Sorry, didn't see this until now. Yes, you use the Yubico Authenticator app, but it's entirely local only (runs fine with all networking switched off). It's a

Sorry, didn't see this until now. Yes, you use the Yubico Authenticator app, but it's entirely local only (runs fine with all networking switched off). It's available for Mac, Linux and Windows, as well as Android and iOS. On computers your key needs to be inserted into a USB port. For Android and iOS I use the NFC key and I just scan it against the phone after launching the app.