A Practical Evaluation Method for EM Information Leakage by Using Audible Signal

A method for evaluating electromagnetic (EM) information leakage through EM emanation from displays is introduced. The basic idea is that the method determines the information leakage by detecting an audio signal without reconstructing the screen image. We propose an image which is called the controlled image. When the controlled image is displayed on a device, an audible frequency range signal is generated at information leakage frequency. By detecting the audio signal, we can confirm the information leakage. Several leakage frequencies of a laptop PC are obtained by the proposed method and we were able to reconstruct the screen image of the laptop at the frequencies we obtained to confirm the validity of our method.