JPS63174445A - Transmission/reception system for enciphered data - Google Patents

Abstract

PURPOSE:To prevent a bit error rate from being deteriorated, by eliminating the distortion of a transmission line by an automatic equalizer, and eliminating the random fluctuation of a transmission symbol position added on a transmission side by a random number group generation circuit. CONSTITUTION:The position of a transmission symbol from a transmission symbol generator 1 fluctuates at random by the random number group generation circuit 2 and an adder circuit 3, then, it is inputted to a modulation circuit 4. A transmission signal, after receiving the distortion on the transmission line 5, is demodulated at a demodulation circuit 6. The distortion on the transmission line 5 is eliminated at the automatic equalizer 7. Since an authorized receiver can generate one and the same identical random number as that of the transmission side by the random number group generation circuit 8, it is possible to eliminate the fluctuation of the symbol position added on the transmission side by using a subtractor 9. A decision circuit 10 decides the output of the subtraction circuit 9.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an encrypted data transmission/reception system.

[Conventional technology]

Conventionally, as a digital data transmission method that allows encrypted communication, the sending side converts a binary data sequence from an information source into an encrypted binary data sequence using a certain encryption algorithm, and the converted sequence is normally On the receiving side, the received signal is input into a normal non-encrypted data transmission device to restore the encrypted binary data sequence, and this sequence is used on the transmitting side. A method is known in which a binary data sequence identical to that generated at the information source is obtained by performing inverse transformation of the encryption algorithm. Here, as an encryption algorithm, for example, DB
The S algorithm is used.

Alternatively, on the transmitting side, a binary data sequence from an information source is input to a normal non-encrypted data transmission device, and the resulting analog transmission signal is sent to another analog random number obtained by a certain algorithm. After adding the signals, it is sent to the transmission path, and on the receiving side, the analog random signal that is the same as that on the sending side is subtracted from the received signal, and the signal is input to a normal non-encrypted transmission device. A method has also been added to obtain the same binary data series as . As the analog random signal to be added and subtracted, for example, the output of a noise generator can be recorded on a tape recorder, and the recorded tape and its copy can be used on the transmitting side and the receiving side.

[Problem that the invention seeks to solve]

In the first method described above, an eavesdropper who has a normal non-encrypted transmission device can obtain at least the encrypted binary data sequence, so he records this binary data sequence once and then There is a risk that, for example, by using a computer to exhaustively destroy the key used for encryption, the key may be deciphered.

In addition, in the second method, even if an eavesdropper has a normal non-encrypted transmission device, the transmission device will not operate properly unless the analog random signal is subtracted, so he cannot obtain the binary data sequence itself. Therefore, it can be said that this method has less risk of being deciphered than the first method. However, in this method, when distortion is added to the transmission path, it is necessary on the receiving side to subtract the signal after distortion has been added, rather than the analog random signal itself added by the transmitting side, and the distortion in the transmission path is Since this cannot be known in advance, it is generally difficult to perform this subtraction accurately. Therefore, depending on the degree of accuracy of the subtraction, at least the bit error rate may deteriorate, or reception may not be possible at all.

[Means for solving problems]

The encrypted data transmission/reception method of the present invention includes a transmission symbol generation circuit that generates transmission symbols according to transmission data, a first random number sequence generation circuit that generates a random number sequence, an output of the transmission symbol generation circuit, and the first random number. a demodulation circuit that demodulates the transmission signal received via a transmission path, the transmission side comprising an addition circuit that adds the outputs of the sequence generation circuit and a modulation circuit that modulates the output of the addition circuit as a transmission signal; , an automatic equalization circuit that equalizes the output of the demodulation circuit, a second random number sequence generation circuit that generates the same random number sequence as that on the transmission side, and a second random number sequence generation circuit that generates the second random number sequence generation circuit from the output of the automatic equalization circuit. This configuration includes a subtraction circuit that subtracts the output, and a determination circuit that determines the output of the subtraction circuit on the receiving side.

〔Example〕

Hereinafter, the present invention will be explained based on the drawings.

FIG. 1 is a block diagram showing the basic concept of the present invention.

In FIG. 1,] is a transmission symbol generation circuit that generates transmission symbols according to transmission data on the transmission side, 2 is a random number sequence generation circuit, 3 is an addition circuit, 4 is a modulation circuit, 5 is a transmission path, and 6 is a demodulation circuit. 7 is an automatic equalizer, 8 is a random number sequence generation circuit, 9 is a subtraction circuit, and 10 is a determination circuit.

Next, FIG. 2 and FIG. 3 will be explained using FIG. 1 together with FIG.

