JPH04297154A - Privacy telephone set - Google Patents

Abstract

PURPOSE:To talk without noise while ciphering voice by controlling the prescribed selector when the third code string is detected and supplying the deciphered output of a deciphering device to a receiver. CONSTITUTION:An N register 72 is connected to an internal bus 21, and the value representing the number of consecutive reception of IDL characters is set in a microprocessor part. A serial/parallel converter 73 converts the serial data with one bit width of a B channel signal 24 to the parallel data, and decodes an output signal 84 of a deciphering device 74 in one byte unit. A selector 75, which is a one byte width selector, is controlled by a control signal 89 of a reception control part 71, selectively outputting either of a signal 84 or a output signal 85 of the deciphering device 74. At this time, a decoder 76 converts a digital signal of the output signal 86 of the selector 75 into a voice signal. An electron sound generation circuit 77 prevents voice signals other than such as ciphered IV from being received to flow from the receiver of a handset as noise when switching the non ciphered speech to a ciphered speech.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secret telephone device that enables encrypted voice conversations over the telephone.

0002

[Prior Art] Spectrum inversion encryption is used as an analog encryption method to directly encrypt voice signals (see, for example, Imamura, Hattori, and Kozono: “Speech quality improvement effect using compander and emphasis in audio spectrum inversion secret conversation”);
IEICE Theory (B), J64-B, 5, pp. 425-432
(Refer to 1982-05)), a method of changing the time order and frequency of sampled sounds (for details, see N.S.
．． Jayant, R. V. Cox, B. J. McDer
mott and a. M. Quinn: “Anal
og scramblers for speech
based on sequential permu
tations in time and frequency
cy”, Bell Syst. Tech. J. 62, 1
, pp. 25-46 (Jan. 1983)), a method of inverting the polarity of sampled audio according to certain rules (
For details, see S. Asakawa, F. Sugi
yama and M. Nakamura: ”A
voice scrambler for mobile
communication", IEEE Tran
s. Veh Technol. 29, 1, pp. 81-
86 (Feb. 1980)). Also, FF
T (Faest Fourier Transform
FFT scrambling method that applies the fast Fourier transform method (For details, see Matsunaga, Okawa, Sakurai, Koga: “
“Full-duplex analog secret communication device using FFT and its basic operation”, IEICE Theory (A), J72-A, 4, pp.692-7
02 (see 1986-04)) has been proposed.

[0003] Furthermore, a digital encryption method has been proposed in which an analog audio signal is encoded using, for example, the μ-law encoding method and then encrypted, in a manner similar to the method used to encode a telegram. Currently, as a security measure for digital communication, either the sender or the receiver decides on an encryption key and sends the same encryption key to the other party, and then the sender sends the data (
A method is used in which a ciphertext is encrypted (plaintext) using the encryption key and the ciphertext is sent, and the receiving side performs inverse conversion, or decryption, on the received ciphertext using the previous encryption key to return it to the original plaintext. The encryption algorithms used in these systems must be made public in order to carry out encrypted communications with unspecified parties. A typical example of algorithm public cryptography is DES (details of the DES algorithm can be found in, for example, D.
W. Davies and W. L. Price (supervising translation): “Network Security”, Nikkei McGraw-Hill Publishing, 1985pp. 55-84), FEA
L (For details of the FEAL algorithm, see, for example, Miyaguchi, Shiraishi, and Shimizu: “FEAL-8 Cryptographic Algorithm,” Kenjitsuho Vol. 37, No. 4/5, 1988 pp. 321-372.
).

[0004] Next, the cryptographic format (details of the cryptographic format can be found in, for example, D.W. Davies and W.L.P.
rice (supervised translation by Uezono): “Network Security”, Nikkei McGraw-Hill Publishing, 1985pp. 85-102
) has the following four formats. ■ ECB format (Electronic Codeb
mode). ■ CBC format (Cipher Block Cha
ining mode).

■ CFB format (Cipher Feedback
mode). ■ OFB format (Output Feedback
mode).

