JP2832447B2 - Secret communication control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Purpose of the Invention] [Industrial application field] The present invention relates to a communication apparatus such as a facsimile apparatus that transmits image information using a public telephone line, for performing confidential communication. The present invention relates to a secret communication control device to be used, and more particularly, to a secret communication control device capable of hiding its own existence.

[Prior Art] Various means for encrypting / decrypting communication information have been conventionally proposed. In a facsimile apparatus, for example, Japanese Patent Application Laid-Open No. 59-221167 discloses a facsimile apparatus having a concealment function. The technology disclosed in Japanese Patent Application Laid-Open Publication No. H10-209686 is known.

Further, as one encryption communication system, Japanese Patent Application Laid-Open No. 61-15438
The technology disclosed in Japanese Patent Application Laid-Open Publication No. H10-209686 is known. This discloses that a large number of different public encryption keys are stored in the device for each communication partner, and the encryption key is automatically selected when the communication partner is specified by a dial operation or the like. .

[Problem to be Solved by the Invention] By the way, when performing confidential communication, if the special device is located at a position where it can be seen by a third party, it is difficult for the third party to perform confidential communication using that device. Will be known.
That is, there is a possibility that the concealment device may be stolen by a malicious third party, or its operation may be detected, and the contents of the confidential communication may be eavesdropped and decoded.

By the way, the present inventors have already invented a concealment device of the type inserted in the middle of a communication line (public communication line) connecting a facsimile and an exchange. In the case of this concealment apparatus, since encryption / decryption is performed via communication between facsimile machines, confidential communication can be performed using a conventional facsimile as it is. Moreover, since the device is inserted in the middle of the communication line, the concealment device can be completely separated from the facsimile main body, and the concealment device can be hidden from the eyes of a third party.

However, in order to perform practical confidential communication,
It is necessary to specially provide a switch for giving an instruction to the concealment device, a display for confirming an input operation, and the like. For example, when the key to be used differs depending on the communication partner, a switch operation is required to specify the key. For this reason, even if the concealment device is separate from the facsimile, in order to actually perform the confidential communication operation, the concealment device must be arranged near the facsimile main body which can be seen by a third party. There are difficulties.

Therefore, the present inventors have further developed a device that can remotely control the operation of a concealment device inserted on a line by operating a dial key of a telephone provided on the facsimile main body. However, in the case of this device, information such as an ID code is included in the tone signal output on the communication line by the dial key operation for remote control of the concealment device, and the cutoff switch is communicated so that it does not leak to the outside. When the signal is inserted into a line and a signal for remote operation passes through the communication line, the communication line needs to be disconnected from the line of the exchange.

However, if the local station's telephone is disconnected from the line, even if there is a call from the other party, the call is not transmitted to the telephone, so the operator at the local station cannot know the call, and Means that the own station side is in the absence state.

The present invention provides a confidential communication control device that can be remotely operated from a telephone, prevents leakage of an ID code or the like to the outside at the time of remote operation, and prevents remote control from being performed even during remote operation. It is an object to enable communication when there is a call.

[Structure of the Invention] [Means for Solving the Problems] In order to solve the above problems, in the present invention, one end is connected to a partner communication unit via an exchange, and the other end is connected to a local station communication unit. Modulation / demodulation means connected to the communication line; tone detection means connected to the communication line for detecting a tone signal applied to the communication line and identifying the type of the tone; Disconnection switch means interposed at a position closer to the exchange than the connection position of the tone detection means; call detection means connected to a position closer to the exchange than the interposition position of the interruption switch means on the communication line; Encryption processing means for encrypting the original information and decrypting the encryption to restore the original information; controlling the cutoff switch means based on the information detected by the tone detection means, and at least Identifying key information to be used in the encryption process; monitoring the output of the call detecting means when the cutoff switch means is blocking the communication line, and detecting the call signal, and transmitting it to the local station side communication means. After the key information is specified, the modulation / demodulation means and the encryption processing means are controlled to input the encryption information to be applied to the communication line by the other communication means via the modulation / demodulation means, and Decoding through processing means, applying the decoded information to the communication means of the own station through the modulation and demodulation means, the transmission information output by the communication means of the own station to the communication line through the modulation and demodulation means And electronic control means for transmitting the encrypted transmission information to the communication means on the other side through the modulation / demodulation means.

According to the present invention, the concealment device includes a communication line, that is, tone detection means for detecting a tone signal on a telephone line, so that a terminal (for example, a telephone) connected to the same communication line Can be detected. A general facsimile machine is equipped with a telephone, and when it is a touch phone, its dial key (0,1,2,3,4,5,6,7,8,9, ♯, * ), A tone signal corresponding to the operated key is output on the communication line. Therefore, in such a case, by operating the dial key of the telephone, a control signal can be transmitted to a separate concealing device via the communication line. In the present invention, key information used for encryption / decryption of confidential communication is specified using the control signal. In other words, since the operation of the concealment device can be performed from a dial key on a separate telephone, it is not necessary to arrange the concealment device at a position accessible to the facsimile operator, and it is not visible to a third party. Can be hidden in position.

When this remote operation is performed, a part of the communication line is cut off by the cut-off switch means, so that there is no danger that information such as an ID code output by key operation of the telephone leaks on the line on the exchange side.

Further, when the cutoff switch means cuts off the communication line, the call detection means connected to a position closer to the exchange than the cutoff switch means detects the presence or absence of a call signal from the exchange side, and when the call signal is detected, This is reported to the communication means of the own station. Therefore, even if the operator of the local station remotely controls the concealment device, if there is a call from the other party, it is possible to know the call, so that the remote operation is interrupted and the call is answered. Can be.

In an embodiment to be described later, when a call is made from the other party, a special signal is output on a communication line to notify the operator of the local station of the call. Also, within a predetermined period of time after notification of the call, on-hook of the local station side communication means (line release).
Is detected, the interruption of the communication line by the interruption switch means is automatically released. In this case, the local station side operator can hear the notification sound of the call with the handset, and in response, hangs up the handset, and the communication line is connected to the exchange,
A ringing tone is generated by the telephone, and the telephone is picked up again (off-hook), so that normal communication can be performed.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

[Embodiment] Fig. 1 shows the configuration of the entire communication system when facsimile communication is performed using the concealing device of the embodiment.

