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I just finished setting up a LUKS encrypted system that is unlocked using a FIDO2 hardware token following this blog post. However, at home I usually leave the hardware token plugged in and I only remove it when traveling. So if someone were to steal the laptop together with the plugged-in hardware token they could easily boot the laptop and decrypt the disk.

To remedy this I'd like to use 2FA with both a password and the hardware token, but so far I only found solutions using a password + HMAC-SHA1 by using the password as the challenge and storing the generated hash as the actual password in LUKS, so this does not generalize to FIDO2. Is there a way to get 2FA working with FIDO2, too?

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Systemd has a module for that since version 248. It's called systemd-cryptenroll. Depending on the capabilities of your FIDO2 stick multiple options are available for 2FA:

  • --fido2-with-user-presence=true configures the system so that you need to touch the FIDO2 stick.
  • --fido2-with-client-pin=true configures the system so that you need the FIDO2 stick and enter the PIN.
  • --fido2-with-user-verification=true configures the system so that you need the FIDO2 stick and authenticate to the system.

An example call would be systemd-cryptenroll --fido2-device=auto --fido2-with-user-verification=true /dev/sda3

But you should experiment with a spare USB drive or an image. Make sure everything works as expected before you enroll the FIDO2 key to your real devices.

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