An Overview of Double JPEG Compression Detection and Anti-detection

JPEG(Joint Image Experts Group)is currently the most widely used image format on the Internet.Existing cases show that many tampering operations occur on JPEG images.The basic process of the operation is that the JPEG file is first decompressed,modified in the null field,and then the tampered image is compressed and saved in JPEG format,so that the tampered image may be compressed several times.Therefore,the double compression detection of JPEG images can be an important part for determining whether an image has been tampered with,and the study of double JPEG compression anti-detection can further advance the progress of detection work.In this paper,we mainly review the literature in the field of double JPEG compression detection in recent years with two aspects,namely,the quantization table remains unchanged and the quantization table is inconsistent in the double JPEG compression process,Also,we will introduce some representative methods of double JPEG anti-detection in recent years.Finally,we analyze the problems existing in the field of double JPEG compression and give an outlook on the future development direction.

真实游戏中的主流显卡

PC显卡总是脱离不了游戏，因为它就是设计为娱乐应用的，传统的考核显卡的方法想必各位都已经非常熟悉了．但也可能熟悉后又更迷惘了．理论性能和“优化”测试究竟哪个是可靠的？谁也没有定论，现在我们另辟蹊径．抛开理论测试和技术分析，用实际游戏的把玩来衡量这些显卡，判断“是骡子是马”的最好办法不是争论，“拉出去遛遛”是最好的办法。

Improving Performance of Virtual Machine Covert Timing Channel Through Optimized Run-Length Encoding

With its wider acceptability,cloud can host a diverse set of data and applications ranging from entertainment to personal to industry.The foundation of cloud computing is based on virtual machines where boundaries among the application data are very thin,and the potential of data leakage exists all the time.For instance,a virtual machine covert timing channel is an aggressive mechanism to leak confidential information through shared components or networks by violating isolation and security policies in practice.The performance of a covert timing channel(covert channel)is crucial to adversaries and attempts have been made to improve the performance of covert timing channels by advancing the encoding mechanism and covert information carriers.Though promising,the redundancy of the covert message is mainly overlooked.This paper applies three encoding schemes namely run-length,Huffman,and arithmetic encoding schemes for data compression of a virtual machine covert timing channel by exploiting redundancy.Accordingly,the paper studies the performance of such channels according to their capacity.Unfortunately,we show that these encoding schemes still contain redundancy in a covert channel scenario,and thereby a new encoding scheme namely optimized Runlength encoding(OptRLE)is presented that greatly enhances the performance of a covert timing channel.Several optimizations schemes adopted by OptRLE are also discussed,and a mathematical model of the behavior of an OptRLE-based covert timing channel is proposed.The theoretical capacity of a channel can be obtained using the proposed model.Our analysis reveals that OptRLE further improves the performance of a covert timing channel,in addition to the effects of the optimizations.Experimental result shows how OptRLE affects the size of covert data and the capacity of covert timing channels,and why the performance of the covert timing channel is improved.