JPH0237145B2 - - Google Patents

Description

[Detailed Description of the Invention] (1) Technical Field of the Invention The present invention divides the frequency spectrum of information into a plurality of parts, and when rearranging the order, uses relatively simple means such as inserting a pseudo spectrum to improve the quality of information. Concerning a method for secret transmission.

(2) Prior art and problems For the audio frequency spectrum (up to 4KHz), such as that used in telephone calls, a large number of bandpass filters, such as 10 to 20, are used to divide the band, and then each subband The arrangement order of the data was changed and sent to the transmission line. Since the arrangement and replacement order are known in advance on the receiving side, subdivision and replacement are performed using a bandpass filter. This replacement order is also changed over time to improve confidentiality. However, this method had the drawback that if there was even the slightest hint that a Japanese person was talking on a particular topic, a trained person could decipher the contents of the call by listening to it over and over again.

(3) Purpose of the Invention The purpose of the present invention is to improve the above-mentioned drawbacks and to provide a secret transmission system that can improve the confidentiality of information by simple means such as inserting a pseudo spectrum.

(4) Structure of the invention The structure of the present invention to achieve the above object is as follows:
The transmitting side inserts a pseudo spectrum into the information to be transmitted, divides it into multiple frequency bands, rearranges the arrangement order according to the prescribed standard, and sends it out to the transmission path, and the receiving side inserts the pseudo spectrum into the information to be transmitted. In a secret information transmission method in which the predetermined rules are reversed to convert the information spectrum to the transmitter's information spectrum and pseudo-spectrums are removed, the transmitter's side converts the original spectrum signal to the 1800 to 2400 Hz band where the power of the audio spectrum is low. After restricting the passage of the frequency band and inserting a pseudo-spectral signal instead to make the total transmission power constant on the transmission path, and further changing the arrangement order of the plurality of frequency bands according to a predetermined rule. A means is provided for transmitting the signal to the transmission path, restoring the arrangement order of the frequency spectrum on the receiving side, and deleting the pseudo spectrum.

(5) Embodiment of the Invention FIG. 1 shows a frequency spectrum when the information is the voice of a telephone conversation, as an embodiment of the present invention.
FIG. 2 is a configuration diagram of the transmitting side showing the configuration of an embodiment of the present invention, FIG. 3 is a configuration diagram of the receiving side, and FIG. 4 shows the frequency spectrum of each part. As shown in FIG. 1, when making a telephone conversation, the frequency band used is limited to 300 to 4000 Hz. The amplitude or power for each frequency is not constant, especially from 1800 to
As shown in the figure, 2400Hz has a valley-like low power level. Therefore, even if this part of the frequency band is not transmitted to the receiving side,
The reception quality hardly changes. Focusing on this, the present invention adopts a configuration in which the frequency band is once removed and then a pseudo spectrum is inserted. FIG. 2 shows a configuration for performing digital processing as an embodiment of the present invention, 1 is a sound source, 2 is an analog-to-digital converter, and the intermediate frequency spectrum between the sound source 1 and the analog-to-digital converter is shown in FIG. , but is reproduced in Figure 4A. In FIG. 2, 3 is a serial/parallel conversion section, 4 is a fast Fourier transform (FFT) section, 5 is an unnecessary spectrum removal section, 6 is a sound source signal power calculation section, 7 is a pseudo spectrum generation section, 8 is an addition section, 9 is a spectral order reordering unit, 10 is an inverse fast Fourier transform unit, and 11 is a parallel/
12 is a digital/analog converter, and 13 is a transmission line. Thin arrow indicates signal 1
Samples flow one by one, and the thick arrow indicates that 256 samples flow as one block. A/
The D converter 2 samples audio up to 4000 Hz using a sampling frequency of 8 kHz.
256 pieces of data every 125 μS are obtained every 32 mS, and this data is made into one block of a serial signal, which is converted into parallel data in the serial/parallel converter 3, and then fast Fourier transform is performed. At this output (point B), the spectrum shown in FIG. 4B is obtained. For mathematical processing, 256 frequencies are arranged at 31.25 Hz intervals between -4 kHz and +4 kHz, but since positive and negative frequency components are mutually exclusive, only the positive components will be considered here.

