Method and communication system for message monitoring in a data network of a motor vehicle and transmission and receiving unit for the communication system

Abstract

The invention relates to a method for operating a motor vehicle (10), wherein in the motor vehicle (10) a plurality of data messages (19) are sent by way of a transmission unit (14) via a data network (12) to a receiving unit (16) and at least some of the sent data messages (19) are received by the receiving unit (16) and a request message (28) is sent by the receiving unit (16) to the transmission unit for authentication, and in response to the request message (28) common transmitter-side check information (26) is generated by the transmission unit (14) from stored payload data (22), which were also contained distributed over the various sent data messages (19), and is sent, in an authentication message (A), to the receiving unit (16). According to the invention, by means of the request message (28) a selection command (31) is specified that selects the data messages (19) to be used to generate the transmitter-side check information (26), and the transmitter-side check information (26) is generated from the selected data messages (19) in accordance with the selection command (31).

Description

[0001] Method and communication system for message monitoring in a data network of a motor vehicle and transmitting and receiving unit for the communication system

[0002] DESCRIPTION:

[0003] The invention relates to a method for operating a motor vehicle, in which a transmitting unit transmits data messages one after the other via a data network to a receiving unit. The transmitting unit and the receiving unit can each be, for example, a control unit of the motor vehicle. The receiving unit receives the data messages (or at least some of them) and must then check whether the transmitting unit is an authentic device of the motor vehicle and not a subsequently installed, unauthorized device, such as might be used, for example, in a tuning measure. The invention also includes the communication system of the motor vehicle with the transmitting unit, the data network, and the receiving unit. The transmitting unit and the receiving unit each also form aspects of the invention.

[0004] A transmitting unit, such as a control unit of a motor vehicle, and a corresponding receiving unit, such as another control unit, can exchange data messages via a data network in which, for example, current measured values ​​and / or status values ​​are signaled from the transmitting unit to the receiving unit. In order to be able to manufacture such control units, i.e. transmitting units and receiving units in general, cost-effectively, they are equipped with just enough computing power to fulfill the respective functionality without excess resources. An additional task of control units used as transmitting units or receiving units is to verify the data messages to ensure that they originate from an authentic transmitting unit that is intended for the operation of the motor vehicle.It may happen that data messages are instead fed into the data network from another message source, i.e. an unauthorized or subsequently installed data source.

[0005] This could, for example, deceive an engine control unit into delivering more power. Verifying the authenticity of a transmitting unit by a receiving unit should be implemented in a motor vehicle without requiring additional, complex computing resources. Therefore, there is an interest in providing efficient or resource-saving algorithms to fulfill this functionality.

[0006] One approach for this is known from DE 10 2018 220 324 A1. Accordingly, to monitor data traffic in a data network with regard to the authenticity of the devices involved, a monitoring device can request the transmitting unit and the receiving unit to generate information from transmitted messages and received messages, respectively, which the monitoring device can use to verify the authenticity. The data network can be a CAN bus (CAN - Controller Area Network).

[0007] In this context, it is known from WO 2020 / 015940 A1 that in order to authenticate messages, i.e. to prove the authenticity of the sender, a MAC - Message Authentication Code can be generated, which can be based on a so-called SHE - Secure Hardware Extension, i.e. an electronic circuit addition of the respective control unit.

[0008] Regarding the frequency of checking authenticity, the DE

[0009] 10 2020 113 451 A1 discloses that the number of data messages per time interval should be greater than the frequency with which authentication information is requested. This results in a shorter cycle time for the data messages than for the authentication information. Each piece of authentication information can be based on the content or data of multiple data messages in order to still be able to authenticate all data messages received at the receiving unit. For example, the data from multiple data messages can be calculated or combined to form a hash value or checksum.

[0010] The calculation of hash values ​​from data messages is described in DE 10 2019 217 808 A1. It also describes the encryption of data messages based on a PKI (Public Key Infrastructure), i.e., asymmetric cryptographic encryption.

