JP6102109B2 - Roadside communication device, wireless communication system, and transmission method - Google Patents

Description

  The present invention relates to a roadside communication device, a wireless communication system, and a transmission method that can be suitably used as, for example, a component of an intelligent transport system (ITS).

In recent years, for the purpose of promoting traffic safety and preventing traffic accidents, an advanced road traffic system that receives information from infrastructure devices installed on the road and uses this information to improve vehicle driving safety has been studied. (For example, refer to Patent Document 1).
A wireless communication system used in such an intelligent road traffic system mainly includes a plurality of roadside communication devices that are infrastructure-side wireless communication devices and a plurality of in-vehicle communication devices (mobile communication devices) that are wireless communication devices mounted on each vehicle. ).

  In this case, the combination of communication performed between each communication subject includes road-to-vehicle (or vehicle-road) communication performed by a roadside communication device and a vehicle-mounted communication device, and vehicle-to-vehicle communication performed between vehicle-mounted communication devices, roadside communication Inter-road communication performed by communication devices is included (see, for example, Patent Document 2).

In the above-mentioned intelligent transportation system, in addition to providing a safe driving support service, security measures for road-to-vehicle or vehicle-to-vehicle communication of the system have been studied.
In Non-Patent Document 1 below, as security measures, verification of the authenticity of the sender in each communication, confirmation of message integrity, and maintenance of confidentiality of communication information are being studied.

As a method for confirming the authenticity of the sender in each communication and the integrity of the message, a public key authentication method using an electronic signature based on a public key algorithm and a common method applying a message authentication code based on a common key algorithm are used. Key authentication methods are introduced.
An encryption method using a common key algorithm has been introduced for maintaining the confidentiality of communication information.

Japanese Patent No. 2806801 JP 2011-114647 A

ITS Information Communication System Promotion Conference, “Security Guidelines for Driver Assistance Communication Systems ITS FORUM RC-009 Version 1.1” [online], April 25, 2012, [Search July 9, 2012], Internet <http : //www.itsforum.gr.jp/Public/J7Database/p41/p41.pdf>

  Among security measures for road-to-vehicle communication and vehicle-to-vehicle communication in the wireless communication system, an encryption method using a common key algorithm is considered suitable for maintaining the confidentiality of communication information.

  In the above wireless communication system, since communication is performed with a mobile communication device that moves from moment to moment, transmission of communication information in road-to-vehicle communication and vehicle-to-vehicle communication does not need to specify a transmission destination. Done by transmission.

In general, in the common key algorithm, the transmission source and the transmission destination have the same common key, and in the relationship between the transmission source and another transmission destination different from the transmission destination, Another common key different from the common key is provided.
For this reason, when an encryption method based on a common key algorithm is applied to the above system, the transmission source communication apparatus needs to have a common key (encryption key) for each communication apparatus that can be a transmission destination.

  It is practically impossible to provide an encryption key for each communication device that can be a transmission destination in the above system that employs broadcast transmission. However, if all roadside communication devices and mobile communication devices have the same encryption key, even if broadcast transmission is performed in road-to-vehicle communication and vehicle-to-vehicle communication, communication at the transmission destination (reception side) Since the machines always have the same encryption key, the received communication information can be decrypted.

  As described above, if each communicator has a common encryption key, it is possible to broadcast the encrypted communication information, so it is possible to maintain confidentiality of communication information in road-to-vehicle communication and vehicle-to-vehicle communication. It is considered that an encryption method using a common key algorithm is suitable.

In the wireless communication system, in addition to road-to-vehicle communication and vehicle-to-vehicle communication, road-to-road communication also exists, and each of these communication shares a predetermined frequency band by time division.
Therefore, when the encryption method using the common key algorithm is adopted in the road-to-vehicle communication and the vehicle-to-vehicle communication, the commonality of the hardware and the same encryption key can be maintained in maintaining the confidentiality of the communication information in the road-to-road communication. Therefore, it is considered that an encryption method using a common key algorithm is suitable.

  Here, the roadside communication device that performs the road-to-road communication and the road-to-vehicle communication transmits the communication information to both the mobile communication device and other roadside communication devices as transmission destinations. Information that the mobile communication device does not want to acquire may be transmitted to the roadside communication device, such as information related to maintenance of equipment on the infrastructure side and information related to traffic management when an emergency occurs.

  However, for example, assuming that the same encryption key is used in each communication, the mobile communication device can decrypt and acquire all communication information wirelessly transmitted by the roadside communication device. For this reason, information that is not desired to be acquired by the mobile communication device among the information transmitted by the road-to-road communication is acquired by the mobile communication device.

  If the same encryption key is used for each communication, if the encryption key leaks, it will be difficult to maintain confidentiality in all communications in the system, and The entire system will be affected, such as the need to change.

  The present invention has been made in view of such circumstances, and even if the encryption key is leaked while preventing the communication information of the communication between the roads from being acquired by the mobile communication device, the entire system is affected. It is an object of the present invention to provide a roadside communication device, a wireless communication system, and a transmission method that can prevent the transmission.

(1) A roadside communication device according to the present invention for achieving the above object is used in a wireless communication system in which a plurality of mobile communication devices and a plurality of roadside communication devices share a predetermined communication frequency band by time division. The communication information transmitted in the communication performed between the communication devices is encrypted with an encryption key for encrypting the communication information, and is a roadside communication device. A communication control unit that uses an encryption key that is different from the encryption key used for communication other than the communication between the communication devices as the encryption key used for the communication between the roads It is characterized by having.

According to the roadside communication device having the above configuration, since the encryption key different from the encryption key used in the communication other than the roadside communication is used for the roadside communication, the mobile communication device uses the communication information of the roadside communication. It cannot be decrypted. Therefore, it is possible to prevent the communication information of the roadside communication from being acquired by the mobile communication device.
Furthermore, for example, even if an encryption key used in communication other than roadside communication leaks, confidentiality in roadside communication can be maintained, and the influence on the entire system can be suppressed. it can.

(2) In the roadside communication device, it is preferable that the communication control unit changes an encryption key used for the roadside communication according to a time during which the roadside communication is performed.
In this case, even if the encryption key used in the road-to-road communication leaks, it is difficult to maintain the confidentiality of the road-to-road communication by using the leaked encryption key. In the time used, the confidentiality in the road-to-road communication can be maintained. Therefore, it is only necessary to change the encryption key for the time when the leaked encryption key should have been used, and the influence on the entire system can be further suppressed.
Further, by specifying the leaked encryption key, the leaked time can be specified.

