JP2017020228A - Electronic key and electronic key system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electronic key and an electronic key system, capable of ensuring security against illegal deciphering of a cipher key.SOLUTION: An electronic key 2 has a motion detecting section 25 that detects a motion (vibration) generated on the electronic key 2. A calculation permission section 26 makes cipher calculation for challenge response authentication impossible when the section has confirmed that there is no motion on the electronic key 2 on the basis of a detection signal Sac of the motion detecting section 25. Thus authentication using a proper cipher key K2 is not implemented in the electronic key 2 due to no motion generated on the electronic key 2 even if the electronic key is subject to, for example, a side channel attack aiming at illegal deciphering of the cipher key K2 by fixing the electronic key 2 to a jig so that the electronic key does not move. Therefore, security against illegal deciphering of the cipher key K2 can be ensured.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electronic key and an electronic key system that can collate electronic key IDs wirelessly.

  2. Description of the Related Art Conventionally, many vehicles are equipped with an electronic key system that performs ID verification (smart verification) by wirelessly transmitting an electronic key ID from an electronic key to the vehicle in response to communication from the vehicle (see Patent Document 1, etc.). ). In this type of electronic key system, in addition to checking whether the electronic key ID is correct or not, it is also checked whether challenge response authentication is established between the vehicle and the electronic key. And if both electronic key ID collation and challenge response authentication are materialized, locking / unlocking of a vehicle door will be permitted or performed, or engine starting operation will be permitted.

JP 2005-262915 A

There is a need to improve security in order to prevent an encryption key used in challenge-response authentication from being illegally decrypted by a third party.
An object of the present invention is to provide an electronic key and an electronic key system that can ensure security against illegal decryption of an encryption key.

  The electronic key that solves the above problem is a movement that occurs in the electronic key in a configuration that performs ID verification by performing authentication using an encryption key when verifying the electronic key ID with the communication master. And a calculation permission unit that permits the authentication calculation only when a motion is detected in the motion detection unit.

  According to this configuration, authentication using a normal encryption key is permitted only when the electronic key is moved. For example, the electronic key is fixed to a jig or the like so that the electronic key is not moved. Even if a side channel attack is received, authentication using a regular encryption key is not performed with the electronic key. Thereby, there is no possibility that the encryption key is illegally decrypted under the side channel attack. Therefore, it is possible to ensure security against illegal decryption of the encryption key.

  In the electronic key, the authentication is a challenge response authentication in which a challenge code, which is a random number, is encrypted with the encryption key and a response code is obtained by both the communication master and the electronic key, and both response codes are confirmed. It is preferable that According to this configuration, it is possible to ensure security against illegal decryption in the encryption key related to challenge response authentication.

  In the electronic key, the ciphertext is calculated by passing the encryption key and the plaintext through the function, and further the process of passing the ciphertext through the function together with another encryption key as a plaintext is obtained by calculating a plurality of times, The authentication program for confirming whether the calculation result is correct or not, and a false encryption key generation unit that generates a false encryption key and executes the authentication with the false encryption key when the operation is not permitted. Is preferred. According to this configuration, since a fake encryption key is used in a situation where computation is not permitted, even if the encryption key is illegally read out due to a side channel attack, it is a wrong encryption key. There is no. Therefore, in this respect, it can be said that the security against illegal decryption of the encryption key is high.

  In the electronic key, when the pseudo encryption key generation unit confirms that no movement occurs in the electronic key during the authentication calculation, the pseudo encryption key generation unit generates the pseudo encryption key and performs the calculation using the pseudo encryption key. It is preferable to continue. According to this configuration, even when the stop of the movement of the electronic key is detected during the calculation of the encryption, it is possible to prevent unauthorized reading of the regular encryption key by continuing the calculation with the fake encryption key.

  An electronic key system that solves the above-described problems is a configuration in which the electronic master key and the electronic key perform ID verification by performing authentication using an encryption key when the electronic key ID is verified wirelessly. Includes a motion detection unit that detects a motion generated in the electronic key, and a calculation permission unit that permits the authentication calculation only when a motion is detected in the motion detection unit.

  According to the present invention, security against illegal decryption of an encryption key can be ensured.

The block diagram of the electronic key and electronic key system of 1st Embodiment. Explanatory drawing which shows the outline | summary of the communication logic of an electronic key system. 6 is a flowchart executed when setting whether or not to perform a cryptographic operation. The example of the electric current and electromagnetic wave measurement system in a side channel attack. The block diagram of the electronic key of 2nd Embodiment. Logic diagram of challenge response authentication.