[0011] However, if a receiving unit cannot verify the authenticity of a sending unit for each data message separately or individually, but instead performs the verification of multiple data messages in combination, for example, by calculating a hash value from the data of multiple data messages and this is intended to represent the verification information for multiple data messages in combination, such a method is susceptible to message loss or packet loss. If the receiving unit calculates the hash value for the data from the last N received data messages on its side, and the sending unit also calculates the hash value for the data from the last N transmitted data messages on the sending side, these two hash values ​​will be based on different data messages in the event of a packet loss, which will lead to a discrepancy in the hash values.

[0012] Furthermore, the subsequently published document DE 10 2021 117 324 A1 reports a method similar to that of the invention. This also addresses the problem that data from a transmitting unit must be verified by a receiving unit, which leads to high latency with a current method in which the verification information is transmitted with the data. For this reason, this document proposes that data verification only takes place in the course of a verification request via a verification response.

[0013] The invention is based on the object of providing an authentication method for a communication system of a motor vehicle which is robust against packet loss, i.e. the loss of individual data messages during transmission from transmitting unit to receiving unit.

[0014] The problem is solved by the subject matter of the independent patent claims. Advantageous further developments are described by the dependent patent claims, the following description, and the figures.

[0015] As one solution, the invention comprises a method for operating a motor vehicle, i.e. the method can be carried out in the motor vehicle. The method is based on the fact that in the motor vehicle, a transmitting unit, for example a control unit (transmitting control unit) or a sensor circuit, successively transmits several data messages via a data network, for example a data bus or an Ethernet network, to a receiving unit, i.e. for example another control unit (receiving control unit). These data messages can, for example, be transmitted cyclically. They can, for example, be data messages containing current measured values ​​and / or status values ​​of the transmitting unit and / or another vehicle component connected to the transmitting unit.

[0016] Accordingly, the receiving units receive the transmitted data messages. However, it cannot be assumed that all data messages will be received; in the case of packet loss (message loss), only some of the transmitted data messages will be received. This is referred to as "packet loss" because data messages are transmitted in data packets over a data network.

[0017] The receiving unit must now also be able to use the received data to determine the correct

[0018] To be able to verify data messages to determine whether the sending unit is authentic or whether all received data messages actually originate from the sending unit and thus represent authentic data messages. To ensure this can be done with minimal resource consumption in terms of the required computing power, the receiving unit does not check each received data message individually. Instead, the receiving unit only sends a request message for authentication to the sending unit upon detection of a predefined trigger event. Thus, between each trigger event, multiple data messages can be received or at least sent by the sending unit.

[0019] The transmitting unit receives this request message, and in response to the request message, the transmitting unit generates a first or sender-side verification information from stored "payload data" and transmits it to the receiving unit in an authentication message. This "payload data" refers to data or content that was also contained in the transmitted or sent data messages. The payload data is therefore a copy of the data that was also distributed across the various sent data messages. In other words, a portion of the payload data was contained in each of the data messages, so that the complete payload data can only be obtained if the complete underlying data messages are also known.A distinction is made here between the data messages themselves and the payload data, since as an alternative to storing entire data messages or entire payloads of data messages, it can also be provided that the payload data does not represent the complete data message or the complete so-called payload (message data), but only a part of it, for example the data part that is worth protecting or to be authenticated.

[0020] In order to prevent the receiving unit from using payload data from different data messages than the one used in the sending unit, for example because a data message was sent by the sending unit but was never received by the receiving unit due to packet loss or message loss, the following is provided. After transmission, the sending unit keeps a copy of the payload data contained in the transmitted data messages in a local data memory of the sending unit. “Local” means that it is contained in the sending unit or in a data memory connected to it, and therefore not in the receiving unit. The data memory can, for example, be a ring buffer which can store the payload data of a predetermined number of the most recently transmitted data messages.

[0021] The receiving unit specifies a selection command via the request message, i.e., the request message contains a selection command that selects the data messages to be used to generate the sender-side check information. The receiving unit uses the selection command in the request message to identify which data messages the payload from the local data memory of the transmitting unit is to be used to calculate or generate the check information. The check information can be written into a check data record. It can digitally represent, for example, a hash value or a checksum of the selected payload data. This sender-side check information is generated by the transmitting unit from the stored payload of the selected data messages in accordance with the selection command.In other words, when generating the check information, the transmitting unit only accesses those payload data in its local data memory that belong to those data messages that were selected by the receiving unit using the selection command.

