JPH0442862B2 - - Google Patents

Description

[Detailed description of the invention] (1) Technical field of the invention The present invention relates to a secure communication system.

(2) Background of the technology General audio and other signals are transmitted from one subscriber to another via a conversion station, either as a baseband signal or as a signal modulated by PCM or the like. Since this transmission is done through a carrier line, there is a possibility that it may be subject to so-called eavesdropping. For this purpose, signals such as voices belonging to trade secrets are subjected to secrecy processing before being transmitted from one subscriber to another subscriber. The other subscriber cancels the ciphering process and then reproduces the original voice or other signal. The present invention refers to such a secure communication system.

(3) Prior art and problems FIG. 1 is a block diagram showing an example of a general communication system. In this figure, 11A and 11B
is a remote subscriber, 11C is a central subscriber, and is connected to an analog exchange (e.g.
Connect to 2W (wire) analog switch) 13.
The central subscriber 11C is connected directly to the analog exchange 13 in the case shown.

By the way, the carrier end station devices 12A and 12A' and 12B and 12B' are connected through carrier lines 14A and 14B, respectively. Therefore, there is a risk that information such as audio signals between subscribers may be intercepted. For this reason, information that requires secrecy is subjected to secrecy processing and then transferred to the transport lines 14A, 14B. Note that 15 in the figure indicates the area of one switching center.

Generally, analog carrier lines are often used as the carrier lines 14A and 14B, and for this reason analog concealment processing must be performed. However, this analog concealment process is usually technically difficult, so the cost of the concealment process is quite high. Therefore, at present, the cost of transmitting information that requires secrecy is high and its usage is low, and this is a problem of the present invention.

(4) Purpose of the Invention In view of the above problems, an object of the present invention is to provide a secure communication system that can transmit confidential information at low cost.

(5) Structure of the Invention In order to achieve the above object, the present invention focuses on the fact that digital concealment devices are generally inexpensive and have high performance, and uses this digital concealment device to carry out concealment processing. It is characterized by the fact that it is designed to be performed.

(6) Embodiment of the Invention FIG. 2 is a block diagram showing an embodiment of a secure communication system based on the present invention. In this diagram, M and P
The parts indicated by sets of and V or V, P, and M are the parts that characterize the present invention, where M is a modem, P is a digital concealment device, and V is a voice analysis and synthesis device. Modem M exchanges analog signals into digital signals or converts digital signals into analog signals. The device P performs security processing on the digital signal. A secret device is another name for a cryptographic device, and the secret device is equipped with an encoder that converts a readable digital signal (hereinafter referred to as plaintext) into an unreadable digital signal (the data has meaning and the content can be confirmed). This is a device that converts the cipher text into a signal (hereinafter referred to as a cipher) and transmits it through a communication line, and on the receiving side, converts this cipher text into the original plain text using a decoder included in the secret device. The encoder converts the plaintext into ciphertext by scrambling (rearranging) the 1s and 0s of the plaintext digital signal, and the decoder descrambles the 1s and 0s of the ciphertext digital signal. (rearranging the scrambled text back to its original form) converts the ciphertext into plaintext. There are various methods of scrambling and descrambling depending on the strength of the encryption (difficulty in deciphering it), but as mentioned above, it is generally a device that encrypts (and decrypts) digital signals, that is, a digital secret device. It is known that devices with higher encryption strength are available at lower cost than devices that encrypt (plain code) analog signals. Any digital concealment device may be used. The speech analysis/synthesis device V is a so-called high-efficiency speech code/decoding device that converts a speech signal into a low-speed digital signal and performs the inverse conversion. When an audio analog signal is input, this device first samples it, digitizes it, and then extracts information representing the characteristics of the audio from the digitized signal. ) Convert it to a digital signal and send it to the transmission line. It also receives a digital signal from the transmission path, decodes and reproduces it so as to restore the characteristics of the original voice that was sent, and outputs it as smooth voice through a filter. Several types of devices have been known for a long time (for example, Nikkei Electronics February 13, 1973 issue, pages 58-75, "New speech analysis and synthesis method 'PARCOR'",
Nikkei Electronics, November 13, 1978 issue P62~
81, “Low-speed digital audio transmission system aimed at improving audio quality”), available at By the way, in the present invention, a normal analog telephone line (frequency band 0.3 to 3.4kHz) is used, and
The purpose is to use an inexpensive digital concealment device with high cryptographic strength. However, the encoding speed of the PCM method, which is a general digital signal encoding method, is 64 kbps, while the encoding speed that can be transmitted over analog lines in the frequency band 0.3 to 3.4 kHz is at most 9.6 kbps. Therefore, it is impossible to transmit the above-mentioned general digital signals directly using an analog telephone line. Therefore, in the present invention, a speech analysis and synthesis device V having the above-mentioned functions is used in order to reduce the speed of the digital signal without impairing the quality of the speech. 2
1A, 21A', 21B and 21B' are normal flat line parts, but V-P-M (or M-P-
Some modifications have been made to cooperate with the set V). That is, the changeover switches 22A, 22B,
23A, 23B, 22A', 22B', 23A', 2
It is newly equipped with 3B'. These changeover switches are driven (to the upper contact or the lower contact) by a detector indicated by DET in the figure. In addition, 22 and 2
The changeover switches marked with 3 are switched in conjunction with each other. By interlocking the switches 22 and 23, the series connection consisting of VPM can be switched from a flat line or back to a flat line at one time. For this reason, the secret device does not operate when the plain line side is connected, and only operates while the switch is switched to the V-P-M side, so the secret device key is set to In a secret device that changes, there is an advantage that the rules of the secret device do not change when a plain line is used.

