Electronic apparatus, host apparatus, and electronic apparatus system

Abstract

This electronic apparatus comprises: a decryption processing unit that uses a first common key to decrypt a session key transmitted, in an encrypted state, from a host device; an encryption processing unit that encrypts the decrypted session key; and a communication unit that transmits the encrypted session key to the host device.

Description

Electronic device, host device and electronic device system

[0001] The present technology relates to electronic devices, host devices, and electronic device systems.

[0002] When multiple electronic devices are used, a method using a key is used for pairing between the electronic devices, establishing a session, detecting tampering, and the like.

[0003] There are two types of key-based systems: public key systems and symmetric key systems. Generally, there is a trade-off between the two: public key systems allow for secure key management but have slow processing speeds, while symmetric key systems are difficult to manage securely and are expensive, but have fast processing speeds.

[0004] A technology has been proposed that combines both key methods, using the public key method when manufacturing electronic devices such as sensors, and the common key method when operating them, to establish sessions between multiple electronic devices and verify tampering (Patent Document 1).

[0005] WO2023 / 127429 publication

[0006] When multiple electronic devices are used, there is a demand for faster session establishment between the electronic devices and a device functioning as a host.

[0007] The present technology has been developed in consideration of such problems, and aims to provide an electronic device, a host device, and an electronic device system that can quickly establish a session between a host device and an electronic device when the host device communicates with multiple electronic devices.

[0008] In order to solve the above-mentioned problems, the first technology is an electronic device that includes a decryption processing unit that decrypts a session key sent from a host device in an encrypted state using a first common key, an encryption processing unit that encrypts the decrypted session key, and a communication unit that sends the encrypted session key to the host device.

[0009] The second technology is a host device that includes a session key generation unit that generates a session key for establishing a session with an electronic device other than a specific electronic device that is one of a plurality of electronic devices, and a communication unit that transmits an encrypted session key to the specific electronic device, receives the session key encrypted and transmitted by the specific electronic device, and transmits the received session key to the other electronic device.

[0010] Furthermore, a third technology is an electronic device system including a host device having a session key generation unit that generates a session key for establishing a session with an electronic device other than a specific electronic device that is one of a plurality of electronic devices, and a communication unit that transmits an encrypted session key to the specific electronic device, receives the session key encrypted and transmitted by the specific electronic device, and transmits the received session key to another electronic device, and an electronic device that is the specific electronic device and has a decryption processing unit that decrypts the session key transmitted from the host device in an encrypted state using a first common key, an encryption processing unit that encrypts the decrypted session key, and a communication unit that transmits the encrypted session key to the host device.

[0011] FIG. 1 is a block diagram showing the configuration of an electronic device system 10. FIG. 2 is a block diagram showing the configuration of a host device 100. FIG. 3 is a block diagram showing the configuration of an electronic device 200 in a first embodiment. FIG. 4 is a sequence diagram showing the processing of the electronic device system 10 in the first embodiment. FIG. 5 is a diagram showing the processing of the electronic device system 10 in the first embodiment. FIG. 6 is a block diagram showing the configuration of an electronic device 200 in a second embodiment. FIG. 7 is a sequence diagram showing the processing of the electronic device system 10 in the second embodiment. FIG. 8 is a diagram showing the processing of the electronic device system 10 in the second embodiment.

[0012] Hereinafter, embodiments of the present technology will be described with reference to the drawings. The description will be made in the following order: <First embodiment> [Regarding public key systems and common key systems] [Configuration of electronic device system 10] [Configuration of host device 100] [Configuration of electronic device 200] [Processing of electronic device system 10] <Second embodiment> [Configuration of electronic device 200] [Processing of electronic device system 10] <Modification>

[0013] First Embodiment [Regarding Public Key Scheme and Shared Key Scheme] First, the characteristics of the public key scheme and shared key scheme used in the present technology will be described. The public key scheme is a scheme in which different keys are used for encryption and decryption, and data is encrypted with a public key and decrypted with a private key. The shared key scheme is a scheme in which a common key is shared between communicating devices, and the same key is used for encryption and decryption.

[0014] The advantage of the public key system is that it is easy to manage and operate the keys. During the manufacturing stage of devices that use keys, a secret value must be stored for each pair of devices that will communicate, but the value stored in each device can be different. Also, there is no need to transfer the key when repairing a device. However, the disadvantage of the public key system is that processing is slow, so it takes time to process and start up the device. Public key system algorithms include RSA, ElGamal, and elliptic curve cryptography.

[0015] On the other hand, the common key method has the advantage of being fast, resulting in short processing times. However, with the common key method, a unique key for each pair of communicating devices must be shared during the manufacturing stage. Also, when repairing a device, the key for the broken device must be transferred to the repair part. Therefore, compared to the public key method, the common key method has the disadvantage of being more complicated to manage and operate. Common key method algorithms include RC4 (Rivest's Cipher 4), DES (Data Encryption Standard), and AES (Advanced Encryption Standard).