[0022] The receiving unit, for its part, can store the received data messages in a local data memory of the receiving unit, thus also providing it with the payload from the received data messages for calculating a second, or receiver-side, check information item for the receiving unit. If the receiving unit, for its part, calculates receiver-side check information from received data messages by extracting corresponding payload data from the received messages and generating the receiver-side check information from it, the receiving unit can use the selection command to inform or instruct the transmitting unit which of the data messages are to be used for the transmitting unit's sender-side check information, namely those that are used by the receiving unit itself for the receiver-side check information.This ensures that the sender-side test information is generated by the transmitting unit and the receiver-side test information is generated by the receiving unit based on payload data that is based exclusively on successfully transmitted data messages. This allows identical test data sets or identical test information to be generated in the transmitting unit and the receiving unit (if the same algorithm is used to generate the sender-side and receiver-side test information).

[0023] The invention provides the advantage of ensuring that the transmitting unit generates its transmitter-side verification information only based on payload data from those transmitted data messages that have also been successfully received by the receiving unit. This prevents the transmitting unit from calculating transmitter-side verification information, for example, the hash value described above, based on data messages of which one or some have not been received or are not present in the receiving unit.If the receiving unit were to then generate receiver-side verification information based only on the received data messages (without knowledge of lost or unsuccessfully transmitted data messages), a discrepancy would arise between the sender-side verification information from the transmitting unit, as transmitted in the authentication message to the receiving unit, and the receiver-side verification information calculated locally in the receiving unit, even if all received data messages should actually be recognized as authentic because they originate from the transmitting unit. This scenario is now prevented.

[0024] The following describes further developments that provide additional benefits.

[0025] According to a further development, the transmitting unit assigns a consecutive identification number and / or a memory location number of the transmitting unit's data memory / or a timestamp of the time of creation or transmission to the data messages it transmits as an identification feature. The memory location number can, for example, be a memory address or a memory field in which the payload data that is also contained in the corresponding data message is stored. The request message sent by the receiving unit explicitly specifies the respective identification feature of all data messages to be used for the sender-side check information. In other words, the receiving unit lists the data messages from which the payload data is to be used to calculate the sender-side check information.Specifying all identification features of the data messages to be used or their payload has the advantage that a continuous series of data messages (i.e., a sequence of data messages without packet loss or message loss) is not necessary; instead, a failure of a data packet can be compensated for by "skipping" this data message. Alternatively, the receiving unit can specify the identification feature of only a first of the data messages in the request message. A corresponding calculation algorithm can be provided in the transmitting unit, which, based on this first data message, calculates or derives the identification features of the remaining data messages to be used or their payload to be used.By using only a single identification feature of the first of the data messages to be used, the advantage is that the request message only has the data requirement or storage requirement or transmission requirement of a single identification feature and is therefore resource-efficient.

[0026] In the event that the request message specifies only the identification feature of the first of the data messages to be used, from which the sender-side check information is to be calculated, a further development provides for the transmitting unit to determine the identification features of the remaining data messages to be used from the identification feature contained in the request message using a predefined calculation algorithm. For example, it is only necessary to specify the starting number in the data memory of the transmitting unit, and the calculation algorithm can then be used to derive or calculate the remaining identification features, thus identifying the remaining data messages whose payload is to be used as the basis for calculating the sender-side check information.In the event that a ring buffer is used as data storage in the transmitting unit, a modulo operation can of course be implemented in the calculation algorithm in order to jump back to the beginning of the ring buffer when the end is reached and to determine the payload of further messages there.

[0027] In order to be able to use a sequence of continuously transmitted and successfully received data messages for calculating the sender's verification information, a further development provides for the transmitting unit to transmit the respective identification feature in the transmitted data messages in the manner described, and for the receiving unit to check whether a sequence of continuous identification features results in the received data messages. In other words, the receiving unit knows the scheme or rule according to which continuous data messages receive their identification feature, for example, as a consecutive counter number or as a position in the aforementioned ring buffer.Accordingly, the data message can be used to check whether the received data messages contain a sequence of consecutive identification features, i.e., whether there is no packet loss or message loss in the data network. If this is detected or recognized in the receiving unit, it can generate the trigger event; i.e., if the sequence is present or recognized, the request message is generated based on this sequence. It is then possible to specify only the identification feature of the first of the data messages to be used, since the sequence of data messages can then be used in the transmitting unit to calculate the sender's check information, ensuring that the entire sequence has been received or is present in the receiving unit.

