JP2018074426A - Communication correctness determination system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a communication correctness determination system capable of making relay attacks difficult.SOLUTION: If reception data is maintained at an L level for a while after the reception data falls to the L level derived from a transmission wave from a vehicle, a reception threshold value changes to downturn involved in fall to the L level, and then when it is maintained at the L level for a long period, the reception threshold eventually reaches a minimum value, and when the reception data rises to an H level, the reception threshold value changes to upward. Under such a premise, by slowing the rise of a transmission radio wave by switching of a Q value, it becomes possible to change demodulation data length as a base point using any position of a slowly rising part to the H level about the reception data. Then, if the demodulation data length is within a prescribed range, radio communication between a vehicle and a mobile device is determined to be normal communication, and on the other hand if the demodulation data length is out of the prescribed range, the radio communication is determined to be unauthorized communication.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a communication correctness determination system that determines the validity of wireless communication performed between a device and a portable device.

  In the so-called smart key system (registered trademark), bidirectional wireless communication called smart communication is performed between a vehicle, which is an example of a device, and a portable device, and the mobile device held as a vehicle key by the smart communication. Authentication (key authentication) is performed. As an example, when a smart communication area is formed around the vehicle by transmitting an LF band radio wave from a vehicle-mounted antenna, and a user with a portable device enters the smart communication area, a key ID unique to the portable device is entered. A UHF band radio wave including a message is returned from the portable device. The vehicle-mounted ECU collates the key ID included in the received UHF radio wave with a pre-registered key ID, and permits the unlocking of the door when key authentication is established when the key ID collates and matches. Allow or execute

  In Patent Document 1, an LF radio wave (RSSI measurement wave) with different electric field strength is output from an in-vehicle antenna, and if there is a certain difference in the RSSI value measured by the portable device, it is determined that there is a regular portable device, and AND There is disclosed a technique for permitting or executing a vehicle operation when key authentication is established by matching a key ID under conditions. Note that if there is no constant difference in the RSSI value measured by the portable device, there is a possibility of fraud using the repeater (relay attack), so even if the key IDs match, vehicle operation is not performed.

JP 2011-229061 A

  If a relay attack repeater can copy up to the electric field strength of the LF radio wave, there is a concern that even if a countermeasure using an LF radio wave having a different electric field strength is implemented, the relay attack can be performed.

  The present invention has been made paying attention to such problems, and an object of the present invention is to provide a communication correctness determination system capable of making a relay attack difficult.

  A communication correctness determination system that solves the above problem is a communication correctness determination system that determines the validity of wireless communication performed between a device and a portable device. The device is a radio wave transmission medium used for the wireless communication. A transmission antenna, an antenna drive circuit that transmits the radio wave from the transmission antenna while driving the transmission antenna, and an envelope of the radio wave transmitted from the transmission antenna by controlling a Q value of the antenna drive circuit The gist of the present invention is to provide transmission radio wave control means.

  According to this configuration, on the portable device side, received data is obtained through envelope detection, and the received data is compared with a reception threshold set in accordance with the reception level of the received data, so that demodulated data is obtained. Is obtained. If the reception data is maintained at the L level for a while after the reception data falls to the L level due to the transmission radio wave from the device, the reception threshold starts to fall with the fall to the L level. After that, when the period maintained at the L level is long, the reception threshold eventually becomes the minimum value, and when the reception data rises to the H level, the reception threshold starts to increase.

  Based on these assumptions, the transmission radio wave is dulled by switching the Q value, so that the demodulated data length varies based on the arbitrary position of the portion of the received data that gently rises to the H level or the portion that gently falls to the L level. It becomes possible to make it. As a result, when the prescribed demodulated data length is obtained, it is determined that the communication is normal, while when the other demodulated data length is used, it can be determined that the communication is illegal communication by the relay attack. Therefore, the relay attack can be made difficult.

  Regarding the communication correctness determination system, the portable device includes a reception antenna that is a reception medium of a radio wave used for the wireless communication, and a reception circuit that generates reception data through envelope detection of the radio wave received by the reception antenna. A reception threshold value is set according to a reception level of the reception data generated by the reception circuit, and a demodulation circuit that generates demodulation data by comparing the reception data with the reception threshold value may be provided. .