[0006]

The first three analog encryption systems have drawbacks such as weak encryption strength, difficulty in conversation due to signal processing delay, and deterioration of decoded sound quality due to encryption. The last method also makes conversation difficult due to signal processing delay, deterioration of decoded sound quality due to encryption, and encrypted conversation (encrypted call) from normal conversation (non-encrypted call).
There are disadvantages such as it takes time to change the state. Furthermore, if the encryption keys on the calling and receiving sides are different, the user will receive an incomprehensible noise at the beginning of the encrypted call, which will make the user feel uncomfortable, and further communication will be impossible. At this time, switching from an encrypted call to a non-encrypted call has the disadvantage that both parties must manually stop the encrypted function.

ISDN (Integrated Se
Prior to the start of service for Rvices Digital Network), 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 audio signal. Digital encryption of telephones using transmission has never been realized from a cost standpoint. However, as ISDN becomes more widespread, it is conceivable that telephone conversations will be encrypted using a digital encryption method. In this case, it is preferable to apply the stream cipher format in order to increase the encryption strength, but the stream cipher format cannot be decrypted unless the other party knows the start point of the encryption. In other words, it is necessary to simultaneously start the operation of the encoders and decoders of the mutual telephones that communicate with each other. However, since telephones do not have protocols such as data communication, it is necessary to implement the following functions.

[0008] A function that starts the encryption of the audio code on the transmitting side and notifies the receiving side of the audio code for which encryption has started.・A function that detects the audio code that started encryption on the receiving side and starts decryption from that audio code.

[0009] It is also necessary to confirm that the person on the other end of the line is the person with whom the user wishes to speak. Therefore, it is necessary to easily synchronize encryption and decryption in a short period of time after confirming the other party in a non-encrypted call. Next, at the start of encryption, an encryption key or an initial variable (hereinafter referred to as "IV") is described in detail, for example, by D.W. Davies and
W. L. Price (translation supervised by Uezono): “Network
Security”, Nikkei McGraw-Hill, 1985 pp.
．． 89-102) are different on the calling and receiving sides, it is necessary to have a function that displays an alarm on both telephones and switches both telephones to a non-encrypted conversation state in a short period of time.

The purpose of the present invention is to prevent eavesdropping on a communication line, to easily switch between non-encrypted conversation and encrypted conversation, and to prevent encrypted conversation from occurring normally due to differences in encryption keys. The object of the present invention is to provide a secret telephone device having a function of displaying a message to that effect on both telephones, automatically switching to a non-encrypted call, and having strong encryption strength.

[0011]

[Means for Solving the Problems] According to the present invention, there is provided an n-bit wide encoder that converts an analog signal from a microphone into a digital signal, and an output of the encoder that converts an analog signal from a microphone into a digital signal. A first code with a bit width (hereinafter, the first character is used as the first code), and a second code with a preset n-bit width (hereinafter, the second code is the second character). (described assuming that K is used)
(K is an integer greater than or equal to 1) and has an n-bit width.
a selector, an encoder applying a stream cipher format that encrypts the output of the first selector in units of n bits, and a second selector that selects either the output of the encoder or the output of the first selector. a selector, a parallel-to-serial converter that serially converts the output of the second selector and sends it out; initially, the first and second selectors are controlled so as to send out the output of the encoder; In response to the encryption start instruction, the first selector is controlled to successively send M first characters (M is an integer of 2 or more), and then the first selector is controlled to send one second character. controlling the first selector, and then controlling the first selector and the second selector to start the operation of the encoder and encrypting and transmitting the third character string;
The first encoder encrypts the output of the encoder and sends it out.
A transmitting control unit that controls the selector, a serial-to-parallel converter that converts the received digital signal into an n-bit wide parallel signal, and a stream encryption format that decodes the output of the serial-to-parallel converter in units of n bits. a decryptor; a third selector for selecting either the output of the decryptor or the output of the serial/parallel converter; (where N is a positive integer), means for detecting a second character from the third selector output, and means for detecting the third character string from the third selector output;
a code decoder that converts the third selector output into an analog signal, a sound generation circuit, and an output of the sound generation circuit;
A fourth selector that selects one of the outputs of the code decoder and supplies it to the receiver (speaker), an interrupt signal line to the outside, and a fourth selector that selects one of the outputs of the code decoder and supplies it to the receiver (speaker); and an interrupt signal line to the outside; and controlling the third and fourth selectors to supply the output of the encoder and decoder to the receiver, and performs an operation of continuously detecting N first characters from the output of the third selector; When the first character is detected N times in a row, the fourth selector is controlled so that the output of the voice generation circuit is supplied to the receiver, and an interrupt is generated externally. , controls the third selector to supply the output of the serial-parallel converter to the decryptor, starts the decryption operation of the decryptor, and outputs the third character from the output of the third selector. performs the action of detecting columns,
When the third character string is detected, the third and fourth selectors are controlled so that the output of the code/decoder is decoded by the code/decoder and supplied to the handset, and an interrupt is generated externally. , a reception control unit having means for transitioning to the first state when the third character string cannot be detected; a push button dial for inputting a telephone number, an encryption key, and an IV; and a manually operated encrypted call start signal. A code switch that outputs the key input, the originating phone number,
a display device that displays alarms, etc.; a third register that holds an encryption key and supplies the encryption key to the encryption device and the encryption decryption device;
A fourth register is provided to hold initial variables and supply them to the encryptor and the decryptor.

