JP3301438B2 - Secret telephone device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a confidential telephone device capable of performing conversation by encrypting voice on a telephone.

[0002]

2. Description of the Related Art As an analog encryption method for directly encrypting a voice signal, a spectrum inversion encryption method (for example, Imamura, Hattori, Kozono: "Speech quality improvement effect by compander and emphasis in voice spectrum inversion confidential",
See IEICE (B), J64-B, 5, pp. 425-432 (Showa 56-05)), a method of exchanging the time sequence and frequency of sampled speech (for example, NSJayant, RVCox, BJM)
cDermott and AMQuinn: "Analog scramblers for spe
ech based on sequential permutations in timeand fr
quency ", Bell Syst. Tech. J. 62, 1, pp. 25-46 (Jan. 1983)), a method of inverting the polarity of sampled voice according to a certain rule (for example, see S. Asakawa, F. Sugiyama and
M. Nakamura: "Avoice scrambler for mobil communi
cation ", IEEE Trans. Veh Technol. 29, 1, pp. 81-86 (Feb. 1
980)). FFT ( Fast Fourier Tra)
nsform: FFT scrambling method applying fast Fourier transform method (for details, for example, Matsunaga, Okawa, Sakurai, Koga: "Full-duplex analog confidential device using FFT and its basic operation", IEICE (A) , J72-A, 4, pp. 692-702 (Showa 64)
-04)) has been proposed.

Further, a digital encryption system has been proposed in which an analog voice signal is encoded by, for example, a μ-law encoding method and then encrypted, in a manner similar to that for encrypting a message. Currently, as a security measure for digital communications, either the sender or the receiver determines the encryption key and sends the same encryption key to the other party, and then encrypts the data (plaintext) to be sent on the transmission side with the encryption key, and encrypts the ciphertext. The transmitting side and the receiving side use a method in which the cipher text received with the above cipher key is subjected to inverse conversion of the cipher, that is, decryption, and the original plain text is restored.
For the encryption algorithm used in these, it is essential to disclose the encryption algorithm in order to perform encrypted communication with an unspecified partner. DES (Details of the DES algorithm are, for example, DW
Davies and WLPrice (Translated by Kamizono): “Network
Security ", Nikkei McGraw-Hill, 1985 pp. 55-84), FEAL (for details of the FEAL algorithm, see, for example, Miyaguchi, Shiraishi, Shimizu:" FEAL-8 Cryptographic Algorithm ", Kenjiho Vol. 37, No. 4/5, 1988 pp. 321-372).

[0004] Next, a cryptographic use format (for details of the cryptographic use format, for example, DWDavies and WLPrice (translated by Kamizono):
"Network Security", Nikkei McGraw-Hill, 1985 pp.85-102) has the following four formats. ECB format (Electronic Codebook mode). CBC format (Cipher Block Chaining mode).

[0005] CFB format (Cipher Feedback mod
e). OFB format (Output Feedback mode).

[0006]

The first three methods of the analog encryption method have drawbacks such as weak encryption strength, difficulty in conversation due to signal processing delay, and deterioration of decoded sound quality due to encryption. In the last method, the difficulty of conversation due to signal processing delay, the deterioration of decryption sound quality due to encryption, and the conversation (encrypted call) encrypted from ordinary conversation (non-encrypted call)
There is a disadvantage that it takes time to switch to the state. Also, if the encryption key is different between the calling side and the called side, the user will receive an incomprehensible noise at the start of the encrypted call, and will feel uncomfortable and will not be able to make any further calls. At this time, switching from the encrypted call to the non-encrypted call has a disadvantage that both parties must manually stop the encryption function.

[0007] ISDN (Integrated Services Digital)
Before the service was started, the transmission network was based on analog transmission. Digital transmission requires about 20 times the frequency band of analog transmission to transmit the same voice signal. There is no example in which digital encryption of a telephone has been realized in terms of cost. However, as ISDN spreads, it is conceivable that telephone conversations are performed by being encrypted by a digital encryption system. In this case, a stream cipher may be applied in order to increase the cipher strength, but the cipher of this stream cipher cannot be decrypted unless the other party knows the cipher start time. That is, it is necessary to simultaneously start the operation of the encryptor and the decryptor of the telephones that are in conversation with each other. However, since the telephone does not have a protocol such as data communication, it is necessary to realize the following functions.

[0008] A function to start encryption of the voice code on the transmitting side and to notify the receiving side of the encrypted voice code. -Receiving side A function to detect the voice code for which encryption has started and start decoding from the voice code.