Referring to FIG. 1, a facsimile machine (FAX) for communicating with each other is connected to a public telephone line connected to an exchange, and between each facsimile connected to the telephone line and the exchange, A security device is inserted. Each of the facsimile devices shown here is a commercially available device having a G3 mode defined by CCITT, and has not been modified at all. That is,
Simply by inserting the concealment device of the embodiment on a telephone line, confidential communication can be performed using an existing facsimile device.

The facsimile apparatus is provided with a general telephone equipped with a numeric keypad KT. Numeric keypad KT has 1,2,3,4,5,
Each of the keys 6, 7, 8, 9, 0, *, and ♯ is provided, and when each key is pressed, a tone signal in which two types of frequencies are superimposed is output as a dial signal on the line. The correspondence between the frequency of the tone signal and each key is shown in Table 1 below.

FIG. 2 shows an outline of the configuration of the concealment device provided on each of the transmission side and the reception side. Referring to FIG. 2, the concealment devices on the transmission side and the reception side have the same configuration. That is,
Each concealment device includes two modems (modulation / demodulation devices), a control device (CPU), and a unit having functions of signal bypass, encryption, and decryption.

When performing confidential communication, the transmitting side inputs image information, that is, a message, transmitted by the facsimile onto the line via a modem, and transmits the encrypted information to the line via another modem. On the receiving side, the encrypted information appearing on the line is input via a modem, decrypted to reproduce the transmitted image information, and the reproduced information is connected to the facsimile via another modem. On the line. Therefore, each facsimile performs only a normal operation, but the message is encrypted on the line between the two concealment devices, and confidential communication is performed.

FIG. 15 shows the appearance of one concealment device shown in FIG. Referring to FIG. 15, on the upper surface of the concealment device 50,
Numeric keypad ST having 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, ♯ and * keys, mode switches SA, SB, SC, SD, SE, and numeric display DP
1, and indicator DP2. Mode switch S
Each of A to SE has a display lamp (light emitting diode)
Is built-in. In addition, a switch SCH, a buzzer BZ, and two insertion ports J1 and J2 are provided on the front surface of the apparatus. J1 is connected to a public telephone line, and J2 is connected to a facsimile. A connector 51 is provided on a side surface of the device, and a memory card 130 is detachably attached to the connector 51.

Next, the configuration of the security device shown in FIG. 3 will be described. A relay RY3 is inserted between the public telephone lines LN1 and LN2 connected to the exchange via the outlet J1 and one end of the lines Li1 and Li2 inside the concealment device, and when the relay RY3 is off, Li1, Li2 and lines LN1, LN2 are connected, and when RY3 is turned on, those connections are cut off.

A line connected to the local facsimile via the inlet J2
A relay RY2 is interposed between LF1 and LF2 and the lines Li1 and Li2 inside the security device. Lines LF1, L on the facsimile side
F2 is connected to a common contact of relay RY2, and lines Li1 and Li2 are connected to one contact of RY2. Further, a line LiB inside the concealment device is connected to the other contact of the relay RY2. In this example, when relay RY2 is off, lines Li1, Li2
Are connected to lines LF1 and LF2, and when RY2 is on, line LF1,
LF2 and line LiB are connected.

Further, the lines Li1 and Li2 are connected to the line LiA inside the concealment device via the normally open contact of the relay RY1. The telephone lines LN1 and LN2 have a polarity inversion detection circuit 210.
And a call detection circuit 220, and a current supply circuit 230 is connected to the line LiB inside the security device.
Further, a tone receiver 190 for detecting a dial tone output from a facsimile telephone and identifying a type of a key is connected to the lines LF1 and LF2.

Other components of the security device include a microcomputer (CPU) 100, a ROM 110, a RAM 120, a memory card 130,
Power supply 140, random number generation circuit 150, input / output interface (I /
O) 180, modems 300 and 400, buffer circuit 500, and encryption / decryption processing circuit 600 are provided.

The two modems 300 and 400 are each CCITT V27ter or G3
It has a communication function that complies with the standard.

The data bus of microcomputer 100 has buffer 5
It is connected to the data bus DBM1 of the modem 300 and the data bus DBM2 of the modem 400 via 00. Therefore, the microcomputer 100 can communicate with the facsimile of the local station via the modem 300 and can communicate with the facsimile of the other party via the modem 400. The buffer 500 and the encryption / decryption processing circuit 600 are connected by the internal data bus (2). By controlling the buffer circuit 500, the data bus (2) can be connected to the data bus DBM1 of the modem 300 or the data bus DBM2 of the modem 400.

Therefore, for example, when a facsimile on the local station side performs transmission, image information to be encrypted is input to the modem 300 from the line LiB and demodulated, and is transmitted from the data bus DBM1 to the buffer 500.
And appears on the data bus of the microcomputer 100, and is applied to the terminals of the X group of the encryption / decryption processing circuit 600. The circuit 600 encrypts data applied to the terminals of the X group and outputs the data to the data bus (2) via the terminals of the Y group. This encrypted data is
The data is output to the data bus DBM2 through the buffer 500. Then, it is modulated by the modem 400 and sent out from the line LiA to the telephone lines LN1 and LN2.

Conversely, when the facsimile of the local station performs reception, the encrypted image information to be decrypted is input to the modem 400 from the line LiA, demodulated, and transmitted from the data bus DBM2 through the buffer 500 to the data bus ( Appears in 2) and is applied to terminals of the Y group of the encryption / decryption processing circuit 600. The circuit 600 decodes or decrypts the information and outputs the decrypted information to the terminals of group X. This information
The data is applied to the modem 300 through the data bus of the microcomputer 100, through the buffer 500, and through the data bus DBM1. The modem 300 modulates the information and sends it out to the local station's facsimile lines LF1 and LF2 via the line LiB.

The memory card 130 is used as a kind of key in the confidential communication, and is detachable from the concealing device by a predetermined connector. The memory card 130 includes a battery for holding stored contents, and a read / write memory for storing an ID code of the card. That is, normal confidential communication can be performed only when a memory card having the same ID code is attached to each concealing device arranged near the facsimile on the transmitting side and the receiving side.

Subsequently, the configuration of each circuit will be described in more detail. Details of each circuit in FIG. 3 are shown in FIGS. 5a, 5b, 5c, 5d,
6a, 6b, 6c, 7a, 7b, 8 and 9 are shown.