0012

[Operation] With this configuration, it operates as follows. - Step 1: The digitized voice code on the transmitting side never has the same value consecutively. Taking advantage of this fact, when an instruction to start encryption is given from the outside, M first characters are continuously sent out instead of the voice code that has been sent out so far, and the process moves to step 2.

[0013] While receiving the voice code on the receiver side, until N (however, N≦M) consecutively receive the predetermined first character, the received data is regarded as the voice code, and the first character is Since the subsequent data is not a voice code, the voice generated by the voice generating circuit in the receiver is sent to the receiver instead of the output of the encoder/decoder, and the receiver is notified of the start of encryption. Step 2 Transition to. Here, the reason why N≦M is determined is to ensure that the next second character can be detected even if a bit error occurs on the communication line.

Step 2 In order to synchronize the start point of the cryptographic operation on the sending side and the receiving side, a second character other than the first character used in step 1 is used.
One character is sent, the cryptographic operation is started, and the process moves to step 3.

[0015] When the second character on the receiver side is detected, the encryption/decryption operation is started from the subsequent data, the encryption operation is synchronized with that on the transmission side, and the process moves to step 3.・Step 3 In order for the receiving side to detect that the encrypted call on the sending side is normal, the sending and receiving sides predetermine K at the start of the encrypted call.
The third character string (IV in this example) consisting of
is encrypted and sent, and the process moves to step 4.

[0016] The decrypted data and the IV are compared from the start of the decryption operation on the receiver side, and if they match, it is assumed that the mutual encryption keys match and a normal encrypted communication is possible, and the process moves to step 4. If they do not match, it is assumed that the encryption keys are different between the sending and receiving sides, and encrypted communication is not possible, a CPU interrupt (alarm) is generated, and both the sending and receiving sides proceed to step 1.

[0017] Here, the data to be compared was decided to be IV because it is a value known only to the person concerned, and the length can be freely selected, that is, the length differs depending on the IV, and it has a simpler configuration. The decision was made for reasons such as the fact that the hardware size is small. Using IV in this way increases the strength of the secret.・Step 4: Encrypt and send the voice code on the sending side.

On the receiver side, the decoded voice code is decoded by a code decoder and sent to the receiver. This device prevents eavesdropping on communication lines,
It is easy to switch from a non-encrypted call to an encrypted call at any time.If the encrypted call cannot be performed normally due to a difference in the encryption key, etc., a message to that effect will be displayed on the display of both the calling and receiving phones. It is possible to automatically switch to a non-encrypted call.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS 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 device (digital telephone with encryption function) according to the present invention. This device consists of a main body 1 and a handset 2 connected to the main body 1.

The main body 1 includes a microprocessor section 4 for controlling the entire main body, a memory section 5 consisting of a ROM for storing programs executed by the microprocessor section 4 and a RAM for temporarily storing data, and a memory section 5 for storing encrypted audio data. A receiver unit 6 that decodes the signal and outputs the audio signal 22 to the receiver 2r of the handset 2, and a transmitter unit that transmits the audio signal 23 from the speaker 2s of the handset 2 with or without encryption. 7, Microprocessor section 4
L that controls layer 2 of the ISDN D channel by
AP-D (Link Access Procedure
eon the D-channel) control unit 8;
A key input control unit 10 that controls each key input from the display control unit 9, push button dial 12, and code switch 13.
and are connected to the internal bus 21.

