Devices and methods for the generating and authentication of at least one data packet to be transmitted in a bus system (BU), in particular of a motor vehicle

1. A method for checking of authentication at a bus subscriber of at least one data packet received via a bus system of a motor vehicle, the at least one data packet having been generated by before transmitting the at least one data packet containing a message to be included in the at least one data packet, at a bus subscriber configured to transmit the at least one data packet, generating a message authentication code to be included in the data packet, using a first encryption apparatus, the generating of the message authentication code comprising:

generating an encrypted message code from the message using a first key and a first encryption method,

generating an encrypted count from a count using a second key and a second encryption method, and

generating using a logic operation the message authentication code to be transmitted from the encrypted message code and from the encrypted count;

the method comprising:

receiving at least one data packet;

generating an encrypted message code from the message contained in the received data packet using a first key and a first encryption method;

generating an intermediate value from the transmitted message authentication code contained in the received data packet and from the generated encrypted message code using a logic device,

generating a current received message count from the intermediate value using a decryption at a decryption device;

comparing the current received message count with a preceding received message count determined for a data packet received before the data packet;

defining the received data packet as authenticated or as unauthenticated based on a difference between the current received message count and the preceding received message count.

2. The method as claimed in claim 1 , wherein the count was either a value, generated using a counter, that

represented a number of messages transmitted and/or received via the bus system since the last restart of the bus system,

or a timer value, of at least one timer, available on multiple or all bus subscribers.

3. The method as claimed in claim 1 , wherein the message authentication code to be transmitted was generated from the encrypted message code and from the encrypted count using a logic “Exclusive-Or” operation.

4. The method as claimed in claim 1 , wherein the difference between the current received message count and the preceding received message count is a basis for defining the received data packet as authenticated or as unauthenticated

by regarding the received data packet as unauthenticated only if the difference is greater than one or greater than a threshold value,

the threshold value being set to a higher value after a restart of the bus system than in other normal operation.

5. The method as claimed in claim 1 , wherein a logic Exclusive-Or operation is used to generate an intermediate value from the transmitted message authentication code also contained in the received data packet and from the generated encrypted message code using a logic device.

6. The method as claimed in claim 1 , wherein a bus subscriber receiving a data packet and a bus subscriber transmitting a data packet use the same first encryption method and/or the same first key and/or the same second encryption method and/or the same second key.

7. The method as claimed in claim 1 , wherein a bus subscriber receiving a data packet and a bus subscriber transmitting a data packet, derive the second key from the result of the first encryption method.

8. The method as claimed in claim 1 , wherein a timer value representing time information relating to global time was securely distributed in a network from one subscriber to all other subscribers.

9. An apparatus for generating at least one data packet to be transmitted in a bus system a motor vehicle, the apparatus comprising:

a first encryption apparatus provided by a bus subscriber transmitting the data packet and configured to, before transmitting the at least one data packet,

generate a message authentication code to be included in the data packet to be transmitted, from the message to be included in the data packet,

wherein on the transmitting bus subscriber:

a first encryption device is configured to use a first encryption method to venerate an encrypted message code from the message by means of a first key,

a second encryption device configured to use a second encryption method to venerate an encrypted count from a count by means of a second key, and

a logic device is configured to generate the message authentication code from the encrypted message code and from the encrypted count using a logic operation;

the apparatus further configured to perform authentication checking of at least one data packet received via a bus system of a motor vehicle,

wherein on a bus subscriber receiving at least the data packet:

a first encryption device is configured to use a first encryption method to generate an encrypted message code from the message contained in the received data packet by means of a first key,

a logic device is configured to generate an intermediate value from the generated encrypted message code and from the message authentication code contained in the received data packet,

a decryption device is configured to determine a current received message count for a current data packet from the intermediate value,

a comparison apparatus is configured to define the received data packet as authenticated or as unauthenticated based on taking a difference between the current received message count and a preceding received message count determined for a data packet received before the data packet.

10. The apparatus as claimed in claim 9 , wherein

the bus system is a CAN bus or a CAN FD bus or a LIN bus or an SPI bus or an I2C bus and/or is provided for communication between ECUs.