Electromagnetic Eavesdropping Risks of Flat-Panel Displays

http://www.springerlink.com/content/twf249exybd86e02/

Electromagnetic eavesdropping of computer displays – first demonstrated to the general public by van Eck in 1985 – is not restricted to cathode-ray tubes. Modern flat-panel displays can be at least as vulnerable. They are equally driven by repetitive video signals in frequency ranges where even shielded cables leak detectable radio waves into the environment. Nearby eavesdroppers can pick up such compromising emanations with directional antennas and wideband receivers. Periodic averaging can lift a clearly readable image out of the background noise. The serial Gbit/s transmission formats used by modern digital video interfaces in effect modulate the signal, thereby making it even better suited for remote reception than emanations from analog systems. Understanding the exact transmission format used leads to new attacks and defenses. We can tune screen colors for optimal remote readability by eavesdroppers. We can likewise modify text-display routines to render the radio emanations unreadable.

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交換器與集線器不同之處是，集線器會將網路內某一使用者傳送之封包傳至所有已連接到集線器的電腦。而交換器則只會將封包傳送到指定目的地的電腦(透過ARP協定)， 相對上能減少數據碰撞及資料被竊聽的機會。交換器更能將同時傳到的封包分別處理，而集線器則不能。