The electron beam excites the phosphor coating on the glass and causes it to glow. In a CRT, the image is generated by an electron beam that sweeps back and forth across the screen. These radio emissions are correlated to the video image being displayed, so, in theory, they can be used to recover the displayed image. These oscillating electric currents create electromagnetic radiation in the RF range. Information that drives the video display takes the form of high-frequency electrical signals. Van Eck phreaking of CRT displays is the process of eavesdropping on the contents of a CRT by detecting its electromagnetic emissions. While phreaking is the process of exploiting telephone networks, it is used here because of its connection to eavesdropping. Also, the van Eck technique was successfully demonstrated to non-TEMPEST personnel in Korea during the Korean War in the 1950s. Additionally, the NSA published Tempest Fundamentals, NSA-82-89, NACSIM 5000, National Security Agency (Classified) on February 1, 1982. Government researchers were already aware of the danger, as Bell Labs had 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 (24 metres).
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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.Īs a consequence of this research, such emanations are sometimes called "van Eck radiation", and the eavesdropping technique van Eck phreaking. In 1985, Wim van Eck published the first unclassified technical analysis of the security risks of emanations from computer monitors. Side-band electromagnetic radiation emissions are present in (and with the proper equipment, can be captured from) keyboards, computer displays, printers, and other electronic devices. Van Eck phreaking, also known as Van Eck radiation, is a form of eavesdropping in which special equipment is used to pick up side-band electromagnetic emissions from electronic devices that correlate to hidden signals or data to recreate these signals or data to spy on the electronic device.
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