cornelinux

There are several open source authentication servers out there. E.g. I am working on privacyidea (http://www.privacyidea.org).

There is one open hardware project I know of. It is the nitrokey (http://nitrokey.com), which is also supported by privacyIDEA starting in the next version of privacyidea. But this is also a USB device similar to yubikey.

There is not open OTP display device I know of. Also, Most of these devices come preseeded, which means the vendor generated the secret key. But if the only concern is your phone - you can use the yubikey with an USB OTG. Or there is the yubikey neo, which works via NFC.

You could use privacyIDEA, which is a two factor auth server and is also capable of sending SMS via HTTP gateways.

BUT: You would rather want to use 2nd factors like HOTP or TOTP token or a yubikey.

Not sure if to use SSH keys? Or Yubikey? Or Google Authenticator? On a whole bunch of machines?

Why not have it all?

Using privacyIDEA [1] you can

* manage SSH Pub keys for several servers * manage your Google Authenticator centrally * manage Yubikeys centrally or whichever OTP token.

In addition you can combine it to use the Google Authenticator or any other OTP ++PLUS++ SSH keys [2].

[1] http://privacyidea.org [2] https://www.privacyidea.org/ssh-keys-and-otp-really-strong-t...