Methods for protecting speech information from leakage through technical channels. Protection of information from leakage through acoustic channels Passive methods of protection of acoustic information
There is no doubt that the highest value is the information transmitted orally. This is explained next specific features characteristic of speech. Verbally communicate information that cannot be entrusted to technical means of transmission. The information received at the time of its voicing is the most operational. Lively speech, carrying the emotional coloring of a personal attitude to the message, makes it possible to draw up a psychological portrait of a person. In addition, modern methods make it possible to uniquely identify the personality of the speaker.
These features explain the unrelenting interest of the opposing sides in direct listening to speech circulating in the premises through vibroacoustic and acoustic (air ducts, windows, ceilings, pipelines) channels. Therefore, the issues of protection of speech information are given priority when addressing issues of protection against information leakage through technical channels.
There are passive and active ways speech protection from unauthorized listening. Passive ones involve the attenuation of directly acoustic signals circulating in the room, as well as products of electroacoustic transformations in HTSS connecting lines, arising both naturally and as a result of HF imposition. Active ones provide for the creation of masking interference, the suppression of sound recording devices and listening devices, as well as the destruction of the latter.
The weakening of acoustic signals is carried out by soundproofing the premises. Passage of information electrical signals and signals of high-frequency imposition is prevented by filters. Active protection is implemented by various kinds of interference generators, suppression and destruction devices.
Passive means of protection of allocated premises Passive architectural and construction means of protection of allocated premises
The main idea of passive means of protecting information is to reduce the signal-to-noise ratio at possible points of information interception by reducing the informative signal.
When choosing the enclosing structures of allocated premises in the design process, it is necessary to be guided by the following rules:
As floors, it is advisable to use structures on an elastic base or structures installed on vibration isolators;
It is expedient to carry out ceilings suspended, sound-absorbing with a sound-insulating layer;
As walls and partitions, it is preferable to use multilayer acoustically inhomogeneous structures with elastic gaskets (rubber, cork, fiberboard, MVP, etc.).
If the walls and partitions are made of single-layer, acoustically homogeneous, then it is advisable to reinforce them with a “retracted slab” type structure installed from the side of the room.
It is desirable to isolate window panes from vibration from the frames using rubber gaskets. It is advisable to use triple glazing of windows on two frames fixed on separate boxes. At the same time, adjacent glasses are installed on the outer frame, and sound-absorbing material is placed between the boxes.
It is advisable to use double doors with a vestibule as doors, while door frames must be vibrationally isolated from each other.
Some options for technical solutions for passive protection methods are shown in Fig. 4.1.
Rice. 4.1. Passive methods for protecting the ventilation duct (a) and the wall (b):
1 - walls of the ventilation duct; 2 - sound-absorbing material; 3 - related plate; 4- Basic structure; 5- sound-absorbing material;
6 - crate; 7- vibration isolator
Soundproofing of premises
The selection of an acoustic signal against the background of natural noise occurs at certain signal-to-noise ratios. Producing sound insulation, they achieve its reduction to the limit, which hinders (excludes) the possibility of isolating speech signals penetrating outside the controlled area through acoustic or vibroacoustic (enclosing structures, pipelines) channels.
For solid, homogeneous, building structures, the attenuation of the acoustic signal, which characterizes the quality of sound insulation at medium frequencies, is calculated by the formula:
Koh \u003d 201d (d og x /) - 47.5 dB, (4.1)
Where<7 0Г - масса 1 м 2 . ограждения, кг; частота звука, Гц.
Since the average volume level of a conversation taking place in a room is 50 ... 60 dB, the sound insulation of allocated rooms, depending on the assigned categories, should be at least the norms given in Table. 4.1.
Table 4.1
Doors (Table 4.2) and windows (Table 4.3) have the weakest insulating qualities.
Table 4.2
Table 4.3
In temporarily used premises, folding screens are used, the efficiency of which, taking into account diffraction, is from 8 to 10 dB. The use of sound-absorbing materials that convert the kinetic energy of a sound wave into thermal energy has some features associated with the need to create an optimal ratio of direct and reflected acoustic signals from an obstacle. Excessive sound absorption reduces the signal level, a long reverberation time leads to a deterioration in speech intelligibility. Sound attenuation values for fences made of various materials, are given in table. 4.4.
Table 4.4
Soundproof cabins of frame type provide attenuation up to 40 dB, frameless - up to 55 dB.
Equipment and methods for active protection of premises from the leakage of speech information
The vibroacoustic leakage channel is formed by: sources of confidential information (people, technical devices), propagation medium (air, enclosing structures of premises, pipelines), means of removal (microphones, stethoscopes).
To protect the premises, white or pink noise generators and vibration noise systems are used, usually equipped with electromagnetic and piezoelectric vibration transducers.
The quality of these systems is evaluated by the excess of the intensity of the masking effect over the level of acoustic signals in air or solid media. The amount of excess interference over the signal is regulated by the governing documents of the State Technical Commission of Russia (FSTEC) of the Russian Federation.
It is known that the best results are obtained by using masking oscillations that are close in spectral composition to the information signal. Noise is not such a signal, in addition, the development of noise cleaning methods in some cases makes it possible to restore speech intelligibility to an acceptable level with a significant (20 dB or more) excess of noise interference over the signal. Therefore, for effective masking, the interference must have the structure of a speech message. It should also be noted that due to the psychophysiological characteristics of the perception of sound vibrations by a person, an asymmetric effect of masking vibrations is observed. It manifests itself in the fact that the interference has a relatively small effect on the masked sounds, the frequency of which is lower than its natural frequency, but greatly complicates the intelligibility of higher-pitched sounds. Therefore, low-frequency noise signals are most effective for masking.
In most cases, for active protection of air ducts, vibration noise systems are used, to the outputs of which loudspeakers are connected. Thus, the acoustic transducer OM8-2000 is supplied as part of the AVS-2000 vibroacoustic protection system (IE!) However, the use of loudspeakers creates not only a masking effect, but also interferes with the normal daily work of personnel in the protected area.
A small-sized (111 x 70 x 22 mm) generator \LShO-O23 in the range of 100 ... 12000 Hz in a small enclosed space creates interference with a power of up to 1 W, which reduces the intelligibility of speech recorded or transmitted over a radio channel.
The efficiency of systems and devices for vibroacoustic noise is determined by the properties of the applied electroacoustic transducers (vibration sensors) that transform electrical vibrations into elastic vibrations (vibrations) of solid media. The quality of the transformation depends on the implemented physical principle, constructive and technological solution and the conditions for matching the vibration sensor with the environment.
As noted, the sources of masking influences must have a frequency range corresponding to the width of the speech signal spectrum (200 ... 5000 Hz), therefore, it is of particular importance to fulfill the conditions for matching the converter in a wide frequency band. The conditions for broadband matching with enclosing structures with high acoustic resistance (brick wall, concrete floor) are best met when using vibration sensors with a high mechanical impedance of the moving part, which are currently piezoceramic transducers.
Rice. 4.2. Amplitude-frequency characteristics of acoustic interference:
1 - AN0-2000 + TRM-2000; 2-VNG-006DM; 3 - USh-006 (1997): 4 - Za-elephant-AM and Threshold-2M; 5 - background acoustic noises of the room
The operational and technical parameters of modern systems of vibroacoustic noise are given in Table. 4.5.
Table 4.5
| Characteristic | Shorokh-1 | Shorokh-2 | AIE-2000 |
| The presence of an equalizer | Eat | Eat | No |
| Maximum number of vibration sensors | KVP-2-72 and KVP-7-48 | KVP-2-24 and KVP-7-16 | TV1Ch-2000-18 |
| Effective range of wall and ford t-chiks on a floor with a thickness of 0.25 m, m | At least 6 (KVP-2) | At least 6 (KVP-2) | 5 |
| Effective range of window vibration sensors on glass 4 mm thick, m | Not less than 1.5 (KVP-7) | Not less than 1.5 (KVP-7) | - |
| Types of vibration sensors | KVP-2, KVP-6, KVP-7 | KVP-2, KVP-6, KVP-7 | TNGM-2000 |
| Vibration sensors dimensions, mm | 040x30, 050x39, | 040x30, 050x39, | 0100x38 |
| Possibility of acoustic noise | Eat | Eat | Eat |
| Notes |
Certificates of the State Technical Commission of the Russian Federation |
Certificate of the State Technical Commission of the Russian Federation (for objects of category II) | |
The appearance of the products is shown in fig. 4.3.
The installation of vibration sensors, as a rule, is associated with the need to perform labor-intensive construction and installation work - drilling, installing dowels, leveling surfaces, gluing, etc.
The original mounting method (Fig. 4.4) of vibration sensors, implemented in the Fon-V mobile system (MASCOM), allows you to significantly expand the range of application of the A!\Yu-2000 generator and TRSh-2000 converters.
Two sets of metal racks allow you to quickly install vibration sensors in unprepared rooms up to 25 m 2 in area. Mounting and dismantling of structures and sensors is carried out within 30 minutes by three people without damaging the enclosing structures and interior decoration elements.