(3) Further, in this case, the communication control unit may further change the encryption key used for the inter-road communication according to the installation location of the own device.
Thereby, the influence on the whole system can be further suppressed.
If the leaked encryption key is specified, the time and place where the encryption key was used can be specified, and the time and place where the encryption key was leaked can be specified. As a result, it is possible to obtain information necessary for further enhancing security, such as grasping the cause of the leakage of the encryption key and countermeasures against the leakage.

(4) The plurality of mobile communication devices and the plurality of roadside communication devices are assigned with the predetermined frequency band by allocating at least one of a plurality of time slots arranged in a communication frame used by each communication device. May be shared by time division, the communication control unit may change the encryption key used for the inter-road communication according to the time slot assigned to the own device.

(5) (6) Further, the roadside communication device further includes a storage unit storing a plurality of different encryption keys, and the plurality of encryption keys are configured by dividing the plurality of encryption keys into a plurality of groups. A plurality of encryption key groups, and the communication control unit selects one mode from a plurality of modes associated with any of the plurality of encryption key groups, and associates the selected mode with the selected mode. The encryption key used for the said road-to-road communication may be selected from the obtained encryption key group.
Furthermore, in this case, the plurality of encryption key groups are used in a specific situation other than the case where they are normally used and the case where the plurality of encryption key groups are normally used. It is preferable to include a low encryption key group.
In this case, the encryption key group that is used less frequently has relatively high confidentiality of the communication information as compared to the encryption key group that is normally used. Therefore, a plurality of levels can be provided for the confidentiality of the communication information, and the confidentiality level of the communication information can be selected by selecting the mode.

(7) Therefore, at the normal time, the communication control unit selects a mode corresponding to a normally used encryption key group, and an emergency situation occurs around the own device, or maintenance work of the wireless communication system is being performed. In this case, it is possible to select a mode corresponding to the encryption key group with low usage frequency.
As a result, in emergency situations where confidentiality of communication information is required and in maintenance work where information on the system that is not recognized by the mobile communication device is handled, it is more confidential than the encryption key group normally used. However, it is possible to select a cryptographic key group with a high frequency of use and use it for roadside communication.

(8) In the roadside communication device, the communication information is preferably encrypted by an encryption method using a common key algorithm.

(9) The present invention is a wireless communication system in which a plurality of mobile communication devices and a plurality of roadside communication devices share a predetermined communication frequency band by time division, and is performed between the communication devices. Communication information transmitted in communication is encrypted with an encryption key for encrypting the communication information, and as each encryption key used for road-to-road communication performed between the plurality of roadside communication devices, It is characterized in that an encryption key different from an encryption key used for communication other than the road-to-road communication is used for communication performed between communication devices.

  According to the wireless communication system having the above-described configuration, as described above, even if the encryption key is leaked while preventing the communication information of the communication between the roads from being acquired by the mobile communication device, the entire system is affected. Can be suppressed.

(10) The present invention is a wireless communication system in which a plurality of mobile communication devices and a plurality of roadside communication devices share a predetermined communication frequency band by time division, and is performed between the communication devices. Communication information transmitted in communication is encrypted with an encryption key for encrypting the communication information, and includes information used by public vehicles used for highly public purposes, The information used by the public vehicle is an encryption key possessed by the plurality of roadside communication devices and the mobile communication device mounted on the public vehicle, and used for information other than the information used by the public vehicle, Is characterized by being transmitted using different encryption keys.

  According to the wireless communication system configured as described above, the information used by the public vehicle is transmitted using an encryption key different from the encryption key used for information other than the information used by the public vehicle. A communication device that does not have an encryption key used for information to be used cannot decrypt information used by public vehicles. Therefore, it is possible to prevent information used by public vehicles from being acquired by mobile communication devices mounted on vehicles other than public vehicles or mobile communication devices carried by pedestrians.

(11) The present invention provides a roadside communication device used in a wireless communication system in which a plurality of mobile communication devices and a plurality of roadside communication devices share a predetermined communication frequency band by time division. A transmission method of transmitting communication information by encrypting the communication information with an encryption key for encrypting the communication information, and as an encryption key used for road-to-road communication with another roadside communication device, It is characterized in that an encryption key different from an encryption key used for communication other than the road-to-road communication is used for communication between the communication devices.

  According to the transmission method having the above-described configuration, it is possible to prevent the communication information of the road-to-road communication from being acquired by the mobile communication device and to prevent the entire system from being affected even if the encryption key is leaked. it can.

  ADVANTAGE OF THE INVENTION According to this invention, even if an encryption key leaks, it can suppress that the whole system is affected, preventing the communication information of roadside communication from being acquired by the mobile communication apparatus.

It is a schematic perspective view which shows the whole structure of the intelligent transport system (ITS) which concerns on one Embodiment of this invention. It is a figure which shows an example of the communication frame of a radio | wireless communications system. It is a block diagram which shows the internal structure of a roadside communication apparatus and a mobile communication apparatus. It is a figure which shows an example of a structure of the communication packet transmitted by a roadside communication apparatus and a mobile communication apparatus. It is a conceptual diagram which shows the encryption key memorize | stored in the memory | storage part of the roadside communication apparatus. It is a conceptual diagram which shows the encryption key memorize | stored in the memory | storage part of a mobile communication apparatus. It is a figure which shows an example which divided on the road traffic for every area. It is a figure which shows an example of the usage schedule of an encryption key. It is a figure which shows an example to which the key ID used for the time slot allocated to each roadside communication apparatus and roadside communication for every time slot was allocated. It is a conceptual diagram which shows the encryption key memorize | stored in the memory | storage part of the mobile communication apparatus which concerns on other embodiment.

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

[Overall system configuration]
FIG. 1 is a schematic perspective view showing an overall configuration of an intelligent road traffic system (ITS) according to an embodiment of the present invention. In FIG. 1, as an example of the road structure, a grid structure in which a plurality of roads in the north-south direction and the east-west direction intersect with each other is assumed.
As shown in FIG. 1, the intelligent traffic system includes a traffic signal 1, a roadside communication device 2, a mobile communication device 3 (see FIG. 2) mounted on a vehicle 5, a central device 4, and various vehicle sensors. The roadside sensor 6 to be included.

The traffic signal 1 and the roadside communication device 2 are installed at each of a plurality of intersections Ji (i = 1 to 12 in the example), and are connected to the router 8 via a communication line 7 such as a telephone line. . This router 8 is connected to the central device 4 in the traffic control center.
The central device 4 constitutes a local area network (LAN) with the traffic signal device 1 and the roadside communication device 2 at each intersection Ji included in the area under its control. Therefore, the central device 4 can perform bidirectional communication with each traffic signal 1 and each roadside communication device 2. The central device 4 may be installed on the road instead of the traffic control center.

