JPH0955713A - Enciphering system for time-division multiplex communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent data from being tapped by synchronizing frames by decoding a synchronizing word according to the algorithm on a reception side station. SOLUTION: When a slave station 2 makes communication, the slave station 2 communicates with a base station 1 after a speaking channel is allocated by the base station 1. In this case, the CPU 31 (41) on a transmission side station changes the position and bit length of a synchronizing word, frame by frame, by using a random number table read out according to a readout rule, and performs transmission. Thus, the CPU 31 (41) on the transmission side superimposes voice information on a data part and sets the synchronizing word, thereby sending the signal in frame units. On the reception-side station, on the other hand, a received frames is temporarily stored in a work area and a random number table is read out according to a readout rule to find the position and bit length of the synchronizing word of the received frame, frame synchronization is performed by taking the synchronizing word out of the received frame according to the position and bit length, and the data part in the frame is read out.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to, for example, TDMA.
(Time Division MultipleAc
The present invention relates to a time-division multiplex communication system such as ces), and particularly to a confidential system of communication.

[0002]

2. Description of the Related Art In a TDMA wireless device such as a digital cellular phone, it is necessary to conceal data in order to prevent eavesdropping. Therefore, conventionally, for example, a method of processing data using an encryption key has been adopted. That is, the frame format of the system is, as shown in FIG. 8, a preamble P for establishing bit synchronization, a synchronization word for establishing frame synchronization, and a header portion indicating whether data is audio information or control information. H, and a data part are included, and a logical operation is performed on the data part on the transmission side by using a binary encryption key,
On the receiving side, the data part is extracted by performing the reverse logical operation on the data part using the encryption key.

[0003]

However, in the above-mentioned confidential system, since the frame format of the communication channel is fixed, it is extremely easy to read the synchronization word by using a waveform analyzer such as a spectrum analyzer, and therefore the format is Since the position of the upper data part is known, there is a concern that the data part may be easily decoded by constantly receiving a specific communication channel and analyzing the data part with a computer or the like. It is expected that personal information will be handled in a wireless channel even in wireless communication as the information becomes multimedia in the future. Therefore, due to the nature of wireless, it is considered that a more sophisticated confidential system is required.

The present invention has been made under such circumstances, and an object of the present invention is to provide a confidential system in a time division multiplex communication system in which it is difficult to eavesdrop on data and the safety is high.

[0005]

According to a first aspect of the present invention, data is placed on a frame format including a synchronization word for frame synchronization to perform communication between a master station and a slave station. In a time division multiplex communication system, a synchronization pattern on the bit pattern or frame format of the synchronization word
An algorithm for determining at least one of the positions of the terminals is stored in the memories of the master station and the slave stations, the transmitting station transmits the synchronization word based on the algorithm, and the receiving station uses the algorithm. It is characterized in that the synchronization word is decoded based on this to synchronize the frame.

A second aspect of the present invention is a time division multiplex communication system in which data is placed on a frame format including a synchronization word for frame synchronization to perform communication between a base station and a slave station. In the above, the algorithm for determining at least one of the bit pattern of the synchronization word and the position of the synchronization word on the frame format is stored in the memory of the base station, and the slave station communicates with the base station. When entering the area, the base station sends the algorithm to the slave station, the transmitting station sends the synchronization word based on the algorithm, and the receiving station receives the synchronization word based on this algorithm. -Decoding the frame to synchronize the frame.

According to a third aspect of the present invention, in the first or second aspect of the invention, the algorithm is a number for specifying the bit pattern of the synchronization word or the position of the synchronization word on the frame format. It is characterized in that it includes a random number table that defines at least one of the numbers for specifying, and a read rule for reading this random number table.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION An example in which the present invention is applied to, for example, a car telephone will be described. The synchronization word is sent to the slave station, and the synchronization word is decoded based on the algorithm in the communication process by the base station and the slave station so that communication is performed.

