JPH0147061B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention provides a method for transmitting signals with non-uniform frequency characteristics, such as voice or data, over wired or wireless transmission lines, such as eavesdropping or interference on the transmission line. This invention relates to a transmission system that increases the concealment of confidential information by processing the frequency characteristics of signals in order to prevent information from being accidentally leaked.

Conventionally, this type of system has the equipment configuration shown in Figure 1, in which the signal is processed one by one to form the spectrum schematically shown in Figure 2, and the signal spectrum on the transmission path is spectrally inverted with respect to the original signal spectrum. Although the secrecy of the transmission path was maintained as long as the receiver did not have a spectrum inversion function, it had the disadvantage that information that was mixed into a receiving device with a spectrum inversion function was not protected at all.

A detailed explanation will be given below with reference to the drawings.

FIG. 1 shows a conventional system configuration and the structure of a spectrum inverter. In Fig. 1, 1 is a transmission line;
2 is a spectrum inverter, 3 and 4 are coefficient multipliers with coefficients of 1 and -1, respectively, 5 and 6 are analog switches, 7 is an inverter, and 8 is a square wave with an oscillation frequency of f ₁ + f ₂ and a duty of 50%. Signal oscillator, 9 is a low-pass filter whose cutoff frequency is f ₁ + f ₂ , 10 and 11 are the input and output terminals of the spectrum inverter on the transmitting side, respectively, 12 and 1
3 are input and output terminals of a receiving side spectrum inverter, respectively. The receiving side spectrum inverter is of the same type as the transmitting side spectrum inverter, and is designated by the number 14.

When the inverted signal is input to input terminal 1 or input terminal 2, the coefficient multiplier 3 multiplies the coefficient by 1, and the coefficient multiplier 4 multiplies the coefficient by -1.
be multiplied. The square wave oscillator 8 has a frequency f ₁ +f ₂ ,
It oscillates at duty 50%, and analog switch 5,
The levels applied to the gates of 6 are inverted by an inverter 7 so that they are complementary to each other, and the inverted signal multiplied by a factor of 1 or -1 is obtained as the analog switch output.

This has an effect equivalent to, for example, an analog mixer, and a signal equal to the fε[f ₁ , f ₂ ] component obtained by multiplying the inverted signal by the local oscillation frequency of frequency (f ₁ +f ₂ ) is obtained. The low-pass filter 9 has f∈[f ₁ , f ₂ ]
It is inserted to remove high frequency components.
Spectrum inverter 2 functions in this manner.

Therefore, a spectrum as shown in FIG. 2 is obtained. That is, if the signal shown in FIG. 2a is the audio spectrum applied to the input terminal 10, then FIG. 2b is the spectrum at the input terminal 12 when the output terminal 11 and the transmission path 1 are ideal, FIG. 2c shows the output spectrum of the output terminal 13.

Since all receiving devices have the same frequency characteristics, the inverted signal from any transmitting device will be correctly demodulated, making it impossible to maintain high confidentiality of communication between a specific pair.

In the present invention, frequencies are divided into n zones [f ₀ , f ₁ ], [f ₁ , f ₂ ],...
..., [f _o-1 , f _o ] (f ₀ < f ₁ < f ₂ <...< f _o-1 < f _o ), and spectrum pattern obtained by performing spectrum inversion processing on each zone. , divided frequencies f ₁ , f ₂ , ..., f _o-1 are used as encryption keys of a specific transmitting/receiving device to provide secret confidentiality, and the zone inversion pattern and divided frequencies f ₁ , f ₂ , ..., The purpose is to sufficiently increase the number of keys using the f _o-1 combination to prevent mixed information from being reproduced on receiving devices other than the specific receiving device.The drawings are explained in detail below. .

FIG. 3 shows a first embodiment of the present invention, in which n=2 and the number of inverted zones m=1. Here, the explanation will be given by limiting the number of zones to 2, but even when the number of zones is 2 or more, f ₁ , f ₂ , ...,
It can be easily inferred that f _o-1 and the zone reversal pattern are the keys, and their effects appear in the same way, so explanations regarding these will be omitted.

As shown in Figure 3, the same type of processing device (the part surrounded by a dotted line, called a half unit) is used for encryption on the sending side and decryption on the receiving side. Confidential communication is carried out by these devices.

