JP2012049993A - Encryption key update system, smart key system, and encryption key update method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a common key update valid for a long time while preventing discrepancy of the common key.SOLUTION: The common key update used between a vehicle and a smart key is achieved by two methods one of which is led by the vehicle and the other by a key distribution center. In the vehicle-led method, after reliability is established with the smart key, the vehicle generates and sends a new common key to the smart key by concealing the new common key with the previous common key. In the center-led method, the center generates and sends a new common key to the vehicle and to the smart key. The smart key communicates with the center with the vehicle as a gateway. For example, the center sends to the vehicle the generated common key which is concealed by a public key of the vehicle and the generated common key which is concealed by a public key of the smart key, the vehicle decodes the message addressed to itself by a secret key while sending the message addressed to the smart key to the smart key.

Description

  The present invention relates to a technique for updating a common key used for encrypted communication.

  Cryptographic technology is an important technology for preventing eavesdropping, tampering, and impersonation. For example, encryption technology is used in a smart key system for locking / unlocking a door lock of a vehicle by wireless communication. Considering the response speed of locking / unlocking, it is conceivable to use a common key encryption method between the vehicle and the smart key. In order to make the decryption of the encryption key difficult and enhance the security, it is preferable to periodically update the encryption key.

  In Patent Document 1, it is difficult to analyze a secret message by concealing a message using a common key and an auxiliary key and updating the auxiliary key every time. However, since the new auxiliary key is transmitted in plain text, effective protection cannot be performed if the common key itself is decrypted.

  In Patent Literature 2, a prime number and a random number generation tool necessary for generating a common key are provided on each of the transmission side and the reception side, and secure communication is realized by generating a common key for each communication. In this case, since the smart key is required for the smart key in addition to the cryptographic engine, the cost increases.

JP 2008-135893 A JP 2009-141767 A

  As described above, it is desired to update the common key safely and with a simple configuration in the common key cryptosystem. In the above description, the smart key system has been described as an example.

  An object of the present invention is to securely update a common key with a simple configuration.

  In order to achieve the above object, according to the present invention, when encrypted communication is performed using a common encryption key (common key) between the first device and the second device, a new information is generated in the first device. The common key is updated by generating a common key and transmitting it to the second device, and the third device generates a common key used between the first device and the second device to generate the first key Two types of update methods of updating the common key by transmitting to the device and the second device are used together.

More specifically, the first aspect of the present invention is an encryption key that is composed of first, second, and third devices and updates a common encryption key used between the first and second devices. Update system. When the cryptographic communication is performed between the first device and the second device, the first device generates a new common cryptographic key, and the second device is configured by the conventional cryptographic communication using the common cryptographic key. And the next encrypted communication between the first device and the second device is performed using the new common encryption key. In addition, the third device newly generates a common key used for encryption communication between the first device and the second device, and transmits the common key to the first device. When the first device receives a new common key from the third device, the first device transmits the common key received from the third device to the second device, and the next first device and second device. Is performed using the common key received from the third device.

  By doing so, the common key between the first device and the second device is periodically updated, and the security against decryption is improved. In addition, the first device not only generates a new common key and distributes it to the second device, but also the third device generates a common key and distributes it to the first and second devices. Even if one common key between the first device and the second device is found, the common keys found in a chain can be limited. Therefore, the security of cryptographic communication between the first device and the second device is further improved. In addition, since the common key is distributed from the third device to the second device via the first device, it is possible to avoid wrinkles in the common key between the first device and the second device. .

  In the present invention, the third device encrypts the generated common encryption key so that only the first device can decrypt it, and the generated common encryption key encrypts the second device so that only the second device can decrypt it. The encrypted second encrypted message is preferably transmitted to the first device. The first device stores a common encryption key obtained by decrypting the first encryption message as a common encryption key used for communication with the next second device, and stores the second encryption message in the first device. It is preferable to transmit to two devices. The second device stores a common encryption key obtained by decrypting the second encrypted message received from the first device as a common encryption key used for communication with the next first device. Is preferred.

