JP2578017B2 - Secret telephone device - Google Patents

Description

Description: 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.

"Conventional technology" 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". Academic Theory (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, BJMcDermott)
and AMQuinn: “Analog scramblers for speech base
d on sequential permutations in time and frquenc
y ", Bell Syst. Tech. J. 62, 1, pp. 25-46 (Jan. 1983)), a method of inverting the polarity of a sampled voice according to a certain rule (for example, see S. Asakawa, F. Sugiyama and
M. Nakamura: “A voice scrambler for mobil communica
tion ", IEEE Trans. Veh Technol. 29, 1, pp. 81-86 ((Fe
b.1980)). In addition, FFT (Faest Fourier T
FFT scrambling method applying ransform (Fast Fourier Transform) method (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.

Also, in the same way as encrypting the message,
A digital encryption system has been proposed in which an audio signal is encoded and then encrypted.

Currently, as a security measure for digital communications, one of the sender and receiver decides a key and sends the same key to the other party, for example, by mail, and then the data to be sent by the sender (plaintext)
Is encrypted with the key and the ciphertext is transmitted, and the receiving side reversely encrypts the ciphertext received with the previous key, that is, decrypts the ciphertext and restores the original plaintext. The cryptographic algorithms used in these methods need to be disclosed in order to perform cryptographic communication with an unspecified partner. DES as a typical example of the algorithm public type encryption (for details of the DES algorithm, see, for example, DWDavies and WLPrice
(Translated by Kamizono): "Network Security", Nikkei McGraw-Hill, 1985 pp. 55-84), FEAL (Details of the FEAL algorithm are, for example, Miyaguchi, Shiraishi, Shimizu: "FEAL
-8 Cryptographic Algorithm ", Ken Jitsuho Vol. 37, No. 4/5, 198
8 PP.321-372).

Next, the encryption usage format (for details of the encryption usage 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).

 CFB format (Cipher Feedback mode).

 OFB format (Output Feedback mode).

[Problems to be Solved by the Invention] 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 decrypted sound quality due to encryption. Further, the last method has drawbacks such as difficulty in conversation due to signal processing delay, deterioration of decoded sound quality due to encryption, and time required to switch from normal conversation to encrypted conversation. In the analog encryption method, even if a ring tone (an audio signal indicating that there is an incoming call from a third party) received from the network is received, it is received as incomprehensible noise during an encrypted call, and the ring tone is received. Service cannot be received because the call cannot be confirmed.

Before the ISDN (Digital Integrated Telecommunications Network) service was launched, the transmission network was based on analog transmission, and digital transmission required about 20 times the frequency band of analog transmission to transmit the same voice signal. Thus, there is no example in which digital encryption of telephone using analog transmission has been realized from the viewpoint of cost. However, as ISDN spreads, it is conceivable to conduct telephone conversations by encrypting them using a digital encryption system. In this case, a stream cipher may be applied to increase the cipher strength. However, the cipher of the stream cipher cannot be decrypted unless the other party knows the cipher start time. In other words, it is necessary to simultaneously start the operations of the encryptor and the decryptor of the telephones that are talking with each other. However, since a telephone does not have a protocol such as a transmission control procedure for data communication, means for notifying the other party of the encryption start time is required. In addition, it is necessary to confirm that the person who answers the other party's phone is the person who wants to talk. Therefore, normal (unencrypted)
After confirming the other party in the conversation, the conversation is transferred to the encrypted conversation. At this time, it is desired that the synchronization between the encryption and the decryption can be easily achieved. When an incoming call is received from a third party, the operation of the encryptor and the decoder of the mutual telephone is stopped at the same time, the other party is put on hold, and a call is made with the third party. Need to talk to the other party again.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a secret telephone device that has an encryption function that can easily switch between a non-encrypted conversation and an encrypted conversation and has a high encryption strength.

