Novel Information Leakage Threat for Input Operations on Touch Screen Monitors Caused by Electromagnetic Noise and its Countermeasure Method

Information leakage of general input operations using button images in graphical user interface on touch screen monitors was experimentally investigated from images reconstructed by receiving the electromagnetic noise. In the experimental investigations for input operations of a personal identiflcation number, it was conflrmed that when a button image was touched, the touched button image can be identifled from the reconstructed button images. This kind of information leakage has originated the fact that the touched button image has changed the color for informing the operator which button image was touched. From the elucidation of the image reconstruction mechanism, it was found that the information leakage has been caused by the magnitude of the emitted signal that results from the analog voltage difierences of the RGB signals between neighboring pixels on the monitor. Therefore, a countermeasure method was proposed from the viewpoint of the combination of the colors of the button images and of the background or of the numerals in the button images. The countermeasure method was then applied to the previous input operations of a personal identiflcation number. From the experimental results for the countermeasure method, it was conflrmed that the touched button image cannot be identifled from the reconstructed button image. As a result, the proposal countermeasure method can prevent efiectively the information leakage of input operations on touch screen monitors due to the electromagnetic noise.