Figure 4 3 External view of modern systems of vibroacoustic noise
a - KVP-2, 6 - KVP-6, c - KVP-7, d - KVP-8, e - Shorokh-1, e - Shorokh-2
Figure 4 4 Mobile system "Fon-V"
Due to the frequency dependence of the acoustic resistance of material media and the design features of vibration transducers at some frequencies, the required excess of the masking noise intensity over the level of the signal induced in the building envelope is not provided.
Optimum interference parameters
When using active means, the signal-to-noise ratio necessary to ensure information protection is achieved by increasing the noise level at possible points of information interception by generating artificial acoustic and vibration interference. The frequency range of interference should correspond to the average speech spectrum in accordance with the requirements of the governing documents.
Due to the fact that speech is a noise-like process with a complex (generally random) amplitude and frequency modulation, the best form of a masking interference signal is also a noise process with a normal distribution of the probability density of instantaneous values (i.e. white or pink noise) .
It should be noted that each room and each element of the building structure has its own individual amplitude-frequency characteristics of the propagation of vibrations. Therefore, during propagation, the shape of the spectrum of the primary speech signal changes in accordance with the transfer characteristic of the path
Rice. 4.5. Technical implementation of active methods for protecting speech information.
1 - white noise generator, 2 - bandpass filter; 3 - octave equalizer with central frequencies 250, 500,1000, 2000, 4000 (Hz); 4- power amplifier; 5- transducer system (acoustic speakers, vibrators)
distribution torii. Under these conditions, in order to create optimal interference, it is necessary to correct the shape of the interference spectrum in accordance with the spectrum of the informative signal at the point of possible interception of information.
The technical implementation of active methods for protecting speech information, which meets the requirements of the governing documents, is shown in fig. 4.5.
In accordance with the structural diagram, the system for setting vibroacoustic and acoustic interference "Shoroh-2" was built, certified by the State Technical Commission of Russia as a means of protecting allocated rooms of categories I, II and III. Below are the main characteristics of the system.
Tactical characteristics
The "Shoroh-2" system provides protection against the following technical means of information retrieval;
Devices using contact microphones (electronic, wired and radio stethoscopes);
Devices for remote information retrieval (laser microphones, directional microphones);
Embedded devices embedded in elements of building structures.
The "Shoroh-2" system provides protection for such elements of building structures as:
External walls and internal stiffening walls made of monolithic reinforced concrete, reinforced concrete panels and brickwork up to 500 mm thick;
Floor slabs, including those covered with a layer of backfill and screed;
Internal partitions made of various materials;
Glazed window openings;
Pipes for heating, water supply, electrical wiring;
Box of ventilation systems;
Tambours.
Generator characteristics
Type of generated interference .............................................................. ....Analog noise with a normal probability density distribution of instantaneous values.
Interference voltage effective value .................. Not less than 100 V
Generated frequency range..............................................157...5600 Hz
Adjusting the Spectrum of Generated Noise............................Five-Band, Octave Equalizer
Center frequencies of the spectrum adjustment bands ........... 250, 500, 1000,
Depth of spectrum adjustment by bands, not less than ........ ± 20 dB
Depth of adjustment of the level of interference .................................. Not less than 40 dB
The total number of simultaneously connected electro-acoustic transducers:
KVP-2, KVP-6 ....................................... .........................6...24
KVP-7 ............................................... .................................4...16
Acoustic speakers (4...8 Ohm) ..........................4.. . 16
Total output power .......................................... Not less than 30 W
Generator power .............................................................. .............220+22V/50Hz
Generator dimensions ............................................................... ...........No more than 280x270x120 mm
Generator weight .................................................. .................No more than 6 kg
Characteristics of electroacoustic transducers
Protected surfaces:
KVP-7 ............................................... ..........Glasses of window openings up to 6 mm thick
KVP-2 ............................................... ..........Internal and external walls, floor slabs, utility pipes. Glass more than 6 mm thick.
Operating range of one transducer:
KVP-7 (on glass 4 mm thick) ........... 1.5 ± 0.5 m
KVP-2, KVP-6 (wall type NB-30
GOST 10922-64) ................6+1 m
Effectively reproduced frequency range .................................................................. ...............175...6300 Hz
Transformation principle............................Piezoelectric
RMS value of input voltage............................................................... ..... No more than 105 V
Overall dimensions, mm, no more
KVP-2 ............................................... ..........0 40x30
KVP-6 ............................................... ..........0 50x40
KVP-7 ............................................... ..........0 30x10
Weight, g, no more
KVP-2 ............................................... ...........250
KVP-6 ............................................... ...........450
KVP-7 ............................................... ...........20
Features of setting acoustic interference
The main danger, from the point of view of the possibility of information leakage through the acoustic channel, is represented by various construction tunnels and ducts intended for ventilation and placement of various communications, since they are acoustic waveguides. When assessing the security of such objects, control points are selected directly at the border of their exit to the allocated premises. Acoustic emitters of the jamming system are placed in the volume of the box at a distance from the outlet equal to the diagonal of the box section.
Doorways, including those equipped with vestibules, are also sources of increased danger and, in case of insufficient sound insulation, also require the use of active protection methods. Acoustic emitters of noise systems in this case, it is desirable to place in two corners located diagonally of the volume of the vestibule. In this case, control over compliance with information security standards is carried out on the outer surface of the outer door of the vestibule.
In case of deficiency of acoustic insulation of walls and partitions that limit the selected room, acoustic emitters of noise systems are located in adjacent rooms at a distance of 0.5 m from the protected surface. The acoustic axis of the emitters is directed to the protected surface, and their number is selected for reasons of ensuring maximum uniformity of the interference field in the protected plane.
Features of setting vibroacoustic interference
Despite the fact that some vibroacoustic interference systems have sufficiently powerful generators and efficient electroacoustic transducers that provide significant ranges, the criterion for choosing the number of transducers and their installation locations should not be the maximum parameters of the systems, but the specific conditions of their operation.
So, for example, if the building in which the allocated room is located is made of precast concrete, electro-acoustic transducers of the noise system should be located on each element of the building structure, despite the fact that measurements during the equipping of the room may show that one transducer is enough to noise several elements (several floor slabs or several wall panels). The need for such a technique for installing transducers is dictated by the lack of temporal stability of acoustic conductivity at the joints of building structures. Within each element of the building structure, it is preferable to choose the location of the transducers in the region of the geometric center of this element.
It should be noted that the technology of attaching the transducer to the building structure is of particular importance. In acoustic terms, fasteners are matching elements between radiation sources - transducers and the environment in which this radiation propagates, i.e. building structure. Therefore, the fixing device (besides being accurately dimensioned) must not only hold firmly in the wall, but also ensure full acoustic contact of its surface with the material of the building structure. This is achieved by eliminating cracks and gaps in the attachment point using adhesives and binders with minimal shrinkage coefficients.
Rice. 4.6. Installing the vibration transducer:
1- main building structure; 2 - converter; 3-cover by placing them in pre-prepared building structures niches closed, for example, with plaster after installing the converter (Fig. 4.6).
The screen is a lightweight rigid structure that separates the converter from the volume of the selected room. The scheme of the installation and the effectiveness of the screens are shown in fig. 4.7.
The graph shows that the use of the screen reduces the acoustic radiation of the transducer by 5 ... 17 dB, with the greatest effect
Rice. 4.7. Installation scheme (a) and screen efficiency (b):
1 - main building structure; 2- converter; 3- acoustic screen; 4 - walls and transducers without a screen; 5 - walls and transducers in the screen; b - the wall itself is achieved in the region of medium and high frequencies, i.e. in the region of greatest audibility. The screen should be installed in such a way that its inner surface does not come into contact with the converter case and there are no gaps and leaks in the places where the screen adjoins the building structure.
Currently, vibroacoustic noise systems are widely represented on the information security market, and interest in them is constantly growing.
It should be noted that comparison of the parameters of different systems only on the basis of data from manufacturers is impossible due to the difference in theoretical concepts, methods for measuring parameters, and production conditions.
The firm "MASCOM" conducted studies of the most well-known systems of vibroacoustic noise in Russia. The purpose of the work was to measure and compare the main electro-acoustic parameters of noisy systems installed on real building structures using a unified methodology.
The analysis of the results of the work made it possible to draw the following conclusions:
1. The most problematic is the noise of massive building structures with high mechanical impedance (walls 0.5 m thick).
2. Most systems of vibroacoustic noise create effective vibration interference only on elements of building structures with a relatively low mechanical impedance (glass, pipes). The level of vibration accelerations created on glass is usually 20 dB higher than on a brick wall.
3. The main element that determines the quality of the generated vibration signal is the vibroacoustic transducer (vibration sensor).
4. In all the considered systems, except for N/N0-006, \ZNG-006DM and Rustle, the generators create an interfering signal that is close in spectral composition to white noise.
5. In most of the considered systems, except for "Threshold-2M" and "Shoroh", the possibility of adjusting the shape of the vibration interference spectra, which is necessary for optimal noise reduction of various building structures, is not provided.
