On the problem of counteracting optical probing means of speech reconnaissance..
Maksimov Andrey Mikhailovich.
ON THE PROBLEM OF COUNTERACTION TO OPTICAL SOUNDING MEANS OF SPEECH RECONNAISSANCE
The problem of counteracting the removal of information using laser radiation remains very relevant and at the same time one of the least studied in comparison with other, less exotic” means of industrial espionage.
The principle of remote interception of acoustic information (speech) from premises using a light beam has been known since the 1930s. The probing beam is directed from the outside onto window panes, mirrors, and other reflectors. The vibrations of these surfaces under the influence of sound signals modulate the radiation falling on them. If a special device receives the reflected beam, it can then be demodulated into a speech signal. All known laser acoustic reconnaissance systems operate on this principle.
The special appeal of such systems is due to the fact that they allow solving the problems of picking up speech information in the safest possible way, at a distance, indirectly, avoiding the need to enter the premises of interest in order to place a listening device there, which is always associated with risk. In addition, identifying a working laser microphone is very difficult, and in some cases technically impossible.
In open publications, including on the Internet, you can read about Western developments of laser microphones. Thus, the SIPE LASER 3-DA SUPER system made in the USA uses a helium-neon laser as a radiation source. The device is aimed at the window glass using a telescopic sight, and the removal of speech information from window frames with double glass with good quality is ensured from a distance of up to 250 meters. The HPO150 laser device from HEWLETT PACKARD ensures the recording of conversations conducted indoors at a distance of up to 1000 m.
Of course, as experts emphasize, the practical use of laser microphones is associated with significant difficulties. The cost of systems sold in the West is tens of thousands of dollars. These are very complex devices, the operation of which requires extensive experience and specially trained specialists. No less important is the fact that the operation of laser microphones is significantly affected by such factors as atmospheric parameters, the quality of the probed surface, the level of background acoustic noise in the probed room and around it, etc. Any of these factors can reduce the quality of the reflected beam, reducing the level of residual speech intelligibility in the demodulated signal to zero. In a modern metropolis, the level of such “noise” — due to the high concentration of dust, exhaust gases, aerosols, powerful ascending and descending air flows, vibrations — can be an order of magnitude higher. There is an opinion of experts that the ranges of laser microphones declared by manufacturers are purely calculated or achieved in ideal, laboratory conditions. It is claimed that in the conditions of a modern city, ensuring satisfactory pickup of speech information using a laser even at a distance of 100 meters is problematic.
On the other hand, it is hardly correct to say that laser microphones are nothing more than a horror story from spy films. For example, there are known cases of using such microphones to collect information from the glass of the Soviet embassy and consulate in the USA, etc. In addition, the rapid development of technology and electronics makes it possible to create more compact and more advanced systems. The use of reflective elements is already being practiced, which ensures that the laser beam returns to the same point from which it was sent. Information has appeared about the creation of an effective diffusion laser, which allows for signal collection from glass at a fairly large angle.
Thus, laser systems exist and, if certain conditions are met, can be a very effective means of technical reconnaissance, although their use is associated with certain difficulties and limitations. What should units engaged in countering attempts at covert information collection do in this situation? Play it safe and spend additional funds on protection against a virtual threat, or simply ignore it?
It is obvious that a balanced approach is needed, based primarily on a real, comprehensive and methodologically competent assessment of the vulnerability of each specific object or room to laser microphones. However, upon closer examination it turns out that in this area there are practically no serious developments, methods and, most importantly, tools that allow for objective research of this kind.
In fact, for each type of technical reconnaissance equipment there is a proven technology for its detection. Software and hardware radio monitoring systems and field indicators are successfully used to search for and localize radio microphones, and nonlinear locators are used to search for devices with semiconductor elements. There are systems that allow you to assess the level of PEMIN, there are detectors of voice recorders, etc. But the problem of assessing the degree of vulnerability of a specific room for the removal of information using laser microphones has not had such developments to date.
In this regard, a new development, presented to the public at the end of 2004 by the Russian company «NERA-S», deserves interest. Hardware and software complex «Pattern»provides for the instrumental assessment of the availability zones of optical sounding systems of speech intelligence using the stereophotogrammetric location method with subsequent assessment of the residual speech intelligibility at the boundaries of the calculated zone.
Fig. 1. Hardware and software complex «UZOR»
1. Photo registration module
2. Response signal simulator
3. Receiving unit
At the first stage, a photo-registration module is deployed in the room, combined with a computer, with the help of which the area of interest is photographed from the window. After processing according to a special algorithm, the computer builds a stereo image, according to which the distance of various objects from the window under study is determined with high accuracy. Taking into account the parameters specified by the operator, the so-called “risk zone” is built, highlighted on the monitor in a special color.
At the second stage, residual speech intelligibility is measured via the acoustic-vibro-optical channel at the measured boundaries of the accessibility zone. For this purpose, a response signal simulator is placed on the window surface — a device that converts the acoustic test signal received from the accelerometer fixed to the glass into optical pulses and transmits them through the window opening to the probable signal reception zones. The simulator beam is directed to the photodetector of the receiving unit installed outside the object under study, at control points within the boundaries of the accessibility zone measured at the first stage.
The unit demodulates the received beam and selects a low-frequency signal subject to further analysis and processing. If the level of residual speech intelligibility is considered sufficient, we can make a reasonable conclusion that it is technically possible to retrieve information from the premises being inspected from this point.
The method for determining the risk zone for information retrieval from windows, developed by NERA-S, is protected by a patent of the Russian Federation. Currently, the company's specialists continue field testing of the second version of the “Uzor” complex, and the refinement and debugging of its individual components.