JPH0761070B2 - Synchronous circuit of confidential communication device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a synchronizing circuit of a confidential communication device for maintaining confidentiality (privacy) of a call in wired or wireless communication.

(B) Conventional Technology In wired or wireless communication, if a proper receiving device is used, the content of communication is intercepted by anyone, and the confidentiality of a call is impaired. As a method to solve this problem, a circuit that scrambles the audio signal and sends it out, and even if this is received by a third party, the content is not understood as it is and the processed signal is reproduced (descrambling process). So-called scrambling technology has been conventionally used in which only a receiver having a circuit) can restore a voice signal. As a conventional confidential communication system,
For example, the journal of the Institute of Electronics and Communication Engineers (August 1982) "Secret Technology" (P8
32-P834) and IEICE Technical Report CS80-149 (1980 1
January) Various methods have been introduced in "About confidential methods". Since the voice information is composed of the spectrum and its change with time, the intelligibility as voice can be lowered by the scrambling process which changes the spectrum structure. From this point of view, examples of the scrambling method that has been practically used so far include a spectrum inversion method and a frequency division replacement method. For example, Japanese Patent Publication 58-8621
(H04K1 / 04) “Secret talk method with frequency correction function” and Japanese Patent Laid-Open No. 58-148541 (H04K1 / 04) “Secret talk circuit” relate to the spectrum inversion secret talk method, and Japanese Patent Publication No. 58-24984 (H04K1 / 06).
"Secret device" relates to a method of performing signal processing after dividing into a predetermined spectrum, and the technical report of the Institute of Electronics and Communication Engineers CS-80-14.
9 proposes a method for improving the frequency axis conversion processing by FFT processing after converting the audio signal into a digital signal once. Therefore, the spectrum inversion method cannot take a sufficient number of combinations (keys) for the secret story. The latter two methods have many keys,
It requires a lot of filters and requires an FFT processing circuit, resulting in a large circuit scale and high cost. There were also problems such as high power consumption. From these points of view, the applicant of the present application proposes as a scramble system that has a large number of keys and is excellent in confidentiality performance and has a simple circuit configuration, in Japanese Patent Application No. 57-164763 “Secretization communication method and device” (September 1982). 20th application),
Proposed Japanese Patent Application No. 57-184916 "Clock circuit for confidential communication system" (filed on October 20, 1982) and Japanese Patent Application No. 58-19702 "application for confidential communication" (filed on October 20, 1983) . This uses a variable delay circuit to periodically change the frequency of the clock that controls the delay time, compressing the time axis,
This is a method in which expansion is repeated to scramble the audio signal and send it out, and the receiving side performs descrambling processing.
In this method, in order to correctly restore the original voice on the receiving side, the signal processing opposite to that on the transmitting side should be performed.
It is necessary to synchronize the operation of the clock applied to the variable delay circuit on the transmitting side and the receiving side. For that purpose, the synchronization signal may be provided on the high frequency side outside the voice band and the synchronization signal may be constantly sent from the transmission side to the reception side, but the transmission band is widened. Therefore, a method of synchronizing the transmitting and receiving sides without widening the transmission band is required.

As a circuit system for synchronizing the transmitting and receiving sides without expanding the transmission band in response to such a request, the present applicant has previously filed Japanese Patent Application No.
-115070 "Synchronous circuit of confidential communication device" (H04K1 / 06 (filed on May 20, 1986) was proposed. This method time-compresses the audio signal transmission section on the transmission side and time-divisions the synchronization signal. This is a method of superimposing and transmitting in a multiplex method, and on the receiving side, the time axis expansion of the voice signal section is performed based on the synchronizing signal to perform the secret story restoration processing.

The configuration of the confidential communication device according to this method is shown in FIGS. 4 and 5. FIG. 4 shows a transmission system, and FIG. 5 shows a reception system. Fourth
5 and 5, (1) and (11) are sample and hold circuits, (2) and (12) are AD converters, and (3) and (13) are RAMs.
Storage means, etc., (4) (14) DA converters, (5) (15)
Is a low-pass filter, and (6) and (16) are storage means (3).
(13) Clock frequency control circuit for writing / reading clock, (7) Sync signal generating circuit, (8)
Is a circuit for adding the sync signal and the scrambled audio signal, and (17) is a sync signal detection circuit. A RAM is used as the storage means (3) (13). In the transmission system shown in FIG. 4, the signal is sampled and AD converted by the output of the clock frequency control circuit (6), and the RAM is
Clock frequency (f1) and RAM when writing to (3)
Scramble processing is performed by changing the clock frequency (f2) when reading from (3).

