A Display Technique for Preventing Electromagnetic Eavesdropping Using Color Mixture Characteristic of Human Eyes

Abstract

The security problem of screen image leakage on a cathode-ray tube (CRT) through electromagnetic radiation from several meters away, “transient electro-magnetic pulse emission surveillance technology” (TEMPEST), has attracted wide interest by security researchers since Van Eck wrote about this problem. On the industry side, the problem is considered a serious risk, especially for computers used in operations related to such areas as critical business and information management at banks. To solve the problem, techniques for reducing the S/N ratio of emanating information by signal reduction and noise generation have been investigated as countermeasures. We have developed a technique that introduces noise to displayed images. With this technique there is less of a quality penalty on the visible images. This is a result of using a human visual characteristic known as additive color mixing, which occurs when an eye is continuously exposed to quickly changing colors. Although we used hardware to implement this technique, using software for low-cost systems is possible. We tested and confirmed the effectiveness of the technique using both analog and digital systems: a computer connected with a CRT or LCD by an analog RGB cable.