RU2428798C2 - Fibre optic detector of voice information leakage threats via fibre optic communications - Google Patents

Abstract

FIELD: information technologies.

SUBSTANCE: detection of acoustic (speech) information leakage channel is carried out monitoring of optical radiations in standard fibre optic communications. For security departments appearance of any non-standard light radiations or occurrence of modulation at acoustic frequencies of standard light flows is a parameter of possible threat of voice information leakage and taking measures for their neutralisation. The device to realise this method comprises a receiver of optical radiation; a system of registration (demodulation) and analysis of received acoustic signals.

EFFECT: increased throughput capacity.

19 cl, 2 dwg

Description

FIELD OF THE INVENTION

The invention relates to the field of ensuring information security of negotiations in dedicated rooms from threats of leakage of acoustic (speech) information through fiber-optic communications by monitoring optical flows in standard communication lines and identifying possible modulation of their acoustic fields. The invention can be used in systems for protecting confidential voice information.

The prior art.

The protection of speech information is an important problem of modern society, which is associated with the importance of information that operates in commercial and government institutions during confidential negotiations. With the advent of new information transfer technologies, such as fiber optic technologies, new threats to information security appear. Modern fiber-optic communication channels are widely used in various information transmission systems from trunk and regional communication lines to local networks, structured cable systems, video transmission in video surveillance systems, cable television systems, etc. Thus, fiber comes to the house, office, institution and is located near / inside the designated premises where confidential negotiations can be held. In this connection, there are dangers of forming new channels for the leakage of speech information, which were not given due attention earlier.

One of these is the acousto-optical fiber leakage channel associated with unauthorized removal of voice information (eavesdropping) through standard fiber-optic channels for transmitting information for various purposes of a given institution (see Grishachev V.V., Khalyapin DB, Shevchenko N.A., Merzlikin VG New channels for leakage of confidential speech information through fiber-optic subsystems SCS // Special equipment, 2009, No. 2, p.2-9). In this leakage channel, the acoustic field from the information carrier acts on the optical fiber of standard information systems built on fiber-optic technologies, and causes modulation of the light flux in the optical fiber or fiber-optic equipment at acoustic frequencies. Thus, the luminous flux modulated by speech over standard fiber-optic communications can go far beyond the place of negotiations, where demodulation can be performed and the attacker gains access to confidential information.

The basis of the leakage channel is the light flux in the optical cable of the communication lines. All light fluxes can be divided into regular ones, associated with the physical implementation of the data transfer protocol, and emergency, specially created by the intruder for unauthorized removal of speech information. Regular light fluxes, for example, generated by digital methods of information transmission, which are most often used in modern communication systems, allow you to create a leak channel without disrupting the operation of the entire system, since the level of acoustic impact on a regular light flux slightly reduces the signal-to-noise ratio. Also, for the collection of speech information, intensity-variable light fluxes can be used, which are used to synchronize the transceiver active equipment at the physical level, operating between data transmission. Abnormal streams include any light sources that are unauthorized connected to fiber optic communications.

Currently, there are many methods and technical solutions for protecting voice information from leakage by spurious electromagnetic radiation and interference, vibroacoustic and acoustic channels. The use of a new type of voice information leakage channel - acousto-optical fiber - can create serious problems for protection systems, which is associated with the widespread use of new information transmission technologies based on fiber-optic cable, as well as with non-standard physical principles of channel formation, which are currently fully opposed volume does not exist. All methods of neutralizing a new leakage channel can be divided into passive (for example, soundproofing a fiber-optic communication channel) and active methods (various methods of filtering, noise).

The effectiveness of any protection depends on the detection of information security threats. Given the small size of the channel, the directivity of the radiation and the absence of incidental light fluxes, it is possible to offer a simple and effective way to detect unauthorized removal of information (eavesdropping) by monitoring the existing light fluxes in the channel. To prevent eavesdropping, the following rules must be followed.

Firstly, regular light fluxes should not be modulated by sound.