(First embodiment)
Hereinafter, a first embodiment of an electronic key and an electronic key system will be described with reference to FIGS.
As shown in FIG. 1, the vehicle 1 includes an electronic key system 3 that performs electronic ID verification with the electronic key 2. The electronic key system 3 is a key operation-free system that executes ID collation by narrowband wireless (communication distance is several meters) triggered by communication from the vehicle 1. Hereinafter, ID collation by the key operation free system is referred to as “smart collation”, and the communication is referred to as “smart communication”.

  The vehicle 1 includes a collation ECU (Electronic Control Unit) 4 that performs ID collation (smart collation), a body ECU 5 that manages the power source of the in-vehicle electrical components, and an engine ECU 6 that controls the engine 7. These ECUs are connected through a communication line 8 in the vehicle. The communication line 8 includes, for example, a CAN (Controller Area Network) and a LIN (Local Interconnect Network). In the memory 9 of the verification ECU 4, a set of the electronic key ID and the encryption key K1 of the electronic key 2 registered in the vehicle 1 is written and stored. The encryption key K1 is used at the time of authentication performed between the vehicle 1 and the electronic key 2. The body ECU 5 controls the operation of the door lock mechanism 10 that switches between locking and unlocking the vehicle door.

  In the memory 9 of the communication master 11 (in this example, the verification ECU 4), an authentication program P1 that is executed between the vehicle 1 and the electronic key 2 during ID verification (smart verification) is written and stored. The authentication in this example is challenge response authentication in which a challenge code, which is a random number, is encrypted with the encryption key K1 and a response code is obtained by both the verification ECU 4 and the electronic key 2 and both response codes are confirmed. .

  The vehicle 1 includes an outdoor transmitter 12 that transmits radio waves outdoors, an indoor transmitter 13 that transmits radio waves indoors, and a radio receiver 14 that receives radio waves in the vehicle 1. The outdoor transmitter 12 and the indoor transmitter 13 transmit, for example, radio waves in the LF (Low Frequency) band. The radio wave receiver 14 receives, for example, UHF (Ultra High Frequency) band radio waves. Thus, the electronic key system 3 of this example is a LF-UHF two-way communication in the UHF band in which the radio wave from the vehicle 1 is in the LF band and the radio wave from the electronic key 2 reaches farther than the LF radio wave. ing.

  The vehicle 1 includes an engine switch 15 that is operated when the vehicle power source is switched. The engine switch 15 is composed of, for example, a push momentary switch. By operating the engine switch 15, the vehicle power supply can transition to any of IG off, ACC on, IG on, and engine start.

  The electronic key 2 includes a key control unit 18 that controls the operation of the electronic key 2, a reception unit 19 that receives radio waves in the electronic key 2, and a transmission unit 20 that transmits radio waves in the electronic key 2. In the memory 21 of the key control unit 18, a set of an electronic key ID and an encryption key K2 that each electronic key 2 has is written and stored. The memory 21 of the key control unit 18 stores a program P2 for authentication (challenge response authentication) similar to that on the vehicle 1 side. The receiving unit 19 receives, for example, LF radio waves. The transmission unit 20 transmits, for example, UHF radio waves.

  The electronic key 2 (electronic key system 3) has a motion determination function for determining whether to communicate with the communication partner 24 (in this example, the vehicle 1) based on the movement (motion) generated in the electronic key 2. Prepare. The motion determination function of this example is executed in the process of performing ID verification by transmitting the electronic key ID from the electronic key 2 to the communication master 11 triggered by communication from the communication master 11 (in this example, the verification ECU 4). The verification ECU 4 processes the ID verification as a condition on condition that the motion determination is also established (the electronic key 2 has a motion) in addition to various verifications (including authentication) in the ID verification.

  The electronic key 2 includes a motion detection unit 25 that detects movement generated in the electronic key 2. The motion detection unit 25 outputs a detection signal Sac corresponding to the movement generated in the electronic key 2 to the key control unit 18. The motion detection unit 25 monitors movements generated in the electronic key 2 by detecting movements in three axial directions, for example, the X axis, the Y axis, and the Z axis. The triaxial detection type motion detection unit 25 is preferably an acceleration sensor or an angular velocity sensor, for example.

  The electronic key 2 includes a calculation permission unit 26 that determines whether or not authentication can be performed based on the detection signal Sac of the motion detection unit 25. The calculation permission unit 26 is provided in the key control unit 18. For example, based on the detection signal Sac input from the motion detection unit 25, the calculation permission unit 26 authenticates the ID verification (in this example, smart verification) only when a movement (for example, vibration) is detected in the electronic key 2. The example permits computation of challenge response authentication.

