METHOD FOR INTERNAL VEHICLE MANAGEMENT OF CRYPTOGRAPHIC KEYS

Description

[0001] The invention relates to a method for managing cryptographic keys in vehicles.

[0002] Furthermore, the invention relates to an in-vehicle communication system with a key generation device, a control unit and at least one control device.

[0003] Within vehicles, cryptographic keys are used to cryptographically secure the in-vehicle communication between different in-vehicle control devices and to cryptographically secure the integrity of the software of the in-vehicle control devices.

[0004] To maintain appropriate cryptographic security throughout a vehicle's lifetime, new cryptographic keys must be regularly generated and distributed within an in-vehicle communication system. In this context, the term "rekeying" has become established.

[0005] Various approaches are known for introducing new key material into an in-vehicle communication system. For example, cryptographic keys are imported directly into the in-vehicle communication system by a technician in a workshop using a test device. It is also known to send a command initiating key generation to a key-generating in-vehicle control device. This can be done, for example, by an authorized technician in a workshop or by a backend via a secure end-to-end connection to the vehicle. Furthermore, it is known to send key material directly from a backend to the vehicle via a secure end-to-end connection.

[0006] However, the existing solutions sometimes pose significant problems. When a technician loads key material or issues commands that initiate key generation, the vehicle must be physically available. This impairs the vehicle's use for the user. If rekeying is performed as part of regular vehicle maintenance, keys may be inactive for extended periods, making internal communication security difficult to guarantee. Furthermore, it cannot be ruled out that third parties may influence the workshop personnel involved in loading key material.

[0007] When transmitting key material or control commands that initiate key generation using a secure Internet connection, there is always a risk of compromise, so secure rekeying cannot be implemented in this way either.

[0008] DE 102015219989 A1 describes a refresh of a symmetric cryptographic key between a first node and a second node of a communication system. A trigger event initiates the refresh, with each node generating a secret bit sequence. The previous secret is combined with the bit sequence to form a second secret, which subsequently replaces the previous secret.

[0009] DE 102012209445 A1 describes a method for secure data transmission. A first and a second key are compared, and if they match, access to a client is established.

[0010] The object underlying the invention is therefore to increase security when generating and providing cryptographic keys for in-vehicle control devices.

[0011] The object underlying the invention is achieved by a method of the type mentioned at the outset, wherein, within the scope of the method according to the invention, at least one secret is provided to a vehicle-internal key generation device and at least one new cryptographic key is generated by the vehicle-internal key generation device on the basis of the at least one secret.

[0012] The invention leverages the insight that in-vehicle key generation eliminates the need for direct key input, for example, via technicians or a backend, thus eliminating the corresponding risk of compromise. The at least one secret to be introduced into the in-vehicle communication system cannot be used for key generation without knowledge of additional generation parameters, such as salt parameters or seed parameters. An attack directed at the provision process of the at least one secret is therefore unsuitable for compromising communication security within the vehicle. The security of the rekeying process is thus significantly increased.

[0013] The key generation device uses, for example, a key derivation function, such as PBKDF2, to generate the at least one key. The at least one secret can be, for example, a secret key, a password, or a passphrase. The at least one secret can, for example, be initially loaded into the key generation device and / or transmitted using a key exchange and / or key agreement method, such as Diffie-Hellman or Elgamal. Multiple secrets can also be provided to the in-vehicle key generation device. The key generation device can also generate multiple new cryptographic keys based on the one or more secrets.

[0014] The method according to the invention comprises providing the at least one new cryptographic key to at least one in-vehicle control device. Alternatively or additionally, the at least one new cryptographic key is used by the in-vehicle control device for cryptographic and / or non-cryptographic security measures. The at least one new cryptographic key can also be provided to or agreed upon by a plurality of in-vehicle control devices by means of a key distribution process, in particular using a key exchange algorithm, wherein the plurality of in-vehicle control devices can then use the at least one new cryptographic key for cryptographic and / or non-cryptographic security measures. The in-vehicle control device can be, for example, an Electronic Control Unit (ECU).A cryptographic security measure, for example, concerns the encryption of messages. A non-cryptographic security measure, for example, concerns the signing of messages. For example, one or more secrets are provided to the in-vehicle key generation device for each in-vehicle control device, so that device-specific cryptographic keys can be generated based on the respective secret or secrets assigned to the respective in-vehicle control devices.

