IT Baseline Protection Manual - The Information Warfare Site

Safeguard Catalogue - Hardware & Software Remarks
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S 4.89 Emission security
Initiation responsibility: IT Security Management
Implementation responsibility: IT Security Management
Every electronic device emits electromagnetic waves of a greater or lesser
strength. These emissions are known as stray radiation or radiated
interference. Their maximum permissible strength is stipulated in the Law on
the Electromagnetic Compatibility of Devices (German abbreviation: EMVG).
In devices which process information (PCs, printers, fax machines, modems
etc.), this stray radiation may also carry the information currently being
processed. Information-bearing radiation of this nature is referred to as
compromising emanations. If the compromising emanations can be received
some distance away, for example in a neighbouring building or in a vehicle
parked nearby, it is possible to reconstruct the information from the
emanations. The confidentiality of the data is therefore called into question.
The limiting values set by the EMVG are generally not sufficient to prevent
interception of compromising emanations. Usually it is necessary to take
additional steps to ensure this.
Compromising emanations can emerge from a room in different ways:
- In the form of electromagnetic waves, which are propagated through free
space in the same way as radio waves.
- As conducted radiation along metallic conductors (cables, air-conditioning
ducts, heating pipes).
- By cross-talking from a data cable to other cables laid parallel. The
radiation propagates along the parallel cables and can be picked off from
these even a long distance away.
- As acoustic radiation, for example in the case of printers. The detailed
information from the printing process is disseminated as sound or
ultrasound, and can be picked up with microphones.
- In the form of acoustic cross-talk to other devices. Sound is converted into
electrical signals by sound-sensitive parts of equipment, which under
certain conditions can function in a similar way to a microphone. The
sound is then propagated further along metallic conductors, or also in the
form of electromagnetic radiation.
- Compromising emanations may also be caused by external manipulation of
devices. If a device is irradiated with high-frequency energy, for example,
the electrical processes in the device can influence the radiated waves in
such a way that they subsequently carry the processed information with
them.
In all of these cases the nature of the installation, in other words the cabling
between the devices and from the devices to the electricity supply system, has
a substantial influence on propagation and hence on the range of the radiation.
The BSI has developed and is still developing various protective measures
which effectively reduce the risk without significantly increasing costs. These
include:
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IT-Baseline Protection Manual: Oktober 2000