A method of protection against the interception of confidential information by highfrequency imposition methods, in which targeted jamming protective signals are introduced into the medium used for the delivery of probing oscillations both at the fundamental frequency and at the combinational harmonics of the probing signal, which provides more effective protection of information from interception, is considered. The results of experimental studies aimed at determining the parameters of effective interfering protective signals capable of destroying the informative parameters of dangerous signals generated by high-frequency imposition methods are presented.
Information that has a certain seal of secrecy
and may contain data that in a certain way
may affect the security of the state and its
citizens circulates on the objects of
information activity. Such information may
be susceptible to interception attempts. As a
result of the action of many factors, technical
channels for the leakage of confidential
information may be formed spontaneously or
intentionally. Taking into account the
importance of information, measures and
means aimed at ensuring the protection of
acoustic information and information
processed in information systems are applied
[
Effective methods of interception of
confidential information on objects of
information activity are methods of
highfrequency imposition (then—HF-imposition,
HFI) [
Currently, two methods of HFI intercepting
information through channels are used:
• Using contact or inductive introduction
of a high-frequency signal into electrical
circuits that have functional or parasitic
connections with the main technical
means.
• By irradiating the source of information
with a high-frequency electromagnetic
signal and receiving the reflected
modulated signal.
The block diagram of the channel of
highfrequency imposition is presented in Fig. 1,
where G is the generator, R is the receiver, CL
is the communication line, CS is the
communication system, WP is ways of
penetration, BTMS is the basic technical means
and systems, ATMS is auxiliary technical
means and systems, ME is the modulating
element.
In work [
Since when intercepting information by HFI methods, amplitude, frequency, and phase modulation of the transmitted signal can occur, it is necessary to take measures to block the possibility of receiving information when using any of these modulations.
As stated in [
Taking into account that the interception of
information can be carried out both on the
main frequency and on the harmonics of a
dangerous signal, it is proposed to create
protective signals not only concerning the
main frequency but also relative to the
harmonics of the dangerous signal [
The essence of the improved method is to
implement the protection system as follows:
1. Using the method of radio monitoring
[
The task of experimental research is an objective assessment of the ability of a protective signal to ensure the destruction of informative parameters of dangerous signals: • Ensuring the protection of information from leakage by blocking interception channels by the method of highfrequency imposition. • The effectiveness of destroying an informative signal due to the formation of a “beating” effect with a dangerous high-frequency imposition signal. • Finding the parameters of protective signals capable of ensuring the maximum possible destruction of informative parameters of dangerous signals at the fundamental frequency and the combinational harmonics of the probing signal, and, as a result, creating countermeasures against the interception of confidential information by interested parties.
A generalized scheme for conducting experimental research is presented in Fig. 2.
A standard oscilloscope, frequency meter, and voltmeter can be used to measure the parameters of the probing signal and interference signal (these devices are not shown in the scheme).
Parameters of Interfering Protective Signals Capable of Destroying the Informative Parameters of Dangerous
Signals
We have already determined the parameters of
effective interfering protective signals aimed
at destroying the informative parameters of
dangerous signals formed by the methods of
high-frequency imposition using simulation
modeling in the LabVIEW environment [
Experimental studies were carried out in a shielded room of the II class using a complex of instruments and devices (Fig. 3) (then— Сomplex), which includes: 1. Arbitrary signal generator Tektronix
AFG 3252. 2. Spectrum and signal analyzer ROHDE&SCHWARZ FSW 13 (Signal&Spectrum Analyser, 2 Hz – 13.6 GHz). 3. Oscillograph Tektronix DPO 7254 (Digital Phosphor Oscilloscope). 4. A complex of dipole antennas Tuned
Dipole Antenna FCC. 5. Folding bilogical antenna SAS-521F-7 25–7000 MHz. 6. Electric antenna EMA-2000 0.009–2000
MHz. 7. Stationary personal computer (monitor, mouse, keyboard, system unit) (then— PC).
Let’s note that this Complex is assembled
from existing devices and devices, the
composition and number of equipment may
change depending on the circumstances.
According to GОСТ 30373-95
“Electromagnetic compatibility of technical
means. Test equipment. Shielded chambers.
Classes, basic parameters, technical
requirements, and test methods” [
A PC is considered as a technical means by which confidential information is processed, and on the elements of which probing signals of high-frequency imposition can be directed.
