Support hardware token SSH ed25519 secret keys

[gnanderson]

Hi there,

Thanks for all your work on this, very cool and easy to use 💯 👍

I would like to utilise resident secret SSH keys that live on my yubikey 5 tokens, however it currently looks like that key type is unsupported:

age: warning: recipients file "/home/graham/.ssh/id_ed25519_sk.pub": ignoring unsupported SSH key of type "[email protected]" at line 1

With support for hardware tokens and these key types in SSH 8.2 and adoption appearing in some online services[1] we no longer have to go through the terrible experience of configuring GPG keys on yubikey devices; and then the additional painful task of making it work with SSH.

So If I'm going to use resident SSH keys on my Yubikey5, for SSH, SSH client certs, etc I would also like to use the same keys with age. One more step towards leaving GPG behind completely!

Does this seem like something reasonable to add to age? I currently don't know what other hardware tokens support SSH resident keys, but I suppose yubikey is probably one of the leaders in this class of product.

[1] https://www.yubico.com/blog/github-now-supports-ssh-security-keys/

[gnanderson]

Apologies - I just found this previous discussion:

#360