RU2509423C2 - Secure information transmission method - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: useful signal is encoded into a binary code; a first generator generates a source deterministic random signal by modulating parameters of the random signal with the useful digital signal and the obtained signal is transmitted over a communication channel to a receiving side where it is divided into two identical signals which are transmitted to a second generator and a third generator, which are identical with respect to control parameters, selected to facilitate a mode for general synchronisation with the first generator; signals obtained from the outputs of said first and third generators are transmitted to a subtractor and presence or absence of oscillations determines presence of a useful digital signal presented in form of a digital code, wherein periodic signals are obtained at the outputs of the second and third generators.

EFFECT: improved stability of the method.

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Description

The invention relates to radio engineering and the transmission of information and may find application in communication systems for noise-free transmission of digital information, including with a high degree of confidentiality.

Currently, methods for covert information transmission based on complete chaotic synchronization are known (Sioto K., Oppenheim A. Communication using synchronized chaotic systems // US Patent No. 5291555 dated 1.03.1994; Dedieu H., Kennedy MP, Hosier M. Chaos shift keying: modulation and demodulation of a chaotic carrier using delf-synchronizing Chua's circuits // IEEE Trans. on Circ. Sys., I. 40, 1993, 634; Dmitriev AS, Panas AI, Starkov SO Experiments on speach and music signals transmission using chaos // Int. J. Bifurcations and Chaos. 5 (4), 1995, 1249; Yang T., Chua LO Secure communication via chaotic parameter modulation // IEEE Trans. on Circ. Sys., I. 43, 1996, 817 ), phase synchronization (With hen JY, Wong KW, Cheng LM, Shuai JW A secure communication scheme based on the phase synchronization of chaotic systems // Chaos. 13, 2003, 508), both General synchronization (Terry J.R., VanWiggeren G. D. Chaotic communication using generalized synchronization // Chaos, Solitons and Fractals. 12, 2001, 145; Koronovsky A.A., Moskalenko O.I., Popov P.V., Hramov A.E. The method of secret information transfer // Patent for the invention No. 2295835 of 03.20.2007), as well as using several types of synchronous behavior together (Murali K., Lakshmanan M. Secure communication using a compound signal from generalized synchronizable chaotic systems // Phys. Lett. A. 241, 1998, 303; Terry JR, Van Wiggeren GD Chaotic communication using generalized synchronization // Chaos, Solitons and Fractals. 12,2001,145; Koronovsky A.A., Moskalenko O.I., Khramov A.E. hidden transmission of information // Patent for invention No. 2349044 of 03/10/2009; Moskalenko OI, Koronovsky A.A., Hramov A.E. Method for hidden transmission of information with changing characteristics ra // noise invention patent №2421923 from 20.06.2011).

The principal disadvantages of most known circuits and devices are, first of all, the instability of their operation when the parameters of the transmitting and receiving generators are located, including those located on different sides of the communication channel, the destructive effect of noise on the quality of information transfer, low confidentiality, difficulties in technical implementation . At the same time, a number of methods for covert information transfer are known (Koronovsky A.A., Moskalenko O.I., Popov P.V., Hramov A.E. Method for secret information transfer // Patent for invention No. 2295835 of 20.03. 2007; Koronovsky A.A., Moskalenko O.I., Hramov A.E. Method for covert transmission of information // Patent for invention No. 2349044 of 03/10/2009; Moskalenko OI, Koronovsky A.A., Hramov A. E. The method of covert transmission of information with changing characteristics of the noise generator // Patent for the invention No. 2421923 from 06/20/2011), in which part of the above disadvantages is corrected or their effects reduced. Moreover, the method (Koronovsky A.A., Moskalenko O.I. “Popov P.V., Hramov A.E. The method of secret information transfer // Patent for invention No. 2295835 of 03.20.2007) is a prototype for the method (Koronovsky A. A., Moskalenko O. I., Hramov A.E. Method for the hidden transmission of information // Patent for invention No. 2349044 of 03/10/2009), which, in turn, can be considered as a prototype for the method (Moskalenko O.I. , Koronovsky A.A., Hramov A.E. A method for covert information transmission with changing characteristics of a noise generator // Patent for invention No. 2421923 from 06.20.2011). They are based on the generalized synchronization mode and are closest to the claimed method.