  The above encryption key update system can be applied to, for example, a smart key system. That is, in the smart key system, the vehicle can function as the first device, the smart key as the second device, and the key distribution center as the third device.

More specifically, a smart key system according to another aspect of the present invention includes a vehicle, a smart key, and a key distribution center, and encryption communication is performed between the vehicle and the smart key by a common key encryption method. .
The vehicle includes a storage unit that stores a common encryption key for encryption communication with the smart key and an encryption key for encryption communication with the key distribution center, and communication between the smart key and the key distribution center. An encryption key for newly generating a common encryption key used for encryption communication between a communication unit for performing communication, an encryption processing unit for performing encryption processing using the encryption key stored in the storage unit, and a smart key When performing cryptographic communication between the generation unit and the smart key, the common encryption key generated by the encryption key generation unit is transmitted to the smart key, and the generated common encryption key is used in the storage unit. An encryption key management unit that updates a common encryption key for encryption communication with the smart key.
The smart key includes a storage unit that stores a common encryption key for encryption communication with the vehicle and an encryption key for encryption communication with the key distribution center, a communication unit for performing communication with the vehicle, A vehicle in the storage unit using a new common encryption key transmitted from the vehicle when encryption communication is performed between the encryption processing unit that performs encryption processing using the encryption key stored in the storage unit and the vehicle. An encryption key management unit that updates a common encryption key for encryption communication with the communication device.
The key distribution center includes a storage unit that stores an encryption key for encryption communication with the vehicle and an encryption key for encryption communication with the vehicle, and a common encryption key for encryption communication between the smart key and the vehicle. The encryption key generation unit to generate, the first encryption message obtained by encrypting the generated common encryption key with the encryption key between the smart key, and the generated common encryption key encrypted with the encryption key between the vehicle A transmission unit that transmits the second encrypted message to the vehicle.
When the vehicle receives the message from the key distribution center, the vehicle transmits a second encryption message to the smart key and uses the common encryption key obtained by decrypting the first encryption message to store the smart key in the storage unit. Update the common encryption key for encrypted communication with
The smart key updates a common encryption key for encryption communication with the vehicle in the storage unit with a common encryption key obtained by decrypting the second encryption message transmitted from the vehicle.

  Here, it is preferable that cryptographic communication between the key distribution center and the smart key and between the key distribution center and the vehicle is performed by a public key cryptosystem.

  The key distribution center preferably transmits the first encrypted message and the second encrypted message to the vehicle when the vehicle and the smart key can communicate with each other.

  The present invention can be understood as an encryption key update system including at least a part of the above means. This encryption key update system can be applied to any specific system including a smart key system. The present invention can also be understood as an encryption key update method for performing these processes, and a program for realizing these methods. Each of the above means and processes can be combined with each other as much as possible to constitute the present invention.

  According to the present invention, the common key can be updated with a safe and simple configuration in the common key cryptosystem.

It is a figure which shows the function structure of the smart key system which concerns on this embodiment. In this embodiment, it is a flowchart which shows the flow of the process which updates a common key between a vehicle and a smart key. In this embodiment, it is a flowchart which shows the flow of a process which updates the common key utilized between a vehicle and a smart key using a key distribution center. It is a figure explaining the advantage of the key update method in this embodiment. The figure explaining the outline | summary of the 1st reference example. The figure explaining the outline | summary of the 2nd reference example. It is a figure explaining the problem of the 2nd reference example.

  Prior to describing the smart key system according to the present embodiment, the system studied by the present inventors and its problems will be described.

