RU2112319C1 - Method for protection of information which is transmitted through wire communication channels and device which implements said method - Google Patents

Abstract

FIELD: communication equipment, in particular, confidential information transmission. SUBSTANCE: method involves noise protection of transmission line in voice range by means of two-channel adaptive filter which receives two signals information and reference ones and subtracts reference signal from information one. Information signal is mix of transmitted signal and noise generator, reference signal is transmitted by noise generator. Corresponding device has noise generator 1 and two-channel digital adaptive filter 3. EFFECT: simplified design of information protection and processing. 2 cl, 1 dwg

Description

 The invention relates to communication technology and can be used in systems designed to transmit information of a confidential nature.

 A device for secreting a spoken signal comprising a masking device for transmitted information, a device for processing masked information and a switching device is known (RF Patent N 2054812, CL N 02 K 1/04, 1996). The known device implements a method of protecting information, in which they carry out the masking of transmitted information and its subsequent processing for the recipient.

 The objective of the invention is to simplify the processes of masking and processing disguised information.

 The solution of the problem in part related to the method lies in the fact that in the method of protecting information received via wired communication channels, in which the transmitted information is masked and subsequently processed for the recipient, the information is masked by noise transmission line in the speech frequency range , and information processing for the recipient is carried out by means of a two-channel digital adaptive filter, which receives two signals - the main and the reference, subtract the reference signal from the ground, with the main signal is the mixed signal from the transmitting side and a noise generator, and reference - signal from the noise generator.

 In terms of the device, the solution of the problem lies in the fact that in the information protection system received via wired communication channels containing a masking device for transmitted information, a device for processing masked information and a switching device, the device for masking transmitted information is made in the form of a noise generator in speech the frequency range connected to the transmitting line, the device for processing masked information is a two-channel digital adaptive filter Wherein the first filter input is coupled to the transmitting line and the first output of the noise generator, the second filter input is coupled to the second output of the noise generator and the filter output is connected to the receiving subscriber line.

 The drawing shows a diagram of an information security system.

 The system for protecting information received via wired communication channels contains a noise generator 1 in the speech frequency range connected to a transmission line 2, a two-channel digital adaptive filter 3, a switching device 4 and a power supply 5.

 The generator 1, the filter 3, the switching device 4 and the power supply 5 can be combined in a single housing 6, located directly at the recipient of the information.

 The first input of the filter 3 is connected to line 2 of the transmitting subscriber A1 and the first output of the generator 1.

 The second input of the filter 3 is connected to the second output of the generator 1.

 The output of the filter 3 is connected to line 7 of the receiving subscriber A2.

 The design of the noise generator 1 can be similar to the well-known noise generators described, for example, in the Hoffman book by L.J. "Modern methods of information security." - M .: Soviet Radio, 1980, p. 89-91.

 Digital adaptive filter 3 may be similar to the well-known ones described, for example, in A. Weiss and D. Mitra, Digital Adeptivs: Conditions for Convergence, Rates of Convergence, Effects of Noise and Errors Arising from the Implementation, IEEE Trans. on Information Theory. vol. IT-25 (Nov.1979), pp. 637-652.

 The method of protecting information received via wired communication channels is implemented when the above-described system is considered, which is considered with respect to telephone wire communication.

 In a normal conversation between subscribers A1 and A2, the switching device 4 is in the position shown in the diagram.

 To transmit confidential information, the switching device 4 is put into a position where the line between A1 and A2 is broken, the generator 1 and the filter 3 from the power supply 5 are turned on, while the subscriber A1 will hear characteristic interference (noise) from the generator 1, thus masking information from subscriber A1 to subscriber A2.

The inputs of the filter 3 receive two signals - the main and reference. The main signal is a mixed signal.
- from the transmitting subscriber A1 and generator 1.

 The reference signal is a "pure" interference, noise from the generator 1. The adaptive filter 3 processes both signals and gives the receiving subscriber A2 information cleared of interference.

 The adaptive filtering algorithm is as follows.

 Compensation of the noise component in a noisy speech signal (ZRS) is carried out by a digital adaptive filter (CAF) with a finite impulse response that implements the algorithm for minimizing the mean square error (ISCED) of the filter.

 At one of the two inputs of the CAF, called the main one, an additive mixture of speech and noise signals is received. The second input of the CAF, called the reference, receives a noise signal. The computational procedure is constructed in such a way that tends to nullify the difference between the signals in the main channel and the prediction channel. This difference is called a filter error signal. The prediction signal is calculated from the N most recent signal reports in the reference channel and N linear prediction coefficients (LPC). The value of N is called the length of the impulse response of the filter or the number of LPCs.

 At each iteration of the calculations (which coincides with the sampling period of the input and output signals of the CAF), new LPCs are calculated depending on the error signals of the filter and the reference signal. As a result, the CAF suppresses all correlating components of the main and reference channels, and a speech signal cleared of noise remains at the error output.

 Mathematical description of the CAF.

e (n) = Z (n) - y (n)
h (n+1,i) = h (n,i) + Ke(n) x (n - i),
где Z(n) - очередной отсчет в основном канале;
X(n) - очередной отсчет в опорном канале;
y(n) - очередной отсчет в канале предсказания;
e(n) - очередной отсчет в канале ошибки;
h(n,i) - КЛП;
К - коэффициент, определяющий скорость адаптации;
N - длина импульсной характеристики ЦАФ.

e (n) = Z (n) - y (n)
h (n + 1, i) = h (n, i) + Ke (n) x (n - i),
where Z (n) is the next count in the main channel;
X (n) is the next count in the reference channel;
y (n) is the next sample in the prediction channel;
e (n) is the next sample in the error channel;
h (n, i) - KLP;
K is a coefficient determining the rate of adaptation;
N is the length of the impulse response of the CAF.

Claims (2)

 1. A method of protecting information received via wired communication channels, in which the transmitted information is masked and subsequently processed for the recipient, characterized in that the information is masked by noise of the transmission line in the speech frequency range, and the information is processed for the recipient through a two-channel digital adaptive filter, which receives two signals - the main and reference, subtracts the reference signal from the main, while the main signal represents a mixed signal from the transmitting subscriber and the noise generator, and the reference signal from the noise generator.  2. A system for protecting information received via wired communication channels, comprising a masking device for transmitting information, a device for processing masked information and a switching device, characterized in that the masking device for transmitted information is made in the form of a noise generator in the operating frequency range connected to the transmission line, the device the processing of masked information is a two-channel digital adaptive filter, while the first input of the filter is connected to the transmission line the subscriber and the first output of the noise generator, the second input of the filter is connected to the second output of the noise generator, and the output of the filter is connected to the line of the receiving subscriber.