  In FIG. 1, for the sake of simplicity, only one signal lamp is depicted at each intersection Ji, which is a crossroad intersection. Four signal lamps are installed.

The roadside sensor 6 is composed of various vehicle detectors installed at appropriate places in the jurisdiction area for the purpose of counting the number of vehicles flowing into each intersection Ji and detecting the end of a traffic jam.
Examples of the vehicle detector include an ultrasonic vehicle detector, a microwave vehicle detector, an optical vehicle detector (light beacon), an “image type vehicle detector”, and a “travel time measurement sensor”. Can be adopted.

[Central equipment]
The central device 4 has a control unit including a workstation (WS), a personal computer (PC), and the like. This control unit collectively collects, processes (calculates) and records various types of traffic information from the roadside communication device 2 and the roadside sensor 6, performs signal control, and provides information.
Specifically, the control unit of the central device 4 performs system control for adjusting the traffic signal group 1 on the same road for the traffic signal 1 at the intersection Ji belonging to its own network, and this system control is applied to the road network. Extended wide area control (surface control) can be performed.

In addition, the central device 4 has a communication unit that is a communication interface connected to the LAN side via the communication line 7. This communication unit transmits a signal control command S1 relating to the color switching timing of the signal lamp and traffic information S2 including traffic jam information to the traffic signal 1 and the roadside communication device 2 every predetermined time (see FIG. 1). .
The signal control command S1 is transmitted every calculation period (for example, 1.0 to 2.5 minutes) of the signal control parameter when performing the system control and the wide area control, and the traffic information S2 is transmitted every 5 minutes, for example. Is done.

Further, the communication unit of the central device 4 receives vehicle information (application data) including the position and speed of the vehicle 5 received from the mobile communication device 3 by the roadside communication device 2 from the roadside communication device 2 corresponding to each intersection Ji. S3 is received, and the sensing information S4 is received from the roadside sensor 6 installed on each road.
The control unit of the central device 4 can execute the system control and the wide area control based on the vehicle information S3 and the sensing information S4 acquired by the communication unit from the roadside communication device 2 and the roadside sensor 6 in the jurisdiction area. .

[Wireless communication systems, etc.]
The intelligent transport system according to the present embodiment includes a plurality of roadside communication devices 2 capable of wireless communication with a mobile communication device 3 and a plurality of mobile communication devices 3 that perform wireless communication using the CSMA method. Includes the system.

The roadside communication device 2 is installed at each roadside intersection Ji, and is attached to, for example, a column of the traffic signal 1 as illustrated in FIG.
The mobile communication device 3 is mounted on a vehicle 5 traveling on a road. The mobile communication device 3 may be carried by a pedestrian.
The roadside communication device 2 can receive a radio signal from the mobile communication device 3 in its own reception area, and when the reception area reaches the antenna of another roadside communication device 2, the other The radio signal from the roadside communication device 2 can also be received.

In the intelligent transportation system of the present embodiment, wireless communication is used for communication between roadside communication devices 2 (roadside communication), and communication between roadside communication device 2 and mobile communication device 3 (between road and vehicle). Communication, including both road-to-vehicle communication from "road" to "car" and road-to-vehicle communication from "car" to "road") and mobile communication devices 3 (vehicle-to-vehicle communication) Communication is used.
As described above, the central device 4 provided in the traffic control center is capable of two-way communication with each roadside communication device 2 by wire, but wireless communication may be performed between these devices.

  A dedicated time slot for wireless transmission by itself is assigned to the roadside communication device 2 by the TDMA method. The roadside communication device 2 does not perform radio transmission in a time zone other than the assigned time slot. Therefore, the time zone other than the time slot dedicated to the roadside is opened as a transmission time by the CSMA method for the mobile communication device 3.

That is, in the wireless communication system, each communication performed by the roadside communication device 2 and the mobile communication device 3 shares a predetermined frequency band by the TDMA method.
FIG. 2 is a diagram illustrating an example of a communication frame of the wireless communication system. The roadside communication device 2 and the mobile communication device 3 communicate according to this communication frame.
The communication frame is set to a predetermined time length (for example, 100 milliseconds). As shown in the figure, the communication frame is configured by arranging time slots in the time axis direction.

As shown in FIG. 2, the time slot includes a first slot T1 and a second slot T2. These time slots T1 and T2 are alternately arranged in the time axis method in the communication frame.
The first slot T1 is a time slot for the roadside communication device 2, and wireless transmission by the roadside communication device 2 is permitted in this time zone. A slot number i is assigned to the first slot T1, and the slot number i is periodically incremented or decremented.

  Each roadside communication device 2 is assigned any one first slot T1 in the communication frame. Therefore, for the one roadside communication device 2, the first slot T1 assigned to the one roadside communication device 2 is set with a period of the time length of the communication frame.

  The roadside communication device 2 is allowed to wirelessly transmit in the first slot T1 allocated to the own device. Therefore, road-to-road communication and road-to-vehicle communication from the roadside communication device 2 to the mobile communication device 3 are performed in the first slot T1.

The second slot T2 is a time slot for the mobile communication device 3. Since this time zone is opened for wireless transmission by the mobile communication device 3, the roadside communication device 2 does not perform wireless transmission in the second slot T2.
The mobile communication device 3 is allowed to transmit in the second slot T2. Therefore, vehicle-to-vehicle communication and road-to-vehicle communication from the mobile communication device 3 to the roadside communication device 2 are performed in the second slot T2.

  As described above, in this system, each communication performed by the roadside communication device 2 and the mobile communication device 3 shares a predetermined frequency band by the TDMA method.

In the communication frame shown in FIG. 2, transmission times of a plurality of roadside communication devices 2 may be assigned to each first slot T1.
That is, in the example shown in FIG. 2, the transmission time of the roadside communication device 2 at the intersections J1 and J7 (see FIG. 1) is assigned to the first slot T1 of the slot number (1), and the slot number (2) The transmission times of the roadside communication devices 2 at the intersections J2 and J8 are allocated to the first slot T1, and the transmission times of the roadside communication devices 2 at the intersections J3 and J9 are assigned to the first slot T1 of the slot number (3). Is assigned. The transmission time of the roadside communication device 2 is also assigned to the other first slot T1 as described above.

Thus, the transmission time of each roadside communication device 2 is not assigned to the first slot T1 in a one-to-one correspondence, but for the roadside communication devices 2 installed at the intersection Ji where no radio wave interference occurs. The same slot number i can be assigned in duplicate.
Such slot allocation can be performed collectively by the central device 4, or each roadside communication device 2 can autonomously perform using the installation position and slot information acquired from other devices.
In addition, one parent device is selected in advance from a plurality of roadside communication devices 2, 2..., And this parent device has a transmission timing at which radio interference does not occur between the child devices that are the other roadside communication devices 2. As can be seen, slot allocation can also be performed.

