Have you taken a look at magic-wormhole[1]? I've started using it recently and it's insanely easy to use.
It does have a centralised signalling server for key exchange between peers, but it does attempt to do peer-to-peer data transfer (only falling back to a TURN-style relay if both clients are behind NATs and aren't on the same local network). An explanation of the cryptography and design was given at PyCon 2016[2]. It also has built-in optional Tor support (though I'm not sure if it attempts to use an onion service for data transfer).
Magic wormhole is good, and I've used it before, but it's never as fast as it could be. Something like piping to netcat is always faster. I know it's possible (albeit with a lot of work) to do this over HTTP, but google drive is probably the only site that can mostly saturate a connection. Can any one link more info on how exactly they achieve this? The only trick I know of is a better TCP congestion control algorithm.
I did not know magic wormhole existed. I made a simple nodejs implementation of a very similar app. It used WebRTC so maybe it could be faster. Let me know if you want to try it out!
This is one of many reasons why I have a terminal on my phone, I can just apt install magic-wormhole and use it like on any other system.
(The technical reader will note that a terminal does not give you apt, but mentioning that I have Debian running on the phone is more confusing, as it sounds like I replaced Android (which I did not) or maybe that it costs a lot of battery (the tools are idle when not in use, unlike many apps unfortunately...).)
Sure, I can use wormhole on iSH on my iPhone/iPad if there are no alternatives. But there are alternatives, so I’ll definitely stay the hell away from it given the terrible ergonomics.
Maybe someone should write a magic-wormhole mobile client. It wouldn't need a complicated UI at all, and you could (try) to use Kivy[1] to avoid having to rewrite all of the Python bits. I might even try to do it as a weekend project, actually (though I suck at mobile development -- anyone else would probably be a better choice ;]).
It does have a centralised signalling server for key exchange between peers, but it does attempt to do peer-to-peer data transfer (only falling back to a TURN-style relay if both clients are behind NATs and aren't on the same local network). An explanation of the cryptography and design was given at PyCon 2016[2]. It also has built-in optional Tor support (though I'm not sure if it attempts to use an onion service for data transfer).
[1]: https://github.com/warner/magic-wormhole [2]: https://youtu.be/oFrTqQw0_3c