With the help of a signal generator, a dangerous high-frequency signal and a targeted active jamming protective signal aimed at destroying the informative parameters of a dangerous signal with various types of carrier frequency modulation are set. With the help of a spectrum analyzer, the presence of dangerous and protective signals in the amplitude-frequency spectrum is recorded. The presence of dangerous and protective signals in the amplitude-time spectrum is recorded by an oscillograph.
According to the operating instructions, the control and measuring devices were prepared for work. The measuring antennas were located at a distance of 1 m from the PC and were in a parallel plane to the front part of the PC. At the same time, the geometric centers of the frame antenna and the imaginary geometric center of the PC were on the same axis. 3.1. Determination of the Effective for Destruction of the Frequency Difference Between the Protective and Dangerous Signal A signal generator was used to create a protective signal and a dangerous signal by choosing arbitrary starting frequencies for both signals.
With the set bandwidth (RBW) of the measuring equipment of 30 Hz and the frequency span (Frequency span) of 500 kHz, a detector of peak values (PK, PEAK) was installed on the spectrum analyzer. When setting the value of the frequency difference to 44 MHz (Fig. 4), the effect of frequency “beating” is not observed (Fig. 5).
When the frequency difference between the dangerous and protective signal was gradually reduced and its value was set to 1 MHz (Fig. 6), signs of the “beating” effect were detected (Fig. 7). Accordingly, this is the extreme value of the frequency at which the effect required for protection is provided. When the frequency difference between the dangerous and protective signal is further reduced and its value is set to 6 kHz (Fig. 8), a steady phenomenon of “beating” is recorded (Fig. 9). 3.2. Research of the Effect of the Phase Difference Between the Protective and Dangerous Signal on Ensuring the “Beating” Effect With the help of a signal generator, a protective signal and a dangerous signal were created, choosing the initial frequencies for both signals that provide the effect of “beating” frequencies. Changes in the phase of the dangerous signal were applied, namely a shift of 10°.
With the set bandwidth (RBW) of the measuring equipment of 30 Hz and the frequency span (Frequency span) of 500 kHz, a detector of peak values (PK, PEAK) was installed on the spectrum analyzer. This experimental research was conducted to investigate the dependence of the formation of the “beating” frequency effect on the signal generators themselves. An auxiliary generator was used for the experiment ROHDE&SCHWARZ SMA100B Signal Generator 8 kHz – 3 GHz. Having determined the signal frequency and the frequency difference, the corresponding levels were set on the two signal generators. Under the same conditions, with the use of a two-channel generator, the effect of “beating” frequencies is observed (Fig. 8). According to the results of using two different generators (Fig. 12), such an effect is not observed (Fig. 13). In the future, it is planned to carry out research according to the generalized scheme (Fig. 2) using the load equivalent. 4. Conclusions 1. High-frequency imposition (probing) is a very effective way of intercepting information circulating in technical means that directly process confidential information if the latter did not include radical measures during its development to prevent the penetration of highfrequency currents inside this equipment. 2. The high-frequency imposition method is based on the use of the physical phenomenon of reflection of highfrequency energy supplied from a special generator from an unmatched load representing the total resistance of any nonlinear or parametric circuit of technical means, the value of which changes under the influence of a dangerous signal according to the law inherent in this signal. 3. The effectiveness of the high-frequency imposition method is generally defined as the result of the interaction of the following technical systems: • Information interception systems. • Information transmission, processsing, and storage systems. • Communication systems.
A priori results of the interaction of these systems can be assessed by conducting a system analysis of the functioning of a complex technical system consisting of the three indicated components. 4. The use of active protection methods— so-called information destruction systems—can only be recommended in conjunction with well-executed passive protection, shielding, filtering, and decoupling, to further increase the degree of protection efficiency. 5. As a measure of quantitative assessment of the degree of information security in technical processes that directly process confidential information, the permissible probability of information leakage can be taken. 6. During experimental investigations, it was established: • to achieve the “beating” effect of frequencies, it is necessary to select signal generators that are as similar to the output characteristics as possible. • when the frequency difference is greater, less than 1 MHz between the vulnerable signal and the probe signal, the effect of “beating” frequencies is not avoided. • changing the phase of one of the signals does not in any way contribute to the effect of “beating” frequencies.