RU2212105C1 - Method for digital data transmission in pseudorandom operating frequency control radio lines - Google Patents

Abstract

FIELD: radio communications and computer engineering; data transmission in computer networks over pseudorandom operating frequency control radio line. SUBSTANCE: on sending end input signal is divided into blocks, transmitter carrier frequency is controlled in compliance with codes of pseudorandom sequences set up by feedback shift register, transmitter carrier is modulated by respective burst, this being followed by radiation of this signal into environment, reception of this signal at receiving end of radio line at all frequencies at a time in compliance with code of pseudorandom sequences, choice of frequency channel involved in transmission, signal conversion into intermediate frequency, amplification, demodulation, and decoding of burst, and data signal supply to terminal device. Novelty is that all pseudorandom sequences are generated as pseudorandom sequences of finite character field F_p having characteristic p = 257 in the form of eight-bit binary vectors by reading out information from eight different places of shift register, and replacement of characters 0 by 256, sequential conversion of input-signal eight-bit blocks using finite-field pseudorandom character sequences, as well as linear or nonlinear cryptographic transformations including addition, multiplication, or exponentiation operations of characters in finite field F_p, and replacement of characters 0 by 256, modulation of transmitter carrier frequency by means of burst of input-signal converted blocs; carrier frequency control code is generated by relatively adding, multiplying, or exponentiating pseudorandom sequences of characters shaped in finite field F_p followed by modulo n reduction of numbers obtained, where n is number of frequency channels used. EFFECT: enhanced stability of communications at active intrusions; ensured privacy of data transmitted. 5 cl, 2 dwg

Description

 The invention relates to the field of radio communications and computer technology, and more particularly to the field of methods and devices for transmitting information in a computer network via a radio link with pseudo-random tuning of the operating frequency.

Known methods for transmitting discrete information in a radio line with pseudo-random tuning of the operating frequency (see, for example, [1] p. 19-35, application for invention 99123808/09, IPC ⁷ H 04 V 1/713 of 10.11.1999 [2]) .

 In known methods, the transmission of discrete information is carried out by modulating a packet of an information signal of a transmitter frequency, the carrier of which is tuned according to a pseudo-random law. However, the known methods do not ensure the confidentiality of the transmitted information.

 The closest in technical essence to the claimed method is the method described in the application 99123808/09 from 10.11.1999. The prototype method includes dividing the input signal at the transmitting end into blocks, rearranging the carrier frequency of the transmitter in accordance with the code of one of two or more pseudorandom sequences created by the feedback shift register, modulating the carrier carrier with the corresponding packet, and then radiating it into space, receiving a signal at the receiving end of a radio link simultaneously at all frequencies according to pseudo-random sequence codes, selecting the frequency channel through which s transmission signal conversion to an intermediate frequency, amplification, demodulation, and decoding the packet flow information signal to the terminal device.

 However, the prototype method has a drawback. Despite the fact that the carrier frequency of the transmitter is tuned in accordance with the pseudo-random sequence code, the communication system is unstable during active intrusions, because timely determination of the transmitter radiation frequency and the creation of interference-correcting interference frequencies for the receiving device for suppressing the information signal are provided. This is because if the structure of the shift register with n bits and linear or nonlinear feedback is known, then when you receive n characters of a pseudo-random sequence by registering the emitted frequencies of the transmitter, the structure of the pseudo-random sequence and the state of the register at the corresponding time moment are opened [3 ] p. 93. If the structure of the linear feedback shift register is unknown, then when 2n characters of the pseudo-random sequence are received within a second, the location of the taps, the number of adders included in the feedback circuit, and also the state of the register at the corresponding time [3] p. 94 can be determined. If the shift register uses non-linear feedback, then the linear complexity (4n) of the non-linear pseudo-random sequence that it creates will slightly differ from the linear complexity (2n) of the linear pseudo-random sequence, since no matter which point of the shift register the pseudorandom sequence is removed, we are dealing with one and the same pseudo-random sequence that is cyclically shifted relative to pseudo-random sequences taken from other points of the shift register on the definition The number of clock cycles and, at the current technological level, a nonlinear pseudorandom sequence can be opened in a few seconds. Since pseudo-random sequences are opened, they cannot be used to encode information in order to ensure its confidentiality.

 The invention is aimed at increasing the noise immunity of a radio link during active intrusions and ensuring the confidentiality of transmitted information.

