RU2421923C1 - Method of hidden transfer of information with variable characteristics of noise generator - Google Patents

Abstract

FIELD: information technologies. ^ SUBSTANCE: useful signal is coded into a binary code, an initial determinate chaotic signal is formed by modulation of the chaotic signal parameters with the useful digital signal, the signal generated in this manner is summed with a noise signal produced by the noise generator, the received signal is sent along the communication channel to a receiving side, where it is divided into two identical signals, they are used to act at the second and third chaotic generators, signals from which are sent to a subtracting device. At the same time the noise generator characteristics are modulated with a digital or analogue signal, containing a false, irrelevant or open information message. ^ EFFECT: increased reliability and expansion of communication channel throughput capacity. ^ 2 dwg

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 with a high degree of confidentiality.

Currently, methods for covert information transmission based on complete chaotic synchronization are known (see US patent No. 5291555, IPC H04K 1/02; H04L 9/28; RF patent No. 2295835, IPC H04L 9/12, H04K 1/02; Dedieu articles H., Kennedy M.R., Hosler 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 (Chen JY, Wong KW, Cheng LM, Shuai JW A secure communication scheme based on the phase synchronization of chaotic systems // Chaos. 13, 2003, 508), generalized synchronization (Terry J.R., VanWiggeren G. D. Chaotic communication using generalized synchronization // Chaos, Solitons and Fractals. 12, 2001, 145), and also 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 , VanWiggeren GD Chaotic communication using generalized synchronization // Chaos, Solitons and Fractals. 12, 2001, 145).

The principal disadvantages of the above methods, schemes and devices are, first of all, their low confidentiality, instability when the parameters of the transmitting and receiving generators are not identical, the destructive effect of noise on the quality of information transfer, difficulties in technical implementation.

A known method of covert information transmission (see RF patent No. 2349044, IPC H04L 9/00). The method is based on the generalized synchronization mode in the presence of noise and is the closest to the claimed method of covert information transmission. According to this method, a useful information signal is encoded as a binary code. One or several 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, but at the same time there remains the possibility of occurrence / destruction of the generalized synchronization mode depending on the transmitted binary bit. To provide additional masking of the information signal and changing the characteristics of the transmitted signal, a noise generator is used. The signal generated by the transmitting system is mixed in the adder to the noise signal 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 transmitting generator. 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.

The principal disadvantage of this method of covert information transmission is the ability to simultaneously transmit only one message over a communication channel. In addition, the signal transmitted through the communication channel in this way does not bear obvious traces of the availability of information, which could potentially make a third party think that useful information is hidden in it and use various statistical tests to decrypt it. Despite the fact that the signal transmitted over the communication channel practically does not differ in its characteristics from the stochastic one, there is a possibility that the use of one or another decryption method will still allow you to decode the original information message. Thus, this method is not reliable when transmitting confidential information.

At the same time, a change in the characteristics of noise, its amplitude, average and dispersion practically does not affect the effectiveness of this particular method of covert information transmission, which was discovered by the authors of the present invention when studying the influence of the characteristics of a noise signal on the performance of various methods of covert information transmission. The identified feature allows you to modulate the characteristics of the signal produced by the noise generator, an information signal containing false, non-essential or open information, throughout the entire transmission time of the signal, thereby pushing a third party to decrypt a false, non-essential or open message. In this case, the signal transmitted through the communication channel will bear traces of amplitude modulation, which will allow a third party to easily decrypt the corresponding message without subsequent application of statistical methods for analyzing the signal transmitted through the communication channel. At the same time, on the receiving side of the communication channel, traces of modulation will not affect the decryption of a hidden message, which allows us to talk about increasing the degree of confidentiality of information transfer by the claimed method. In addition, the inventive method allows you to expand the bandwidth of the communication channel, that is, allow you to send two information messages at once, containing useful and false information, respectively. The transmission of the second message may be interpreted as an undisclosed transmission of an information message over a communication channel.

The objective of the present invention is to improve the method of covert transmission of information in order to increase its reliability and expand the bandwidth of the communication channel.

The technical result achieved in the claimed method consists in the fact that the characteristics of the noise signal produced by the noise generator are modulated by an information signal containing a false (open) message, which provides not only for hiding the traces of modulation of the control parameters by a digital signal containing useful information, but also pushes a third party to decrypt a false message, and therefore, guarantees the confidentiality of the proposed method of covert transmission of information. In the case of transmitting an open message, the inventive method extends the bandwidth of the communication channel, allowing you to simultaneously transmit a hidden and open message.