On fig. 4.8, 4.9 shows the spectra of vibration noise generated by the studied systems when working on a brick wall
Rice. 4.8. Spectral characteristics of systems on a brick wall 0.5 m thick at a distance from the vibrator to the control point of 3 m:
1 - system "Rustle"; 2-VNG-006DM; 3- system "Threshold 2M" at a distance of 0.8 m; 4-VNG-006 (1997); 5-VAG-6/6; b - system "Threshold 2M" at a distance of 3 m; 7-ANG-2000; 3-accelerations excited by an acoustic > 75 dB signal; 9-VNG-006 (1998); 10-system NG-502M
0.5 m thick and concrete floor 0.22 m thick.
According to operational and technical characteristics existing systems vibroacoustic noise can be divided into several groups:
Systems that have a "blockage" in the lower frequency range of the spectrum (as a rule, at frequencies up to 1 kHz) with a sufficient integral level of noise. The powerful interference they create in a narrow frequency band greatly reduces intelligibility, but can be neutralized by narrow-band filtering methods. This group includes VAG 6/6, VNG-006 (1997).
Systems providing effective noise suppression in the band from 450 to 5000 Hz. Data retrieval using such systems is hardly possible, however, they still do not fully satisfy the requirements of the State Technical Commission of Russia. This group includes UMO-OOb (1998) and Li0-502M.
Systems certified by the State Technical Commission of Russia. These include AI6 "2000, certified for the second category. Systems that meet the requirements of the State Technical Commission of Russia for the first category in the entire frequency range and are able to qualify for certification in this category - "Threshold-2M" and "Shoroh", are adaptive, their parameters can vary widely and thus provide optimal protection.
Rice. 4.9. Spectral characteristics of systems on a concrete floor with a thickness of 0.22 m at a distance from the vibrator to the control point of 3 m:
1 ~ "Rustle" system; 2-U AO-6/6; 3-UMS-006 (1997), 4-USh-0060M] 5-AMS-2000; 6-\ZNG-006 (1997); 7-system Yv-502M; 8-accelerations excited by acoustic vibrator 75 dB
The Threshold-2M system is configured automatically. The system reproduces a speech signal, analyzes in narrow bands the vibrational vibrations of a building structure caused by this signal, generates a spectrum of vibrational interference necessary to ensure the selected level of protection, evaluates the result and draws a conclusion about the completed task. Very impressive is the presence of voice accompaniment of the operations performed by the system. The consumer qualities of the system are somewhat reduced by the insufficient efficiency of vibrators, the range of which on structures with a thickness of 0.5 m is about 0.8 m. In addition, the automatic adjustment mechanism under conditions high level structural interference.
The Rustle system is not automatic; the adjustment is made by the operator after its installation in a dedicated room. Rough selection of the spectrum shape is performed by the filter switches, which form white noise, pink noise and noise falling towards the high frequencies at a rate of 6 dB / oct. Fine adjustment of the shape of the spectrum is made in octave bands using the built-in equalizer. The radius of effective action of the vibrators of the "Shoroh" system on a brick wall of 0.5 m is about 6 m.
Voice recorder suppression
The sharp reduction in size and increased sensitivity of modern voice recorders has led to the need to separately consider the issue of their suppression.
To suppress portable voice recorders, devices are used that are generators of powerful noise signals in the decimeter frequency range. Impulse interference signals act on microphone circuits and amplifying devices of voice recorders, as a result of which they are recorded along with useful signals, causing severe distortion of information. The suppression zone, determined by the radiation power, the directional properties of the antenna, and the type of noisy signal, is usually a sector with a width of 30 to 80 degrees and a radius of up to 5 m.
The range of suppression by modern means is highly dependent on several factors:
Voice recorder case type (metal, plastic);
An external or built-in microphone is used;
Dictaphone dimensions;
Orientation of the recorder in space.
According to the type of application, voice recorder jammers are divided into portable and stationary. Portable suppressors ("Shumo-tron-3", "Storm", "Sturm"), as a rule, are made in the form of cases, have a device remote control, and some ("Shumotron-3") and devices remote control. Stationary ("Buran-4", "Ramses-Double"), most often, are made in the form of separate modules: a generator module, a power supply module, an antenna module. Such constructive solution allows you to most optimally place the suppressor on a specific object. Due to the fact that the suppressor has a limited suppression area, in some cases it is possible to use several stationary suppressors to form the required coverage area. When the voice recorder enters the zone of the suppressor, its low-current circuits (microphone, external microphone cable, microphone amplifier) induce a noise signal, which modulates the carrier frequency of the voice recorder suppressor. The magnitude of these pickups is directly dependent on the geometric dimensions of these circuits. The smaller the voice recorder, the lower the suppression efficiency. Below are the test results of some models of modern suppressors.
Initial data:
Tests are carried out in the absence of powerful electromagnetic interference on a test bench;
The stand is a table installed in the center of the room with an area of 50 sq. m, on which a voice recorder suppressor is installed in a state prepared for operation;
The effectiveness of suppression is evaluated by a group of 10 experts on a five-point system. The evaluation criteria are given in Table. 4.6.
Table 4.6
The message under investigation is the text read in turn by each of the experts;
The expert reading the text sits at a distance of 1 m from the voice recorder microphone outside the jammer coverage area;
The built-in microphone of the voice recorder is used; The recorder in the recording mode is located in the horizontal plane at an angle of 20 degrees to the axis of the main lobe and in the vertical plane at an angle of 30 degrees to the normal of the main lobe, i.e. in two spatial positions corresponding to the minimum and maximum values of the suppression efficiency;
Evaluation of the suppression results is carried out after moving the voice recorder by 50 cm or 25 cm (if the distance is less than 1 m) towards the suppressor antenna. The results of the studies are summarized in table. 4.7.
Table 4.7
|
Dictaphone |
Distance to suppressor, m |
||||||||||||
| 3,0 | 2,5 | 0,25 | |||||||||||
|
"Shumotron-3" |
|||||||||||||
| Sputnik 2000 | 4 | 0 | 0 | ||||||||||
| Wayfarer | 4 | 1 | 0 | ||||||||||
| Olympus L-400 | 1 | 0 | 0 | ||||||||||
| Samsung SVR-S1300 | 0 | 0 | 0 | ||||||||||
| Papyrus | 4 | 4 | 4 | ||||||||||
|
"Buran-4" |
|||||||||||||
| Sputnik 2000 | 4 | 2 | 2 | ||||||||||
| Wayfarer | 1 | 0 | 0 | ||||||||||
| Olympus L-400 | 3 | 2 | 2 | ||||||||||
| Samsung SVR-S1300 | 0 | 0 | 0 | ||||||||||
| Papyrus | 4 | 3 | 3 | ||||||||||
|
"Ramses-double" |
|||||||||||||
| Sputnik 2000 | 4 | 4 | 3 | ||||||||||
| Wayfarer | 4 | 2 | 1 | ||||||||||
| Olympus L-400 | 4 | 2 | 1 | ||||||||||
| Samsung SVR-S1300 | 4 | 2 | 1 | ||||||||||
| Papyrus | 4 | 4 | 4 | ||||||||||
|
Dictaphone |
Distance to suppressor, m |
|||||||
| 3,0 |
2,5 2,0 1,5 1,0 0,75 0,50 |
0,25 | ||||||
| Sputnik 2000 | 4 | 4 | 3 | 2 | 1 | 0 | 0 | 0 |
| Wayfarer | 4 | 4 | 3 | 1 | 0 | 0 | 0 | 0 |
| Olympus L-400 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| Samsung SVR-S1300 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| Papyrus | 4 | 4 | 4 | 4 | 4 | 4 | 4 | 4 |
As can be seen from the results of the study, the range of suppression, first of all, depends on the specific model of the voice recorder. For shielded voice recorders, the suppression range is noticeably lower and lies within: 0.1. ..1.5 m. The suppression efficiency of voice recorders in a plastic case is higher compared to shielded ones. The suppression range of these voice recorders lies within: 1.5 ... 4 m.
This suppression range of voice recorders, as a rule, does not provide the required degree of protection against leakage of voice information and therefore the most effective, in protecting against unauthorized recording on a voice recorder, are organizational measures based on preventing people from entering a controlled room with voice recorders at the time of important negotiations.
Currently, voice recorder suppression devices have appeared, which are RF signal generators with a special type of modulation. Influencing the circuits of the recording device, the signal, after imposing, is processed in the AGC circuits together with the useful signal, significantly exceeding it in level and, accordingly, distorting it. One such device is the Sapphire Dictaphone Suppressor. Let's dwell on it in more detail.
Home distinctive feature"Sapphire" is the use of a high-frequency signal modulated by speech-like noise, which makes it possible to achieve poor intelligibility even with a signal-to-noise ratio of 1. Also, a feature of the new suppressor is the ability to form an optimal suppression zone due to the distributed suppressor antenna system. "Sapphire" has three types of antennas with different radiation patterns, the joint use of which allows you to create the necessary radiation pattern to protect the meeting room, or for use in a portable version with an autonomous power source (Table 4.8).