Secondly, there should be no abnormal flows not provided for by the physical implementation of the data transfer protocol on the network, and if they exist, they should not be modulated by sound.

All these simple rules make it possible to detect an attack on a security system.

In the maintenance technology of fiber-optic communication systems, there are devices that record the presence of optical radiation in the fiber. For example, Fujikura FID-20R / 21R fiber optical signal determiner (Japan, http://www.fujikura.ru/), which allows one to determine the presence and propagation direction of an optical signal in a fiber coated with 250 μm, 900 μm, and in standard optical cords up to 3 mm thick.

Known methods for detecting an acoustic field-induced modulation of electromagnetic radiation of a radio range or electrical information signal in wire lines, the so-called high-frequency imposition, which are used to combat electromagnetic field detectors. For example, the Kassandra radio monitoring complex, which is designed for continuous, periodic or operational monitoring of the radio environment and the detection of unauthorized radio emissions from the audited premises (Kassandra. Operation manual. / STT Group of Companies, www.detektor.ru).

However, such methods for detecting eavesdropping through fiber-optic channels for transmitting information are unknown, due to the novelty of the problem. In this connection, the prototype of the invention does not exist.

Disclosure of invention

The invention as a technical solution

The essence of the invention as a technical solution consists in the fact that for detecting an acousto-optical fiber channel for leakage of confidential speech information in a fiber-optic channel for transmitting information, all light fluxes are recorded and an analysis of the possibility of eavesdropping is performed. The danger of leakage of acoustic (speech) information is determined by the following criteria:

i) abnormal luminous flux is detected in the information transmission channel;

ii) the standard luminous flux has acoustic modulation in one of the parameters of optical radiation (amplitude, phase, polarization, frequency) and / or simultaneously in several parameters;

iii) abnormal light fluxes separated by the optical spectrum have acoustic modulation at a given optical wavelength in one of the parameters of the optical radiation (amplitude, phase, polarization, frequency) and / or simultaneously in several parameters.

Fulfillment of at least one of these conditions is sufficient to form a channel for leakage of acoustic (speech) information and can be used to assess information security threats.

The problem to which the invention is directed, indicating the technical result

The invention solves the problem of detecting the possibility of leakage of speech information through standard fiber-optic communications by installing special technical equipment that records light fluxes in a fiber-optic channel for transmitting information. The device for detection can be made in the form of a separate unit and / or built into a standard network fiber-optic equipment and allows you to detect all types of attacks on the acousto-optic leakage channel.

The features used to characterize the methods

Signs of the proposed methods of protection are as follows. Any attack on a security system through a fiber-optic channel to gain access to acoustic (speech) information is associated with optical streams in it. Control of the light fluxes in the channel, their characteristics allows you to identify any possibility of unauthorized removal. To do this, it is necessary to register the radiation passing through the fiber-optic elements, to select authorized media (standard radiation), to identify unauthorized flows (abnormal radiation) and modulations at acoustic frequencies. Abnormal radiation (from external sources) can have a spectral composition that intersects with regular radiation, and disjoint with it, which is modulated by an external acoustic signal with confidential information. These signs of an acousto-optic leakage channel make it possible to detect and neutralize a leak.

Features used to characterize devices

Implementation of the proposed methods is based on standard or specially created elements, which include: power supply; a photodetector connected to a fiber optic channel; optical, electronic and optoelectronic analytical element for distinguishing acoustic fluctuations in the parameters of the recorded optical radiation.