First, the hardware configuration of the main parts of the base station and the slave stations will be described with reference to FIG.
CPU (central processing unit) 31, ROM (Read only)
memory 32, 33, RAM (Random)
An access memory 34 and a wireless unit 35 are provided. The ROM 32 stores an execution program on the base station 1 side, and the ROM 33 stores a random number table to be transferred to the slave station 2 and its read rule. The RAM 34 is used as a work area and further stores variables and the like.

On the other hand, the slave station 2 includes a CPU 41, a ROM 42,
RAM 43, 44 voice input unit 45 and voice output unit 46,
The wireless unit 47 is provided. The ROM 42 stores an execution program and an authentication ID on the slave station 1 side, and a RAM 4
A random number table and a read rule sent from the base station 1 are stored in the area 3. The RAM 44 is used as a work area and stores variables and the like.

FIGS. 2 and 3 show examples of the random number table and the read rule, respectively. In the random number table, information on the position of the synchronization word, for example, from which bit after the preamble of the frame format the synchronization word is made, is provided. , A column in which the bit length of the synchronization word is defined as a set is arranged in, for example, 20 stages. The bit length of the synchronization word is, for example, a reference synchronization word of a certain length is determined in advance, and up to how many bits of this reference synchronization word are taken out to use that bit pattern as the synchronization word. When the bit length of the reference sync word reaches its maximum value or exceeds the bit length of the reference sync word, the excess bit length is returned to the beginning and is extracted.

The read rule is software that determines how to read the random number table. For example, first every second row is read, after reading the 20th row, every second row is read. , And the procedure returns to the second row after reading the 19th row. The read rule can be defined as various rules such as the reverse reading from the 20th step, one step at a time, or the reading method such as 1st step, 20th step, 2nd step, 19th step ,.

Next, the operation of the above system will be described with reference to FIGS. As shown in FIG. 4, when the slave station 2 located in the communication area A of the base station 1A moves into the communication area B of the base station 1B, for example, the slave station 2 first enters the area B. Immediately after that, an authentication request is issued to the base station 1B as shown in FIG. In response to this, the base station 1B makes an authentication response, and further transmits the random number table and the read rule in the ROM 32 to the slave station 2.

Here, the authentication ID is a code unique to the slave station 2, and the random number table and the read rule are unique to each authentication ID. That is, each slave station 2 is assigned a random number table and a read rule unique to that slave station 2. The slave station 2 writes a random number table and a read rule in the RAM 43 and then makes a confirmation response to the base station 1B. Such a series of transmission and reception is performed using a control channel dedicated to control information.

When the slave station 2 makes a call, a call request is made to the base station 1B through the control channel, and the base station 1B is called.
After the call channel is allocated from B, the call is performed between the slave station 2 and the base station 1B (specifically, with another slave station connected to the communication through the base station 1B) by the call channel. In this case, at the transmitting station, the CPU 31 (4
1) reads the random number table according to the read rule, and based on this random number table, the position and bit length of the synchronization word are changed for each frame and transmission is performed. For example, as shown in FIG. 6, the position and bit length (a1, b1), (a2, b2) of the synchronization word in frames n, n + 1, and n + 2,
(A3, b3) correspond to the numerical values of each stage read from the random number table. However, as described above, for example, in the case of the bit length b1, as shown in FIG. 7, the code portion from the head to the b1th bit becomes the synchronization word of the bit length b1 with respect to the code forming the reference synchronization word. In the illustrated example, the sync word of the frame n is interrupted in the middle of the header part H, and the sync words of the frames n + 1 and n + 2 are interrupted in the middle of the data part.

Thus, the CPU 31 (41) on the transmitting side
The voice information is placed in the data section, and the synchronization word is set as described above, and transmission is performed in frame units. On the other hand, at the receiving station, the received frame is temporarily stored in the work area, and the random number table is read according to the read rule to find the position and bit length of the sync word of the received frame. To retrieve the data portion in the frame.