Table 4.8
|
Purpose, technical characteristics |
DN width |
Mini Mal suppression |
||
| Horizon- tal flat |
Verti cal | |||
| №1 | Designed for installation under the table surface. The radiation pattern has two lobes directed in opposite directions. | 110° | yu o | 2m in each direction |
| №2 | Designed for installation under the table surface, or on a false ceiling directly above the table surface. The radiation pattern has one lobe perpendicular to the plane of the antenna | 70° | <о | 2m |
| №3 | Designed for installation under the surface of the table, or in a mobile version. The radiation pattern has one lobe directed along the plane of the antenna | 60° | SO | 2m |
"Sapphire" is used in a mobile version. In this case, it is placed in a case (a), in a bag (b) it works from an autonomous power supply with an antenna with the desired radiation pattern. The stationary version (c) can also be used. Management is carried out covertly using a small-sized radio remote control.
Neutralization of radio microphones
Neutralization of radio microphones as a means of picking up speech information is advisable when they are detected at the time of search activities and there is no possibility of their removal or for tactical reasons.
Neutralization of the radio bookmark can be carried out by setting targeted interference at the frequency of the illegal transmitter. Such a complex contains a broadband antenna and a jamming transmitter.
The equipment operates under the control of a PC and allows you to create interference simultaneously or alternately at four frequencies in the range from 65 to 1000 MHz. Interference is a high frequency signal modulated with a tone or phrase.
To influence radio microphones with a radiation power of less than 5 mW, generators of spatial electromagnetic noise of the type ER-21 / V1, up to 20 mW - ZR-21 / V2 "Spectrum" can be used.
Power grid protection
Acoustic bookmarks broadcasting information over the mains are neutralized by filtering and masking. Isolating transformers and noise suppression filters are used for filtering.
Isolating transformers prevent the penetration of signals appearing in the primary winding into the secondary. Undesirable resistive and capacitive couplings between the windings are eliminated with the help of internal screens and elements with high insulation resistance. The degree of interference level reduction reaches 40 dB.
The main purpose of noise suppression filters is to pass without attenuation signals whose frequencies are within the operating range, and to suppress signals whose frequencies are outside these limits.
Low-pass filters pass signals with frequencies below its cutoff frequency. The operating voltage of the filter capacitors should not exceed the maximum values of the allowed voltage surges of the power supply circuit, and the current through the filter should cause saturation of the inductors. Typical parameters of filters of the FP series are given in Table. 4.9.
Table 4.9
Note. Overall dimensions of filters FP-1 and FP-2 are 350 x 100 x 60 mm, filters FP-3 - 430 x 150 x 60 mm, and filters FP-4, FP-5, FP-6 - 430 x 150 x 80 mm .
Noise suppression filters such as FP, FSP are installed in the lighting and socket networks at the point of their exit from the allocated premises. For noisy power lines, generators ER-41 / S, certified by Grom-ZI-4, Gnome-ZM, etc. are used. The appearance of the Gnom-ZM and FSP devices is shown in fig. 4.10.
Protection of terminal equipment of low-voltage lines
Due to the microphone effect or HF interference, almost all end devices of telephony, fire and burglar alarm systems, broadcasting and warning,
Rice. 4.10. The appearance of the devices "Gnom-ZM" (a) and FSP (6)
containing acoustic-transforming elements, create electrical signals in the supply lines, the level of which can range from a few nanovolts to tens of millivolts. Thus, the elements of the ringing circuit of the AvSEI telephone set, under the action of acoustic vibrations with an amplitude of 65 dB, feed a converted signal with a voltage of 10 mV into the line. Under the same conditions, a similar signal of an electrodynamic loudspeaker has a level of up to 3 mV. Transformed, it can rise to 50 mV and become available for interception at a distance of up to 100 m. The irradiating imposing signal, due to its high frequency, penetrates the galvanically disconnected microphone circuit of the on-hook and is modulated by an information signal.
Passive protection against microphone effect and RF interference is carried out by limiting and filtering or switching off sources of dangerous signals.
In limiter circuits, back-to-back semiconductor diodes are used, the resistance of which for small (converted) signals, amounting to hundreds of kiloohms, prevents them from passing into a low-current line. For high-amplitude currents corresponding to useful signals, the resistance turns out to be hundreds of ohms, and they freely pass into the line.
Filtering is a means of combating RF interference. The role of the simplest filters is performed by capacitors included in the microphone and ringing circuits. By shunting the high frequency intrusion signals, they do not affect the useful signals.
To protect telephones, as a rule, devices are used that combine the properties of a filter and a limiter. Instead of the obsolete device "Granite", certified products "Korund" and "Gran-300" are used.
Active protection of terminal devices is carried out by masking useful signals. Products of the MP series, equipped with filters from RF interference, generate noise-like oscillations in the line. The MP-1 A device (for analog lines) implements this mode only when the handset is on, and the MP-1C (for digital lines) - all the time. Protection of three-program broadcast receivers is provided by devices MP-2 and MP-3, secondary electric clocks - MP-4, notification speakers - MP-5, which additionally galvanically disconnects them from the line in the absence of useful signals.
The appearance of the MP-1 A, MP-2, MP-3, MP-4, "Korund", "Gran" devices is shown in fig. 4.11.
Rice. 4.11. Appearance of devices MP-1 A (a), MP-2 (®, MGN4 (vU, Korund (d), Gran (b)
Subscriber area protection telephone line
The telephone line can be used as a power source or an information transmission channel for an acoustic bookmark (AZ) installed in a room.
Passive protection of the subscriber line (AL) involves blocking acoustic bookmarks powered by the line when the handset is on. Active protection is carried out by noise of the subscriber line and the destruction of acoustic bookmarks or their power supplies with high-voltage discharges.
The main ways to protect the subscriber line include:
Submission to the line during a conversation of masking low-frequency signals of the audio range, or ultrasonic vibrations;
Increasing the voltage in the line during a conversation or compensating the constant component of the telephone signal with a constant voltage of reverse polarity;
Submission of a masking low-frequency signal to the line with the handset on-hook;
Line generation with subsequent compensation on a certain section of the subscriber line of a voice range signal with a known spectrum;
Supply of pulses up to 1500 V to the line for burning electronic devices and their power supplies
A detailed description of active subscriber line protection devices is given in a special manual.
Protection of information processed by technical means
Electric currents of various frequencies flowing through the elements of a functioning information processing tool create side magnetic and electric fields, which cause electromagnetic and parametric leakage channels, as well as interference of information signals in extraneous current-carrying lines and structures.
Weakening of side electromagnetic radiation of TSPI and their interference is carried out by shielding and grounding the means and their connecting lines, leakage into the power supply circuit is prevented by filtering information signals, and noise systems are used to mask PEMIN, which are discussed in detail in a special manual.
Shielding
There are electrostatic, magnetostatic and electromagnetic shielding.
The main task of electrostatic shielding is to reduce the capacitive coupling between the protected elements and is reduced to ensuring the accumulation of static electricity on the screen, followed by discharge of charges to the ground. The use of metal screens allows you to completely eliminate the influence of the electrostatic field.
The effectiveness of magnetic shielding depends on the frequency and electrical properties of the shield material. Starting from the medium wave range, a screen made of any metal with a thickness of 0.5 to 1.5 mm is effective; for frequencies above 10 MHz, a metal film with a thickness of about 0.1 mm gives a similar result. Grounding the shield does not affect the effectiveness of the shield.
The high-frequency electromagnetic field is weakened by the reverse field created by eddy currents induced in a metal solid or mesh screen. A screen made of copper mesh 2 x 2 mm attenuates the signal by 30...35 dB, a double screen by 50...60 dB.
Along with instrument nodes, mounting wires and connecting lines are shielded. The length of the shielded installation wire must not exceed a quarter of the length of the shortest wavelength in the signal spectrum transmitted over the wire. Shielded twisted pair and high-frequency coaxial cables provide a high degree of protection. The best protection against both electric and magnetic fields is guaranteed by lines such as bifilar, trifilar, insulated coaxial cable in an electric screen, metallized flat multi-wire cable.
Walls, doors, windows are screened indoors. Doors are equipped with a spring comb that provides reliable electrical contact with the walls of the room. The windows are covered with a copper mesh with a cell of 2x2 mm, ensuring reliable electrical contact of the removable frame with the walls of the room. In table. 4.10 shows data characterizing the degree of attenuation of high-frequency electromagnetic fields by various buildings.
Table 4.10
grounding
Shielding is effective only if the TSPI equipment and connecting lines are properly grounded. The grounding system should consist of a common ground, ground cable, busbars and wires connecting the ground electrode with objects. The quality of electrical connections must ensure the minimum contact resistance, their reliability and mechanical strength under vibration and harsh climatic conditions. As grounding devices, it is forbidden to use "zero" wires of power networks, metal structures of buildings, sheaths of underground cables, pipes of heating, water supply, alarm systems.
The value of ground resistance is determined by the specific soil resistance, which depends on soil moisture, composition, density, temperature. The values of this parameter for various soils are given in Table. 4.11.
