I am thinking of creating a small chatting server. I want it to be as secure as possible so I found it to be very helpful if some expert could guide me a little bit.
Has there been any research on or perhaps a completely built prototype of a chatting server that doesn't know who chats with whom? That means, even if someone was to alter the code of the server, he wouldn't be able to learn the recipients of the messages.
I would like my server not to know who the recepient of the message I sent is. I figured something could be done with FHE cryptosystems, but for a simpler version which doesn't use any FHE, it should be possible to build something that can hide the recipients until the recipient receives the message. The simplest way to achieve what I want is to make every message broadcast. But, it is trivial and impractical so I am looking for something better. Broadcasting notifications, but sending the message to only one person seems to make some achievements. Using FHE cryptosystems should exclude all broadcastings and resolve my problem, but FHE systems are extremely slow.
Any guidance and hint is very welcome.