Differential Signaling Compromises Video Information Security through AM and FM Leakage Emissions

Video display units (VDUs) using differential signaling technology significantly increase the risk of compromising video information security through leakage emissions. This article shows that differential signaling cables act as substantial video leakage sources. A concept is proposed that explains the video leakage principles of VDUs using differential signal cables such as the high-definition multimedia interface (HDMI) cable, digital visual interface (DVI) cable, and the low-voltage differential signaling (LVDS) cable. The emanations of the LVDS cable are closely examined by measuring simultaneously the differential video signal on the LVDS lines and its near- and far-field leakage emissions. From these measurements, several conclusions are drawn that give new insights into the video eavesdropping risk of VDUs using differential signaling methods. Furthermore, a novel video image reconstruction method is proposed that exploits the compromising emanations of a VDU by using frequency demodulation techniques. This article shows that leaked video emanations of VDUs using differential signaling cables are not only amplitude modulated (AM) but also frequency modulated (FM). This strongly implies that the possible algorithmic toolset of malicious video eavesdroppers is much larger than currently assumed. This article investigates several VDU setups at a distance of 10 m, including an ultrahigh-definition video display, three different HDMI cables and two notebooks. Additionally, the AM-based and FM-based video image reconstruction results are discussed and compared.