Method for operating a touch-sensitive, planar input device of a complete device, and complete device

A method for operating a touch-sensitive and flat input device of a complete device, wherein the input device is connected via a bus connection to a control device of the complete device and messages comprising touch datasets describing touch events are transmitted from the input device to the control device, the method comprising:

• evaluating the messages for sensitive input information for an application program implemented by the control device;
• pre-calculating encryption data elements as a key stream for encryption of the touch datasets, different pre-calculated encryption data elements being used for each of the touch datasets;
• holding the pre-calculated encryption data elements in the input device until the pre-calculated encryption data elements are used for the encryption;
• determining decryption data elements for decryption based on shared information of the input device and the control device;
• encrypting the touch datasets based on the pre-calculated encryption data elements when a security function of the application program in the control device queries the sensitive input information;
• transmitting the encrypted touch datasets via the bus connection from the input device to the control device;
• outputting, via an output device, a warning when an error in the encryption is detected by the control device during the decryption, wherein the output device is independent of the input device and cannot be addressed by an aftermarket device;
• and
• terminating the transmission of the encrypted touch datasets when the sensitive input information is completed.