[Roadside communication device]
FIG. 3 is a block diagram showing the internal configuration of the roadside communication device 2 and the mobile communication device 3.
The roadside communication device 2 includes a wireless communication unit (transmission / reception unit) 21 having an antenna 20 for wireless communication, a wired communication unit 22 that performs bidirectional communication with the central device 4, and a processor (CPU: Central) that performs communication control thereof. And a storage unit 24 including a storage device such as a ROM or a RAM connected to the control unit 23.

  The storage unit 24 is a computer program for communication control processing executed by the control unit (computer) 23, communication device IDs of the communication devices 2 and 3, time slot assignment information assigned to the own device, and will be described later. The encryption key is stored. The processing executed by the control unit 23 is performed by executing a computer program by the control unit 23.

The control unit 23 has a communication control function that comprehensively controls ITS application data transmitted and received by the wireless communication unit 21 and the wired communication unit 22.
For example, the control unit 23 temporarily stores the vehicle information (application data) S3 received by the wireless communication unit 21 from the mobile communication device 3 in the storage unit 24 and transfers the vehicle information (application data) S3 to the central device 4 through the wired communication unit 22. Further, the control unit 23 temporarily stores traffic information (application data) S2 and the like received by the wired communication unit 22 from the central device 4 in the storage unit 24, and transmits a communication packet including the traffic information S2 to the wireless communication unit. 21 is broadcast.

In addition, the control unit 23 controls the wireless communication unit 21 to perform wireless transmission in the first slot T1 (FIG. 2) that is the transmission time assigned to the own device.
Further, the control unit 23 broadcasts a communication packet including time slot allocation information (application data) S 5 stored in the storage unit 24 via the wireless communication unit 21. The allocation information S5 is information for notifying the mobile communication device 3 of the first slot T1 (FIG. 2) that is the transmission time of the roadside communication device 2.
The mobile communication device 3 of the vehicle 5 that has acquired the assignment information S5 from the roadside communication device 2 can grasp the first slot T1 assigned to the roadside communication device 2 that is the transmission source of the assignment information S5. Furthermore, the mobile communication device 3 performs radio transmission by the carrier sense method in the second slot T2 (FIG. 2), which is a time zone during which the roadside communication device 2 that has transmitted the allocation information S5 does not transmit.

  As will be described later, the control unit 23 has a function of selecting one operation mode from the three operation modes of the normal mode, the emergency mode, and the maintenance mode in the road-to-road communication. The control unit 32 selects an operation mode according to the maintenance-related information S6 received through wired communication or wireless communication and the emergency information S7.

The maintenance related information (application data) S6 is information transmitted when maintaining infrastructure devices such as the roadside communication device 2 and the traffic signal 1, and is information regarding maintenance of the infrastructure devices.
The emergency information (application data) S7 is information transmitted in response to the occurrence of an emergency such as a natural disaster or a traffic accident. Information for notifying the occurrence of an emergency or information on traffic management due to an emergency. Etc.
The maintenance related information S6 and the emergency information S7 are given from the central device 4 to one or a plurality of roadside communication devices 2 by wired communication, and transferred to other roadside communication devices 2 by roadside communication.

  The maintenance-related information S6 and the emergency information S7 are information that the driver of the vehicle 5 and pedestrians do not want to obtain, and are not transmitted by road-to-vehicle communication, but are transmitted only by road-to-road communication. .

The control unit 23 performs broadcast transmission in both road-to-vehicle communication and road-to-road communication. For this reason, the control unit 23, for example, in the time slot (first slot T1) allocated to the own device, the transmission time (slot for road-to-vehicle communication) for transmitting road-to-vehicle communication, the road The transmission time (slot for roadside communication) for transmitting roadside communication is set. Thereby, the roadside communication device 2 can perform broadcast transmission for road-to-vehicle communication and broadcast transmission for road-to-road communication.
In this case, the control unit 23 broadcasts traffic information S2 and vehicle information S3 in the road-to-vehicle communication slot, and broadcasts maintenance-related information S6 and emergency information S7 in the road-to-road communication slot.

  In addition, the control unit 23 sets time slots dedicated to inter-road communication at a rate of, for example, once every plural cycles among the time slots periodically assigned to the own device for each communication frame. You can also.

  Since the roadside communication device 2 needs to control the transmission timing so as to coincide with the time slot, it has a time synchronization function with other roadside communication devices 2. The time synchronization of the roadside communication device 2 is performed by, for example, GPS synchronization that adjusts its own clock to the GPS time, air synchronization that adjusts its own clock to a transmission signal from another roadside communication device 2, or the like.

[Mobile communication equipment]
The mobile communication device 3 is connected to a communication unit (transmission / reception unit) 31 having an antenna 30 for wireless communication, a control unit 32 including a processor that performs communication control on the communication unit 31, and the control unit 32. And a storage unit 33 including a storage device such as a ROM or a RAM.
The storage unit 33 stores a computer program for communication control processing executed by the control unit (computer) 32, communication device IDs of the communication devices 2 and 3, an encryption key described later, and the like. The processing executed by the control unit 23 is performed by executing a computer program by the control unit 32.

The control unit 32 of the mobile communication device 3 causes the communication unit 31 to perform wireless communication by the carrier sense method for vehicle-to-vehicle communication, and a communication control function in a time division multiplexing method with the roadside communication device 2. Does not have.
Therefore, the communication unit 31 of the mobile communication device 3 always senses the reception level of a predetermined carrier frequency, and when the value is above a certain threshold, wireless transmission is not performed, and when the value is below the threshold Only intended to perform wireless transmission.

The control unit 32 of the mobile communication device 3 sends a communication packet including vehicle information (application data) S3 including the current position, direction, speed, etc. of the vehicle 5 (mobile communication device 3) via the communication unit 31. Wireless transmission by broadcasting to the outside.
In addition, the control unit 32 of the mobile communication device 3 determines the position, speed, and direction included in the vehicle information S3 received directly from the other vehicle 5 and the vehicle information S3 of the other vehicle 5 received from the roadside communication device 2. Based on this, it is possible to perform safe driving support control for avoiding a right-handed collision or a head-on collision.

Further, when the communication unit 31 receives the time slot allocation information S5 broadcasted by the roadside communication device 2, the control unit 32 of the in-vehicle communication device 3 broadcasts the allocation information S5 via the communication unit 31. The allocation information S5 is transferred to the mobile communication device 3 of the mobile phone.
Thereby, the radio signal transmitted by the roadside communication device 2 in the downlink and the radio signal broadcast by the mobile communication device 3 outside the transmission area of the roadside communication device 2 are moved within the transmission area of the roadside communication device 2. It does not reach the communication device 3 at the same time.

