JPH0774732A - Ciphering device - Google Patents

Abstract

PURPOSE:To avoid deterioration in a voice signal by multiplying a window function with each segment of the voice signal at a sender side, matching the position of the voice signals and replacing a waveform of several preceding pitches at a receiver side. CONSTITUTION:A window function is outputted from a window function generator 3 while keeping a relation in which a timing signal and a bottom level of the window function are coincident. The window function and a voice signal subject to A/D conversion 2 are multiplied by a multiplier 2 and a position equivalent to a joint of segments is suppressed. The result of multiplication is alternately written in a 1st buffer 4 and a 2nd buffer 5 one frame each. The content of each buffer is alternately read and given to a D/A converter 7 as a scrambled signal and the result is led to an LPF 8. Since the vicinity of the joint of segments is smoothly suppressed, no waveform distortion around the joint is caused even when the signal is filtered by the LPF 8. At the receiver side, a similar waveform in the vicinity thereof is copied to the joint of segments to joint smoothly the signal waveform.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secret communication device in voice communication, and more particularly to a secret communication device for scrambling and descrambling on a time axis.

[0002]

2. Description of the Related Art In recent years, the protection of information confidentiality in communication has become a social problem, and in voice communication in particular, there is an increasing demand for an effective confidential communication method for preventing eavesdropping by a third party. As one of the secret talk systems, there is scrambling on a time axis in which a voice signal is divided at a predetermined time interval and the order is changed. FIG. 3 shows a conventional example of a confidential communication device that performs such communication.

(1) Cryptographic key (see Table 1) The cryptographic key defines a method of scrambling (encryption). For example, as shown in Table 1, the audio signal is divided into segments. Prepare multiple types of indices consisting of the time interval Tn of each segment when doing and the order in which the segments are rearranged, and attach key numbers to each. Table 1 shows an example of an encryption key in which one frame is composed of 7 segments.

An example of a method of creating an encryption key will be described. Although not shown, for example, an encryption key setting means including a key number setting means, an index setting means and a storage means is provided, and a desired key number is input from the key number setting means. -Enter the index (time interval of segment division and order of segment rearrangement) corresponding to the key number. The data input in the above two steps is stored in the storage means in the format shown in Table 1. The encryption key setting means may be installed individually in the transmitter / receiver, or may be created by setting means prepared externally and only the storage means (for example, ROM) may be installed in the machine.

Each of the transmitting side and the receiving side has a key number table shown in Table 1, determines a key number prior to communication, and sets the key number in the transmitter and the receiver. Scramble and descrambling are done automatically.

[0006]

[Table 1]

(2) Transmission side of confidential device (see FIG. 3) The configuration and operation of the conventional device will be described by taking the case where the key number "01" is set from the encryption keys shown in Table 1 as an example. The audio signal (analog signal) is converted into a digital signal by the A / D converter 1 and guided to the first buffer 4 and the second buffer 5. An example of a voice signal waveform is shown in FIG.
Shown in.

The index generator 9 includes storage means and reads out the index corresponding to the set key number (01) from the storage means. Further, the index generator 1 outputs a signal for switching the read / write of the first buffer 4 and the second buffer 5 and a signal for switching the switch 6 for each frame (7 segments). First state: When the first buffer 4 is write, the second state
The buffer 5 is read, and the switch 6 is switched to the second buffer 5 side. Second state: when the first buffer 4 is read, the second state
The buffer 5 is written, and the switch 6 is switched to the first buffer 4 side. When the signal of the first state is output from the index generator 9, A
The output of the / D converter 1 for one frame (7 segments) is written in the first buffer 4. Meanwhile, the contents of the second buffer 5 are sequentially read. When the index generator 1 outputs the signal in the second state, the subsequent output of one frame (7 segments) of the A / D converter 1 is written in the second buffer 5. Meanwhile, the contents of the first buffer 4 are sequentially read.

The address generator 10 generates the addresses of the first buffer 4 and the second buffer 5 according to the index from the index generator 9. The write address is specified as follows. Divided segment Sorting order Write address 1st segment 4th 400 to 499 2nd segment 6th 600 to 699 3rd segment 1st 100 to 199 4th segment 5th 500 to 599 5th segment 3rd 300th to 399th segment 7th segment 700th to 799th segment 7th segment 2nd segment 200 to 299 Output signals of the A / D converter 1 are sent to the respective buffers according to the rearrangement order (key number 01) shown in Table 1. I will write it. The read address is sequentially generated from the lower address to the upper address. The procedure of generating the write address and the read address may be reversed. That is, the write address is sequentially generated from the lower address to the higher address, and the read address is generated in the segment rearrangement order.