In Figure 3, 15 is a low-pass filter with a cutoff frequency of _f1 , and 18 is a low-pass filter with a cutoff frequency of f1.
A circuit having the same function as a high-pass filter f ₁ , 16 is a zone 1 whose inversion reference frequency is f ₀ + f ₁
17 is an adder, and 1 is a transmission line.

Also, letters a, b, c, . . . i in the figure indicate observation points, and a, b, c . . . in FIG. The horizontal axis in FIG. 4 represents frequency, and the vertical axis represents amplitude.

To operate the device according to the embodiment of the present invention, a signal in the frequency band [f ₀ , f ₂ ] is input to the input terminal 10, and a signal in the frequency band [f 0 , f 1 ] is input to the input terminal 10, and a signal in the frequency band [f ₀ , f ₁ ] is An adder in the circuit 18 divides the signal into signals consisting of components [f ₁ , f ₂ ]. That is, the input signal in FIG. 4a is the output (b) of the low-pass filter 15.
and the output (c) of circuit 18. The spectrum of the signal shown in FIG. 4b is inverted by the spectrum inverter 16 to obtain the signal shown in FIG. 4d. A composite wave of the outputs of the spectrum inverter 16 and the circuit 18 is obtained by the adder 17, and the wave shown in FIG. 4e is obtained.

By transmitting the signal shown in FIG. 4e through the transmission line 1 and subjecting it to the same processing as on the transmitting side, a decoded signal appears at the output terminal 13 as the output of the half unit.

Although the input signal 18 in FIG. 3 is divided using a subtracter, the same result can be obtained even if a high-pass filter having the same cutoff frequency as the low-pass filter 15 is used.

Therefore, the spectrum on the transmission path has the shape shown in Figure 4e, and even if the spectrum is inverted, it cannot be reshaped to the original spectrum.If _f1 does not match, the original spectrum cannot be restored even if the same processing is performed. is not obtained.

FIGS. 5 and 6 show spectra obtained by performing similar processing when f ₁ does not match. In the figure, a, b, c, etc. correspond to observation points a, b, c, etc. in FIG.

FIG. 5 shows a case where f ₁ '>f ₁ , the divided frequency on the transmitting side is f ₁ and the divided frequency on the receiving side is f ₁ '.

FIG. 6 shows a case where the divided frequency on the transmitting side is f ₁ ' and the divided frequency on the receiving side is f ₁ .

As shown in Figure 5 i and Figure 6 i, even in similar processing, if f ₁ and f ₁ ' are different from each other, the decrypted signal will not be obtained correctly, and f ₁ and f ₁ ' will not be used as the encryption key. It becomes clear what will happen.

For example, f ₁ = αf ₀ + (1-α) f ₂ , α=0.3, 0.4,
If you choose 0.5, 0.6, and 0.7, you can obtain five types of keys as f ₁ . By further subdividing α, it becomes possible to increase the number of keys.

FIG. 7 shows a second embodiment of the present invention, where n=
2, in the case of m=1. A spectrum inverter with an inversion reference frequency of f ₀ tf ₂ was inserted after the half unit of the first embodiment, and the spectrum on the transmission path was replaced with zone 1 and zone 2 with respect to the spectrum on the transmission path of the first embodiment. It is designed to have a relationship. The half unit in FIG. 7 is equal to the half unit in FIG.
is a spectrum inverter whose inversion reference frequency is f ₀ + f ₂ . a, b, c...k in Figure 7
are observation points, and the spectra at each observation point are shown in Figure 8 a, b, c...(k).

The operation of the second embodiment is similar to that of the first embodiment, and it is easy to understand that f ₁ is the encryption key. However, even if f ₁ matches, the transmission signal of the second embodiment cannot be received by the receiving device of the first embodiment. This is because the received signal has a spectrum inverted relationship with respect to the original signal.

The number of replacement patterns when the number of zones is n is (ni−
1), and the number of keys becomes extremely large. and,
Any replacement pattern can be realized by repeating the number of compatibility.