It is also necessary to confirm that the person who answers the other party's telephone is the one who wants to talk. Therefore, a function of switching to an encrypted call in a short period of time after confirming the other party in a non-encrypted call is required. Furthermore, if the encryption key differs between the calling and called parties at the start of encryption, the user of both phones is notified that the encryption key is different, and both phones switch to a non-cryptographic conversation state in a short period of time. is necessary.

An object of the present invention is to prevent wiretapping on a communication line and to easily switch between a non-encrypted conversation and an encrypted conversation. An object of the present invention is to provide a confidential telephone device having a function of displaying an alarm on both telephones and automatically switching to non-encrypted communication and having a high encryption strength.

[0011]

According to the present invention, an encoder having an n-bit width for converting an analog signal from a transmitter (microphone) into a digital signal, an output of the encoder, and a preset n A first code having a bit width (hereinafter described as using the first character as the first code) and a second code having a preset n-bit width
(Hereinafter, described as using the second character as the second code)
, A cipher that applies a stream cipher that encrypts the output of the first selector in n-bit units, and a second selector that selects one of the output of the cipher and the output of the first selector. And a parallel-to-serial converter that converts the output of the second selector into serial and sends it out.
A first timer output whose output is turned on at an arbitrary time within a time period from the operation start instruction to T1;
2 (where T2> T1 + the time for transmitting (M + 1) characters), a timer having a second timer output whose output is turned on, a transmission control unit for sequentially controlling the following operations, The first selector and the second selector are controlled so as to transmit an output. According to an encryption start instruction from outside, M first characters (M
Is an integer of 2 or more). Controls the first selector to continuously transmit, controls the first selector to transmit one second character, starts the operation of the encryptor and the operation of the timer. And controls the first selector and the second selector so that the output of the encoder is encrypted and transmitted. When the first timer output of the timer is turned on, M first characters are encrypted. Control the first selector so as to transmit
The first selector is controlled so that one second character is encrypted and transmitted. The first selector is controlled so that the output of the encoder is encrypted and transmitted. A serial-to-parallel converter that converts the width into parallel, an encryption / decryption unit that applies a stream encryption format that decrypts the output of the serial-to-parallel unit in units of n bits, an output of the encryption / decryption unit, A third selector for selecting any one of the outputs, and N consecutive first characters (where N
≤ M and N is a positive integer) means for detecting, a means for detecting a second character from the output of the third selector, a code decoder for converting the output of the third selector into an analog signal, A circuit, an output of the audio generation circuit, an output of the codec, a fourth selector for supplying the output to a receiver (speaker), an interrupt signal line to the outside, and the following operations are sequentially performed. A receiving control unit, supplying the output of the serial / parallel converter to the codec, controlling the third selector and the fourth selector to supply the output of the codec to the receiver,
From the third selector output, the first character is continuously N
When detecting N consecutive first characters, the fourth selector is controlled so that the output of the voice generating circuit is supplied to the receiver, and the first interrupt is transmitted to the external interrupt signal line. When the second character is detected, the third selector is controlled so as to supply the output of the serial-parallel converter to the decryption device, and the decryption operation of the decryption device is started. 3, the operation of detecting the first N consecutive characters from the selector output of No. 3, the operation of detecting the second character when detecting the first consecutive N characters, the operation of detecting the second character, The third selector and the fourth selector are controlled so that the output is decoded by the code decoder and supplied to the receiver, and the second interrupt signal line is connected to the external interrupt signal line. If the second timer output of the timer is turned on during the above operation, a third interrupt is generated on the interrupt signal line to the outside, and the operation of the transmission control unit is shifted to the operation of receiving. Transition to the operation of the control unit, a push button dial for inputting a telephone number and an encryption key, an encryption switch which is manually operated to output the above-mentioned encryption call start signal, and a key input, a source telephone number, an alarm and the like are indicated. And a third register for holding an encryption key and supplying the encryption key to the encryption device and the encryption / decryption device.

[0012]

[Operation] The above configuration operates as follows. Step 1 Transmitting side When an analog voice signal is digitized by, for example, the μ-law coding method, the same value does not continue in the digital voice code. Therefore, utilizing this fact, if there is an encryption start instruction from the outside, M first characters are continuously transmitted instead of the voice code transmitted so far, and the process proceeds to step 2.

On the receiving side, the received data is regarded as a voice code until N (where N ≦ M) consecutive first voices of a first character for which a voice code is predetermined during voice reception, and N first characters are used. If the data is continuously received, the subsequent data is not a voice code, so the voice generated by the voice generation circuit in the receiver is sent to the receiver instead of the code decoder output, and the receiver is notified of the start of encryption, and the process proceeds to step 2. . Here, the value of N is determined to be N ≦ M in order to reliably detect the next second character even if a bit error occurs on the communication line.

