JP3040801B2 - 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.

"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
based on sequential permutations in time and
frquency ", Bell Syst. Tech. J. 62, 1, pp. 25-46 (Jan. 1
983)), a method of inverting the polarity of the sampled voice according to a certain rule (for details, see, for example, S. Asakawa, F. Sugiya
ma and M. Nakamura: “Avoice scrambler for mobi
l communication ", IEEE Trans.Veh Technol.29,1, p
p.81-86 (Feb. 1980)). In addition, FFT (Fae
st Fourier Transform: Fast Fourier Transform (FFT) scrambling 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. 69
2-702 (see 64-64) has been proposed.

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

"Problems to be Solved by the Invention" The first three methods of the analog encryption method have drawbacks such as low encryption strength, difficulty in conversation due to signal processing delay, and deterioration of decrypted sound quality due to encryption. 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 state.

Before the ISDN service was launched, the transmission network was based on the analog system, and digital transmission required about 20 times the frequency band of analog transmission to transmit the same voice signal. There is no example in which digital encryption for telephone using a road network has been realized in terms of cost. However, with the spread of ISDN, it is conceivable to conduct telephone conversations by encrypting them using a digital encryption system. In this case, in order to increase the encryption strength, it is preferable to use an encryption to which the stream encryption format is applied. However, this encryption in the stream encryption format cannot be decrypted unless the encryption start time is known by the other party. In other words, it is necessary to synchronize the encryptor and the decryptor of the telephones that are talking with each other. However, on the telephone, it is necessary to confirm that the other party wants to talk. Therefore, after confirming the other party by the non-encrypted conversation, the conversation is transferred to the encrypted conversation. It is demanded that synchronization can be easily achieved.

SUMMARY OF THE INVENTION An object of the present invention is to provide a secret telephone apparatus which can switch between non-encrypted conversation and encrypted conversation, can perform encryption with high encryption strength, and can easily switch from non-encrypted conversation to encrypted conversation. It is in.

[Means for Solving the Problems] According to the present invention, an analog signal from a transmitter is converted into a digital signal and output, and its specific digital value (hereinafter referred to as “A pattern”) is different. An encoder that converts and outputs a specific digital value; an encoder that applies a stream encryption format that encrypts the output of the encoder in units of its output bit width (n bits); A first register for storing the first pattern, a first selector, and one of the A patterns from the state in which the output of the encoder is transmitted by a signal generated first among the encryption communication start signal and the interrupt signal. And a transmission section having transmission control means for switching and controlling the first selector so as to transmit the output of the encryptor; and converting a digital signal into an analog signal and supplying the analog signal to the receiver. A decoder that applies a stream encryption format for decoding a received digital signal in n-bit units; a comparator that detects the A pattern from the received digital signal and generates the interrupt signal; When the interrupt signal is supplied from the second selector and the comparator, the output of the cipher decoder is supplied to the code decoder from the state where the received digital signal is supplied to the code decoder. Receiving unit having a receiving control means for switching the second selector and instructing the encryption / decryption device to start decryption, a switch manually operated to output the encryption communication start signal, and an encryption key A second register for supplying the encryption key to the encryption device and the encryption / decryption device.

[Operation] According to this configuration, the other party is mutually confirmed by non-encrypted conversation, and then, when an encryption communication start signal is generated by operating the switch, the A pattern is output and then encrypted.
When the A-pattern is received, decryption of the encryption starts and synchronization is easily achieved. Since the A pattern does not occur from the encoder, that is, is not included in the digital signal converted from the audio signal, there is no possibility of malfunction.

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) according to the present invention. This device comprises a main body 1, a handset 2 connected to the main body 1,
A line termination unit (DSU) 3 for connecting to a subscriber line 4 of an Integrated Services Digital Network (ISDN).

The main body 1 has a transmitting section 5 for encrypting and transmitting a voice signal from the transmitter 2s of the handset 2, and a receiving section 6 for decrypting the encrypted voice signal and outputting the voice signal to the receiver 2r of the handset 2. Connected to the driver / receiver 7, driver / receiver 7, transmitter / receiver 7, and receiver 6 for performing interface conversion with the line terminating device 3, and controls the ISDN B channel layer 1 and the D channel layers 1 and 2. Layer 1 and 2 control unit 8 and the layer 1 and 2 control unit 8
A layer 3 control unit 9 for controlling the layer 3 of the D channel of
A switch 10 for instructing the start of encryption of the contents of a call (this switch 10 is a toggle switch, and when pressed again, instructs the end of encryption), and an input button 11 for inputting an encryption key known only to the communicating parties (the input button is (It may also be used as a dial button or another function button), and a register 12 for holding the inputted encryption key.