The problem is solved in that in a method for covertly transmitting information containing a useful digital signal, which consists in encoding the useful signal in binary code, generating an initial deterministic chaotic signal by modulating the parameters of the chaotic signal with a useful digital signal, by summing the signal thus generated with noise signal produced by the noise generator, transmitting the received signal over the communication channel to the receiving side, its de two identical signals, their impact on the second and third chaotic generators, identical to each other in control parameters, selected with the possibility of providing a generalized synchronization mode with the first chaotic generator, feeding the signals taken from the outputs of the second and third generators to a subtractor, and determining when observation or absence of chaotic fluctuations in the presence of a useful digital signal, presented in the form of a binary code, according to the decision of the characteristics of the mode noise generator they are detected by a digital or analog signal containing a false, non-essential or open informational message.

The invention is illustrated by drawings, where figure 1 presents a diagram for implementing the proposed method for the hidden transmission of information; figure 2 - presents graphs characterizing the process of signal transmission: the original useful digital signal (a); a signal transmitted over a communication channel (b); the transmitted useful digital signal restored in the receiver of chaotic self-oscillations (e),

Where

1 - useful binary signal m (t);

2 - the first (transmitting) chaotic generator;

3 - noise generator;

4 - information signal r (t) containing false information;

5 - adder;

6 - communication channel;

7 - second (receiving) chaotic generator;

8 - the third generator, identical to the second generator 7 in control parameters;

9 - subtractive device;

.10 - restored useful signal

.

The inventive method for the secret transmission of information is based on the phenomenon of generalized chaotic synchronization (Rulkov N.F., Sushchik M.M., Tsimring L.S., Abarbanel H. D. I. Generalized synchronization of chaos in directionally coupled chaotic systems // Phys. Rev. E 51, 1995, 980). 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 (figure 1) is as follows. The wanted signal m (t) 1 is encoded as a binary code. One or several control parameters of the transmitting (first) chaotic 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 realize 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 rapidly. To provide additional masking of the information signal and change the characteristics of the transmitted signal, a noise generator 3 is used. The characteristics of the noise generator 3 are modulated by an analog or digital information signal r (t) 4 containing false information. For example, when transmitting binary bit 0, noise generator 3 produces a stochastic signal obeying a uniform probability density distribution, while transmitting a 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 and then transmitted through the communication channel 6, where it is affected by noise and distortion, which is inevitably present in real devices. The receiving device is located on the other side of the communication channel 6. It consists of two identical chaotic generators, the second 7 and the third 8, which can be in the generalized synchronization mode with the transmitting 2. The operating principle of the receiving device is based on the diagnosis of the generalized synchronization mode using the auxiliary system method. The signal from the communication channel 6 is supplied to the generators of the receiving device 7, 8. The signals received at the output pass through the subtractor 9, and then the reconstructed useful signal is detected

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.

As an example of a specific implementation of the proposed method, one can cite numerical modeling of unidirectionally coupled Rössler systems selected as transmitting and receiving devices generators. The schematic diagram of the Rössler generator is given in (Rico-Martinez R., Kreischer K.E., Flatgen G., Anderson J.S., Kevrekidis I.G. Adaptive Detection of Instabilities: An Experimental Feasibility Study // Physica D. 176, 2003, 1).

The transmitting generator is described by the following system of differential equations:

where x (t) = (x ₁ , x ₂ , x ₃ ) is the state vector of the transmitting generator, which characterizes the voltage fluctuations taken in different parts of the circuit, and = 0.15, p = 0.2, and c = 10 are the control parameters (which are the composition parameters of the system itself), ω _x is the control parameter characterizing the natural frequency of the system’s vibrations.

The value of the parameter ω _{x is} modulated by a useful digital signal, as follows. If binary bit 1 is transmitted at a given time interval, then ω _x = 0.91 throughout this interval. When transmitting binary bit 0, the parameter ω _x takes a random value from the range ω _x ∈ [0.9, 0.91) (Hramov AE, Koronovskii AA, Moskalenko OI Generalized synchronization onset // Europhysics Letters. 72 (6), 2005, 901).

The receiving device contains two identical chaotic generators, the second and third, each of which is described by the following system of equations:

Here u (t) = (u ₁ , u ₂ , u ₃ ) is the state vector of the second generator. Let v (t) = (v ₁ , v ₂ , v ₃ ), also satisfying (2), be the state vector of the third generator (see figure 1). The control parameters a, p and c will be chosen identical to the latter for the transmitting generator. The control parameter ω _u characterizing the eigenfrequency of the receiving oscillators is chosen to be equal to ω _u = 0.95 throughout the entire transmission time of the signal.