According to the present invention, an encryptor for encrypting an input signal in a stream encryption format, an encrypted output from the encryptor,
A first selector for switching and transmitting an unencrypted signal, a cipher decoder for decrypting a received input signal in a stream cipher format, and switching between a decrypted output of the cipher decoder and the received input signal A second selector which takes in the first character, and normally the first selector transmits an unencrypted signal, and the first character is generated by the first signal of the encryption start instruction and the first interrupt signal. (M is an integer of 2 or more) continuously, then one second character is transmitted, and the audio data is encrypted by the encryptor and transmitted from the next character. A transmission control unit for encrypting and transmitting M consecutive one characters and one of the second characters thereafter by the encryptor, and transmitting unencrypted voice data from the next; Usually, the second The collector and uptake of the received input signals, (in N ≦ M N is a positive integer) N number consecutively the first character as the received input signal when detecting, the first
When the second character is detected, the output of the encryption / decryption device is fetched, and the first character is continuously output as the output of the encryption / decryption device.
A receiving control unit that returns to an initial state when the second character is detected after the individual detection.

"Operation" A telephone calls the B telephone, and the callee of the B telephone and the caller of the A telephone mutually confirm each other through a normal conversation without encryption, and then enter a cryptographic conversation. When the switch is operated, an encryption communication start signal is generated, and the transmission control unit sends M first characters, and then sends one first character.
After the transmission signal is encrypted by the encryptor and transmitted, and after detecting N consecutive first characters, when the second character is detected, a first interrupt signal is generated and the signal is transmitted to the code decoder. The output of the decryption unit is supplied in place of the received digital signal, the encryption unit and the decryption unit in one direction are synchronized, and the first interrupt signal sends out M characters of the first character. 2 is transmitted, and then the transmission signal is encrypted and transmitted by the encryption device. In response to this, the reception control means operates in the same manner, and the encryption device and the decryption device in the other direction are transmitted. Are synchronized, and the A telephone and the B telephone enter a state of conversation by encryption.

In this state, if there is an incoming call from phone C to phone A,
When the person using the telephone at that time controls the second switch to generate a line hold start signal, the first character is continuously transmitted M times, and then the second character is transmitted one time. And then outputs the output of the encoder in place of the output of the encryptor. When the B telephone detects N consecutive first characters, and then detects the second character, it outputs a first interrupt signal. And outputs the received digital signal to the codec in place of the output of the decryptor, so that the B telephone is ready to receive the hold tone from the network, and transmits M first characters continuously. ,
After that, one second character is transmitted, the output of the encoder is transmitted in place of the output of the encryptor, and the first character and the second character are received by the A telephone, and the receiving part of the telephone receives a normal conversation. Then, the user can talk with the caller of the C telephone. When the user enters the encrypted conversation between the A telephone and the C telephone, the user may perform the same operation as when entering the encrypted conversation between the A telephone and the B telephone. When the conversation between the A-phone and the C-phone is terminated and the hold is released on the A-phone, the same operation as at the start of the hold is performed so that both the A-phone and the C-phone are in a normal conversation state, and the C-phone is in the A-state. Disconnected from the phone,
The A telephone is reconnected to the B telephone and is normally in a state of universal conversation.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows the configuration of an embodiment of a secret telephone apparatus (digital telephone with an encryption function) showing one embodiment of the present invention.
This device consists of a main unit 1, a handset (handset) connected to the main unit 1, a main unit 1 and ISDN (Integrated Services Digital).
And a line termination unit (DSU) 3 for connecting to a subscriber line 4 of the network.

The main unit 1 includes a microprocessor unit 5 for controlling the entire main unit, a memory unit 6 including a ROM and a RAM for temporarily storing a program executed by the microprocessor unit 5 and temporarily storing data, and receiving a call from a third party during a call. If there is, an operation start instruction is performed by the microprocessor unit 5 and a sound notifying that there is an incoming call is output to the receiver 2r of the handset 2.
A ring tone generating circuit 7 that outputs to the receiver 2, a receiver 8 that decodes the encrypted voice signal and outputs a voice signal to the receiver 2r of the handset 2, and encrypts a voice signal from the transmitter 2s of the handset 2. The transmitting unit 9 for transmitting, the layer 3 for controlling the ISDN D channel layer 3 by the microprocessor unit 5 is controlled 10, and the display unit 1 is controlled by the microprocessor unit 5.
Display control section 11 to control 6, push button dial
Key input control unit 12 for controlling 15 key inputs, driver / receiver for performing interface conversion with line termination device 3
13, a layer 1 and 2 control unit 14 for controlling the ISDN B-channel layer 1 and the D-channel layer 1 and 2, a telephone number input or a push button dial 15 for inputting an encryption key known only to the parties involved in the call, Display 16, which shows the communication mode, channel used, operation status such as outgoing / incoming / calling, etc.If there is an incoming call from a third party during a call, the caller is put on hold and the incoming third party Hold switch 17 that instructs the start of hold and the release of hold to complete the call and the call with the third party and re-establish the call with the original party (The hold switch 17 is a toggle switch. A decryption instruction), and an encryption switch 18 for instructing the start and decryption of the contents of the call (the encryption switch 18 is a toggle switch, and when depressed again, provides an decryption instruction). .

