It is known that information is transmitted by a field or substance. This is either an acoustic wave (sound), or electromagnetic radiation, or a sheet of paper with text. But neither the transferred energy, nor the sent substance in themselves have any value, they serve only as information carriers. A person is not considered as a carrier of information. He acts as the subject of relations or the source.
Means of transferring information by physical nature
Based on this, it can be argued that the following means of transferring information are possible by physical nature:
- light rays;
- sound waves;
- electromagnetic waves;
- materials and substances.
Using one or another physical field to his advantage, a person creates a certain information transfer system. Such systems are commonly called communication systems. Any communication system (information transmission system) consists of an information source, a transmitter, an information transmission channel, a receiver and a recipient of information. These systems are used in everyday practice in accordance with their intended purpose and are official means of transmitting information, the operation of which is monitored to ensure reliable, reliable and safe transmission of information, excluding unauthorized access to it from competitors. However, there are certain conditions under which the formation of a system for transmitting information from one point to another is possible, regardless of the desire of the object and source.
In this case, of course, such a channel in an explicit form should not manifest itself. By analogy with the information transfer channel, such a channel is called an information leakage channel. By information leakage channel we mean the physical path from the source of confidential information to an attacker through which leakage or unauthorized receipt of protected information is possible. The movement of information in such a channel is carried out only in one direction – from the source to the attacker.
For the occurrence (formation, establishment) of an information leakage channel, certain spatial, energy and temporal conditions are necessary, as well as appropriate means of perceiving and fixing information on the side of the attacker. In practice, taking into account the physical nature of education, information leakage channels can be divided into the following groups:
- material and material.
Each type of information leakage channel has its own specific features.
Visual-optical leakage channels are usually direct or remote monitoring, including photo and video shooting. The information carrier is the light emitted by the source of confidential information or reflected from it in the visible, infrared and ultraviolet ranges.
Acoustic leakage channels. For a person, hearing is the second most informative after vision. Therefore, one of the fairly common channels of information leakage is the acoustic channel. In the acoustic channel, the information carrier is sound lying in the ultra (more than 20,000 Hz) band, audible and infrasound bands. The range of sound frequencies audible by a person lies in the range from 16 to 20,000 Hz, and contained in human speech – from 100 to 6000 Hz.
When an acoustic wave propagates in air, air particles acquire vibrational motion, transferring vibrational energy to each other. If there is no obstacle in the way of sound, it spreads evenly in all directions. If on the way of the sound wave any obstacles arise in the form of partitions, walls, windows, doors, ceilings, etc., sound waves exert corresponding pressure on them, leading them also to the oscillatory mode. These effects of sound waves are one of the main reasons for the formation of an acoustic channel for information leakage.
In free airspace, acoustic channels are formed in the premises during negotiations in the case of open doors, windows, windows. In addition, such channels are formed by the air ventilation system of the premises. In this case, the formation of channels significantly depends on the geometric dimensions and shape of the ducts, the acoustic characteristics of the shaped elements of the valves, air distributors and similar elements.
Structural sound is understood to mean mechanical vibrations in solid media. Mechanical vibrations of walls, ceilings or pipelines that occur in one place are transmitted over considerable distances, almost without attenuation. The danger of such a leakage channel lies in the uncontrolled range of sound propagation.
Electromagnetic leakage channels. The information carrier is electromagnetic waves ranging from extra-long with a wavelength of 10,000 m (frequencies less than 30 Hz) to submillimeter waves with a wavelength of 1-0.1 mm (frequencies from 300 to 3000 GHz). Each of these types of electromagnetic waves has specific propagation features both in range and in space. Long waves, for example, spread over very large distances, millimeter waves, on the contrary, to remove only line of sight within units and tens of kilometers. In addition, various telephone and other wires and communication cables create magnetic and electric fields around themselves, which also act as elements of information leakage due to interference with other wires and equipment in the near zone of their location. This effect is also called secondary electromagnetic radiation and interference.
Spurious electromagnetic radiation and interference are inherent in any electronic devices, systems, products by the very nature of manifestation. The fact that spurious electromagnetic radiation and interference can form a channel of information leakage has long been known. An interesting fact took place in 1884 in London. It was discovered that some telegraph transmissions were tapped on telephone sets on Gray Stone Road. Verification showed that the cause of these signals were telegraph wires laid shallow underground, running along a long distance parallel to telephone wires. We can assume that this was the first hint of the possibility of uncontrolled receipt of information (leakage) due to spurious emissions.
Thus, technical means and systems can not only directly radiate into space signals containing the processed information, but also capture acoustic or magnetic (electromagnetic) radiation due to their microphone or antenna properties, convert them into electrical signals and transmit via their communication lines, as a rule, uncontrolled, which even more increases the risk of information leakage.
The reasons for the formation of sources of secondary electromagnetic radiation and interference are also the imperfection of circuit solutions and operational wear of the product elements.