Tempest (codename)
[9] Compromising emissions are defined as unintentional intelligence-bearing signals which, if intercepted and analyzed (side-channel attack), may disclose the information transmitted, received, handled, or otherwise processed by any information-processing equipment.
Later, Bell informed the Signal Corps that they were able to detect electromagnetic spikes at a distance from the mixer and recover the plain text.
Meeting skepticism over whether the phenomenon they discovered in the laboratory could really be dangerous, they demonstrated their ability to recover plain text from a Signal Corps’ crypto center on Varick Street in Lower Manhattan.
Instead, relevant commanders were warned of the problem and advised to control a 100-foot (30 m)-diameter zone around their communications center to prevent covert interception, and things were left at that.
Then in 1951, the CIA rediscovered the problem with the 131-B2 mixer and found they could recover plain text off the line carrying the encrypted signal from a quarter mile away.
Filters for signal and power lines were developed, and the recommended control-perimeter radius was extended to 200 feet (61 m), based more on what commanders could be expected to accomplish than any technical criteria.
The Friden Flexowriter, a popular I/O typewriter at the time, proved to be among the strongest emitters, readable at distances up to 3,200 ft (0.98 km) in field tests.
The resulting Directive 5200.19, coordinated with 22 separate agencies, was signed by Secretary of Defense Robert McNamara in December 1964, but still took months to fully implement.
TEMPEST standards continued to evolve in the 1970s and later, with newer testing methods and more nuanced guidelines that took account of the risks in specific locations and situations.
According to NSA's David G. Boak, "Some of what we still hear today in our own circles, when rigorous technical standards are whittled down in the interest of money and time, are frighteningly reminiscent of the arrogant Third Reich with their Enigma cryptomachine."
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.
[21] Markus Kuhn has discovered several low-cost techniques for reducing the chances that emanations from computer displays can be monitored remotely.
[22] With CRT displays and analog 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.
[23][24] 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 least significant bits of pixel values may render the emanations from flat-panel displays unintelligible to eavesdroppers but is not a secure method.
From the 1970s onward, Soviet bugging of US Embassy IBM Selectric typewriters allowed the keypress-derived mechanical motion of bails, with attached magnets, to be detected by implanted magnetometers, and converted via hidden electronics to a digital radio frequency signal.
[27] In 2014, researchers introduced "AirHopper", a bifurcated attack pattern showing the feasibility of data exfiltration from an isolated computer to a nearby mobile phone, using FM frequency signals.
[30] In February 2018, research was published describing how low frequency magnetic fields can be used to escape sensitive data from Faraday-caged, air-gapped computers with malware code-named ’ODINI’ that can control the low frequency magnetic fields emitted from infected computers by regulating the load of CPU cores.
[32] This kind of attack targets mixed-signal chips — containing an analog and digital circuit on the same silicon die — with a radio transmitter.
