I see there are implementations of both RSA, AES encryption as well as a stream cipher in the source code but i am not able to find any calls to these in the engine. How do these work, are they used for all network communication by default or is this something that need to be specified somehow in the project files, if so how? and can they be used with replicated variables in a blueprint project? I read somewhere that unreal does not use network encryption but that i believe was an old question somewhere so have this changed?
No, some of this stuff is used by online subsystems; but the server/client network engine will not encrypt anything afaik.