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Warning: ubuntu tpm recovery key cannot unlock disk outside of boot (self.linux)

submitted 11 months ago* (last edited 11 months ago) by ichbinjasokreativ to c/[email protected]

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Hi everybody, bit of a warning here: The recovery key generated during the installation of Ubuntu 23.10 (if you select tpm-backed fde) cannot be used to unlock the disk outside of boot, as in any 'cryptsetup' command and so on will not accept the recovery key. unlocking when accessed from different system does not work etc.

You can use it to unlock the disk while booting if your tpm somehow fails, but ONLY in that specific situation.

I kind of purposefully broke my tpm keys to see if it could be restored with 23.10 and ended up having to reinstal, as I ended up having to enter the recovery key at boot every time and no way of adding additional unlock options to the volume, as cryptsetup would not accept the recovery key as passphrase.

This bug could be very bad for new users.

See this bug report: https://bugs.launchpad.net/ubuntu-desktop-installer/+bug/2039741

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[–] MAFoElffen 12 points 11 months ago* (last edited 11 months ago) (1 children)

As you can see by my UserName, I am the person who filed that Bug as a danger to users... Specifically brought up by @ichbinsokreativ, me trying to help him...

Thank you Skull giver for the golang code, I had to debug your code, to get it to run, because of the forum transposing HTML char codes for some characters... Unfortunatley, displaying the result onto console displays 'jibberish', as you thought might happen. Console cannot display raw hex characters.

Redirecting the output as you posted doesn't work, as the script then doesn't get the input of the recovery key, so errors.

I have a request... I know a lot of languages, but GO isn't one of them. Please... Could you please add a few lines to write the result directly to a file called recovery.key? Then if raw or hex, it would get to a key-file... Then I can test if that is going to work to add additional keys to the LUKS containers, and to be able to help people re-enroll the TPM key.

If you could, they we would have a recovery work-around.

Yes. They did something similar for past ZFS encryptions i their canned installs, but used native ZFS encryption, with a locked encrytped keyfile stored within a LUKS container, that had to be unlocked and mounted before unlocking the ZFS pools. Sometimes I don't follow the logic behind some things.

It seems like they often add complication to what should be simpler.