Table 4.11
The grounding resistance of the TSPI should not exceed 4 ohms, and to achieve this value, a multi-element grounding is used from a number of single, symmetrically located ground electrodes, interconnected by busbars by welding. Grounding lines outside the building are laid at a depth of 1.5 m, and inside the building in such a way that they can be checked by external inspection. TSPI devices are connected to the line by bolting at one point.
Annotation: The lecture discusses methods and means of protecting acoustic (speech) information: sound insulation, noise, suppression of voice recorders. The main requirements and recommendations of STR-K for the protection of speech information are given.
Methods for protecting acoustic (speech) information are divided into passive and active. Passive methods are aimed at attenuating direct acoustic signals circulating in the room, as well as products of electroacoustic transformations in HTSS and OTSS and connecting circuits. Active methods include the creation of masking interference and the suppression / destruction of technical means of acoustic reconnaissance.
Soundproofing
The main passive method of protecting acoustic (speech) information is soundproofing. Allocation of an acoustic signal by an intruder is possible if the signal-to-noise ratio lies within a certain range. The main purpose of using passive information security tools- reduction of the signal-to-noise ratio at possible points of interception of information by reducing the informative signal. Thus, soundproofing localizes radiation sources in a closed space in order to reduce the signal-to-noise ratio to the limit, which excludes or significantly hinders the removal of acoustic information. Consider a simplified soundproofing scheme from the point of view of physics.
When falling acoustic wave on the boundary of surfaces with different specific planes, most of the incident wave is reflected. The reflectivity of a surface depends on the density of the material from which it is made and the speed of sound propagation in it. Reflection acoustic wave can be imagined as a result of the collision of air molecules m with the molecules of the reflecting surface M. Moreover, if M>>m, then the speed of the massive ball is close to zero after the impact. In this case, almost all of the kinetic energy acoustic wave is converted into the potential energy of elastic deformation of stationary balls. When the shape is restored, the deformed balls (surfaces) inform the air molecules hitting them with a speed close to the original one, but opposite in direction - this is how a reflected wave arises.
Smaller part acoustic wave penetrates the soundproofing material and spreads in it, losing its energy.
For solid, homogeneous, building structures, the attenuation of acoustic signals, which characterizes the quality of sound insulation, is calculated as follows (for medium frequencies):
Mass of the fence, kg;
Sound frequency, Hz.
At the stage of designing allocated premises, when choosing enclosing structures, it is necessary to adhere to the following:
- use acoustically heterogeneous structures as a floor;
- as a floor, use structures installed on vibration isolators, or structures on an elastic base;
- better use dropped ceilings with high sound absorption;
- as walls and partitions, it is preferable to use multilayer acoustically inhomogeneous structures with gaskets made of materials such as rubber, cork, fiberboard, MVP, etc.
In any room, doors and windows are the most vulnerable in terms of acoustic intelligence.
Window panes vibrate strongly under pressure acoustic wave, so it is advisable to separate them from the frames rubber gaskets. For the same reason, it is better to use triple or at least double glazing on two frames fixed in separate boxes. In this case, install adjacent glasses on the outer frame, and sound-absorbing material between the boxes.
The doors have significantly lower surface densities of the panels compared to other enclosing structures and gaps and crevices that are difficult to seal. Thus, a standard door is very poorly protected, so doors with increased sound insulation should be used. For example, the use of sealing gaskets increases the sound insulation of doors by 5-10 dB. It is better to install double doors with a vestibule and vibration decoupling from each other. Characteristics of sound-absorbing properties various designs are given in tables 14.1, 14.2.
| Type | Design | ||||||
|---|---|---|---|---|---|---|---|
| 125 | 250 | 500 | 1000 | 2000 | 4000 | ||
| Panel door lined with plywood on both sides | without gasket | 21 | 23 | 24 | 24 | 24 | 23 |
| 27 | 27 | 32 | 35 | 34 | 35 | ||
| Standard door P-327 | without gasket | 13 | 23 | 31 | 33 | 34 | 36 |
| with foam rubber gasket | 29 | 30 | 31 | 33 | 34 | 41 | |
| Type | Sound insulation (db) at Hz frequencies | |||||
|---|---|---|---|---|---|---|
| 125 | 250 | 500 | 1000 | 2000 | 4000 | |
| Single glazing | ||||||
| thickness 3 mm | 17 | 17 | 22 | 28 | 31 | 32 |
| thickness 4 mm | 18 | 23 | 26 | 31 | 32 | 32 |
| thickness 6 mm | 22 | 22 | 26 | 30 | 27 | 25 |
| Double glazing with air gap | ||||||
| 57mm (thickness 3mm) | 15 | 20 | 32 | 41 | 49 | 46 |
| 90 mm (thickness 3 mm) | 21 | 29 | 38 | 44 | 50 | 48 |
| 57mm (thickness 4mm) | 21 | 31 | 38 | 46 | 49 | 35 |
| 90 mm (thickness 4 mm) | 25 | 33 | 41 | 47 | 48 | 36 |
The use of sound-absorbing materials has some features associated with the need to create an optimal ratio of direct and reflected acoustic signals from the barrier. Excessive sound absorption reduces the signal strength. The value of sound attenuation by various fences is given in table 14.3.
| Fencing type | Sound insulation (db) at Hz frequencies | |||||
|---|---|---|---|---|---|---|
| 125 | 250 | 500 | 1000 | 2000 | 4000 | |
| Brick wall | 0,024 | 0,025 | 0,032 | 0,041 | 0,049 | 0,07 |
| wood upholstery | 0,1 | 0,11 | 0,11 | 0,08 | 0,082 | 0,11 |
| Single glass | 0,03 | - | 0,027 | - | 0,02 | - |
| lime plaster | 0,025 | 0,04 | 0,06 | 0,085 | 0,043 | 0,058 |
| Felt (thickness 25mm) | 0,18 | 0,36 | 0,71 | 0,8 | 0,82 | 0,85 |
| pile carpet | 0,09 | 0,08 | 0,21 | 0,27 | 0,27 | 0,37 |
| Glass wool (thickness 9mm) | 0,32 | 0,4 | 0,51 | 0,6 | 0,65 | 0,6 |
| Cotton fabric | 0,03 | 0,04 | 0,11 | 0,17 | 0,24 | 0,35 |
Sound-absorbing materials - materials used for interior decoration rooms to improve their acoustic properties. Sound-absorbing materials can be simple and porous. IN simple materials sound is absorbed as a result of viscous friction in the pores (foam concrete, gas glass, etc.). In porous materials, in addition to friction in the pores, there are relaxation losses associated with the deformation of a non-rigid skeleton (mineral, basalt, cotton wool). Usually two types of material are used in combination with each other. One of the common types of porous materials is facing sound-absorbing materials. They are made in the form of flat slabs ("Akmigran", "Akminit", "Silakpor", "Vibrostek-M") or relief structures (pyramids, wedges, etc.), located either close to or at a short distance from a solid building structures (walls, partitions, fences, etc.). Figure 14.4 shows an example of a sound absorbing board. For the production of plates such as Akmigran, mineral or glass granulated cotton wool and binders consisting of starch, carboxycellulose and bentonite. From the prepared mixture, plates 2 cm thick are formed, which, after drying, are subjected to finishing (calibrated, polished and painted). The front surface of the plates has a cracked texture. The density of the sound-absorbing material is 350-400kg/m3. Sound-absorbing boards are usually fastened to the floor with the help of metal profiles.
Rice. 14.1.
Porous sound-absorbing materials are ineffective at low frequencies. A separate group of sound-absorbing materials are resonant absorbers. They are divided into membrane and resonator. Membrane absorbers are a stretched canvas (fabric), a thin plywood (cardboard) sheet, under which a well damping material is placed (material with high viscosity, for example, foam rubber, sponge rubber, construction felt, etc.). In absorbers of this kind, the absorption maximum is reached at resonant frequencies. Perforated resonator absorbers are a system of air resonators (for example, Helmholtz resonators), at the mouth of which a damping material is located.
The signal level behind the barrier is estimated by the following formula:
Consider the example of soundproofing a fence and a floor.
In the case when it comes to building a partition with high soundproofing properties, it is proposed to consider a partition on two independent frames with two layers of gypsum-fiber sheets on each side as an effective design. In this case, a system is used that consists of two independent metal frames with a thickness of 50, 75 or 100 mm, which are sheathed on both sides with GVL sheets in two layers with a thickness of 12.5 mm each. When installing this structure, all elements of the metal frames, as well as the ends of the GVL sheets, are adjacent to all other structures, including the supporting ones, through a layer of vibration-proof material 6 mm thick. Metal frames are mounted parallel to each other with a gap of at least 10 mm to exclude possible connections between them. Inner space partitions are filled with sound-absorbing basalt slabs to a thickness equal to at least 75% of the total internal thickness of the partition. The index of airborne noise insulation by a partition on two frames of 100 mm each with a total thickness of 260 mm is Rw = 58 dB, a partition based on profiles 50 mm thick provides sound insulation equal to Rw = 54 dB with a thickness of 160 mm
2 layers of soundproofing material, such as glass staple fiber, are laid on the floor slab. At the same time, on all walls this room a gasket is started from one layer of material with a thickness of 20 mm and a height slightly greater than the height of the screed being arranged. A separating layer of polyethylene film is laid on top of the material, along which a concrete leveling screed 80 mm thick is laid, reinforced with a metal mesh to give it increased mechanical strength.