The photodetector uses standard photodiodes used in active equipment to register regular light fluxes. Registration of light fluxes of the spectral optical range outside the standard spectral bands is performed by photodetectors with a maximum spectral sensitivity in the visible region, for example, silicon p-i-n-photodiodes. To register weak optical signals of information leakage, a photoelectron multiplier, an avalanche photodiode, and other highly sensitive photoelectric converters are used. The connection to the fiber optic channel can be made directly through a detachable connection, or through an integral connection based on mechanical splicing or welding of fibers, or through an input / output device of radiation on the bend of the fiber so that light radiation passes through the device without significant optical loss, corresponding to conventional compounds. Also, the device can be located at the end of the optical channel in the place of conversion into an electrical signal (receiver / transceiver) and be integrated into existing active fiber-optic equipment. In the case of connecting with the free passage of light streams, it is necessary to divert the radiation both forward and backward to control the leakage channels in all (two) directions. In the case of connecting to the receiver / transceiver, control is necessary both on the receiving and transmitting paths, which is associated with the possibility of using each of them in both directions.

The analytical element is performed for a preliminary analysis of optical radiation, for example, in order to isolate the spectral range (see Kalinin V.A., Preslenev L.N. Optical fibers and passive components of fiber-optic communication lines: academic village // St. Petersburg: State University of Aerospace Instrumentation, 2008. - 80 pp. Or Semenov AB Fiber-optic subsystems of modern SCS // M: DMK-Press, 2007. - 631 pp.), In which the leakage channel is most sensitive to external acoustic impact. Increased sensitivity may be associated with the structural features of the fiber, its nonlinear optical properties, interference processes during signal output. Spectral separation is also necessary because of the possibility of an attacker using optical sources with a narrow emission band operating in the wavelength region outside the limits of standard emitters. The pre-processed optical signal of a possible leakage channel is fed to a photodetector, and then to the electronic processing system. For example, after digitization, the signal enters the computer with special software for analyzing sound signals, which measures the overall level of the acoustic leakage signal, its spectral composition, or the analog processing system — a selective amplifier — to extract the acoustic signal at frequencies characteristic of speech of other sounds.

Brief Description of the Drawings

In the future, the invention is illustrated by specific examples of its implementation and drawings, in which:

figure 1. Schematic optoelectronic diagram of a method for detecting leakage channels: A - attack detector, 1 - standard fiber optic line, 2 - detachable or integral fiber-optic connections to the attack detector, 3 - optical filter that transmits regular or abnormal light fluxes, 4 - spectrum analyzer optical radiation, 5 - a line of photodetectors for the selected emission spectra, 6 - an analog-to-digital converter for each selected optical channel, 7 - an output electric digital signal supplied to the computer for Work and hazard assessment.

figure 2. Schematic optoelectronic circuit of a leak threat detector built into the active equipment of a standard network: A - attack detector, B - standard active network equipment, C - standard receiver / transceiver with radiation tap into the detector, 1 - standard fiber optic line, 2 - detachable or permanent fiber-optic connections to standard active equipment, 3 - an optical filter that transmits regular and reflecting abnormal light fluxes, 4 - an optical radiation spectrum analyzer based on a diffraction grating, 5 - a photographic array receivers for the selected emission spectra, 6 - an analog-to-digital converter for each allocated optical channel, 7 - an output electric digital signal supplied to a computer for processing and determining the degree of danger, 8 - analog signal processing with a hazard level indication system, 9 - digital electric input / output of the receiver / transceiver, 10 - analog electrical output of the receiver, 11 - analog electrical output of the attack detector.

The implementation of the invention

The invention related to the method and device

Example 1. A General description of the functioning of the method is given in figure 1. The device (leak detector - A) is connected to the optical line (1) using standard connectors or connections (2). Luminous fluxes passing through the line in both directions are output to the optical processing system (3, 4). Using the optical filter (3), separation is made into regular and non-standard light fluxes, which makes it possible to simplify the analysis. For example, the appearance of abnormal light flows is already the basis for the conclusion about an attack on the security system. In this case, the spectral decomposition of the optical signal into components occurs, each of which is studied separately for acoustic modulation. This is due to the possibility of an attacker using narrow-band light sources in an area not used for data transmission. Complex spectral analysis in the acoustic modulation region can be performed using conventional computer methods, for which a signal at acoustic frequencies from the photodetector system (5) is digitized for each optical channel (6) and transmitted to a computer. Based on the software processing of the acoustic signal, a decision is made about the danger of leakage of speech information. In the simplest cases, the analysis can be carried out according to parameters such as the general level of the acoustic signal, the appearance of spectral components characteristic of the human voice, etc. In particular, the level of the acoustic signal gives a general idea of the effectiveness of the leakage channel: the higher the level, the greater the danger.