In this way, the first buffer 4 and the second buffer 4
The digital signal scrambled alternately by one frame (7 segments) can be taken out from the buffer 5 of. This signal is converted into an analog signal by the D / A converter 7,
A high pass signal component is removed by an LPF (Low Pass Filter) 8. An example of a signal (scrambled) waveform converted into analog by the D / A converter 7 is shown in FIG.
At the output terminal, an analog signal is displayed which is divided into segments at the time interval defined by the key number 01, and each segment is rearranged. When the transmitting side is a wireless transmitter, the carrier signal is modulated by the signal obtained at the output terminal and transmitted from the antenna.

(3) Receiving side of confidential communication device (see FIG. 3) The receiving side has the same configuration as the transmitting side shown in FIG. 3, but the descrambling operation is different. On the receiving side, a key number that has been negotiated with the transmitting side in advance is set in the index generator 9. The configuration and operation of the conventional device will be described by taking as an example the case where the key number “01” is set, which is given as an example in the description of the transmitting side.

The scrambled audio signal (analog signal) is converted into a digital signal by the A / D converter 1 and guided to the first buffer 4 and the second buffer 5.
When the receiving side is a radio receiver, a signal obtained by demodulating the signal induced in the antenna after frequency conversion into an intermediate frequency signal corresponds to the scrambled voice signal.

The index generator 9 includes storage means and reads out the index corresponding to the set key number (01) from the storage means. Further, the index generator 1 outputs a signal for switching the read / write of the first buffer 4 and the second buffer 5 and a signal for switching the switch 6 for each frame (7 segments). First state: When the first buffer 4 is write, the second state
The buffer 5 is read, and the switch 6 is switched to the second buffer 5 side. Second state: when the first buffer 4 is read, the second state
The buffer 5 is written, and the switch 6 is switched to the first buffer 4 side. When the signal of the first state is output from the index generator 9, A
The output of the / D converter 1 for one frame (7 segments) is written in the first buffer 4. Meanwhile, the contents of the second buffer 5 are sequentially read. When the index generator 1 outputs the signal in the second state, the subsequent output of one frame (7 segments) of the A / D converter 1 is written in the second buffer 5. Meanwhile, the contents of the first buffer 4 are sequentially read.

The address generator 10 generates the addresses of the first buffer 4 and the second buffer 5 according to the index from the index generator 9. The write address is specified as follows. Scrambled descrambling Write address Segment reordering order 1st segment 3rd 300-399 2nd segment 7th 700-799 3rd segment 5th 500-599 4th segment 1st 100-199 5th Segment 4th 400 to 499 6th segment 2nd 200 to 299 7th segment 6th 600 to 699 The output signals of the A / D converter 1 are arranged according to the rearrangement order (key number 01) shown in Table 1. Write to each buffer. The read address is sequentially generated from the lower address to the upper address. The procedure of generating the write address and the read address may be reversed. That is, the write address is sequentially generated from the lower address to the higher address, and the read address is generated in the segment rearrangement order.

In this way, the first buffer 4 and the second buffer 4
The descrambling digital signal can be taken out alternately from the buffer 5 of each frame by one frame (7 segments). This signal is converted to an analog signal by the D / A converter 7, and the high frequency signal component is removed by the LPF 8. At the output terminal, an analog signal, which is divided into segments at the time interval defined by the key number 01, and in which each segment is rearranged, that is, a signal obtained by restoring the original voice signal on the transmission side appears. This is called descrambling or descrambling. The output signal can be heard by loudspeakers or headphones.

(4) Synchronous signal On the receiving side, the scrambled voice signal is divided into segments, and the order of arrangement of the segments is restored based on the encryption key (descrambling). At this time, it is necessary to know the timing of the start of each segment so that the transmission can be divided at the same position as the divided position. Therefore, generally, the synchronization signal is transmitted from the transmitting side. An example of transmission and reception of the synchronization signal will be described. In the case of wireless communication, the transmission side frequency-modulates (FM) a carrier signal with a synchronization signal (generally several Hz), and the reception side FM-detects the intermediate frequency signal to reproduce the synchronization signal and then obtain a timing signal. ing.

[0017]

It is necessary to make the occupied bandwidth as narrow as possible in order to increase the number of channels of a line in wired communication and to improve the utilization efficiency of frequency resources in wireless communication. In the case of voice communication, the upper limit frequency of the voice band is set near 3 kHz. Therefore, on the transmitting side, the LPF is provided, as described above, in order to block high frequency components of the audio signal that is the modulated signal.
Further, the wireless receiver is provided with an LPF to prevent interference with adjacent channels.

When scrambling is performed on the time axis, FIG.
As shown in (b), when the signal becomes discontinuous at the segment joint and this discontinuous signal is filtered by the LPF, the waveform distortion after the joint expands in the time axis direction, and The sound quality deteriorates significantly. The state of waveform distortion at the segment joint is shown in FIG.

