TLDR at the bottom. It seems the answer is Brian Warner's magic-wormhole. You're gonna see lots of file transfer sites with wormhole in their name, but if you

TLDR at the bottom. It seems the answer is Brian Warner's magic-wormhole. You're gonna see lots of file transfer sites with wormhole in their name, but if you want security you should use the original one, which is BW's m-w. It is implemented in Python [1], so it's hard to install. So someone made a Go version of it [2] that has binaries for windows, Mac, Linux, BSD etc. But it's command line so maybe not suitable for lay people. So another person made a GUI for it that also has binaries for all OS [3]. Also there is an android app [4]. Someone needs to implement an iOS one. [1] https://github.com/magic-wormhole/magic-wormhole/ https://github.com/magic-wormhole/magic-wormhole/ [2] https://github.com/psanford/wormhole-william/ https://github.com/psanford/wormhole-william/ [3] https://github.com/Jacalz/wormhole-gui/ https://github.com/Jacalz/wormhole-gui/ [4] https://github.com/psanford/wormhole-william-mobile/ https://github.com/psanford/wormhole-william-mobile/ TLDR: ask them to install [5] and [6]. [5] https://github.com/Jacalz/wormhole-gui/releases/ https://github.com/Jacalz/wormhole-gui/releases/ (click on 'Assets' under 'Latest release' and download the zip or tar.gz for your OS) [6] https://play.google.com/store/apps/details?id=io.sanford.wormhole_william https://play.google.com/store/apps/details?id=io.sanford.wor... Try it, it's usage is cute and really feels like magic. . . Edit: Discussion from few days ago. The creator is in the comments. https://news.ycombinator.com/item?id=27262193 https://news.ycombinator.com/item?id=27262193