Furthermore, ISDN line termination unit (DSU)
A display device 1 controlled by a layer 1 control unit 11 and a display control unit 9 that control Layer 1 of the B channel and Layer 1 of the D channel of ISDN, which performs interface conversion with
4 is provided. The pushbutton dial 12 is used to enter a telephone number or an encryption key known only to the parties involved in encrypted communication.
is used to instruct the start of encryption and decryption of the contents of the call, and this encryption switch 13 is a toggle switch, and repeats the instruction to start encryption and the instruction to decrypt it each time it is pressed. The display 14 displays key inputs, caller telephone numbers, alarms, and the like. The layer 1 control unit 11
It is connected to a DSU (not shown) using an SDN plug 3.

The B channel signal 24 from the layer 1 control section 11 is supplied to the receiver section 6, the B channel signal 25 from the transmitter section 7 is supplied to the layer 1 control section 11, and the output signal 26 of the push button dial 12 is supplied to the receiver section 6. is supplied to the key input control section 10, the cipher request signal 27 of the cipher switch 13 is supplied to the key input control section 10, the CPU interrupt signal 29 from the receiver 6 is supplied to the microprocessor section 4, and the cipher request signal 27 from the cipher switch 13 is supplied to the microprocessor section 4, A display signal 28 from is provided to the display 14.

FIG. 2 shows the internal structure of the receiver section 6 and the transmitter section 7 of FIG. 1. The transmission control section 41 controls the entire transmission section 7 . Internal bus 21 includes IDL register 42, EOC register 43, IV register 44, KEY register 45, M
A register 46 and a control register 47 are connected. I
The DL register 42 receives the first character (hereinafter referred to as "I") by the microprocessor unit 4.
A second character (hereinafter this 1-byte character will be referred to as an "EOC character") is set in the EOC register 43 by the microprocessor unit 4, and the IV register 44 is set in the EOC register 43 by the microprocessor unit 4. IV (8 bytes) is set by , KEY register 45 is set after the encryption key input from push button dial 12 in FIG. 1 is processed by microprocessor section 4, and M register 46 is set by ID.
A value indicating the number of consecutively transmitted L characters (hereinafter this value will be referred to as “
M") is set by the microprocessor section 4, and the control register 47 is used to send operation instructions to the transmitting control section 41 and the receiving control section 71 from the microprocessor section 4.
is set by

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 regulations for converting this analog signal into a digital signal are specified in CCITT Recommendation G. According to 711 etc. The selector 49 is a 1-byte wide selector that is controlled by the control signal 70 of the transmitter control section 41 and outputs the output signal 61 of the encoder 48, the IDL character 55 from the IDL register 42, and the EOC character from the EOC register 43. 56 and IV register 44
A signal obtained by sequentially converting IV57 (8 bytes) to a 1-byte width signal is selected and output. The encoder 50 encrypts a 1-byte digital signal in units of 1-byte. The 8-bit feedback of the OFB format, which is a stream cipher format, is applied to the cipher format. selector 51
is a 1-byte wide selector, which is controlled by the control signal 66 of the transmission control unit 41, and the output signal 6 of the selector 49
2 and the output signal 63 of the encoder 50 are 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 1 each time one IDL character is sent. Comparator 54 is counter 53
When the contents of the count value output 68 and the output signal 59 of the M register 46 match, the encryption key (generally 8 bytes) 58 from the KEY register 45 turns on the output 69 and notifies the transmission control unit 41. are the encoder 50 and the decryptor 7
A signal 65 for controlling the encoder 50 is output from the transmission control section 41 which is supplied to the transmitter 4 .

The reception control section 71 controls the reception section 6 as a whole. N register 72 is connected to internal bus 21 and IDL
A value indicating the number of consecutively received characters (hereinafter this value will be referred to as “N”)
” (where N≦M) is set by the microprocessor unit 4. The serial/parallel converter 73 converts the 1-bit width serial data of the B channel signal 24 into 1-byte width parallel data, and 74 is a serial-parallel converter 73
The output signal 84 (1-byte digital signal) is decoded in 1-byte units. The selector 75 is a 1-byte wide selector that is controlled by a control signal 89 from the reception control unit 71 and selects either the output signal 84 of the serial/parallel converter 73 or the output signal 85 of the decryptor 74. and output it. The code decoder 76 receives the output signal 86 (1
Converts a digital signal (byte width) into an audio signal (analog signal). The electronic sound generation circuit (sound generation circuit) 77 receives non-audio signals such as IDL characters, EOC characters, and encrypted IVs when switching from a non-encrypted call to an encrypted call, and generates this as an unpleasant sound on the handset 2. In order to prevent this unpleasant sound from being heard from the receiver 2r, the electronic sound generation circuit 77 generates another sound (analog signal) and supplies it to the receiver 2r instead of this unpleasant sound. It also serves to notify the user that a non-encrypted call is being switched to an encrypted call.

