I've been using Krypton[1-4] for 2FA PGP and ssh. It uses a phone as a security token, instead of using a Yubikey. (I'm not affiliated, or even a paying custom

I've been using Krypton[1-4] for 2FA PGP and ssh. It uses a phone as a security token, instead of using a Yubikey. (I'm not affiliated, or even a paying customer. I just benefit from freeloading off their freemium model.) This is not in any way to take away from how impressive the OP's work is, how nicely it's written up, or the merits of: understanding this yourself, running on a Yubikey instead of a phone, and running independently of someone else's distribution chain (unless you build the phone app and daemon yourself) and infrastructure. If you're in the subset whose response to OP includes “I wish I could do this with my phone, and that someone else would set this up for me so I didn't have to understand it”, [1] might be of interest; otherwise, not. [1] https://krypt.co https://krypt.co [2] https://github.com/kryptco https://github.com/kryptco [3] https://news.ycombinator.com/item?id=14490766 https://news.ycombinator.com/item?id=14490766 – previous, mostly-skeptical, HN discussion [4] https://news.ycombinator.com/item?id=16915819 https://news.ycombinator.com/item?id=16915819 – more recent discussion