On the other hand, in the receiving system of FIG. 3, conversely, the audio signal is restored by writing to the RAM (13) at the clock frequency (f2) by the clock frequency control circuit (16) and reading at the clock frequency (f1). The scramble process on the transmitting side is performed by, for example, periodically changing the clock frequency (f2), and the secret key can be changed by changing the rate of change of (f2). Also, the clock frequency (f
RAM by making the average frequency of 2) slightly higher than f1
A gap occurs in the output data of (3) as shown in FIG. In the transmission system, a synchronization signal (for example, a sine wave having a predetermined frequency) is time-axis-multiplexed and transmitted in this gap. In the receiving system, the time-axis multiplexed synchronizing signal is detected, and the clock frequency control circuit (16) is preset to synchronize the clock frequency (f2) with the transmitting side to restore the audio signal.

(C) Problems to be solved by the invention When communication is performed using the secret communication device as described above,
A transmission system and a reception system are provided in one device, and bidirectional communication is often performed like a telephone. Further, in many cases, a two-line type transmission line such as a public telephone network is used to transmit the upstream and downstream signals on the same transmission line. In a two-wire type transmission line such as a public telephone network, a normal side tone is generated, and a part of the transmitted signal is mixed with its own reception signal and received.
When two-way communication is performed between the confidential communication device and the confidential communication device in such a state, as shown in FIG. 5, a transmission signal (a) of the confidential communication device and a transmission signal (b) of the confidential communication device. When and are operating independently of each other, for example, as shown in FIG. 7 (c), the synchronizing signal generated by itself is mixed with the scrambled audio signal and received. Since the synchronization signal is transmitted even in the silent state, it is heard as noise especially in the silent state or when the level of the audio signal is low. In addition, the self-generated sync signal may be detected as a sync signal sent from the other party, resulting in an erroneous sync state.

(D) Means for Solving the Problem In order to solve the above-mentioned problems, in the present invention, the confidential communication device is operated as a master, the confidential communication device is operated as a slave, and the transmission system on the master side is operated in a free-running state, and the slave The side presets the reception system at the timing of the received synchronization signal and also presets the transmission system to an appropriate state so that the position of the synchronization signal can be determined by the upstream and downstream signals as shown in FIGS. 2 (a) and 2 (b). Generally match. Also,
As shown in FIGS. 2A and 2B, if the positions of the sync signals are aligned with the upstream and downstream signals, they interfere with each other and the waveform of the sync signals is disturbed, which causes a problem that detection becomes difficult in the receiving system. In the present invention, as shown in FIGS. 2 (d) and (e), when the synchronization signal is inserted into the time gap generated in the transmission system and the scrambled voice signal is time-division multiplexed, every other one. The slave side and the master side alternately transmit the synchronization signal.

(E) Action Even if the side signal is generated in the 2-wire transmission line and the synchronization signal transmitted by itself is mixed in the reception signal by transmitting the synchronization signal as described above, the reception system generates it in the transmission system. Since the audio signal is restored by ignoring the portion of the time gap, the sync signal is not mixed as noise. Further, since the master side and the slave side alternately transmit the synchronization signals, there is no fear of the synchronization signals interfering with each other and disturbing the waveform.

(V) Example FIG. 1 shows an example of the present invention. FIG. 1 is a combination of the confidential communication device (transmission system) shown in FIG. 4 and the confidential communication device (reception system) shown in FIG. 5 for performing full-duplex confidential communication. In FIG. 1, the same numbers as those in FIGS. 4 and 5 indicate equivalent circuits. Also, the two switches (SW1) and (SW2) are opened when operating as a master and closed when operating as a slave. When the confidential communication device of FIG. 1 operates as a master, SW1 and SW2 are open, and the transmission system and the reception system operate completely independently. In the transmission system, a sync signal is inserted in the time gap created by raising the average frequency of the clock frequency (f2) to be slightly higher than (f1) as described above, and the sync signal is time-division multiplexed with the scrambled audio signal. Then, when sending out, as shown in FIG. 2 (d), they are inserted into every other gap. It should be noted that the gap where the sync signal is not inserted is kept silent.

When the confidential communication device in FIG. 1 operates as a slave,
Since SW1 and SW2 are closed, the reception system is preset at the timing of the received synchronization signal as described above, and the transmission system is also preset at an appropriate timing. As a result, the time gaps generated by the transmission system on the master side and the transmission system on the slave side can be made approximately the same, and when the synchronization signal is inserted by the transmission system on the slave side, the timing when the master side does not send the synchronization signal. By inserting the synchronization signal on the slave side into the time gap of, the master side and the slave side alternately transmit the synchronization signal as shown in FIGS. 2 (d) and 2 (e). Therefore, even if the signal transmitted by itself due to the side tone is mixed in the received signal, the synchronizing signal is not reproduced as noise, and the synchronizing signals do not interfere with each other. With the above operation, the problem that the sync signal is mixed as noise due to the sidetone during communication is solved, but the sync signal mixed by the sidetone is mistakenly detected at the time of synchronization pull-in, and the sync state is incorrect. There is a possibility of falling into. Therefore, in the present invention, the following processing is performed.

