Page 659 - (ISC)² CISSP Certified Information Systems Security Professional Official Study Guide

equipment or cabling by applying physical security controls. By

reducing the signal strength and increasing the physical buffer around
sensitive equipment, you can dramatically reduce the risk of signal
interception.

As discussed previously, several TEMPEST technologies could provide
protection against EM radiation eavesdropping. These include
Faraday cages, jamming or noise generators, and control zones. A
Faraday cage is a special enclosure that acts as an EM capacitor.

When a Faraday cage is in use, no EM signals can enter or leave the
enclosed area. Jamming or noise generators use the idea that it is
difficult or impossible to retrieve a signal when there is too much
interference. Thus, by broadcasting your own interference, you can
prevent unwanted EM interception. The only issue with this concept is
that you have to ensure that the interference won’t affect the normal
operations of your devices. One way to ensure that is to use control
zones, which are Faraday cages used to block purposely broadcast

interference. For example, if you wanted to use wireless networking
within a few rooms of your office but not allow it anywhere else, you
could enclose those rooms in a single Faraday cage and then plant
several noise generators outside the control zone. This would allow
normal wireless networking within the designated rooms but

completely prevent normal use and eavesdropping anywhere outside
those designated areas.