[0028] As already explained, the entire data message does not have to be used to calculate the check information. Instead, a fraction or part of the data message can be used for the check information, which is referred to here as the payload of the data message. This can, for example, be the so-called payload or just a part of the payload.

[0029] As described, according to a further development, the receiving unit preferably generates receiver-side verification information from the payload contained in the selected received data messages. This means that the calculation of the verification information is replicated or also performed in the receiving unit. For this purpose, the receiving unit can, of course, use the same algorithm as in the transmitting unit, so that the same verification information, for example, the same hash value or the same checksum, must result as in the transmitting unit if the data messages are authentic, i.e., they actually originate from the transmitting unit and / or have remained unmanipulated or tamper-free during transmission over the data network.The receiving unit then compares the receiver-side verification information with the sender-side verification information from the authentication message. Only if a match is detected between the sender-side and the receiver-side verification information are the received data messages signaled as authentic with regard to their origin from the transmitting unit and / or their authenticity. Otherwise, a protective measure can be initiated, which may, for example, include discarding the received data messages. Additionally or alternatively, a signal can be stored in an error memory of the motor vehicle indicating that non-authentic data messages were present in the data network.

[0030] In order to prevent the sender-side verification information in the transmitted authentication message from being manipulated during transmission in the event of manipulation within the data network, and thus to conceal or mask the manipulation from the receiving unit, a further development provides for the sender-side verification information to be generated by the transmitting unit and the receiver-side verification information to be generated by the receiving unit, each by applying a cryptographic protection function, e.g. an encryption function and / or signature function, using a common cryptographic key.The transmitting unit applies cryptographic encryption and / or signature with a cryptographic key to the sender-side verification information, and the receiving unit applies the same cryptographic encryption / signature with this key to the receiver-side verification information it has calculated. This means that a copy of this key is present in both the transmitting unit and the receiving unit. The comparison of the transmitting and receiving verification information is then performed in the receiving unit by comparing the cryptographically encrypted and / or signed verification information. If the transmitting and receiving verification information are identical, their cryptographically encrypted / signed versions are also identical.Comparing the cryptographically encrypted / signed verification information has the advantage that the transmitting unit can transmit its sender-side verification information in a cryptographically secured manner in the authentication message over the data network, thus making manipulation of the sender-side verification information in the data network impossible without the cryptographic key, or at least only possible with disproportionate effort.

[0031] As already explained, it is specifically intended that the payload comprise only a portion of a payload of data messages, with the remaining portion of the payload being reused without being checked. This allows the storage requirements in the data memory, for example, in the aforementioned ring buffer, to be kept to a minimum. The payload used to calculate the check information can also be referred to as safety data. It can, for example, include a measured value or a signal value from driving functions that may be necessary for ferry operation (i.e., not, for example, for the operation of an infotainment system), such as an engine speed, to name just one example.

[0032] The respective test information can be calculated as a hash value of the payload data and / or (for example in the case of measured values) as an average of measured values ​​described by the payload data.

[0033] According to a further development, the receiving unit additionally sends a test value in its request message, which can in particular be a random number, such as one generated by a TRNG (True Random Number Generator), i.e., a hardware circuit for random numbers. The transmitting unit incorporates this test value when generating the sender-side verification information. For example, the test value can be included, considered, or used as additional "payload data," i.e., as an additional payload data set, for example, when calculating the aforementioned hash value or mean value. Of course, this test value is also incorporated in the same way in the receiving unit when calculating the described receiver-side verification information.The advantage of using such a test value is that it is impossible to conceal manipulated data messages, for example, by a hacker reading and storing authentication messages in the data network and feeding an old authentication message into the data network as a response to a current request message, thereby simulating authentic data messages to the receiving unit. If different test values ​​are used in the request messages, different verification information must also be generated on the sender side in the sending unit, so that old authentication messages cannot be used for a so-called replay attack.