First, a description will be given with reference to FIG. 5a. This circuit includes the microcomputer 100 and its peripheral circuit elements. The microcomputer 100 used here is an HD6
3B03R. Latch LT1 is a microcomputer 100
Function as an address latch for extracting the lower 8 bits of address information (A7-A0) superimposed as the data bus signal. The address bus contains a microcomputer 10
The higher 8 bits (AD15-AD8) directly output by 0 and the lower 8 bits (AD7-AD0) output by the address latch LT1 are 16 bits.
A bit signal appears.

Various chip select signals selected by various peripheral circuits connected to the microcomputer 100 are supplied to a decoder.
It is generated by an address decoder composed of DE2 and various logic gates (G5, G6, G7, G8, G9). That is, when an address previously assigned to each of the peripheral circuits appears on the address bus, the corresponding chip select signal is decoded and the signal becomes active.

FIG. 5b shows the ROM 110, the RAM 120, and the memory card 130. These circuits are connected to the microcomputer 100 via an address bus, a data bus, and a control bus. DE1 is a decoder. In addition,
The memory card 130 is detachably connected to a circuit by a connector (not shown).

FIG. 5c shows the input / output interface 180. This circuit includes an integrated circuit 181 connected to an address bus, a data bus, and a control bus of the microcomputer 100, and a switch SW1 connected to its port.
−SW6, light emitting diode LED1−LED7, buzzer BZ, numeric keypad S
T, indicator DP1 is connected. Switches SW1 to SW6
Correspond to the switches SA, SB, SC, SD, SE, and SCH in FIG.

FIG. 5d shows a power supply circuit 140 and a random number generation circuit 150. The power supply circuit 140 has a function of converting the power of the commercial AC power supply (AC100V) into various DC voltages, and does not have a particularly new configuration.

On the other hand, the random number generation circuit 150 forms an analog voltage comparison circuit. The voltage of one of the two comparison input terminals is stabilized, and the pulsating voltage output from the power supply circuit 140 is applied to the other input terminal. This pulsating voltage is obtained by smoothing a full-wave rectified AC (50 Hz) waveform, and the voltage constantly changes slightly and contains various noises mixed in the power supply line. . The threshold level of the analog voltage comparison circuit is set to an intermediate level in a range where the level of the pulsating signal changes.

Therefore, a pulse signal RMD having a small periodicity appears at the output terminal of the comparison circuit. By sampling the signal RMD sequentially, random random data can be obtained, depending on the sampling period. In this embodiment, the random number data generated in this manner is used as a key code for performing confidential communication.

Next, refer to FIG. 6a. In this circuit, a polarity inversion detection circuit 210, a call detection circuit 220, and relays RY12 and RY2 are shown. Relays RY1 and RY2 output signals NCU-RL1 and NCU-
ON / OFF controlled by RL2.

The polarity reversal detection circuit 210 identifies the presence or absence of a current flowing through the telephone lines LN1 and LN2 and identifies the type of the current. In order to detect the current of the line LN1, photocouplers PC1 and PC2 each composed of a light emitting diode and a phototransistor are provided.
Is provided. Since the light emitting diodes of each photocoupler are interposed on the line LN1 with opposite polarities, when a current flows in one direction, PC1 turns on and PC2 turns off, and when a current flows in the other direction, PC1 turns off. And PC2 turns on. When no current flows, two photocouplers PC1, PC2
Are both turned off.

In a telephone line, no current flows through the line when the line is on-hook, that is, when the line is open, and current flows when the line goes off-hook, that is, when the line is used. Therefore, in this embodiment, the off-hook signal is activated when a current flows in any direction. Two signals POL1 and PO
L2 is turned on / off according to the direction of the current. Telephone line LN
1. Since the polarity of the voltage on LN2 is inverted by the exchange, this function is provided to check the polarity of the line at that time. This function disconnects the local station facsimile from the lines LN1 and LN2 and, when connected to the concealment device, changes the polarity of the voltage supplied to the lines LF1 and LF2 on the facsimile side to the telephone line L.
Used to match N1, LN2.

The call detection circuit 220 has a function of detecting a call signal appearing on the telephone lines LN1 and LN2. Since the call signal is an AC signal, in this circuit, the signal whose DC component is cut off by the capacitor is passed through a full-wave rectifier circuit to be rectified, and when a signal of a predetermined level or more appears on the rectified output, the incoming call signal is turned on. It is configured in.

FIG. 6b shows the current supply circuit 230. This circuit has a function of supplying a voltage to the lines LF1 and LF2 of the facsimile apparatus of the own station side when the facsimile of the own station side is disconnected from the telephone lines LN1 and LN2 and connected to the line LiB on the concealment mounting side. The polarity of the voltage is determined by the telephone line LN1, LN2 at that time.
The polarity signals POL1 and POL2 output from the polarity inversion detection circuit 210 described above are used in order to make the polarities coincide with each other.

Therefore, even if the existing facsimile apparatus monitors the voltage and current of the line to which it is connected and performs control according to the state, the connection of the facsimile line is kept secret from the telephone line. Switching to the device does not cause any problem. In addition, a voltage of 48 V normally appears on the telephone lines LN1 and LN2,
The current supply circuit 230 supplies a voltage of 28V.

FIG. 6c shows a tone receiver 190. Sixth
Referring to FIG. 3C, this circuit includes a detection circuit 193 for detecting an AC signal on the lines LF1 and LF2, an amplifier 192, and an integrated circuit 191. Integrated circuit 191 is MT8870B manufactured by Mitel.
The frequency of the input tone signal is identified, and the operated key is identified in a manner corresponding to Table 1. The information of the identified key is applied to the microprocessor 100 via the I / O port.

FIG. 7a shows the modem 300. Most of the circuitry of this modem is a single-chip integrated circuit (R48PC
J) 310. This integrated circuit 310 is a CCITT
It has a function conforming to V27ter. Basically, as a function of the integrated circuit 310, a function of converting a digital signal applied to its data terminal (D7-D0) into a serial signal, performing modulation, and outputting it to a serial transmission output terminal TXOUT,
Data signal (D7-D0) by demodulating the serial signal applied to serial reception input terminal RXIN and converting it to parallel data
There is a function to output.

The signal output from the serial transmission output terminal TXOUT of the integrated circuit 310 passes through the signal processing circuit 320, passes through the transformer 330, and is output to the line LiB. The signal input from the line LiB passes through the transformer 330, passes through the signal processing circuit 320, and is applied to the serial reception signal input terminal RXIN of the integrated circuit 310. The data terminals (D7-D0) of the integrated circuit 310 are connected to the data bus DBM1.