According to this configuration, it is possible to differentiate from the demodulated data length derived from the radio wave copied by the relay attack repeater that cannot switch the Q value.
For the communication correctness determination system, the device or the portable device analyzes the demodulated data obtained by the portable device derived from the radio wave transmitted from the device, and the demodulated data length is within a specified range. The wireless communication may be determined as regular communication, and a communication correctness determination unit may be provided that determines that the wireless communication is unauthorized communication when the demodulated data length is out of a specified range.

  According to this configuration, even if the relay attack relay is capable of copying up to the electric field strength of the communication radio wave, it is possible to determine that the relay attack is being performed because the prescribed demodulated data length cannot be obtained.

  According to the present invention, the relay attack can be made difficult.

The block diagram which shows the structure of a communication correctness determination system. The conceptual diagram which shows a mode that the demodulated data is obtained in the portable device side derived from the transmission radio wave from the vehicle side.

Hereinafter, an embodiment of a communication correctness determination system will be described.
As shown in FIG. 1, a communication correctness determination system 1 is applied to a so-called smart key system (registered trademark), and wireless communication performed between a vehicle 2 and a portable device 3 that are components of the smart key system. Determine validity. The vehicle 2 is an example of a device.

  The vehicle 2 is a transmission medium that transmits a radio wave as an in-vehicle device of a transmission system that forms a smart communication area around the vehicle 2 by transmitting an LF band radio wave that triggers wireless communication with the portable device 3. In addition to the antenna 21, an antenna drive circuit 22 that drives the transmission antenna 21 and a transmission radio wave control circuit 23 that switches the Q value of the antenna drive circuit 22 are provided. Under the control of the transmission radio wave control circuit 23, the envelope of the LF band radio wave transmitted from the transmission antenna 21 is controlled by switching the Q value of the antenna drive circuit 22 (a value representing the sharpness of the resonance peak). On the other hand, it is possible to blunt the rising of the transmission radio wave (see FIG. 2). The transmission radio wave control circuit 23 corresponds to transmission radio wave control means.

  The portable device 3 includes a receiving circuit 32 that generates received data through envelope detection of a radio wave received by the receiving antenna 31 in addition to a receiving antenna 31 that is an LF band radio wave receiving medium, and a receiving circuit 32 thereof. A demodulating circuit 33 for generating demodulated data by comparing the generated received data with a receiving threshold value; A reception threshold is set according to the reception level of the reception data. That is, when the reception data is maintained at the L level for a while after the reception data falls to the L level due to the transmission radio wave from the vehicle 2, the reception threshold decreases with the fall to the L level. Then, when the period that is maintained at the L level after that is long, the reception threshold value eventually becomes the minimum value, and when the reception data rises to the H level, the reception threshold value starts to increase (see FIG. 2).

  Under such a premise, by slowing the rising of the transmission radio wave by switching the Q value, it is possible to change the demodulated data length based on an arbitrary position of the portion where the reception data gently rises to the H level. In the example of FIG. 2, it is understood that there is a difference between the upper demodulated data length Ta and the lower demodulated data length Tb.

  The demodulation data length (bit width) is defined as a specified range as a determination threshold for determining the validity of wireless communication, and the demodulation data length obtained by the demodulation circuit 33 of the portable device 3 is within the specified range. In this case, the wireless communication between the vehicle 2 and the portable device 3 is determined to be regular communication. On the other hand, if the demodulated data length is outside the specified range, the wireless communication is determined to be unauthorized communication. The vehicle 2 has a Q value and a transmission timing at which a demodulated data length within a specified range is obtained on the portable device 3 side in consideration of a reception threshold set in accordance with reception data derived from transmission radio waves. A transmission radio wave is transmitted.

  Note that the analysis of the demodulated data including the determination of whether or not the demodulated data length is within the specified range may be performed by either the vehicle 2 or the portable device 3. For example, when demodulated data is analyzed on the vehicle 2 side, demodulated data is demodulated by an in-vehicle ECU (communication correctness judging means) by transmitting demodulated data length information from the portable device 3 to the vehicle 2 using UHF band radio waves or the like. It can be determined whether or not the data length is within the specified range. On the other hand, when analyzing the demodulated data on the portable device 3 side, after determining whether or not the demodulated data length is within a specified range by a microcomputer (communication correctness determining means) built in the portable device 3, Information indicating the determination result is transmitted from the portable device 3 to the vehicle 2 by radio waves in the UHF band or the like.