For example, if the zone is [1, 2, 3, 4,],
The mapping to the permutation pattern [4, 3, 1, 2] is
For example, with compatibility (2, 3) we get [1, 3, 2, 4], then with compatibility (1, 3), (2, 4) we get [3,
1, 4, 2], and the third is compatible (1, 4) with [3, 4,
1, 2], and finally (3, 4) [4, 3, 1, 2]
get. Permutation that inverts the entire range, i.e. f ₀ = f ₀
When using an inverter with +f ₄ , firstly [4, 3,
2, 1] is obtained, and then the final permutation pattern [4, 3, 1, 2] is obtained by interchange of (2, 1).

Zone 2 and zone 3 are interchangeable using the spectrum inverter f ₀ = f ₁ + f ₃ .
After the signal components of the zone are interchanged with inversion, each zone component is inverted within the zone.

Above, we have explained the inversion and replacement processing separately, but since each zone component is inverted each time compatibility is performed, it is easy to infer that inversion and replacement can be handled in an integrated manner to reduce the amount of processing and process efficiently. . Also, explain n=
2, that is, the number of zones is 2, but n
> When dividing into more zones than 2,
It can be easily inferred that the division frequencies f ₁ , f ₂ , ..., f _o-1 , the inversion pattern, and the substitutions become secret keys.

Furthermore, signal processing is not limited to analog processing.
After AD conversion, digital signal processing is performed using a signal processing processor or the like, DA conversion is performed, and aliasing noise is removed. Digital processing can be performed similarly, and the digital signal processing format of the present invention can be easily inferred.

As explained above, according to the present invention, the cutoff frequencies f ₁ , f ₂ , . . .
Since f _o-1 and the transmission spectrum pattern can be used as a secret key, it can be applied directly to analog transmission lines, etc., without adding a synchronization signal during transmission _. ) x (transmission spectrum pattern), which has the advantage of dramatically improving confidentiality.

[Brief explanation of drawings]

Figure 1 shows an example of the system configuration of a conventional inverted secret message transmission system.
FIGS. 2a to 2c are spectrum diagrams at observation points a to c in FIG. 1, FIG. 3 is a diagram showing the configuration of the first embodiment of the present invention, and FIGS.
Spectrum diagram at observation points a to i in the figure.
Figures 5a to 5i are spectrum diagrams of each observation point when the transmitting side divided frequency f ₁ is lower than the receiving side divided frequency f ₁ ' in the configuration of Figure 3, and Figures 6a to i are the spectrum diagrams shown in Figure 3. The split frequency of the transmitter in the configuration of
A spectrum diagram of each observation point when f ₁ ′ is higher than the dividing frequency f ₁ on the receiving side, FIG. 7 is a diagram showing the configuration of the second embodiment of the present invention, and FIGS. A spectrum diagram at each observation point a to k. 1... Transmission line, 2, 14... Spectrum inverter, 3, 4... Coefficient unit, 5, 6... Analog switch, 7... Inverter, 8... Square wave oscillator, 9... Low pass filter, 10, 12... Input terminal, 11, 13... Output terminal, 15... Low pass filter, 16, 19... Spectrum inverter, 17... Adder, 18... Circuit having the same function as the high pass filter.

Claims (1)

[Claims] 1. The occupied frequency band of the signal to be transmitted is [f ₀ , f _o ]
(f ₀ , f _o are the lower and upper limit frequencies of the band), a frequency band division circuit and a spectrum inversion circuit are provided on the transmitting and receiving sides, and the transmitting side divides the signal band into [f ₀ , f ₁ ], [f ₁ , f ₂ ], ...,
Divide into n zones [f _o-1 , f _o ] (where f ₁ < f ₂ <...< f _o ^- ₁ < f _o ) (each zone is zone 1, zone 2,..., (referred to as zone n) Spectrum inversion of the signal components corresponding to m (0<mn) zones among the zones, or replacing the frequency arrangement order of each zone, or inverting and ordering the frequencies. The sum of the signal components of n zones obtained as a result is transmitted, and the divided frequencies are transmitted to the receiving side as f ₁ , f ₂ ,
...The information of the zone name which is inverted and/or permuted with the information of f _o-1 is transmitted, and on the receiving side, using the information as a key, the frequency band of the received signal is divided and the spectrum is inverted. A confidential transmission method characterized by performing decoding by re-inverting the spectrum of a zone and/or restoring the order.