[Configuration of communication packet]
FIG. 4 is a diagram illustrating an example of a configuration of communication packets transmitted by the roadside communication device 2 and the mobile communication device 3. As shown in the figure, this communication packet includes, in order from the top, a PHY header (physical header), a communication control header, an L7 header (layer 7 header), a security management header, encryption processing information, an application data body, and an FCS. (Frame Check Sequence) is included.

The PHY header includes information used for processing in the physical layer.
The communication control header includes information used for processing in the data link layer such as the MAC layer and the LLC layer, and the IVC-RVC layer.
The L7 header includes information used for processing in layer 7.
The security management header includes information related to security processing. The security processing includes authentication processing using an electronic signature and application data encryption processing, which will be described later.

  An EL (Extended Layer) header may be added between the L7 header and the security management header. The EL header includes information related to processing performed by the enhancement layer. Since the enhancement layer also performs processing related to security management, information related to security processing is also included in the EL header.

  In this embodiment, encryption processing is performed in order to maintain the confidentiality of communication information. Therefore, as shown in FIG. 4, an encryption process field including information necessary for the encryption process is added to the communication packet.

  In the encryption processing field, information indicating the protocol version related to the encryption processing, the key ID of the encryption key used for the encryption processing, and different encryption processing results even if the encryption processing is performed using the same encryption key. Variable information to be obtained and data length to be encrypted are included.

After the encryption processing field, an application data body converted into encrypted data within a predetermined data length range by the encryption processing by the communication devices 2 and 3 on the transmission side is included. The communication devices 2 and 3 that have received this communication packet can decrypt the encrypted application data body using the information in the encryption processing field and an encryption key to be described later. The encrypted application data body cannot be decrypted without the encryption key.
Therefore, since the encrypted application data body cannot be acquired by a third party who does not have the encryption key, the confidentiality of the communication information is maintained.

  The contents of the application data include the above traffic information S2, vehicle information S3, allocation information S5, maintenance related information S6, and emergency information S7.

[About communication security]
In the wireless communication system described above, the user of the system can be obtained by attacking such as illegally acquiring application data or impersonating the roadside communication device 2 or the mobile communication device 3 to transmit fake information or falsified information. Service may be affected.

  For this reason, in order to ensure communication security, in the wireless communication system of the present embodiment, confirmation of the authenticity of the sender in the communication between the communication devices 2 and 3, confirmation of the integrity of the received message (application data), In addition, processing for maintaining confidentiality of communication information (application data) is performed.

For the confirmation of the authenticity of the sender and the integrity of the received message, a public key authentication method applying a digital signature with a public key algorithm or a common key authentication method applying a message authentication code with a common key algorithm Either method is adopted.
The control units 23 and 32 of the respective communication devices 2 and 3 have a function of performing an authentication process based on the above-described method. By performing communication while performing these processes, the authenticity of the sender and the message Ensure integrity.

  In the present embodiment, for maintaining the confidentiality of the communication information, the encryption process is performed on the application data included in the communication packet as described above. By encrypting application data, even if a third party other than the communication devices 2 and 3 belonging to the system intercepts communication information transmitted and received in the system, the contents are acquired. Is preventing.

[About encryption processing]
In this embodiment, an encryption method using a common key algorithm is employed.
This encryption method based on the common key algorithm includes a common encryption key between the two parties, ie, the transmission source and the transmission destination. The transmission source encrypts communication information such as application data to be encrypted using an encryption key, and transmits the encrypted data. Since the transmission destination that received the encrypted data has the same encryption key as that used for encryption, the encrypted data can be decrypted and the communication information can be obtained by using this encryption key. be able to.

  The encryption method using the common key algorithm can be processed as long as the transmission source and the transmission destination have the common encryption key as described above. For example, encryption is performed using a public key algorithm using an electronic signature. Compared with, the overhead during communication is small and the processing load is small. For this reason, it is a system suitable for the mobile communication device 3 that is mounted on the vehicle 5 or carried by a pedestrian and whose cost and device size are limited.

However, in the common key algorithm, in general, the transmission source and the transmission destination have the same common key, and in the relationship between the transmission source and another transmission destination different from the transmission destination, Another common key different from the common key is provided.
For this reason, when an encryption method based on a common key algorithm is applied to the above system, the transmission source communication apparatus needs to have a common key (encryption key) for each communication apparatus that can be a transmission destination. However, in the system of this embodiment that broadcasts application data, it is practically impossible to provide an encryption key for every communication device.

Therefore, in the system of the present embodiment, the communication devices 2 and 3 that communicate with each other perform encryption using a common key algorithm by providing the same encryption key.
The control units 23 and 32 of the communication devices 2 and 3 have a function of performing an encryption process based on the above method. The storage units 24 and 33 store encryption keys used for encryption processing.

  Here, in the wireless communication system of the present embodiment, the encryption key used for the road-to-road communication and the communication performed between the communication devices 2 and 3 and other than the road-to-road communication (road-to-vehicle communication and It is configured to use an encryption key that is different from an encryption key used for communication between roads).

FIG. 5 is a conceptual diagram showing encryption keys stored in the storage unit 24 of the roadside communication device 2.
The storage unit 24 stores a plurality of encryption keys used for communication with other communication devices 2 and 3 other than the own device. The plurality of encryption keys stored in the storage unit 24 have different key information.

The plurality of encryption keys includes a plurality of key groups configured by dividing the plurality of encryption keys into a plurality of groups. More specifically, the plurality of encryption keys stored in the storage unit 24 includes a roadside machine key group used for road-to-road communication and a mobile machine key group used for road-to-vehicle communication and vehicle-to-vehicle communication. Contains.
The key group for mobile devices includes a plurality of encryption keys S1, S2, S3.
The control unit 23 selects an encryption key used for road-to-vehicle communication and vehicle-to-vehicle communication from among the encryption keys S1, S2, S3... Included in the mobile device key group.

  The roadside machine key group includes a plurality of key groups by dividing a plurality of keys included in the roadside machine key group into a plurality of groups. The roadside machine key group includes a normal key group, an emergency key group, and a maintenance key group as a plurality of key groups. These normal key group, emergency key group, and maintenance key group are encryption keys P1, P2, P3..., Encryption keys Q1, Q2, Q3... And encryption keys R1, R2, R3. Contains

As will be described later, the control unit 23 has a function of selecting one operation mode from among three operation modes (normal mode, emergency mode, and maintenance mode) in road-to-road communication. In each operation mode, as a key group used in each operation mode, any one of a normal key group, an emergency key group, and a maintenance key group is set in association with each other.
The control unit 23 selects an encryption key used for road-to-road communication from among encryption keys included in a key group associated with the operation mode to be selected.