What should be noted in the above configuration is that the system as a whole still constitutes an analog network. In other words, it is possible to introduce an inexpensive and high-performance digital concealment device P without disrupting the analog network configuration. Therefore, the cost of transmitting information that requires secrecy is reduced.

The operation is as follows. First, when connecting from subscriber 11A to subscriber 11C, subscriber 11A goes off-hook and dials the other subscriber 11C. The detector DET detects this off-hook and first switches the changeover switch 2.
Connect 2A (also 23A) to the upper contact. In other words, set it to the flat line side. This can also be done automatically as will be described later. At this time, both changeover switches 23A' and 22A' are connected to the upper contact, and unless instructed otherwise (described later), the
Select the 1A′ side.

The 2W analog exchange 13 receives the above-mentioned dialing and connects to the other party subscriber 11C. A normal analog flat line is established here.

If you wish to communicate confidentially, please contact subscriber 11A.
selects the secret line side, that is, the VPM set. For example, by pressing the # button on a push-button telephone, the detector DET is activated and the contacts of the changeover switches 22A and 23A are connected to the lower side. Further, the signal from the # button operates the detector DET on the flat line 21A' side through the carrier line 14A, and connects the contacts of the changeover switches 23A' and 22A' to the lower side, that is, to the secret line side. A secret line is thus established.

The confidential voice on the analog line from the subscriber 11A is converted into a low-speed digital signal by the voice analysis and synthesis device V, and then applied to the digital concealment device P, where it is subjected to security processing. Furthermore, in order to transmit it to a normal analog communication network, it is converted into a confidential analog signal by a modem M.

The secret analog signal thus carried on the carrier circuit 14A enters the modem M through the lower contact of the changeover switch 23A', and converts the secret analog signal into a digital signal. Further, in the device P, the secrecy is canceled, and in the next stage device V, the audio signal is returned to an analog signal. In addition,
The M, P, and V each include two processing systems, and the processing systems are different depending on whether the signal is transferred from V→P→M or when the signal is transferred from M→P→V.

As described above, the secrecy of the analog signal reaching the exchange 13 and further reaching the other subscriber 11C should be completed in as short a time as possible. This is to minimize the chance that a third party will decipher the secret. Therefore, to end a confidential call, immediately press the * button on a push-button telephone, activate the detector DET with the signal corresponding to the * button, and switch the changeover switches 22A, 23A and 22A', 2.
3A' back to the upper contact, ie, the normal flat line side.

Next, when connecting from subscriber 11A to subscriber 11B, ' Dial to subscriber 11B at the other end in the same manner as above, and select the plain line side. ′ mentioned below
It can also be done automatically.

'Similarly to the above, a normal analog flat line to subscriber 11B is established.