Step 2 Sender The second character other than the first character used in Step 1 is used to synchronize the start point of the encryption operation between the sender and the receiver.
It is determined that an encryption call is to be started from the next data of the character, and after transmitting one second character, the encryption operation is started and the process proceeds to step S3.

When the second character is detected on the receiving side, an encryption / decryption operation is started from the subsequent data to synchronize the encryption operation with the transmitting side. Step 3 Sender The dummy data that changes each time from the start of the cipher call to detect that the cipher call is normal on the receiving side to detect that the cipher call is normal. Is determined by the output of the first timer), M consecutive first characters and one of the second characters are sequentially encrypted and transmitted, and the process proceeds to step 4.

On the receiving side, in the decrypted data from the start of the decryption operation,
Wait for N (where N ≦ M) consecutive detections of the first character, wait for detection of the second character if N first characters are detected, and wait for detection of the second character. Assuming that communication is possible, that is, that the mutual encryption keys match, the voice supplied to the receiver is switched from the voice generated by the voice generation circuit to the received voice output from the code decoder, and the process proceeds to step 4. .

The reason why the first and second character detection methods are the same as in step 1 and step 2 is to reduce the number of hardware to be realized. Also the first
This character and the second character have already been transmitted to the line without encryption, and thus have been known to eavesdroppers. Therefore, in order to increase the encryption strength, before transmitting the first character, an arbitrary code, that is, dummy data that changes each time, is transmitted in an arbitrary number, that is, as necessary, with a different time length, and encrypted. The existing positions of the first and second characters are not fixed.

Step 4 Transmitting side The voice code is encrypted and transmitted. Receiver The decoder decodes the encrypted and decoded voice code and sends it to the receiver.

If the second timer output is turned on before step 4, ie, before step 4, it is considered that the encryption keys input on the calling side and the called side are different,
That is, it is considered that the encrypted call is impossible, an interrupt (alarm) is generated to the CPU (external), and both the transmitting side and the receiving side transit to step 1. This device prevents wiretapping on the communication line and makes it easy to switch from a non-encrypted call to an encrypted call at any point in time. It is possible to notify the user of both telephones by voice, display, etc., and automatically switch to non-encrypted communication.

[0020]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of an embodiment of a secret telephone apparatus (digital telephone with an encryption function) according to the present invention. This device comprises a main body 1 and a handset 2 connected to the main body 1.

In the main unit 1, a microprocessor unit 4 for controlling the entire main unit, a memory unit 5 including a ROM for storing a program to be executed by the microprocessor unit 4 and a RAM for temporarily storing data, and an encrypted voice A receiver 6 for decoding a signal and outputting a voice signal 22 to a receiver 2r of the handset 2, a transmitter 7 for encrypting and transmitting a voice signal 23 from a transmitter 2s of the handset 2, and a microprocessor 4 LAP-D (Link Access Pr
ocedure on the D-channel) control unit 8 and display control unit 9
A key input control unit 10 for controlling key inputs from the push button dial 12 and the encryption switch 13 is connected to the internal bus 21.

Further, a line termination unit (DSU) of ISDN
A layer 1 control unit 11 for controlling the layer 1 of the B channel and the layer 1 of the D channel of the ISDN which performs an interface conversion with the display unit 14 and a display unit 14 controlled by the display control unit 9 are provided. The push-button dial 12 is used to input a telephone number or an encryption key known only to the parties making an encrypted call.
Reference numeral 3 is used for instructing the start and descrambling of the contents of a call. The cipher switch 13 is a toggle switch, and repeats the start and descrambling instructions each time the switch is pressed. The display 14 is a key input, a telephone number of a caller.
Display numbers , alarms, etc. The layer 1 control unit 11
It is connected to a DSU (not shown) using the SDN plug 3.

The B channel signal 24 from the layer 1 controller 11 is supplied to the receiver 6, the B channel signal 25 from the transmitter 7 is supplied to the layer 1 controller 11, and the output signal 26 of the push button dial 12 Is supplied to the key input control unit 10, the encryption request signal 27 of the encryption switch 13 is supplied to the key input control unit 10, the CPU interrupt signal 29 from the reception unit 6 is supplied to the microprocessor unit 4, and the display control unit 9 Is supplied to the display 14.

FIG. 2 shows the internal structure of the receiver 6 and the transmitter 7 shown in FIG. The transmission control section 41 controls the entire transmission section 7. An IDL register 42, an EOC register 43, a timer 44, a KEY register 45, an M register 46, and a control register 47 are connected to the internal bus 21. The IDL register 42 is set with a first character (hereinafter, this one-byte character is referred to as an “IDL character”) by the microprocessor unit 4, and the EOC register 43
Is set by the microprocessor unit 4 to a second character (hereinafter, this one-byte character is referred to as an "EOC character").
The first timer output (output signal 96) is turned on at an arbitrary time within the time T1 from the operation start instruction, and the KEY register 4
5 is set after the encryption key input from the push-button dial 12 of FIG. 1 is processed by the microprocessor unit 4. The M register 46 is a value indicating the number of consecutive IDL characters to be transmitted (hereinafter, this value is referred to as "M"). Is set by the microprocessor unit 4 and the control register 47
The microprocessor 4 sets an operation instruction to the transmission control unit 41 and the reception control unit 71.