This is achieved by the fact that in the known method of transmitting discrete information in a radio line with pseudo-random tuning of the operating frequency, which consists in dividing the input signal at the transmitting end into blocks, tuning the carrier frequency of the transmitter in accordance with the code of one of two or more pseudorandom sequences created by the shift register with feedback, modulation of the transmitter carrier by the corresponding packet and its subsequent emission into space, receiving a signal at the receiving end of the radio link simultaneously and at all frequencies according to the codes of pseudorandom sequences, the choice of the frequency channel through which the signal was converted to an intermediate frequency, amplification, demodulation, decoding of the packet and the supply of an information signal to the terminal device, according to the invention, all pseudorandom sequences are formed as pseudorandom sequences of characters of the final field F _p with characteristic p = 257 in the form of binary vectors 8 bits long by removing information from 8 different bits of the register and shift and replace the character "0" with the character "256", alternately transform the blocks of the input signal 8 bits long by using pseudo-random sequences of characters of the final field, as well as linear or nonlinear cryptographic transformations, including operations of addition, multiplication or raising to the power of the characters in the final field F _p , modulate the carrier of the transmitter with a packet of converted blocks of the input signal, and the code for tuning the carrier frequency is formed by adding, multiplying or raising to a power each other the other characters of the generated pseudo-random sequences in the final field F _p followed by the reduction of the resulting numbers modulo n, where n is the number of frequency channels used.

 In the totality of the features of the proposed method, a binary vector is understood as a signal in the form of a sequence of zero and single bits corresponding to the representation of a number in a binary system of calculus.

The listed set of essential features ensures the confidentiality of the transmitted information. In this case, the generated pseudo-random character sequences in the form of binary vectors 8 bits long are the pseudo-random character sequence {0, 1, 2, ..., 255} of the final field F ₂₅₇ , have the same period N = 2 ⁿ -1 as the pseudo-random sequences of binary numbers, and ensure the statistical uniformity of the characters used. When replacing the characters "0" with the characters "256", the formation of pseudo-random sequences of characters of the multiplicative group of the final field F ₂₅₇ {1, 2, ..., 255} is ensured. This allows you to create in the field F _{257 a} variety of functions for encoding the characters of the source text α, including operations of adding characters modulo p, multiplying the characters modulo p, raising characters to the power modulo p and their various combinations, unlike the field F ₂ , in which to encode one binary character of the source text, modulo two addition will be the only way to build a reversible decoding function.

Выбор в качестве характеристики конечного поля числа р=257 обусловлен тем, что для воспроизведения мультимедийных данных современные вычислительные машины используют 256 символов и ближайшим простым числом к числу 256 является 257.Since several pseudo-random sequences of symbols of the finite field {x, ..., y} can be removed from one shift register, each of which will not be cyclically shifted relative to other pseudorandom sequences, both linear and nonlinear cryptographic transformations can be implemented using several pseudo-random sequences of symbols of the final field F _p to obtain encoded symbols β of the final field F _p
αx + y ≡ β (mod p);
α ^x + y ≡ β (mod p);
α ^x • y ≡ β (mod p), ...
Since the symbols of the pseudo-random sequences x and y are elements of the multiplicative group of a finite field F _p , inverse quantities can be calculated
x ^-1 ≡ x ^p-2 (mod p);
y ^-1 ≡ y ^p-2 (mod p), ...
and conjugated elements
x * = p-x; y * = p-y, ...,
which allow you to implement cryptographic transformations to decode text characters
(β + y ^* ) x ^-1 ≡ α (mod p);

The choice as the characteristic of the final field of the number p = 257 is due to the fact that modern computers use 256 characters to play multimedia data and the closest prime number to the number 256 is 257.

Since the pseudo-random sequences of symbols of the final field F _p are removed from eight bits of the shift register, one symbol of the final field F _{p is} not reproduced, since the maximum number represented by 8 binary digits is 255, therefore, the removed pseudorandom sequences are not pseudorandom sequences of the maximum length in field F _p (M-sequences), and represent non-linear pseudo-random sequences. The total number of possible pseudorandom sequences of characters of the final field will be determined by the number of possible combinations of eight bits of the shift register from which information can be taken, and the number of permutations within one combination, each of which determines the reading order of the information for the shift register, consisting of n = 256 bits, the number of different pseudorandom sequences of characters of the final field F ₂₅₇ will be Q = 8! C $\genfrac{}{}{0ex}{}{\text{8}}{\text{256}}$ ≈ 10 ¹⁹ , while for the field F ₂ , from whatever points of the shift register the information would be taken, the pseudo-random sequence of binary numbers will only be cyclically shifted relative to other pseudorandom sequences of binary numbers taken from other bits of the shift register.