[0016] In the electronic device system 10 in which the host device 100 communicates with a plurality of electronic devices 200, the present technology uses a public key system to establish a session with a specific electronic device 200 that establishes a session first, and uses a common key system to establish sessions with the second and subsequent other electronic devices 200. This combines the advantages of the public key system and the common key system, enabling high-speed establishment of a session between the host device 100 and the electronic device 200 and facilitating key management and operation.

[0017] [Configuration of Electronic Device System 10 ] The electronic device system 10 is configured by a host device 100 and a plurality of electronic devices 200 .

[0018] The host device 100 is capable of communicating with each of the multiple electronic devices 200, and manages, controls, and transmits and receives keys to each of the electronic devices 200. The host device 100 is, for example, an ECU (Electronic Control Unit) that is mounted in an automobile and performs electronic control of the entire automobile and each part thereof.

[0019] The electronic device 200 is capable of communicating with the host device 100 and performs various processes and controls. The electronic device 200 is, for example, an on-board sensor mounted in an automobile. The on-board sensor may be an external sensor or an internal sensor. Examples of the sensor include a camera, an image sensor, a time-of-flight (ToF) sensor, a light detection and ranging (LiDAR), an infrared sensor, a millimeter-wave radar, a polarization sensor, a multi-wavelength (multispectral) sensor, a temperature sensor, a humidity sensor, and an inertial measurement unit (IMU).

[0020] The host device 100 and the electronic device 200 can communicate with each other using a communication method such as I2C (Inter-Integrated Circuit). I2C is a synchronous serial communication method that communicates data in synchronization with a clock, and is mainly used for data communication with EEPROMs (Electrically Erasable and Programmable Read Only Memory) and sensors. However, the communication method is not limited to I2C and may be another method, and may be either wired communication or wireless communication.

[0021] In the example of FIG. 1 , the electronic device system 10 includes two electronic devices 200: a first electronic device 200A and a second electronic device 200B. However, the number of electronic devices 200 included in the electronic device system 10 is not limited to two and may be any number. The first electronic device 200A corresponds to a specific electronic device in the claims. The electronic device 200 that first establishes a session with the host device 100 by exchanging public keys with the host device 100 is the first electronic device 200A. The second electronic device 200B that establishes a session with the host device 100 after the first electronic device 200A corresponds to another electronic device in the claims. If there are a third electronic device, a fourth electronic device, etc. after the second electronic device 200B, these also correspond to other electronic devices in the claims.

[0022] For example, if the host device 100 is an ECU that operates in an automobile and the electronic device 200 is an on-board sensor mounted on the automobile, the manufacturer that produces the host device 100 may be different from the manufacturer that produces the electronic device 200, and further, the manufacturer that produces the automobile, which is the final product, may also be different (e.g., an OEM (Original Equipment Manufacturer)). In this case, the manufacturer of the host device 100 corresponds to Tier 1 that provides the host device 100 to the automobile manufacturer. Also, the manufacturer of the electronic device 200 corresponds to Tier 2. A user is someone who purchases and uses an automobile equipped with the host device 100 and electronic device 200.

[0023] [Configuration of Host Device 100] Next, the configuration of the host device 100 will be described with reference to FIG.

[0024] The storage unit 101 stores keys used in processing, various data, etc. Specifically, the storage unit 101 stores a public key pair consisting of a private key sh and a public key ph that are unique to the host device 100, a public key certificate, etc. The public key pair is stored in the storage unit 101 in advance by the manufacturer of the host device 100 during the manufacturing stage of the host device 100. The storage unit 101 is configured with a non-volatile memory such as an OTP (One Time Programmable) memory that does not lose data even when the power of the host device 100 is turned off.

[0025] The communication unit 102 is a communication module that performs communication processing with the electronic device 200. As described above, the communication method is, for example, I2C, but other methods may also be used. The host device 100 transmits and receives keys and the like to and from the electronic device 200 via the communication unit 102.

[0026] The control unit 103 is composed of a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), etc. The CPU executes various processes and issues commands according to programs stored in the ROM, thereby controlling the host device 100 as a whole and each unit, and also manages the transmission and reception of keys and data between each processing unit.

[0027] The first common key generation unit 104 generates a first common key Kd to be shared with the first electronic device 200A using the private key sh of the public key pair that the host device 100 already has and the public key pe sent from the first electronic device 200A, using ECDH (Elliptic Curve Diffie-Hellman key exchange) and KDF (Key Derivation Function).

[0028] The session key generating unit 105 generates a random key as a session key Ks, which is a key for establishing a secure session between the host device 100 and the second electronic device 200B.

[0029] The encryption processing unit 106 encrypts the session key Ks using the first common key Kd, and further generates a MAC (Message Authentication Code) for tamper detection using the first common key Kd, and adds the generated MAC to the encrypted session key Ks.

[0030] The host device 100 is configured as described above.

[0031] [Configuration of Electronic Device 200] Next, the configuration of electronic device 200 will be described with reference to FIG.

