I have been working on an Android App quite a while now, starting from a simple idea.
A messenger where messages travel directly between phones with no servers in between. Using direct WebRTC encrypted connections (SRTP/DTLS), there are no servers that stores, reads, or relays content. Group chats use a gossip protocol where members relay to other members.
The only infrastructure the app touches is a signalling relay to set up the connection (no message content), a push notification to wake up a sleeping phone (also no content), and a TURN relay for restricted networks (encrypted packets only).
I wrote a detailed white paper explaining the full architecture: https://www.mindtheclub.com/white-paper.html
The app is in Open Testing on Google Play (1,000 tester cap): https://www.mindtheclub.com/beta-signup.html
I’m interested in this community's perspective on whether the architecture holds up.
Not quite, SimpleX runs on a client-server architecture, messages route through relay servers that hold them temporarily until delivered, then delete them. MTC messages go device to device with nothing storing them in between, not even temporarily.