(Reference Example 1)
FIG. 5 is a diagram for explaining the outline of the first reference example. It is necessary to conceal communication such as a door lock unlocking request exchanged between the vehicle 101 and the smart key 102. In order to satisfy the requirement to increase the response speed, it is preferable to use a common key cryptosystem. Therefore, the vehicle 101 and the smart key 102 have the common key A. In consideration of security, it is desirable to update to a new common key as appropriate. In the first reference example, the key distribution center 103 generates a new common key B and transmits the common key B to the vehicle 101 and the smart key 102 by wireless communication. Subsequent communication between the vehicle 101 and the smart key 102 is concealed using the latest common key B. Communication between the key distribution center 103 and the vehicle 101 or the smart key 102 is also performed in a concealed manner. Here, it is important to increase security, and response speed is not required so much, so it is preferable to use a public key cryptosystem.

In this method, since communication between the key distribution center 103 and the vehicle 101 or the smart key 102 is wireless communication, only one of the vehicle 101 and the smart key 102 receives a new common key and the other cannot receive the other. Can be considered. For example, when the vehicle 101 is stored in an underground parking lot and the user carries the smart key 102, the smart key 102 can receive a new common key from the key distribution center 103, but the vehicle 101 cannot receive a new common key. When the common key held by the vehicle 101 and the smart key 102 is flawed, there arises a problem that encryption communication cannot be performed between the two.

(Reference Example 2)
FIG. 6 is a diagram for explaining the outline of the second reference example. Here, the vehicle 201 generates a new common key and transmits it to the smart key 202. For example, if the common key is generated and transmitted while the vehicle is running or after the door lock unlock request processing, the vehicle 201 and the smart key 202 are close to each other and communication is easily established. Therefore, it is possible to avoid a habit of the common key stored between the two.

  When the vehicle 201 generates a new common key B, the common key B is concealed by the common key A that has been used until then, and is transmitted from the vehicle 201 to the smart key 202. The vehicle 201 stores the common key B generated by itself, and the smart key 202 stores the common key B obtained by decrypting the confidential message received from the vehicle with the encryption key A. The next communication between the vehicle 201 and the smart key 202 is performed by concealing using the latest common key B. Thereafter, as shown in FIG. 7, the newly generated common key is repeatedly concealed using the common key so far, and the common key is updated.

  In the common key cryptosystem, the common key is determined by analysis such as a brute force attack. Regardless of the key length of the common key, in principle, the common key can be found over time. The common key is frequently updated in consideration of such decryption of the common key, but if the attacker sniffs and stores all secret messages between the smart key and the vehicle, one common key If it becomes clear, all the common keys after that will be found. In FIG. 7, it is assumed that the message concealed by the common key A is analyzed and the common key A is found. Then, when the secret message for key distribution is decrypted with the common key A, the common key B is obtained. By decrypting the next key distribution confidential message using the common key B, the common key C is obtained. By repeating this, the latest common key can be obtained. That is, this method has a problem in terms of long-term operation of the common key.

(This embodiment)
In the present embodiment, a common key update method that prevents the common key held between the smart key and the vehicle from shifting and that can withstand long-term safe and safe operation is realized. Although this embodiment relates to a smart key system, the common key update method described below can be applied to any other system, and its application is not limited to the smart key system.
[System Overview]
The smart key system according to the present embodiment controls the unlocking of the door lock by wireless communication between the vehicle 1 and the smart key 2. The vehicle 1 and the smart key 2 perform secret communication using a common key encryption method. In this system, with the support from the key distribution center (hereinafter referred to as the center) 3, the above-described problems in the common key update are solved. The vehicle 1, the smart key 2, and the center 3 correspond to the first, second, and third devices in the present invention, respectively.

  In the present embodiment, after a trust relationship is established between the vehicle 1 and the smart key 2, a new common key generated by the vehicle 1 is transmitted to the smart key 2 by secret communication. When the next secret communication is required, a new common key is used to prevent unauthorized use due to message and common key leakage.

Here, the generation of a new common key is performed not only in the vehicle 2 but also by the center 3. The center 3 periodically generates a new common key and transmits it to the vehicle 1 and the smart key 2. By using the common key transmitted from the center 3 in this way, it is possible to avoid finding all the common keys in a chain when one common key is found.