Since cryptographic transformations use two or more pseudo-random sequences of characters of the final field F ₂₅₇ , then if there are how many characters of the source and corresponding characters of the encoded text are there, the possibility of determining the characters of pseudorandom sequences is excluded, since the number of equations will always be twice less than the number of unknowns. At the same time, the code is resistant to attacks based on known and selected source texts, since opening the state of the shift register in this case can be achieved only by total enumeration of the entire set of possible states of the shift register. Since the US standard for DES data encryption uses a shift register having 128 bits (key length 128 bits) [4], the power of the set of possible states of the shift register will be 10 ³⁸ . If the opening of the state of the shift register is carried out using a computer with a clock frequency of 10 GHz, the number of operations performed by this computer during the year will be 3 • 10 ¹⁹ , and the opening time is 10 ¹⁸ years.

In accordance with the Russian standard GOST 28147-89 for a shift register having 256 bits (key length 256 bits) [5], the opening time of the state of the shift register will be 10 ⁵⁷ years. This ensures the confidentiality of the transmitted information.

Since the obtained pseudo-random sequences of symbols of the final field F _p do not reproduce one symbol, their formation can be considered as applying a compression algorithm to generate the M-sequence of symbols of the final field F _p by skipping (not using) those clock cycles of the generator on which the irreproducible symbol should appear. In this case, a nonlinear pseudorandom sequence is realized due to the non-uniform movement of the shift register (“compression generator”). In this case, the linear complexity of the obtained pseudorandom sequences will have a lower boundary of ≈10 ¹⁹ for the shift register with n = 256 bits. Since the code for tuning the carrier frequency defines a pseudo-random sequence that is generated by two or more compressing pseudo-random sequences, its linear complexity will have a lower bound equal to y = N / 3, where N = 2 ⁿ -1 is the length of nonlinear pseudorandom sequences of characters of the final field F _p . This eliminates the opening of the pseudo-random sequence that controls the tuning of the transmitter frequency during the transmission of information, and therefore, the possibility of creating targeted interference is excluded, which increases the stability of communication during active intrusions.

 The possibility of technical implementation of the claimed method is illustrated as follows.

The formation of a pseudo-random sequence of maximum length containing 2 ⁿ -1 characters can be accomplished by using a linear shift register with n bits, the feedback of which is determined by the form of the selected primitive polynomial of degree n. Finding primitive polynomials of degree n is described in [3] on p. 74 and 75.

В этом случае за счет возведения в степень порождающего числа l₀ мы будем переходить от одного элемента поля F_q к другому. При этом, как показано в [4] с. 44, если l₀ - элемент порядка К, то все элементы l₀, l₀ ², l₀ ³,..., l₀ ^K-1 будут различны. Значение q выбирается из простых чисел и для регистра сдвига, имеющего 256 разрядов q=257. Для регистра сдвига, имеющего 128 разрядов, q=127. В псевдослучайных последовательностях х и у двоичных векторов осуществляют замену символов "0" на "256".The formation of pseudorandom sequences of characters of the final field F ₂₅₇ in the form of binary vectors of 8 bits in length can be accomplished by taking information from eight different bits of the shift register, the numbers of which can be determined by the value of the security key K. For example, by determining the generating element
l ₀ ≡К (mod q), if l ₀ <2, then i ₀ = 2,
calculating the shift register bit number by the formula
l ₁ = l ₀ , l _i ≡l ₀ l _i-1 (mod q),

In this case, by raising to the power of the generating number l ₀ we will pass from one element of the field F _q to another. Moreover, as shown in [4] p. 44, if l ₀ is an element of order K, then all elements l ₀ , l ₀ ² , l ₀ ³ , ..., l ₀ ^K-1 will be different. The value of q is selected from primes and for the shift register having 256 bits q = 257. For a shift register having 128 bits, q = 127. In the pseudo-random sequences x and y of the binary vectors, the characters "0" are replaced by "256".

The formation of pseudo-random sequences of symbols of the final field F _p can also be carried out as a “compression generator” by taking information from eight bits of the shift register and skipping those clock cycles of the shift register for which at least one of the pseudorandom sequences contains the symbol “0”.

