Definition

van Eck phreaking

Van Eck phreaking is a form of eavesdropping in which special equipment is used to pick up telecommunication signals or data within a computer device by monitoring and picking up the electromagnetic fields (EM fields) that are produced by the signals or movement of the data.

Van Eck phreaking is one of the first documented side-channel attack vectors. Van Eck phreaking is identified in the U.S. government project known as Tempest and, although some information remains classified, has probably been used to spy on suspected criminals and in espionage. The Tempest project has also led to advice and some standards development for how to shield devices so that eavesdropping is not possible.

Depending on the type of equipment that is emitting an electromagnetic field, the sensitivity of the detection equipment and the general level of EM energy in the area, Van Eck phreaking can be done over distances ranging from a few meters up to several hundred meters. The cost of shielding means that many commercial devices are still vulnerable and, for this and other reasons, some of the details about what equipment is required to do van Eck phreaking remains classified. Susceptibility to eavesdropping can be minimized by designing equipment that generates little EM energy.

The term gets its name from Wim van Eck, who authored an academic paper that described this form of electronic eavesdropping in 1985. In general, phreaking is the practice of using special equipment to get something for free. From the 1950s through the 1970s, phone phreaking (making phone calls for free) was a popular hobby for individuals interested in telecommunications.

How van Eck phreaking was discovered

On an old-fashioned computer monitor, the image that appeared on a cathode ray tube (CRT) screen was created by electron beams that scanned across the screen in a series of horizontal lines from left-to-right and top-to-bottom. The scans occurred at a specific frequency for each individual monitor. (In the early days of personal computing, there were only a few standard frequencies in existence, and every monitor used one of them.)

Once computer engineers understood that the intensity of the electron beams determined the relative red, blue, and green brightness for each pixel (picture element) on the screen, it became possible to reverse engineer the modulated EM field produced by the cathode ray tubes and see what was being displayed on a computer screen at any given moment. The eavesdropped information looked like a meaningless, irregular waveform if viewed directly on an oscilloscope, but it could be intercepted from some distance away and demodulated with special equipment, just like a television signal.

This was last updated in April 2019

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