Privacy communication method

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to a wireless communication system such as a PHS (Personal Handy Phone System), and particularly to a secret communication method thereof.

【0002】

[Conventional technology and its problems]

Various secret communication methods have been developed so far in order to more reliably prevent leakage and eavesdropping of communication contents. For example, the method of confidential communication performed between a PHS mobile station (PS) and a base station (CS) is specified in the 2nd generation cordless telephone system standard RCR STD-28 established by the Association of Radio Industries and Businesses. There is. In this method, the secret key code is first determined by the PS, and the determined secret key code is wirelessly transmitted from the PS to the CS prior to the start of the secret communication. In PS and CS, a secret code, which is a pseudo-noise (PN) code, is generated by performing bit shift, EOR processing, etc. on this secret key code. The generated secret code is used as a scramble code for converting the transmitted signal into a PN and as a descramble code for restoring the received signal converted into a PN. In this method, the secret code is determined by a two-step process of determining the secret key code in PS and then generating the secret code in PS and CS, so the communication content is concealed despite the simplicity of the process. It has the advantage of high quality.

【0003】

However, when the secret key code is wirelessly transmitted from PS to CS, the secret key code may be intercepted and stolen. Therefore, improvements in confidentiality are still required for systems such as PHS that use this secret talk method.

【0004】

[Summary of Invention]

One of the objects of the present invention is a PS that can execute secret communication with higher confidentiality of the communication content than before and can be used in an existing system, and more specifically, a secret story executed between the PS and CS. The purpose is to provide procedures and means for communication methods.

【0005】

In order to achieve this object, in the present invention, first, PS determines which of a plurality of types of secret talk methods is prepared. When it is decided to use the first secret communication method (for example, STD-28 compliant method) that uses the secret key code, PS sends the secret key code to CS prior to the start of secret communication. PS and CS each generate a secret code, which is a PN code, based on the secret key code. When deciding to use the second secret talk method that does not use the secret key code, prior to the start of secret talk communication, PS will notify CS that it will use the predetermined secret talk code, which is the PN code, and the initial secret talk code. Send the value or the code that identifies it. Regardless of which secret talk method is used, after the start of the secret talk communication, the transmitted signal is scrambled and the received signal is descrambled by using the generated or received secret talk code or a predetermined secret talk code.

【0006】

In this way, by deciding whether or not to use the secret key code in the secret talk communication in PS and executing the secret talk communication according to the secret talk method according to the result, there is a risk of leakage and eavesdropping of the communication contents due to the theft of the secret key code. Decreases. Moreover, since the decision theory of the secret talk method may be programmed in the PS, no special effort is required to switch the secret talk method.

【0007】

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

【0008】

FIG. 1 shows an outline of the functional configurations of PS100 and CS200 according to the embodiment of the present invention. The PS100 inputs the speaker's voice (101), converts it to adaptive pulse code modulation, that is, ADPCM (102), and wirelessly transmits it to the CS200 (103). The CS200 wirelessly receives this voice (201), converts it to reverse ADPCM (202), and sends it to an external, for example, a wired digital or analog line (203). In addition, when an audio signal is input from the outside (204), the CS200 converts it to ADPCM (205) and wirelessly transmits it to the PS100 (206). The PS100 wirelessly receives this voice (104), converts it to reverse ADPCM (105), and outputs it as voice to the speaker (106).

【0009】

Further, after the ADPCM conversion (102,205) and before the reverse ADPCM conversion (105,202), the audio is scrambled (107,207) and descrambled (108,208). Specifically, an exclusive OR (EOR) of the ADPCM-converted voice and the secret code is required, and the obtained EOR is used for wireless transmission (103,206) or reverse ADPCM conversion (105,202). One of the features of the present invention is that the secret code used in the scramble / descramble processing or the determination method thereof can be selected and determined according to a program on the PS100.

【0010】

That is, prior to the start of voice communication, the PS100 determines the secret talk method to be used according to the program given in advance (109). When the determined secret talk method is the same secret talk method as the conventional secret talk method, that is, the secret talk method using the secret key code, the PS100 wirelessly transmits this secret key code to the CS200 (110), and the PN described later based on the secret key code. The secret story code is generated by the generation process (111). The CS200 wirelessly receives the secret key code transmitted from the PS100 (209), and based on this, generates the secret code in the same manner as the PS100 (210). The PS100 and CS200 temporarily store the generated secret code (112,211) and use the stored secret code for scrambling / descramble processing (107,108,207,208). Therefore, in the present embodiment, if the secret talk method determined by the PS100 is a conventional method, for example, STD-28, the secret talk communication can be executed according to the method conforming to the method.