 Three more options for the formation of pseudo-random sequences of symbols of the final field in the form of binary vectors can be used.

1. Elements of one of the selected and generated pseudo-random sequences of symbols of the finite field y in the form of binary vectors are used as generating elements of y _n for an additional pseudo-random sequence z, the elements of which at each cycle of the shift register are defined as the generated elements of the field F _p .

z≡z • y _n (mod p).

If in the process of computing at some i clock cycle of the shift register it turns out that z = 1, then in this case the generating element of _{n of the} field F _p changes. Moreover, as a new generating element y _{n, we} take the element formed at this cycle of the shift register of the selected pseudorandom sequence for the symbols of the final field F _p , y _n = y, if y <2, then _n = 2. The generated additional pseudorandom sequence of the finite field z is used in cryptographic transformations when converting the data stream into an encoded message, for example
α • x + y + z ≡ β (mod p) or α • x + z ≡ β (mod p).
Since in the additional pseudorandom sequence of the finite field, the elements are formed by raising to the power a generating element of _n having order K, then all elements y _n , y _n ² , y _n ³ , ..., y _n ^k will be different on the interval shift register operation. Since generating elements y _n may be a different order in the finite field F _p, the shift generating elements will be carried out according to a pseudorandom. This ensures the statistical uniformity of the characters of the encoded text on an interval equal to p-1 clock cycles of the shift register, which eliminates the use of statistical methods of cryptanalysis to determine the state of the shift register.

3. Изменяют порядок считывания информации для одной из формируемых псевдослучайных последовательностей символов конечного поля в соответствии с изменением поражающего элемента дополнительной псевдослучайной последовательности символов, например, с использованием соотношений
l_i=l_k,
k≡i±y_n(mod 8),

Формирование псевдослучайных последовательностей символов конечного поля по п.1, 2 и 3 повышает стойкость кода к атакам на основе известных и подобранных исходных текстов при формировании ключа защиты малой длины.2. Change the numbers of bits of the shift register, from which information is removed for one of the pseudo-random sequences of characters of the final field in accordance with the change in the generating element of the additional pseudo-random sequence, for example, using the relations:
l ₀ = y _n , l _i ≡y _n l _i-1 (mod q),

3. Change the reading order of information for one of the generated pseudo-random sequences of characters of the final field in accordance with the change of the striking element of the additional pseudo-random sequence of characters, for example, using the relations
l _i = l _k ,
k≡i ± y _n (mod 8),

The formation of pseudorandom sequences of characters of the final field according to claim 1, 2 and 3 increases the resistance of the code to attacks on the basis of known and selected source texts when generating a short protection key.

 Code generation for tuning the carrier frequency of the transmitter can be obtained, for example, by adding or multiplying the characters of all the generated pseudorandom sequences, followed by bringing the resulting numbers modulo n, where n is the number of frequency channels used.

The conversion of the blocks of the input signal α into a coded message can be carried out by calculating the values of the symbols β in the final field F _p in accordance with the selected encoding function, for example, α • x + y ≡ β (mod p). and converting the resulting number β to a binary vector to modulate the carrier frequency of the transmitter.

The proposed method can be implemented using the device represented by the flowchart in figure 1, where
block 1 - signal source,
block 2 - the first shift register,
block 3 - the first generator of pseudo-random sequences,
block 4 - encoding device,
block 5 - the first frequency synthesizer,
block 6 - transmitter
block 7 - the second frequency synthesizer,
block 8 - the receiver,
block 9 - the second shift register,
block 10 - the second generator of pseudo-random sequences,
block 11 - decoding device,
block 12 - terminal device.

 Figure 2 shows the structural diagram of the shift register, where 13-18 are blocks of bits 1-6 of the shift register; 19 - block adder modulo two.

 A device that implements the method operates as follows.

For simplicity, the description of the operation of the device will use small numbers. We assume that the shift register has 6 digits (the key length is 6 bits), and the entire alphabet of the source text contains 16 characters, then a binary vector 4 bits long can be used to transmit one character, and F _p can be selected as a characteristic of the final field the number p = 17.

