Data Leakage Channels of Speech Information

Speech information – is a voice apparatus of a human being.
Voice apparatus of the human being is a primary source of acoustic fluctuations, which present themselves as disturbance of air in shape of wave compression and extension (longitudinal waves).
Under the influence of acoustic fluctuations in the enclosing building constructions and engineered communications of the premise, in which the source of speech information is, vibrational fluctuations appear. In such manner, in its original state speech signal is present in the room, in a form of acoustic and vibro-acoustic fluctuations. Different converters of acoustic and vibro acoustic fluctuations are a secondary source. They are: speakers, telephones, microphones, accelerometers and other devices. Dependently from the distribution environment of speech signals and their interception methods, technical channels of information leakage can be divided to: acoustic, vibrational, acoustoelectronic, opto-electrical and parametric.
Let’s review these channels in detail.

ACOUSTIC CHANNELS - In acoustic channels of information, the distribution environment of speech signals is air, and for their interception high-sensitivity microphones, special pointed microphones are being used, which are connected with special miniature transmitters. Autonomous devices, constructively connected microphones and transmitters are called embedded devices of speech information interception. Intercepted by an embedded device „BUG“ can be transmitted through radio channel, electrical power lines, optical (IR) channel, connected lines of auxiliary means, outsider conductors, engineer communications in ultra-sound frequencies diapason, telephone lines with call from outside telephone client. Reception of information, transmitted by embedded device, is being done, to the special reception devices, working in according diapason of wave lengths. Usage of portable dictaphones and embedded devices requires penetration into the monitored room. Only if there is no possibility to use the directed microphone for interception of speech information.

VIBRO-ACOUSTIC CHANNELS – In vibro-acoustic channels of information leakage the distribution environment of speech signals are building constructions( walls, floors, ceilings) and engineered communications (heating systems, ventilation shachts and so on). For interception of speech signals, vibro-sensors (accelerometers) are being used. Vibro sensor connected to the electronic amplifier is called an electronic stethoscope. Electronic stethoscope enables the listening to the speech using head phones and recording to the dictaphone. Through vibro-acoustic channel interception of information using embedded devices is also possible. For transmission of information radio channel is used and the devices are called radio stethoscopes. Also embedded devices with transmission of information through optical channel in the near infrared wavelength diapason and ultrasound devices, are being used (in the engineered communications).

ACOUSTOELCTRONIC CHANNELS - Acoustoelectronic channels of information leakage appear using, transformations of acoustic signals in to electronic. Some elements of main technical tools and systems, transformers, induction rolls, electromagnets of secondary electro casts, telephone ring bells and so on, have the ability to change its parameters (capacity, inductivity, resistance) under the influence of acoustic field, created by the origin of the speech signal. Main technical tools and systems can have acoustoelectrical converters. Some types of fire alarms and security detectors, relaying network loudspeakers and so on. The interception of acoustoelectric fluctuations is made through connection lines to main technical tools and systems using high-sensitivity low frequency amplifier.
OPTIC-ELECTORNIC (LASER) CHANNEL - Optic-electronic (laser) channel of speech information leakage is made by irradiating using laser beam, of the surface of the reflective surfaces of the premises (window glass, mirrors and so on). The reflected laser emissions are modulated at the amplitude and faze, and received by the laser emission receiver, when modulated speech information can be acquired for interception of which complex laser systems are being used. 
ACOUSTOELECTROMAGNETIC CHANNEL (Parametric channel) - Acoustoelectromagnetic or as it is also called Parametric information leakage channel, appears in result of the influence of acoustic field to the elements of high frequency generators. As a result of such cables in the induction element (dimension between loops), drossels, places between the air condesator plates and so on., which can result in changes of the parameters of the high frequency signal, for example, modulation of the information signal, high frequency fluctuations can be intercepted and detected by the means of radio surveillance.
Parametric channel of information leakage can be made using “high frequency irradiation“ of the premise, where semi-active embedded devices, having elements, some parameters of which (for example: quality and resonance frequency of the voluminous resonator) changes according to the changes of the acoustic (speech) signal. For interception of information through this channel besides the embedded device, special transmitter with directed antenna and receiver, are needed.


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