To increase sound insulation in rooms, acoustic screens can be installed on the path of sound propagation in the most dangerous directions in terms of leakage. As a rule, screens are used to protect temporary premises.
To conduct confidential conversations, so-called soundproof cabins have also been developed, which are divided into frame and frameless. The former have metal carcass on which sound-absorbing panels are attached. Cabins with two-layer sound-absorbing plates provide sound attenuation up to 35 ... 40 dB. Frameless cabs are more efficient. They are assembled from prefabricated multilayer panels connected with soundproof elastic pads. The efficiency of such cabins lies in the range of 50…55 dB.
protection of information from leakage through an acoustic channel is a set of measures that exclude or reduce the possibility of confidential information leaving the controlled area due to acoustic fields.
5.3.1. General [A]
The main measures in this type of protection are organizational and organizational and technical measures.
Organizational measures involve the implementation of architectural and planning, spatial and regime measures, and organizational and technical - passive (sound insulation, sound absorption) and active (sound suppression) measures. The implementation of technical measures through the use of special secure means of conducting confidential negotiations is not excluded (Fig. 49).
Architectural and planning measures provide for the presentation of certain requirements at the design stage of buildings and premises or their reconstruction and adaptation in order to exclude or weaken the uncontrolled propagation of sound fields directly in the airspace or in building structures in the form of 1/10 structural sound. These requirements may include both the choice of the location of premises in the pro -
spatial plan, and their equipment with elements necessary for acoustic safety, excluding direct or reflected in the direction of the possible location of the attacker sound propagation. For these purposes, doors are equipped with drills there, windows are oriented towards the territory protected (controlled) from the presence of unauthorized persons, etc.
Regime measures provide for strict control of the stay in the controlled area of employees and visitors.
Organizational and technical measures provide for the use of sound-absorbing means. porous and soft materials such as wool, fleecy carpets, foam concrete, porous dry plaster are good soundproofing and sound-absorbing materials - they have a lot of interfaces between air and a solid body, which leads to repeated reflection and absorption of sound vibrations.
For cladding surfaces of walls and ceilings, special hermetic acoustic panels are widely used, made of high-density glass wool and various thicknesses (from 12 to 50 mm). Such panels provide sound absorption and exclude its propagation in wall structures. The degree of sound absorption a, reflection and transmission of sound by barriers is characterized by the coefficients of sound absorption, reflection b, transmission t.
The degree of reflection and absorption of sound energy is determined by the frequency of the sound and the material of the reflective (absorbing) structures (porosity, configuration, thickness).
It is advisable to arrange soundproofing wall coverings in small rooms, since in large rooms sound energy is absorbed to the maximum before reaching the walls. It is known that the air environment has a certain sound-absorbing capacity and the sound intensity decreases in air in proportion to the square of the distance from the source.
Indoors, the volume level sounds higher than outdoors due to multiple reflections from various surfaces to keep the sound going even after the sound source stops (reverb). The level of reverberation depends on the degree of sound absorption.
The sound absorption value A is determined by the coefficient
sound absorption a and the dimensions of the sound-absorbing surface:
The values of the sound absorption coefficients of various materials are known. For ordinary porous materials - felt, cotton wool, porous plaster - it ranges from a = 0.2 - 0.8. Brick and concrete almost do not absorb sound (a = 0.01 -0.03).
The degree of sound attenuation when using sound-absorbing coatings is determined in decibels.
For example, when processing brick walls(a = 0.03) with porous plaster (a = 0.3) the sound pressure in the room is attenuated by 10 dB (8 = 101g £).
5.3.2. Methods and means of protection [A]
Sound level meters are used to determine the effectiveness of sound insulation protection. Sound level meter is measuring device, which converts sound pressure fluctuations into readings corresponding to the sound pressure level. In the field of acoustic speech protection, analog sound level meters are used (Fig. 50).
According to the accuracy of readings, sound level meters are divided into four classes. Zero class sound level meters are used for laboratory measurements, the first - for full-scale measurements, the second - for general purposes; sound level meters of the third class are used for oriented measurements. In practice, to assess the degree of protection of acoustic channels, sound level meters of the second class are used, less often - the first.
Acoustic immunity measurements are carried out using the reference sound source method. An exemplary source is a source with a predetermined power level at a certain frequency (frequencies),
A tape recorder with a signal recorded on tape at frequencies of 500 Hz and 1000 Hz, modulated by a sinusoidal signal of 100-120 Hz, is selected as such a source. Having an exemplary sound source and noise meter, it is possible to determine the absorption capacity of the room, as shown in Fig. 51.
The value of the acoustic pressure of an exemplary sound source is known. The signal received from the other side of the wall was measured according to the sound level meter. The difference between the indicators gives the absorption coefficient.
Table 4
|
Signal frequency (Hz) |
|
So-called electronic stethoscopes are used to evaluate the protection of premises from leakage through acoustic and vibration channels. They allow you to listen to ongoing conversations in the room.
through walls, floors, ceilings, heating systems, water supply, ventilation communications and other metal structures. As a sensitive element, they use a sensor that converts mechanical sound vibrations into an electrical signal. The sensitivity of stethoscopes ranges from 0.3 to 1.5 v/dB. At a sound pressure level of 34 - 60 dB, corresponding to the average conversation volume, modern stethoscopes allow you to listen to rooms through walls and other enclosing structures up to 1.5 m thick. After checking possible leak channels with such a stethoscope, measures are taken to protect them. An example is the Breeze (Eleron) electronic stethoscope. Operating frequency ranges - 300 - 4000 Hz, autonomous power supply. Designed to detect vibratory-acoustic channels of information leakage circulating in a controlled room through structure or communication fences, as well as to monitor the effectiveness of information security tools.
In cases where passive measures do not provide the necessary level of security, active means are used. Active means include noise generators - technical devices that produce noise-like electronic signals. These signals are fed to the appropriate acoustic or vibration transducers. Acoustic sensors are designed to create acoustic noise indoors or outside, and vibration sensors - for masking noise in building envelopes. Vibration sensors are glued to protected structures, creating sound vibrations in them.
As an example of noise generators, we can cite the system of vibroacoustic noise "Barrier" ("Mask"). The system allows you to protect up to 10 conditional surfaces, has automatic activation of vibration transducers when an acoustic signal appears. Effective noise bandwidth 100 - 6000 Hz (Fig. 53). On fig. 54 shows an example of placing a system of acoustic and vibration sensors in a protected area.
Figure 54. Variant of placement of acoustic sensors
Modern noise generators have an effective frequency band ranging from 100 - 200 Hz to 5000 - 6000 Hz. Some types of generators have a frequency band of up to 10,000 Hz. The number of sensors connected to one generator is different - from 1 - 2 to 20 - 30 pieces. This is determined by the purpose and design of the generator.
Noise generators used in practice make it possible to protect information from leakage through walls, ceilings, floors, windows, doors, pipes, ventilation communications and other structures with a sufficiently high degree of reliability. IN
So, protection against leakage through acoustic channels is implemented:
the use of sound-absorbing linings, special additional vestibules for doorways, double window frames;
using means of acoustic noise reduction of volumes and surfaces;
closure ventilation ducts, input systems for heating, power supply, telephone and radio communications;
the use of special certified premises, excluding the appearance of information leakage channels.
Weakening of acoustic (speech) signals at the border of the controlled zone to values that ensure the impossibility of their selection by means of reconnaissance against the background of natural noise;
Weakening of information electrical signals in the connecting lines of VTSS, which incorporate electro-acoustic transducers (having a microphone effect), to values that ensure the impossibility of their selection by means of reconnaissance against the background of natural noise;
Exclusion (weakening) of the passage of HF-imposing signals to auxiliary technical means that incorporate electro-acoustic transducers (having a microphone effect);
Detection of radiation of acoustic bookmarks and spurious electromagnetic radiation of voice recorders in the recording mode;
Detection of unauthorized connections to telephone lines.
Active Methods defenses are aimed at:
Creation of masking acoustic and vibration interference in order to reduce the signal-to-noise ratio at the border of the controlled zone to values that ensure the impossibility of isolating an information acoustic signal by means of reconnaissance;
Creation of masking electromagnetic interference in the connecting lines of VTSS, incorporating electro-acoustic transducers (having a microphone effect), in order to reduce the signal-to-noise ratio to values that ensure the impossibility of isolating an information signal by means of reconnaissance;
Electromagnetic suppression of voice recorders in recording mode;
Ultrasonic suppression of voice recorders in recording mode;
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Creation of targeted radio interference to acoustic and telephone radio bugs in order to reduce the signal-to-noise ratio to values that ensure the impossibility of isolating an information acoustic signal by means of reconnaissance;
Suppression (disruption of functioning) of means of unauthorized connection to telephone lines;
Destruction (disabling) of means of unauthorized connection to telephone lines.
