nearby VS ukey2

Did they? I know of https://github.com/google/nearby, but I don't think it's enough to implement. I could be wrong but...

nearby is open, hence my suggestion :) https://github.com/google/nearby

You may want to check this project out: https://github.com/google/nearby. It is in C++, though. It is a medium agnostic socket over bt and wifi. It seems similar to what you are trying to do.

Yeah, I respect the fact that Google made Nearby Share open-source recently (https://github.com/google/nearby-connections).

No plans for Linux right now. You're right that parts of the port would be easier for Linux than Windows. We have a /platform folder (https://github.com/google/nearby-connections/tree/master/cpp/platform/impl) that has abstractions for concepts like 'file', 'lock', and 'bluetooth_classic'. We're having to rewrite a lot of the core files ('file', 'lock', 'thread') for Windows while we could have reused what we already have if we were targeting Linux/MacOS. But rewriting the radio classes ('bluetooth_classic', 'wifi_lan', 'ble') would have had to happen regardless.

See: https://github.com/google/nearby-connections

The encryption scheme Google uses here is called "UKEY2" and the reference implementation is already open source and well-documented. It does feel robust enough to me if you compare the PIN codes on both devices to prevent a MitM attack. Standard practice for end-to-end encrypted anything, really.

Encryption: https://github.com/google/ukey2