The ISDN subscriber line 4 is connected to the line terminating device 3, and includes a microprocessor unit 5, a memory unit 6, a ring tone generation circuit 7,
The receiving unit 8, the transmitting unit 9, and the control units 10, 11, and 12 are internal buses.
19, the reception signal 20 (analog signal) from the receiver 8 is supplied to the receiver 2r of the handset 2, and the transmission signal 21 (analog signal) from the transmitter 2s of the handset 2 is transmitted to the transmitter 9. The B channel signal 22 from the layer 1 and 2 control unit 14 is supplied to the receiving unit 8, the B channel signal 23 from the transmitting unit 9 is supplied to the layer 1 and 2 control unit 14,
The ring tone 24 (analog signal) from the ring tone generating circuit 7 is supplied to the receiver 2r, and the output signal 25 of the push button dial 15 is output.
Is supplied to the key input control unit 12, and the display control unit 11
Is supplied to the display 16, the hold request signal 27 of the hold switch 17 is supplied to the transmitter 9, the encryption request signal 28 of the encryption switch 18 is supplied to the transmitter 9, and the transmitter 9 Hold instruction signal 29 (first interrupt) of layer 3
It is supplied to the control unit 10.

FIG. 2 shows the internal configuration of the transmitting section 9 and the receiving section 8 of FIG. The transmission control section 31 in the transmission section 9 is a control section for controlling the entire transmission section, and the IDL register 32 is a microprocessor section 5.
The EOC register 33 stores a first character (hereinafter, this one-byte character is referred to as an “IDL character”) by the microprocessor unit 5. ") Is set in the register, K
The EY register 34 is a register that sets the encryption key input from the push button dial 15 in FIG. 1 through the key input control unit 12 and the microprocessor unit 5 through the internal bus 19, and the M register 36 is a sequence of IDL characters. A register and an encoder that set a value indicating the number of transmissions (hereinafter, this value is referred to as “M”) by the microprocessor unit 5
37 converts the audio signal 21 (analog signal) 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 in accordance with CCITT recommendation G.711. Selector 38
Is a 1-byte wide selector for selecting and outputting one of the output signal 48 of the encoder 37, the IDL character signal 44 from the IDL register 32, and the EOC character signal 45 from the EOC register 33 by the transmission control unit 31, The transmitter 39 is supplied with the output signal 50 of the selector 38 and encrypts the digital signal of one byte in units of one byte (the encryption will be described in detail later). A 1-byte-wide selector that selects and outputs one of the output signal 51 and the output signal 50 of the selector 38. The parallel-serial converter 41 is supplied with the output signal 52 of the selector 40. The counter 42 is converted to serial data having a width and output as a B channel signal 23.
When the 31 is instructing the selector 38 to select the IDL character signal 44, the counter 43 increases the count value by one each time an IDL character is transmitted. When the content of the output signal 47 of the M register 36 matches, the output 57 is turned on to notify the transmission control unit 31 of the encryption key (8-byte width) 4 from the KEY register 34
Reference numeral 6 denotes a signal 53 for controlling the encryptor 39, a signal 54 for controlling the selector 40, and a signal 55 for controlling the counter 42, which are supplied from the transmission control unit 31 to the encryptor 39 and the decryptor 63 of the receiver 8.
Is output.