According to these methods, a useful information signal is encoded as a binary code. One or more control parameters of the transmitting chaotic generator is modulated by an information signal in such a way that the characteristics of the transmitted signal change insignificantly, which does not affect the spectral and power characteristics of the transmitted signal, but there remains the possibility of occurrence / destruction of the generalized synchronization mode between the chaos generator in the transmitting device and identical chaos generators in the receiving device depending on the transmitted binary bit. To provide additional masking of the information signal and changing the characteristics of the transmitted signal in the methods (Koronovsky A.A., Moskalenko O.I., Hramov A.E. Method for hidden transmission of information // Patent for invention No. 2349044 of 03/10/2009; Moskalenko O. I., Koronovsky A.A., Hramov A.E. A method for covert information transmission with changing characteristics of a noise generator // Patent for invention No. 2421923 of 06.20.2011) a noise generator is also used.

The characteristics of the noise generator in the method (Moskalenko OI, Koronovsky A.A., Hramov A.E. The method of covert transmission of information with changing characteristics of the noise generator // Patent for the invention No. 2421923 from 06/20/2011) are modulated by a digital or analog signal, containing a false, immaterial or open informational message. The signal generated by the transmitting system is mixed in the adder to a noise signal (in the case of a noise generator) and then transmitted through the communication channel. Here it is also affected by the noise inevitably present in real devices. The receiving device is on the other side of the communication channel. It represents two identical chaotic generators capable of being in the mode of generalized synchronization with the transmitter. The signal from the communication channel is fed to the generators of the receiving device. The signals obtained at the output pass through a subtractor, and then the reconstructed useful signal, which is presented in the form of a binary code, is detected.

As follows from the above description, the improvements discussed in the methods (Koronovsky A.A., Moskalenko O.I., Hramov A.E. Method for the hidden transmission of information // Patent for invention No. 2349044 of 03/10/2009; Moskalenko O.I. , Koronovsky A.A., Hramov A.E. A method for covert information transmission with changing characteristics of a noise generator // Patent for invention No. 2421923 dated 06/20/2011) were aimed at increasing the confidentiality of information transmission. At the same time, the problem associated with the instability of these methods when the parameters of the transmitting and receiving generators are not identical was only partially eliminated in them. As in the method (Koronovsky A.A., Moskalenko O.I., Popov P.V., Hramov A.E. Method for secret information transfer // Patent for invention No. 2295835 of 03.20.2007), two methods are present in these methods identical chaotic generators, but unlike the known analogues, they are located on one side of the communication channel, which allows them to be adjusted.

Alignment of chaotic oscillation generators is not always possible. Moreover, this problem is exacerbated during the long-term operation of the devices, the temperature dependences of the parameters of the generators at the transmitting and receiving ends of the circuit, which makes the above methods inoperative in the long term. At the same time, the generalized synchronization mode can be observed not only in the case of the influence of a chaotic signal on chaotic generators, but also when the same chaotic signal affects periodic oscillators, which was discovered by the authors of the present invention when studying the influence of the characteristics of the oscillators of the receiving device on the establishment of the mode generalized synchronization. It was found that the simpler the mode implemented in the generator, the lower the threshold value of the communication parameter corresponding to the establishment of a synchronous mode. The development of identical generators of periodic oscillations is less difficult than the implementation of chaotic generators. Moreover, in this case, the instability of the operation of the generators with non-identical parameters is much less pronounced than in the case of using chaos generators, which will make such a scheme stable and efficient for a long time. In this case, the quality of information transfer will be higher.

Thus, the object of the present invention is to improve the method of covert information transfer in order to improve the stability of its operation and improve the quality of information transfer.

The problem is solved in that in a method for covert transmission of information, namely, that the useful signal is encoded into binary code, the initial deterministic chaotic signal is generated by the first generator by modulating the chaotic signal parameters with the useful digital signal and the received signal is transmitted via the communication channel to the receiving side, where it is divided into two identical signals, which affect the second and third generators, identical to each other in control parameters, selected with the possibility providing a generalized synchronization mode with the first generator, the signals taken from the outputs of the second and third generators are fed to a subtractor and, when observing or in the absence of oscillations, they determine the presence of a useful digital signal, presented in the form of a binary code, according to the invention, periodic signals are removed from the outputs of the second and third generators . The deterministic chaotic signal generated by the first generator is added to the noise signal produced by the noise generator before being transmitted over the communication channel. The characteristics of the noise generator are modulated by a digital or analog signal containing a false, non-essential or open informational message.

