In my Cyber Security Practicum class we need to make a python program where three computers all have access to a public file, but only one other computer can decrypt the file.

So lets say that A is trying to send a file to C, B can open the file, but only C can decrypt / read it.

Or if B is trying to send something to A, C can open it but only A can decrypt, etc.

What is a basic python program that can be started off with?