In the receiving section 8, the receiving control section 61 controls the entire receiving section, and the serial / parallel converter 62 controls the (of the B channel signal 22).
The encryption / decryption unit 63 converts 1-bit serial data into 1-byte parallel data. The encryption / decryption unit 63 decodes the 1-byte digital signal from the serial / parallel converter 62 in units of 1 byte (decryption will be described in detail later). , The selector 64 is controlled by the reception control unit 61 through a signal 75,
1-byte selector for selecting and outputting one of the output signal 72 of the
A comparator 66 converts a digital signal of an output signal 74 (1 byte width) of the selector 64 into an audio signal (analog signal).
Turns on the output 77 when the output signal 74 of the selector 64 and the EOC character signal 45 match, and the comparator 67
When the output signal 74 of the comparator 67 and the IDL character signal 44 match, the output 78 is turned on. When the output 78 of the comparator 67 is on, the count value increases by one, and when the output 78 of the comparator 67 is on. When the count value becomes 0, the comparator 69
When the count value output 79 of 68 and the signal 80 indicating N match, the output 81 is turned on to notify the transmission control unit 31 and the reception control unit 61.
A signal 75 for controlling 64 is output. N register 70
A value indicating the number of consecutive receptions of IDL characters (hereinafter, this value is referred to as “N”: N ≦ M) is set to the microprocessor unit 5.
Is a register set by

In this example, the digitized audio signal is 8 bits (1
8 bytes of the OFB format, which is a stream encryption format, by being in units of bytes, requiring real-time performance for conversation, minimizing the effects of bit errors on the line, and increasing the encryption strength. Apply feedback.

INDUSTRIAL APPLICABILITY The present invention can be applied to a digital telephone for making a telephone call by encoding voice using the information channel (B channel) of the ISDN basic interface subscriber line, and this telephone receives an incoming call from a third party during an encrypted telephone call. Can temporarily hold the other party on the call and talk to the third party who has received the call. In the following, taking this digital telephone as an example, FIG.
The operation of the present invention will be described with reference to FIG. 2 and FIG.

The circuit-switched call setup function provided by the ISDN service (for details on the ISDN circuit-switched service and its call setup function, see, for example, Nippon Telegraph and Telephone Corporation: “Technical Reference IN
For details on the S-Net service interface, 3rd volume (Layer 3 round exchange), Telecommunications Association, 1989), call-in-call notification function, call-waiting function (call-in-call notification function, call-waiting function) Edited by Telegraph and Telephone Co., Ltd .: "Technical Reference Material: INS Net Service Interface Part 4 (Layer 3 Circuit Switching Supplementary Service)", Telecommunications Association, 1989, P7-22
), A digital telephone on the transmitting side (hereinafter referred to as “A telephone”) to which the present invention is applied, a digital telephone on the receiving side (hereinafter referred to as “B telephone”) to which the present invention is applied, and the present invention. In a digital telephone (hereinafter, referred to as a "C telephone") that receives a call to the A telephone to which is applied, the description will be made from the point in time after the B channel of the A telephone and the B channel of the B telephone are connected.

Before encrypting the voice and making a call, check if the person who took the handset of the B telephone is the person who wants to talk to the person who called the A telephone in order to prevent leakage to a third party. Need to check. As a method of this confirmation, a communication method using a conversation or an encryption key (a combination of numbers known only to the parties) that has been sent in advance by some means (for example, direct delivery to the person by registered mail) is used. There is a method of decrypting with the key. Judging from the conversation content, if the person who picks up the handset of the telephone B is not the one who wants to talk to the person who calls the telephone A, he or she can hang up the telephone at that time. If the person who picked up the handset of telephone B is not sure whether the person who called telephone A is the person who wants to talk, the next step is to enter an encryption key from the push button dial of each telephone. After confirming that both parties have entered the encryption key in a conversation, one or both parties turn on the encryption switch 18 to start an encrypted call. If the encryption key input on the B telephone is incorrect, communication becomes impossible (only noise is sent to the receiver), and the contents of the call do not leak to the other party. Also, even if an attempt is made to eavesdrop on the ISDN network or anywhere on the line, eavesdropping is not possible unless the telephone using the invention decrypts the contents of the call with the same encryption key as above.

Further, when there is an incoming call from the C telephone to the A telephone during the encrypted call between the A telephone and the B telephone (incoming call), the communication between the A telephone and the C telephone is initially encrypted in the same manner as between the A telephone and the B telephone. It is necessary to make an unencrypted call, and a hold tone is transmitted from the network to the held B telephone, and since the held music is not encrypted, it is necessary to return to an unencrypted call between the A telephone and the B telephone. is there. Thereafter, the procedure between the A telephone and the C telephone proceeds in the same procedure as that between the A telephone and the B telephone.
When the call is completed, the hold (call waiting) state between the A telephone and the B telephone is released, and the telephone call is made again.