Next, using FIG. 2 to FIG. 4, the operation of the communication partner correctness determination function provided in the electronic key 2 (electronic key system 3) will be described.
As shown in FIG. 2, it is assumed that a regular user who has the electronic key 2 approaches the vehicle 1. The vehicle 1 (verification ECU 4) activates the electronic key 2 in order to confirm whether or not the electronic key 2 has entered the LF radio wave communication area Ea formed by the outdoor transmitter 12 (indoor transmitter 13). A wake signal Swk is periodically transmitted from the outdoor transmitter 12 (indoor transmitter 13). Note that transmission of the wake signal Swk may be started in response to a certain user operation. For the user operation, for example, a lock button or a touch sensor provided on the door handle outside the vehicle may be operated. The lock button is operated when the vehicle door is locked, and the touch sensor detects that the outside door handle is touched when the vehicle door is unlocked.

  When receiving the wake signal Swk transmitted from the vehicle 1, the electronic key 2 is activated upon reception of the wake signal Swk. When activated, the electronic key 2 transmits an ACK signal Sack to the vehicle 1 by UHF.

  When the verification ECU 4 can receive the ACK signal Sack from the electronic key 2 within a predetermined time after transmitting the wake signal Swk, the verification ECU 4 sends the challenge signal Sch to the outdoor transmitter 12 (indoor). LF is transmitted from the transmitter 13). The challenge signal Sch preferably includes a challenge code (random number) whose value changes every time it is transmitted.

  When receiving the challenge signal Sch, the electronic key 2 calculates a response code using the encryption key K2 and the program P2 registered in its own memory 21. Specifically, the response code is calculated by passing the challenge code received from the vehicle 1 as a plaintext and passing it through a function (algorithm) together with the encryption key K2. The electronic key 2 sends a response signal Sre to the vehicle 1 by UHF when the response code is calculated. The response signal Sre preferably includes, for example, a response code that is a calculation result of challenge response authentication and an electronic key ID registered in the electronic key 2.

  When the verification ECU 4 transmits the challenge code to the electronic key 2, it itself calculates the response code using its own encryption key K1 and program P1. When the verification ECU 4 receives the response signal Sre from the electronic key 2, the verification ECU 4 performs challenge response authentication by comparing the response code included therein with the response code calculated by itself. Further, the verification ECU 4 performs electronic key ID verification by confirming whether the electronic key ID included in the response signal Sre is correct.

  FIG. 3 illustrates determination logic for determining whether or not challenge response authentication can be performed in the electronic key 2. Note that the flowchart shown in FIG. 3 starts when the electronic key 2 receives the challenge signal Sch.

  In step 101, the calculation permission unit 26 determines whether or not the electronic key 2 has a movement based on the detection signal Sac input from the motion detection unit 25. At this time, when the operation permission unit 26 confirms that the electronic key 2 is moving, the calculation permission unit 26 permits the execution of challenge response authentication. Accordingly, if there is a movement in the electronic key 2, the process proceeds to step 102 and challenge response authentication is continued. On the other hand, when the operation permission unit 26 confirms that the electronic key 2 does not move, it does not permit the challenge response authentication to be performed. Therefore, when the electronic key 2 does not move, the process is forcibly terminated.

In step 102, the key control unit 18 calculates a response code for the challenge code received from the vehicle 1.
In step 103, the key control unit 18 transmits a response signal Sre including the response code calculated in step 102 to the vehicle 1. Thereby, the correctness of challenge response authentication is confirmed in the vehicle 1.

  In the case of the example of FIG. 2, the authorized user has the electronic key 2 and approaches the vehicle 1 while moving, so challenge response authentication is executed. Further, since the electronic key 2 is possessed by the authorized user, both challenge response authentication and electronic key ID verification are established. When the verification ECU 4 confirms that these verifications (authentication) are established, the verification ECU 4 processes the smart verification as establishment. When the collation ECU 4 confirms that the smart collation triggered by the electronic key 2 receiving the wake signal Swk transmitted from the outdoor transmitter 12 is established, the collation ECU 4 establishes the outdoor smart collation, and the body ECU 5 Permit or execute the locking / unlocking operation. When the verification ECU 4 confirms that the smart verification is triggered when the electronic key 2 receives the wake signal Swk transmitted from the indoor transmitter 13, the verification ECU 4 establishes the indoor smart verification and sets the engine in the driver's seat. The transition of the vehicle power source by the operation of the switch 15 is permitted.