  The smart key 2 receives a new common key from the center 3 using the vehicle 1 as a gateway. That is, when the center 3 generates a new common key, only the vehicle 1 and the smart key 2 are concealed so that they can be decrypted, and a secret message is transmitted to the vehicle 1. The vehicle 1 passes the received confidential message to the smart key 2 so that both the vehicle 1 and the smart key 2 obtain a new common key. By doing so, the common key of the vehicle 1 and the smart key 2 can be prevented from shifting.

[Constitution]
<Vehicle>
FIG. 1 is a diagram showing a functional configuration of the smart key system according to the present embodiment. As shown in the figure, the smart key system includes a vehicle 1, a smart key 2, and a key distribution center 3. The vehicle 1 and the smart key 2, and the vehicle 1 and the center 3 can perform wireless communication. The smart key 2 can communicate with the center 3 using the vehicle 1 as a gateway.

The vehicle 1 includes a short-range communication unit 11, an external communication unit 12, an encryption processing unit 13, an encryption key management unit 14, a protocol determination unit 15, a door unlocking control unit 16, and a common key generation unit 17 as functional units. These functional units may be configured by dedicated hardware. Further, it may be realized by a computer (ECU: Electronic Control Unit) including an MPU (Micro Processor Unit) or the like loading and executing a program stored in a memory. Note that at least the encryption processing unit 13, the encryption key management unit 14, the protocol determination unit 15, the door unlocking control unit 16, and the common key generation unit 17 in the vehicle 1 are independent of other domains and ensure reliability. Executed in the domain. The trust domain is configured by a tamper resistant device. A tamper-resistant device is a device that is resistant to unauthorized acquisition and alteration of internal information. Such a configuration can be realized using ARM's TrustZone (registered trademark) technology.

  The near field communication unit 11 performs near field communication with the smart key 2. The external communication unit 12 performs wireless communication with the center 3. The encryption processing unit 13 performs data encryption and decryption processing. A common key encryption method such as AES, Triple DES, or DES is used between the vehicle 1 and the smart key 2, and a public key encryption method such as RSA encryption, elliptic curve encryption, or DSA is used between the vehicle 1 and the center 3. Use. The cryptographic processing unit 13 performs both cryptographic processing with the smart key 2 and cryptographic processing with the center 3. The encryption key management unit 14 stores an encryption key (common key) used for encryption communication with the smart key 2, and an encryption key (secret key, public key) used for encryption communication with the center 3, Update to a new encryption key. The protocol determination unit 15 interprets a message transmitted from the smart key 2 or creates a message to be transmitted to the smart key 2. The door unlock control unit 16 is a functional unit that unlocks the door lock of the vehicle 1. The common key generation unit 17 is a functional unit that newly generates a common key used for encrypted communication between the vehicle 1 and the smart key 2. The common key generation unit 17 generates a new common key using a random number, for example.

<Smart key>
The smart key 2 includes a short-range communication unit 21, an encryption processing unit 22, an encryption key management unit 23, a protocol determination unit 24, and an ID storage unit 25 as functional units. These functional units can also be configured by dedicated hardware or MPU. It should be noted that at least the encryption processing unit 22, the encryption key management unit 23, the protocol determination unit 24, and the ID storage unit 25 in the smart key 2 are executed in a trust domain that is independent of other domains and secures reliability.

The short-range communication unit 21 performs short-range wireless communication with the vehicle 1. The encryption processing unit 22 performs data encryption and decryption processing. The smart key 2 uses a common key encryption method with the vehicle 1 and uses a public key encryption method with the center 3. The cryptographic processing unit 22 performs both cryptographic processing with the vehicle 1 and cryptographic processing with the center 3. The encryption key management unit 23 stores an encryption key (common key) used for encryption communication with the vehicle 1, an encryption key (secret key, public key) used for encryption communication with the center 3, or a new key Update to an encryption key. The protocol determination unit 24 interprets a message transmitted from the vehicle 1 or creates a message to be transmitted to the vehicle 1. The ID storage unit 25 stores the ID of the smart key 2.