The weakening of acoustic (speech) signals is carried out by soundproofing. The weakening of informative electrical signals in the HTSS lines and the exclusion (weakening) of the passage of high-frequency interference signals is carried out by the signal filtering method.
Active methods of protecting acoustic information are based on the use of various types of field generators, as well as the use of special technical means.
3.1. Soundproofing of premises
Sound insulation of premises is aimed at localizing the sources of acoustic signals inside them and is carried out in order to exclude the interception of acoustic (speech) information through direct acoustic (through slots, windows, doors, ventilation ducts, etc.) and vibration (through building envelopes, water pipes). , heat, gas supply, sewerage, etc.) channels.
Sound insulation is estimated by the value of the attenuation of the acoustic signal, which for solid single-layer or homogeneous fences at medium frequencies is approximately calculated by the formula /5/:
K og = 
, dB,
Where q p- weight of 1m 2 fences, kg;
f is the sound frequency, Hz.
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Soundproofing of premises is ensured by architectural and engineering solutions, as well as by the use of special building and finishing materials.
One of the weakest soundproofing elements enclosing the structures of allocated premises are windows and doors. An increase in the soundproofing ability of doors is achieved by tightly fitting the door leaf to the frame, eliminating gaps between the door and the floor, using sealing gaskets, upholstery or lining of the door leafs with special materials, etc. If the use of door upholstery is not enough to provide sound insulation, then double doors are installed in the room , forming a tambour. The inner surfaces of the vestibule are also lined with absorbent coatings.
The soundproofing ability of windows, as well as doors, depends on the surface density of the glass and the degree of pressing of the porches. The sound insulation of windows with single glazing is commensurate with the sound insulation of single doors and is not sufficient to reliably protect information in the room. Double or triple glazing is used to provide the required degree of sound insulation. In cases where it is necessary to provide increased sound insulation, windows of a special design are used (for example, a double window with filling the window opening with organic glass 20 ... 40 mm thick). The designs of windows with increased sound absorption based on double-glazed windows with sealing the air gap between the panes and filling it with various gas mixtures or creating a vacuum in it have been developed.
To increase the sound insulation of the room, acoustic screens are used, which are installed on the path of sound propagation in the most dangerous (from the point of view of intelligence) directions. The actions of acoustic screens are based on the reflection of sound waves and the formation of sound shadows behind the screen.
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Porous sound-absorbing materials are ineffective at low frequencies. Separate sound-absorbing materials make up resonant absorbers. They are divided into membrane and resonator.
Membrane absorbers are a stretched canvas (fabric) or a thin plywood (cardboard) sheet, under which a well damping material is placed (a material with a high viscosity, for example, foam rubber, sponge rubber, construction felt, etc.). In absorbers of this kind, the absorption maximum is reached at resonant frequencies.
Perforated resonator absorbers are a system of air resonators (Helmholtz resonator), at the mouth of which damping material is located. Increasing the sound insulation of walls and partitions of rooms is achieved by using single-layer and multi-layer (more often - double) fences. In multilayer barriers, it is advisable to select materials of layers with sharply different acoustic resistances (concrete - foam rubber). The level of the acoustic signal behind the fence can be approximately estimated by the formula /5/:
Where Rc- the level of the speech signal in the room (in front of the fence), dB;
S og– fence area, dB;
K og- sound insulation of the fence, dB.
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Special soundproof booths have been developed for conducting confidential conversations. Structurally, they are divided into frame and frameless. In the first case, sound-absorbing panels are attached to the metal frame. Cabins with two-layer sound-absorbing plates provide sound attenuation up to 35…40 dB.
Frameless cabs have a higher acoustic efficiency (large attenuation coefficient). They are assembled from prefabricated multilayer shields interconnected through soundproof elastic pads. Such cabins are expensive to manufacture, but the sound level reduction in them can reach 50 ... 55 dB.
Similar information.
Anyone who has something to keep secret from others, when using the phone, sooner or later thinks about how to protect themselves from listening telephone conversation. There is a problem of choosing a means of protection from the abundance available on the Russian market. Special meaning this task acquires with the development of IP-telephony technology.
When using a telephone, we wittingly or unwittingly trust him with information, which is sometimes of a confidential nature. This may be information relating to personal life, or personal data of employees of organizations. Information containing commercial or banking secrets may be transmitted by telephone. Generally speaking, when two people communicate on the phone, it is assumed that no one else can hear them, and the communication line is protected from eavesdropping by third parties.Unfortunately, this is far from the case. In the PSTN, electrical signals propagate in clear communication lines.
Almost any intruder, with the appropriate equipment, can gain access to confidential information transmitted over the PSTN using:
Direct connection to telephone lines;
Contactless retrieval of information and "bugs";
Radiation in radio and optical frequency spectra.
So how do you protect speech information? Currently, two areas of protection of speech information are being actively developed. One of them is related to the physical protection of telephone lines and acoustic protection of conversations. Another direction of protection of telephone voice communications is based on the information transformation of telephone signals and messages.
MEANS OF PHYSICAL PROTECTION OF VOICE INFORMATION
Speech masking - effective remedy providing a high degree of protection for telephone conversations. The masker is a noise generator whose correlation characteristics can change dynamically during negotiations. When transmitting voice information, the masker on the receiving side outputs intense noise into the line in the frequency band of the telephone channel, which propagates along the entire communication line, creating strong interference for the attacker. Simultaneously, the masker's noise signal is used to compensate for interference in the incoming "mixture" of the speech signal and interference (using an adaptive filter). As a result, on the receiving side, the subscriber hears speech without interference, and the attacker hears it with interference. As a rule, the masker is connected from the side of the receiving subscriber (one-sided masker), although it is also possible to connect on the side of the transmitting subscriber (two-way masker). In the latter case, the possibility of duplex telephone conversations disappears, since it will be necessary to turn on and off each masker in turn. The inconvenience when using maskers is the presence of strong noise on the transmitting side. One-way speech maskers are built into a number of devices, among which are: the "Tu-man" device, which has a blocking noise level of up to 1 W in the frequency band of 0.5 - 3.5 kHz; Soundpress device with a noise power of 2 W; as well as the SI-2001 security telephone module.
Connectivity Neutralizers to the telephone line provide the creation of irreversible physical and chemical transformations in the technical means used by the attacker. The neutralizer outputs a short-term signal (over 1.5 kV) or a series of short pulses into the line, which destroy the input circuits of the connected devices. Usually, devices for the physical destruction of devices for unauthorized removal of voice information burn out "bugs" at a distance of 200-300 m. Such neutralizers are Bugroaster (bug burner), PTL-1500 (telephone line burner) and "Cobra" (embedded device burner). Passive protection means are frequency filters, blockers and other devices, which, as a rule, are installed in a break in a telephone line or in a telephone circuit to exclude the possibility of listening to conversations through a telephone line in the "clear" mode. Such devices, however, do not protect the telephone line from being intercepted during a conversation. Means of passive protection of speech information: device "Korund-M", blocking filter MT202, blocker of telephone "bugs" MT201, telephone line indicator LST 1007A. Means of setting active jamming are used to protect the "telephone set - PBX" section. They provide barrage interference in the telephone line and some change in the standard parameters of the telephone channel (for example, the level of transmission / reception of a telephone signal). The interference exceeds the nominal level of the telephone signal by one or two or more orders of magnitude and, acting on the input stages and power devices of the means of intercepting voice information in the communication channel, brings them out of the linear mode. As a result, the attacker hears only noise instead of the desired information. In order for the interference not to affect the quality of the speech signal, it is compensated before being sent to the transmitting telephone set and is selected from signals that are attenuated before they arrive at the exchange or are filtered out from the useful signal. Means of setting active jamming have a high efficiency of protecting telephone lines from almost all types of listening devices. Among them: the electronic module for the integrated protection of the wired telephone line "Octopus" and "Sonata-03M", noise generators for standard telephone lines SEL SP-17 / T, "Cicada", "Gnome", "Proton", etc.
Telephone line analyzers and are designed to search for channels to intercept telephone conversations and detect cases of unauthorized connection to a telephone line. There are two main classes of analyzers. The first includes devices that detect changes in the parameters of a telephone line in case of unauthorized connection to it: the direct current component, the active and reactive components of the telephone line impedance. Changes in these characteristics are recorded and serve as the basis for making decisions about the possibility of unauthorized connection to the telephone line.