The technical result achieved in the inventive method for the hidden transmission of information is that the generators located on the receiving side of the communication channel are periodic oscillators, which eliminates the instability of the method when the parameters of the receiving generators are not identical and improves the quality of information transfer.

The invention is illustrated by drawings, where Fig. 1 shows diagrams for implementing the inventive method for covert information transfer; figure 2 - graphs characterizing the process of signal transmission: the original useful digital signal (a); a signal transmitted over a communication channel (b); transmitted useful digital signal reconstructed in a receiver of chaotic self-oscillations (c).

.The positions in figure 1 indicate: 1 - a useful binary signal m (t), 2 - the first (transmitting) generator, 3 - noise generator, 4 - information signal r (t) containing false information, 5 - adder, 6 - channel communications, 7 — second (receiving) generator, 8 — third generator identical to the second generator 7 in control parameters, 9 — subtractor, 10 — reconstructed useful signal $$\tilde{m}(t)$$

.

The inventive method for covert information transmission is based on the phenomenon of generalized chaotic synchronization (Rulkov NF, Sushchik MM, Tsimring LS, Abarbanel HDI Generalized synchronization of chaos in directionally coupled chaotic systems // Phys. Rev. E 51, 1995, 980) in the presence of noise (Moskalenko OI, HramovA.E., Koronovskii AA, Ovchinnikov AA Effect of noise on generalized synchronization of chaos: theory and experiment // Eur. Phys. JB 82, 1, 2011, 69-82). The method actively uses the auxiliary system method (Abarbanel HDI, Rulkov NF and Sushchik M. Generalized synchronization of chaos: The auxiliary system approach // Phys. Rev. E 53, 1996, 4528), which is one of the most effective methods for diagnosing the generalized synchronization mode , including in the presence of external noise.

10, представляющий собой чередующуюся последовательность участков с несинхронным и синхронным поведением, по которой исходный информационный сигнал может быть легко детектирован.The method of covert transmission of information (figa) is as follows. The useful information signal m (t) 1 is encoded as a binary code. One or several control parameters of the transmitting (first) generator 2 is modulated by an information signal so that the characteristics of the transmitted signal change insignificantly, but at the same time there remains the possibility of occurrence / destruction of the generalized synchronization mode depending on the transmitted binary bit. To implement this feature, the boundary of the appearance of the generalized synchronization mode on the plane of the parameters “modulation parameter - communication intensity” should have some peculiarity: with a small change in the control parameter, the threshold for the appearance of the synchronous mode should change quite sharply. The signal generated by the transmitting system is transmitted via communication channel 6, where it is affected by noise and distortion inevitably present in real devices. The receiving device is on the other side of the communication channel. It consists of two identical generators of periodic oscillations, the second 7 and third 8, capable of being in generalized synchronization mode with transmitting 2. The principle of operation of the receiving device is based on the diagnosis of generalized synchronization mode using the auxiliary system method. The signal from the communication channel is fed to the generators of the receiving device. The signals obtained at the output pass through the subtractor 9, and then the reconstructed useful signal is detected $$\tilde{m}(t)$$

10, which is an alternating sequence of sections with non-synchronous and synchronous behavior, according to which the initial information signal can be easily detected.

The methods of hidden information transfer (figb, c) differ from the method described above in the structure and functions of the transmitting device (they are similar to their prototypes (Koronovsky A.A., Moskalenko O.I., Hramov A.E. Method for the hidden transmission of information // Patent for invention No. 2349044 dated 03/10/2009; Moskalenko OI, Korolevsky AA, Hramov A.E. Method for covert information transmission with changing characteristics of a noise generator // Patent for invention No. 2421923 of 06/20/2011), respectively ) To provide additional masking of the information signal and change the characteristics of the transmitted signal, both methods use a noise generator 3. The characteristics of the noise generator in the method (Fig. 1c) are modulated by an information signal r (t) 4 containing false information: when transmitting a binary bit 0, the noise generator produces stochastic signal, obeying a uniform probability density distribution, when transmitting binary bit 1 - δ-correlated Gaussian noise with zero mean. The signal generated by the transmitting system is mixed in the adder 5 to the noise signal. The signal transmission through the communication channel, as well as the structure and functions of the receiving device are similar to those described above for the method (figa).