Further, when the synchronization is slightly deviated (when the position at which each segment is divided when descrambled is different from the position at which each segment is divided when scrambled), the signals of the adjacent segments are joined to each other. Since it is included in the section, the reproduced sound quality is significantly deteriorated. An object of the present invention is to provide a secret-talking device in which deterioration of sound quality due to the discontinuity of the signal waveform at the above-mentioned segment joint is reduced.

[0020]

In order to solve this problem, the present invention is shown in FIG. 4 (a), in which voice signals are highly correlated (especially in Japanese, the ratio of voiced sounds is high). This feature is utilized, paying attention to the feature that similar waveforms are repeated. That is, the transmitting side is provided with means for multiplying the voice signal by a window function (a window having a raised cosine characteristic) at a position corresponding to the junction for each segment. Then, the receiving side is provided with means for replacing the waveform of the voice signal several pitches ago by aligning the position with the segment joint portion suppressed by the window function.

[0021]

On the transmitting side, the voice signal is multiplied by a window function (a window having a raised cosine characteristic) for each segment,
The discontinuous signal at the segment junction is suppressed. Since the discontinuous signal at the segment joint is removed,
Even when filtered by the LPF, the distortion of the segment joint does not expand in the time axis direction. On the receiving side, the suppressed audio signal of the segment joint is reproduced by aligning the positions and replacing the waveform several pitches ago. Since the voice signal at the segment junction removed on the transmitting side is reproduced by replacing a similar waveform several pitches ago, the voice quality does not deteriorate.

[0022]

EXAMPLE An example will be described with reference to FIG. (1) Transmitting side of confidential device The difference from the prior art shown in FIG. 3 is that the window function generator 3 is
It is provided with a means (multiplier 2) for suppressing the junction of each segment by the window function. Since other configurations and operations are the same as those of the conventional art, the description thereof will be omitted and only the difference will be described in detail.

The window function generator 3 generates a window function having a waveform as shown in FIG. The leading edge a of the waveform is −π / 2 to 0 of the cosine square wave, and the trailing edge c is 0 to + π of the cosine square wave.
It corresponds to the / 2 portion and changes gently between 0 and 1. The flat portion b has a variable length in the time axis direction in relation to the time interval Tn when the audio signal is divided into segments. The horizontal axis (time axis) direction of the window function waveform is divided at predetermined intervals, and the vertical axis direction data (0 to 1) corresponding to each division point
Is stored in the memory in advance and is read with a predetermined clock signal to obtain a window function (digital signal).

The window function and the audio signal converted into the digital signal by the A / D converter 1 are guided to the multiplier 2 where they are multiplied. The output of the multiplier 2 (multiplication result) is
It is guided to the first buffer 4 and the second buffer 5.

Next, details of the junction between the window function and the segment will be described with reference to FIG. Timing signal (a) is
It occurs at the position corresponding to the joint of each segment.
Incidentally, the synchronizing signal generally has a longer cycle than the timing signal (the cycle corresponding to one frame or two frames). Therefore, the synchronization signal is obtained by dividing the timing signal by the number of segments forming one frame.

The timing signal and the bottom of the window function (d in FIG. 5).
Window function (b) while maintaining a relationship such that
Are output from the window function generator 3. The window function (b) and the audio signal (c) are multiplied by the multiplier 2. The multiplication result is
As shown in FIG. 6D, the position corresponding to the joint portion of the segment is suppressed.

The multiplication result is 1 in the first buffer 4 and the second buffer 5 as described in (2) Transmission side of the conventional example.
It is written alternately frame by frame. The contents of each buffer are read out alternately, subjected to D / A conversion as a scrambled signal, and then introduced to the LPF 8. Since the vicinity of the junction of the segments is smoothly suppressed, LP
Waveform distortion near the junction does not occur even if it is filtered by F8.

In the above embodiment, the position corresponding to the splicing part of the audio signal is suppressed in advance by the window function, and then scrambled (permuted). As another embodiment, the procedure may be reversed, that is, after scrambling (permuting) the audio signal, the vicinity of the joint may be suppressed by the window function. As a configuration, the output of the A / D converter 1 is guided to the first buffer 4 and the second buffer 5, and the output of the switch 6 is guided to the multiplier 2. That is, the multiplier 2 is provided in all stages of the D / A converter 7.

(2) Reception side of confidential device The difference from the prior art shown in FIG. 3 is that the lag calculator 22, the controller 23, and a part of the unsuppressed signal at the joint of each suppressed segment. Is provided with a means for copying (data replacement unit 21). Since other configurations and operations are the same as those of the conventional art, the description thereof will be omitted and only the difference will be described in detail.

