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Monday, May 03, 2010


1. Imagine someone sitting in a van outside a person's house can read the EMR that is emanating from the user's laptop computer inside the house and reconstruct the information from the user's monitor on a different device. Different devices have different levels of susceptibility to Tempest radiation. A handheld calculator gives off a signal as much as a few feet away, and a computer's electromagnetic field can give off emissions up to half a mile away. The distance at which emanations can be monitored depends on whether or not there are conductive media such as power lines, water pipes or even metal cabinets in the area that will carry the signals further away from the original source.

2. This problem is not a new one; defence specialists have been aware of it for over twenty years.Information on the way in which this kind of "eavesdropping" can be prevented is not freely available. Equipment designed to protect military information will probably be three or four times more expensive than the equipment likely to be used for processing of non-military information.Until recently it was considered very difficult to reconstruct the data hidden in the radiated field, and it was therefore believed that eavesdropping on digital equipment could only be performed by professionals with access to very sophisticated detection and decoding equipment. As a result, digital equipment for processing information requiring medium or low level protection, such as private and business information, is not protected against eavesdropping of this kind.

3. The EMR that is emitted by electric devices contains the information that the device is displaying or storing or transmitting. With equipment designed to intercept and reconstruct the data, it is possible to steal information from unsuspecting users by capturing the EMR signals. The U.S. government originally began studying this phenomenon in order to prevent breaches in military security. The government was using the technology to their advantage during WWII and realized that they needed to protect themselves against others using the same tactics against them. The name Tempest, or Tempest radiation originated with the U.S. military in the 1960s as the name of the classified study of what was at the time called "compromising emanations."

4. Today the phenomenon is more commonly referred to as van Eck phreaking, named after Wim van Eck, the Dutch computer scientist who brought it to general attention in 1985 when he published his paper "Electromagnetic Radiation from Video Display Units: An Eavesdropping Risk?," in which he demonstrated that the screen content of a video display unit could be reconstructed at a distance using low-cost home-built equipment - a TV set with its sync pulse generators replaced with manually controlled oscillators.

5. Van Eck phreaking is a major security concern in an age of increasing pervasive computing. High-security government agencies are protecting themselves by constructing safe rooms that through the use of metallic shielding block the EMR from emanating out of the room or by grounding the signals so that they cannot be intercepted. It is possible, though costly, for individual users to shield their home computer systems from EMR leakage.


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