<Center>
The center 3 includes functional units such as an external communication unit 31, an encryption processing unit 32, and a common key generation unit 33. The external communication unit 31 performs wireless communication with the vehicle 1. The encryption processing unit 32 performs a process for concealing communication between the vehicle 1 and the smart key 2. As described above, concealment is performed here using a common key cryptosystem. The common key generation unit 33 generates a common key used for encryption communication between the vehicle 1 and the smart key 2.

[Operation example]
Next, a method of updating the common key only by communication between the vehicle 1 and the smart key 2 (vehicle-driven method) and a method of updating the common key also using the center 3 (center-driven method) explain.

-Vehicle-driven update method First, a method for updating the common key only by communication between the vehicle 1 and the smart key 2 will be described with reference to FIG. The vehicle 1 periodically transmits a message including a random value from the short-range communication unit 11 (S2). After the random number is transmitted, the vehicle 1 waits for a confidential message to be transmitted from the smart key 2 within a predetermined time (S4). If the confidential message is not obtained after waiting for a certain time (S4-NO), a random number is generated and transmitted again. When the smart key 2 receives a message including a random number (S6), the smart key 2 proceeds to processing for generating and transmitting a message for requesting unlocking of the door lock. Here, in order for the user to unlock the door lock without pressing the button or the like of the smart key 2, a random number is periodically transmitted from the vehicle 1, and the smart key is triggered by reception of the random number. The unlock request message is generated. Of course, when the user presses the button of the smart key 2 or the like, the processing after step S8 may be started (in this case, the random number is not used but the encryption is performed using only the common key).

  When the smart key 2 receives a random value from the vehicle 1 (S6), the protocol determination unit 24 extracts the ID unique to the smart key 2 from the ID storage unit 25 and generates an unlock request message (S8). This unlock request message includes the ID of the smart key 2. Then, the encryption processing unit 22 extracts the common key for the vehicle 1 from the encryption key management unit 23, and conceals the unlock request message using the extracted common key and the random value received in step S6 (S10). . The encryption processing unit 22 may use a bit string obtained by combining the common key and the random value as the encryption key, or may use a bit string obtained from the common key and the random value by a predetermined algorithm as the encryption key. The short-range communication unit 21 transmits the concealed unlock request message to the vehicle (S12). The smart key 2 waits for the reception of the confidential message from the vehicle 1 after transmitting the unlock request message (S14).

When the vehicle 1 receives the confidential message from the smart key 2 within a predetermined time from the random number transmission (S16), the encryption processing unit 13 takes out the common key for the smart key 2 from the encryption key management unit 14 and takes it out. The secret message is decrypted using the common key and the random number value transmitted in step S2 (S18). The encryption processing unit 13 determines a bit string to be used as an encryption key from the common key and the random number value by the same algorithm as the encryption processing unit 22 of the smart key 2. The protocol determination unit 15 analyzes the decrypted message and determines whether the request is an unlock request from the smart key having the assumed ID (S20). If the unlock request is not valid (S22-NO), the process is terminated and the process returns to the transmission of random numbers (S2) again. If the unlock request is valid (S22-YES), the door unlock control unit 16 unlocks the door lock (S24).

  Furthermore, the common key generation part 17 produces | generates the new common key used for the encryption communication between the vehicle 1 and the smart key 2 (S26). The protocol determination unit 15 receives a new common key from the common key generation unit, generates a common key update message, and conceals it by the encryption processing unit 13 (S28). The short-range communication unit 11 transmits the concealed common key update message to the smart key 2 (S30), and the encryption key management unit 14 stores the new common key generated by the common key generation unit 17 (S32).