Here, as an example, the four-level AM modulation method is -be, 5- +l! , shall be deemed to have been used. FIG. 2 shows transmission symbols generated by the transmission symbol generation circuit 1. As shown in FIG. Set the value of the transmitted symbol to 3.1. -1. -3. The transmission symbol is a random number sequence generation port f ¥82 that generates uniform random numbers between +1 and -1.
After the adder circuit 3 changes the position randomly as shown in FIG. 3, the signal is input to the modulator circuit 4. The transmitted signal is subjected to distortion in the transmission path 5, and then received and demodulated in the demodulation circuit 6. Since the distortion in the transmission line 5 is removed by the automatic equalizer 7, the output of the automatic equalizer 7 is equal to the output of the adder circuit 3. Since the legitimate receiver can use the random number sequence generation circuit 8 to generate the same uniform random numbers as those on the transmitting side, the subtraction circuit 9 can be used to remove variations in the position of the transmitted symbols added on the transmitting side. . That is, the output of the subtraction circuit 9 is equal to the output of the transmission symbol generation circuit 1. Judgment circuit 1.
0 is determined by the output of this subtraction circuit 9, and a valid receiver can restore the transmitted data 〇- without deteriorating the bit error rate despite the presence of distortion in the transmission path 5. Ru. On the other hand, the eavesdropper can obtain the same output as the legitimate receiver up to the output of the automatic isolator 7 shown in Fig. 3, but he cannot generate the same uniform random numbers as the sender, at least immediately. Therefore, it is impossible to obtain a signal such as shown in FIG. 2 in which fluctuations in the positions of transmitted symbols have been correctly removed, at least not in any way. Even if you record a binary data sequence once and then try to decrypt it using a computer, for example by exhausting the key used for encryption, the output of the judgment circuit 10 at the time of recording is The determination must be made without subtracting random numbers from the output of the automatic equalizer 7, or by performing random subtraction. Of course, this judgment result is different from the transmitted data, but since this information has already been lost due to the nonlinear operation of judgment, as long as the output of the judgment circuit 10 is recorded and used, it will not be possible to use it from now on. No matter how you manipulate it, it is impossible to restore the transmitted data. Although it seems possible for an eavesdropper to record the output of the automatic equalizer 7 and then attempt to decrypt it using a computer, the automatic equalizer 7 generally uses the output of the determination circuit 1o. Therefore, normal operation cannot be expected when the output of the determination circuit 10 differs from the transmitted data. Therefore, in this case, the output of the automatic equalizer 7 is the same as the output of the adder circuit 3. Even if the output of the automatic equalizer 7 were recorded, it would still be impossible to use it to restore the transmitted data.

FIG. 4 shows a specific example of the configuration of the present invention. In FIG. 4, numeral 11 is a 2-bit shift register, and 12 is a 2-bit multiplied by 8-bit ROM. .

The input/output relationship of ROM12 is input “OO”, “01”
"010", "10", "11"
00000", "00100000", "1]
It is assumed that ``10000o'' and ``11000000'' are output, respectively. 20 is an M-sequence generation circuit, and 21 is a 5-bit shift register. 30 is an 8-bit adder, 40 is an 8-bit D/A converter, 41 is a low pass filter (LPF), 42 is a sine wave generator, and 43 is a multiplier. 5o is a transmission line, 6° is a sine wave generator, 61 is a multiplier, 62 is a low pass filter (LPF), 63 is 8
70 is an automatic equalizer, 8o is an M-sequence generation circuit, 81 is a 5-bit shift register, 9o is an 8-bit subtracter, and 100 is a determiner.

In this configuration, binary transmission data is input to the shift register 11, and 4-value data, that is, 64, 64,
32. -32. -64 symbols are selected. The output of the M-sequence generation circuit 2o is grouped into 5-bit units by the shift register 21, resulting in a uniform random number between +32 and -32.

After the position of the transmission symbol is randomly varied by the adder 30, it is converted into an analog signal by the D/A converter 4o. After passing through the LPF 41, this signal is modulated by the multiplier 43 and sent to the transmission path 50. On the receiving side, the received signal is demodulated by a multiplier 61 and L
After passing through the PF 62, the signal is converted into an 8-bit digital signal by an A/D converter 63. Distortion in the transmission path 50 is removed from this signal by an automatic equalizer 70, and random fluctuations in the positions of transmission symbols added on the transmitting side are removed by an M-sequence generating circuit 80, which is the same as that on the transmitting side, using a subtracter 90. Since the transmission data is removed, the transmitted data is restored as the output of the determiner 100. Further, the tap coefficients of the automatic equalizer 70 are updated using the output of the determiner 100 using a normal taradiendo method.

〔Effect of the invention〕

As explained above, according to the present invention, an eavesdropper with a normal non-encrypted transmission device cannot obtain the binary data sequence itself, and a legitimate receiver can suffer a deterioration in the bit error rate. It is possible to send and receive encrypted data without

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the basic concept of the present invention, Figures 2 and 3 are diagrams showing transmitted symbols before and after receiving random position fluctuations to illustrate the principle of the present invention, and Figure 4 is a diagram showing the basic concept of the present invention. FIG. 3 is a diagram showing a specific configuration example of the invention. 1: Transmission symbol generation circuit, 2, 8: Random number sequence generation circuit, 3: Addition circuit, 4-modulation circuit, 5: Transmission line, 6: Demodulation circuit, 7: Automatic equalizer, 9: Subtraction circuit, 10: Judgment circuit, 11, 21, 81: Shift register, 12: RO
M, 20.80: M-sequence generation circuit, 30/adder, 4
0: D/A converter, 43.62: LPF, 42.60:
Sine wave generator, 41.61: Multiplier, 63: A/D
Converter, 70: Automatic equalizer, 90: Subtractor, 100: Determiner. 1: Transmission) Pole's birthday jumps, 2. and: Color and several books.”
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Claims (1)

[Claims] a transmission symbol generation circuit that generates transmission symbols according to transmission data; a first random number sequence generation circuit that generates a random number sequence; and an output of the transmission symbol generation circuit and an output of the first random number sequence generation circuit that are added together. A transmitting side includes an adder circuit and a modulation circuit that modulates the output of the adder circuit as a transmit signal, a demodulator circuit that demodulates the transmit signal received via a transmission path, and equalizes the output of the demodulator circuit. a second random number sequence generation circuit that generates the same random number sequence as that on the transmission side; a subtraction circuit that subtracts the output of the second random number sequence generation circuit from the output of the automatic equalization circuit; An encrypted data transmission/reception method comprising a determination circuit for determining the output of a subtraction circuit on a receiving side.