Example 2. As a device that implements a method for detecting leakage channels, we consider an attack detector (A) built into regular active network equipment (Fig. 2), such as, for example, a network adapter, media converter, etc. (B). In any active equipment there is a converter of the optical signal into electrical and vice versa - receiver / transceiver (C). Using selective mirrors (3), abnormal radiation is extracted from the incoming radiation, and regular radiation is transmitted in the transmitter channel and any radiation traveling in the opposite direction is diverted to the transmitter, which by definition is abnormal. The radiation is diverted to the attack detector (A) on the element (4) of the optical analysis of radiation - a diffraction grating. The spectrally separated optical abnormal radiation from the diffraction grating is fed to a line of photodetectors (5) with an acoustic filter at the output. Next, the analogue electrical signal of the acoustic range through one channel enters the analog-to-digital converter (6) and then to the computer (7), and through the other channel to the electric system of analog signal processing (8). Analog processing of the electrical signal includes an integrating circuit that generates an attack signal - the presence of abnormal radiation. Here, in parallel, selective separation of the signals according to the spectrum by fixed acoustic frequencies is performed, for example, 2, 3, 4, 5, 6 kHz, the signal level of which also makes it possible to determine the level of danger. The danger level of three degrees - safe, careful and alarm - is displayed in the light indication on the panel of active equipment, and also enters the computer (11). The analogue electrical signal (10), coming from the standard receiver (B) to the analog signal processing system (8), is subjected to a similar analysis. Thus, a preliminary analog analysis is carried out to attack the security system via a fiber optic channel.

A more accurate analysis is carried out using the computing means of the security system, located here or in another place, where digital information about the acoustic signals comes through the same communication channels.

Example 3. Explanation to paragraph 4 of the formula. One of the possible ways to increase the signal-to-noise ratio when registering an acoustic signal during demodulation of light in an optical fiber by an intruder can be applied by high-frequency modulation of the probe optical radiation at ultrasonic frequencies. For example, probing optical radiation is modulated at a frequency of 100 MHz according to one of the radiation parameters - amplitude, phase, polarization, frequency; then, when demodulating acoustic signals, the use of a narrow-band filter at this frequency in recording equipment can significantly increase the signal-to-noise ratio. Therefore, the presence of high-frequency modulation of transmitted radiation is an increased danger of eavesdropping. An analysis of the high-frequency component of the acoustic signal for the presence of confidential information is required to be included in the attack detector, for which the spectrum of the recorded acoustic signal is limited not only to the sound spectrum, but also to analyze the ultrasonic components.

Example 4. Explanation to paragraphs 13, 14, 15 of the formula. One of the main ways to increase the signal-to-noise ratio for an attacker is to extract a useful signal and reduce the contribution of noise. This problem can be solved by isolating the signal according to one of the parameters of the light wave - frequency, polarization, phase (claim 6 of the formula).

Frequency selection is technically implemented by spectral fiber-optic elements, for example, using fiber-optic demultiplexers created by a fiber circulator, a diffraction grating, a dispersion prism and other fiber-optic devices for demultiplexing an optical signal, as well as by filtering an optical signal based on a fiber Bragg grating (see Ubaidullaev PP Fiber Optic Networks // M .: Eco-Trends, 2001. - 268 p .; Budaragin R.V., Maistrenko V.K., Nazarov A.V., Raevsky S. B. I Integral optics: academic village // N. Novgorod: Nizhny Novgorod State Technical University, 2008. - 105 p.).

