浅论计算机犯罪案件的侦查

计算机犯罪带来了极坏的社会影响和破坏作用,它直接危害国家的政治、经济、文化等各个方面的正常秩序。在司法的滞后和全社会的信息安全意识淡薄等诸多因素的影响下,计算机犯罪被侦查取证并能提起诉讼的非常少。因为取证棘手,很多案件由于证据缺乏而放弃起诉。本文总结计算机犯罪侦查的线索及侦查途径,并分析计算机犯罪证据的获取,以期能为我国计算机犯罪案件的侦破有所帮助。     

关于HFS+文件系统数据恢复的研究

本文首先介绍HFS+磁盘的文件系统结构,然后介绍了HFS+文件系统存储和删除数据时的工作流程;在此基础上针对HFS+文件系统存储文件时的特点,对在其环境下恢复文件的可能性进行了探讨,通过对进入废纸篓文件的恢复、完全删除的文件的恢复以及对磁盘的关键字搜索和虚拟内存的搜索这三方面初步证明了在HFS+的系统中对文件进行数据恢复是可行的。     

Digital image splicing detection based on approximate run length

Image splicing is very common and fundamental in image tampering, which severely threatens the integrity and authenticity of images. As a result, the detection of image splicing is of great importance. In this paper, an approximate run length based scheme is proposed to detect this specific artifact. Firstly, the edge gradient matrix of an image is computed, and approximate run length is calculated along the edge gradient direction. Then, some features are constructed from the histogram of the approximate run length. To further improve the detection accuracy, the approximate run length is applied on the predict-error image and the reconstructed images based on DWT to obtain more features. Finally, support vector machine (SVM) is exploited to classify the authentic and spliced images using the constructed features. The experiment results demonstrate that the proposed approach can achieve a relatively high accuracy with less computational cost and fewer features when compared with other methods.     

图像隐写分析技术综述

通过归纳典型专用隐写分析方法和通用隐写分析方法的机制,指出在该领域中,低嵌入率的检测问题、图像源不匹配问题和隐写分析方法的适用性问题是3个亟待解决的问题,进而提出基于富模型和数字取证的隐写分析是两大研究趋势,前者合并不同域的差异特征后,利用集成分类器区分载体和含密图像,后者先用数字取方法证识别图像的类型,再采用该类的隐写分析器检测图像,由此克服图像源不匹配问题,提高检测性能.     

基于Tanimoto系数的JPEG碎片数据识别方法

当前市面上存在多种功能强大的电子取证工具,但这些取证工具缺乏对特定碎片数据类型的识别。提出满足当前实际需求的一种碎片数据类型识别方法。该方法以数据的字节频率分布为基础,首次将Tanimoto系数应用于JPEG碎片数据类型识别,利用文件类型特有的结构特征以及相邻碎片数据的关联性作为优化参数,提高识别率。实验结果表明,该方法能较好地识别出JPEG碎片数据类型。     

关于计算机取证与司法鉴定的研究

计算机犯罪是21世纪破坏性最大的一类犯罪,要打击和遏制此类犯罪,计算机取证与司法鉴定的配合起着不可替代的作用。由于目前关于计算机科学与法学紧密结合的学科还处于刚刚起步阶段,我国网络信息安全面临诸多亟需解决的问题。本篇文章将对计算机取证与司法鉴定相关问题进行研究。     

增强卷积神经网络的人脸篡改检测方法

由于人脸篡改具有很大的危害,关于人脸篡改的判别方法的研究十分重要。已有的基于卷积神经网络的人脸篡改判别研究取得了一定的进展,但是判别结果不尽如意。现有的篡改判别方法大多只关注于假脸的某一类特征,但越来越多样化的人脸篡改手段容易使得现有的篡改判别方法失效。针对这些问题,使用一个性能优异的预训练模型,并利用一种数据增强方式和一种标签平滑化的损失函数,在篡改过的人脸视频的检测上取得了准确度的显著提高。而且,由于采用了“抽帧”处理的方式,提出的方法具有很高的计算效率。     

基于噪声水平估计的帧复制篡改取证算法

基于视频噪声的时域变化规律,提出一种可鉴别帧复制篡改的噪声水平检测方法。对各视频帧实施小波变换,利用小波系数的绝对中位差估计各视频帧中混入高斯噪声的标准差,并对标准差时域序列进行快速傅立叶变换,计算幅频谱的峰均比,再通过对峰均比作硬阈值判决,判断标准差时域序列是否存在周期性,自动识别帧复制篡改。结果表明,噪声水平检测方法可确保伪造视频幅频谱具有较大的峰均比,检测准确度比较高,相比于现有检测方法,避免噪声干扰带来的性能损失,表现出较好的检测性能。     

Deformation of compensated piled raft foundations with deep embedment in super‐tall buildings of Shanghai

This paper presents a synergetic approach based on a statistical‐empirical method, conservation of energy method and superstructure‐foundation interaction theory, and this paper aims to estimate the deformation level of a compensated piled raft foundation. The advantages and main characteristics of such a compensated piled raft foundation are described, and a history of the heave, recompression deformation and final settlement data measurements is provided. Case studies of four super‐tall buildings, the 88‐story Jinmao Building, 66‐story Henglong Plaza, 101‐story Shanghai World Financial Center and 121‐story Shanghai Center Tower in Shanghai, all of which are engineering projects that the second author participated in, are provided to illustrate the effectiveness of different calculations for heave, recompression deformation and final settlement. This study demonstrates that the deformation process can be reasonably projected for a piled raft foundation with deep embedment in Shanghai using superstructure‐foundation interaction methods, statistical‐empirical formulas and a method based on the conservation of energy. The coefficients in the statistical‐empirical method are also further optimized. This deformation estimation considering compensation for deep embedment unloading is reasonable and can be used to avoid excessively conservative designs, and the synergetic approach is applicable to any compensated piled raft foundation with deep embedment in Shanghai. Copyright © 2014 John Wiley & Sons, Ltd.     

Modelling of an ethanol–water distillation column with vapour recompression

This paper presents a simulation study of an ethanol–water distillation column with vapour recompression. The compression of the overhead vapour from the distillation column and the use of condensing vapours to reboil the bottom products were modelled. Predicted results were compared with those from a simulation model for an ethanol–water distillation column assisted by an external heat pump, as previously developed by the authors. Copyright © 2001 John Wiley & Sons, Ltd.