  In any case, the in-vehicle ECU permits the unlocking of the door when the demodulated data length is within the specified range and the key ID is verified by matching the key ID under the AND condition. When the door handle is touched, the door is actually unlocked. The smart communication technology including key ID verification is becoming known in recent years, and a detailed description thereof will be omitted.

As described above, according to the present embodiment, the following operational effects can be achieved.
(1) By demodulating the transmission radio wave by switching the Q value, the demodulated data length can be changed. As a result, when the prescribed demodulated data length is obtained, it is determined that the communication is normal, while when the other demodulated data length is used, it can be determined that the communication is illegal communication by the relay attack. Therefore, the relay attack can be made difficult.

(2) It is possible to differentiate from the demodulated data length derived from the radio wave copied by the relay attack repeater that cannot switch the Q value.
(3) Even if a relay attack repeater can copy up to the electric field strength of a communication radio wave, it can be determined that a relay attack is being performed because a predetermined demodulated data length cannot be obtained.

In addition, the said embodiment can also be changed and actualized as follows.
The frequency band used for the transmission radio wave that is at least partially blunted by switching the Q value is not limited to the LF band. For example, the UHF band may be used.

  In place of or in addition to blunting the rising of the transmission radio wave according to the above embodiment, the demodulation that fluctuates due to the transmission radio wave while slowing the fall of the transmission radio wave by switching the Q value The validity of wireless communication may be determined through analysis of data length.

  While comparing the demodulated data length with a specific threshold value based on an absolute value, for example, when the demodulated data length exceeds the specific threshold value, it may be determined that the communication is unauthorized. In this case, if the demodulated data length is longer than necessary through copying at the repeater, it can be determined that the communication is unauthorized.

A relative value with respect to the previous demodulated data length may be used as the current threshold value.
The present invention is applied not only to the unlocking of doors but also to smart key systems for buildings that permit or execute the operation of doors or lights or electrical appliances of buildings as well as smart key systems for vehicles that permit or execute engine starting. You may apply.

Next, a technical idea that can be grasped from the above embodiment and another example will be described.
(A) A device that is applied to a communication correctness determination system that determines the validity of wireless communication performed between a device and a portable device,
A transmission antenna that is a radio wave transmission medium used for the wireless communication, an antenna drive circuit that transmits the radio wave from the transmission antenna while driving the transmission antenna, and switching the Q value of the antenna drive circuit to switch the transmission antenna Transmitting radio wave control means for controlling an envelope of the radio wave transmitted from the device.

(B) A portable device that is applied to a communication correctness determination system that determines the validity of wireless communication performed between a device and a portable device,
On the premise of controlling the envelope of the radio wave used for the wireless communication by switching the Q value of the antenna drive circuit of the device,
A reception antenna that is a radio wave reception medium used for the wireless communication; a reception circuit that generates reception data through envelope detection of the radio wave received by the reception antenna; and the reception data generated by the reception circuit A portable device comprising: a demodulation circuit that sets a reception threshold according to a reception level and generates demodulated data by comparing the reception data with the reception threshold.

  DESCRIPTION OF SYMBOLS 1 ... Communication correctness determination system, 2 ... Vehicle (equipment), 3 ... Portable machine, 21 ... Transmission antenna, 22 ... Antenna drive circuit, 23 ... Transmission radio wave control circuit (transmission radio wave control means), 31 ... Reception antenna, 32 ... Receiving circuit 33... Demodulating circuit.

Claims (3)

In a communication correctness determination system for determining the validity of wireless communication performed between a device and a portable device
The device switches a transmission antenna that is a radio wave transmission medium used for the wireless communication, an antenna drive circuit that transmits the radio wave from the transmission antenna while driving the transmission antenna, and a Q value of the antenna drive circuit. And a transmission radio wave control means for controlling an envelope of the radio wave transmitted from the transmission antenna. The portable device is generated by a reception antenna that is a radio wave reception medium used for the wireless communication, a reception circuit that generates reception data through envelope detection of the radio wave received by the reception antenna, and the reception circuit The communication correctness determination system according to claim 1, further comprising: a demodulation circuit that sets a reception threshold according to a reception level of the reception data and generates demodulated data by comparing the reception data with the reception threshold. When the demodulated data length is within a specified range while analyzing the demodulated data obtained by the mobile device derived from the radio wave transmitted from the device, the device or the portable device transmits the wireless communication as normal communication. The communication correctness determination system according to claim 1, further comprising: a communication correctness determination unit that determines that the wireless communication is unauthorized communication when the demodulated data length is outside a specified range.

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