The selector 78 is an analog signal selector, and is controlled by the control signal 90 of the reception control section 71, and selects either the output 87 of the code decoder 76 or the output 88 of the electronic sound generation circuit 77. Output. Comparator 82
When the contents of the output signal 86 of the selector 75 and the output EOC character 56 of the EOC register 43 match, the output 95 is turned on. The comparator 79 outputs the output signal 86 of the selector 75 and the output IDL character 5 of the IDL register 42.
When the contents of 6 match, the output 91 is turned on. The count value of the counter 80 increases by 1 when the output 91 of the comparator 79 is on, and becomes 0 when the output 91 of the comparator 79 is off. When the count value output 92 of the counter 80 and the output 93 of the N register 72 match, the comparator 81 turns on the output 94 and notifies the reception control section 71. The comparator 83 receives the start signal 9 from the reception control section 71.
6 is turned on, the output 86 of the selector 75 is compared with the most significant byte of the signal 57 (8 bytes) to which IV is applied, and if all 8 bytes match, the output 96 is turned on and the reception control is performed. Department 71 is notified. If a mismatch occurs during the comparison, the comparison operation is stopped. A signal 89 for controlling the decryptor 74 and the selector 75 and a CPU interrupt signal 29 for generating an interrupt to the microprocessor section 4 are output from the reception control section 71 .

The present invention can be applied to a digital telephone that encodes voice and makes a call using the information channel (B channel) of an ISDN basic interface subscriber line. The operation of the present invention will be explained below using this digital telephone as an example, with reference to FIGS. 1, 2, and 3. A digital telephone with an encryption function on the calling side (hereinafter referred to as “
In a digital telephone with an encryption function on the receiving side (hereinafter referred to as "Telephone Y") to which this invention is also applied, the B channel of the X telephone and the B channel of the Y telephone
The explanation begins after the channel is connected.

[0028] Before making an encrypted call, in order to prevent leakage to a third party, the person who picks up the handset of the Y telephone must:
It is necessary to judge whether the person who called the X telephone is the person with whom the user wants to talk. First, from the conversation content, Y
If the person who picked up the telephone handset does not want to talk to the person who called the X-telephone, he or she can simply hang up at that point. Next, both parties enter the encryption key and IV (a combination of numbers known only to the two parties) by some means, such as the push-button dial on each telephone, which has been sent in advance by mail. Both parties confirm that the communication has been completed, and one or both parties press the encryption switch to begin encrypted communication. If the encryption key entered by both parties and the IV match, you can have an encrypted conversation, but if the encryption key or ID entered on the Y phone side
If V is different from that of X phone, communication will be impossible,
Both phones generate an alarm and display it on the display. This prevents the contents of a confidential call from being accidentally leaked to anyone other than the parties involved. Furthermore, even if the encryption key or IV is entered incorrectly, an alarm will be generated and a non-encrypted call will be made, allowing subsequent calls to be made, allowing the parties to confirm the identity of the parties by having a conversation again.

Even if an attempt is made to eavesdrop somewhere on the line, it will not be possible to eavesdrop unless a telephone to which this invention is applied is used, the same encryption key and IV are used, and the contents of the encrypted call are decrypted from the beginning. be. In this invention, since the audio signal to be encoded is in units of 8 bits (1 byte) and real-time performance is required for conversation, CFB, which encodes in units of 8 bits in a stream cipher format, is used.
OFB mode is applied and the initial variable (IV) is fixed.

Next, the above operation will be explained in detail by taking as an example the transmitting side of telephone X and the receiving side of telephone Y. Transmitting Side There are five operating phases on the transmitting side. In the first operation phase, the input audio code is sent without being encrypted (hereinafter referred to as "phase 1").

