Just use the existing magic wormhole protocol. It works and has been deployed for a long time.

▲ ho_schi 2 days ago | parent [-]

No. It is using a central “well known server” and requires internet.

Test:

    * Does it work in an airplane?
    * Does it work in a submarine?
    * Does it work in the mountains, when a thunderstorm is approach and you need to share the GPX?

Basically my Garmin Edge and iPhone can do this. Magic-Wormhole fails in all test cases.

Implementation shall be able to negoiate a connection locally (e.g. Bluetooth) and upgrade to peer-to-peer WiFi if need (Garmin doesn’t need that part, GPX are usually smaller than 1024 KB).

	▲	ddtaylor 2 days ago \| parent [-]
		Modifications can be made to do that minimal peer exchange over BT. They may already exist, but I haven't used that part yet. It seems like a lot of extra work to reinvent the wheel and get the security wrong instead of extending a well established protocol with many other tools built on top of it.