Next, the above operation will be described in detail for the transmitting side and the receiving side of the telephone.

Sender The sender has six phases of operation.

The first operation phase is performed after the pre-setting until the encryption start instruction is issued (hereinafter, referred to as “phase 1”).

In the second operation phase, M IDLs are issued according to the encryption start instruction.
Until the character is transmitted, and the transition to phase 3 occurs (hereinafter referred to as “phase 2”).

In the third operation phase, one ECO character is transmitted, and the state transits to phase 4 (hereinafter, referred to as “phase 3”).

In the fourth operation phase, the input audio signal is encrypted and is being transmitted until a decryption instruction is issued (hereinafter, referred to as “phase 4”).

In the fifth operation phase, M encrypted IDL characters are transmitted in response to the decryption instruction, and the state transits to phase 6 (hereinafter, referred to as “phase 5”).

In the sixth operation phase, one encrypted EOC character is transmitted, and the state transits to phase 1 (hereinafter, referred to as “phase 6”).

Prior to the start of the operation, the microprocessor unit 5 sets the NL consecutive reception number value (N) in the N register 70 of the receiving unit 8 by executing the initial program, and
The first character (IDL character) in the IDL register 32
Is set, the second character (EOC character) is set in the EOC register 33 of the transmitting section 9, the number of consecutive transmissions of IDL characters (M) is set in the M register 36 of the transmitting section 9, and the layer 3 The control unit 10, the display control unit 11, and the key input control unit 12 are made operable.

Phase 1 The output 21 (analog signal) of the transmitter 2s of the handset 2 in FIG. 1 is converted into a 1-byte-width digital signal by the encoder 37 of the transmitter 9. At this time, the output 58 of the transmission control unit 31 instructs the selector 38 to select the output 48 of the encoder 37, and the output 54 of the transmission control unit 31 outputs the output 50 of the selector 38 to the selector 40. Instruct the user to make a selection.

Therefore, in this phase, the output 23 of the transmitting section 9 in FIG.
Is sent a normal (unencrypted) audio signal.

Also, during this phase operation, the person who placed the A-phone and the person who took the handset of the B-phone mutually confirm the other party through a conversation, and both parties press, for example, the * key and the predetermined specific number from the push button dial 15 of each telephone. Key, followed by an encryption key. These key inputs are supplied to the microprocessor unit 5 through the key input control unit 12 and the internal bus 19, and the microprocessor unit 5 It is determined from the specific number key that an encryption key has been input, and the input encryption key is set via the internal bus 19 in the KEY register 34 of the transmitting section. After confirming by conversation that both have completed the input of the encryption key, either one or both of them press the encryption switch 18 for instructing the start of encryption attached to the telephone. Crypto switch
When the button 18 is pressed, the signal 28 is turned on and the state transits to the phase 2.

・ Phase 2 Press the encryption switch 18 in FIG. 1 (encryption start: FIG. 3)
111) or the output 81 of the comparator 69 in FIG. 2 (interrupt signal)
Is turned on (N consecutive IDL characters are received: when the other party presses the encryption switch 18 before this side), the output 58 of the transmission control unit 31 in FIG.
An instruction is issued to select the output 44 of the register 32, and the signal 55 is turned on to start the counter 42.
As a result, every time one IDL character is transmitted, the count value of the counter 42 is incremented by one. When the value of the count value output 56 of the counter 42 becomes the value (M) set in the M register 36, the comparator 43 starts counting. The output 57 is turned on, and transition to phase 3 is made.

Therefore, in this phase, the output 23 of the transmitting section 9 in FIG.
, M IDL characters are transmitted (112 in FIG. 3).

・ Phase 3 When the output 57 of the comparator 43 is turned on, the transmission control unit 31 turns off the output 55, sets the counter 42 to 0, and outputs the signal
58 instructs the selector 38 to select the output 45 of the EOC register 33. When one EOC character is transmitted, the state transits to Phase 4.

Therefore, in this phase, the output 23 of the transmitting section 8 in FIG.
Is sent one EOC character (11 in FIG. 3).
3).

・ Phase 4 The transmission control unit 31 outputs the output 58 to the
The output 53 instructs the encryptor 39 to start encryption, and the output 54 instructs the selector 40 to select the output 51 of the encryptor 39.

