The embodiments relate to a near field communication system including a plurality of near field communication devices which communicate with each other via a radio interface. During generation of a common cryptographic key between the near field communication devices of the near field communication system, at least one of the two near field communication devices monitors during generation of the cryptographic key via the radio interface in a generation period whether an additional near field communication device which could be a potential active attacker communicates with one of the near field communication devices via the radio interface. If such a suspicious type of communication is detected, generation of the common cryptographic key is optionally terminated.