'Similarly to the above, the changeover switches 22A, 23A, 23A', 22A', 22B',
Each contact point of 23B', 23B, and 22B (system B is controlled by each DET) is connected to the lower side to establish a secret line.

' Through the same procedure as above, the analog signal from the subscriber 11A that reaches the analog exchange 13 is looped back here and transferred to the changeover switch 22.
It reaches subscriber 11B from the lower contact point of B' through the route V→P→M→14B→lower contact of changeover switch 23B→M→P→V.

'Similarly to the above, for example, press the * button to cancel concealment and end the call.

The secret communication system operates as described above.

(7) Effects of the Invention As explained above, according to the present invention, secure communication can be performed using an inexpensive and high-performance digital concealment device even though it is an analog communication network.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of a general communication system, and FIG. 2 is a block diagram showing an embodiment of a secure communication system based on the present invention. 11A, 11B, 11C...Subscriber, 13...Analog exchange, 14A, 14B...Carrier line, 15...
Exchange area, 21A, 21A', 21B, 21
B'...Planar line system, 22A, 23A, 23A', 2
2A', 22B, 23B, 22B', 23B'...changeover switch, M...modem, P...digital concealment device, V...speech analysis and synthesis device.

Claims (1)

[Scope of Claims] 1. A push-button analog communication device for a plurality of subscribers, an analog exchange that connects at least two of the push-button analog communication devices for the plurality of subscribers, and the analog exchange and the In a communication system comprising an analog line connecting a plurality of subscriber push-button analog communication devices, each of the subscriber push-button analog communication devices and each subscriber push-button analog communication device. A first secret line, in which a voice analysis and synthesis device, a digital concealment device, and a modem are connected in series from the subscriber side, is provided between the analog line from the subscriber side to the analog exchange, in parallel with the analog line; No secret communication is performed between both ends of the first secret line, so that when carrying out secret communication, the subscriber push-button analog communication device and the analog line are connected via the first secret line. When the subscriber and the analog line are directly connected, first and second changeover switches are provided that can be switched at the same time, and the first and second changeover switches are connected to each other via the analog line. A first detector is attached for detecting a transmitted predetermined push button signal and an off-hook signal, and the first and second changeover switches are arranged such that the attached first detector detects the predetermined push button signal. Then, the subscriber push-button analog communication device and the analog line are switched to be connected via the first secret line, and when the attached first detector detects the off-hook signal, Switching is performed so that the subscriber push-button analog communication device and the analog line are directly connected, and the analog switch and the analog line from each of the subscriber push-button analog communication devices to the analog exchange A second switch which has a voice analysis and synthesis device, a digital concealment device, and a modem connected in series from the analog exchange side to the
A secret line is provided in parallel with the analog line, and the analog exchange and the analog line are connected to each other through the second secret line when performing secret communication at both ends of the second secret line. To,
Third and fourth changeover switches are provided that are switched simultaneously so that the analog exchange and the analog line are directly connected when secret communication is not performed, and the third and fourth changeover switches include the above-mentioned switch. A second detector is attached to detect a predetermined push button signal and an off-hook signal transmitted via an analog line, and the third and fourth changeover switches When a predetermined push button signal is detected, the analog exchange and the analog line are switched to be connected via the second secret line, and when the attached second detector detects the off-hook signal, The analog exchange and the analog line are switched to be directly connected, and the modem converts the analog signal input from the analog line side into a digital signal, and also converts the digital signal input from the digital secret line side. converting it into an analog signal, the digital concealment device performs concealment processing on the digital signal input from the voice analysis and synthesis device side, and also deciphers the digital signal input from the modem side, and performs concealment processing on the digital signal input from the voice analysis and synthesis device side, The device samples audio analog signals input from the subscriber side or the exchange side.
By converting the audio analog signal into a digital signal that is slower than the sampled and digitized signal by digitizing and then extracting the characteristics of the audio, It performs the inverse conversion of the above conversion on the digital signal input from the secret device, and is provided between each analog line connecting the analog switchboard and the push-button analog communication devices for the plurality of subscribers. Said first, second,
A secret communication system characterized in that the third and fourth changeover switches are simultaneously switched in response to the push button signal and the off-hook signal.