The B channel signal 13 from the transmission unit 5 is supplied to the layer 1 and 2 control unit 8, and the B channel signal 14 from the layer 1 and 2 control unit 8 is supplied to the reception unit 6 and the transmission signal from the handset 2 15 is supplied to the transmission section 5 and the reception signal from the reception section 6
16 is supplied to handset 2. The encryption start signal 12 from the switch 10 is supplied to the transmitting section 5, the output signal 18 of the input button 11 is supplied to the register 12, and the output signal 19 of the register 12 is supplied to the transmitting section 5 and the receiving section 6. .

FIG. 2 shows an example of the internal configuration of the transmitting section 5 and the receiving section 6 in FIG.

The encoder 21 is a voice signal from the transmitter 2s of the handset 2.
15 (analog signal) is converted into a 1-byte (8-bit) width digital signal (refer to CCITT recommendation G.711 for rules for converting an analog signal into a digital signal by the encoder 21). The encoder 21 converts a specific digital value (referred to as an A pattern) of the converted digital signal into another specific digital value and outputs the converted digital signal. In this embodiment, the μ-law of CCITT recommendation G.711 is used. (Used in Japan, the United States, etc.). That is, in the μ-law, the use of an output pattern (1 byte width) of all “0” (corresponding to the A pattern) is prohibited, and an output pattern of all “0” (A pattern)
Are to be converted into “00000010” (another specific digital value) in order from the MSB (most significant bit) side and output. On the other hand, since any bit pattern can be transmitted in ISDN, this all-zero pattern is used as a control signal. The encoder 21 has this pattern conversion function. The encryptor 22 encrypts a one-byte digital signal 26 output from the encoder 21 in units of one byte (the encryption will be described in detail later). 26, a 1-byte-wide selector that selects and outputs one of the signal lines 27 and 28, and a parallel-to-serial converter 24 to which an output 29 of the selector 23 is supplied. It is converted into data and output as a B channel signal 13. Transmission control unit 25
Controls the entire transmitting section 5. The output (1 byte width) of the encryptor 22 is supplied to the signal line 27, all "0" is set in the register 61, and output to the signal line (1 byte width) 28. Under control, the encryptor 22 is controlled by the transmission control unit 25 through the signal line 31.

The serial / parallel converter 32 converts 1-bit serial data (B channel signal 14) into parallel data of 1 byte width. The encryption / decryption unit 33 outputs 1 which is the output 38 of the serial / parallel converter 32.
The byte digital signal is decoded in byte units (decoding will be described in detail later). The selector 34 controls the output signal 38 of the serial-to-parallel converter 32 and the output signal 39 of the encryption / decryption decoder 33 by the reception control unit 37. A one-byte-wide selector for selecting and outputting any one of them, the codec 35 converts the digital signal of the output 40 (one-byte width) of the selector 34 into an audio signal (analog signal) and outputs it as a reception signal 16. When the output 38 of the serial / parallel converter 32 matches the content of the register 61, the output of the comparator 36 turns on, and this is supplied to the transmission control unit 25 and the reception control unit 37 as an interrupt signal. The receiving control section 37 controls the entire receiving section 6.

Here, encryption / decryption in the present invention will be described.

Currently, as a security measure for digital communications, either the sender or the receiver determines a key, encrypts data (plaintext) to be sent on the transmitting side with the key, and transmits the ciphertext, and the receiving side uses the same key as the previous key. In this method, a cipher text received with the key of (i) is inversely converted, that is, decrypted, and the original plain text is restored. DES (DES (Data Encryption Standard)
For details of the algorithm, see, for example, DWDavies and WLPri
ce (Translated by Kamizono): “Network Security”, Nikkei McGraw-Hill, 1985 pp.55-84), FEAL (FEAL)
For details of the algorithm, see, for example, Miyaguchi, Shiraishi, and Shimizu: “FEAL-8 Cryptographic Algorithm”, Kenjiho, Vol. 37, No. 4/5, 1988 pp. 321-2.
72), and any of these can be used in the present invention. Next, the encryption format (for details of the encryption format, for example,
DWDavies and WLPrice (Translated by Kamizono): "Network Security", Nikkei McGraw-Hill, 1985 pp.85
-102), in this embodiment, the encoded audio signal is 8 bits, real-time communication is enabled, bit error on the line is prevented from expanding, and strong encryption strength is set. Thus, an 8-bit feedback encryption format of OFB (Output Feedback), which is a stream encryption format, is applied. In the present invention, the purpose of encryption is to prevent eavesdropping on a network and to prevent leakage to a third party (for example, if the person who took the handset of the telephone on the receiving side is a third party, there is no Leakage prevention).