In FIG. 7b, the modem 400 is shown. Most of the circuits of this modem are constituted by a single-chip integrated circuit 410. The integrated circuit 410 is the same as the integrated circuit 310. Serial transmission output terminal T of integrated circuit 410
The signal output from XOUT passes through the signal processing circuit 420,
Output to the line LiA through the transformer 430. Also, track
The signal input to the LiA passes through the transformer 430, passes through the signal processing circuit 420, and passes through the serial reception input terminal of the integrated circuit 410.
Applied to RXIN. Data terminal of integrated circuit 410 (D7-D
0) is connected to the data bus DBM2.

The logical sum of the interrupt request signal IRQ1 output by the modem 300 shown in FIG. 7a and the interrupt request signal IRQ2 output by the modem 400 shown in FIG. 7b is output from the logic gate G15. Is applied to the interrupt request input terminal INT of the microcomputer 100.

FIG. 8 shows the buffer circuit 500. Referring to FIG. 8, each of these circuits functions as a bidirectional three-state bus buffer. Integrated circuits (74HC245) 510,520 and
530. A group A terminal of the integrated circuit 510 is connected to the data bus DBM2 of the modem 400,
The terminal of group A is connected to the data bus DBM1 of the modem 300, and the terminal of group A of the integrated circuit 530 is connected to the data bus of the microcomputer 100. Also,
The terminals of each B group of the integrated circuits 510, 520, 530 are commonly connected to the internal data bus (2).

Therefore, by controlling the integrated circuits 510 and 530, data can be transmitted in any direction between the data bus of the microcomputer 100, the internal data bus (2), and the data bus DBM2 of the modem 400. By controlling the integrated circuits 520 and 530, the data bus of the microcomputer 100, the internal data bus (2),
And data bus DBM1 of modem 300, data can be transmitted in any direction.

FIG. 9 shows a specific configuration of the encryption / decryption predetermined circuit 600. Referring to FIG. 9, this circuit is roughly divided into a key code holding circuit 610, an encryption circuit 620, and a decryption circuit 630.

First, the key code holding circuit 610 will be described. This circuit comprises a PROM (programmable ROM) 611 and two latches 612,
It consists of 613. Address terminals of PROM611 (A0 to A
7), the information of the master key is applied from the microcomputer 100. In the PROM 611, different key codes are stored in advance at each address, and by giving address information, an 8-bit key code existing at the address is output to the data terminals (D0 to D7).

By controlling the latch control signals KLT1 and KLT2,
The information output by PROM 611 is stored in latches 612 and 61, respectively.
3 can be held. By changing the master key given to the PROM 611 between when the latch control signal KLT1 is output and when the KLT2 is output, the data held in the latch 612 and the data held in the latch 613 have different values. The 8-bit data held in the latch 612 is applied as a key code KA, and the 8-bit data held in the latch 613 is applied as a key code KB to the encryption circuit 620 and the decryption circuit 630, respectively.

Next, the encryption circuit 620 will be described. This circuit includes 4-bit full adders 621 and 622, an exclusive OR circuit 623 and 624, and a three-state output buffer 62.
Consists of five. Information (X0-X3) of the lower 4 bits of the information X to be encrypted is applied to the input terminal of group A of the full adder 621 via the data bus, and the key code KA is applied to the input terminal of group B. The lower 4 bits (K0-K3) are applied. The upper 4 bits (X4-X7) of the information X to be encrypted are applied to the input terminal of the group A of the full adder 622 via the data bus, and the key code KA is applied to the input terminal of the group B. The upper 4 bits (K4−K7) are applied. The carry output of full adder 621 is applied to the input terminal of full adder 622.

The output terminal of each E group of the full adders 621 and 622 is applied to the input terminal of the A group of the exclusive OR circuits 623 and 624, respectively. Also, the exclusive OR circuit 623 B
The lower 4 bits (K8
−K11) is applied, and the upper 4 bits (K12−K15) of the key code KB are applied to the input terminal of the B group of the exclusive OR circuit 624.
Is applied.

4 output from the output terminal Y of the exclusive OR circuit 623
The bit signal and the 4-bit signal output from the output terminal Y of 624 pass through the buffer 625 and are output to the internal data bus (2) as 8-bit encrypted information Y.

Next, the decoding circuit 630 will be described. This circuit includes 4-bit full adders 633 and 634, exclusive OR circuits 631 and 632, a three-state output buffer 635, and an inverter group. The lower 4 bits (Y0-Y3) of the encrypted information Y are input to the input terminal of the group A of the exclusive ethics sum circuit 631.
Is applied from the internal data bus (2), and the lower 4 bits (K8-K11) of the key code KB are applied to the input terminal of group B.
Is applied. The upper 4 bits (Y4-Y7) of the encrypted information Y are applied to the input terminal of the group A of the exclusive OR circuit 632 from the internal data bus (2).
For the input terminal of the group, the upper 4 bits 8K of the key code KB
12-K15) is applied.

The signals output from the output terminals of the respective E groups of the exclusive OR circuits 631 and 632 are supplied to the full adders 633 and 6 respectively.
It is applied to the input terminal of the 34 B group. Full adder 633
A signal obtained by inverting the lower 4 bits (K0-K3) of the key code KA is applied to the input terminal of the group A of FIG.
The 634 A group input terminals have the top 4 key codes KA.
Signals obtained by inverting the bits (K4-K7) are applied.

4-bit information output by full adder 633 and full adder 634
Outputs the 4-bit information via the buffer 635,
The information is output to the data bus of the microcomputer 100 as the decoded 8-bit information X.

Note that the method of the encryption process performed by the encryption circuit 620 and the decryption circuit 630 is basically known in the related art, and therefore a description thereof will not be necessary. FIG. 4 shows a simplified version of the processing of the encryption / decryption processing circuit 600 shown in FIG.

FIG. 10 shows the internal structure of the memory card 130 used in this embodiment. Referring to FIG. 10, the memory card includes a read / write memory (RAM), a battery, a control circuit, and a connector 134. The connector 134 makes the memory card detachable from the main body of the secret circuit. Each terminal of the connector 134 includes a power supply line (Vcc), a card set signal terminal (CST), a chip select signal terminal (CS),
A write control output (WPOUT), a write control input (WE), an output enable input (OE), an address bus (A0-A12) and a data bus (D0-D7) are allocated. In the RAM 131, an ID code (pre-assigned) unique to the memory card is written. In this embodiment, in order to perform confidential communication, a memory card in which the same ID code has been written is required for both the transmitting and receiving concealing devices.

