Methods of Evaluating Information Leakage from PC Displays

To evaluate the possibility of information leakage (tapping) by observing electromagnetic disturbance radiated from a PC display, the most straightforward way is to reconstruct the displayed image from the measured signal using a special receiver. However, such a receiver is neither popular nor commercially available. Therefore, we propose two types of evaluation methods that are based on (1) the measurement of the difference in level when different images are displayed, and (2) the measurement of the frequency component of the horizontal sync signal within the electromagnetic disturbance. In both proposed methods, we only need a spectrum analyzer that is commonly used for EMI measurement.