When the circuit of FIG. 1 operates as the master side, the transmission system (A) operates in the free-running state, and the synchronization signal is inserted at every other time gap generated as shown in FIG. 3 (f). To send. When the synchronization signal is detected by the reception system (B) on the master side, as shown in FIG. 3 (g), the transmission system transmits the synchronization signal only near the gap where the synchronization signal is not inserted. The sync signal is detected only in the vicinity of the timing expected. As a result, the master side can correctly perform synchronization without erroneously detecting its own synchronization signal mixed by sidetone.

On the other hand, when operating as a slave, the receiving system (B) always detects a sync signal at the time of synchronization pull-in. Further, at this time, the operation of the clock frequency control circuit (16) of the receiving system (B) is not fixed and the timing of generating the synchronizing signal is also not fixed. Therefore, the transmitting system (A) is prohibited from generating the synchronizing signal. After the synchronization of the receiving system (B) is established, the generation timing of the sync signal is controlled, and the sync signal is generated only near the timing at which the master side is expected to send the sync signal as shown in FIG. Is detected. As described above, according to the present invention, stable detection of the sync signal can be performed.

Although the confidential communication device has been described above, it is needless to say that the present invention can be applied to devices using a similar synchronization method other than the confidential communication device.

(G) Effect of the Invention According to the present invention, a time gap is provided in the scrambled confidential voice at a constant cycle, and a synchronization signal is time-division-multiplexed in the time gap to be transmitted. In full-duplex communication using a transmission line having sidetone or crosstalk such as a two-wire transmission line in a confidential communication device that synchronizes with each other, one side operates as a master and the other side operates as a slave. By inserting the synchronization signal in every other gap and inserting the synchronization signal in the gap at the timing when the master side does not send the synchronization signal on the slave side and transmitting it, the synchronization signal mixed by sidetone etc. is reproduced as noise. Also, since the master side and the slave side alternately transmit the synchronization signals, there is no interference between the synchronization signals. Further, by detecting the synchronization signal only near the timing when the other party seems to be transmitting the synchronization signal, there is no erroneous detection of the own synchronization signal mixed with side sounds or the like.

[Brief description of drawings]

FIG. 1 is a block circuit diagram of a synchronizing circuit of a secret communication device of the present invention, FIGS. 2 and 3 are drawings for explaining the circuit, and FIG. 4 is a block diagram of a conventional synchronizing circuit, and FIG. , FIG. 6 and FIG. 7 are explanatory views of a conventional block circuit. (1), (11) ... Sample and hold circuit, (2), (1
2) ... AD converter, (3), (13) ... RAM, (4), (14)
… DA converter, (5), (15)… Low-pass filter,
(6), (16) ... Clock frequency control circuit, (7) ... Synchronous signal generation circuit, (17) ... Synchronous signal detection circuit.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H04L 9/12 (56) References JP 62-271534 (JP, A) JP 63- 261934 (JP, A) JP-A-61-48250 (JP, A)

Claims (3)

[Claims] 1. A first memory circuit comprising a memory element which stores an audio signal sampled and stored in synchronization with a clock pulse, and which is read out at a predetermined timing and is associated with an address, and a write address of the memory circuit. A first address control circuit that generates a read address and a write address and a read address that are generated from this address control circuit are made different in time change to convert the frequency of the audio signal, thereby outputting the audio signal in a secret state. And a circuit for providing a time gap in the output signal of the first memory circuit and time-division-multiplexing and transmitting the synchronization signal during the gap, and the first memory circuit and the first address control circuit. A second memory circuit and a second address control circuit having the same configuration as the above are provided, and a voice signal in a secret state and a synchronization signal are time-division multiplexed. By detecting a sync signal from the signal signal, first has a function to restore the audio signal of privacy while reception control to the operation of the second address control circuit 1
When the confidential communication device and the second confidential communication device having the same function as the first confidential communication device are connected using a two-wire transmission line to perform full-duplex communication of the confidential voice signal, 1
A synchronization circuit for a confidential communication device, wherein the confidential communication device and the second confidential communication device substantially match the timing of generating the time gap. 2. The first confidential communication device is a master, the second confidential communication device is a slave, and the timing at which the second confidential communication device causes a time gap is a synchronization received by the second confidential communication device. The synchronization circuit for a confidential communication device according to claim 1, wherein the synchronization circuit substantially matches the signal timing. 3. The second confidential communication device when the synchronizing signal is inserted into every other gap when the synchronizing signal is inserted into the time gaps provided at regular intervals in the first confidential communication device. 3. The synchronizing circuit for a confidential communication device according to claim 2, wherein the first confidential communication device inserts and outputs the synchronizing signal in a time gap between the timings at which the synchronizing signal is not inserted.