A method and a configuration are described for mutual authentication of two data processing units. The mutual authentication of two data processing units is normally carried out in two separate authentication processes, which are carried out successively. A challenge and response method is normally used. For this purpose, a first challenge is sent from a first data processing unit to a second data processing unit, which transmits a first response back. A second response is produced by the first data processing unit, and is transmitted to the second data processing unit.