и представлены в таблице.To determine the structure of the shift register, a primitive polynomial of the sixth degree is chosen, for example
λ ⁶ + λ ⁵ +1.
For the selected primitive polynomial, the block diagram of the feedback shift register will have the form shown in FIG. 2. 6-bit security key generated using a random number generator
<λ ₆ , λ ₅ , λ ₄ , λ ₃ , λ ₂ , λ ₁ >,
where λ ₁ = 0, λ ₂ = 0, λ ₃ = 0, λ ₄ = 1, λ ₅ = 1, λ ₆ = 1 - enters the shift register and is used for the initial filling of the bits of the shift register. Binary symbols from the 5th and 6th bits of the shift register arrive at each input of the adder 19 modulo two, and from the output of the adder modulo two characters ε = λ ₅ ⊕λ ₆ go to the input of the first bit of the shift register (block 13). In this case, the state of the discharges for each cycle during the operation of the shift register is determined by the expression

and are presented in the table.

If the characters are removed from the sixth digit λ ₆ of the shift register (block 18), then the binary pseudorandom sequence of the maximum period will have the form
{1110000010000110001010011110100011100100101101110110011010101111}
Note that on the period of this sequence, any nonzero set of six digits 0 and 1 occurs only once.

If we take binary numbers from the 1st, 2nd, 3rd and 4th digits of the shift register (blocks 13, 14, 15, 16) and at each clock cycle of the shift register and with the set <λ ₁ , λ ₂ , λ ₃ , λ ₄ > we will to compare the binary vector (number) x = λ ₁ + 2λ ₂ +2 ² λ ₃ +2 ³ λ ₄ , then the sequence of binary numbers in the process of register operation can be considered as a sequence of x numbers (characters) x {0, 1, 2 ,. .., 15} in the form
x = {8, 0, 0, 1, 2, 4, 8, 0, 1, 3, 6, 12, 8, 1, 2, 5, 10, 4, 9, 3, 7, 15, 14, 13 , 10, 4, 8, 1, 3, 7, 14, 12, 9, 2, 4, 9, 2, 5, 11, 6, 13, 11, 7, 14, 13, 11, 6, 12, 9 , 3, 6, 13, 10, 5, 10, 5, 11, 7, 15, 15, 15, 14, 12, ...}
If we take binary numbers simultaneously with the 1st, 2nd, 5th, 6th digits of the shift register (blocks 13, 14, 17, 18) and at each clock cycle of the shift register with the set <λ ₆ , λ ₅ , λ ₂ , λ ₁ > we to compare the number in the form y = λ ₆ + 2λ ₅ +2 ² λ ₂ + 2 ³ λ ₁ , then the sequence of binary numbers in the process of the shift register can be considered as a sequence of characters for {0, 1, 2, ..., 15} as
y = {3, 3, 1, 8, 4, 0, 0, 2, 9, 12, 4, 0, 2, 11, 5, 8, 4, 2, 9, 14, 13, 12, 6, 11 , 7, 3, 1, 10, 13, 12, 4, 2, 11, 7, 1, 8, 6, 9, 12, 6, 9, 14, 15, 5, 10, 15, 7, 1, 10 , 15, 5, 8, 6, 11, 5, 10, 13, 14, 13, 14, 15, 7, 3, ...}
The analysis of the generated sequences x and y shows that on the interval corresponding to the period equal to 63 clock cycles of the shift register, each of the symbols {1, 2, ..., 15} occurs exactly four times. The symbol corresponding to zero occurs exactly three times in both sequences, and the x and y sequences cannot be obtained from each other as a result of a cyclic shift. There are no hidden periodicities in the x and y sequences and the statistical uniformity of the symbols used is ensured. Since one of the symbols of the pseudorandom sequences of the final field F _{17 is} not reproduced, the symbol "0" in both sequences is replaced by the symbol "16".

In addition to the pseudo-random sequences of symbols x, for the final field F _p , the table shows the formation of an additional pseudo-random sequence z by using the pseudo-random sequence of symbols y as generating elements, as well as the formation of the pseudo-random sequence of symbols of the finite field ν by changing the reading order of the information for the pseudo-random sequence of symbols of the final field x in accordance with the change in the generating element of the additional pseudo learning sequence z.

The formulated pseudorandom sequences of symbols of the final field x and y in the form of binary vectors are fed to the encoding device 11, where the incoming data stream is converted into an encoded message by using pseudo-random sequences of symbols x and y of the final field F ₁₇ in accordance with the selected cryptographic transformation in the final field F ₁₇ . The generated pseudo-random sequences of symbols x and y generate a pseudo-random sequence θ by adding the characters in the final field F _p followed by the reduction of the obtained numbers modulo 7, where 7 is the number of frequency channels used. The characters of the sequence θ are converted into binary vectors and supplied as a code to the frequency synthesizer to set the carrier frequency of the transmitter.

