Method for detecting an unauthorized physical access to a bus system

An arithmetic-logic unit configured to detect an unauthorized physical access to a bus system, in which data are transmitted according to a bus specification utilizing signal-level sequences in a voltage signal, the arithmetic-logic unit configured to:

• acquire a measuring signal which assumes a first state when the voltage signal lies above a threshold voltage, and assumes a second state when the voltage signal does not lie above the threshold voltage;
• detect a test-level sequence in the voltage signal;
• form a measuring-signal pattern based on the measuring signal during a period of time corresponding to the test-level sequence;
• compare the measuring-signal pattern to a reference pattern that is assigned to the detected test-level sequence and was determined based on a reference measuring signal for the test-level sequence in a state of the bus system in which no unauthorized physical access was present, the measuring-signal pattern and the reference pattern assigned to the test-level sequence indicating at least points in time of transitions between the first and the second state in the measuring signal and the reference measuring signal, respectively;
• and
• determine that a possible unauthorized physical access is present based on the comparison ascertaining that the measuring-signal pattern and the reference pattern differ from each other in one or more predetermined properties by more than a specific tolerance.

A non-transitory machine-readable storage medium on which is stored a computer program for detecting an unauthorized physical access to a bus system, in which data are transmitted according to a bus specification utilizing signal-level sequences in a voltage signal, the computer program, when executed by an arithmetic-logic unit, causing the arithmetic-logic unit to perform the following steps:

• acquiring a measuring signal which assumes a first state when the voltage signal lies above a threshold voltage, and assumes a second state when the voltage signal does not lie above the threshold voltage;
• detecting a test-level sequence in the voltage signal;
• forming a measuring-signal pattern based on the measuring signal during a period of time corresponding to the test-level sequence;
• comparing the measuring-signal pattern to a reference pattern that is assigned to the detected test-level sequence and was determined based on a reference measuring signal for the test-level sequence in a state of the bus system in which no unauthorized physical access was present, the measuring-signal pattern and the reference pattern assigned to the test-level sequence indicating at least points in time of transitions between the first and the second state in the measuring signal and reference measuring signal, respectively;
• and
• determining that a possible unauthorized physical access is present based on the comparison ascertaining that the measuring-signal pattern and the assigned reference pattern differ from each other in one or more predetermined properties by more than a specific tolerance.