[0034] For use cases or application situations that may arise during the method and which are not explicitly described here, it may be provided that, in accordance with the method, an error message and / or a request to enter user feedback is issued and / or a default setting and / or a predetermined initial state is set.

[0035] By providing the transmitting unit, the receiving unit, and the data network, a communication system for a motor vehicle is obtained, which is also considered a component of the invention. The communication system comprises the data network, for example, a data bus such as a CAN bus, and / or an Ethernet network, as well as the described transmitting unit for transmitting multiple data messages via the data network and the receiving unit for receiving the data messages from the data network. The transmitting unit and the receiving unit can each be configured as a control unit (i.e., a transmitting control unit and a receiving control unit). The transmitting unit can, for example, represent a control unit of a sensor circuit, to name just one example. The receiving unit can, for example, be a central computer of the motor vehicle or a control unit for a driver assistance function, to name just a few examples.The data network can also be a hybrid network with several different network technologies, for example, Ethernet and CAN bus. In the manner described, the communication system is configured to perform the steps of an embodiment of the method according to the invention, i.e., the steps to be performed by the transmitting unit and the receiving unit, respectively.

[0036] The described transmitting unit also represents an independent part of the invention for the communication system, wherein the transmitting unit has a processor circuit which is configured to carry out those steps of an embodiment of the method according to the invention which are provided for the transmitting unit, as has been described.

[0037] The receiving unit for the communication system also represents an independent part of the invention, wherein the receiving unit has a processor circuit which is designed to carry out those steps of an embodiment of the method according to the invention which are provided in the receiving unit in the manner described.

[0038] The transmitting unit and the receiving unit can each have a processor circuit for carrying out the described steps. For this purpose, the processor circuit can have at least one microprocessor and / or at least one microcontroller and / or at least one FPGA (Field Programmable Gate Array) and / or at least one DSP (Digital Signal Processor). Furthermore, the processor circuit can have program code which, when executed by the processor circuit, is configured to carry out the embodiment of the method according to the invention. The program code can be stored in a data memory of the processor circuit. A processor circuit of the processor circuit can, for example, have at least one circuit board and / or at least one SoC (System on Chip).

[0039] Finally, the invention also provides a motor vehicle having an embodiment of the communication system according to the invention. The motor vehicle according to the invention is preferably designed as a motor vehicle, in particular as a passenger car or truck, or as a passenger bus or motorcycle.

[0040] The invention also encompasses combinations of the features of the described embodiments. The invention therefore also encompasses implementations that each comprise a combination of the features of several of the described embodiments, unless the embodiments are described as mutually exclusive.

[0041] Exemplary embodiments of the invention are described below. The single figure shows:

[0042] Fig. a schematic representation of an embodiment of the motor vehicle according to the invention.

[0043] The exemplary embodiments explained below are preferred embodiments of the invention. In the exemplary embodiments, the described components of the embodiments each represent individual features of the invention that can be considered independently of one another, each of which also develops the invention independently of one another. Therefore, the disclosure is intended to encompass combinations of the features of the embodiments other than those illustrated. Furthermore, the described embodiments can also be supplemented by further features of the invention already described. In the figure, the same reference numerals designate functionally equivalent elements.

[0044] The figure shows a motor vehicle 10, which may be a motor vehicle, in particular a passenger car or a truck. A communication system 11 may be arranged in the motor vehicle 10, which may have a data network 12, via which at least one transmission control unit 13 as a transmission unit 14 can be connected to a reception control unit 15 as a reception unit 16 for exchanging or transmitting data. By way of example, it is stated here that a data message is sent every 10 milliseconds in this example. The data network 12 may, for example, comprise an Ethernet and / or a CAN bus, and the transmission unit 14 and the reception unit 16 can each be connected to the data network 12 in a manner known per se.

