Electromagnetic wave security is a problem stealthily between the specialists.

Electromagnetic wave security is to take out information signal by means of monitoring weak electromagnetic wave that leak out from the personal computer and the business machine.

It is being called tempest (a literal translation is a storm) which include this information interception and the countermeasure.

It give big damage to the user's daily business directly, injustice access to the information network and computer virus damage are greatly reported, and it has been taken a countermeasure though it repeated damage and countermeasure.

The size of the leakage electromagnetic wave is shown as follows

F=dV/dtxC

where

F :size of the leakage electromagnetic wave

dV/dt:movement speed of the electronic circuit

C :static electric capacity

A personal computer and the circumference machine are composed of the electronic circuit such as the semiconductor, which does a high-speed movement.

Static electric capacity exists in the cable and so on which connects electronic parts, print boards and etc.

It is radiated as an electric wave which contains an information signal through the static electric capacity because switching movement of the semiconductor is high speed though static electric capacity itself is very small.

As information technology developed highly today, it is possible to catch subtle electric wave and regeneration by the high sensitivity receiver.

Please remember that a scene to pick up the secret radio sent by a spy with a vehicle equipped the high performance radio and an antenna, even to the second great war film many times.

Though contents and a level are very different, it is a theoretical problem, which exist from the old days.

The order that the possibility of the electric wave interception is a CRT display> plasma display> liquid crystal display> keyboard> printer> personal computer.

Therefore, as for the countermeasure,

① change CRT display into the liquid crystal display.

②install shield box.

③ shield whole building.

In case of under 2MHz,it is never radiated as an electromagnetic wave, leakage can be prevented by the filter.

It is difficult that victim to know the tempest, information interception, unless assailant declare, though it was punished as a crime as for accessing a stealing information network.

We should think that a military spy by tempest is done in the considerable scale from the above, and the possibility of the industrial spy as well.

Even an individual level can't say that there is no person who is being blackmailed and who is crying without claim about the secret information.

We can say that the realization of ubiquities society (the society where and who can always use information processing) is difficult otherwise high morals is kept between the people.

17 August '03 Y.Noguchi

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