Similarly, on the receiving side, pseudo-random sequences of symbols of the final field x, y and θ in block 10 are generated and the symbols x and y are used in the decoding device 11 to restore the transmitted message in accordance with the selected cryptographic conversion, and the symbols θ are used to set the frequency in block 8 for converting the received signal to an intermediate frequency. The following is the use of pseudo-random character sequences x and y in frequency conversion procedures (pseudo-random character sequence θ)
θ = {4, 2, 0, 2, 6, 3, 0, 1, 3, 1, 3, 4, 3, 5, 0, 6, 0, 6, 1, 0, 3, 3, 3, 0 0, 0, 2, 4, 2, 2, 1, 0, 3, 2, 5, 0, 1, 1, 6, 5, 5, 1, 5, 2, 6, 2, 6, 6, 2 , 1, 4, 4, 2, 2, 1, 1, 0, 4, 4, 5, 6, 4, 1,},
as well as in procedures for encoding and decoding information (see the end of the description).

 The implementation of the proposed method does not cause difficulties, since all the blocks and nodes included in the device that implements the method are well known and widely described in the technical literature.

Sources of information
1. Borisov V.I., Zinchuk V.M., Limarev A.E., Mukhin N.P., Shestopalov V.I. Interference immunity of radio communication systems with the expansion of the spectrum of signals by the method of pseudo-random tuning of the operating frequency. -M .: Radio and communications, 2000.

2. A method for transmitting discrete information in a radio line with a pseudo-random tuning of the operating frequency and a device implementing it, RF application for invention 99123808/09 of 10.11.1999, IPC ⁷ N 04 V 1/713.

 3. Voronkov B.N., Tupota V.I. Toolkit for the development of information security tools in computer networks. - Voronezh, Voronezh State University, 2000.

 4. Maftik S. Protection mechanisms in computer networks. - M., 1993.

 5. The Russian standard GOST 28147-89. Information processing systems. Cryptographic protection. Cryptographic conversion algorithm.

Claims (5)

1. A method of transmitting discrete information in a radio line with a pseudo-random tuning of the operating frequency, including dividing the input signal into blocks at the transmitting end, tuning the carrier frequency of the transmitter in accordance with codes of pseudorandom sequences created by a feedback shift register, modulating the carrier of the transmitter with an appropriate packet and subsequent radiation it into space, receiving a signal at the receiving end of a radio link simultaneously at all frequencies according to pseudorandom codes in series selection of the frequency channel through which the signal was transmitted, converting the signal to an intermediate frequency, amplifying, demodulating, decoding the packet, and supplying an information signal to the terminal device, characterized in that all pseudorandom sequences are formed as pseudorandom sequences of characters of the final field F _p with the characteristic p = 257 in the form of binary vectors 8 bits long by taking information from 8 different bits of the shift register and replacing the characters "0" with the characters "256", alternately converting blocks of the input signal with a length of 8 bits by using pseudo-random sequences of characters of the final field, as well as linear or nonlinear cryptographic transformations, including the addition, multiplication or raising to the power of the characters in the final field Fp and replacing the characters "0" with the characters "256", modulate the transmitter carrier with a packet of converted blocks of the input signal, and the code for tuning the carrier frequency is formed by adding, multiplying or raising to the power of each other the symbols formed pseudorandom sequences in the final field Fp with subsequent reduction of the obtained numbers modulo n, where n is the number of frequency channels used.  2. The method according to p. 1, characterized in that during the operation of the shift register, those cycles of its operation are missed (not used) in which at least one of the generated pseudorandom sequences of characters of the final field Fp has the symbol "0".  3. The method according to p. 1 or 2, characterized in that the symbols of one of the generated pseudo-random sequences of the final field are used as generating elements to form an additional pseudo-random sequence, the symbols of which at each cycle of the shift register are defined as the generated elements of the final field Fp.  4. The method according to any one of paragraphs. 1-3, characterized in that the numbers of the bits of the shift register are changed, from which information is removed for one of the generated pseudo-random sequences of characters of the final field in accordance with the change in the generating element of the additional pseudo-random sequence.  5. The method according to any one of paragraphs. 1-3, characterized in that they change the reading order of information for one of the generated pseudo-random sequences of characters of the final field in accordance with the change in the generating element of the additional pseudo-random sequence.

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