In this way, the control unit 23 selects an encryption key used for road-to-road communication from encryption keys included in the roadside machine key group, and includes an encryption key used for road-to-vehicle communication and vehicle-to-vehicle communication in the mobile machine key group. Select the encryption key that will be used.
Thus, the control unit 23 selects the encryption key used for road-to-road communication and the encryption key used for road-to-vehicle communication and vehicle-to-vehicle communication to be different from each other.

The storage unit 24 stores roadside device key schedule information and mobile device key schedule information.
The roadside device key schedule information and the mobile device key schedule information include a schedule regarding which encryption key to select when the control unit 23 selects an encryption key from each key group. .

The roadside machine key schedule information includes contents indicating a use schedule set in advance as to which encryption key is to be used according to the period and installation location.
Each roadside communication device 2 includes the same roadside machine key schedule information. Accordingly, for example, even when any encryption key is selected from a plurality of encryption keys P1, P2, P3,. If the encryption key is selected based on the above, the same encryption key can be selected at both the transmission source and the transmission destination.

  As a result, the roadside communication device 2 has changed the encryption key to be used, for example, by selecting one of the plurality of encryption keys P1, P2, P3... Included in the normal key group. However, encryption processing can be performed using the same encryption key with other roadside communication devices 2, and communication between roads can be performed.

Further, the mobile device key schedule information includes contents indicating a use schedule set in advance as to which encryption key is used according to the period.
The mobile device key schedule information is also stored in the storage unit 33 of the mobile communication device 3 as described later.

FIG. 6 is a conceptual diagram showing encryption keys stored in the storage unit 33 of the mobile communication device 3.
The storage unit 33 stores a plurality of encryption keys used for communication with other communication devices 2 and 3 other than the own device. The storage unit 33 stores the same encryption keys S1, S2, S3,... As those included in the mobile device key group stored in the storage unit 24 of the roadside communication device 2.

The storage unit 33 of the mobile communication device 3 also stores mobile device key schedule information having the same contents as the mobile device key schedule information stored in the storage unit 24 of the roadside communication device 2.
Therefore, even when the mobile communication device 3 selects one of the encryption keys S1, S2, S3,... And performs road-to-vehicle communication, the encryption key is determined based on the mobile device key schedule information. If selected, the same encryption key can be selected at both the transmission source and the transmission destination. Thereby, it is possible to perform road-to-vehicle communication while performing encryption processing with the roadside communication device 2 using the same encryption key.

  Each mobile communication device 3 includes the same encryption keys S1, S2, S3... And mobile device key schedule information. Therefore, the mobile communication device 3 can select the same encryption key at both the transmission source and the transmission destination even when performing inter-vehicle communication with other mobile communication devices 3. Thereby, vehicle-to-vehicle communication can be performed while performing encryption processing.

  Since the mobile communication device 3 does not include the roadside device key group, even if the communication information of the roadside communication is received, it cannot be decrypted and the communication information cannot be acquired.

Thus, in this embodiment, since the encryption key different from the encryption key used in road-to-vehicle communication and vehicle-to-vehicle communication is used for road-to-road communication, the mobile communication device 3 uses the communication information of road-to-road communication. It cannot be decrypted. Therefore, it is possible to prevent the mobile communication device 3 from acquiring communication information for road-to-road communication.
Furthermore, for example, even if an encryption key included in a mobile device key group used in road-to-vehicle communication and vehicle-to-vehicle communication leaks, confidentiality in road-to-road communication can be maintained, affecting the entire system. Can be suppressed.

[About encryption key usage schedule]
In the wireless communication system of the present embodiment, as described above, a usage schedule is set in advance as to which encryption key is used according to the period and installation location. The set schedule is reflected in the roadside device key schedule information and the mobile device key schedule information stored in the storage units 24 and 33 of the respective communication devices 2 and 3.

FIG. 7 is a diagram illustrating an example in which road traffic is divided into areas. The diagonal line in the figure represents a road, and the circle at the intersection represents the roadside communication device 2.
The installation location of each roadside communication device 2 is specified for each of the areas A1 to A9 in FIG. Further, the current position of the mobile communication device 3 is also specified for each of the areas A1 to A9 in FIG.

  FIG. 8 is a diagram illustrating an example of the encryption key usage schedule. FIG. 8 shows a use schedule for the normal key group in the inter-road communication. In FIG. 8, “P1” and “P2” of the encryption keys P1, P2,.

As shown in the figure, the encryption key used for road-to-road communication and the encryption key used for road-to-vehicle and vehicle-to-vehicle communication are set according to the period and area (installation location or current position), respectively. .
For example, during the period h1 to h2, in the area A1, the encryption key P1 is selected as the encryption key for road-to-road communication, and the encryption key S1 is selected as the encryption key for road-to-vehicle and vehicle-to-vehicle communication. . Therefore, in FIG. 7, the roadside communication device 2a installed in the area A performs encryption processing using the encryption key P1 during the period h1 to h2, and performs roadside communication.
In addition, during the period h1 to h2, the mobile communication device 3 located in the area A1 performs encryption processing using the encryption key S1, and performs road-to-road and road-to-road communication.

Also, during the period h1 to h2, in area A2, the encryption key P2 is selected as the encryption key for road-to-road communication, and the encryption key S2 is selected as the encryption key for road-to-vehicle and vehicle-to-vehicle communication. . Therefore, in FIG. 7, the roadside communication devices 2b, 2c, and 2d installed in the area A2 perform encryption processing using the encryption key P2 during the periods h1 to h2, and perform roadside communication.
In addition, during the period h1 to h2, the mobile communication device 3 located in the area A2 performs encryption processing using the encryption key S2, and performs road-to-road and road-to-road communication.

In the period h2 to h3, in the area A1, the encryption key P2 is selected as the encryption key for road-to-road communication, and the encryption key S2 is selected as the encryption key for road-to-vehicle and vehicle-to-vehicle communication.
In the period h2 to h3, in the area A2, the encryption key P3 is selected as the encryption key for road-to-road communication, and the encryption key S3 is selected as the encryption key for road-to-vehicle and vehicle-to-vehicle communication.

  The intervals between the periods h1 to h2 and h2 to h3 are set in units of several tens of minutes or several hours, for example.

  As described above, in the wireless communication system according to the present embodiment, each of the communication devices 2 and 3 selects from a plurality of encryption keys according to a period (time) and an installation location (current position) based on a predetermined schedule. Therefore, a different encryption key is used for each area on road traffic, and a different encryption key is used for each period to which the current time belongs even in the same area.