[0045] The transmitting unit 14 can, for example, have a sensor 17 or be coupled thereto and, for example, transmit measurement data 18 of the sensor 17 regularly or cyclically in a respective data message 19 via the data network 12 to the receiving unit 16, where, on the basis of message data or signal data 20 from the respective data message 19, a device functionality 21 of the receiving unit 16 can be operated, for example an automated driving function, to name just one example.However, it must be ensured in the receiving unit 16 that the data messages 19 used or received actually contain signal data 20 from a transmitting unit 14 authorized, for example, by a manufacturer of the motor vehicle 10, and not, for example, manipulated signal data from a subsequently installed transmitting unit, for example, a tuning kit, and / or signal data 20 that were falsified or manipulated during transmission via the data network 12. In order to verify the authenticity of received data messages 19 in the receiving unit 16 with regard to their origin and / or authenticity from the transmitting unit 14, the following method can be provided. In a step S10, the receiving unit 16 can store a predetermined portion of the received data messages 19, referred to here as payload data 22 (DS), in a data memory 23 of the receiving unit.The data memory 23 can be a ring buffer in which the new payload data 22 (DS) are stored cyclically. This results in a storage position 24 in the data memory 23 for each stored payload data, for example, a position in the ring buffer. Overall, the figure shows, by way of example, that the data memory 23 can accommodate a storage capacity of N data entries or payload data 22 from a corresponding total of N data messages 19.

[0046] When sending the data messages 19, the payload portion, i.e., the payload data 22 (DS), can also be stored in a data memory 23 of the transmitting unit 14, resulting in a corresponding storage position C. In the respective data message 19, the storage position C can also be included as a data component of the data message 19, as shown in the figure.

[0047] A data message 19 is referred to here as a message intended for transmitting the described signal data 20 from the transmitting unit 14 to the receiving unit 16. In contrast, an authentication message A can be provided, which can include an authentication credential in the form of sender-side verification information 26 for several transmitted data messages 19. For example, as shown in the figure, an authentication message A can be provided every 100 milliseconds.

[0048] For this purpose, a corresponding triggering event E can be provided in a step S11, for example a timer or the recognition that, according to an identification feature 27 contained in the respective data message 19, for example the storage position value C, a continuous sequence of data messages 19 was received, i.e., without message loss, and thus the payload 22 from a consecutive data message 19 received without data loss (i.e., without a missing data message in the sequence) is present in the data memory 23 of the receiving unit 16. A request message 28 can then be sent from the receiving unit 16 to the transmitting unit 14, requesting the generation of an authentication message A. The request message 28 can, for example, contain a test value 30, for example, a random number.The request message 28 may contain a selection command 31 which specifies which payload data 22 in the data memory 25 are to be generated or used by the transmitting unit 14 to generate the check information 26.

[0049] The selected payload data 22, i.e., the payload data 22 from the correspondingly selected data messages 19, as successfully received by the receiving unit 16 and represented by corresponding payload data 22 in the data memory 23, can be combined or calculated in a step S12, for example, to form a hash value or average value 34. Furthermore, the test value 30, for example, the random number RND, from the receiving unit 16 is preferably also included using an algorithm 35. A cryptographic key 36 is preferably also used to generate the verification information 26 as an encrypted value and / or signed value. The figure illustrates, by way of example, that the verification information can be based on a SipHash, i.e., an 8-byte hash value, but this is only an example. This results in a MAC (Message Authentication Code) as the authentication message A.The authentication message A can be received by the receiving unit 16. The payload 22 selected by the receiving unit 16, which was also selected in the transmitting unit 14 using the selection command 31 and taken from the data memory 25, can be correspondingly taken from the data memory 23 in the receiving unit 16, and a check value, for example, an average value 34', can also be calculated. In the receiving unit 16, the test value 30 and the cryptographic key 36 can also be calculated in the same way as in the transmitting unit 14 using the algorithm 35, which is implemented accordingly in both the transmitting unit and the receiving unit. This results in a receiver-side check information 40.