As an example of a specific implementation of the proposed method for the hidden transmission of information, one can cite a numerical simulation of a chain of two unidirectionally coupled low-voltage vircators (Frolov N.S., Korolevsky A.A., Hramov A.E. Study of the generation characteristics in a chain of unidirectionally coupled low-voltage vircators // Izv. RAS, Ser. Physical. 75, 12, 2011, 1697-1700), selected as generators of the transmitting and receiving devices.

A low-voltage vircator is a span which is formed by two grids (Egorov E.N., Kalinin Yu.A., Levin Yu.I., Trubetskov D.I., Hramov A.E. Vacuum generators of broadband chaotic oscillations based on nonrelativistic electron beams with a virtual cathode. Izv. RAS. Ser. physical. 69, 12 (2005) 1724-1726; Kalinin Yu.A., Koronovsky A.A., Hramov A.E., Egorov E.N., Filatov R. A. Experimental and theoretical study of chaotic oscillatory phenomena in a nonrelativistic electron beam with a virtual cathode. a plasma. 31, 11 (2005) 1009-1025). The intergrid space permeates the stream injected by the electron gun with a supercritical perveance determined by the additional braking of the electrons by creating a negative potential difference between the input and output grids. In a certain range of braking potential values, a virtual cathode (VC) is formed in the beam, which performs non-stationary oscillations both in space and in time. The output of the oscillation power of the VC is carried out using a segment of a broadband spiral electrodynamic system (OSES).

The numerical simulation of the leading low-voltage vircator, which is a transmitting device, is based on the particle-in-cell method, which reduces to solving a self-consistent system of equations (1) describing the dynamics of the electron beam and a system of telegraph equations (2) that allow describing the output of the microwave signal by excitation by the beam in the OSES, using the equivalent circuit method (Egorov E.N., Kalinin Yu.A., Koronovskii A.A., Hramov A.E., Morozov M.Yu. Study of microwave power in a nonrelativistic electron beam with virtual Odom in a decelerating field // Technical Physics Letters 32, 9, 2006, 71-78).

$$\frac{d^2{x}_i}{d{t}^2}=-E(x_i),$$

$$\rho (x)={\displaystyle \sum _i\Theta (x_i-x)},$$

$$\Theta (\eta )=\{\begin{array}{l}\mathrm{one}-|\; |\; |\eta |\; |\; |/\Delta x,|\; |\; |\eta |\; |\; |<\Delta x\\ 0,|\; |\; |\eta |\; |\; |>\Delta x\end{array},(\mathrm{one})$$

$$\frac{d^2\phi }{d{x}^2}=\alpha \rho (x),$$

where α is a parameter proportional to the electron beam current, Δх is the spatial grid step. The boundary condition for solving the Poisson equation for finding the field in the system was the condition for applying a braking potential difference between the grids of the system: φ (0) = 0, φ (1) = Δφ.

$${}_{\frac{\partial U_{out}}{\partial t}=-\frac{\mathrm{one}}{C}\frac{\partial I}{\partial x}+\frac{\mathrm{one}}{C}\frac{\partial q}{\partial t},}^{\frac{\partial I}{\partial t}=-\frac{\mathrm{one}}{L}\frac{\partial U_{out}}{\partial x},}\text{(2)}$$

where U _out is the output signal of the low-voltage vircator (integral value characterizing the state of the system).

The model of the slave generator differs from the model of the master in the presence of an element that communicates in a system - a modulating helix, built-in between the electron gun and the mesh space. The output signal of the leading generator is supplied to the modulating spiral, thereby preliminary modulating the electron beam in terms of speed at the entrance to the span.

In the numerical model of the driven vircator, in addition to the indicated systems (1) and (2), a system of equations describing the modulating spiral appears:

$${}_{\frac{\partial U_{2in}}{\partial t}=-\frac{\mathrm{one}}{C}\frac{\partial I_{2in}}{\partial x},}^{\frac{\partial I_{2in}}{\partial t}=-\frac{\mathrm{one}}{L}\frac{\partial U_{2in}}{\partial x},}\text{(3)}$$

The system of telegraph equations (3) is supplemented by the boundary condition:

$$U_{2in}(0,t)=\sqrt{\epsilon }{U}_{\mathrm{one}out}(\mathrm{one},t-T),(\mathrm{four})$$

where ε is the coupling coefficient in the system, which is introduced as the ratio of the power of the signal supplied to the modulating helix to the output power of the lead generator.