The simplest analyzers - devices for monitoring telephone lines KTL-2 and TPU-5 - allow you to determine the resistive changes in line parameters and measure the voltage in them. More sophisticated analyzers allow you to identify the approximate place of connection to the line, as well as the facts of a contactless connection: telephone line analyzers ALT-01, AT-23, "Alder", "Bager-01", MT205, search device RT 030, cable radar "Vector" , non-linear location systems and others. The second class consists of software and hardware for radio monitoring and scanning, the principle of operation of which is based on the control and analysis of radio emissions by means of interception and connection to telephone lines. Such devices can effectively detect "bugs". There are means of control - from relatively cheap field indicators D-006 to universal complexes for monitoring technical channels of information leakage "Krona-6000" and expensive scanners AR-3000. Weakness telephone line analyzers - a high probability of false positives, as well as the inability to determine all types of connections to the telephone line.
Therefore, the so-called complexes for monitoring and analyzing the results of monitoring signals from unauthorized access tools have been created.
Such complexes can solve the following tasks:
Identification of radiation from unauthorized access and their localization;
Detection of side electromagnetic radiation and pickups;
Evaluation of the effectiveness of the use of technical means of protecting speech information;
Monitoring the implementation of restrictions on the use of radio electronic means;
Evaluation of the type and parameters of the original information flow contained in the processed analog signal;
Maintaining a database of signal parameters and their sources.
Programs for detecting means of retrieving speech information are installed on a PC. They implement most of the radio bug detection algorithms. Radio monitoring software and hardware systems: the universal program for detecting means of covert information retrieval "Filin", the universal monitoring program Sedif Plus, the professional monitoring program Sedif Pro, the system for collecting and processing data and controlling measurements "Regulation-P".
IN Lately multifunction devices. For example, the Barrier-4 telephone line security system provides:
Monitoring the state of the power grid and detecting high-frequency signals in it;
Ability to connect scanning and analyzing devices;
Suppression of listening and sound recording devices;
Indication of the connection of information retrieval devices, etc.
Multifunctional devices for protecting telephone conversations from listening and recording of the Prokrust series, the complex protection of the wired line from unauthorized retrieval of information "Octopus", the complex protection of the telephone line "Storm", as well as the above-mentioned security system of the telephone line of the "Barrier" series, etc.
MEANS OF ACOUSTIC PROTECTION OF SPEECH INFORMATION
To ensure the confidentiality of telephone conversations, it is not enough to protect the information on the telephone line. The probability of picking up speech information is very high before the conversion of sound vibrations into electrical signals in the handset. Protection at this stage is called acoustic. It is based on the use of speech masking by acoustic masking noise operating in the speech frequency band and having a "smooth" spectral response. There are three main groups of means of acoustic protection of speech information. The first group includes barrage acoustic jammers, which are used for acoustic protection of premises and, as a rule, are used with vibration protection equipment: "Baron", "Shoroh", "Storm". They allow you to protect information from interception using stethoscopes, laser microphones through vibroacoustic propagation channels. The complex consists of a noise generator and several radio receivers, which, due to mixing, significantly reduce the probability of distinguishing a speech signal from a noisy one. The second group includes acoustic noise generators, which are located near the place of telephone conversations and mask the speech of the negotiators with their noise. At the same time, the person speaking into the handset is not protected from the effects of acoustic noise. These devices include the acoustic noise generator ANG-2000 (creates interference up to 2 W in the band 2 - 10 kHz). Intercom headsets (TF-011D, OKP-6, etc.) are used to protect against generator noise. The third group of means is represented by acoustic maskers: the masking noise comes from the generator simultaneously to the electro-acoustic emitter and to the input of the signal mixer filter, the second input of which receives a signal from the output of the receiving microphone. In the mixer of acoustic signals, the noise component of the signal is compensated, and the purified speech enters the telephone line. The masker is implemented in the acoustic protection equipment for confidential negotiations CNDS, provides suppression of masking noise in the signal to a depth of 26 - 30 dB. INFORMATION CONVERSION OF SPEECH SIGNALS AND MESSAGES Scramblers became the first hardware and software devices for protecting voice information during its transmission in analog form in a telephone channel. In analog scrambling, the original speech signal is converted in such a way that the line signal on the telephone line becomes unintelligible, although it occupies the same frequency band. The speech signal can be subjected to frequency inversion, frequency and time permutations, and in addition, mosaic transformation (frequency inversion and time permutation). Analog scrambling provides only temporary stability of speech information. At the same time, durability is understood as the number of operations (transformations) that are necessary to decrypt a certain speech message without knowing the keys. However, having a sufficiently powerful complex of measuring and converting equipment, it is possible to restore the original speech signal with acceptable quality. To increase the stability of the speech signal conversion, scramblers are equipped with cryptoblocks to control scrambling. Such scramblers on the transmitting and receiving sides must ensure the synchronization of devices before starting work and maintain it during a telephone conversation. Cryptographic control of scrambling leads to a signal delay, which generates a so-called echo in the telephone set. The more powerful the cryptographic algorithm, the worse the quality of the speech signal on the receiving side of the telephone line. To eliminate this shortcoming, keys with a length of about 30 bits for a symmetric key system and about 100 bits in an asymmetric key system are used. There is a large selection of various scramblers: telephone/fax scramblers of the SCR-M 1.2 series, "Selena", "Oreh-A", "Line-1" and others. communication in digital form using scramblers, but not analog, but digital. Encryption and decoding of speech information is carried out according to one algorithm. The use of speech information encoders is possible when they are synchronized on the transmitting and receiving sides of the telephone channel: on the transmitting side, synchronization bits are added to the information stream, which are allocated on the receiving side to synchronize devices, or time pulse generators and synchronization circuits with memory are used to synchronize encoders . A significant disadvantage of scramblers is their instability to the falsification of speech information. In addition, with the advent of packet-switched networks, it became possible to use block encryption to protect voice information, which, compared to streaming, has much greater strength. Guaranteed strength of protection of speech information can be obtained by encryption of audio speech codes. Digitization of an analog speech signal, compression and coding of a digital signal is carried out using a vocoder (from the English voice coder). The principle of operation of vocoders is based on the digitization of a speech signal by recognizing sounds and encoding them at a low speed (1 - 2 kbit / s), which makes it possible to accurately represent any sound in digital form. If a cryptographic transformation is applied to a digital stream, then encoded information of guaranteed security will be obtained, which is practically impossible to decrypt without knowing the keys and cryptographic algorithms used. Most vocoders and scramblers use a public Diffie-Hellman cryptographic key distribution system and digital stream encryption based on various algorithms, including triple DES, CAST-128, Blowfish, IDEA and Russian GOST 28147-89. The disadvantage of vocoders is some signal delay, as well as distortion of speech information. One of the best is the codec that implements the CELP algorithm, which is used in a modified form in the "Referent" equipment. Commercial vocoders are relatively expensive, but their number is growing every year: the Voice Coder-2400 telephone, the Orekh-4130 prefix for the telephone set for protecting speech information, and the SKR-511 Referent telephone conversation protection devices. PROTECTION OF VOICE INFORMATION IN IP-TELEPHONY In IP-telephony, there are two main ways to transfer packets with voice information over the network: via the Internet and via corporate networks + dedicated channels. There are few differences between these methods, but in the second case it is guaranteed best quality sound and a small fixed delay of voice information packets during their transmission over the IP network. To protect voice information transmitted in IP networks, cryptographic algorithms for encrypting source packets and messages are used, which, generally speaking, make it possible to ensure the guaranteed stability of IP telephony. There are effective cryptographic algorithms implemented on a PC, which, when using 256-bit secret and 1024-bit public encryption keys (for example, according to GOST 28147-89), make it practically impossible to decrypt a speech packet. However, when using such algorithms in IP telephony, several important factors should be taken into account, which can negate the capabilities of many modern means cryptographic protection of information. To ensure acceptable sound quality on the receiving side when transmitting voice packets in an IP network, the delay in their delivery from the receiving side should not exceed 250 ms. To reduce latency, the digitized speech signal is compressed and then encrypted using streaming encryption algorithms and transmission protocols in the IP network. Another problem of secure IP telephony is the exchange of cryptographic encryption keys between network subscribers. Typically, cryptographic protocols are used with public key using the Diffie-Hellman protocol, which prevents the interceptor from receiving any useful information about the keys and at the same time allows the parties to exchange information to form a common session key. This key is used to encrypt and decrypt the stream. In order to minimize the possibility of intercepting encryption keys, various technologies authentication of subscribers and keys. All cryptographic protocols and the speech stream compression protocol are selected dynamically and imperceptibly by the user by IP telephony programs, providing him with a natural interface similar to a conventional telephone. Implementing efficient cryptographic algorithms and ensuring sound quality require significant computing resources. In most cases, these requirements are met when using sufficiently powerful and productive computers, which, as a rule, do not fit in the telephone body. But computer-to-computer exchange of voice information does not always suit users of IP telephony. It is much more convenient to use a small, but better mobile IP-telephony device. Such devices have already appeared, although they provide the encryption strength of the speech stream is much lower than computer systems IP telephony. These telephones use the GSM algorithm to compress the voice signal, and encrypt it using the Wireless Transport Layer Security (WTLS) protocol, which is part of the Wireless Application Protocol (WAP) implemented in networks mobile communications. According to the forecasts of experts, the future belongs to such telephones: small, mobile, reliable, with guaranteed durability of voice information protection and high quality.