[0050] The calculation of this receiver-side verification information 40 represents a step S14. In a step S15, the transmitter-side verification information 26 from the received authentication message A and the receiver-side verification information 40 from the receiver-side verification information 40 generated from the payload data 22 taken from the data memory can be compared. If a match is found, the received data messages 19 can be confirmed as authentic with regard to their origin and / or their authenticity by the transmitter unit 14 in a confirmation signal 41.If, however, a difference or discrepancy arises, a protective measure 42 can be used to signal that at least one of the received data messages 19 is not authentic. For example, as a protective measure 42, the received data messages 19 (more precisely, all of them in the last large cycle covered by the test information, 100 ms in the example) can be discarded or deleted, or not used for the device functionality 21. Additionally or alternatively, as a protective measure 42, a warning message 43 can be generated, for example, and stored, for example, in an error memory of the motor vehicle 10 (error memory not shown), so that this event can be recognized during a later workshop visit.

[0051] Thus, a common piece of verification information 26 may be sufficient for verifying the authenticity of multiple data messages 19. Thus, fewer authentication messages A are required than data messages 19. Furthermore, the described algorithm can be implemented with minimal computing resources in a transmitting unit 14 and a receiving unit 16. By using only some of the signal data 20 as payload data 22, only a small amount of storage space is required to implement the data memories 23, 25.

[0052] Data transmission in the vehicle network or data network 12 can thus be used even in situations with increased attack potential. For example, route information or data for activating paid functions can be transmitted in a tamper-proof manner. Additionally, signal data from sensors (especially for monitoring the functioning of internal combustion engines) that could potentially be manipulated for tuning purposes can be protected.

[0053] To protect such payload data 22 that must be protected against manipulation, the described steps can be implemented in a microcontroller for sensors. Nevertheless, due to the low resource requirements for processing the actual sensors and converting them to a network protocol (typically CAN), sufficient computing power remains. The use of powerful encryption methods is not necessary due to the low computing power of the microcontrollers used. The described cryptographic key can be used, for example, for encryption (signing) according to the AES (Advanced Encryption Standard) and / or SipHash, as mentioned above.

[0054] To reduce the computational load on the sensor side (generally the transmitting unit 14), a method is proposed that avoids these disadvantages. The basic idea is as follows:

[0055] • to apply a cryptographic operation only to a “summary” of the data that is actually to be protected and

[0056] • to send the resulting check information (e.g. hash values) with a longer cycle time than the data message actually to be sent.

[0057] This can provide the following benefits: • Detection of manipulation of the transmitted data that is worthy of protection,

[0058] • less computing effort in the transmitter control unit, only a slight increase in the bus load and

[0059] • simple synchronization between transmitter and receiver by sending the identification feature 27 in the associated data message 19.

[0060] The presented idea meets the requirements for the transmission from a sensor control unit (low computing power, generally transmitting unit 14) to a receiver control unit (sufficient computing power, generally receiving unit 16).

[0061] Of the data to be transmitted by the sensor (generally transmitting unit 14), only a small portion is truly worthy of protection (e.g., 1 or 2 bytes out of 8 bytes, generally payload data DS). Additionally, with each message containing this protected payload data DS, a timestamp or storage position value / counter C is transmitted as an identification feature.

[0062] Possible configurations:

[0063] • The receiver of the messages has a TRNG to generate a test value,

[0064] • both transmitter and receiver are at least able to calculate a cryptographic protection function with a key 36, whereby both transmitter and receiver have the symmetric key 36 (optimally vehicle-specific).

[0065] The counter C is circulating when a respective ring buffer is used as data storage 23, 25.

[0066] A ring buffer of size N is created on both the sender and receiver sides. The sender stores the payload data and the associated timestamp (generally, identification feature 27 of the data message 19) in the ring buffer or data memory 25. The position in the ring buffer correlates with the counter C. The receiver does the same with received data messages.

[0067] To establish regular security, after a short start-up phase of the receiver, a verification request is sent regularly with a specified cycle time (longer than the cycle time of the actual signal message). Technically, this is a challenge (request message), for example, with a test value (e.g., a random number from the TRNG). This challenge also contains, for example, the so-called counter position as a selection command. This counter position can represent a pointer to the ring buffer for both participants in the communication.

[0068] In the next calculation step, an average value (or a hash value or another summary value) is calculated on both sides from a specified number M (M < N), starting from this counter position. This verification information is used to calculate a cryptographic protection function (plus key 36 and the test value 30 from the request message).