In the second operation phase, M IDL characters are sent in response to an instruction to start encryption from the microprocessor section, until transition to phase 3 (hereinafter referred to as "phase 2"). The third operation phase consists of one EO
Until the C character is sent and transition to phase 4 (hereinafter referred to as "phase 3").

The fourth operation phase is IV (8 bytes)
until it is encrypted and sent, and transitions to Phase 5 (hereinafter referred to as "Phase 4"). In the fifth operation phase, the input audio code is encrypted and sent out (hereinafter referred to as "phase 5"). Prior to the start of operation, the microprocessor section 4 executes an initial program to set an IDL character in the IDL register 42 of the transmitting section 7, set an EOC character in the EOC register 43 of the transmitting section 7, and set an EOC character in the EOC register 43 of the transmitting section 7. Set the continuous transmission number M of IDL characters in the M register 47, and set the ID number in the N register 72 of the receiver 6.
Set the continuous reception number N of L characters, and
The controller 47 instructs the control register 47 to set the transmitting control section 41 and the receiving control section 71 to the initial state, and makes the LAP-D control section 8 and the key input control section 10 ready for operation.

Phase 1 The output signal 23 (analog signal) of the transmitter 2s of the handset 2 in FIG. 1 is converted into 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 using the control signal 70,
The control signal 66 causes the selector 49 to
to select the output signal 62 of.

Therefore, in this phase, an unencrypted input voice code is sent as the output signal 25 of the transmitter 7 in FIG. Also, if the person who picks up the handset of telephone Y during this phase operation is the person with whom the person operating telephone X wants to talk, both parties input the encryption key and IV from the push-button dial 12 of the telephone. The microprocessor section 4 processes the input encryption key and IV, and outputs the KEY register 45 and IV of the transmitting section 7, respectively.
Set in V register 44. The contents set in the KEY register 45 are set in the encoder 50 and decryptor 74 as an encryption key, and the contents set in the IV register 44 are set in the encoder 55 and decryptor 74 as an IV.

- Phase 2 After confirming that both parties have completed inputting the encryption key and IV in Phase 1, both parties or one of them presses the encryption switch 13 attached to the telephone to instruct the start of an encrypted call. Press down. Signal 2 is generated by pressing the code switch 13.
7 is turned on and notifies the key input control section 10, and the key input control section 10 notifies the microprocessor section 4 that the encryption switch 13 has been pressed. In response to this, the microprocessor section 4 instructs the control register 47 to start encryption (at point 101 in FIG. 3).

Furthermore, if the other party (telephone Y) presses the code switch 13 before the other party presses the code switch 13, the reception control unit 71 of the reception unit 6 continuously sends IDL characters to the microprocessor unit 4 using the CPU interrupt signal 29. Report that N pieces have been received (details will be explained on the receiving side). Upon receiving this report, the microprocessor unit 4 issues an instruction to the control register 47 to start encryption in the same manner as when the encryption switch 13 is pressed.

In response to the instruction to start encryption 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 the control signal 70, and also outputs the control signal 67. Turn it on and start the counter 53. The counter 53 is the ID
Each time one L character is sent, the count value is increased by 1, and 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 signal is sent. In response to this, the speech control section 41 sends a control signal 67
At the same time as turning off the counter 53 and clearing it to 0,
Transition to phase 3 operation.

Therefore, in this phase, M IDL characters are sent out as the output signal 25 of the transmitter 7 in FIG. 1, and the process shifts to phase 3 (period 101 to 102 in FIG. 3).・Phase 3 The transmitter control unit 41 sets the selector 49 to E according to the control signal 70.
Instructs to select the output signal 56 of the OC register 43, sends one EOC character, and transitions to the operation of phase 4. In this phase, one EOC character is sent as the output signal 25 of the transmitter 7 in FIG. 102 and transitions to phase 4 (period 102 to 103 in FIG. 3).

Phase 4 The transmitting control section 41 selector 49 is set to I by the control signal 70.
Signal 57 (8) to which IV is given from V register 44
The control signal 65 instructs the encoder 50 to start encryption, and the control signal 66 instructs the selector 51 to select the converted code from the upper byte. Instruct them to select 63,
Sends the encrypted IV (8 bytes) and transitions to phase 5.