The encoder 48 converts the transmission signal (analog signal) 23 from the transmitter 2s of the handset 2 in FIG. 1 into a 1-byte (8-bit) digital signal. The conversion of this analog signal into a digital signal is described in CCITT Recommendation G. 711 etc. The selector 49 is a 1-byte-wide selector which is controlled by a control signal 70 of the transmission control unit 41, and outputs an output signal 61 of the encoder 48, an IDL character 55 from the IDL register 42, and an EOC character from the EOC register 43. 56 is selected and output. The encryptor 50 encrypts a 1-byte digital signal in 1-byte units. An 8-bit feedback of an OFB format which is a stream encryption format is applied to the encryption format. The selector 51 is a 1-byte-wide selector, and is controlled by a control signal 66 of the transmission control unit 41.
Either the output signal 62 of the selector 49 or the output signal 63 of the encryptor 50 is selected and output. The parallel-serial converter 52 converts the 1-byte width parallel data of the output signal 64 of the selector 51 into 1-bit width serial data, and outputs it as the B channel signal 25. The count value of the counter 53 increases by one each time one IDL character is transmitted.
When the content of the count value output 68 of the counter 53 matches the content of the output signal 59 of the M register 46, the comparator 54 outputs
The encryption key (generally 8 bytes) 58 from the KEY register 45, which notifies the transmission control unit 41 by turning on 9, is supplied to the encryptor 50 and the decryptor 74. From the transmission control unit 41, a signal 65 for controlling the encryptor 50, a counter 5
3 is output.

The receiving control section 71 controls the receiving section 6 as a whole. The N register 72 is connected to the internal bus 21 and has an IDL
The microprocessor unit 4 sets a value indicating the number of consecutive characters received (hereinafter, this value is referred to as “N”: N ≦ M). The serial / parallel converter 73 converts the 1-bit width serial data of the B channel signal 24 into parallel data of 1 byte width, and the encryption / decryption unit 74 outputs the output signal 84 (1 byte digital signal) of the serial / parallel converter 73. 1
Decode in byte units. For the decryption, an 8-bit feedback of an OFB format which is a stream cipher format is applied. The selector 75 is a 1-byte-wide selector, which is controlled by a control signal 89 of the reception control unit 71 and selects one of the output signal 84 of the serial / parallel converter 73 and the output signal 85 of the encryption / decryption unit 74. Output. The code decoder 76 converts the digital signal of the output signal 86 (1 byte width) of the selector 75 into an audio signal (analog signal).
The rule for converting this digital signal into an analog signal is C
CITT Recommendation G. 711 etc. When switching from non-encrypted communication to encrypted communication, the electronic sound generation circuit (speech generation circuit) 77 receives an audio signal other than an audio signal such as an IDL character or an EOC character, and outputs this as unpleasant sound from the handset 2r of the handset 2. In order to prevent the unpleasant sound, another sound (analog signal) is generated from the electronic sound generation circuit 77 instead of the unpleasant sound and supplied to the receiver 2r. It also serves as a signal that you are in the process of switching to an encrypted call.

The selector 78 is an analog signal selector, which is controlled by a control signal 90 of the reception control unit 71, and outputs the output 87 of the code decoder 76 and the electronic sound generation circuit 77.
And the output 88 is selected and output. Comparator 8
2 is the output signal 86 of the selector 75 and the EOC register 43
When the content of the output EOC character 56 matches, the output 95 is turned on. The comparator 79 turns on the output 91 when the output signal 86 of the selector 75 matches the content of the output IDL character 56 of the IDL register 42. When the output 91 of the comparator 79 is on, the count value of the counter 80 increases by one, and when the output 91 of the comparator 79 is off, the count value becomes zero. When the content of the count value output 92 of the counter 80 matches the content of the output 93 of the N register 72, the comparator 81 turns on the output 94 to notify the reception control unit 71. The reception control unit 71 outputs a signal 89 for controlling the encryption / decryption unit 74 and the selector 75, and a CPU interrupt signal 29 for generating an interrupt to the microprocessor unit 4.

