What you need to do is a bit platform-dependent, but Trammell's guide for MacOS is good: https://trmm.net/Yubikey https://trmm.net/Yubikey I run Linux but adap

What you need to do is a bit platform-dependent, but Trammell's guide for MacOS is good: https://trmm.net/Yubikey https://trmm.net/Yubikey I run Linux but adapting his guide to what I use was the clearest path I found. Do note that only some of the Yubikeys support GPG. The cheaper ones (that you might be getting for free) are OTP only. Git signing is pretty straightforward once you have it set up for GPG. I have not attempted mobile at all.