JPH0453326A - Privacy telephone system - Google Patents

Abstract

PURPOSE:To obtain a privacy telephone system with high privacy security by applying cryptographic processing to signal depending on the combination of plural sets of cryptographic algorithm. CONSTITUTION:This telephone system is provided with a line control section 10, a telephone set 11, a cryptographic algorithm selector 12, an algorithm accommodation memory 13 and a cryptographic processing unit 14. Then the combination of plural sets of cryptographic algorithm selected among the cryptographic algorithm group is informed to an opposite ISDN terminal equipment with the prescribed information element of a prescribed message in the D- channel of the ISDN to execute the cryptographic processing/decoding of transmission information according to the combination of plural sets of algorithm. Thus, the danger of the perception of the cryptographic processing system by the 3rd party due to an increased number of keys for the cryptographic processing is eliminated and the privacy telephone system with the privacy security is obtd.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention is directed to an integrated service digital network (hereinafter referred to as 15D).
The present invention relates to a confidential communication device for preventing communication interception by a third party in a terminal device (referred to as N).

[Conventional technology]

FIG. 5 is shown in Japanese Patent Publication No. 147061, for example.
FIG. 1 is a block diagram showing a conventional confidential communication device. In the figure,
1 has a frequency of f. - A low-pass filter that removes frequency components higher than the cutoff frequency f1 of the input signal of f2 (
2 is a synthesis circuit that subtracts the output of this low-pass filter 1 from the input signal. 3 is connected to the low-pass filter 1, and the inversion reference frequency is f. Ten f.

This is a spectrum inverter that inverts the spectrum for each zone. This is a synthesis circuit that adds the output of the 4-cigarette spectrum inverter 3 and the output of the synthesis circuit 2.

Next, the operation will be explained. Here, FIG. 6 is an explanatory diagram showing the spectrum of the portion indicated by ai in FIG. 5.

On the transmitting side, the frequency shown in FIG. 6(a) is f.

An input signal of ~f2 is input to the low-pass filter 1, and its high-frequency components are removed, resulting in a frequency of f2 shown in FIG.

-f, becomes the signal. The signal output from this low-pass filter 1 is sent to a synthesis circuit 2, and the synthesis circuit 2 subtracts the signal from the input signal. Therefore, as shown in FIG. 6(c), from the synthesis circuit 2, the input signal frequencies f, ~f2
Only the high frequency components of are output.

On the other hand, the output signal of the low-pass filter 1 is also input to the spectrum inverter 3, and the spectrum is inverted and input to the synthesis circuit 4 as shown in FIG. 6(d). The synthesizing circuit 4 adds the signal and the signal output from the synthesizing circuit 2, synthesizes the signal into a signal having the spectrum shown in FIG.

On the receiving side, the received signal is input to a low-pass filter 1 and a synthesis circuit 2 to obtain a frequency f as shown in FIG. 6(f). -f
+ signal and frequency f shown in the same figure (g).

Separate into signals of ~f2. The output signal of the low-pass filter 1 is also input to the spectrum inverter 3, and the spectrum is inverted as shown in FIG. 6(h). The signal is further input to the combining circuit 4 and added to the output signal of the combining circuit 2.

As a result, the input signal on the transmitting side is restored as shown in FIG. 6(i).

In this case, even if the signal sent from the transmitting side to the receiving side is intercepted by a third party, it will not be deciphered because the dividing frequency, spectrum inversion processing zone, rearrangement order, etc. are unknown.

Further, FIG. 7 is an explanatory diagram showing the principle of another conventional private conversation device. On the transmitting side, first, spectrum inversion processing is performed on the frequency spectrum of the input signal shown in (a) of the same figure to obtain an inverted signal shown in (b) of the same figure. Next, this inverted signal is subjected to pre-emphasis with the frequency characteristics shown in FIG. 7(C), and then transmitted to the receiving side. On the receiving side, the receiver performs de-emphasis on the received signal using the frequency characteristics shown in Figure 7 (D) to obtain the inverted signal shown in Figure 7 (B), which is subjected to spectrum inversion processing to produce the signal shown in Figure 7 (A). Restore the original input signal shown in .

Here, such a confidential communication device is, for example,
This is shown in Publication No. 062.

[Problem to be solved by the invention]

Since conventional secret message devices are configured as described above, there is only one algorithm for secret message processing, and the number of secret message keys is fixed, making the secret message method known to a third party. The problem was that it was dangerous and confidential.