The voice signal has a very high correlation in the case of voiced sound, and similar waveforms appear repeatedly. A group of repeating similar waveforms is called a pitch. Utilizing this feature, at the joint of each segment suppressed on the transmitting side,
A similar waveform portion in the vicinity thereof is copied to smoothly connect signal waveforms.

An embodiment will be described with reference to FIGS. 2 and 7. As described on the receiving side (3) in the conventional example, the descrambled voice signal (however, the splicing portion of the segment is suppressed) appears on the switch 6. A similar waveform near the junction is copied, but it is necessary to identify the position of which part of the waveform is similar. As a method for identifying this position, an autocorrelation method, a cepstrum method, an AMDF (Average Magnitude Difference Function)
)and so on. Here, AMDF will be described as an example.

As shown in FIG. 7 (a), two fixed windows, area I and area II, are provided immediately before the junction of the segments, and digital data arriving in each area is stored in the lag calculator 22. It is stored in the memory provided in. The position where the window is provided is determined based on the time interval Tn that divides the junction and the segment that occurs one time before. Next, the movement amount kp of the waveform is calculated using the equation 1. This calculation is achieved by correlating the data stored in the memory with the data that reaches the lag calculating unit 22 at that time.
When the data stored in the memory is moved backward by kp on the time axis, the waveform of the area II in FIG. 7A and the waveform of the area I in FIG. 7B match after the wavy line. At this time, the data in the period W in the area II in FIG. 7B is replaced (overwritten with data) by the data replacement unit 21 at the junction of the segments.

[0033]

[Equation 1]

Although not described in detail, if the timing signal generated based on the synchronization signal from the transmitting side is applied, the above-mentioned segment junction can be identified. Furthermore, the waveforms of the rising and falling parts of the window function generated on the transmitting side are
It is constant regardless of the time interval Tn when dividing into segments. If the waveform is stored in the storage means on the receiving side, the data replacement position W can be set based on the timing signal.

It can be intuitively understood that the waveform of FIG. 7A has a discontinuous portion, but the waveform of FIG. 7C restored by replacing the waveform has a discontinuous portion. It turned out to be difficult to find, and if you actually heard it, the sound quality improved considerably. As a result of the simulation, the discontinuity noise at the junction is about 20d.
B improved. When the waveform was not replaced, a noise called variability was generated, but it was confirmed that the noise almost disappeared when the waveform was replaced.

[0036]

According to the present invention, the transmitting side is provided with means for suppressing the junction of each segment with respect to the voice signal by the window function (window having a raised cosine characteristic).
Since the receiving side is provided with means for replacing the voice signal of the splicing part of the segment suppressed by the window function with the waveform of several pitches in front of the position, the transmitting side has a problem in the segment splicing part. Even if the continuous signal is removed and filtered by the LPF, the waveform distortion of the segment junction does not expand in the time axis direction,
At the receiving side, the voice signal at the splicing part of the segment suppressed at the transmitting side is restored, and the voice quality does not deteriorate.

[0037]

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a transmission side of the present invention.

FIG. 2 is a block diagram showing an embodiment of a receiving side of the present invention.

FIG. 3 is a block diagram showing a conventional confidential communication device.

FIG. 4 is a waveform chart showing a scramble mode.

FIG. 5 is a waveform diagram of a window function.

FIG. 6 is a timing chart showing a mode of windowing.

FIG. 7 is a timing diagram showing an aspect of waveform replacement.

[0038]

[Explanation of symbols]

 1 A / D converter 2 Multiplier 3 Window function generator 4 First buffer 5 Second buffer 6 Switch 7 D / A converter 8 LPF 9 Index generator 10 Address generator 11 A / D converter 14th 1 buffer 15 2nd buffer 16 switch 17 D / A converter 18 LPF 19 index generator 20 address generator 21 data replacer 22 lag calculator 23 controller

Claims (1)

[Claims] 1. A scrambler on a time axis is executed by holding an input audio signal, dividing the audio signal into a plurality of segments, and changing the arrangement of the plurality of segments from the input order. A scrambler (4, 5, 9, 10) for outputting a scrambled signal on the time axis, a window function generator (3) for generating a window function for suppressing a signal at the segment and the junction portion of the segment, and the voice. A transmitter having a multiplier (2) for multiplying the signal by the window function, and a descrambler (14,15,1) for receiving the scrambled signal on the time axis and descrambled
9 and 20) and the window function to perform the waveform replacement on the audio signal portion suppressed by the multiplier, the lag calculation for obtaining the movement amount of the predetermined portion of the waveform output from the descrambler with respect to the time axis. Bowl (22,23)
And a data replacer for substantially outputting the audio signal by replacing the waveform obtained by moving the predetermined portion by the movement amount in response to the output waveform from the descrambler and the output from the lag calculator. A secret-talking device including a receiver having (21).