Van Eck phreaking is the process of eavesdropping on the contents of a CRT display by detecting its electromagnetic emissions. It is named after Dutch computer researcher Wim van Eck, who in 1985 published the first paper on it, including proof of concept. [1] Phreaking is the process of exploiting telephone networks, used here because of its connection to eavesdropping. Van Eck phreaking might also be used to compromise the secrecy of the votes in an election using electronic voting. This caused the Dutch government to ban the use of NewVote computer voting machines manufactured by SDU in the 2006 national elections, under the belief that ballot information might not be kept secret. [2][3]
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Basic principle
Information that drives the video display takes the form of high frequency electrical signals. These oscillating electric currents create electromagnetic radiation in the RF range. These radio emissions are correlated to the video image being displayed, so, in theory, they can be used to recover the displayed image.
CRTs
In a CRT the image is generated by an electron beam that sweeps back and forth along the screen. The electron beam excites the phosphor coating on the monitor glass and causes it to glow. The beam intensity determines the intensity of the pixel (see CRT for a detailed description). The electron beam is deflected by several electromagnetic coils. The voltage in the coils is modulated at a high frequency and contains information related to the video image. These high frequency, high voltage signals create electromagnetic radiation that has, according to van Eck, "a remarkable resemblance to a broadcast TV signal". What these radiated signals lack is the synchronizing portion of the TV signal. By supplying external synchronization, the radiated signal can be displayed on another television. In the paper, van Eck reports that in February 1985 a successful test of this concept was carried out with the cooperation of the BBC. Using a van filled with electronic equipment and equipped with a VHF antenna array, they were able to eavesdrop from a "large distance".
LCDs
In April 2004 new academic research has revealed that flat screens and laptop displays are also vulnerable to an FPGA-driven electromagnetic eavesdropping. The required equipment for espionage was constructed in a university lab for less than 2000 US dollars. [4]
Countermeasures
Countermeasures are detailed in the article on TEMPEST, the NSA's standard on spy-proofing digital equipment. One countermeasure involves shielding the equipment to minimize electromagnetic emissions. Another method, specifically for video information, scrambles the signals such that the image is perceptually undisturbed, but the emissions are harder to reverse engineer into images. Examples of this include low pass filtering, fonts and randomizing the LSB of the video data information.
Limited use
Van Eck phreaking potentially offers non-proximate eavesdropping options without the interested person having to compromise the affected system's hardware or software. However, the practical applications are likely to be limited, unless substantial breakthroughs occur in operability.
In popular culture
- In Neal Stephenson's 1999 novel Cryptonomicon, van Eck phreaking (of a laptop LCD) serves as a significant plot device.
- Van Eck phreaking was referenced directly in the Numb3rs season 1 episode, 'Sacrifice', on an LCD flat screen rather than a CRT monitor.
- Phillip Finch's 1995 novel f2f features the main character Ellis Hoile building a van Eck scanner, and the device is used to finalize the plot of the book.
See also
- TEMPEST--(US government standards for limiting electric or electromagnetic radiation emanations from electronic equipment)
- RINT--(Radiation INTelligence, military application)
- Election fraud
References
- ^ van Eck, Wim (1985). "Electromagnetic Radiation from Video Display Units: An Eavesdropping Risk?". Computers & Security 4: 269-286.
- ^ Dutch government scraps plans to use voting computers in 35 cities including Amsterdam (Herald tribune, 30. October 2006)
- ^ Use of SDU voting computers banned during Dutch general elections (Heise, October 31. 2006)
- ^ Kuhn, M.G. (2004). "Electromagnetic Eavesdropping Risks of Flat-Panel Displays". 4th Workshop on Privacy Enhancing Technologies: 23-25.
External links
- van Eck phreaking
- Tempest for Eliza is a program that uses your computer monitor to send out AM radio signals. You can then hear computer generated music in your radio.
- Open source van Eck phreaking implementation
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