Process for securing the privacy of data transmission

A method of secure data transmission between at least two control units arranged within a motor vehicle, said at least two control units being connected to each other via a data bus for the data transmission, said method comprising the steps of:

• a) storing an encoded internal key (20′) in each of said control units (1,2);
• b) generating a random bit sequence in a receiving one (2) of said control units (1,2) from existing sensor data present in said receiving one (2) of said control units (1,2) in response to a wake-up signal (24) transmitted to said receiving one (2) of said control units (1,2) over the data bus from a transmitting one (1) of said control units (1,2) and transmitting the random bit sequence (21) from the receiving one (2) of the control units (1,2) on the data bus;
• c) storing the random bit sequence (21) transmitted on the data bus in each of said control units;
• d) producing a key code (22) with the random bit sequence (21) and the internal key (20′) stored in each of said control units (1,2);
• e) encoding a message (23) including redundant data with said key code (22) in the transmitting one (1) of said control units and transmitting said message (23) on said data bus;
• f) receiving the message (23) produced in said transmitting one (1) of said control units and transmitted on said data bus in at least one other of said control units, wherein said at least one other of said control units includes said receiving one (2) of said control units;
• g) reading and checking said message (23) received in said at least one other of said control units by means of the redundant data contained in said message (23) to verify correct encoding of said message with said key code;
• and
• h) generating a signal in said at least one other of said control units when said encoding of said message is found to be correct in step g).