This invention was made in order to solve the above-mentioned problems, and an object of the present invention is to obtain a confidential communication device with higher communication confidentiality.

[Means to solve the problem]

The secret communication device according to the present invention selects a plurality of encryption algorithms from a group of encryption algorithms at the time of transmission, and
A cryptographic algorithm selection device that writes combination information of the cryptographic algorithm into a predetermined information element of a predetermined message on the D channel of the call, and selects a cryptographic algorithm based on the combination information received at the time of incoming call, is connected to the cryptographic algorithm selection device via the line control unit. A cryptographic processing device connected to the D channel of the I5DN and encrypting and decoding information on the B channel of the I5DN according to each cryptographic algorithm selected by the cryptographic algorithm selection device is installed between the line control unit and the telephone device. This is what was inserted into the B channel of.

[For production]

The cryptographic algorithm selection device in this invention selects a plurality of cryptographic algorithms from a cryptographic algorithm group at the time of transmission, writes the combination information in a predetermined information element of a predetermined message, and sends it to the line control unit.
In addition to transmitting to the D channel of N, when receiving a call,
The cryptographic algorithm is selected based on the combination information received from the D channel of the I5DN via the line control unit, and the cryptographic processing device inserted in the B channel between the line control unit and the telephone device receives the outgoing call. By notifying the combination of encryption algorithms selected at the time or at the time of reception, and having the information on the B channel of the l5DN be encrypted and decrypted according to each encryption algorithm, encryption is performed using a combination of multiple encryption algorithms, and more To realize a confidential communication device with high concealment property.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, 10 is a line control unit where a line consisting of a D channel and a B channel in 15DN is terminated,
Reference numeral 11 denotes a telephone device connected to this line control section 10 through its D channel and B channel.

12 is connected to the D channel of the l5DN via the line control unit 10, and selects a plurality of cryptographic algorithms from a group of cryptographic algorithms at the time of a call, and sends a predetermined message on the D channel of the l5DN, for example, a call setup message. The cryptographic algorithm selection device writes combination information of the selected cryptographic algorithm into an information element, for example, a called subaddress, and selects an encryption algorithm based on the combination information received at the called subaddress of a call setting message when a call is received. .

Reference numeral 13 denotes an algorithm storage memory in which programs for each cryptographic algorithm of the aforementioned cryptographic algorithm group are stored. 14 is inserted into the B channel between the line control unit 10 and the telephone device 11, and encrypts and decodes information on the B channel of the 15DN according to the program of each encryption algorithm selected by the encryption algorithm selection device 12. This is a cryptographic processing device that performs

Next, the operation will be explained. At the time of transmission, the cryptographic algorithm selection device 12 selects a plurality of cryptographic algorithms from a group of cryptographic algorithms and determines a combination thereof. Next, the combination information of the selected cryptographic algorithms is written to the destination subaddress of the call setting message on the D channel of the 15DN, and sent to the D channel of the 15DN line via the line control unit IO.

Here, FIG. 2 is an explanatory diagram showing the format of the destination subaddress of the call setting message.

In the figure, 21 is a terminal identification code for identifying the possibility of cryptographic communication. 22 is a cryptographic algorithm selection key part in which a method of combining cryptographic algorithms is specified, and 23 is a cryptographic key part in which a cryptographic key for each cryptographic algorithm is designated.

Further, the cryptographic algorithm selection device 12 loads the corresponding program in the algorithm storage memory 13 into the internal memory of the cryptographic processing device 14 based on the cryptographic algorithm selection key and the cryptographic key specified in the destination subaddress of the call setting message. . This algorithm storage memory 1
3 contains encryption programs Ac, Bc, . . . for each encryption algorithm A, B, . . .
and decryption programs Ad, Bd, . . . are stored in pairs, and each pair is loaded into the internal memory of the cryptographic processing device 14. The load order of the cryptographic algorithm programs is, for example, the order of cryptographic algorithm processing.

The call setup message sent to the D channel of the l5DN is received by the line control unit 10 of the l5DN terminal device on the called side, and the called subaddress is also transferred to the cryptographic algorithm selection device 12. FIG. 3 is a flowchart showing the operation procedure of the cryptographic algorithm selection device 12 when a call is received.

In step ST1, the cryptographic algorithm selection device 12 refers to the terminal identification code 21 in the destination subaddress and identifies whether or not cryptographic communication is possible.

As a result, if cryptographic communication is not possible, the cryptographic processing device 14 is instructed not to perform cryptographic processing on the B channel in step ST2, and the line control unit 10 is notified of completion of reception preparation.