The signal generated by the transmitting device 2 is summed with the signal produced by the noise generator 3, and then transmitted via the communication channel 6. In this model, this is realized by connecting the receiving generators 7, 8 with the transmitting 2, i.e. by adding the component ε (s (t) -u ₁ ) to the first equation of system (2). Here s (t) = x ₁ + Dξ is the so-called signal in the communication channel. The term Dξ simulates the noise produced by the noise generator. The characteristics of the noise signal ξ (t) are modulated by an information signal r (t) containing false, irrelevant or open information: if binary bit 0 is transmitted, the stochastic signal obeys a uniform probability density distribution, if binary bit 1 is transmitted - a Gaussian distribution with zero mean. Parameter D determines the total intensity of added noise. It should be noted that it is possible to provide amplitude modulation not only by changing the nature of the distribution of a random variable, but also by varying the parameter D, for example, D = 10 if binary bit 1 is transmitted, D = 5 if binary bit 0 is transmitted, etc. . Moreover, it is possible to modulate the amplitude of the noise signal with an analog signal.

The strength of the connection between transmitting 2 and receiving 7, 8 generators is characterized by the parameter ε. It was chosen equal to ε = 0.14. In this case, it is known that both in the absence and in the presence of noise, the generalized synchronization mode in system (1) - (2) takes place for ω _x ∈ [0.9; 0.91), while for ω _х = 0.91, generalized synchronization onset // Europhysics Letters. 72 (6), 2005, 901; Moskalenko OI, (see Hramov AE, Koronovskii AA, Moskalenko OI. Hramov AE, Koronovskii AA, Ovchinnikov AA Effect of noise on generalized synchronization: theory and experiment // Phys. Rev. E. 2009, submitted)).

10 будет представлять собой последовательность областей с различными типами поведения.The subtractor performs the operation (u ₁ -v ₁ ) ² . Then, after passing through it, according to the method of the auxiliary system, there should be a lack of oscillations for ω∈ [0.9; 0.91) and the presence of chaotic oscillations for ω _x = 0.91. Recovered signal

10 will be a sequence of areas with different types of behavior.

As a useful signal m (t) we choose a sequence of binary bits 0/1, presented in figure 2 (a). To integrate stochastic equation (2), we will use the 4-order Runge-Kutta method adapted to solve stochastic differential equations (Nikitin N.N., Pervachev S.V., Razevig V.D. On solving stochastic differential equations of tracking systems on a computer / / Automation and telemechanics. 41975133), with a time discretization step h = 0.001.

. Нетрудно видеть, что при помощи пропускания через фильтр нижних частот и выбора пороговых значений полезный цифровой сигнал может быть легко детектирован, также как и в случае скрытия следов модуляции управляющего параметра стохастическим сигналом с постоянными характеристиками или при отсутствии такового вовсе.We choose a noise intensity large enough, for example, D = 10 and show how the inventive method of covert information transmission in this case works. We will modulate the characteristics of the noise generator with a simple sequence of binary bits 0/1. It should be noted that it is possible to modulate the characteristics of the stochastic signal and a more complex information message (both digital and analog). Figure 2 (b) shows a fragment of the signal s (t) transmitted via communication channel 6. It is easy to notice the presence of traces of amplitude modulation in the signal s (t), by the presence of which a third party can easily decrypt a false, non-essential, or open message r ( t). At the same time, in the signal s (t), neither traces of modulation of the control parameter ω _{x 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

. It is easy to see that by passing a low-pass filter and selecting threshold values, a useful digital signal can be easily detected, as well as in the case of hiding traces of the modulation of the control parameter by a stochastic signal with constant characteristics or in the absence thereof.

It should be noted that similar results are observed with a further increase in the noise intensity D and with a change in the nature of the distribution of a random variable. The method becomes inoperative if the ratio of energy per bit to spectral density of noise power E _b / N ₀ = -10.01 dB, which once again confirms the constructive role of noise in the transmission of information by the claimed method.

Thus, the positive effect of the proposed method of covert information transmission is to provide additional masking of the signal transmitted through the communication channel by modulating the characteristics of the noise generator with an information message containing false, non-essential or open information, pushing a third party to decrypt this message and, therefore, guarantee a high degree of confidentiality information transfer.

Claims (1)

A method for covertly transmitting information containing a useful digital signal, namely, that the useful signal is encoded in binary code, the initial deterministic chaotic signal is generated by the first chaotic generator by modulating the parameters of the chaotic signal with a useful digital signal, and the signal thus generated is combined with the noise signal produced noise generator, and transmit the received signal over the communication channel to the receiving side, where it is divided into two identical signals, which affect wave to the second and third chaotic generators, identical to each other in control parameters, selected with the possibility of providing a generalized synchronization mode with the first chaotic 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 chaotic oscillations, they determine the presence of useful digital signal, presented in the form of a binary code, characterized in that the characteristics of the noise generator are modulated by a digital or analog signal containing a false, immaterial or open informational message.

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