The invention relates to a first network unit (See) which comprises a secure hardware component (HK) for saving and running software. A second network unit (P) comprises a secure software component (SK) for saving and running software. A method for secure communication comprises: saving a first common secret, a first algorithm and a second algorithm on the network units; sending a first date from the second network unit to the first network unit; running the first algorithm on the first network unit and on the second network unit wherein the input is in each case formed by the second common secret and the first date; sending of a second date from the first network unit to the second network unit; running the second algorithm on the first network unit and on the second network unit; wherein the input is formed in each case by the second common secret and the second date; and use of the third common secret for a secure communication.