In the concealment device of this embodiment, a special operation performed by the operator for confidential communication is performed from a dial key (numeric keypad KT) of a telephone provided in the facsimile. Specifically, among a number of keys that can be output by a memory card attached to the concealment device, an operation for specifying a predetermined key with a communication partner can be remotely controlled from a telephone. . When the specification of the key is completed, the confidential communication using the key becomes possible.

This remote control will be described. The operation of the concealment device is shown in FIGS. 13a and 13b.

To perform remote control, the line is set to off-hook (the telephone receiver is lifted up: the line is in use), and a predetermined key operation is performed from the numeric keypad KT of the telephone. In this case, the processing of the microcomputer 100
In FIG. 13a, the process proceeds to steps A2-A3-A4-A5, and in step A5, the tone signal output to the line (LF1, LF2) is monitored via the tone receiver 190, and step A5-A
The processing of 6-A7-A8-A5 is repeatedly executed.

In this embodiment, “*** xxx” (where ○ indicates one of the numbers 0 to 9) is defined as a key input combination for selecting a key to be used. Various other combinations of key inputs are possible, but it is necessary that the combinations do not affect the exchange connected to the public telephone line.

First, when the input of "**" is detected by the tone signal, the process proceeds from step A7 to A14 to turn on the relays RY1 and RY3. As a result, the public telephone lines LN1 and LN2 are disconnected from the lines Li1 and Li2, and the modem 400 is connected to the lines LF1 and LF2 on the facsimile side via the lines Li1 and Li2. The reason why the relay RY3 is turned on to disconnect the lines LN1 and LN2 from the lines Li1 and Li2 is to prevent information of a selection number (described later) for specifying key information from leaking to the public telephone line. Also, the relay RY1 is turned on and the modem 400 is connected to the lines LF1 and LF2 because information on the operation state of the concealment device is transmitted by the modem
This is to send a confirmation sound to the facsimile telephone via 400.

In the next step A15, a confirmation sound is output to the facsimile telephone. That is, since the modem 400 has a function of outputting a tone signal of an arbitrary frequency to a line, the modem 400 outputs the tone signal as a confirmation sound to the lines Li1 and Li2 and sends it to the telephone.

Specifically, a data group corresponding to the content of each confirmation sound is provided in a memory as a tone output table as shown in FIG. 14a, and is confirmed by the processing in FIG. 13c while referring to the table. Output sound. Referring to FIG. 14a, this table contains M sets of data that define a frequency, an output level, and a time, and by sequentially generating tone signals based on the data, a relatively large number of data such as a melody can be obtained. It can be seen that a signal that is complicated and easy to confirm can be generated. In this example, four sets of tone output tables each having different data are provided.

Referring again to FIG. 13a. After outputting the confirmation sound in step A15, step A1 is performed until a 5-digit key input is detected.
The processing of 6-A17-A18 is repeated. If the operator is "*
* ”Followed by“ ○○○○ ＊ ”
From A17 to A20, proceed to step A21.

FIG. 13b shows the specific contents of the used key selection subroutine in step A21, and FIG. 14b shows the data arrangement on the memory card 130.

Referring to FIG. 14b, in this example, on the memory card, the data that is the basis of the key to be used is continuously arranged in a form divided into 16 data blocks. The information of the key to be used is generated based on the contents of these 16 data blocks. The contents of the processing will be described with reference to FIG. 13b.

If there is no memory card in the security device, step
The process proceeds from B0 to B11 and outputs a confirmation sound determined by the tone output table 3. When the memory card is inserted into the security device, the process proceeds to step B1, where the first four digits of the five-digit key input read in step A16 of FIG. 13a are extracted as a selection number, and the number is extracted. Store in register RN as a 16-bit binary number. That is, each digit of the selection number is
Allocated to 4 bits of the binary number, the total of 4 digits is a 16-bit binary number.

In step B2, the initial value 1 is stored in the register RB,
Clear the flag F3.

At step B3, bit n of the register RN is identified as either 1 or 0. n is the content of the register RB.

If the bit n of the RN is 1, the process proceeds to step B4 and subsequent steps. Since the flag F3 is initially 0, the process proceeds to step B5 after step B4, in which the content of the n-th data block on the memory card 130 is transferred to the memory MEM (on the RAM 120), and the flag F3 is set.

In step B7, the contents of the register RB are incremented.

As a result of Step B7, if the content of the register RB does not exceed 16, the process returns to Step B3 to repeat the processing.

When step B5 is executed, the flag F3 is set, so that in the next process, the process proceeds to step B6 after step B4.

In step B6, the exclusive OR of the contents of the n-th data block on the memory card 130 and the contents of the memory MEM is calculated in bit units, and the result is stored in the memory MEM.

Therefore, for all the data blocks corresponding to the 1 bit of the contents of the register RN, they are exclusive ORed in bit units, and the result is stored in the memory ME.
Held in M. For example, when “1234” is input as the selection number, the contents of the register RN are “0100 0011 0010 000”
1 "(MSB on the left and LSB on the right), so 1,6,9,10 and
The result of exclusive OR operation on all data of the fifteenth five data blocks in bit units is finally generated on the memory MEM, and is output as key data used in step B9.

In other words, in this example, the key data of 16 blocks on the memory card 130 is the data that is the basis of the key that is actually used, but usually, the data obtained by calculating the combination of the contents of a plurality of data blocks is used. Key data.
Since the selection number is a four-digit decimal number, in this example, data of 16 data blocks held in one memory card is used, and a maximum of 10 to the fourth power, that is, 10,000 types Keys having different contents can be used.

In confidential communication, etc., communication cannot be performed unless the keys on the transmitting side and the receiving side match, so by assigning a selection number of a different key to be used to each communication partner as a PIN, a third party who does not know the PIN The contents of the confidential communication can be prevented from leaking to the user. In other words, even if a memory card holding the same key data is passed to a third party,
Since no key data that directly matches the key to be used does not exist on the memory card, and the personal identification number does not exist on the memory card, a third party cannot read the actual key to be used.

