Communications method for at least two system components of a motor vehicle
In a communications system for at least two system components over a network connection, e.g., a CAN bus system of a motor vehicle, system components have ready in each case a prespecified, fixed number of test codes known only to them. Based on a time-variable signal which is accessible to both system components, at the start of the vehicle, one of the test codes is selected by both system components via an assignment function present as a hash function, and with this test code, the payload data that are to be transmitted are coded. The assignment function and the test codes are stored in data areas of system components that are secured against unauthorized access.
1 . A communication method for at least two system components of a motor vehicle via a network connection, each of the first system component and the second system component having available, via at least one hash function, at least one natural number n and a plurality of test codes, comprising:
(a) computing, by a first one of the first system component and the second system component, a hash chain according to the relationship a i+1 =h(a i ) having a length equal to the natural number n and based on a random number representing a 0 ;
(b) linking, by the first one of the first system component and the second system component, the test codes to a respective member of the hash chain;
(c) sending, by the first one of the first system component and the second system component, a last member of the hash chain a n as a start code;
(d) for each subsequent authentication after the steps (a), (b) and (c), transmitting, by the first one of the first system component and the second system component, one of (a) a payload datum together with the test code linked to a current member of the hash chain a i , uncoded, and (b) the payload datum together with the test code linked to the current member of the hash chain a i , coded, to a second one of the first system component and the second system component;
(e) after the step (d), and for each subsequent authentication after the steps (a), (b) and (c), transmitting, by the first one of the first system component and the second system component, the current member of the hash chain a i to the second one of the first system component and the second system component;
(f) after step (e), and for each subsequent authentication after the steps (a), (b) and (c), checking, by the second one of the first system component and the second system component, the current element of the hash chain a i transmitted by the first one of the first system component and the second system component with the hash chain, and, if the current element of the hash chain a i transmitted by the first one of the first system component and the second system component agrees with the hash chain a i+1 =h(a i ), at least one of (a) accepting and (b) decoding, by the second one of the first system component and the second system component, the payload datum;
(g) at each renewed vehicle start, decrementing a counter by 1 to select a new member of the hash chain a i−1 ; and
(h) restarting the method at step (a) when the counter is decremented to 0.
2 . The method according to claim 1 , wherein the network connection includes a CAN bus system of the motor vehicle.
3 . The method according to claim 1 , wherein the first system component and the second system component include access-protected data regions, the hash function and the test codes stored in the access-protected data regions.
4 . The method according to claim 1 , wherein the steps (a), (b) and (c) are preformed as a final test of the first system component and the second system component.
5 . The method according to claim 1 , wherein the first system component and the second system component are each arranged as senders and receivers, the method further comprising a pair-wise exchange of respective start codes between the first system component and the second system component.
6 . The method according to claim 1 , wherein the at least one hash function includes a plurality of different hash functions used according to one of (a) a predefined scheme and (b) a scheme communicated in coded form.
7 . The method according to claim 1 , wherein the at least one natural number includes a plurality of different natural numbers used according to one of (a) a predefined scheme and (b) a scheme communicated in coded form.
8 . The method according to claim 1 , wherein the start code is sent in the sending step in a coded manner.
9 . The method according to claim 1 , wherein the first system component includes an ESP control unit and the second system component includes a steering system control unit.
10 . A communications method for two system components of a motor vehicle via a network connection, each system component including a prespecified, fixed number of test codes known only to the system components, comprising:
selecting, based on a time-variable signal accessible to both system components at a start of the motor vehicle, one of the test codes by both system components;
coding payload data to be transmitted with the selected one of the test codes; and
storing the assignment function and the test codes in data areas of the system components that are secured against unauthorized access.
11 . The method according to claim 10 , wherein the network connection includes a CAN bus of the motor vehicle.
12 . The method according to claim 10 , wherein the assignment function includes a hash function.
13 . A communications method for two system components of a motor vehicle via a CAN bus system of the motor vehicle, comprising:
providing payload data of a CAN bus message packet with an additional CRC checksum different from a standard CRC checksum of the CAN bus system.
14 . The method according to claim 13 , further comprising:
sending messages on at least two physically separate media; and
subsequently comparing the messages at a receiver.
15 . The method according to claim 14 , wherein the at least two physically separate media include CAN bus lines.