2 cissp ® Official Study Guide Eighth Edition

Emanation Security
Many electrical devices emanate electrical signals or radiation that can be intercepted by 
unauthorized individuals. These signals may contain confidential, sensitive, or private data. 
Obvious examples of emanation devices are wireless networking equipment and mobile 
phones, but many other devices are vulnerable to interception. Other examples include 
monitors, modems, and internal or external media drives (hard drives, USB thumb drives, 
CDs, and so on). With the right equipment, unauthorized users can intercept electromag-
netic or radio frequency signals (collectively known as 
emanations
) from these devices and 
interpret them to extract confidential data.
Clearly, if a device emits a signal that someone outside your organization can intercept, 
some security protection is needed. The types of countermeasures and safeguards used to 
protect against emanation attacks are known as TEMPEST countermeasures. 
TEMPEST
was originally a government research study aimed at protecting electronic equipment from 
the electromagnetic pulse (EMP) emitted during nuclear explosions. It has since expanded 
to a general study of monitoring emanations and preventing their interception. Thus, 
TEMPEST is now a formal name for a broad category of activities.
TEMPEST countermeasures include Faraday cages, white noise, and control zones.
Faraday Cage
A 
Faraday cage
is a box, mobile room, or entire building designed with an 
external metal skin, often a wire mesh that fully surrounds an area on all sides (in other 
words, front, back, left, right, top, and bottom). This metal skin acts as an electromagnetic 
interference (EMI)-absorbing capacitor (which is why it’s named after Michael Faraday, a 
pioneer in the field of electromagnetism) that prevents electromagnetic signals (emanations) 
from exiting or entering the area that the cage encloses. Faraday cages are quite effective 
at blocking EM signals. In fact, inside an active Faraday cage, mobile phones do not work, 
and you can’t pick up broadcast radio or television stations.