Therefore, in this phase, an 8-byte long IV encrypted with the encryption key and IV set from the push-button dial 12 is used as the output signal 25 of the transmitter 7 in FIG.
(period 103 to 104 in FIG. 3). - Phase 5 The transmission control unit 41 instructs the selector 49 to select the output signal 61 of the encoder 48 using the control signal 70, and transmits the encrypted input audio code.

Therefore, in this phase, the input voice code encrypted with the cryptographic key set from the push button dial 12 and the IV is sent out as the output signal 25 of the transmitter 7 in FIG. 1 (from 104 in FIG. 3). Receiver There are four operating phases on the receiver.

In the first operation phase, the received voice code is output as is, and if N consecutive IDL characters are detected, the process transitions 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 the EOC character is waited. When the EOC character is detected, the process transitions to phase 3 (hereinafter referred to as "phase 2").

The third operation phase consists of processing the received data (
The encrypted IV) is decrypted, the decrypted IV is compared with the contents of the IV register 44, and if they match, the phase 4
If they do not match, the process transitions to Phase 1 (hereinafter referred to as "Phase 3"). In the fourth operation phase, the received data (encrypted audio code) is decrypted and the audio code is output (hereinafter referred to as "phase 4").

Phase 1 The receiving control section 71 instructs the selector 75 to select the output signal 84 of the serial/parallel converter 73 using the control signal 89, and the control signal 90 instructs the selector 78 to select the output signal 84 of the serial/parallel converter 73. Since the user is instructed to select the output signal 87, the voice from the other party is output as is without being decrypted to the receiver 2r of the handset 2 in FIG.

Furthermore, since the counter 80 is in operation, a plurality of I
DL characters can be detected at any time. Comparator 79
counter 80 each time detects one IDL character.
The count value increases by 1 (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 95 of the comparator 81 is turned on, and in response to this, the reception control section 71 shifts to the phase 2 operation. At the same time, C to the microprocessor section 4
The PU interrupt signal 29 is used to report that N consecutive IDL characters have been received. In response to this, the microprocessor section 4 issues an instruction to the control register 47 to start encryption if it has not yet instructed the control register 47 to start encryption (see point 106 in FIG. 3). Furthermore, if an encryption start instruction has already been given to the control register 47, this interrupt is ignored.

Therefore, in this phase, the received audio signal (digital signal) is directly converted to an analog signal and output as the output signal 22 of the receiver 6 in FIG.
It is in a state of waiting for N consecutive L characters to be detected.・Phase 2 The receiving control unit 71 selects the selector 78 according to the control output signal 90.
to select the output signal 88 of the electronic sound generating circuit 77. Therefore, the sound generated by the electronic sound generation circuit 77 is heard from the receiver 2r of the handset 2 in FIG.

Further, if the comparator 82 detects an EOC character, the output signal 95 of the comparator 82 turns on and informs the reception control section 71, and upon receiving this, the reception control section 71 shifts to the phase 3 operation ( (time point 107 in FIG. 3). Therefore, in this phase, the voice from the electronic sound generation circuit is played on the receiver 2r, and the receiver 2r is in a state of waiting for an EOC character. - Phase 3 The receiving control unit 71 instructs the decryptor 74 to start decoding the received data (encrypted IV) using the control signal 89, and sends the output signal 85 of the decryptor 74 to the selector 75. Instruct them to choose.

Also, IV8 decoded by the control signal 96
6 and the contents of the IV register 44, and if they match (
At point 108 in FIG. 3), the output 97 of the comparator 83 turns on and informs the reception control section 71, and upon receiving this, the reception control section 71 shifts to phase 4 operation. If signal 86 and I
If the contents of the V register 44 do not match, the output signal 97 of the comparator 83 is turned off, and the receiver control unit 71 receives this and sends a CPU interrupt signal 29 to the microprocessor unit 4 to inform the microprocessor unit 4 that the encryption key or IV does not match. Report what happened.

[0049] The fact that the decrypted IV and the contents of the IV register match here means that the encryption key and the IV are the same as those input on the X telephone and the Y telephone. Further, when the microprocessor section 4 receives a report that the encryption keys or IVs do not match, it sends an alarm to the display control section 9 on the display 14.
It also instructs the control register 47 to restart the operation, and the transmitting control unit 41 and the receiving control unit 7
1 to start operation from phase 1.