The present invention can be applied to a digital telephone which carries out a telephone call by encoding voice using the information channel (B channel) of the ISDN basic interface subscriber line. The operation of the present invention will be described below with reference to FIGS. 1, 2 and 3 taking this digital telephone as an example. A digital telephone with an encryption function on the transmitting side to which the present invention is applied (hereinafter referred to as "X telephone"), and a digital telephone with an encryption function on the receiving side to which the present invention is applied (hereinafter referred to as "Y telephone")
Will be described from the point in time after the B channel of the X telephone and the B channel of the Y telephone are connected.

Before taking a cipher call, to prevent leakage to a third party, the person who took the handset of the Y telephone first
It is necessary to determine whether or not the person who called the X telephone is the one who wants to talk. First, from the conversation,
If the person who took the handset of the telephone does not want to talk to the person who called the X telephone, he or she may hang up the telephone at that time. Then, some means, for example, both the pre-sent and that encryption key (a combination of numbers known only only at that time who each other) by mail is push-button input Ri by dialing <br/> of each phone, the input Both sides confirm that it is completed,
Either or either person presses the encryption switch to start an encrypted call. If the encryption keys entered by both sides match, the conversation can be made in the encrypted call state, but if the encryption key entered on the Y telephone is different from that of the X telephone, communication will be disabled and both telephones will generate an alarm. And display it on the display. As a result, the secret call contents are not accidentally leaked to anyone other than the parties. In addition, even if you enter the encryption key incorrectly, an alarm is generated and the phone enters the
Since subsequent calls are possible, the parties can be confirmed again by conversation.

Also, even if an attempt is made to eavesdrop anywhere on the line, the telephone to which the present invention is applied uses the same encryption key as above,
In addition, eavesdropping is impossible unless the contents of the call are decrypted from the start of the encrypted call. In the present invention, since the audio signal to be encoded is in units of 8 bits (1 byte) and real-time performance is required for conversation, a CFB mode in which encryption is performed in units of 8 bits in a stream cipher format is applied. , And the initial variable (IV) is fixed.

Next, the above operation will be described in detail by taking the transmitting side of the X telephone and the receiving side of the Y telephone as examples. Sender The sender has seven phases of operation. In the first operation phase, the input voice code is transmitted without encryption (hereinafter, referred to as “phase 1”).

In the second operation phase, M IDL characters are transmitted in response to an encryption start instruction from the microprocessor unit, and transition to phase 3 (hereinafter, referred to as “phase 2”). The third operation phase is one EO
The C character is transmitted until the transition to phase 4 (hereinafter, referred to as “phase 3”).

In the fourth operation phase, the input voice code is encrypted and transmitted for an arbitrary time, and the phase shifts to phase 5 (hereinafter referred to as "phase 4"). In the fifth operation phase, the M IDL characters are encrypted and transmitted, and transit to phase 6 (hereinafter, referred to as “phase 5”). In the sixth operation phase, one EOC character is encrypted and transmitted, and transitions to phase 7 (hereinafter, referred to as “phase 6”).

In the seventh operation phase, the input voice code is encrypted and transmitted (hereinafter referred to as "phase 7").
Prior to the start of the operation, the microprocessor unit 4 executes the initial program, and stores the ID in the IDL register 42 of the transmitting unit 7.
The DL character is set, the EOC character is set in the EOC register 43 of the transmitting unit 7, the continuous transmission number value M of the IDL character is set in the M register 47 of the transmitting unit 7, and the N register 72 of the receiving unit 6 is set. The continuous reception number value N of the IDL character is set, and the control register 47 of the transmission unit 7 is instructed to set the transmission control unit 41 and the reception control unit 71 to the initial state. The input control unit 10 is set in an operable state.

Phase 1 The output signal 23 (analog signal) of the transmitter 2 s of the handset 2 in FIG. 1 is converted to a 1-byte digital signal (voice code) by the encoder 48 of the transmitter 7. At this time, the transmission control unit 41 instructs the selector 49 to select the output signal 61 of the encoder 48 by the control signal 70,
The selector 49 is given to the selector 51 by the control signal 66.
To select the output signal 62 of.

Therefore, in this phase, an unencrypted input voice code is transmitted as the output signal 25 of the transmitting section 7 in FIG. If the person who picks up the handset of the Y telephone during the operation of this phase is the other party who wants to talk to the person who operates the X telephone, both enter the encryption key from the push button dial 12 of each telephone. The microprocessor unit 4 processes the input encryption keys and sets each in the KEY register 45 of the transmission unit 7. The content set in the KEY register 45 is set in the encryptor 50 and the decryptor 74 as an encryption key.

Phase 2 After confirming that both parties have completed the input of the encryption key in phase 1, both or one of them depresses the encryption switch 13 for instructing the start of the encryption call attached to the telephone. . When the encryption switch 13 is pressed, the signal 27 is turned on to notify the key input control unit 10 and the key input control unit 10
Informs the microprocessor unit 4 that the encryption switch 13 has been pressed. In response to this, the microprocessor unit 4 instructs the control register 47 to start encryption (at the point 101 in FIG. 3).