Therefore, in this phase, the output 23 of the transmitting section 9 in FIG.
, An audio signal encrypted with the encryption key set from the push button dial 15 is transmitted.

If there is an incoming call from the C telephone to the A telephone during this phase operation (the incoming call is notified via the D channel), the layer 3 control unit 10 detects this and notifies the microprocessor unit 5. I do. The microprocessor unit 5 receives the information such as the caller number from the layer 3 control unit 10 in response to the
16 is instructed to display a caller ID and the like, and the ring tone generation circuit 9 is turned on to notify the person using the A telephone that the incoming call has occurred. The person using the telephone A confirms the caller number by looking at the display 16 from the ring tone and presses the hold switch 17 (hold start instruction). When the hold switch 17 is pressed, the signal 27 is turned on and the phase 5
Transitions to.

-Phase 5 When the hold switch 17 in Fig. 1 is pressed, the output 58 of the transmission control unit 31 in Fig. 2 instructs the selector 38 to select the output 44 of the IDL register 32 and turns on the signal 55. And the counter 42 is started. Thus, every time one encrypted IDL character is transmitted, the counter 42
Count value is incremented by one, and the count value output of the counter 42 is
When the value of 56 becomes the value (M) set in the M register 36, the output 57 of the comparator 43 is turned on.

In addition, when the telephone A and the telephone B are currently on hold, this phase is changed also by pressing the hold switch 17 of FIG. 1 again (hold release instruction).

Therefore, in this phase, the output 23 of the transmitting section 9 in FIG.
Sends M encrypted IDL characters to phase 6
Transitions to. The B telephone can decrypt this encrypted IDL character.

・ Phase 6 When the output 57 of the comparator 43 is turned on, the transmission control unit 31 turns off the output 55, sets the counter 42 to 0, and outputs the signal
58 instructs the selector 38 to select the output 45 of the EOC register 33. When one EOC character is transmitted, the transmission control unit 31 turns on the output 29 (starts holding operation or ends holding operation).

When the output 29 is turned on, the layer 3 control unit 10 notifies the network to hold or release the hold between the A telephone and the B telephone.

At this time, if the telephone A and the telephone B are put on hold, the network transmits an unencrypted holding tone to the telephone B via the channel B during the hold period.

Therefore, in this phase, the output 23 of the transmitting section 9 in FIG.
Sends one encrypted EOC character to layer 3
The control unit 10 is instructed to start the suspending operation, and transitions to phase 1 (transmission of an unencrypted audio signal).

When the encryption switch 18 is pressed again in any phase, a decryption instruction is issued, and the process returns to the phase 1. This is used to return to the initial state when cryptographic conversation with the other party cannot be performed due to a difference in cryptographic key. When the conversation ends, the handset is returned, and the line is restored, the transmitting unit 9 and the receiving unit 8
Is also reset to the initial state.

Receiver The receiver has four phases of operation. The first operation phase is performed after the call is set and until N consecutive IDL characters are detected (hereinafter, referred to as “phase 1”).

The second operation phase is performed until an EOC character is detected (hereinafter, referred to as “phase 2”).

The signal (encrypted audio signal) received in the third operation phase is decrypted, and N consecutive encrypted IDL characters are detected (hereinafter, referred to as “phase 3”).

The fourth operation phase is performed until an encrypted EOC character is detected (hereinafter, referred to as “Phase 4”).

Phase 1 After the call is set up, the output 75 of the reception control unit 61 instructs the selector 64 to select the signal 72, so that the codec 65 receives the reception data (normal unencrypted voice data). 1), and the other party's voice is output to the receiver 2r of the handset 2 in FIG.

After the call is set, the counter 68 operates, so that the IDL character (the character set in the IDL register 32) sent out before the other party starts the voice encryption can be detected at any time. Each time the comparator 67 detects one IDL character, the count value of the counter 68 increases by one (when the signal 74 is other than the IDL character, the output 7 of the comparator 67 becomes 7).
8 is turned off and the counter 68 becomes 0), and the counter 68
When the value of the count output 79 of (2) reaches the value (N) set in the N register 70, the output 81 of the comparator 69 is turned on, and the reception control unit 61 receives this and makes a transition to phase 2 (third phase). 114 in the figure).

Therefore, in this phase, the output 20 of the receiver 8 in FIG.
, The received voice signal (digital signal) is directly converted to analog and output.