  The smart key 2 waits for the reception of the confidential message from the vehicle 1 after transmitting the confidential unlock request message to the vehicle 1. When the confidential message is received, the encryption processing unit 22 extracts the vehicle common key from the encryption key management unit 23 and decrypts the confidential message (S34). The protocol determination unit 24 understands that the decrypted message is a common key update message, and registers the new common key received from the vehicle 1 in the encryption key management unit 23 (S36).

  By doing in this way, whenever it communicates between the vehicle 1 and the smart key 2 using a common key, it is updated to a new common key. Although it is not always necessary to update the vehicle 1 and the smart key 2 every time a common key is used, this ensures more safety. However, only by updating the common key between the vehicle 1 and the smart key 2, as described above, when one common key (how old it is) can be found, the latest common key is chained. Will be revealed.

  Therefore, it is necessary to update the common key using the center 3. Hereinafter, a method for updating the common key used between the vehicle 1 and the smart key 2 using the center 3 will be described with reference to FIG.

Center-initiated update method First, the common key generation unit 33 of the center 3 generates a new common key to be used between the vehicle 1 and the smart key 2 (S52). This common key is generated regardless of the common key currently used between the vehicle 1 and the smart key 2. Note that the timing at which the center 3 generates a new common key may be periodically performed or may be executed in response to a request from the vehicle 1. When the vehicle 1 issues a request to the center 3, it is preferable to issue the request when the vehicle 1 and the smart key 2 can communicate. For example, a request may be issued to the center 3 after confirming that communication is established between the vehicle 1 and the smart key 2, and the vehicle 1 and the smart key 2 can communicate with each other while the vehicle is running. Since it is considered, a request may be issued to the center 3 while the vehicle is traveling. Alternatively, the center 3 periodically generates and transmits a key, and the vehicle 1 may perform the key update process only when the vehicle 1 can communicate with the smart key 2 when receiving the update message. . It should be noted that the common key update interval led by the center 3 does not have to be so frequent, and it is sufficient if the interval is shorter than the time required for decrypting the common key message. In the present embodiment, for example, the common key of the vehicle 1 and the smart key 2 is updated with the common key generated by the center 3 at a frequency of about once a week.

  When the center 3 generates a new common key, the cipher processing unit 32 conceals the new common key for the vehicle 1 using an encryption key for transmission to the vehicle 1 (S54). Since communication is performed between the center 3 and the vehicle 1 using the public key cryptosystem, the encryption processing unit 32 conceals a new common key using the public key of the vehicle 1.

  Similarly, the encryption processing unit 32 of the center 3 conceals a new common key for the smart key 2 using an encryption key for transmission to the smart key 2 (S56). Here, the cryptographic processing unit 32 conceals the new common key with the public key of the smart key 2.

  When communication with the vehicle 1 is established (S58-YES), the external communication unit 33 transmits the two confidential messages concealed in steps S54 and S56 to the vehicle 1 (S60).

  When the external communication unit 12 of the vehicle 1 receives the confidential message from the center 3 (S62), the confidential message for the smart key 2 among the received confidential messages is transmitted to the smart key 2 using the short-range communication unit 11. (S64). Since this secret message is already concealed so that only the smart key 2 can be decrypted, the vehicle 1 does not need to conceal this message. The encryption processing unit 13 extracts the encryption key for encryption communication with the center 3 from the encryption key management unit 14, and decrypts the confidential message for the vehicle 1 among the received confidential messages (S66). Here, the encryption processing unit 13 decrypts the confidential message from the center 3 using the private key of the vehicle 1. The protocol determination unit 15 interprets the decrypted message and registers a new common key for the vehicle in the encryption key management unit 14 (S68).