  In this case, even if an encryption key used in road-to-road communication leaks, by specifying the leaked encryption key, the period and area in which the encryption key was used can be specified, and the encryption key leaked The period and area can be specified. As a result, it is possible to obtain information necessary for further enhancing security, such as grasping the cause of the leakage of the encryption key and countermeasures against the leakage.

  In addition, in the roadside communication device 2 (mobile communication device 3) of the present embodiment, a plurality of encryption keys used for road-to-road communication (road-car, vehicle-to-vehicle communication) depending on the period and installation location (current position) Although it was configured to select from among the encryption keys, for example, it may be configured to select only according to the period, or may be configured to select only according to the installation location (current position). .

[About operation modes and key groups]
The roadside communication device 2 according to the present embodiment selects one operation mode from the three operation modes of the normal mode, the emergency mode, and the maintenance mode based on the situation around the own device.
The emergency mode is an operation mode that is selected when an emergency situation is determined due to the occurrence of a natural disaster or a traffic accident.
The maintenance mode is an operation mode selected when maintenance of infrastructure equipment such as the roadside communication device 2 and the traffic signal 1 is performed.
The normal mode is a mode that is selected in a case other than the specific situation as described above, and is a mode that is normally used.

  The control unit 23 of the roadside communication device 2 determines the situation around the own device according to whether or not the maintenance related information S6 and the emergency information S7 are received. If the maintenance-related information S6 is received, the control unit 23 determines that infrastructure maintenance is being performed around the device itself. In this case, the control unit 23 selects the maintenance mode as the operation mode.

If the emergency information S7 is received, the control unit 23 determines that an emergency has occurred around the aircraft. In this case, the control unit 23 selects the emergency mode as the operation mode.
If it is not determined that an emergency has occurred and it is determined that infrastructure maintenance has not been performed, the control unit 23 selects the normal mode.

When the normal mode is selected, the control unit 23 selects an encryption key used for road-to-road communication from among the encryption keys P1, P2, P3,... Included in the normal key group.
Further, when the emergency mode is selected, the control unit 23 selects an encryption key to be used for road-to-road communication from among the encryption keys Q1, Q2, Q3... Included in the emergency key group. Similarly, when the maintenance mode is selected, the control unit 23 selects an encryption key to be used for the inter-road communication from among the encryption keys R1, R2, R3... Included in the maintenance key group.
As described above, the control unit 23 selects and changes the encryption key used for the inter-road communication from the key group associated with the selected mode according to the period and the area.

  Here, since maintenance of infrastructure and emergency situations do not occur frequently, in most cases, the control unit 23 selects the normal mode. For this reason, the encryption key included in the emergency key group and the maintenance key group is used less frequently than the encryption key of the normal key group.

As described above, the plurality of encryption keys stored in the storage unit 24 are emergency keys that are used less frequently than the normal key group, in addition to the normal key group that is normally used. Key group for maintenance and maintenance key group.
In this case, the emergency key group and the maintenance key group, which are used less frequently, have relatively higher confidentiality of communication information than the normal key group that is normally used. Therefore, a plurality of stages can be provided for the confidentiality of communication information, and the confidentiality level of communication information can be selected by selecting an operation mode.

Therefore, the control unit 23 of the roadside communication device 2 normally uses an encryption key group that is normally used, and when the surroundings of the own device is in an emergency situation or when maintenance work is being performed in this system. A key group with low usage frequency can be selected and used for road-to-road communication.
As a result, it is used with higher confidentiality than the normal key group in emergency situations where confidentiality of communication information is required and maintenance work where information on the system that is not recognized by the mobile communication device is handled. A key group with a low frequency can be selected and used for road-to-road communication.

[Effect]
According to the roadside communication device 2 and the wireless communication system configured as described above, an encryption key different from the encryption key used in road-to-vehicle communication and vehicle-to-vehicle communication is used for road-to-road communication. Cannot decode the communication information of the road-to-road communication. Therefore, it is possible to prevent the mobile communication device 3 from acquiring communication information for road-to-road communication.
In addition, for example, even if an encryption key used in road-to-vehicle communication and vehicle-to-vehicle communication leaks, confidentiality in road-to-road communication can be maintained, and the influence on the entire system can be suppressed. it can.

  Further, the roadside communication device 2 of the present embodiment selects an encryption key used for roadside communication according to the period and installation location from a plurality of encryption keys (roadside device key group). Even if the encryption key used in communication is leaked, it is difficult to maintain the confidentiality of the road-to-road communication using the leaked encryption key, but in the period and area where the encryption key other than the leaked encryption key is used, Confidentiality in road-to-road communication can be maintained. Therefore, it is only necessary to change the encryption key for the period and area where the leaked encryption key should have been used, and it is possible to further suppress the influence on the entire system.

[Other Embodiments]
The present invention is not limited to the above embodiment. In the above embodiment, the case where the period for selecting the same encryption key is set in units of several tens of minutes or several hours in the encryption key usage schedule is exemplified. However, for example, it can be set in a shorter period. .

For example, an encryption key used for road-to-road communication can be selected and changed according to a time slot to which the roadside communication device 2 is assigned.
FIG. 9 is a diagram illustrating an example in which a time slot assigned to each roadside communication device 2 and a key ID used for roadside communication are assigned to each time slot.
As shown in FIG. 9, for example, the roadside communication device 2 at the intersection J2 (j7) (FIG. 1) is assigned the first slot T1 of the slot number (1). Also, in the figure, the encryption key P1 is selected as the encryption key used by the roadside communication device 2 at the intersection J2 for the communication between the roads in the first slot T1 of the slot number (1) included in the radio frame located on the left side. As scheduled.

In addition, in the first slot T1 of the slot number (1) included in the next radio frame, the roadside communication device 2 at the intersection J2 is scheduled to select the encryption key P2 as the encryption key used for roadside communication. Yes.
As described above, the encryption key can be selected and changed for each radio frame unit.

In the above-described embodiment, the mobile communication device 3 includes only the encryption keys S1, S2, S3,... Included in the mobile device key group as the encryption key used for road-to-vehicle communication. It is shown that the communication information of the road-to-road communication is prevented from being acquired and the confidentiality of the communication information of the road-to-road communication to the mobile communication device 3 is increased.
However, for example, the mobile communication device 3 mounted on an emergency vehicle such as an ambulance, a fire engine, or a police car (a public vehicle used for a highly public purpose) is related to the emergency when an emergency occurs. The emergency information S7 that is information may be required.