[0032] The storage unit 201 stores keys and various data used in processing. Specifically, the storage unit 201 stores a public key pair consisting of a private key se and a public key pe that are unique to the electronic device 200, and a public key certificate. The storage unit 201 also stores a second common key Kc, which is a random value. The second common key Kc is unique, for example, to each type of final product (model type in the case of an automobile) or each manufacturer of the final product. If the second common key Kc is unique to each type (model type) of final product, the same second common key Kc is stored in the storage units 201 of all electronic devices 200 installed in the same type of final product (model type). If the second common key Kc is unique to each manufacturer of the final product, the same second common key Kc is stored in the storage units 201 of all electronic devices 200 installed in final products manufactured by that manufacturer.

[0033] The public key pair and the second common key Kc are stored in advance in the storage unit 201 by the manufacturer of the electronic device 200 during the manufacturing stage. Note that a manufacturer other than the manufacturer of the electronic device 200, such as the manufacturer of the host device 100 or the manufacturer (OEM) of the final product, may generate the second common key Kc and store it in the storage unit 201 of the electronic device 200. The storage unit 201 is configured with a non-volatile memory such as an OTP, which retains data even when the power of the electronic device 200 is turned off. Therefore, the second common key Kc does not change even when the power of the electronic device 200 is turned off and then started up.

[0034] The communication unit 202 is a communication module that performs communication processing with the host device 100. As described above, the communication method is, for example, I2C, but other methods may also be used. The electronic device 200 transmits and receives keys and the like to and from the host device via the communication unit 202.

[0035] The control unit 203 is composed of a CPU, RAM, ROM, etc. The CPU executes various processes and issues commands according to programs stored in the ROM, thereby controlling the entire electronic device 200 and each unit, and also managing the transmission and reception of data between each processing unit.

[0036] The first common key generation unit 204 generates a first common key Kd to be shared with the host device 100 using the private key se of the public key pair that the electronic device 200 already has and the public key ph sent from the host device 100, using ECDH and KDF.

[0037] The decryption processing unit 205 decrypts the session key Ks sent from the host device 100 using the first common key Kd generated by the first common key generation unit 204, and further detects whether the session key Ks has been tampered with by comparing the MAC attached to the session key Ks.

[0038] The encryption processing unit 206 encrypts the session key Ks sent from the host device 100 using the second common key Kc.

[0039] The electronic device 200 is configured as described above. The first electronic device 200A and the second electronic device 200B have the same configuration.

[0040] When the processing method according to the present technology is realized by executing a program, the program is installed in the host device 100 and the electronic device 200 in advance by the manufacturer.

[0041] The functions performed by the components described herein may be implemented in circuitry or processing circuitry, including general-purpose processors, application-specific processors, integrated circuits, ASICs (Application Specific Integrated Circuits), a CPU (Central Processing Unit), conventional circuits, and / or combinations thereof, programmed to perform the described functions. Processors include transistors and other circuits and are considered circuitry or processing circuitry. A processor may also be a programmed processor that executes a program stored in memory. In this specification, a circuit, unit, or means is hardware that is programmed to perform or executes the described functions. The hardware may be any hardware disclosed herein or any hardware known to be programmed to perform or execute the described functions. When the hardware is a processor, which is considered a type of circuitry, the circuit, means, or unit is a combination of hardware and software used to configure the hardware and / or processor.

[0042] [Processing in Electronic Device System 10] Next, processing in the electronic device system 10 will be described with reference to FIGS. 4 and 5. FIG.

[0043] In the following description, an encrypted session key Ks is referred to as a "session key Ks (encrypted)," and an unencrypted session key Ks is referred to as a "session key Ks (plaintext)."

[0044] As a premise for the processing in the electronic device system 10, it is assumed that, at the manufacturing stage, the manufacturer of the electronic devices 200 stores the second common key Kc in the storage units 201 of all the electronic devices 200 that make up the electronic device system 10. The second common key Kc stored in the storage units 201 of all the electronic devices 200 used by one user is the same.

[0045] It is also assumed that the manufacturer of the host device 100 stores a unique public key pair consisting of a public key ph and a private key sh, and a public key certificate in the storage unit 101 of the host device 100 during manufacturing.

[0046] It is also assumed that at the manufacturing stage, the manufacturer of the electronic devices 200 stores a unique public key pair consisting of a public key pe and a private key se, and a public key certificate in the storage unit 201 of each of the electronic devices 200.

[0047] Then, the host device 100 transmits the public key ph of its public key pair to one of the multiple electronic devices 200 via communication such as I2C. Since the public key ph is included in the public key certificate, when the host device 100 transmits the public key certificate to the electronic device 200, it does not need to transmit the public key ph separately. Then, upon receiving the public key ph and the public key certificate from the host device 100, the electronic device 200 transmits the public key pe of its public key pair and the public key certificate to the host device 100.

