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sgillespie / nixos-yubikey-luks

Set up a LUKS-encrypted filesystem for Yubikey in NixOS
MIT License
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Authentication failed after update from nixos-23.11 to nixos-24.05 #10

Open Skyfold opened 2 months ago

Skyfold commented 2 months ago

I've successfully been using this setup for awhile now, but after updating from nixos-23.11 to nixos-24.05 it fails to boot from any version. Any ideas what could have gone wrong and any hope I might decrypt my hard drive within my lifetime?

Specifically, I booted nixos-24.05 successfully, but then failed on the reboot. That means, nixos-24.05 was able to create the luks key from the salt created in a previous version, but something about the new salt from nixos-24.05 is causing my issue.

I did try to manually decrypt from the nixos installer using the maintenance instructions, but no luck.

There are two important details:

  1. The salt file only has one line, there is no iterations count awk 'NR == 2 {print}' < /mnt/boot/crypt-storage/default returns nothing (zero bytes).
  2. Interestingly awk 'NR == 1 {print}' < /mnt/boot/crypt-storage/default is not the same as /mnt/boot/crypt-storage/default according to diff.
  3. the yk-luks-open.sh script fails because it assumes there is an iterations count, resulting in an empty LUKS_KEY which causes hextorb to fail.
  4. I get a warning from running yk-luks-open.sh saying "command substitution: ignored null byte in input" for the line that reads the salt. I see two null bytes with hexdump. This may be the culprit.
sgillespie commented 1 month ago

Can you just add a line with a number for iterations?

sgillespie commented 1 month ago

Any ideas what could have gone wrong and any hope I might decrypt my hard drive within my lifetime?

I think you probably can, as long as you know the correct key length and iterations values, but you'll need to do some reverse engineering. I sometimes follow the README from the bottom up when I mess something up. I only created the script because I got tired of copy/pasting the same commands over and over

Skyfold commented 1 month ago

I know the correct key length from my configuration.nix and I set the iterationStep to 0, so it should have been whatever I initially set it to during setup. I used the commands from the Maintenance section in the wiki since they pipe the output to avoid command substitution: ignored null byte in input. Just to be sure I tested with multiple iterations (0, 10, 100, ..., 1000000). Nothing has worked.

The reason I cannot decrypt my drive is most likely because the salt is incorrect. Think about it. I upgraded my system to nixos-24.05 and rebooted successfully. It was the next reboot that failed. The problem is not the decryption on nixos-24.05, it was the process that updates the salt and LUKS authentication key. My guess is that it failed part way. Either the LUKS authentication key was never updated or the salt was improperly updated (why else is the iterations missing).

If you want to prevent this happening, the previous salt should be kept and some logs written to know what happened. However, the better option is to create an encrypted backup of the LUKS authentication key using a provided public key on the boot partition. That way, when the update fails part way, you can still have a chance to decrypt the drive.