INDUSTRIAL APPLICABILITY The present invention can be applied to a digital secret telephone which performs communication by encoding voice using an information channel (B channel) of an 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 secret telephone as an example.

Circuit-switched call setting function provided by ISDN service (Details of the ISDN circuit-switched service and its call setting function are, for example, supervised by Akiyama: "ISDN picture and text reader", Ohmsha, 1988
pp. 92-106) and a B-channel of a digital secure telephone on the transmitting side (hereinafter abbreviated as "A telephone") to which the present invention is applied, and a digital secure telephone on the receiving side to which the present invention is also applied. (Hereinafter abbreviated as "B telephone")
Will be described from the point in time after connection with the B channel.

Before encrypting voice and conducting a telephone call, it is necessary to confirm whether the person who picked up the handset of the telephone B is the person who wants to talk with the person who called the telephone A while talking. Furthermore, in order to confirm whether or not 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, an encryption key (for example, mail between parties) sent in advance by some means (for example, mail) Before performing communication by encrypting the only known combination of numbers), both enter the encryption key from the input button 11 of each telephone. After confirming through conversation that both parties have entered the encryption key, either one of them or both parties press the switch 10 for instructing the start of encryption on the telephone. Since the subsequent communication is encrypted, if the encryption keys input by both are different, communication becomes impossible (only noise is sent to the receiver),
The contents of the call do not leak to the other party. Even if wiretapping is performed somewhere on the network, the original call contents cannot be heard unless the communication contents are decrypted with the same encryption key as before. Here, if either one of the parties inputs an incorrect encryption key, the two sides press the switch 10 again, so that normal voice communication is performed, and the above operation may be performed again.

 Next, the operation of the transmitting side and the receiving side will be described.

Sender The sender has three phases of operation. The first operation phase is performed after the call is set and before an encryption start instruction is issued (hereinafter, referred to as “phase 1”). The second operation phase is until the transmission of 1-byte all “0” by the encryption start instruction (hereinafter, referred to as “0”).
"Phase 2"). In a third operation phase, the input audio signal is encrypted and transmitted (hereinafter, referred to as “phase 3”).

 See FIG. 3 for each operation phase.

Phase 1 The transmitter output 15 (analog signal) of the handset 2 in FIG. 1 is converted into a 1-byte digital signal by the encoder 21 in FIG. At this time, the output 30 of the transmission control unit 25 is a selector.
Instruct 23 to select signal line 26.

Therefore, in this phase, a normal (unencrypted digital signal) voice signal is transmitted to the output 13 of the transmitting section 5 in FIG.

Also, during this phase, the person who placed the A telephone and the person who took the handset of the B telephone confirm that they are both parties to talk to each other, input the encryption key from the input button 11 of each telephone, and After confirming through a conversation that the key has been input, either one or both of them presses the switch 10 for instructing the start of encryption attached to the telephone.

・ Phase 2 The switch 10 in FIG. 1 is pressed (at the time of 51 in FIG. 3) or the output 42 of the comparator 36 in FIG. 2 is turned on (all “0” is received: the other party receives the switch 10 before this side). Is pressed, the output 30 of the transmission control unit 25 in FIG.
To select the signal line 28 (all "0" is set). Therefore, in this phase, the first
One all "0" is transmitted to the output 13 of the transmitting section 5 in the figure (52 in FIG. 3).

Phase 3 The transmission control unit 25 issues an encryption start instruction to the encryptor 22 at the output 31, and instructs the selector 23 to select the signal line 27.

Therefore, in this phase, an encrypted audio signal is transmitted to the output 13 of the transmitting section 5 in FIG.

When the switch 10 is pressed again in any phase, the encryption function is stopped and the process returns to the phase 1.

Receiver The receiver has two phases of operation. The first operation phase is performed after the call is set and until one all “0” is detected (hereinafter, referred to as “phase 1”). In the second operation phase, the received signal (encrypted voice signal) is decrypted (hereinafter, referred to as “phase 2”).

 See FIG. 3 for each operation phase.

Phase 1 After the call is set, the output 43 of the receiving control section 37 is off, and the selector 34 selects the signal 38 at this time. Signal) is input, and the voice of the other party is output to the receiver of the handset 2 in FIG. After the call setup, the comparator
Since the 36 is operating, it is possible to detect all “0” transmitted before the other party starts encryption of the voice at any time.
When the comparator 36 detects all "0", the output 42 is turned on, and the reception control section 37 receives this and shifts to phase 2 (53 in FIG. 3).