  FIG. 4 shows a specific example of a current / electromagnetic wave measurement system in a side channel attack. By the way, as a side channel attack targeting current consumption, for example, a technique is known in which a large number of current consumption is acquired by executing cryptographic processing many times, and these are statistically analyzed. In this case, the decoding success rate increases or decreases according to the number of acquisitions. As a countermeasure, for example, a detection circuit that detects that the current consumption is measured is provided in the electronic key 2, and a countermeasure that does not execute encryption processing at the time of measurement detection is known. However, this measure is ineffective for side channel attacks targeting electromagnetic waves. For this reason, it is assumed that a countermeasure is taken by providing a detection circuit for electromagnetic wave measurement, but there is a current situation that it is difficult to apply to devices operating in various electromagnetic environments.

  The statistical side channel attack as shown in FIG. 4 is a technique for analyzing minute fluctuations in the magnitude of current and electromagnetic waves. In the case of this attack technique, the measurement value changes by a slight movement of the measurement probe (a kind of antenna) 31, so it is necessary to fix the positional relationship between the electronic key 2 and the measurement probe 31 during measurement. That is, the side channel attack should be performed in a state where the electronic key 2 is fixed to the fixing jig 32.

  With this in mind, there should be no movement in the electronic key 2 when receiving a statistical side channel attack. That is, in the determination of the movement of the electronic key 2, no movement has occurred in the electronic key 2, and the challenge response authentication is not permitted to be performed. Thereby, smart communication is forcibly terminated on the way. That is, when receiving a side channel attack, the electronic key 2 does not perform an authentication operation (encrypted communication), so that an illegal decryption of the encryption key K2 for challenge response authentication is not performed. Therefore, security against illegal decryption of the encryption key K2 is ensured.

According to the configuration of the present embodiment, the following effects can be obtained.
(1) The motion detection unit 25 is provided in the electronic key 2 to monitor the movement (vibration) generated in the electronic key 2, and only when the electronic key 2 moves, authentication using the regular encryption key K2 is performed. Allow implementation. For this reason, for example, even if the electronic key 2 is fixed to the fixing jig 32 so that the electronic key 2 is not moved and subjected to a side channel attack in which an illegal decryption of the encryption key K2 is attempted, the electronic key 2 does not move. In the electronic key 2, authentication using the regular encryption key K2 is not executed. Thereby, there is no possibility that the legitimate encryption key K2 is illegally decrypted under the side channel attack. Therefore, security against unauthorized decryption of the encryption key K2 can be ensured.

  (2) Authentication performed between the vehicle 1 and the electronic key 2 is challenge response authentication. Therefore, it is possible to secure security against illegal decryption in the encryption key K2 related to challenge response authentication.

(3) In taking measures against the side channel attack, it is possible to cope with a simple process in which challenge-response authentication is not performed.
(Second Embodiment)
Next, a second embodiment will be described with reference to FIGS. Note that this example is an example in which when a movement (vibration) is detected in the electronic key 2 during the encryption process, the encryption process is continued using a fake encryption key. Therefore, the same parts as those in the first embodiment are denoted by the same reference numerals, detailed description thereof is omitted, and only different parts are described in detail.

  As shown in FIG. 5, the electronic key 2 (electronic key system 3) includes a false encryption key generation unit 35 that generates a false encryption key Kd when the operation is not permitted by the determination of the operation permission unit 26. The pseudo encryption key generation unit 35 is provided in the key control unit 18. The pseudo encryption key generation unit 35 of this example generates a pseudo encryption key Kd when the operation permission unit 26 does not permit the operation of challenge response authentication, and continues the authentication with the pseudo encryption key Kd, thereby enabling the ID. Ensure security against unsuccessful verification.

  As shown in FIG. 6, the challenge-response authentication calculation of this example is performed by calculating a plaintext challenge code with a regular encryption key K2 to obtain a ciphertext, and again using this ciphertext as a plaintext and another regular A series of processes calculated with the encryption key K2 is repeated a plurality of times. Specifically, for example, a challenge code and an encryption key K2-0 are passed through a function F0 to obtain a ciphertext, and this ciphertext and another encryption key K2-1 are passed through a function F1 to obtain a ciphertext. A series of processing is repeated a plurality of times (in the case of the figure, 10 times). Then, the ciphertext finally obtained as the calculation result is returned to the vehicle 1 as a response code.