When the key selection is normally completed in the use key selection subroutine, the flag D is set in step B10. However, if the memory card has not been mounted for a long time, step B13 is executed to clear the flag D.

Returning to FIG. 13a, the description will be continued. If the key selection is completed normally, that is, if the flag D is 1, the step A2
Proceeding to 4, the confirmation sound of the tone output table 2 is output, and then the flag F1 is set to 1. Now that the key has been selected, confidential communication is possible thereafter.

That is, when the own station is the calling side, the hook is turned off and the number of the other station is dialed in a state where there is no incoming call signal, so that the processing proceeds to steps A2-A3-A4-A5-A6-A8-A5. . Then, when the partner station is hooked off, the polarity of the line is reversed, which is detected in step A6.
The process proceeds to A11, and since the flag F1 is set (the used key has been selected), the process proceeds to step A12, and the process of the confidential communication is started.

Also, when the called station is called from the partner station, an incoming call signal is detected, so the process proceeds to steps A2-A10-A11,
Since the flag F1 has been set, the process proceeds to step A12, and the process of the confidential communication is started.

When the confidential communication ends, step A13 is executed, and the flag F1 is cleared. Therefore, it is necessary to select a key to be used every time confidential communication is performed. However, since the operation is performed by remotely controlling the concealment device from the telephone on the facsimile, it is not necessary to arrange the concealment device near the operator.

When performing remote control, the relay RY3 is turned on in step A14 of FIG. 13a, whereby the lines LN1 and LN2 are disconnected from the lines Li1 and Li2. In that case, even if the exchange side calls the local station, the facsimile and telephone of the local station cannot detect it. In order to enable communication even in such a case, in this embodiment, after executing steps A15 to A18 shown in FIG. 13a, executing steps A16 to A24, and FIG. After each step is executed, the processing shown in FIG. 13d is executed.

This will be described with reference to FIG. 13d. In this process, first, in step D1, the presence or absence of an incoming call signal is checked. That is, the third
By referring to the incoming call signal output by the call detection circuit 220 shown in the figure, it is determined whether or not a call signal has appeared on the lines LN1 and LN2. As shown in FIG. 3, the call detection circuit 220 is connected to the lines LN1 and LN2 at a position closer to the exchange than the relay RY3, so that even when the relay RY3 is on, the line LN1. The presence or absence of a call signal on LN2 can be detected.

If there is no incoming call signal in step D1, step D1
Proceed to the step following the step executed before executing.

When the presence of an incoming call signal is detected in step D1, the process proceeds to step D2. Initially, the flag FC is set to 0, so that steps D3 and D4 are executed next. First, in step D3, the tone output table 4 is selected and the "confirmation sound output" subroutine is executed. That is, the signal of the notification sound determined by the tone output table 4 is output to the communication lines LF1 and LF2.
The notification sound in this case informs the own station that there is a call, and can be heard by the operator as a sound by the receiver of the telephone of the own station facsimile.

In step D4, the flag FC is set to 1 and the timer TM
Start C

If a call signal arrives from the exchange during the remote operation and informs the operator in step D3, step D5
To check if it is on-hook. That is, when the operator takes down the telephone receiver in response to the call notification, the line is released, that is, the line is released.

When the on-hook is detected in step D5, the process jumps before step A19 shown in FIG. 13a. And step A
When 19 is executed, the relay RY3 is turned off and the lines LF1, LF2
Is connected again to the public communication lines LN1 and LN2. Therefore,
The call signal applied from the exchange to the lines LN1 and LN2 is
The signal is applied to the telephone of the own station facsimile via the lines LF1 and LF2, thereby generating a ringing tone from the telephone. In this case, as usual, if the operator picks up the telephone receiver, it goes off-hook and can communicate with the partner station.

If the on-hook is not detected in step D5, the process returns to D1 through step D6, and waits for the on-hook to be detected. However, when the count value of the timer TMC exceeds a predetermined time, the process proceeds from Step D6 to Step D7. In step D7, the flag FC is cleared and the timer TM
Clear C

Therefore, in this embodiment, even if the operator is performing remote control on the concealment device, if there is a call from the partner station, the operation of the concealment device can be interrupted and the call can be answered.

Next, an actual communication operation will be described. 11a, 11b, 11
c, 11d, 11e, 11f and 11g,
The specific contents of the communication control operation of the concealment device, that is, the processing of step A12 in FIG. 13a are described in FIG. 12a, FIG. 12b, FIG.
2d, 12e, 12f, 12g, 12h, 12i
Figures, 12j and 12k. Since the content of the processing of the facsimile machine itself is the same as that of the conventional machine,
That part will be described briefly.

Hereinafter, the contents of the processing will be described with reference to the respective drawings. In the description, it is assumed that the communication system is configured as shown in FIG. In the following description,
The symbols of the signals transmitted in the communication process (shown in parentheses)
Abbreviations defined by CCITT recommendations are used. Further, the facsimile is described assuming that both the calling side and the called side operate in the automatic mode.

In the calling facsimile, the hook is turned off (corresponding to the operation of lifting the handset), and upon detecting a dial tone from the exchange, the number of the partner station is dialed (No. 11a).
See figure).

When the called side detects a ringing tone (ring tone) from the exchange, the hook is turned off, and then a called station identification signal (CED) indicating that it is a facsimile is transmitted to the line. The calling side continues to transmit a calling tone (CNG) indicating that the calling side is a facsimile to the line until this signal (CED) is detected.

After detecting the signal (CED), the calling side enters a facsimile communication mode. After sending the signal (CED), the called party indicates that the called device has the standard capability of CCITT.
Transmits a digital identification signal (DIS). That is, the signal (D
IS) determines which mode (G
1, G2, G3, etc.) Inform the calling side whether communication capability exists.

The calling side checks from the contents of the digital identification signal (DIS) transmitted from the called side whether or not it matches the communication capability of its own facsimile, determines a communication mode suitable for both communication capabilities, and A digital command signal (DCS) responsive to the signal is returned to the called party. Following that, a training check signal (TC
F) Send. After receiving the signal (DCS), the called party
A signal (TCF) is received in a specified mode, and a signal (CFR or FTT) indicating the reception result is returned.

On the calling side, according to the returned reception result, if the communication condition is good, the process proceeds to the next message transmission step. If the condition is not good, the communication mode is changed (generally, the communication speed is reduced), and the signal (TCF) is again transmitted. ) Is sent.

