Unlocking LUKS with NitroKey/Yubikey: FIDO2, HMAC-SHA1, or OpenPGP?

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Which approach do you think is better, and why?

  1. FIDO2
  2. HMAC-SHA1
  3. OpenPGP (alternative guide)

Or do you think there is an even better way to use a hardware security token to unlock drives having LUKS full disk encryption?

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OP edited

Progress report 1

  • I’m ruling out HMAC-SHA1, because:

  • If using systemd, pick FIDO2:

    • Avoids flaws of HMAC-SHA1.
    • Native support in systemd, so “future-proof”.
    • Wider support than OpenPGP. More HST vendors to choose from, including cheaper options than NitroKey or Yubikey: useful if each sysadmin (or colleague, or relative) needs an HST.
    • Compatible with QubesOS.

  • Otherwise, OpenPGP:

    • Like FIDO2, solves HMAC-SHA1 flaws.
    • However:
      • smartcard-key-luks seems unmaintained on GitHub and on GitLab.
      • LUKS with OpenPGP isn’t well-documented for non-Debian-based distros.

  • TBD: Clevis/Tang:

    • Remote/network-based unlocking.
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https://support.nitrokey.com/t/unlocking-luks-volume-with-nitrokey-3-on-debian-12-2/5553/15 could be useful too

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OP

Thank you for this! That thread is helpful in itself, and also links to other relevant resources - including by Lennart Poettering (controversial guy, but the canonical source on systemd).

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edited

I try to follow a multi-factor, multi-domain model.

So if I am wanting to verify that data is on the system I except it to be then TPM keys and measured boot is what I use. To verify it is on the network I expect I use a Tang server. To verify I have possession of a device I use, a hardware token and password.

You could do all the above, or mix match depending on the system. For example for servers I assume they need to boot without user intervention, so password is set as backup to the Tang server. I still use hardware token to buy just for quick revoktion of verification (i.e. I know a server is compromised or could be soon, I can just pull a USB out).

The same setup works for my laptops, which makes my network because of Tang act as trusted domain as well.

So again multi-factor (something you have, know, are, do) and multi-domain (network, user, machine).

I use Clevis to do the multi-key unlocks.

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wouldn’t doing this require that building a ram disk image with the yubikey software included?

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All 3 mechanisms are native to a yubikey, and do not require yubikey-specific software/drivers to function as they use USB standards like FIDO2, keyboard for HMAC, and PIV/CCID for OpenPGP.

FIDO2 is built-in out-of-the-box, HMAC just requires adding the key to HMAC on slot 1 or 2 (tap vs long-hold key-inputs) using the personalization tool, or using gpg(2) to card-edit for OpenPGP.

None of these require YK software to operate.

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OP

Which of the 4 recipes I posted are you referring to as “this”?

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read them and you will see that only ones mentions initrd at all.

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OP edited

I read them before writing my OP. I’m still not sure what you’re getting at.

I would be grateful if you could say what you mean, instead of initiating an oblique guessing game.

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instead of initiating an oblique guessing game.

i don’t understand the hostility.

i asked a question about needing yubikey software in a ramdisk image to enable decryption at boot time and most of the sources you provided don’t mention it at all.

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i don’t understand the hostility.

Bystander observation: you were asked to clarify but essentially refused in a way that took more effort than simply doing so.

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Oic. They didn’t understand that I was asking a question and thought that I was addressing one of their links

Thanks for helping clarify.

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It’s not mentioned because it’s not required, yubikeys in general mostly leverage pre-existing “smartcard” facilities

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