The selection of signals by polarization and phase is also carried out by standard fiber elements. For polarization, special fibers are used to hold the polarization, twisted fibers, and other elements (see Kulchin Yu.N. Distributed fiber-optic measuring systems // M .: FIZMATLIT, 2001. - 272 p.)

Phase selection can be performed on the basis of standard fiber-optic interferometers (Okosi T. et al. Fiber-optic sensors. Translated from Japanese. // L .: Energoatomizdat, 1990. - 256 pp.).

Such devices are widely used in fiber-optic communication systems, measuring systems and are commercially available by industry. They can be applied without significant changes in the attack detector.

Claims (18)

1. A method for detecting leakage of speech information through the fiber-optic communications of the allocated premises, leading to unauthorized transmission of speech information, which consists in registering with the acoustic frequencies demodulating the parameters of the optical radiation passing through the elements of the fiber-optic communications and determining the leakage of speech information. 2. The method according to claim 1, characterized in that the separation of the recorded optical radiation is carried out into radiation, which relates to light streams for data transmission in a cable system, and / or to radiation, which does not apply to light streams for data transmission in a cable system and is of artificial and / or natural origin from external and / or internal sources. 3. The method according to claim 1, characterized in that the spectral decomposition or scanning of the detected optical radiation is carried out and radiation is emitted at optical wavelengths at which there is the most effective acoustic modulation of the optical radiation parameters. 4. The method according to claim 1, characterized in that when performing the demodulation of optical radiation, the electrical signal is analyzed at frequencies shifted to the ultrasonic region of the acoustic spectrum, which carries or can carry sensitive acoustic information and / or is modulated by an audio signal. 5. The method according to claim 1, characterized in that the registration of light fluxes passing through the elements of fiber-optic communications in the forward and / or reverse direction of propagation. 6. The method according to claim 1, characterized in that the light flux is demodulated in the fiber optic communications in amplitude and / or phase and / or polarization and / or frequency and vibrations at acoustic frequencies are detected. 7. The method according to claim 1, characterized in that they carry out a spectral analysis of the acoustic vibrations of the demodulated light flux, highlighting the characteristic spectral components for speech, sounds. 8. The method according to claim 1, characterized in that the analysis of acoustic vibrations of the demodulated light flux by the integral level of the sound signal. 9. The method according to claim 1, characterized in that the analysis of acoustic vibrations of the demodulated light flux by the articulation method by listening to the selected signal by the operator. 10. The method according to claim 1, characterized in that the registration of optical radiation through a fiber optic transceiver of active network equipment, such as a media converter, adapter, hub, router. 11. A device for detecting leakage of voice information through fiber-optic communications in selected rooms, leading to unauthorized transmission of voice information, consisting of a device for connecting to a fiber-optic channel and an optical signal processing element, after which the optical signal is fed to a photodetector with an amplifier, a demodulator, and an element analysis of the electrical signal. 12. The device according to claim 11, characterized in that the device for connecting to a fiber optic channel is made in the form of a device for outputting / introducing optical radiation into a fiber at its bend, or at detachable joints, or a fiber optic coupler, or mechanical splicing or fiber welding. 13. The device according to claim 11, characterized in that the optical signal processing element includes a spectral filter and / or a demultiplexer. 14. The device according to claim 11, characterized in that the optical signal processing element includes a radiation polarization analyzer. 15. The device according to claim 11, characterized in that the optical signal processing element includes a Fabry-Perot fiber optic interferometer and / or Mach-Zehnder and / or Michelson and / or Sagnac and / or a single-fiber multimode. 16. The device according to claim 11, characterized in that the element of analysis of the electric signal includes an integrating element at acoustic frequencies, and / or a selective amplifier at acoustic frequencies with an adjustable passband, and / or a spectrum analyzer of the signal at acoustic frequencies. 17. The device according to claim 11, characterized in that the device for detecting eavesdropping devices through optical fiber elements of structured cable systems is integrated into the active network equipment. 18. The device according to claim 11, characterized in that the electrical demodulated signal is digitized and for its analysis the computing resources of the information system are used.

Images