Method for tamper-proof data transmission between a plurality of communication partners, the communication partners each having a synchronisation means, comprising the steps of: - transmitting of encrypted data packets (DP) by one of the communication partners as sender (S) by means of broadcast/multicast protocols to the remaining communication partners as receivers (E), each data packet (DP) comprising an authentication section, an information section and an image of the synchronisation means of the sender (S), - receiving, decrypting and authenticating the data packet (DP) by the receivers (E) using the authentication section and the image of the synchronisation means, the receivers (E) distinguishing between a first case in which authentication is unsuccessful, a second case in which authentication is successful, and in which an identical data packet has already been received at an earlier time, a third case in which authentication is successful and the image of the synchronisation means has a predetermined synchronicity with the synchronisation means of the respective receiver (E), and a fourth case in which authentication is successful and the image of the synchronisation means has no predetermined synchronicity with the synchronisation means of the respective recipient (E), - processing the data packet (DP) in the recipient (E) depending on the different case, wherein the information section is only accepted in the third case, and wherein in the fourth case, the receiver (E) sends a response packet (AP) to the sender (S), at least in encrypted form, by means of the broadcast/multicast protocols to a plurality of the remaining communication partners as receivers, which packet contains an authentication section and a request for synchronisation of the synchronisation means using an image of the synchronisation means of the receiver (E), wherein the plurality of communication partners comply with the request after successful decryption and verification. - transmitting of encrypted data packets (DP) by one of the communication partners as sender (S) by means of broadcast/multicast protocols to the remaining communication partners as receivers (E), each data packet (DP) comprising an authentication section, an information section and an image of the synchronisation means of the sender (S), - receiving, decrypting and authenticating the data packet (DP) by the receivers (E) using the authentication section and the image of the synchronisation means, the receivers (E) distinguishing between a first case in which authentication is unsuccessful, a second case in which authentication is successful, and in which an identical data packet has already been received at an earlier time, a third case in which authentication is successful and the image of the synchronisation means has a predetermined synchronicity with the synchronisation means of the respective receiver (E), and a fourth case in which authentication is successful and the image of the synchronisation means has no predetermined synchronicity with the synchronisation means of the respective recipient (E), - processing the data packet (DP) in the recipient (E) depending on the different case, wherein the information section is only accepted in the third case, <EOS>