[0048] In this way, among the plurality of electronic devices 200, the electronic device 200 that exchanges public keys with the host device 100 and establishes a session becomes the first electronic device 200A. Any one of the plurality of electronic devices 200 that can communicate with the host device 100 may become the first electronic device 200A, and which electronic device 200 becomes the first electronic device 200A may be determined by the manufacturer of the host device 100, or may be determined by the manufacturer of the electronic device 200, or may be automatically determined by the host device 100 based on a predetermined algorithm or the like.

[0049] Then, during the operation of the electronic device system 10, public key technology such as certificate chain verification is used to confirm through public key mutual authentication that the host device 100 and the first electronic device 200A are mutually trustworthy devices, and a session is established.

[0050] The operation stage is a stage in which a final completed product including the host device 100 and the electronic device 200 is delivered to a user and becomes available for use. If the final completed product including the host device 100 and the electronic device 200 is a car, this is the stage in which the car is shipped, delivered to the user who purchased it, and the engine is started so that the car can be driven.

[0051] In the processing in the electronic device system 10 during the operation phase, first, in step S1, the first common key generation unit 104 of the host device 100 generates a first common key Kd using ECDH and KDF using the private key sh of the public key pair that the host device 100 already has and the public key pe sent from the first electronic device 200A.

[0052] When the first symmetric key generation unit 104 of the host device 100 generates the first symmetric key Kd, the inputs to ECDH are the private key sh held by the host device 100 and the public key pe transmitted from the first electronic device 200A. The first symmetric key generation unit 104 first generates Z (an output called a shared secret or the like) by ECDH, and uses Z (the shared secret) as an input to the KDF to generate the first symmetric key Kd for encryption and MAC by the KDF.

[0053] In step S2, the first common key generation unit 204 of the first electronic device 200A generates a first common key Kd by ECDH and KDF using the private key se of the public key pair that the first electronic device 200A has in advance and the public key ph transmitted from the host device 100. As a result, the host device 100 and the first electronic device 200A share the first common key Kd.

[0054] Note that steps S1 and S2 do not necessarily have to be performed in this order, and may be performed in the reverse order, or may be performed simultaneously or nearly simultaneously. The first electronic device 200A only needs to generate the first common key Kd before using it in step S7 described later.

[0055] When the first symmetric key generation unit 204 of the first electronic device 200A generates the first symmetric key Kd, the ECDH inputs are the private key se held by the first electronic device 200A and the public key ph transmitted from the host device 100. The first symmetric key generation unit 204 first generates the first symmetric key Kd to be used for decryption using ECDH. Then, the KDF uses the first symmetric key Kd generated by ECDH as input to generate another first symmetric key Kd for tamper detection using MAC.

[0056] Next, in step S3, session key generating section 105 of host device 100 generates a random key as session key Ks.

[0057] Next, in step S4, the encryption processing unit 106 of the host device 100 encrypts the session key Ks (plaintext) using the first common key Kd generated by the first common key generation unit 104, and further generates a MAC for tamper detection and adds it to the session key Ks (encryption). This allows the host device 100 to securely transmit the session key Ks (encryption) to the first electronic device 200A. Note that the encryption processing unit 106 may add the MAC to the session key Ks (plaintext) and then encrypt the session key Ks (plaintext) using the first common key Kd.

[0058] Then, in step S5, the host device 100 transmits the session key Ks (encrypted) to the first electronic device 200A via the communication unit 102. In step S6, the first electronic device 200A receives the session key Ks (encrypted) transmitted from the host device 100.

[0059] Next, in step S7, the decryption processing unit 205 of the first electronic device 200A decrypts the session key Ks (encryption) using the first common key Kd generated by the first common key generation unit 204.

[0060] Furthermore, the decryption processing unit 205 of the first electronic device 200A generates a MAC using the decrypted session key Ks (plain text) and the first common key Kd that it generated itself, and compares the generated MAC with the MAC sent from the host device 100 to detect whether the session key Ks (plain text) has been tampered with. If the MACs do not match, this means that the session key Ks (plain text) has been tampered with. Examples of tampering include bit inversion. Using the MAC in this way makes it possible to detect whether the session key Ks (plain text) has been tampered with.

[0061] When the encryption processing unit 106 of the host device 100 encrypts the session key Ks (plain text) and then adds a MAC to the session key Ks (encryption), the decryption processing unit 205 of the first electronic device 200A performs tampering detection using the MAC on the session key Ks (encryption) before decrypting it. On the other hand, when the encryption processing unit 106 of the host device 100 adds a MAC to the session key Ks (plain text) before encrypting it, the decryption processing unit 205 of the first electronic device 200A performs tampering detection using the MAC after decrypting it.

[0062] Next, in step S8, the encryption processing unit 206 of the first electronic device 200A encrypts the session key Ks (plain text) with the second common key Kc that has been stored in advance in the storage unit 201. In this way, by the first electronic device 200A encrypting the session key Ks (plain text) with the second common key Kc, the second electronic device 200B, which has the same second common key Kc, becomes able to decrypt the session key Ks (encryption).

