Encryption of program instructions on numerical control devices

The invention relates to a method for operating a numerical control device for controlling a manufacturing machine for manufacturing workpieces, comprising the following steps: providing workpiece data; providing CAM software, generating program instructions (3) for manufacturing the workpiece by means of the manufacturing machine, the program instructions (3) being generated from the workpiece data by means of the CAM software or by means of post-processor software downstream of the CAM software; encrypting the program instruction (3) with a first encryption key (5) in order to generate a first encrypted program instruction (7); in order to generate a first decrypted program instruction, the first encrypted program instruction (7) is decrypted by means of the numerical control device using a first decryption key (6). In order to provide an OEM customer with a feasible solution that protects the program instructions generated by the OEM customer from unauthorized access and at the same time ensures that the s