When the other party (Y telephone) presses the encryption switch 13 before the other party, the reception control section 71 of the reception section 6 continuously transmits the IDL character to the microprocessor section 4 by the CPU interrupt signal 29. It reports that N pieces have been received (details will be explained on the receiving side). Upon receiving this report, the microprocessor unit 4 instructs the control register 47 to start ciphering, as in the case where the cipher switch 13 is pressed.

In response to an encryption start instruction to the control register 47, the transmission control unit 41 instructs the selector 49 to select the output signal 55 of the IDL register 42 by a control signal 70, and also outputs a control signal 67 to the selector 49. Turn on to start the counter 53. Counter 53 is ID
Each time one L character is transmitted, the count value is increased by one. When the value of the count value output signal 68 reaches the value M set in the M register 46, the output signal 69 of the comparator 54 is turned on, and the transmission is performed. The talk control unit 41 receives this and the control signal 67
To clear the counter 53 to 0,
Transition to the operation of phase 3.

Therefore, in this phase, M IDL characters are transmitted as the output signal 25 of the transmitting section 7 in FIG. 1 and the phase shifts to phase 3 (periods 101 to 102 in FIG. 3).・ Phase 3 The transmission control unit 41 determines that the selector 49
The output signal 56 of the OC register 43 is instructed to be selected, one EOC character is transmitted, and the operation transits to the phase 4 operation.

Therefore, in this phase, one EOC character is transmitted as the output signal 25 of the transmitting section 7 in FIG. 1, and the phase shifts to phase 4 (periods 102 to 103 in FIG. 3). Phase 4 The transmission control unit 41 instructs the selector 49 to select the output signal 61 of the encoder 48 by the control signal 70, instructs the encryptor 50 to start encryption by the control signal 65, and controls the control signal 66 by the control signal 65. Instructs the selector 51 to select the output signal 63 of the encryptor 50, and starts the operation of the timer 44. In this phase, the output signal 96 of the timer 44 (first
(Timer output of the second timer) is turned on, the phase shifts to phase 5.

Therefore, in this phase, the output signal 2 of the transmitting section 7 of FIG.
As 5, the input voice code (for example, the ambient noise captured by the transmitter 2s at that time) encrypted with the encryption key set from the push button dial 12 is transmitted. This voice code is transmitted as dummy data that changes every time the encryption start instruction is issued, and a different code is used for each encryption start instruction, such as ambient noise and the time at that time.

Phase 5 When the output signal 96 of the timer 44 is turned on, the transmission control unit 4
In response to this, the control signal 70 instructs the selector 49 to select the output signal 55 of the IDL register 42 by the control signal 70, and turns on the control signal 67 to start the counter 53. The counter 53 increments the count value by one every time one encrypted IDL character is transmitted.
And the value of the count value output signal 68 is
Is reached, the output signal 69 of the comparator 54 is obtained.
Is turned on, the transmission control unit 41 receives this, turns off the control signal 67, clears the counter 53 to 0, and transitions to the operation of phase 6.

Therefore, in this phase, M IDL characters encrypted with the encryption key set from the push-button dial 12 are transmitted as the output signal 25 of the transmitting section 7 in FIG. 1, and the process proceeds to phase 6 (FIG. 3). Period from 104 to 105).・ Phase 6 The transmission control unit 41 determines that the selector 49
It instructs to select the output signal 56 of the OC register 43, sends out one encrypted EOC character, and transitions to the operation of phase 7.

Therefore, in this phase, one EOC character encrypted with the encryption key set from the push-button dial 12 is transmitted as the output signal 25 of the transmitting section 7 in FIG. 1, and the phase shifts to phase 7 (FIG. 3). 105 to 106). Phase 7 The transmission control unit 41 instructs the selector 49 to select the output signal 61 of the encoder 48 by the control signal 70, and transmits the encrypted input voice code.

Therefore, in this phase, the input voice code encrypted with the encryption key set from the push button dial 12 is transmitted as the output signal 25 of the transmitting section 7 in FIG. 1 (106 and thereafter in FIG. 3). Receiver The receiver has five operating phases.

In the first operation phase, the received voice code is output as it is, and if N consecutive IDL characters are detected, the phase shifts to phase 2 (hereinafter referred to as "phase 1"). In the second operation phase, the output of the received voice code is stopped and the detection of an EOC character is awaited. If an EOC character is detected, the process transits to phase 3 (hereinafter, referred to as “phase 2”).

