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The widespread use of the NFC technology (Near Field Communication) arouses interest to various security aspects. There are known examples of information exchange with card at a distance greater than standard 5-10 cm. It is also interesting to use signals of higher harmonics, which potentially may be radiated in the form of electromagnetic waves, rather than exists as a magnetic field of scattering. In this work, the radiation of third harmonic by card of standard ISO 14443-3А with the fundamental frequency 13.56 MHZ for various excitation modes using the RFID-RC522 reader, smartphone Sony Xperia Z5 Premium, and continuous 10% amplitude modulated 13.56 MHz signal from generator with the subcarrier of imitated smart card response 847.5 kHz was investigated. The card response at third harmonic was simulated in circuit analysis software. Both simulation and experiment proved, that the third harmonic with its side frequencies 40,68 ± 0,8475 MHz have the highest level after the fundamental. To receive the third harmonic signal, the resonant loop antenna in the form of ring vibrator loaded on capacitor was used. This allows the sizes of the received system to be reduced, but the problem of complex field structure in the near-field zone remains. Due to narrow bandwidth of the receiver antenna, the registration of card response signal was complicated. The experiments with three methods of signal generation proved, that third-harmonic signal is registered at the distance more than 1.5m, which may pose a threat for contactless smart-cards transactions security. At the same time, the influence of high level of noise at such a distance may cause difficulties to decode the short-duration signals, which requires further study.

The information security of modern society is in constant counteraction and constant improvement of technical means used for unauthorized information pickup, and technical means that prevent it. The paper analyzes examples of methods of applying noise interference to counteract the unauthorized pickup. The possibility of unauthorized pickup by passive radio devices using noise interferences is shown and analyzed using noise interferences, which are used to suppress the eavesdropping devices. The transfer of picked up information is possible both by radio wave and low-frequency channels using metal structures or water pipes. As a model of noise interference, a random narrow-band signal with a Gaussian distribution was used. The electrical model of the device was simulated by a transmission line with a high-frequency diode at its end. The idealized exponential dependence of the diode current on the voltage was used. The reflected wave spectra are obtained for different ratios of the transmission line resistance, the differential resistance of diode, and the external offset voltage at the diode. The modes and features of analog and digital information transmission by the radio tab device using energy of radio noises are analyzed. In the radio tab device, the information is transmitted by reflected wave, the spectrum of which is distorted at a nonlinear element placed at the end of transmission line. An analysis of the device operation was carried out along the full possible frequency range associated with the spectrum of the incident noise interference. The optimal elements parameters for the passive electrical circuit are calculated: the resistance of the transmission line, the differential resistance of the diode, the offset voltage, and the modulation mode, depending on the frequency range in which the leak is possible.

The use of noise interference has become a common practice for information security. Recently appeared publications showing a potential possibility to use the noise radio frequency interference for information skimming by passive radio eavesdropping device. In particular, the vulnerability of the premises protected from eavesdropping devices is increased, if the radio frequency noising is switched on when confidential negotiations are being conducted. The use of radio noise waves energy for eavesdropping makes such devices invisible to nonlinear locators for listening devices if they activated only by noise signals. The paper shows that the use of non-steady state noise allows counteracting the unauthorized pickup of information. The analysis of non-steady state radio frequency noise effectiveness was carried out using the correlation receiver model. The correlation receiver has the highest sensitivity, and it works more efficiently with noise-like signals. It is shown that for counteracting the information pickup, it is necessary to use a noise, amplitude modulated by a random signal, whose spectrum coincides with a spectrum of a potential informational signal. Imposition a more powerful modulation noise to a weak informational signal makes impossible the information transfer. It is shown on the example of changing the power of a monochromatic signal while “beetle” transmits using steady-state and non-steady state noises, that due to the signal energy parametric redistribution over the non-steady-state noise modulation spectrum, the power of monochromatic signal is reduced by more than 10 dB compared to the transmission of the same signal using a steady-state noise. It can be concluded that the use of non-steady state noise signals for radio frequency suppression makes impossible their use for passive eavesdropping devices operation.