When the calling side receives the signal (CFR), it sends a training signal, synchronizes the called side, and then sends a message. The called side receives the message after synchronizing with the training signal.

On the called side, after the calling side transmits the one-page document, it continues to receive the signal until it detects a signal (RTC) to be transmitted to indicate the end.

When the original of one page is transmitted, the calling side detects whether or not the original is the final original. If the original is not the final original, the multi-page signal (MPS) is transmitted, and then the reception confirmation signal (MCF) transmitted from the receiving side Or, it receives a retraining signal (RTP, RTN). Then, based on the received signal, the transmission mode is changed, the training is transmitted, or the line is disconnected.

If it is the last document, the procedure is interrupted by an interrupt, and it is determined whether or not the mode is changed. If the mode is not changed, a procedure end signal (EOP) is transmitted, and then the circuit disconnection operation is started. To change the mode, use signals (MCF, RTP, RT
N), the digital identification signal (DIS)
Wait until you receive.

On the called side, signals (MPS), (EOP),
(EOM: message end), and responds with one of signals (MCF), (RTP), and (RTN).
Return to the command receiving state. Otherwise, a circuit disconnection operation is started.

 Next, secret communication control of the secret device will be described.

First, refer to FIG. 12a. In step A60, it is determined whether the facsimile of the own station belongs to the calling side or the called side. That is, since the called side detects the incoming call signal before the hook-off, the step A in FIG.
At 10, 1 is stored in the register C ₁ , and if it is the calling side, a hook-off is detected when an incoming call signal is not detected. Therefore, 0 is stored in the register C ₁ at step A 3 of FIG. 13A. Therefore, in step A60 of FIG.
Referring to C _1, it identifies the calling / called.

If the own station is the called side, in step A69, the switch (FAX
-SW: sw1) is checked to determine whether the facsimile mode of the own station is manual or automatic. If it is manual, proceed to step A70, turn on relay RY2, and set
F1 and LF2 are connected to the line LiB in the concealment device, and a signal (CED) is transmitted to the other party, that is, the calling station in step A71.

If the facsimile of the own station is in the automatic mode, the process proceeds to step G51 in FIG. 12g. Then, when detecting the signal (CED) from the facsimile of the own station, after a predetermined time T _x2, relay RY
2 is turned on, and the lines LF1 and LF2 of the own station facsimile are connected to the line LiB in the concealment device.

Next, the state of the secret switch (SW2) is checked.
If the switch is on, it is regarded as secret
Store the ACTC, otherwise store the NACTC in Mr. Next, the process proceeds to step G61 to set a state in which the signal (DIS) can be received.

Next, the process proceeds to step H51 in FIG. 12h to send the contents of the register Mr to the partner station.

Here, a case where the own station is the calling side will be described. In that case,
The process proceeds to step B51 shown in FIG. 12b, and first waits until a signal (CED) is detected. When this signal (CED) is detected, the process proceeds to step B56. If the called station is a normal facsimile, a DIS or DTC is sent here, but if the concealment device of the called station is operating, the DIS following the signal (CED) will be sent.
Alternatively, instead of the DTC, the content of Mr is sent in step H51 in FIG. 12h. In that case, when the predetermined time T _x2 elapses,
Proceeding from step B57 to step B58, the relay RY2 is turned on to switch the connection of the line. In step B59, the state of the secret switch (SW2) is identified, and the register Mt is set in accordance with the result.
Set the contents of Then, since the content of the register Mr is received, the process proceeds from the step B66 to the step C51 in FIG. 12c. If one of the registers Mr and Mt is ACTC, that is, the secret is desired, the process proceeds to step C55.

In step C55, the level of the signal RDM output from the random number generation circuit is repeatedly sampled, thereby generating a random number code R. In step C56, the generated random number code R is provided as an input X of the encryption / decryption processing circuit 600, and the ID code obtained from the memory card 130 is provided to the encryption / decryption processing circuit 600 as a master key.
Key codes KA and KB corresponding to the master key are generated, and information Ct obtained by encrypting the random number R is generated. In the next step C57, information Xt obtained by adding the code Ct to the code ACTC is transmitted to the called station.

The called station receives the information Xt from the calling station in step H52 of FIG. 12h. If Xt is not NACTC, the process proceeds to step H56. In step H56, the ID code obtained from the memory card 130 of the called station is given to the encryption / decryption processing circuit 600 as a master key, and key codes KA and KB corresponding to the master key are generated. Then, the received encryption is given to the encryption input Y of the encryption / decryption processing circuit 600, and the encryption is decrypted. The decrypted information R 'is output to the data bus. In the next step H57, the decrypted information R 'is used as a master key, and the encryption / decryption processing circuit 600
To generate a key code KA, KB corresponding to the master key. Then, the information R 'is input to the encryption / decryption processing circuit 600 as input information X, which is encrypted, and the obtained encryption Xr is sent to the calling station.

Upon receiving the encryption Xr in step C58, the calling station proceeds to step C59. In Step C59, the encryption Xr is
The data is input to the encryption input Y of the encryption / decryption processing circuit 600, and is given to the encryption / decryption processing circuit 600 as the master key with the same value as the initially transmitted random number to decrypt the encryption Xr. The information R ″ to be decrypted in this manner is: R ″ = Dr (Er ′ (R ′)) (1) where R ′: Re ′ decrypted by the called side Er ′: encryption of the called side Since the function Dr is a function of decryption on the calling side, if all the encryption and decryption conditions on the calling side and the called side match, R ″ becomes equal to the random number R sent first. If the ID codes stored in the memory card of the calling party and the memory card of the called party are different, R
Does not match R ". The calling station compares R and R" in step C60, and if they match, the process proceeds to step C62, where 1 is stored in the register Rf and transmitted to the called side. I do. If they do not match, the sending of the cipher and the checking of the returned cipher are repeated three times. If there is no match in the three checks, the operation of the confidential communication is prohibited.

On receiving the Rf at step H58 in FIG. 12h, the called side proceeds to the processing after step H61.

Until the confidential communication is enabled as described above, the facsimile of the called station continues to transmit the digital identification signal (DIS), and the facsimile of the calling station continues to wait for the signal. ing. When the concealment device on the called station side proceeds to step H65, it has already received the digital identification signal (DIS) from its own facsimile, and transmits the signal to the station on the other side (calling side). I do.