In the third operation phase, the received data is decoded, and the IDL
If the number is detected, the phase shifts to phase 4 (hereinafter, referred to as “phase 3”). The fourth operation phase decodes the received data, waits for detection of an EOC character from the decoded data, and if an EOC character is detected, transitions to phase 5 (hereinafter referred to as “phase 4”).

In the fifth operation phase, the received data (encrypted voice code) is decrypted and the voice code is output (hereinafter referred to as "phase 5"). Phase 1 The reception control unit 71 instructs the selector 75 to select the output signal 84 of the serial / parallel converter 73 by the control signal 89, and the control signal 90 sends the output signal of the code decoder 76 to the selector 78. Since it is instructed to select 87, the voice from the other party is directly output to the receiver 2r of the handset 2 in FIG.

Also, since the counter 80 is operating, a plurality of I / Os transmitted before the other party starts the voice encryption.
DL characters can be detected at any time. Comparator 79
Counter 80 each time an IDL character is detected.
(When the signal 86 is not an IDL character, the output signal 91 of the comparator 79 is turned off and the counter 80 is cleared to 0). When the value of the count value output signal 92 of the counter 80 reaches the value N set in the N register 72, the output signal 94 of the comparator 81 is turned on, and the reception control unit 71 receives this and transits to the operation of phase 2. And C to the microprocessor unit 4
The PU interrupt signal 29 reports that N consecutive IDL characters have been received. The microprocessor unit 4 receives this, and if the encryption start instruction has not been issued to the control register 47, the microprocessor unit 4 issues an encryption start instruction to the control register 47 (see the point 111 in FIG. 3). If the encryption start instruction has already been issued to the control register 47, this interrupt is ignored.

Therefore, in this phase, the received voice signal (digital signal) is directly converted into an analog signal and output as the output signal 22 of the receiver section 6 in FIG.
It is in a state of waiting for detection of N consecutive L characters. Phase 2 The reception control unit 71 uses the control output signal 90 to select the selector 7.
8 to select the output signal 88 of the electronic sound generation circuit 77. Therefore, the sound generated by the electronic sound generation circuit 77 flows from the receiver 2r of the handset 2 in FIG.

When the comparator 82 detects the EOC character, the output signal 95 of the comparator 82 is turned on to notify the reception control unit 71, and the reception control unit 71 receives the signal and makes a transition to the operation of phase 3 ( (At time point 113 in FIG. 3). Therefore, in this phase, the sound from the electronic sound generation circuit is played to the receiver 2r, and the receiver 2r is in a state of waiting for the EOC character.

Phase 3 The reception control unit 71 instructs the encryption / decryption unit 74 to start the reception data decryption operation by the control signal 89,
5 is instructed to select the output signal 85 of the decryption unit 74. Also, since the counter 80 is in operation, a plurality of encrypted IDL characters can be detected at any time. Each time the comparator 79 detects one IDL character, the count value of the counter 80 increases by one.
The value of the count output signal 92 of the counter 80 is set to the N register 7
When the value N set to 2 is reached, the output signal 9 of the comparator 81 is output.
4 is turned on, and the reception control unit 71 transitions to the operation of phase 4 in response to this.

Therefore, in this phase, the sound from the electronic sound generation circuit flows to the receiver, and the IDL is decoded from the decoded reception data.
If N consecutive IDL characters are detected from the decoded reception data in a state of waiting for the detection of N consecutive characters, the process shifts to phase 4 (at the point 114 in FIG. 3). The detection of N consecutive IDL characters from the decrypted received data means that the encryption keys input to the X telephone and the Y telephone are the same.

Phase 4 The reception control section 71 instructs the encryption / decryption unit 74 to decode the reception data by the control signal 89 and outputs the output signal 8 of the encryption / decryption unit 74 to the selector 75 in the same manner as in phase 3.
Instruct the user to select 5.

When the comparator 82 detects the EOC character, the output signal 95 of the comparator 82 is turned on to notify the reception control unit 71, and the reception control unit 71 receives the signal and transits to the phase 5 operation. Therefore, in this phase, the sound from the electronic sound generation circuit is played to the receiver, and if an EOC character is detected from the decoded received data in a state of waiting for the detection of the EOC character from the decoded received data, the phase shifts to phase 5 (FIG. 3). 115).

Phase 5 The reception control unit 71 instructs the selector 78 to select the output signal 87 of the code decoder 76 by the control unit signal 90. Therefore, in this phase, the encrypted voice signal received as the output signal 22 of the receiver 6 in FIG.
It is converted into an analog signal and output.

