A code management 62 that represents the third sector of the PLC 10 sits on top of the operating system 46. The code management 62 substantially serves to execute a user program 64. The user program 64 can serve for the control of an automation plant, for example. The operating system 46 of the PLC 10 can generally also be called firmware and the user program 64 software or an application program.

To execute the user program 64, the code management 62 comprises libraries 66 that are not included in the information contained in the user program 64. The code management 62 furthermore comprises websites 68 that can be displayed by the web server 20 as well as a key management 70.

The key management 70 present in the embodiment essentially provides the functionality shown in FIG. 1 of the authentication at different levels 18, 22, 26, 30 by means of a plurality of authentication processes 34. The key management 70 additionally comprises a user management (not shown) in the form of an access control matrix (ACM). For the authentication, the key management generates the random numbers for the respective authentication processes 34. The key management 70 communicates with the different functional blocks 20, 24, 28, 32, 60 by means of a DBus 72. In this respect, communication takes place with the I/O management 58 for authentication for the first level 30 to permit hardware accesses 32 and accesses to the operating system kernel of the operating system 46 in the second level 26.