【0011】

In addition, when the secret voice method determined by PS100 according to the program is another method, PS100 generates a secret voice code to be used in scramble / descramble processing (107,108,207,208) (113) and wirelessly transmits this to CS200. On the other hand (114), it is memorized once (112). The CS200 wirelessly receives (212) and stores the secret code transmitted from the PS100 (211). The stored secret code is used in the scramble / descramble process (107,108,207,208). Therefore, in the present embodiment, confidential communication can be performed between the PS100 and CS200 by a method other than the conventional method using the secret key code. As a result, the confidentiality of the contents of the transmitted / received voice is improved as compared with the conventional system in which the secret communication can be performed only by the conventional method using the secret key code.

【0012】

In order to clarify the explanation of the functions, in Fig. 1, the block related to the transmission and reception of the secret key code and the secret voice code and the block related to the transmission and reception of voice are set as separate blocks, but in reality, these functions are common. It can be realized by using the transmission / reception circuit or the antenna of. In addition, an example of sending a secret code from PS100 to CS200 when a secret method that does not use a secret key code is selected is shown, but this is just an example, and it is not necessary to actually send the secret code. For example, instead of the secret code, a code that can identify the secret code may be simply transmitted from the PS100 to the CS200. Alternatively, a "secret key code indicating that secret communication using the secret key code is not performed" is defined in advance, and when the secret key code is transmitted from the PS100 to the CS200, the predetermined secret code is initially set. In this form, the PS100 may give a notification to the CS200 that the secret communication using the secret key code will not be performed. In addition, the PHS has a public system that makes a call via a CS installed in a telephone pole, a telephone booth, a station yard, etc., and a specific PS that makes a call via a CS installed in a factory, a company premises, etc. There is a self-employed system. In this embodiment, highly confidential voice communication can be realized in both public and self-employed systems. In particular, in a self-employed system, confidentiality can be further ensured because confidential communication can be executed using a specific confidential code defined by the factory, the company, or the like.

【0013】

FIG. 2 shows an example of a circuit that can be used to realize the procedure from determining the secret talk method to storing the secret talk code. The circuit shown in this figure includes a storage circuit 10 for storing a secret code. The address bus ABUS of the storage circuit 10 is switched and connected to either the address bus ABUS1 or ABUS2 by the ABUS switching circuit 12, and the data bus DBUS of the storage circuit 10 is switched to either the databus DBUS1 or DBUS2 by the DBUS switching circuit 14. Be connected. DBUS1 and ABUS1 give the secret key code determined by CUP16 and its write-to address to the PN generator 18 when the secret method determined by CPU 16 according to the program is the secret method using the secret key code, and PN This is a bus for giving a PN code generated based on the secret key code generated in the generator 18, that is, a secret code and its writing destination address. Further, DBUS2 and ABUS2 are buses for giving the secret code determined by the CPU 16 and its writing destination address when the secret method determined by the CPU 16 according to the program is a secret method that does not use the secret key code. The CPU 16 sets the switching information in the register 20 according to the secret communication method determined according to the program. The ABUS switching circuit 12 and the DBUS switching circuit 14 indicate a secret communication method in which DBUS1 and ABUS1 are not used when the switching information set on the register 20 points to a secret talk method using a secret key code. Sometimes DBUS2 and ABUS2 are connected to DBUS and ABUS.

【0014】

FIG. 3 shows an example configuration of the PN generator 18. The PN generator 18 shown in this figure has a 16-stage shift register 22 in which latches S0 to S15 are continuously connected. Also, EOR24, which finds the exclusive OR of the contents of S0 and S4, and EOR26, which finds the exclusive OR of the output of EOR24 and the contents of S13, finds the exclusive OR of the output of EOR26 and the contents of S15, and asks S15. An EOR28 for input is provided. The configuration shown in this figure is suitable for generating a secret code from a secret key code in accordance with STD-28. That is, the secret key code specified in STD-28 is a hexadecimal 4-digit or 16-bit code, and the CPU 16 first shifts each bit of this secret key code when starting to generate the secret code. Initialize to the corresponding latch in 22. The output of each latch in the shift register 22 is latched by the next-stage latch or input to the EOR. The PN generator 18 collects 160 bits of SO output, and the obtained 160 bits of information is used as a secret code.

[Simple explanation of drawings]

[Figure 1]

It is a block diagram which shows the functional structure of PS and CS in one Embodiment of this invention.

[Figure 2]

It is a block diagram which shows an example of the circuit which concerns on the secret talk system determination, the secret talk code generation, and the memory thereof in this embodiment.

[Fig. 3]

It is a block diagram which shows the method of PN code generation.

[Explanation of symbols]

100 PS, 200 CS, 103,206 Voice transmission, 104,201 Voice reception, 107,207 Scramble processing, 108,208 Desk rumble processing, 109 Confidential key code determination, 110 Confidential key code generation, 111,113,210 Confidential code generation, 112,211 Memory, 114 Confidential code transmission, 209 Confidential key Code reception, 212 scramble code reception.