Method and terminal device for cryptographically secured transmission of data within a communication system

A method for cryptographically secured transmission of data within a communication system in which the communication system comprises at least one switch or router and a plurality of terminal devices which exchange data for controlling machines or apparatuses, the method comprising:

• generating, by terminal devices which each comprise a local certification instance, a first key pair for the terminal device and a request when a respective terminal device is commissioned to create a certificate assigned to the first key pair;
• transmitting, by the terminal devices, the request to a higher-level certification instance during protected operation of the respective terminal device, only communication between the respective local certification instance and the higher-level certification instance being possible during the protected operation of the terminal devices;
• checking, by the higher-level certification instance, requests of each of the local certification instances of the terminal devices and creating a certificate assigned to the respective first key pair and transmitting the certificate to the respective local certification instance if the check is successful;
• terminating, by the terminal devices, each protected operation after receiving the certificate generated by the higher-level certification instance;
• and
• generating, by each local certification instances, at least a second key pair and a certificate for the second key pair for cryptographically secured exchange of data from and to the terminal devices after termination of protected operation;
• wherein the generated certificate is signed via a private key comprising the first key pair.