When the phase 2 signal 74 becomes the same character (EOC character) as the character set in the EOC register 33, the comparator 66
Is turned on, and the reception control unit 61 receives this and makes a transition to phase 3 (115 in FIG. 3).

Therefore, in this phase, it is in a state of waiting for decryption of the encrypted audio signal to be received next to the EOC character.

Phase 3 The reception control unit 61 turns on the output 75, whereby the encryption / decryption unit 63 starts decoding the received data (encrypted audio signal), and the selector 64 selects the output 73 of the encryption / decryption unit 63. . Here, if the same encryption key as the encryption key input by the other party for encrypting the voice is set in the KEY register 34 of the transmitting section 9 by the microprocessor section 5, the encrypted voice signal becomes completely the original. Although the audio signal can be restored, the encrypted audio signal cannot be restored to the original audio signal if the encryption key is different from that of the other party.

When the other party receives an incoming call from a third party during a call and temporarily suspends the call with the telephone, it is necessary to release the encryption of the call. For this reason, the other party informs the telephone of the request for decrypting the call (transmits the encrypted M IDL characters and the encrypted EOC character). At this time, since the counter 68 is operating, each time the comparator 67 detects one IDL character, the count value of the counter 68 increases by 1 (when the signal 74 is not an IDL character, the output of the comparator 67 is output). When the value of the output 79 of the counter 68 reaches the value (N) set in the N register 70, the output 81 of the comparator 69 is turned on, and the reception control unit 61 Transitions to phase 4 in response to this.

Therefore, in this phase, the encrypted audio signal is decrypted at the output 20 of the first receiver 8 and converted to analog for output.

-Phase 4 The selector 64 selects the output 73 of the decoder 63. At this time, when the signal 74 becomes an EOC character, the output 77 of the comparator 66 is output.
Is turned on, and the reception control unit 61 receives the
Transitions to.

Therefore, this phase is a phase of waiting for a decryption instruction.

Further, referring to FIG. 4, a call procedure between the A telephone, the B telephone, and the C telephone will be described in order.

At first, the conversation between the telephone A and the telephone B is performed in a normal (unencrypted) state (see 91 in FIG. 4). In the meantime, as described with reference to FIG. 3, both parties input the encryption key from the push button dial 15 of each telephone.

Next, after confirming that both sides have completed the input of the encryption key, either one of them or both sides depress the encryption switch 18 for instructing the start of encryption attached to the telephone. Here, if the encryption keys input by both parties are the same, an encryption conversation state is established (see 92 in FIG. 4).

Next, when there is an incoming call from the C telephone to the A telephone during the encryption conversation state (see 93 in FIG. 4)
A ringing tone is transmitted from the network to the B channel of the telephone (see 94 in FIG. 4), and a ring tone is generated in the receiver 2r of the A telephone (see 95 in FIG. 3).

Next, the person who is calling the A telephone confirms the caller by looking at the display 16 by the ring tone and presses the hold switch 17. As a result, the telephone communication between the A telephone and the B telephone is changed from the encrypted telephone communication state to the normal telephone communication state (see 96 in FIG. 4).

Next, the network sends a hold tone to the B channel of the B telephone (see 97 in FIG. 4), and the B channel of the A telephone and the C channel are transmitted.
Connect the B channel of the telephone. In the same way as when the A telephone and the C telephone are connected, both enter the encryption key from the push button dial 15 of each telephone during this time (the fourth key).
See Figure 98).

Next, in the same manner as in the case of the A telephone and the C telephone, after confirming that both have completed the input of the encryption key, either one of them or both of them operates the encryption switch 18 for instructing the start of the encryption attached to the telephone. Press. Here, if the encryption keys input by both parties are the same, an encryption conversation state is established (see 99 in FIG. 4).

Next, when the conversation between the A telephone and the C telephone is completed, the person using the A telephone presses the hold switch 17 again. Thereby, the telephone A and the telephone C are changed from the cipher conversation state to the normal normal state (see 100 in FIG. 4).

Next, the network restores the call disconnection between the A telephone and the C telephone (see 101 in FIG. 4), and the B channel and the B
The B channel of the telephone is connected again (see 102 in FIG. 4).

The same operation as described below is performed (see 103 in FIG. 4).