[0069] This calculated value of the cryptographic protection function is transmitted and can be compared on the receiving side with the receiver-side verification information.

[0070] Overall, the examples show how message monitoring can be provided in a motor vehicle.

Claims

PATENT CLAIMS:

1. A method for operating a motor vehicle (10), wherein in the motor vehicle (10) a plurality of data messages (19) are transmitted by a transmitting unit (14) via a data network (12) to a receiving unit (16), and at least some of the transmitted data messages (19) are received by the receiving unit (16), and a request message (28) for authentication is transmitted to the transmitting unit (14) by the receiving unit (16), and in response to the request message (28), the transmitting unit (14) generates a common transmitter-side check information (26) from stored user data (22), which was also distributed among the various transmitted data messages (19), and transmits it to the receiving unit (16) in an authentication message (A), characterized in thatthat the transmitting unit (14) keeps a copy of the payload data (22) contained in the transmitted data messages (19) in a data memory (25) of the transmitting unit (14) after transmission, and the receiving unit (16) uses the request message (28) to specify a selection command (31) which selects the data messages (19) to be used to generate the transmitter-side check information (26), which is a predetermined portion of the received data messages, and the transmitter-side check information (26) is generated by the transmitting unit (14) according to the selection command (31) from the stored payload data (22) of the selected data messages (19).

2. Method according to claim 1, wherein the transmitting unit (14) assigns a consecutive identification number and / or a storage position number of the data memory (25) of the transmitting unit (14) and / or a time stamp as an identification feature (27) to the transmitted data messages (19) and by the The receiving unit (16) specifies in the request message (28) the respective identification feature (27) of all data messages (19) to be used or the identification feature (27) of a first of the data messages (19) to be used for generating the sender-side check information (26). The method according to claim 2, wherein the request message (28) specifies the identification feature (27) of only the first of the data messages (19) to be used, and the transmitting unit determines the identification features (27) of the remaining data messages (19) to be used from the identification feature (27) contained in the request message (28) using a predetermined calculation algorithm (35).Method according to claim 2 or 3, wherein the transmitting unit (14) transmits the respective identification feature (27) in the transmitted data messages (19), and the receiving unit (16) checks whether a sequence of consecutive identification features (27) results in the received data messages (19), and the recognition of the sequence represents the trigger event (E), and the request message (28) is generated based on the sequence. Method according to one of the preceding claims, wherein the receiving unit (16) generates receiver-side check information (40) from the payload data (22) contained in the selected received data messages (19) and compares it with the sender-side check information (26) from the authentication message (A), and the received data messages (19) are only signaled as authentic if a match is detected between the sender-side and receiver-side check information (40).Method according to claim 5, wherein the transmitter-side test information (26) is transmitted by the transmitting unit (14) and the receiver unit (16). the receiver-side verification information (40) is generated by applying a cryptographic protection function using a common cryptographic key (36), and the cryptographically encrypted and / or signed verification information is compared. Method according to one of the preceding claims, wherein the payload (22) comprises only a portion of a payload of the data messages (19), and a remaining portion of the payload is reused without verification. Method according to one of the preceding claims, wherein the respective verification information is calculated as a hash value of the payload (22) and / or as an average value of measured values ​​described by the payload (22).Method according to one of the preceding claims, wherein a test value (30), in particular a random number, is sent along with the request message (28) by the receiving unit (16), and the test value (30) is included by the transmitting unit (14) when generating the transmitter-side test information (26). Communication system for a motor vehicle (10), wherein the communication system comprises: a data network (12), a transmitting unit (14) for transmitting a plurality of data messages (19) via the data network (12), a receiving unit (16) for receiving the data messages (19) from the data network (12), wherein the communication system is configured to carry out the steps of a method according to one of the preceding claims. Transmitting unit (14) for a communication system according to claim 10, wherein the transmitting unit (14) has a processor circuit which. is configured to carry out the steps of a method according to one of claims 1 to 9 relating to the transmitting unit (14). Receiving unit (16) for a communication system according to claim 10, comprising a processor circuit configured to carry out the steps of a method according to one of claims 1 to 9 relating to the receiving unit (16). A motor vehicle (10) comprising a communication system according to claim 10.

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