  In the case of this example, for example, when it is detected that there is no movement (vibration) in the electronic key 2 at the time of the third cryptographic computation, a false cryptographic key Kd is generated, and the cryptographic processing is continued thereby. Specifically, when the electronic key 2 stops operating during the third cryptographic computation, the pseudo cryptographic key generation unit 35 creates the pseudo cryptographic key “Kd-2” corresponding to the regular cryptographic key K2-2 during the third computational operation. ”Is generated, and the encryption process is continued with the pseudo encryption key Kd-2. This process is repeated until the encryption process is completed. Thereby, since the calculated response code does not take a normal value, challenge response authentication does not have to be established illegally.

According to the configuration of the present embodiment, in addition to (1) to (3) described in the first embodiment, the following effects can be obtained.
(4) When the electronic key 2 does not move and cryptographic operations are not permitted, authentication using the fake encryption key Kd is performed. For this reason, even if the encryption key K2 is read illegally by a side channel attack, there is no problem because it is the wrong encryption key K2. Therefore, in this respect, it can be said that the security against illegal decryption of the encryption key K2 is high.

  (5) When it is confirmed that no movement occurs in the electronic key 2 during the cryptographic calculation, the pseudo cryptographic key generation unit 35 generates the pseudo cryptographic key Kd, and the calculation is continued using the pseudo cryptographic key Kd. The Therefore, even when the stop of the movement of the electronic key 2 is detected in the middle of the cryptographic calculation, unauthorized reading of the regular cryptographic key K2 can be prevented by continuing the calculation with the false cryptographic key Kd.

Note that the embodiment is not limited to the configuration described so far, and may be modified as follows.
In each embodiment, the determination that the electronic key 2 has moved includes, for example, a state before a predetermined time. In other words, the electronic key 2 has a grace period for allowing a cryptographic operation for a predetermined time after the movement, and even if the electronic key 2 does not move during the grace time, the cryptographic operation is permitted. Also good.

  In the second embodiment, when the electronic key 2 does not move and the cryptographic calculation is disabled, it is possible to take measures against unauthorized reading of the cryptographic key K2 by performing a calculation using the fake cryptographic key Kd from the beginning. .

In the second embodiment, the pseudo encryption key Kd is not limited to a value that changes for each repeated operation, but may be a value that is fixed in each repeated operation.
In each embodiment, the communication format and frequency used in the electronic key system 3 can be changed to other modes other than the embodiment.

-In each embodiment, the electronic key system 3 is not limited to a key operation free system, What is necessary is just the system of ID collation through the two-way communication between the vehicle 1 and the electronic key 2. FIG.
In each embodiment, authentication is not limited to challenge-response authentication, and may be encryption processing using the encryption key K2.

In each embodiment, the electronic key 2 may be various terminals such as a high-function mobile phone.
-In each embodiment, the electronic key 2 is not limited to vehicles, For example, it can change into other uses, such as a key for house doors.

  In each embodiment, the communication master 11 and the communication partner 24 can be changed to various devices and devices.

DESCRIPTION OF SYMBOLS 1 ... Vehicle which is an example of a communication partner, 2 ... Electronic key, 3 ... Electronic key system, 4 ... Verification ECU which is an example of a communication master, 25 ... Motion detection part, 26 ... Operation permission part, 35 ... False encryption key generation Part, K1, K2 ... encryption key, Kd ... fake encryption key, Sac ... detection signal of motion detection part, P1, P2 ... authentication program.

Claims (5)

In verifying the electronic key ID with the communication master, by performing authentication using an encryption key,
A motion detection unit for detecting movement generated in the electronic key;
An electronic key comprising: a calculation permission unit that permits the authentication calculation only when a motion is detected by the motion detection unit. 2. The authentication is challenge response authentication in which a challenge code, which is a random number, is encrypted with the encryption key to obtain a response code by performing both of the communication master and the electronic key and confirming the response code of both. Electronic key as described in The ciphertext is calculated by passing the encryption key and plaintext through the function, and the process of passing the ciphertext through the function together with another encryption key as plaintext is obtained a plurality of times to obtain the operation result. The authentication program to confirm
The electronic key according to claim 1, further comprising: a false encryption key generation unit that generates a false encryption key and executes the authentication using the false encryption key when the operation is not permitted. The false encryption key generation unit generates the false encryption key and continues the operation with the false encryption key when confirming that the electronic key no longer moves during the authentication operation. Electronic key as described in When the communication master and the electronic key collate the electronic key ID wirelessly, the electronic key system that performs the ID collation by performing authentication using the encryption key,
The electronic key is
A motion detection unit for detecting movement generated in the electronic key;
An electronic key system comprising: a calculation permission unit that permits the authentication calculation only when a motion is detected by the motion detection unit.