The control parameters in the system of coupled low-voltage vircators are the braking potential difference Δφ between the grids of the span, the beam current α, as well as the coupling coefficient ε. By varying the braking potential of the output grid and the Pierce parameter, one can achieve a change in the dynamics of the electron beam in the generator and a change in the vibration mode of the VC. In this scheme, the transmitting generator, characterized by the output signal x (t) = U _out1 (t), is selected by a selection of control parameters to a chaotic mode, which is implemented in the range of braking potentials Δφ = (0.48-0.58). The dimensionless beam current was chosen constant and equal to α = 0.9. The magnitude of the braking potential Δφ is modulated by a useful digital signal as follows. If binary bit 1 is transmitted at a given time interval, then Δφ = 0.52 throughout this entire interval. When transmitting binary bit 0, the parameter Δφ takes the value Δφ = 0.54.

The receiving device is a combination of two identical slave generators, the second and third, each of which is described by equations (1) - (4). Then u (t) = U _out2 (t) is the signal of the second generator, v (t) = U _out3 (t), also satisfying (1) - (4), is the signal of the third generator (see Fig. 1). The vircators making up the receiving device are configured in the stand-alone case (without the influence of an external signal) to operate in periodic mode by choosing the parameters α = 0.9 and Δφ = 0.6.

The strength of the connection between the transmitting and receiving generators is characterized by the parameter ε. It was chosen equal to ε = 0.1. In this case, the generalized synchronization mode in the system of unidirectionally coupled low-voltage vircators occurs at Δφ = 0.54, while for Δφ = 0.52, generalized synchronization is not observed.

будет представлять собой последовательность областей с различными типами поведения. В качестве информационного сигнала m(t) выберем последовательность бинарных битов 0/1, представленную на фиг.2(а).The subtractor performs the operation (u (t) -v (t)) ² . Then, after passing through it, according to the method of the auxiliary system, there should be a lack of oscillations for Δφ = 0.54 and the presence of chaotic oscillations for Δφ = 0.52. Recovered signal $$\tilde{m}(t)$$

will be a sequence of areas with different types of behavior. As the information signal m (t), we select the sequence of binary bits 0/1, presented in figure 2 (a).

. Нетрудно видеть, что полезный цифровой сигнал может быть легко детектирован.The characteristics of the transmitting chaotic generator will be modulated by a simple sequence of binary bits 0/1. Figure 2 (b) shows a fragment of the signal s (t) transmitted over the communication channel. In the transmitted signal s (t), neither traces of modulation of the control parameter Δφ by the useful signal m (t), nor any other signs of the presence of the initial hidden information message are visible. Figure 2 (c) illustrates the reconstructed signal $$\tilde{m}(t)={(u(t)-v(t))}^2$$

. It is easy to see that a useful digital signal can be easily detected.

Thus, the positive effect of the proposed method for the hidden transmission of information is the elimination of the instability of the method when the parameters of the receiving generators are not identical and the quality of information transfer is improved.

Claims (3)

1. The method of covert information transmission, namely, that the useful signal is encoded into binary code, the initial deterministic chaotic signal is generated by the first generator by modulating the chaotic signal parameters with the useful digital signal, and the received signal is transmitted via the communication channel to the receiving side, where it is divided into two identical signals that affect the second and third generators, identical to each other in control parameters, selected with the possibility of providing a generalized sync mode ization with the first generator, taken from the outputs of said second and third signal generator is fed to the subtracter and by observing or absence of oscillations determine the presence of a useful digital signal represented in binary form, characterized in that a second and third generators outputs remove periodic signals. 2. The method according to claim 1, characterized in that the deterministic chaotic signal generated by the first generator is added to the noise signal produced by the noise generator before being transmitted over the communication channel. 3. The method according to claim 2, characterized in that the characteristics of the noise generator are modulated by a digital or analog signal containing a false, non-essential or open informational message.

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