Tempest (codename) - Public Research

Public Research

In 1985, Wim van Eck published the first unclassified technical analysis of the security risks of emanations from computer monitors. This paper caused some consternation in the security community, which had previously believed that such monitoring was a highly sophisticated attack available only to governments; van Eck successfully eavesdropped on a real system, at a range of hundreds of metres, using just $15 worth of equipment plus a television set.

In consequence of this research such emanations are sometimes called "van Eck radiation," and the eavesdropping technique van Eck phreaking, although government researchers were already aware of the danger, as Bell Labs noted this vulnerability to secure teleprinter communications during World War II and was able to produce 75% of the plaintext being processed in a secure facility from a distance of 80 feet. Additionally the NSA published Tempest Fundamentals, NSA-82-89, NACSIM 5000, National Security Agency (Classified) on February 1, 1982. In addition, the van Eck technique was successfully demonstrated to non-TEMPEST personnel in Korea during the Korean War in the 1950s.

Markus Kuhn has discovered several low-cost techniques for reducing the chances that emanations from computer displays can be monitored remotely. With CRT displays and analogue video cables, filtering out high-frequency components from fonts before rendering them on a computer screen will attenuate the energy at which text characters are broadcast. With modern flat panel displays, the high-speed digital serial interface (DVI) cables from the graphics controller are a main source of compromising emanations. Adding random noise to the less significant bits of pixel values may render the emanations from flat-panel displays unintelligible to eavesdroppers but is not a secure method. Since DVI uses a certain bit code scheme for trying to transport an evenly balanced signal of 0 and 1 bits there may not be much difference between two pixel colours that differ very much in their colour or intensity. It may also be that the generated emanations may differ totally even if only the last bit of a pixel's colour is changed. The signal received by the eavesdropper does also depend on the frequency where the emanations are detected. The signal can be received on many frequencies at once and each frequency's signal differs in contrast and brightness related to a certain colour on the screen. Usually, the technique of smothering the RED signal with noise is not effective unless the power of the noise is sufficient to drive the eavesdropper's receiver into saturation and thus overwhelming the receiver input.

LED indicators on computer equipment can be a source of compromising optical emanations. One such technique involves the monitoring of the lights on a network switch. Almost all network switches flash to show activity, and it is normal for the flashes to be directly taken from the data line. As such, a fast optical system can easily see the changes in the flickers from the data being transmitted down the wire.

Further, recent research has shown it is possible to detect the radiation corresponding to a keypress event from not only wireless (radio) keyboards, but also from traditional wired keyboards, and even from laptop keyboards.