When the confidential communication is enabled in this manner, the information is transmitted in the same procedure as in the normal facsimile communication. In this case, the confidential device is connected to the facsimile of its own station and the counterpart station (the confidential device). ), The information transmitted by the facsimile of the local station is transmitted to the partner station via the concealment device, and the information transmitted from the partner station is transmitted to the partner station via the concealment device. Sent to the office facsimile. When mediating, the image information is encrypted or decrypted. In that case, the information to be encrypted is applied to the input terminal X of the encryption / decryption processing circuit 600, and the information to be decrypted is applied to the input terminal Y. Further, as a master key code of the encryption / decryption processing circuit 600, a random number which has already been transferred between the own station and the other station, confirmed and collated, is used in any station. That is, different values are used for the key used in the confidential communication, that is, the session key every time the communication is performed. Therefore,
Extremely safe.

In the above embodiment, the encryption / decryption is performed by the arithmetic addition and the exclusive OR operation. However, the encryption method may be modified by using various other conventionally known methods. The invention can be implemented as well.

Further, in the embodiment, the confidential communication in the case of performing communication between facsimile devices has been described. However, as long as the device performs communication in the same communication procedure, not only the facsimile but also the confidential communication using the device of the present invention is used. It is possible to do.

In the embodiment, two modems are used to perform the encryption / decryption processing on the information appearing on the line in real time. However, a configuration is provided in which a memory capable of storing all of one communication message is provided. , The reception and the transmission can be performed at a time shifted from each other, so that one modem is not required in that case. In that case, the encryption / decryption of the message is performed by a hardware circuit (600).
Alternatively, it may be performed by microcomputer software.

Further, in the embodiment, when a call is detected in the middle of the remote operation, a signal for notifying the call is output from the telephone as a sound, but the configuration may be changed to notify by, for example, turning on a lamp. Good.

[Effects] As described above, according to the present invention, the concealment device can be completely separated from the communication device, and the remote control of the concealment device can be performed on the communication device side. Leakage can be prevented. Moreover, when a call is received during the remote operation, the remote operation can be interrupted to perform communication.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of the entire communication system using the concealment device of the embodiment. FIG. 2 is a block diagram showing an outline of a configuration of a concealment device provided on each of a transmission side and a reception side. FIG. 3 is a block diagram showing a configuration of one concealment device of the embodiment. FIG. 4 is a block diagram schematically showing functions of the encryption / decryption processing circuit 600. 5a, 5b, 5c, 5d, 6a, 6b,
6c, 7a, 7b, 8, 9 and 10
FIG. 5 is a block diagram showing a detailed configuration of each unit shown in FIG. 4. 11a, 11b, 11c, 11d, 11e, 11f
FIG. 11 and FIG. 11g are flowcharts showing the contents of the facsimile communication process. 12a, 12b, 12c, 12d, 12e, 12f
FIG. 12, FIG. 12g, FIG. 12h, FIG. 12i, FIG. 12j, and FIG. 12k are flowcharts showing the details of step A12 in FIG. 13a. 13a, 13b, 13c and 13d are flowcharts showing the operation of the security device. FIG. 14a is a memory map showing the configuration of a set of tone output tables. FIG. 14b is a memory map showing a data array on the memory card 130. FIG. 15 is a perspective view showing the appearance of the concealment device. 100: microcomputer (electronic control means) 110: ROM, 120: RAM 130: memory card, 134: connector 140: power supply, 150: random number generation circuit 180: input / output interface 190: tone receiver (tone detection means) 210: polarity Inversion detection circuit 220: Call detection circuit (call detection means) 230: Current supply circuit 300,400: Modem (modulation / demodulation means) 310,410: Integrated circuit 320,420: Signal processing circuit 330,430: Transformer 500: Buffer circuit 600: Encryption / decryption processing circuit (Cryptographic processing means) 610: key code holding circuit, 611: PROM 612,613: latch, 620: encryption circuit 621,622: full adder 623,624: exclusive OR circuit 625: buffer, 630: decryption circuit 631,632: exclusive logic Sum circuit 633,634: Full adder 635: Buffer, RY1, RY2: Relay RY3: Relay (meaning switch means) LN1, LN2: Public telephone line (communication line) LF1, LF2: Line, LiA: Line LiB: Line, LT1: Latch DE1, DE2: Decoder SW1-SW6: Switch L ED1-LED7: Light-emitting diode BZ: Buzzer PC1, PC2: Photocoupler

──────────────────────────────────────────────────続 き Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04K 1/00-3/00 H04L 9/00-9/38 G09C 1/00-5/00 H04N 1 / 32-1/44

Claims (3)

(57) [Claims] 1. A communication line having one end connected to a partner communication unit via an exchange, and the other end connected to a local station communication unit; a modulation / demodulation unit connected to the communication line; Tone detection means for detecting a tone signal applied to the communication line and identifying the type of the tone; a cut-off switch inserted at a position closer to the exchange than the connection position of the tone detection means on the communication line Means: a call detecting means connected to a position closer to the exchange than the insertion position of the cut-off switch means on the communication line; encryption processing means for encrypting the original information, decrypting the encryption and restoring the original information; The cutoff switch is controlled based on the information detected by the tone detector, and at least key information used in the encryption process is specified; When the call is blocked, the output of the call detecting means is monitored, and when a call signal is detected, the signal is notified to the local station side communication means; after the key information is specified, the modulation / demodulation means and the encryption processing means And the other communication means inputs the encryption information to be applied to the communication line through the modulation and demodulation means, decrypts the encrypted information through the encryption processing means, and automatically decrypts the decrypted information through the modulation and demodulation means. The transmission information applied to the communication means on the office side, the transmission information output from the communication means on the own station side to the communication line is input via the modulation / demodulation means, and the transmission information is encrypted by passing through the encryption processing means. An electronic control unit that outputs to the communication unit on the other side via the modulation / demodulation unit. 2. The electronic control unit according to claim 1, wherein when the disconnection switch unit disconnects the communication line, the electronic control unit detects a call signal and notifies the local station communication unit of the call signal. 2. The secret communication control device according to claim 1, wherein upon detection, the cutoff of the communication line by the cutoff switch is released. 3. The electronic control means monitors the output of the call detection means when the cutoff switch means cuts off the communication line, and when a call signal is detected, sends a predetermined signal to the communication line. The secret communication control device according to claim 1, wherein the secret communication control device outputs the call to the local station side communication means.