[0063] Next, in step S9, the first electronic device 200A transmits the session key Ks (encrypted) to the host device 100 via the communication unit 202. In step S10, the host device 100 receives the session key Ks (encrypted) transmitted from the first electronic device 200A.

[0064] In this way, the host device 100 securely transmits the session key Ks for establishing a session with the second electronic device 200B to the first electronic device 200A over the session established with the first electronic device 200A. Then, the first electronic device 200A encrypts the session key Ks (plain text) with the second common key Kc that is the same between the electronic devices 200 and transmits it back to the host device 100.

[0065] Next, in step S11, the host device 100 transmits the session key Ks (encryption) to the second electronic device 200B via the communication unit 102. In step S12, the first electronic device 200A receives the session key Ks (encryption) transmitted from the host device 100. As described above, with this technology, the host device 100 does not need to store the session key Ks (encryption) transmitted from the first electronic device 200A in the storage unit 101.

[0066] Next, in step S13, the decryption processing unit 205 of the second electronic device 200B decrypts the session key Ks (encryption) using the second common key Kc that is identical between the electronic devices 200 and that is stored in the storage unit 201 in advance.

[0067] As described above, the session key Ks may be encrypted using the second common key Kc and tampering detection may be performed using the MAC, in the same way as the session key Ks is encrypted using the first common key Kd and tampering detection is performed using the MAC. In this case, in step S8, the encryption processing unit 206 of the first electronic device 200A encrypts the session key Ks (plain text) using the second common key Kc and adds a MAC, and in step S13, the decryption processing unit 205 of the second electronic device 200B decrypts the session key Ks (encrypted) using the second common key Kc and performs tampering detection using the MAC.

[0068] Then, the second electronic device 200B can establish a session with the host device 100 using the session key Ks (plain text).

[0069] Note that steps S3 to S13 are executed for the third and subsequent electronic devices 200, for example, the third electronic device 200C. In step S3, the host device 100 generates a session key Ks for the third electronic device 200C, encrypts the session key Ks (plaintext) in step S4, and transmits it to the first electronic device 200A in step S5. Having received the session key Ks (encrypted) in step S6, the first electronic device 200A decrypts the session key Ks (encrypted) in step S7, encrypts the session key Ks (plaintext) using the second common key Kc in step S8, and transmits the session key Ks (encrypted) to the host device 100 in step S9. In step S10, the host device 100 transmits the session key Ks (encrypted) to the third electronic device 200C in step S11. Then, the third electronic device 200C receives the session key Ks (encrypted) in step S12, and decrypts the session key Ks (encrypted) in step S13.

[0070] If the session key Ks for the second electronic device 200B and subsequent electronic devices 200 (the second electronic device, the third electronic device, the fourth electronic device, ...) can be common, the host device 100 transmits the common session key Ks (encrypted) to each electronic device 200. Then, each electronic device 200 receives the common session key Ks (encrypted) and decrypts it to obtain the common session key Ks (plaintext).

[0071] The processing of the present technology is performed each time the electronic device system 10, which is composed of the host device 100 and the electronic device 200, is started. For example, if the host device 100 is an ECU operating in an automobile and the electronic device 200 is an on-board sensor, the processing of the present technology is performed each time the engine is started and the ECU and the on-board sensor electronic device 200 are started. However, the startup of the electronic device 200 is not necessarily linked to the automobile engine. There may also be a configuration in which the ECU and the electronic device 200 start up independently of the engine. In this case, the processing of the present technology is performed each time the ECU and the electronic device 200 start up, regardless of whether the engine is started or not.

[0072] The processing in the first embodiment is performed as described above. In the present technology, the public key system is used to establish a session with the first electronic device 200A, which is a specific electronic device 200 among the multiple electronic devices 200, and the common key system is used to establish sessions with the other electronic devices 200 other than the first electronic device 200A. This shortens the time required to establish a session compared to when a public key is used to establish sessions with all of the electronic devices 200, and enables sessions between the host device 100 and the multiple electronic devices 200 to be established quickly.

[0073] Furthermore, with this technology, it is possible to reduce the time required for processing because there is no need to perform processing to store the session key Ks when the host device 100 generates the session key Ks or when the session key Ks is transmitted from the first electronic device 200A to the host device 100. Furthermore, because the host device 100 does not need to have a storage device for storing the session key Ks, it is possible to reduce the manufacturing cost of the host device 100 and reduce the risk of the session key Ks being leaked.

[0074] The host device 100 transmits the session key Ks to the first electronic device 200A with which a session has been securely established by public key authentication, and the first electronic device 200A then encrypts the session key Ks with the second common key Kc so that the second electronic device 200B can decrypt it with the second common key Kc. This allows the second electronic device 200B to securely receive the session key Ks generated by the host device 100 and use it to establish a session with the host device 100.

[0075] Since the manufacturers of the host device 100 and the electronic device 200 only need to store the public key pair and the second common key Kc, the manufacturing efficiency of the host device 100 and the electronic device 200 can be improved.

