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Context

I am lazy. But I am also (a bit) concerned with security.

So on my machine (running Fedora), I want to be able to both:

  • log into my session using a strong passphrase,
  • log into my session using a quick-to-type password when my Yubikey is plugged in.

There are 3 reasons for that:

  1. I want to be able to log into my machine with a passphrase only (if I lose my Yubikey, or if I'm comfy in my bed and I don't want to get up grab the Yubikey in my jacket — remember, I'm lazy).
  2. Yet if I've my Yubikey plugged in (e.g. at work), I'd like to log in with a quick-to-type password only (remember, I'm lazy) as I frequently lock my session — and so have to log in back.
  3. I wouldn't want to use my Yubikey alone (without password), though, as I might forget to unplug the key when I lock the session (lazy… and concerned about security).

Question

How to setup my user account, so I can log in using either of these two different authentication methods?

  • passphrase only,
  • password + Yubikey
1
  • FYI, this piece of documentation details how to set up a Yubikey + password authentication. I intend to test it but, by the read of it, it seems that the Yubikey will be required, so authenticating through passphrase only wouldn't be available any more (for that user). – ebosi Sep 15 '20 at 16:12
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Here is the solution strategy I have come up so far:

  1. One can create multiple accounts with same UID (cf. Why can I create Users with the same UID) — i.e. both accounts would be the same users from the OS perspective, but we could have a separate authentication method for each (one with passphrase, another with Yubikey + password). Whether it's a good idea is debated.
  2. It is possible to require both a Yubikey and password as authentication strategy. It is defined in the Linux PAM system. (It is also possible to require a password only!)

The points I haven't solved so far:

  • How to assign a spefic PAM-rule per account (cf. point 1 above)?
  • How to implement the Yubikey + passphrase authentication strategy in GDM (GNOME Display Manager — i.e. the GUI to authenticate in Fedora)?

(I'll update this post once I've made progress on these issues.)

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