1800-2400Hz in unnecessary spectrum removal section 5
The 19 spectral signals corresponding to
get. This signal is applied to one of the power calculation section 6 and the addition section 8. The power calculation unit 6 calculates the power P for each input signal for each block,
The signal is input to the pseudo spectrum generator 7. The pseudo spectrum generator calculates x=(Po-P)/N using a predetermined expected maximum power Po of the input signal. However, N refers to the number of samples removed by the unnecessary spectrum removal section 5, 19. Then, N pseudo spectra of equal amplitude x are created and applied to the other side of the adder 8 as the spectrum shown in FIG. 4D. The adder 8 adds the two signals and interchanges the spectra shown in FIG. 4E for each block according to a predetermined rule. Since an irregular spectrum as shown in FIG. 4F is obtained, it is then inversely transformed in an inverse fast Fourier transformer 10, converted into a serial signal (11), and then subjected to D/A conversion (12). It is then sent out to line 13 (see FIG. 4G).

The receiving section has the configuration shown in FIG.
Perform the reverse signal transformation shown in the figure. That is, the A/D converter 15
Using a sampling frequency of 8kHz, the digital signal is converted into a digital signal, and then the serial/parallel converter 16 converts it into a 256
Divide each sample into blocks. The fast Fourier transform section 17 transforms the signal, resulting in the signal spectrum shown in FIG. 4F. The spectral order restoring unit 18 returns the spectral arrangement order to the original according to the above-mentioned predetermined rules,
Figure 4E is obtained. When the pseudo spectrum removing section 19 removes the portion corresponding to 1800 to 2400 Hz, FIG. 4C is obtained. The inverse fast Fourier transform unit 20 performs fast inverse Fourier transform on each block, and
Converted by serial converter 21, then D/A converter 22
An analog signal is obtained and output to the receiver 23 (see FIG. 4H). This signal is from the original audio
Although the frequency from 1800 to 2400Hz has been removed, experiments have shown that it is almost the same as the original audio.

Although fast Fourier transform is used to separate and extract frequency components in the above example, the same effect can be obtained even if a large number of bandpass filters are used.

The pseudo spectrum does not need to be uniform as shown in FIG. 4D, and can have any shape. The key is to prevent the total signal power shown in FIG. 4E from changing from block to block.

The arrangement order of the spectra can be further changed after a predetermined period of time has elapsed.

(6) Effects of the Invention In this way, according to the present invention, since the power of a specific frequency is changed before changing the arrangement order of information spectra, the spectrum after changing the arrangement order is the same as the spectrum of the original signal. It has changed considerably in comparison. Therefore, even if there is a slight hint about information, it is extremely difficult to decipher it, and confidentiality can be maintained better than before.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the frequency spectrum of a telephone conversation voice, FIG. 2 is a transmitting side block diagram showing the configuration of an embodiment of the present invention, FIG. 3 is a receiving side block diagram, and FIG. It is a figure which shows the frequency spectrum of each part about FIG.3. 1...Sound source, 2...Analog-digital conversion section, 4...Fast Fourier transform section, 5...Unnecessary spectrum removal section, 7...Pseudo spectrum generation section, 9
. . . Spectrum order reversing section, 10 . . . Inverse fast Fourier transform section, 13 . . . Transmission line, 23 . . .

Claims (1)

[Claims] 1. On the transmitting side, a pseudo spectrum is inserted into the information to be transmitted, the pseudo spectrum is divided into a plurality of frequency bands, the arrangement order is changed according to a predetermined rule, and the pseudo spectrum is transmitted to the transmission path, and the pseudo spectrum is transmitted on the receiving side. Now, in a secret information transmission method in which the frequency spectrum of a received signal is converted into an information spectrum for the transmitting side by reversing the above-mentioned predetermined rules, and pseudo-spectra are removed, on the transmitting side, when transmitting the information to be transmitted block by block, , the spectral power of the voice is small.
For the band from 1800 to 2400 Hz, a means is provided to limit the passage of the original spectrum signal and insert a pseudo spectrum signal instead, thereby making the total transmission power on the transmission path constant for each block, and furthermore, A secret transmission of information characterized in that the arrangement order of frequency bands is changed in accordance with a predetermined rule and then sent to a transmission path, and on the receiving side, a means is provided for restoring the arrangement order of frequency spectra and removing pseudo spectra. method.