[0076] Furthermore, since the second common key Kc stored in all electronic devices 200 is not different for each electronic device 200, but is a key specific to the user of each electronic device 200, management of the electronic devices 200 and the second common key Kc is also made easier.

[0077] In the prior art, a key generated during the manufacturing stage is temporarily stored in storage to complete the manufacturing stage, and then the key must be retrieved from the storage during the operation stage to execute processing. This raises the question of who should process the key and establish a session between the host device 100 and the electronic device 200: the manufacturer of the host device 100, the manufacturer of the electronic device 200, the manufacturer of the final product, or the user. In addition, there are cases where the manufacturer of the host device 100 needs to request the automobile manufacturer to perform processing to establish a session between the host device 100 and the electronic device 200 during the automobile manufacturing process.

[0078] In contrast, with the present technology, as long as the public key pair and the second common key Kc are stored in the host device 100 and the electronic device 200 in advance during the manufacturing stage, key processing and session establishment can be performed solely through processing between the host device 100 and the electronic device 200. This makes session establishment easy and eliminates the problem of who should perform the processing. Furthermore, there is no need to request the automobile manufacturer to perform processing for session establishment during the automobile manufacturing stage. Furthermore, there is no need to request the dealer or repair shop involved in automobile repair to perform processing for session establishment. Therefore, the electronic device system 10 according to the present technology is easy to implement. This also applies when the final finished product is not an automobile.

[0079] Second Embodiment Next, a second embodiment of the present technology will be described. The configurations of the electronic device system 10 and the host device 100 are the same as those of the first embodiment, and therefore description thereof will be omitted.

[0080] [Configuration of Electronic Device 200] The configuration of the electronic device 200 in the second embodiment will be described with reference to Fig. 6. The electronic device 200 differs from the first embodiment in that it includes a true random number generation unit 211, a second storage unit 212, and a temporary key generation unit 213. The other configurations are the same as those in the first embodiment, and therefore will not be described again.

[0081] The true random number generation unit 211 generates a true random number Nonce (hereinafter referred to as true random number N) for generating the temporary key Ke from the second common key Kc. The true random number generation unit 211 generates a new true random number N every time the electronic device 200 is started up. In other words, the value of the true random number N changes every time the electronic device 200 is started up.

[0082] The second storage unit 212 holds the true random number N until it is used to generate the temporary key Ke. The second storage unit 212 is a volatile memory in which the data held therein is erased when the power of the electronic device 200 is turned off. The second storage unit 212 may also store and hold the first common key Kd between the host device 100 and the first electronic device 200A. Furthermore, the second electronic device 200B may store and hold the decrypted session key Ks in the second storage unit 212.

[0083] The temporary key generation unit 213 generates a temporary key Ke based on the second common key Kc and the true random number N. The temporary key Ke can be generated by, for example, KDF or the like.

[0084] The control unit 203 obtains the second common key Kc from the storage unit 201 and also obtains the true random number N from the second storage unit 212 , and supplies them to the temporary key generation unit 213 .

[0085] The electronic device 200 in the second embodiment is configured as described above. Note that, since all of the electronic devices 200 constituting the electronic device system 10 can become either the first electronic device 200A or the second electronic device 200B, the first electronic device 200A and the second electronic device 200B may have the same configuration. However, in the electronic device 200 that has become the first electronic device 200A, the true random number generation unit 211 does not need to perform processing.

[0086] [Processing in the Electronic Device System 10] Next, processing in the electronic device system 10 of the second embodiment will be described with reference to Fig. 7 and Fig. 8. Processing similar to that in the first embodiment will be assigned the same step numbers and detailed description will be omitted.

[0087] The premise of the processing of the electronic device system 10 in the manufacturing stage is the same as that of the first embodiment.

[0088] In the processing of the electronic device system 10 in the operation stage, in step S21, the true random number generation unit 211 of the second electronic device 200B generates a true random number N, and in step S22, the second electronic device 200B transmits the true random number N to the host device 100. The second electronic device 200B generates the true random number N upon startup and transmits it to the host device 100. Note that the true random number N does not need to be encrypted when transmitted to the host device 100, but encryption is not excluded.

[0089] In step S23, the host device 100 receives the true random number N, and in step S24, the host device 100 transmits the true random number N to the first electronic device 200A. Then, in step S25, the first electronic device 200A receives the true random number N.

[0090] In step S26, the temporary key generation unit 213 of the first electronic device 200A generates the temporary key Ke based on the second common key Kc and the true random number N. Note that the temporary key Ke may be generated at any time after receiving the true random number N in step S25 and before using the temporary key Ke in step S27.

[0091] Then, in step S27, the encryption processing unit 206 of the first electronic device 200A encrypts the session key Ks (plaintext) using the temporary key Ke. In the first embodiment, the session key Ks is encrypted using the second common key Kc, but in the second embodiment, the session key Ks is encrypted using the temporary key Ke generated based on the second common key Kc and the true random number N. Note that the first electronic device 200A may store the session key Ks (plaintext) in the second storage unit 212 until it is encrypted using the temporary key Ke.