  When the short-range communication unit 21 of the smart key 2 receives the confidential message transmitted from the center 3 via the short-range communication unit 11 of the vehicle 1 (S70), the encryption processing unit 22 performs encryption with the center 3. The encryption key for communication is extracted from the encryption key management unit 23, and the secret message for the smart key 2 is decrypted (S72). Here, the encryption processing unit 22 decrypts the confidential message from the center 3 using the secret key of the smart key 2. The protocol determination unit 24 interprets the decrypted message and registers a new common key for the smart key 2 in the encryption key management unit 23 (S74).

[Operation / Effect of this Embodiment]
An example of common key update according to this embodiment is shown in FIG. When the vehicle and the smart key use the common key A, the common key B generated by the vehicle is concealed by the common key A and transmitted to the smart key. Further, the common key C generated by the vehicle is concealed by the common key B and transmitted to the smart key. Next, the common key X generated by the center is transmitted to the vehicle and the smart key. The center transmits the common key X to the vehicle and the smart key using the public keys α and β of the vehicle and the smart key. Next, the vehicle generates a new common key D, conceals it with the common key X, and transmits it to the smart key.

  According to the present embodiment, even if the common key is found, the common key that can be acquired in a chain can be limited to the common key until a new common key is transmitted from the center. Consider a case where a third party decrypts a message concealed with the common key A and the common key A is found. At this time, the common key B can be obtained by using the common key A, and the common key C can be obtained by using the common key B. However, the common key that can be obtained in a chain is up to the common key C, and in order to obtain the common key X, it is necessary to newly perform a brute force attack or the like. Since it takes time to decrypt the encryption key, when the common key is found, it can be expected that the common key used by the vehicle and the smart key is updated to the one transmitted from the center. Further, since a response speed is not so required for communication with the center, it is possible to employ a strong encryption key.

  In addition, since the smart key receives a new common key from the center using the vehicle as a gateway, it is possible to prevent a situation in which the common key is shifted between the smart key and the vehicle. In particular, if communication is established between the smart key and the vehicle at the common key update timing from the center, the common key can be prevented from shifting.

[Other]
In the above description, public key cryptography is used for cryptographic communication between the key distribution center and the vehicle or smart key, but it can be used for long-term operation by adopting a complex algorithm or lengthening the key length. A common key cryptosystem may be adopted as long as it is secure enough to withstand.

  According to the above-described embodiment, the key is updated in a situation where it can be assumed that the vehicle and the smart key can communicate with each other, and it is possible to avoid a flaw in the common key of the vehicle and the smart key. . Accordingly, the vehicle and the smart key update the common key stored in the vehicle and the smart key without confirming that the other party has completed the update of the common key. In order to perform more reliable update, it is preferable to confirm that the update of the common key is completed. For example, when renewing a key led by a vehicle, after the vehicle generates a new common key, keep both the old common key and the new common key, and after receiving notification of the completion of the key renewal from the smart key The common key in the vehicle may be updated to a new common key. In addition, when the key is renewed by the key distribution center, when the vehicle receives a new common key from the center, both the old common key and the new common key are retained, and the key update completion notification is sent from the smart key. After receiving, the common key in the vehicle may be updated to a new common key.

  In the above description, the common key is updated for the smart key system. However, it will be apparent that the common key update method of the present invention can be applied to systems other than the smart key system. The common key update method according to the present invention is applicable to any system that communicates using a common key encryption method.

DESCRIPTION OF SYMBOLS 1 Vehicle 11 Short-range communication part 12 External communication part 13 Encryption processing part 14 Encryption key management part 15 Protocol judgment part 16 Door lock control part 17 Common key generation part 2 Smart key 21 Short-range communication part 22 Encryption processing part 23 Encryption key management Unit 24 protocol determination unit 25 ID storage unit 3 key distribution center 31 external communication unit 32 encryption processing unit 33 common key generation unit

Claims (6)