In this case, the emergency information S7, which is information used by the public vehicle, is not acquired by the mobile communication device 3 mounted on a general vehicle other than the public vehicle or the mobile communication device 3 carried by a pedestrian. The mobile communication device 3 mounted on the public vehicle needs to be acquired.
That is, it is necessary to conceal communication information performed between the communication devices 2 and 3 other than the mobile communication device 3 mounted on a general vehicle or the like from the mobile communication device 3 mounted on the general vehicle or the like.

  For this reason, as shown in FIG. 10, the mobile communication device 3 mounted on a public vehicle such as an emergency vehicle has an emergency key provided in the roadside communication device 2 in addition to the encryption key included in the mobile device key group. The same encryption keys Q1, Q2, Q3... As the encryption keys included in the key group may be provided.

In this case, the mobile communication device 3 mounted on the public vehicle normally performs road-to-vehicle communication by using an encryption key included in the emergency key group for transmission and reception related to the emergency information S7 that is performed only in road-to-road communication. It can be carried out.
The mobile communication device 3 mounted on the public vehicle is a roadside device key that includes encryption keys Q1, Q2, Q3,... Included in the emergency key group and a schedule necessary for using them. Schedule information is also provided.

  Thereby, the mobile communication device 3 of the public vehicle can transmit information for notifying the occurrence of an emergency or the situation thereof to the roadside communication device 2 as emergency information S7. Moreover, emergency information S7 transmitted by road-to-road communication in the emergency mode can be acquired and used for activities of the public vehicle using various information included in the emergency information S7. it can.

In the above case, the information used by the public vehicle such as the emergency information S7 is an encryption key of the roadside communication device 2 and the mobile communication device 3 mounted on the public vehicle, and is used by the public vehicle. It is transmitted using an encryption key different from the encryption key used for information other than information.
That is, the information used by the public vehicle such as the emergency information S7 is an encryption key of the roadside communication device 2 and the mobile communication device 3 mounted on the public vehicle, and is mounted on a general vehicle other than the public vehicle. Since the mobile communication device 3 is transmitted using an encryption key different from the encryption key possessed by the mobile communication device 3, the mobile device mounted on a general vehicle or the like that does not have the encryption key used for information used by the public vehicle The communication device 3 cannot decrypt information used by public vehicles.

Therefore, it is possible to prevent information used by the public vehicle from being acquired by the mobile communication device 3 mounted on a vehicle other than the public vehicle or the mobile communication device 3 carried by a pedestrian.
As a result, information used by public vehicles can be kept secret from the mobile communication device 3 mounted on a general vehicle or the like.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the meanings described above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

2 Roadside communication device 3 Mobile communication device 4 Central device 5 Vehicle 23 Control unit 24 Storage unit

Claims (8)

A roadside communication device used in a wireless communication system in which a plurality of mobile communication devices and a plurality of roadside communication devices share a predetermined communication frequency band by time division,
Communication information transmitted in communication performed between the communication devices is encrypted with an encryption key for encrypting the communication information,
As an encryption key used for road-to-road communication performed with other roadside communication devices, an encryption key that is communication performed between the communication devices and different from an encryption key used for communication other than the road-to-roadway communication a communication control unit using,
A storage unit storing a plurality of different encryption keys,
The said communication control part is a roadside communication apparatus which selects the encryption key used for the said roadside communication from among these several encryption keys so that the encryption key used for the said roadside communication differs for every period and installation area . The plurality of mobile communication devices and the plurality of roadside communication devices time-divide the predetermined frequency band by assigning at least one of a plurality of time slots arranged in a communication frame used by each communication device. Shared by
The roadside communication device according to claim 1, wherein the communication control unit changes an encryption key used for the roadside communication according to a time slot assigned to the own device. Before SL plurality of encryption keys includes a plurality of encryption key group that is configured by dividing the plurality of encryption keys into a plurality of groups,
The communication control unit selects one mode from a plurality of modes associated with any of the plurality of encryption key groups, and selects the path from the encryption key group associated with the selected mode. The roadside communication device according to claim 1 or 2 , wherein an encryption key used for roadside communication is selected.   The plurality of cipher key groups are cipher key groups that are normally used and cipher key groups that are used less frequently than the cipher key groups that are normally used by being used in a specific situation other than when they are normally used. The roadside communication device according to claim 3, including: A roadside communication device used in a wireless communication system in which a plurality of mobile communication devices and a plurality of roadside communication devices share a predetermined communication frequency band by time division,
Communication information transmitted in communication performed between the communication devices is encrypted with an encryption key for encrypting the communication information,
As an encryption key used for road-to-road communication performed with other roadside communication devices, an encryption key that is communication performed between the communication devices and different from an encryption key used for communication other than the road-to-roadway communication a communication control unit using,
A storage unit storing a plurality of different encryption keys,
The plurality of encryption keys include a plurality of encryption key groups configured by dividing the plurality of encryption keys into a plurality of groups,
The communication control unit selects one mode from a plurality of modes associated with any of the plurality of encryption key groups, and selects the path from the encryption key group associated with the selected mode. Select the encryption key to be used for the road-to-road communication,
The plurality of cipher key groups are cipher key groups that are normally used and cipher key groups that are used less frequently than the cipher key groups that are normally used by being used in a specific situation other than when they are normally used. Including
It said communication control unit, around the emergency ship, or the radio when the maintenance of the communication system is being carried out, you select a mode in which the use frequency corresponds to a low encryption key group roadside communication device .   The roadside communication device according to any one of claims 1 to 5, wherein the communication information is encrypted by an encryption method using a common key algorithm. A wireless communication system in which a plurality of mobile communication devices and a plurality of roadside communication devices share a predetermined communication frequency band by time division,
Communication information transmitted in communication performed between the communication devices is encrypted with an encryption key for encrypting the communication information,
As an encryption key used for the road-to-road communication performed between the plurality of roadside communication devices, the encryption key is a communication performed between the communication devices and different from an encryption key used for communication other than the road-to-roadway communication. using,
Further, the encryption key used for the road-to-road communication is selected from a plurality of encryption keys so that the encryption key used for the road-to-road communication differs for each period and installation area. Wireless communication system. The communication information transmitted by the roadside communication device used in the wireless communication system in which a plurality of mobile communication devices and a plurality of roadside communication devices share a predetermined communication frequency band by time division A transmission method in which communication information is encrypted and transmitted with an encryption key for encrypting communication information,
As an encryption key used for road-to-road communication performed with other roadside communication devices, an encryption key that is communication performed between the communication devices and different from an encryption key used for communication other than the road-to-roadway communication using,
Further, the encryption key used for the road-to-road communication is selected from a plurality of encryption keys so that the encryption key used for the road-to-road communication differs for each period and installation area. Transmission method.

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