[str4d]

> and also a mobile app that can do this (right now I use PasswordStore on Android, which communicates with OpenKeyChain which is basically GPG for Android with a nice shell around it). So I use the Yubikey over NFC there (though USB is also possible if you really want), to access my passwords. It works pretty well after some initial hiccups.

The age plugin system and its currently-specified IPC [0] focuses on easy interoperability via plugin discovery in the PATH. This works very well for native desktop applications (and even between e.g. a Windows host and WSL guest [1]), but obviously not for web or mobile. I'm not optimistic about dynamic plugin discovery ever being feasible for web, but in theory alternate plugin-discovery mechanisms could be figured out for mobile (e.g. Android Intents).

Fortunately, the age plugin system is _also_ a relatively thin wrapper around the core age concepts of Recipients and Identities, so it's possible to write code for an age plugin that can also be used directly as a library! I haven't tried this with age-plugin-yubikey yet specifically, but it should be possible (after some refactoring) to produce a library that can be used to statically include support for YubiKeys directly in an age mobile app, backed by whatever Android library is currently used to provide YubiKey PIV access.

[0] https://github.com/C2SP/C2SP/pull/5

[1] https://github.com/str4d/age-plugin-yubikey#windows-subsyste...