Therefore, in this phase, if the decoded IV and the contents of the IV register 44 match, the process moves to phase 4; if they do not match, an alarm is generated and the process moves to phase 1. -Phase 4 The reception control unit 71 instructs the selector 78 to select the output signal 87 of the code/decoder 76 using the control signal 90.

Therefore, in this phase, the encrypted audio signal received as the output signal 22 of the receiver 6 in FIG. 1 is decoded, converted into an analog signal, and output.

[0052]

Effects of the Invention As understood from the above explanation, the present invention has the following effects. ■ Strong encryption strength due to encryption algorithms such as DES and FEAL and stream encryption format. ■ Since encryption and decoding are performed using digital signals, there is no deterioration in decoded sound quality due to encryption.

[0053] Since the encryption and decoding processes are performed in units of the output width of the encoder and encoder/decoder, there is little signal processing delay, and conversation is not difficult. ■ While switching from a non-encrypted call to an encrypted call, other voices are generated and supplied to the handset instead of the received data (dummy data, first character, second character, IV, etc.), so there is no discomfort. It is possible to confirm that the state has changed from a non-encrypted call to an encrypted call.

[0054] ■ The sending side automatically uses the first
A predetermined number of characters are transmitted, and the receiving side can easily detect this particular character even if a bit error occurs on the transmission path, since the number of successive detections of the first character received at this time is smaller than the number of transmitted characters. . ■ If an encrypted call cannot be performed normally due to a difference in the encryption key, etc., a message to that effect will be displayed on both the calling and receiving phones, and the call will automatically switch to a non-encrypted call.

■ The encryption strength is strong because an initial variable character string that cannot be known by an eavesdropper is used to confirm the consistency of the encryption keys input on the calling side and the called side. (2) It is suitable for the stream cipher format because decoding on the receiver side only needs to start after the encrypted second character. - Since the structure is simple, the hardware scale is small and can be easily integrated into a single chip using current LSI technology, making it possible to realize the device at low cost.

[0056] In the above, the first and second codes may be used instead of the first and second characters.When the encryption key is deemed to be inconsistent and the state is returned to the non-encrypted communication state,
An audible warning may be used without any display to alert you, or if the device is configured to always indicate whether it is in a non-encrypted or encrypted call state. The warning may be provided by display. The electronic sound generation circuit does not necessarily have to be provided.

[Brief explanation of the drawing]

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 receiver section 6 and a transmitter section 7 in FIG. 1.

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

Claims (1)

[Claims] Claim 1: An encoder that converts an analog signal from a transmitter into a digital signal, and the output of the encoder, a first code, and a second code. a first selector that selects and outputs one from a third code string (an integer greater than or equal to 1); an encoder that encrypts the output of the first selector in a stream cipher format; an output, a second selector for selecting one of the outputs of the first selector, and initially controlling the first selector and the second selector to send out the output of the encoder; In response to an encryption start instruction from , the first selector is controlled to continuously transmit M first codes (M is an integer of 2 or more), and then one second code is transmitted. controls the first selector, then starts the operation of the encoder, and
The first selector and the second selector are controlled to encrypt and send out the third code string, and the first selector is then controlled to encrypt and send out the output of the encoder.
a transmitter control unit that controls the selector of the transmitter, and a decryptor that decodes the received digital signal in a stream cipher format;
A third selector that selects either the output of the decryptor or the received digital signal, and a third selector that selects either the output of the decryptor or the received digital signal, and the first code from the output of the third selector. ) detecting means for detecting the second code from the third selector output; means for detecting the third code string from the third selector output; and means for detecting the third code string from the third selector output. a code decoder for converting into an analog signal; a handset to which the output of the code decoder is supplied; initially, the received digital signal is supplied to the code decoder and the output of the code decoder is supplied to the handset; The third selector is controlled as follows, and the third selector is controlled as follows.
When the first code is detected N consecutively from the selector output, and the second code is detected, the received digital signal is sent to the encoder/decoder. At the same time, the third selector is controlled to supply the third code string, and the decryption device starts the decryption operation, and detects the third code string from the output of the third selector, and detects the third code string. When detected,
controlling the third selector so that the output of the code decoder is decoded by the code decoder and supplied to the handset;
A secret telephone device comprising: a receiver control unit having means for transitioning to a first state if the third code string cannot be detected and notifying that the call is in a non-encrypted call state.