When the output signal (second timer output) 97 of the timer 44 is turned on without entering the phase 5, it is considered that the encryption keys input from the push button dial 12 to the X telephone and the Y telephone are different, and In response to this, the control unit 71 reports to the microprocessor unit 4 that the encryption keys do not match by using the CPU interrupt signal 29. Upon receiving this, the microprocessor unit 4 instructs the display control unit 9 to display an alarm on the display unit 14 and also instructs the control register 47 to restart the operation.
It instructs the transmission control unit 41 and the reception control unit 71 to start the operation from phase 1. The timer period during which the second timer output (output signal 97) of the timer 44 is turned on is the longest time period T assigned to dummy data transmission.
1 (the longest one at time 103 to 104 in FIG. 3) and an appropriate value longer than the sum of the transmission period of M IDL characters and the transmission period of one EOC character (time 104 to 106 in FIG. 3). I do.

[0059]

As will be understood from the above description, the present invention has the following effects. Since encryption algorithms such as DES and FEAL and a stream encryption format are used, the encryption strength is high. Since encryption and decryption are performed using digital signals, there is no deterioration in the decoded sound quality due to the encryption.

Since the encryption and decryption processes are performed in units of the output width of the encoder and the codec, the signal processing delay is small and conversation is not difficult. During switching from the non-encrypted call to the encrypted call, another voice is generated and supplied to the receiver instead of the reception data (dummy data, the first character, the second character, etc.), and there is no discomfort, and It can be confirmed that the state is switched from the non-encrypted call to the encrypted call state.

The transmitting side automatically transmits a predetermined number of first characters at the start of encryption, and the receiving side determines that the number of consecutively detected first characters to be received at this time is smaller than the number of transmitted characters. Even if an error occurs, the specific character can be easily detected. If the encrypted call cannot be performed normally due to the difference in the encryption key, this is displayed on both the calling and called telephones, and the call is automatically switched to the non-encrypted call.

[0062] calling and prior to confirmation of the coincidence of the encryption key entered in the called party, a strong encryption strength because it inserts dummy data in any number of arbitrary code. Since the decryption start on the receiving side may be performed after the encrypted second character, it is suitable for the stream encryption format. Since the configuration is simple, the hardware scale is small, and it is within the range that can be easily integrated into one chip by the current LSI technology, and the device can be realized at low cost.

In the above description, the first and second codes may be used in place of the first and second characters.
A warning tone may be used instead of displaying a warning to that effect, and if the device is configured to always indicate whether the device is in an unencrypted or encrypted call state, the state The warning may be displayed. The electronic sound generation circuit is not necessarily provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a block diagram showing an example of the internal configuration of a receiver 6 and a transmitter 7 in FIG. 1;

FIG. 3 is a time chart showing a conversion operation from a non-encrypted call to an encrypted call.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04L 9/16 H04L 9/28 H04M 1/68

Claims (1)

(57) [Claims] An encoder for converting an analog signal from a transmitter into a digital signal, and an output of the encoder, a first code, a second code, and dummy data selected and output. A first selector, an encryptor for encrypting the output of the first selector in a stream cipher format, a second selector for selecting one of the output of the encryptor and the output of the first selector, Controls the first selector and the second selector so as to transmit the output of the encoder, and outputs M first codes (M is an integer of 2 or more) in response to an external encryption start instruction. ) Controlling the first selector to transmit, then controlling the first selector to transmit one second code, and then starting the operation of the encryptor and the timer And each time The first selector and the second selector are controlled so as to encrypt and transmit dummy data to be encrypted, and encrypt and transmit M first codes at an arbitrary time equal to or less than a certain timer value. Control the first selector as described above,
A transmission control unit that controls the first selector to encrypt and output one code of the first code, and then controls the first selector to encrypt and output the output of the encoder; An encryption / decryption device for decrypting a received digital signal in a stream encryption format, an output of the encryption / decryption device, a third selector for selecting any of the received digital signals, and a first selector output from the third selector output. N consecutive codes
Means (where N ≦ M and N is a positive integer); means for detecting the second code from the third selector output; and code decoding for converting the third selector output into an analog signal. a vessel, a receiver the output of the code decoder is supplied, initially, the third selector selects the digital signal received, this third N consecutive detecting a first code from the selector output performs an operation, when the first code N consecutive detection performs an operation for detecting a second code, SL on upon detecting the second code third selector above decryption
The output of the vessel starts decoding operation of Rutotomoni the encryption decoder select performs the third consecutive first code from the selector output the N detection operates, when the first code N consecutive detection It performs an operation of detecting the second code, the second
When the selector 3 selects the received digital signal.
Even if a predetermined time has passed since the detection of the second code, the third
The second when the selector selects the output of the decryptor
A secret telephone device, comprising: a receiving control unit having means for notifying that the transmission control unit and the receiving control unit are in the initial state and not in the non-encrypted call state when no code is detected .