Method and apparatus for identifying an electrical machine

The invention relates to a method for generating a challenge-response pair in an electric machine as a basis for identification or authentication, wherein the electrical machine comprises a stator and a rotor, said challenge a first AC voltage (V2) between two points of a first set pair of points (12, 14) of the electric machine wherein a size is determined depending on the induction response caused is created which causes an induction in the electrical machine, characterized, in that the first AC voltage (V2) having a frequency which is higher than the operating frequency of the electrical machine.