[0015] Furthermore, the invention provides that the generation of the at least one new cryptographic key and / or the provision of the at least one new cryptographic key is triggered by a key exchange event or a combination of key exchange events and / or occurs automatically. The key exchange event can be a security incident, such as a firewall alarm, intrusion detection, a faulty identity check, or a certificate rule violation (false identity proof via own signed backend certificate). The key exchange event can be an environmental change, such as a change in position, a change in route, and / or the exceeding of physical limit parameters. Furthermore, the key exchange event can also be a timeout.The key exchange event can also be a vehicle internal change, which can be detected via anomaly detection.

[0016] The method according to the invention further comprises detecting the key exchange event by an in-vehicle control unit, wherein the control unit initiates the generation of the at least one new cryptographic key and / or the provision of the at least one new cryptographic key. The in-vehicle control unit thus functions, in particular, as a rekeying manager. Preferably, the method detects the detection of a key exchange event or a combination of key exchange events by the in-vehicle control unit. The key generation device and the control unit can be separate electronic modules or combined in a common electronic module.

[0017] In another embodiment of the method according to the invention, the control unit monitors the key generation performed by the key generation device and / or adapts the key generation performed by the key generation device. According to the invention, the control unit monitors the provision and / or distribution of new cryptographic keys to one or more control devices and / or adapts the provision and / or distribution of new cryptographic keys to one or more control devices. Because the control unit allows adaptation of the key generation and / or adaptation of the key distribution, the rekeying process can be dynamically changed. Preferably, the control unit specifies the secrets to be used for key generation to the key generation device.By changing the specification, it can be ensured that one or more secrets are no longer used for key generation, for example, after their compromise has been detected. Furthermore, the control unit of the key generation device can specify the parameters to be used in the key derivation function. By changing the parameters, new keys can thus be generated based on an unchanged secret.

[0018] In a preferred embodiment of the method according to the invention, key generation parameters are provided to a vehicle-external computer system, which allow the vehicle-external computer system to generate at least one cryptographic key used by an in-vehicle control device. Alternatively or additionally, the method comprises the generation of at least one cryptographic key used by an in-vehicle control device by the external computer system. The external computer system can, for example, be a backend operated by the vehicle manufacturer or a third-party provider. Providing the key generation parameters can, for example, comprise sending the key generation parameters from the in-vehicle communication system to the vehicle-external computer system, in particular using a secure internet connection.In particular, the vehicle-external computer system also knows the at least one secret that was provided to the vehicle-internal key generation device for key generation. Based on the provided key generation parameters and the at least one secret, the vehicle-external computer system is capable of generating corresponding cryptographic keys, which are also used within the vehicle-internal communication system.

[0019] Furthermore, a method according to the invention is advantageous in which authorization information is provided for the in-vehicle key generation device, and the generation of the at least one new cryptographic key by the in-vehicle key generation device is also carried out on the basis of the authorization information. The authorization information can also be referred to as credentials and can include, for example, a counter, token, and / or authorization credentials. In particular, the authorization information is provided to the key generation device by the control unit.

[0020] Preferably, a key generation device is provided, wherein the key generation device according to the invention has a computing unit configured to generate at least one new cryptographic key based on the at least one secret. The key generation device is preferably configured to be used in the method for in-vehicle management of cryptographic keys according to one of the embodiments described above. Regarding the advantages and modifications of the key generation device according to the invention, reference is made to the advantages and modifications of the method according to the invention for in-vehicle management of cryptographic keys.

[0021] The object underlying the invention is further achieved by an in-vehicle communication system of the type mentioned above, wherein the in-vehicle communication system is configured to implement the method for managing cryptographic keys in-vehicle according to one of the embodiments described above. Regarding the advantages and modifications of the in-vehicle communication system, reference is made to the advantages and modifications of the in-vehicle method for managing cryptographic keys in-vehicle.

[0022] Preferred embodiments of the invention are explained and described in more detail below with reference to the accompanying drawings. Fig. 1 shows an embodiment of the communication system according to the invention in a schematic representation; Fig. 2 shows a further embodiment of the communication system according to the invention in a schematic representation; Fig. 3 shows a further embodiment of the communication system according to the invention in a schematic representation; and Fig. 4 shows a schematic flow diagram of the method according to the invention.

[0023] According to the Fig. 1 The in-vehicle communication system 100 comprises a key generation device 10, a control unit 12 and several, namely three, control devices 18a-18c.

[0024] The key generation device 10 has a storage device for storing provided secrets 24a, 24b, wherein the secrets 24a, 24b can be, for example, secret keys, passwords, or passphrases. The secrets 24a, 24b can be provided to the key generation device 10, for example, by an initial upload during the implementation of the communication system 100 and / or subsequently using a key exchange and / or key agreement method, such as Diffie-Hellman or Elgamal.