An encryption key update system configured to update a common encryption key configured between first, second, and third devices and used between the first and second devices,
When the cryptographic communication is performed between the first device and the second device, the first device generates a new common cryptographic key, and the second device is configured by the conventional cryptographic communication using the common cryptographic key. And the next encrypted communication between the first device and the second device is performed using the new common encryption key,
The third device newly generates a common encryption key used for encrypted communication between the first device and the second device, transmits the common encryption key to the first device,
When the first device receives a new common encryption key from the third device, the first device transmits the common encryption key received from the third device to the second device. The cryptographic communication between the second devices is performed using the common cryptographic key received from the third device.
Encryption key update system. The third device includes a first encrypted message obtained by encrypting the generated common encryption key so that only the first device can decrypt, and a second device obtained by encrypting the generated common encryption key so that only the second device can decrypt. Sending the encrypted message to the first device;
The first device stores a common encryption key obtained by decrypting the first encryption message as a common encryption key used for communication with the next second device, and stores the second encryption message in the second To the device,
The second device stores a common encryption key obtained by decrypting the second encrypted message received from the first device as a common encryption key used for communication with the next first device.
The encryption key update system according to claim 1. A smart key system including a vehicle, a smart key, and a key distribution center.
A storage unit for storing a common encryption key for encryption communication with the smart key and an encryption key for encryption communication with the key distribution center;
A communication unit for performing communication with the smart key and communication with the key distribution center;
A cryptographic processing unit that performs cryptographic processing using the cryptographic key stored in the storage unit;
An encryption key generation unit for newly generating a common encryption key used for encryption communication with the smart key;
When performing cryptographic communication with the smart key, the common encryption key generated by the encryption key generation unit is transmitted to the smart key, and the generated common encryption key is used to communicate with the smart key in the storage unit. An encryption key management unit for updating a common encryption key for encrypted communication;
Have
Smart key
A storage unit for storing a common encryption key for encryption communication with the vehicle and an encryption key for encryption communication with the key distribution center;
A communication unit for communicating with the vehicle;
A cryptographic processing unit that performs cryptographic processing using the cryptographic key stored in the storage unit;
An encryption key management unit that updates a common encryption key for encryption communication with the vehicle in the storage unit with a new common encryption key transmitted from the vehicle when performing encryption communication with the vehicle;
Have
The key distribution center
A storage unit for storing an encryption key for encryption communication with the vehicle and an encryption key for encryption communication with the vehicle; and
An encryption key generator for generating a common encryption key for encryption communication between the smart key and the vehicle;
A first encrypted message obtained by encrypting the generated common encryption key with an encryption key between the smart key and a second encrypted message obtained by encrypting the generated common encryption key with an encryption key between the vehicle and the vehicle. A transmission unit for transmission;
Have
When the vehicle receives the message from the key distribution center, the vehicle transmits a second encryption message to the smart key and uses the common encryption key obtained by decrypting the first encryption message to store the smart key in the storage unit. Update the common encryption key for encrypted communication with
The smart key updates a common encryption key for encryption communication with the vehicle in the storage unit with a common encryption key obtained by decrypting the second encryption message transmitted from the vehicle.
Smart key system.   The smart key system according to claim 3, wherein cryptographic communication between the vehicle and the key distribution center and between the smart key and the key distribution center is performed by a public key cryptosystem.   5. The smart key system according to claim 3, wherein the key distribution center transmits the first cipher message and the second cipher message to the vehicle when the vehicle and the smart key can communicate with each other. An encryption key update method for updating a common encryption key used between a first device and a second device in a system composed of first, second and third devices,
When the cryptographic communication is performed between the first device and the second device, the first device generates a new common cryptographic key, and the second device is configured by the conventional cryptographic communication using the common cryptographic key. And the next encrypted communication between the first device and the second device is performed using the new common encryption key,
The third device newly generates a common encryption key used for encrypted communication between the first device and the second device, and transmits the common encryption key to the second device.
When the first device receives a new common encryption key from the third device, the common encryption received from the third device when performing encrypted communication with the first device. A key is transmitted to the second device, and the next encrypted communication between the first device and the second device is performed using the common encryption key received from the third device;
Encryption key update method.

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