[0092] In step S28, the temporary key generation unit 213 of the second electronic device 200B generates a temporary key Ke based on the second common key Kc and the true random number N. Then, in step S29, the decryption processing unit 205 of the second electronic device 200B decrypts the session key Ks (encryption) using the temporary key Ke.

[0093] Then, the second electronic device 200B can establish a session with the host device 100 using the decrypted session key Ks (plain text).

[0094] The second electronic device 200B may store the decrypted session key Ks (plain text) in the second storage unit 212.

[0095] For the third or subsequent electronic devices 200, for example, the third electronic device 200C, steps S3 to S12 and steps S21 to S29 are executed. The third electronic device 200C also generates a true random number N in the same manner as the second electronic device 200B. The true random number N generated by the third electronic device 200C is a different value from that generated by the second electronic device 200B. Each electronic device 200 generates its own unique true random number N and transmits it to the host device 100. If all electronic devices 200 generate a true random number N upon startup and transmit it to the host device 100, and the host device 100 arbitrarily selects an electronic device 200 to become the first electronic device 200A, the host device 100 may ignore or discard the true random number N transmitted from the first electronic device 200A.

[0096] In step S3, the host device 100 generates a session key Ks (plaintext) for the third electronic device 200C, encrypts the session key Ks (plaintext) in step S4, and transmits it to the first electronic device 200A in step S5. The first electronic device 200A receives the session key Ks (encrypted) in step S6, decrypts the session key Ks (encrypted) in step S7, encrypts the session key Ks (plaintext) using the temporary key Ke in step S27, and transmits the session key Ks (encrypted) to the host device 100 in step S9. The host device 100 receives the session key Ks (encrypted) in step S10, and transmits it to the third electronic device 200C in step S11. The third electronic device 200C then receives the session key Ks (encrypted) in step S12 and decrypts the session key Ks (encrypted) using the temporary key Ke in step S29.

[0097] If the session key Ks for the second electronic device 200B and subsequent electronic devices 200 (the second electronic device, the third electronic device, the fourth electronic device, ...) can be common, the host device 100 transmits the common session key Ks (encrypted) to each electronic device 200. Then, each electronic device 200 receives the common session key Ks (encrypted) and decrypts it to obtain the common session key Ks (plaintext).

[0098] The processing in the second embodiment is carried out as described above. In the second embodiment, the session key Ks is encrypted not using the second common key Kc but using the temporary key Ke generated based on the second common key Kc and the true random number N. Therefore, even if the second common key Kc is leaked, the session key Ks (encrypted) cannot be decrypted using only the second common key Kc, thereby improving the security of the session key Ks.

[0099] Furthermore, even if the true random number N exchanged between the host device 100 and the first and second electronic devices 200A and 200B is leaked, a new true random number N with a different value is generated each time the second electronic device 200B is started, so the leaked true random number N cannot be reused. This also improves security.

[0100] When the first electronic device 200A encrypts the session key Ks (plain text) for the second electronic device 200B, it uses the true random number N, which is information specific to the second electronic device 200B, so that the encrypted session key Ks sent back to the host device 100 cannot be used anywhere other than the second electronic device 200B. This also enhances security. It also prevents so-called replay attacks, in which an attacker steals information such as the key and true random number N transmitted and received between the host device 100 and the electronic device 200 and retransmits that information to gain unauthorized access.

[0101] <Modifications> Although the embodiments of the present technology have been specifically described above, the present technology is not limited to the above-described embodiments, and various modifications based on the technical ideas of the present technology are possible.

[0102] It has been explained that ECDH and KDF are used to generate the first common key Kd in the first common key generation unit 104 of the host device 100. However, since KDF generates the second common key Kc for tamper detection using MAC, it is possible to execute only ECDH if tamper detection is not required.

[0103] The host device 100 and the electronic device 200 that constitute the electronic device system 10 are not limited to an ECU and an on-board sensor in an automobile. For example, the electronic device system 10 may be a surveillance camera system, the electronic device 200 may be a surveillance camera as a sensor, and the host device 100 may be a personal computer or a server that manages the surveillance camera.

[0104] In addition to sensors, electronic device 200 may be devices such as IoT (Internet of Things) devices, smartphones, tablet terminals, personal computers, game consoles, and wearable devices, or may be semiconductor chips used in various devices that use semiconductors.

