Computer security compromised by hardware failure: Difference between revisions

Revision as of 19:23, 16 January 2017

Revision as of 19:24, 16 January 2017

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==== Compromising reflections ====

What is displayed by the monitor is reflected on the environment. The time-varying diffuse reflections of the light emitted by a CRT monitor can be exploited to recover the original monitor image.<ref name="[Back4]">[[#Back1|Backes, 2010, p.4]]</ref> This is an eavesdropping technique for spying at a distance on data that is displayed on an arbitrary computer screen, including the currently prevalent LCD monitors.

The technique exploits reflections of the screen’s optical emanations in various objects that one commonly finds in close proximity to the screen and uses those reflections to recover the original screen content. Such objects include eyeglasses, tea pots, spoons, plastic bottles, and even the eye of the user. This attack can be successfully mounted to spy on even small fonts using inexpensive, off-the-shelf equipment (less than 1500 dollars) from a distance of up to 10 meters. Relying on more expensive equipment allowed to conduct this attack from over 30 meters away, demonstrating that similar attacks are feasible from the other side of the street or from a close-by building.<ref name="[Back1]"/>

Many objects that may be found at a usual workplace can be exploited to retrieve information on a computer’s display by an outsider.<ref name="[Back4]">[[#Back2|Backes, 2008, p.4]]</ref> Particularly good results were obtained from reflections in a user’s eyeglasses or a tea pot located on the desk next to the screen. Reflections that stem from the eye of the user also provide good results. However, eyes are harder to spy on at a distance because they are fast-moving objects and require high exposure times. Using more expensive equipment with lower exposure times helps to remedy this problem.<ref name="[Back5]">[[#Back2|Backes, 2008, p.11]]</ref>

The reflections gathered from curved surfaces on close-by objects indeed pose a substantial threat to the confidentiality of data displayed on the screen. Fully invalidating this threat without at the same time hiding the screen from the legitimate user seems difficult, without using curtains on the windows or similar forms of strong optical shielding. Most users, however, will not be aware of this risk and may not be willing to close the curtains on a nice day.<ref name="[Back2]">[[#Back2|Backes, 2008, p.2]]</ref> The reflection of an object, a computer display, in a curved mirror creates a virtual image that is located behind the reflecting surface. For a flat mirror this virtual image has the same size and is located behind the mirror at the same distance as the original object. For curved mirrors, however, the situation is more complex.<ref name="[Back6]">[[#Back2|Backes, 2008, p.3]]</ref>