According to the above-described embodiment, since the frame structure of the communication channel, that is, the synchronization word is different, it is difficult for a third party to determine the synchronization word even with a commercially available measuring instrument, and the safety is improved. Can be achieved. Moreover, since the base station creates a random number table and a read rule and sends it to the slave station,
Even if there is a suspicion of eavesdropping, another random number table and read rule can be retransmitted to the slave station and used to determine the synchronization word, so it is easy to change the encryption algorithm. High safety. Further, since the encryption algorithm of the synchronization word is composed of the random number table and the read rule, it is simple, and therefore the processing load can be small, so that it does not particularly depend on the processing capacity of the slave station side.

In the above, according to the present invention, only the position of the sync word may be changed by the cryptographic algorithm and the bit length of the sync word may be fixed, or conversely, only the bit length of the sync word may be changed and the position fixed. You may do it. As the encryption algorithm, a plurality of types of bit patterns of the synchronization word (arrangement pattern of "1" and "0") are prepared, for example, pattern 1 and pattern 2
An algorithm in which n patterns n are prepared and the order of using these patterns (which pattern is used) may be described. In this case, if a random number table is used, the numbers in the random number table correspond to pattern numbers, for example.

Further, the slave station may have an encryption algorithm in advance so that the slave station transmits the encryption algorithm to the base station when it enters the communication area of the base station. Furthermore, the cryptographic algorithm may be changed each time a call is made. Note that the present invention is not limited to a digital cellular or the like that communicates between a base station and a slave station, but may be applied to a transceiver or a cordless telephone that communicates between a master station and a slave station.

[0020]

According to the present invention, since at least one of the bit pattern of the sync word and the position on the frame format is changed by an algorithm, for example, the frame structure is changed for each frame, so that the wiretapping of communication can be performed. Difficult and safe.

[Brief description of drawings]

FIG. 1 is a block diagram showing a hardware configuration of an apparatus used in an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an example of a random number table which is a synchronization word encryption algorithm.

FIG. 3 is an explanatory diagram showing an example of a read rule of a random number table.

FIG. 4 is an explanatory diagram showing a communication area of a car phone.

FIG. 5 is a sequence diagram showing a processing flow according to the embodiment of the present invention.

FIG. 6 is an explanatory diagram showing a frame format according to the embodiment of the present invention.

FIG. 7 is an explanatory diagram showing a relationship between a reference sync word and a bit length of a sync word in a frame.

FIG. 8 is an explanatory diagram showing a frame format in the conventional method.

[Explanation of symbols]

 1 Base Station 2 Slave Station 31, 41 CPU 32, 33, 42 ROM 34, 43, 44 RAM 35, 47 Radio Section P Preamble H Header Section

Claims (3)

[Claims] 1. A time division multiplex communication system for carrying out communication between a master station and a slave station by placing data on a frame format including a synchronization word for frame synchronization. Bit pattern or frame format
An algorithm that determines at least one of the positions of the synchronization words on the mat is stored in the memories of the master station and the slave station, and the transmitting station transmits the synchronization words based on the algorithm and the receiving side In the station, the time division multiplex communication system is characterized in that the synchronization word is decoded based on the above algorithm to synchronize the frame. 2. A time division multiplex communication system in which data is placed on a frame format including a synchronization word for frame synchronization for communication between a base station and a slave station. -Bit bit pattern or frame format
An algorithm for determining at least one of the positions of the synchronization words on the mat is stored in the memory of the base station, and when the slave station enters the communication area of the base station, the base station causes the slave station to perform the algorithm. And the transmitting station transmits the synchronization word based on the above-mentioned algorithm, and the receiving station decodes the synchronization word based on this algorithm to synchronize the frame. And time division multiplex communication system. 3. The algorithm comprises a random number table which defines at least one of a number for specifying a bit pattern of a synchronization word and a number for specifying a position of the synchronization word on a frame format. The time division multiplex communication system according to claim 1 or 2, further comprising: a reading rule for reading the random number table.