[0025] Authorization information 22 is also provided to the key generation device 10 via the control unit 12. The authorization information 22 may also be referred to as "credentials" and may include, for example, a counter, a token, and / or credentials.

[0026] The key generation device 10 has a computing unit that generates cryptographic keys 26a, 26b based on the secrets 24a, 24b and the authorization information 22. The generated cryptographic keys 26a, 26b are provided to a plurality of in-vehicle control devices 18a-18c via a distribution device 14 using key exchange algorithms. In the illustrated embodiment, the key generation device 10 generates the cryptographic key 26a based on the secret 24a and the cryptographic key 26b based on the secret 24b. The cryptographic key 26a is provided to the in-vehicle control devices 18a, 18b. The cryptographic key 26b is provided to the in-vehicle control device 18c.

[0027] The vehicle-internal control devices 18a-18c are designed as electronic control units (ECUs) and use the provided cryptographic key 26a, 26b within the framework of cryptographic and non-cryptographic security measures 16a-16c, such as the encryption or signing of messages.

[0028] The generation of the cryptographic keys 26a, 26b and the provision of the generated cryptographic keys 26a, 26b are triggered by a key exchange event 20a-20c or a combination of key exchange events 20a-20c and occur automatically upon the occurrence of the key exchange event 20a-20c or upon the occurrence of the combination of key exchange events 20a-20c.

[0029] The key exchange event 20a-20c is detected by an in-vehicle control unit 12, so that the control unit 12 also initiates the generation of the new cryptographic keys 26a, 26b and the provision of the generated cryptographic keys 26a, 26b. Furthermore, the control unit 12 serves to monitor the key generation performed by the key generation device 10 and to adapt the key generation performed by the key generation device 10.

[0030] The key exchange event 20a-20c can be a vehicle internal change 20a, an environmental change 20b, or a security incident 20c. The vehicle internal change 20a can be detected by anomaly detection. The environmental change 20b can, for example, relate to a change in the vehicle's position, a change in the planned route, or the exceeding of physical limit parameters. Furthermore, the environmental change 20b can also relate to time-based changes or limits. The security event 20c can, for example, be a firewall alarm, intrusion detection, a faulty identity check, or a certificate rule violation (false identity proof via an own signed backend certificate).

[0031] The in-vehicle communication system 100 is further configured to provide key generation parameters to an external computer system 102, for example, via an internet connection. The key generation parameters allow the external computer system 102 to generate the cryptographic keys 26a, 26b used by the in-vehicle control devices 18a-18c. This allows the keys 26a, 26b generated internally to be generated even outside the vehicle.

[0032] The Fig. 2 The communication system 100 shown comprises two separate key generation devices 10a, 10b, wherein the key generation device 10a is a component of the in-vehicle control device 18a and the key generation device 10b is a component of the in-vehicle control device 18b. The secret 24 is provided to the key generation devices 10a, 10b, and the key generation devices 10a, 10b are configured to derive a cryptographic key based on the secret 24, which can be used directly by the respective control device 18a, 18b within the framework of security measures 16a, 16b.

[0033] The key generation devices 10a, 10b use, for example, a key derivation function to generate the respective keys. Due to the integration of the key generation devices 10a, 10b into the vehicle's internal control devices 18a, 18b, distribution of the generated keys is not necessary.

[0034] The Fig. 3 shows an in-vehicle communication system 100 in which two in-vehicle control devices 18a, 18b, each configured as an electronic control unit (ECU), exchange encrypted and signed messages 32a, 32b with each other. The messages 32a, 32b have an identifier 34, such as a cipher or a MAC tag. An intrusion detector 30 is used to detect attacks by external attackers 104.

[0035] The intrusion detector 30 can thus determine whether a security incident 20 has occurred that requires the regeneration of keys. Based on the detected security event 20, the control unit 12 initiates the generation and distribution of a new cryptographic key 26, which the control devices 18a, 18b can use for further communication with each other. In this way, the old key 28 is automatically replaced by the new key 26 at the control devices 18a, 18b, which is triggered by the detection of an external attack.

[0036] The Fig. 4 The flowchart shown shows an example of the method sequence 200 during the method for managing cryptographic keys in the vehicle.

[0037] In step 202, a message is encrypted and signed by an in-vehicle control device 18a. The message includes an identifier. In step 204, the message is sent to the in-vehicle control device 18b. The message addressed to the control device 18b is intercepted and tampered with by the attacker 104 in step 206. The tampering is detected by the in-vehicle intrusion detector 30 in step 208, and the tampered message is sent by the attacker 104 to the in-vehicle control device 18b in step 210.