Further, as a result of the identification, if cryptographic communication is possible, the cryptographic algorithm selection key portion 22 in the destination subaddress is analyzed in step ST3, and the cryptographic algorithm to be used is selected. Next, in step ST4, each of the selected cryptographic algorithms is loaded from the algorithm storage memory 13 to the internal memory of the cryptographic processing device 14 in accordance with the order of processing. At this time, in step ST5, the cryptographic key setting based on the analysis of the cryptographic key part 23 in the destination sub-address is executed on the cryptographic algorithm selection device 12, and then the line control unit 10 is notified of the completion of reception preparation. Be notified.

The line control unit 10 that received the notification of completion of reception preparation
Sends a response message to the calling terminal on the line,
After that, communication with the calling terminal becomes possible.

Here, FIG. 4 is a flowchart showing the operating procedure of the cryptographic processing device 14, in which (a) shows the operating procedure at the time of transmission, and (b) shows the operating procedure at the time of receiving.

That is, at the time of transmission, as shown in FIG. 4(a), the cryptographic processing device 14 first executes the encryption program Ac of the cryptographic algorithm A on the transmitted information from the telephone device 11, and then executes the cryptographic program Ac of the cryptographic algorithm B, C, and D on the transmitted information from the telephone device 11. The encryption programs Bc, Cc, and Dc are executed in this order. The transmission information encrypted in this way is sent to the line control section 10,
It is sent to the B channel of the 15DN line.

On the other hand, at the time of reception, as shown in FIG. 4(b), the cryptographic processing device 1
4 receives the received information from the B channel of the 15DN line from the line control unit 10, first executes the decoding program Dd of the encryption algorithm D on the received information, and then performs the following steps.
Deciphering programs Cd and Bd in the order of cryptographic algorithms C2B and A, respectively.

Execute Ad. In this way, by executing each decryption program Dd-Ad in the reverse execution order of the encryption, the encrypted received information is decrypted and sent to the telephone device 1.
Sent to 1.

In the above embodiment, the encryption algorithm selection key and the encryption key are written together with the terminal identification code in the destination subaddress of the call setup message on the D channel of 1SDN. It may also be written in an information element, for example a user-user information element of a protocol message. By using the user-to-user information elements of the protocol message in this way, it becomes possible to change the encryption key during communication, and it is possible to perform communication with higher privacy.

〔Effect of the invention〕

As described above, according to the present invention, a combination of a plurality of cryptographic algorithms selected from a group of cryptographic algorithms is
The system is configured to notify the other party's 15DN terminal device using a predetermined information element of a predetermined message on the D channel of the 15DN, and encrypt/decode the transmitted information according to the combination of the plurality of encryption algorithms. Since the number of keys increases, there is almost no risk that the confidential communication method will be known to a third party, and a confidential communication device with high secret communication concealment performance can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a private communication device according to an embodiment of the present invention, FIG. 2 is an explanatory diagram showing the format of the destination subaddress of a call setup message, and FIG. FIG. 4 is a flowchart showing the operation procedure of the cryptographic processing device,
FIG. 5 is a block diagram showing a conventional confidential communication device, FIG. 6 is an explanatory diagram showing the spectrum of each part thereof, and FIG. 7 is an explanatory diagram showing the principle of another conventional confidential communication device. 10 is a line control unit, 11 is a telephone device, 12 is a cryptographic algorithm selection device, 13 is an algorithm storage memory, 14
is a cryptographic processing device. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] A comprehensive service digital network terminal device comprising: a line control unit where a line of a comprehensive service digital network consisting of a D channel and a B channel is terminated; and a telephone device connected to the line control unit via the D channel and the B channel. and a secure communication device for preventing communication interception by a third party, which is connected to the D channel of the integrated service digital network via the line control unit, and selects a plurality of cryptographic algorithms from a group of cryptographic algorithms at the time of transmission; Combination information of the cryptographic algorithm is written in a predetermined information element of a predetermined message on the D channel of the comprehensive service digital network, and the cryptographic algorithm is written based on the combination information received by the predetermined information element of the predetermined message when an incoming call is received. a cryptographic algorithm selection device that selects a cryptographic algorithm, an algorithm storage memory that stores the cryptographic algorithm group, and a cryptographic algorithm that is inserted into a B channel between the line control unit and the telephone device, and each cryptographic algorithm selected by the cryptographic algorithm selection device; A secret communication device according to the invention, comprising: a cryptographic processing device for encrypting and decoding information on the B channel of the comprehensive service digital network.