Proposal of an Information Signal Measurement Method in Display Image Contained in Electromagnetic Noise Emanated from a Personal Computer

The display image on the monitor can be reconstructed by receiving and analyzing the unexpected electromagnetic noise emanated from a personal computer system. This fact is one of information leakage threats in information security. Therefore, it is important to evaluate and prevent the information leakage caused by the unexpected electromagnetic noise. In this paper, we propose a measurement method of the information signal, which is contained in electromagnetic noise from a personal computer. The information signal is correlated with the RGB signal constructing a display image, because it can reconstruct the similar image to the display image. In order to detect the information signal, we displayed a vertical stripes pattern with a specific periodicity on the monitor as a test image. Then the RGB signal constructing the test image has the specific frequency component, so the information signal has also the same frequency component. Thus the information signal can be defined as the periodical signal frequency of the vertical stripes pattern. By means of this definition, the information signal can be detected and measured in the electromagnetic noise. This measurement method is possible to evaluate quantitatively the information signal leaking through the electromagnetic noise. In order to check the validity of our proposed method, test experiments were carried out. These results showed the correspondence with the reconstructed images and the measured levels.