[0105] The present technology may also be configured as follows. (1) An electronic device comprising: a decryption processing unit that decrypts an encrypted session key transmitted from a host device using a first common key; an encryption processing unit that encrypts the decrypted session key; and a communication unit that transmits the encrypted session key to the host device. (2) The electronic device according to (1), comprising: a first common key generation unit that generates the first common key to be shared with the host device using a private key of a public key pair held by the electronic device and a public key of a public key pair held by the host device. (3) The electronic device according to (1) or (2), in which all electronic devices that establish a session with the host device have a second common key in advance. (4) The electronic device according to (3), in which the encryption processing unit encrypts the session key with the second common key. (5) The electronic device according to (3), in which the encryption processing unit generates a temporary key using a random number transmitted from the host device and the second common key. (6) The electronic device according to (5), in which the encryption processing unit encrypts the session key using the temporary key. (7) A host device comprising: a session key generation unit that generates a session key for establishing a session with another electronic device other than a specific electronic device that is one of a plurality of electronic devices; and a communication unit that transmits the encrypted session key to the specific electronic device, receives the session key encrypted and transmitted by the specific electronic device, and transmits the received session key to the other electronic device. (8) The host device of (7) that includes an encryption processing unit that encrypts the session key using a first common key shared with the specific electronic device. (9) The host device of (7) or (8) that includes a first common key generation unit that generates the first common key using a private key of a public key pair held by the host device and a public key of a public key pair held by the specific electronic device. (10) The host device of any of (7) to (9) that encrypts the session key by the specific electronic device using a second common key that is shared in advance by the plurality of electronic devices. (11) The host device of any of (7) to (11) that decrypts the session key encrypted by the specific electronic device by the other electronic device using the second common key that is shared in advance by the plurality of electronic devices.(12) The host device according to any one of (7) to (11), which acquires a random number generated by the other electronic device and transmits the random number to the specific electronic device. (13) The host device according to any one of (7) to (12), which establishes a session with the specific electronic device using a public key system and establishes a session with the other electronic device using a common key system. (14) An electronic device system comprising: a host device comprising: a session key generation unit that generates a session key for establishing a session with another electronic device other than a specific electronic device that is one of a plurality of electronic devices; and a communication unit that transmits the encrypted session key to the specific electronic device, receives the session key encrypted and transmitted by the specific electronic device, and transmits the received session key to the other electronic device; and the specific electronic device, which comprises: a decryption processing unit that decrypts the encrypted session key transmitted from the host device using a first common key, an encryption processing unit that encrypts the decrypted session key, and a communication unit that transmits the encrypted session key to the host device.

[0106] REFERENCE SIGNS LIST 10 Electronic device system 100 Host device 102 Communication unit 104 First symmetric key generation unit 105 Session key generation unit 106 Encryption processing unit 200 Electronic device 200A First electronic device 200B Second electronic device 202 Communication unit 204 First symmetric key generation unit 205 Decryption processing unit 213 Temporary key generation unit

Claims

1. An electronic device comprising: a decryption processing unit that decrypts a session key sent from a host device in an encrypted state using a first common key; an encryption processing unit that encrypts the decrypted session key; and a communication unit that sends the encrypted session key to the host device.

2. The electronic device according to claim 1, further comprising a first symmetric key generation unit that generates the first symmetric key to be shared with the host device using the private key of the public key pair that the electronic device possesses and the public key of the public key pair that the host device possesses.

3. The electronic device according to claim 1, wherein all electronic devices that establish a session with the host device have a second common key in advance.

4. The electronic device according to claim 3, wherein the encryption processing unit encrypts the session key with the second common key.

5. The electronic device according to claim 3, further comprising a temporary key generation unit that generates a temporary key using the random number transmitted from the host device and the second common key.

6. The electronic device according to claim 5, wherein the encryption processing unit encrypts the session key using the temporary key.

7. A host device comprising: a session key generation unit that generates a session key for establishing a session with another electronic device other than a specific electronic device that is one of a plurality of electronic devices; and a communication unit that transmits the encrypted session key to the specific electronic device, receives the encrypted and transmitted session key from the specific electronic device, and transmits the received session key to the other electronic device.

8. The host device according to claim 7, further comprising an encryption processing unit that encrypts the session key using a first common key shared with the specific electronic device.

9. The host device according to claim 8, further comprising a first symmetric key generation unit that generates the first symmetric key using the private key of the public key pair that the host device possesses and the public key of the public key pair that the specific electronic device possesses.

10. The host device according to claim 7, wherein the session key is encrypted by the specific electronic device using a second common key that is shared in advance by the plurality of electronic devices.

11. The host device according to claim 7, wherein the session key encrypted by the specific electronic device is decrypted by the other electronic device using a second common key shared in advance by the plurality of electronic devices.

12. The host device according to claim 7, which acquires a random number generated by the other electronic device and transmits the random number to the specific electronic device.

13. The host device according to claim 7, wherein a session with the specific electronic device is established using a public key system, and a session with the other electronic device is established using a common key system.

14. An electronic device system comprising: a host device comprising: a session key generation unit that generates a session key for establishing a session with another electronic device other than a specific electronic device that is one of a plurality of electronic devices; and a communication unit that transmits the encrypted session key to the specific electronic device, receives the encrypted and transmitted session key from the specific electronic device, and transmits the received session key to the other electronic device; and the specific electronic device comprising: a decryption processing unit that decrypts the encrypted session key transmitted from the host device using a first common key; an encryption processing unit that encrypts the decrypted session key; and a communication unit that transmits the encrypted session key to the host device.

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