Research On Countermeasure And Detection Of Electromagnetic Leakage Of Digital Video Information

In recent years,electric devices such as computers and various communication equipment have been widely used in both civil and military fields.Information security has drawn much attention from the researchers and is becoming a hot topic in relevant field.However,electric devices usually radiate electromagnetic wave when they are working,which may cause electromagnetic interference and leads to information security problems.In most cases,the net security and the information storage security are emphasized while the information security caused by the non-contacting electromagnetic radiation is often neglected.Taking the kinds of digital video systems as the objective of research,this dissertation focuses on the analysis of the electromagnetic leakage source,and the investigation on the features of the electromagnetic radiation in both time and frequency domain.The digital video information is firstly studied and the relationship between the frequency bandwidth and the obtained figures is investigated according to the electromagnetic interception and reconstruction technique.Then,the reduction of the electromagnetic leakage is studied,implemented,and further demonstrated by measurement.Finally,we propose a new method for testing the electromagnetic leakage for the digital video information.The main work and contribution of this dissertation are as follows:The electromagnetic leakage that occurs during the various digital video systems transmission is analyzed,and the features of the electromagnetic leakage for a video cable in both time and frequency domain are studied.For characteristics of differential transmission in video transmission channel,the model of the video cable is built and the common-mode noise,which is caused by the asymmetric of the circuit and the time delay of the differential singal,is discussed in detail.It is found that the electromagnetic radiation signal caused by common mode noise corresponds to the transmitted video signal.It shows that the electromagnetic radiation signal caused by common mode noise of video channel is the main reason for the electromagnetic radiation leakage of video information.Research on the relationship between the receiving bandwidth and the reconstructed figure according to the digital video information interception and reconstruction technique.Because the electromagnetic radiation spectrum of video cables presents the shape of lobes,the relationship between the receiving bandwidth and the bit error rate of the restored signal is found by choosing the complete lobes and some lobes for signal restoration simulation.It is found out that the narrower the receiving bandwidth is,the less information will be reconstructed,and then the more the bit error rate will be.By studying the relationship between the error rate of image data and image quality,it is found that the higher the error rate of the restored signal,the worse the image quality.The lobe width corresponding to the error rate when the image quality reaches readability is the important conclusion that the minimum receiving bandwidth of the restored video information can be intercepted.Research on the electromagnetic leakage suppression technology of digital video information.Research on the suppression strategy of the electromagnetic leakage from the wireless communication model.By comparing various suppression techniques,we proposed two electromagnetic leakage suppression methods based on human vision principle.The video data is superimposed by noise and the color is changed,then the image can not be restricted by the emission of video information.Under the condition of guaranteeing the display effect of the video image,the electromagnetic radiation of the video information can not restore the image informationWe propose a rapid testing method for the electromagnetic leakage based on the analysis of the electromagnetic radiation frequency spectrum.The electromagnetic radiation spectrum of typical red information(image)transmitted by HDMI cable is simulated to obtain the corresponding red information template.The electromagnetic radiation spectrum of the computer when transmitting the same image as the typical red information(image)is obtained by conduction and radiation EMC test methods.The correlation between the red information template signal and the test spectrum is analyzed,and the correlation coefficient is used to judge whether the computer has produced the electromagnetic leakage of video information.The analysis and test results show that when the correlation coefficient is greater than 0.5,the electromagnetic leakage of computer video information can be judged.