Im am currently writing a project in C using OpenSSL/TLS and I am not very experienced in encryption. I have successfully established unencrypted OpenSSL connections and I am relatively experienced in C/C++. The Project involves the actuation of hardware so the data sent is very repetitive and not confidential (Just a few bytes, like turn commands for a servo or a temperature readout)
Basically I have multiple clients in a local network which I want to securely connect to a local server. The system has to work offline. All I want right now is to establish a connection between the client and the server to prevent unauthorized connections. Authentication and User restriction will be restricted by the application on the server.
I have been looking at Public Key Encryption but from my understanding that requires a connection to the CA which might not be available at all times. How correct is this and what are my alternatives?
A simple C implementation would be helpful too. Thank you