In this way, if there is an incoming call from the C telephone to the A telephone during the cryptographic conversation between the A telephone and the B telephone, the B telephone is returned to the normal conversation state, put on hold, and the conversation between the A telephone and the C telephone is performed. After the conversation is over, the conversation between the A telephone and the B telephone can be returned.

"Effects of the Invention" As can 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 decrypted sound quality due to encryption.

Since the encryption and decryption processes are performed in units of the output width of the encoder 37 (in the embodiment, in units of 8 bits), the signal processing delay is small. This makes the conversation difficult.

At the start of encryption, a certain number of specific characters are automatically
Next, another specific character sends one, and the other party (receiver)
Since the number of detected specific characters that are transmitted first is smaller than the number of transmitted characters, even if a bit error occurs on the transmission path, the specific character can be easily detected.
Also, since the start of the encryption / decryption may be performed after the other specific characters, it is easy to synchronize in the stream encryption format. In addition, since these operations are performed at high speed, switching from a normal conversation to an encrypted conversation state can be performed instantaneously.

When a call is received from a third party during a cryptographic conversation, simply pressing the hold switch temporarily suspends the other party on the call and returns to the normal conversation state so that the person on hold can hear the hold tone. The person who put the call on hold can have a normal conversation with the other party who has received the call, and the normal conversation with the original party can be resumed by pressing the hold switch again.

Because of the simple configuration, the hardware scale is small,
It is a range that can be easily integrated into one chip with current LSI technology,
The device can be realized at low cost.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing an example of the internal configuration of a transmitting unit 5 and a receiving unit 6 in FIG. 1, and FIG. FIG. 4 is a sequence chart showing an operation procedure when an incoming call is received from a third party during a telephone conversation. 1: Main unit, 2: Handset, 3: Line terminator, 4: Subscriber line, 5: Microprocessor, 6: Memory, 7: Ringtone generator, 8: Receiver, 9: Transmitter, 10 : Layer 3 control unit, 11:
Display control unit, 12: Key input control unit, 13: Driver / receiver, 14: Layer 1 and 2 control unit, 15: Push button dial, 16: Display, 17: Hold switch, 18: Encryption switch, 31: Transmission Control unit, 32: IDL register, 33: EOC register, 34: KEY register, 36: M register, 37: encoder, 39:
Encryptor, 42: counter, 61: receiver control unit, 63: encryption / decryption device, 65: compound decryption device, 68: counter, 70: N register.

Continuation of the front page (56) References JP-A-54-3402 (JP, A) JP-A-61-292436 (JP, A) JP-A-59-74744 (JP, A) JP-A-60-100238 (JP) JP-A-63-63232 (JP, A) JP-A-63-261933 (JP, A) JP-A-59-77745 (JP, A) JP-A-62-76876 (JP, A) JP-A-4-81039 (JP, A) JP-A-4-189045 (JP, A) Journal of IEICE, Vol. 65, No. 8, August 1982, p. 832-834, Akaiwa, "Secret Talk Technology", (Issued 57-8-25) Ikeno, Koyama, "Modern Cryptography Theory", 3rd edition (Hiramoto-5-20) IEICE, P.S. 67−76

Claims (1)

(57) [Claims] An encryptor for encrypting an input signal in units of n bits in a stream encryption format, an encrypted output from the encryptor, and an unencrypted n
A first selector for switching and transmitting a bit code signal, a cipher decoder for decoding a received input signal into an n-bit code signal in a stream cipher format, a decrypted output of the cipher decoder and the received input n bits A second selector for switching and taking in the code signal, and always sending the first selector an unencrypted signal, and the first selector of the encryption start instruction signal and the first interrupt signal is generated. The signal transmits M n-bit first characters (M is an integer of 3 or more) continuously, and then transmits one n-bit second character. Encrypted and transmitted, and the M consecutive characters of the first character and the subsequent one of the second characters are encrypted and transmitted by the encryptor by the decryption command, and are subsequently encrypted. Not voice de A transmission control unit for transmitting data, and the second selector always accepts a received input signal, and continuously receives the first character as N (where N ≦ M and N is positive) as the received input signal. (Integer), the first interrupt signal is generated, and then, when the second character is detected, the output of the decryptor is taken in and the first character is continuously output as the output of the decryptor. And a reception control unit that returns to an initial state when the second character is detected after detecting N characters.