验证编码技术,使感知节点对采集到的数据进行加密和编码处理,并上传至存储节点;存储节点利用PMV机制实现在无需感知数据明文参与下的数值线性关系比较,进而计算包含查询结果的最小候选密文数据集,并发送给Sink节点;最终由Sink解密密文数据,完成Top-k查询结果计算.为了降低感知节点能耗,给出基于Hash技术的能量优化策略.理论分析和实验结果表明,该方法能够确保数据的隐私安全性,且性能表现优于现有工作.     

传感器网络中基于LT码的提高数据持续性方案

在环境恶劣且无固定Sink的无线传感器网络,节点为了避免意外死亡而丢失数据,需要能量有效地将数据分发到其他一部分节点上存储,以等待移动Sink进行采集.提出了一种新的基于Luby变换码(Luby transform codes)、简称LT码的数据持续性提高方案(LT-codes based scheme for improving data persistence,LTSIDP),其中LT码是一类纠删码.LTSIDP将数据的存储过程分为2个步骤:第1步,节点根据一段时间内接收数据包的情况估计网络中数据包的数量和节点的总数,进而计算出基于LT码存储数据所需要的参数;第2步,节点再根据获得的参数对接收到的数据进行存储.每一轮LTSIDP执行结束后,移动Sink可以在一定时间段内的任意时刻和任意地点进入网络,访问少量仍然存活的节点就能获得所有源数据.理论分析和实验表明,LTSIDP不仅能获得比已有算法更高的数据持续性,而且能量更有效.     

光电编码器抗振动测速法在飞行器内弹道参数测量中的应用

针对水下发射飞行器内弹道参数测量的特殊性和复杂性,介绍一种基于拉线式测速器和光电编码器的抗振动测速方法.该方法将编码器的抗振动测速巧妙地应用到内弹道参数测量中,具有实现简单、精度高、易于安装和调试等特点,可满足多种冷发射的飞行器出筒速度测量的要求,具有较高的实用价值.     

输电线路智能巡检系统中GPS技术的研究与应用

在高压输电线下进行GPS数据录入,不可避免受电磁场等因素的影响,一是导致伪距测量中的误差增大,使定位精度降低;二是干扰GPS信号,影响接收机的捕获和跟踪,造成GPS信号接收失败、精度降低、轨迹数据的丢包、人员巡检的监督功能失效.为此,通过GPS相位平滑伪距方法提高相对伪距观测值精度,通过设计轨迹坐标监测程序对GPS信息数据的存储情况进行定时检测,有效避免轨迹坐标数据的大量丢包,保证人员的巡检轨迹完整,对巡检人员工作起到良好的监督作用,保证高压输电线路智能巡检系统的正常运行.     

基于后缀数组的克隆检测

程序员对源代码的拷贝、粘贴及修改活动会导致软件中出现大量克隆代码,增加软件开发和维护的成本。为解决该问题,提出一种新的克隆检测方法。利用基于后缀数组的算法查找重复的 Token 子串,进而检测出克隆代码,开发相应的克隆检测工具SaCD,用其检测29款C语言开源软件。实验结果表明,SaCD能快速有效地检测软件中的Type-1和Type-2语句克隆,其检测速度比传统的克隆检测工具CCFinderx快了近20倍。     

基于RFID技术的物流信息跟踪系统构建

基于RFID技术,提出了一种贯穿供应链全过程的物流信息跟踪系统模型,为多种用户提供物流信息跟踪平台.根据模型构建了物流信息跟踪系统,对系统的基本工作过程进行了设计.针对物流信息跟踪系统分析了EPCIS事件类型,并对提取的EPC数据进行数据存储设计,以聚合事件为例,进行XML语言定义,对EPCIS事件进行描述,最后对聚合事件进行跟踪算法的实现.物流信息跟踪系统应用将对物流过程监管、物流可视化管理起到重要作用.     

The Pathology of Cryptology—A Current Survey

Abstract

“The Pathology of Cryptology” is the title of a chapter in David Kahn's book The Codebreakers. This chapter mainly deals with hidden messages, which amateur scientists claim to have discovered in the works of William Shakespeare and in other literary works. The present article picks up this subject and provides it with a theoretic framework under the name of “para-steganography.” Moreover, further case studies are added to those given by Kahn, including many examples that only became known after the publication of The Codebreakers. These considerations show that a hidden code can be found almost anywhere, provided that one looks for it in a suitable manner.     

PAPERS DISCLOSE ALLIES' EDGE IN KNOWING GERMAN CODES

Pless has proposed a stream cipher based on J-K flip-flops that uses 8 linear shift registers with feedback, having a combined length of 97 bits, 4 J-K flip-flops, and a 4-stage cycling counter. The cipher has 2.54×10⁵¹ initial states (keys), and generates a presumably pseudorandom stream whose period is 1.52×10²⁹ bits. Despite these impressive statistics, it is computationally feasible to solve such a cipher with a known-plaintext attack, using as few as 15 characters.