计算机电磁信息泄漏文字再现

Text Recovery from EM Leakage of Computers

设计了针对计算机电磁信息泄漏的接收和再现系统.用宽带天线截获电磁信息泄漏信号后,经带通滤波和放大,再用锁相环电路捕获帧同步与行同步信号.同步信号经模数转换后,得到视频数字信号的输出.然后,用平均滤波法对数字视频信号降噪.最后,用匹配滤波器获得再现的文字.测试结果表明,用平均滤波的方法使同步信号的信噪比提高了18.7 dB,可在12 m范围内获取奔腾486主机及阴极射线管显示器泄漏的文字信息.

A text receiving and recovery system was designed for EM information leakage from computers. After EM leakage is intercepted by a broad band antenna, band-pass filtered and amplified, the vertical and horizontal synchronization signals are captured by a phase locked loop circuit. The synchronization signals are sampled and processed by an analog-digital converter to get digital video signals. Then, the noises of video signals are filtered using an average filter. At last, the text in the digital video is recovered using a matched filter. An experimental result shows that text can be recovered from EM leakage 12 m away for a Pentium 486 computer with a CRT display, and the signal to noise ratios of the vertical and horizontal synchronization signals are increased by 18.7 dB with the average filter.