Therefore, in this phase, the received voice signal is directly converted into an analog signal and output to the output 16 of the receiver 6 in FIG.

-Phase 2 The reception control unit 37 turns on the output 43. As a result, the decoder 33 starts decoding the reception data (the encrypted audio signal), and the selector 34 selects the signal 39. Here, if the same encryption key as that input by the other party in order to encrypt the voice is set in the register 12 in FIG. 1, the encrypted voice signal is completely returned to the original voice signal. If the encrypted key is different from that of the other party, the encrypted audio signal does not return to the original audio signal.

Therefore, in this phase, the received encrypted voice signal is decoded at the output 16 of the receiver 6 shown in FIG. 1, converted into an analog signal and output.

When the switch 10 is pressed again in any phase, the decryption function is stopped and the process returns to the phase 1.

"Effects of the Invention" As described above, the present invention has the following effects.

Since encryption is performed in a stream encryption format using an encryption algorithm such as DES or FEAL, the encryption strength is high.
(These encryption keys are 64 bits long.) Since encryption and decryption are performed using digital signals, there is no deterioration in the decoded sound quality due to encryption.

Since the encryption and decryption processes are performed in units of the output width of the encoder (in the embodiment, in units of 8 bits), there is no signal processing delay.
As a result, there is no delay in voice from the other party, so that conversation can be performed smoothly.

Since only a specific pattern such as 1-byte all “0” is detected and the normal conversation is switched to the encrypted conversation state, the switching can be performed instantaneously.

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.

Switching from normal conversation to cipher conversation uses a specific pattern that never occurs in the encoding of a voice signal, so that there is no risk of malfunction due to a specific digital signal in the voice signal.

[Brief description of the drawings]

FIG. 1 is a block diagram of a secret telephone apparatus showing one embodiment of the present invention, FIG. 2 is a block diagram showing an example of the internal configuration of a transmitting section 5 and a receiving section 6 in FIG. 1, and FIG. FIG. 3 is a time chart for explaining the operation of FIG. 1 and FIG. 1: Main unit, 2: Handset, 3: DSU (Line Terminating Unit), 5:
A transmitting section for encrypting and transmitting a voice signal, 6: a receiving section for decoding and outputting an encrypted voice signal, 7: a driver / receiver, 8: a layer 1, 2 control section, 9: a layer 3 control section , 10: a switch 10 for instructing the start of encryption, 11: an input button for inputting an encryption key, 12: a register for holding an encryption key, 21: an encoder applying μ-law for converting an analog signal to a digital signal, 22: Encryptor that encrypts 1-byte digital signals in 1-byte units, a selector with a 23: 1 byte width, a converter that converts parallel data with a 24: 1 byte width into 1-bit serial data, and 25: the entire transmission section Transmission control section, which controls the
A converter that converts bit serial data into parallel data of 1 byte width, an encryption / decryption unit that decodes 33: 1 byte digital signals in 1-byte units, 34: selectors, and 35: 1 digital signals of analog width , A codec for converting to 36, a comparator, 37: a reception control unit for controlling the entire reception unit.

──────────────────────────────────────────────────続 き Continuation of front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H04K 1/00-3/00 H04L 9/00-9/38 G09C 1/00-5/00 H04M 1 / 68

Claims (1)

(57) [Claims] An analog signal from a transmitter is converted into a digital signal and output. A specific digital value (hereinafter referred to as "A pattern") is converted into another specific digital value and output. An encoder, an encoder applying a stream encryption format for encrypting the output of the encoder in units of its output bit width (n bits), a first register for storing the A-pattern having an n bit width, A selector, and one of the A patterns is transmitted from a state in which the output of the encoder is transmitted by a signal generated first among the cryptographic communication start signal and the interrupt signal. A transmission section having transmission control means for switching and controlling the first selector so as to transmit the signal; a codec for converting a digital signal into an analog signal and supplying the analog signal to a receiver; An encryption / decryption device that applies a stream encryption format for decoding a signal in units of n bits, a comparator that detects the A pattern from the received digital signal and generates the interrupt signal, a second selector, and the comparator When the interrupt signal is supplied from, the second selector is switched so that the output of the encryption / decryption device is supplied to the codec from the state in which the received digital signal is supplied to the codec. A receiver having reception control means for instructing the encryption / decryption unit to start decryption, a switch manually operated to output the encryption communication start signal, and an encryption key held by the encryption / decryption unit, A second register for supplying the encryption key.