Best way to go about rednet communication?

Recently I've been working on a modded server for my friends and I to test my modpack. The modpack is World War Two themed, and has been going great. The only thing I've wondered about is adding an Enigma type machine to transmit and receive messages over long distance because our team speak isn't secure (yes, I know computers even remotely close to ours didn't exist back then, CC is the closest thing I can find). So I was curious what the best way to go about this would be. Keep in mind that the user shouldn't have access to the main console, only to the program that is sending messages. Thanks.

I have a Program that uses rednet and rednet protocols to have channels where its all groups chats, you can just think of a rednet protocol to use for the channel to make it secure aswell