Research On Circuit Design Of Preventing Video Information Leakage From HDMI

Protecting the display system of computer from eavesdropping by electromagnetic compromising emanations always plays an important part in computer TEMPEST. The HDMI is applied more and more popularly in digital display system and the high speed HDMI cable from graphics controller is a main source of comproming emanations. So a digital signal process circuit board is designed in this paper in order to prevent video information leakage from the HDMI.Adding random noise to the less significant bits of pixel values is the typical method to prevent video information leakage in digital visual interface. However this method also deceases the quality of the images. As the higher definition digital visual interface developing like HDMI, the disadvantage against the purpose of high definition becomes much more serious.The HDMI can support deep color depths of 30, 36 or 48 bits per pixel besides 24 bits per pixel according to the HDMI Specification 1.3 which was released in 2006. However the deep color video resources and displays are not so popular in non-professional field of image. So there are 12 bits redundancy in 36 bits per pixel as to the common computer display system. It is what we can use to adding random noise.A HDMI repeater can used to pad 4 bits pseudorandom sequence after the least significant bit on each component channel. And the video with color depths of 36 bits per pixel is sent to the display. The receiver on the display will decode the income deep color video and convert the 36 bits pixels to 24 bits pixels in order to accommodate the downstream display panel with a color depth of 24 bits per pixel. Finally the 12 bits pseudorandom sequence per pixel are ignored and the images rendered on the panel are not changed.This paper specifies the scheme and demonstrates the possibility of the redundant color depth randomizing technology. A high speed printed circuit board is designed to apply the technology in reality. And the signal integrity and power integrity simulations are implemented to ensure the quality of the high speed signal and the integrated circuit being powered stably. After being assembled and debugged, the circuit can process videos with a format of 1920 1080p@60. And the eavesdrop test is carried out to verify this method.