[0038] In step 212, the intrusion detector informs the in-vehicle control unit 12 of the attack on the communication between the control device 18a and the control device 18b. Subsequently, in step 214, the control unit 12 identifies the cryptographic key used in the communication between the control device 18a and the control device 18b and initiates the generation of a new cryptographic key via a corresponding generation command, which is sent to the key generation device 10 in step 216. Furthermore, in step 218, a computer system external to the vehicle is informed that the cryptographic key previously used for communication between the control device 18a and the control device 18b is now invalid and that a new key is generated internally in the vehicle to replace the invalid key.

[0039] The key generation device 10 now uses a previously provided secret stored in a memory of the key generation device 10 to generate a new cryptographic key for securing the communication between the control device 18a and the control device 18b in step 220. Via a key distribution process, the generated cryptographic key is provided to the control device 18a in step 222 and to the control device 18b in step 224.

[0040] In step 228, the control device 18a replaces the previously used and now invalid cryptographic key with a newly generated cryptographic key provided by the key generation device 10. In step 226, the control device 18b replaces the previously used and now invalid cryptographic key with a newly generated cryptographic key provided by the key generation device 10. The communication between the control device 18a and the control device 18b is now secured using the newly generated cryptographic key.

[0041] The invention thus allows for automatic in-vehicle elimination of security gaps, which is initiated by the identification of a key exchange event and does not require any further action by an external technician or data exchange with an external computer system. List of reference symbols

[0042] 10, 10a, 10bKey generation devices 12Control unit 14Distribution device 16a-16cSecurity measures 18a-18cControl devices 20, 20a-20cKey exchange events 22Authorization information 24, 24a, 24bSecrets 26, 26a, 26bKey 28Old key 30Intrusion detector 32a, 32bMessages 34Labeling 100Communication system 102Computer system 104Attacker 200Procedure flow 202-228Procedure steps

Claims

1. Method for the vehicle-internal management of cryptographic keys, comprising the steps of: - providing at least one secret (24, 24a, 24b) for a vehicle-internal key generation device (10, 10a, 10b); and - generating at least one new cryptographic key (26, 26a, 26b) by means of the vehicle-internal key generation device (10, 10a, 10b) on the basis of the at least one secret (24, 24a, 24b), - providing the at least one new cryptographic key (26, 26a, 26b) for at least one vehicle-internal control device (18a-18c); - using the at least one new cryptographic key (26, 26a, 26b) by means of the vehicle-internal control device (18a-18c) in cryptographic and / or non-cryptographic security measures (16a-16c), wherein - the generation of the at least one new cryptographic key (26, 26a, 26b) and / or the provision of the at least one new cryptographic key (26, 26a, 26b) is triggered by a key-exchange event (20, 20a-20c) or a combination of key-exchange events (20, 20a-20c), and / or takes place automatically, and the method is characterized by further steps, wherein - the key-exchange event is captured by a vehicle-internal monitoring unit (12), wherein the monitoring unit (12) initiates the generation of the at least one new cryptographic key (26, 26a, 26b) and / or the provision of the at least one new cryptographic key (26, 26a, 26b), wherein the following further steps are carried out: - monitoring the provision and the distribution of new cryptographic keys (26, 26a, 26b) to one or more control devices (18a-18c) by means of the monitoring unit (12); - adapting the provision and the distribution of new cryptographic keys (26, 26a, 26b) to one or more control devices (18a-18c) by means of the monitoring unit (12).

2. Method according to Claim 1, characterized by at least one of the following steps: - monitoring the key generation carried out by the key generation device (10, 10a, 10b) by means of the monitoring unit (12); - adapting the key generation carried out by the key generation device (10, 10a, 10b) by means of the monitoring unit (12).

3. Method according to one of the preceding claims, characterized by the step of: - providing authorization information (22) for the vehicle-internal key generation device (10, 10a, 10b); wherein the at least one new cryptographic key (26, 26a, 26b) is also generated by the vehicle-internal key generation device (10, 10a, 10b) on the basis of the authorization information (22).

4. Vehicle-internal communication system (100), with - a key generation device (10, 10a, 10b), - a monitoring unit (12), and - at least one control device (18a-18c), characterized in that the communication system (100) is configured to carry out the method for the vehicle-internal management of cryptographic keys (26, 26a, 26b) according to one of Claims 1 to 3.