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Remote solution to decrypt disk at boot (jlai.lu)

submitted 2 years ago by Jean_Mich_Much@jlai.lu to c/selfhosted@lemmy.world

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Hi there ! I have a little box at home, hosting some little services for personal use under freebsd with a full disk encryption (geli). I'm never at home and long power outage often occurs so I always need to come back home to type my passphrase to decrypt the disk.

I was searching this week a solution to do it remotely and found the "poor-guy-kvm" solutions turning a Raspberry like board (beaglebone black in my case) in a hid keyboard. It works fine once the computer has booted but once reboot when the passphrase is asked before it loads the loader menu, nothing. When I plug an ordinary USB keyboard I can type my passphrase so USB module is loaded.

Am I missing something ? Am I trying something impossible ?

(I could've asked on freebsd forum but... Have to suscribe, presentation, etc... Long journey)

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[–] raldone01@lemmy.world 10 points 2 years ago* (last edited 2 years ago) (2 children)

If you have a TPM 2 you can use secure boot (custom keys) to allow Linux to decrypt itself if nothing has changed.

[–] Jean_Mich_Much@jlai.lu 2 points 2 years ago

Didn't know this thing, I will check about that, thanks !

[–] johntash@eviltoast.org 1 points 2 years ago (1 children)

What do you mean by if nothing has changed? Wouldnt this mean someone could physically steal the machine and then boot it up somewhere else and it'd auto decrypt itself?

[–] raldone01@lemmy.world 4 points 2 years ago* (last edited 2 years ago)

Yes. That is possible. However if the hardware configuration/software configuration changes the TPM should trip and prevent decryption.

The attackers would have to break you ssh/terminal/lock screen/other insecure software. However code injection should be impossible because you used custom secure boot keys and ideally a signed unified kernel image. (Can't even change kernel params without tripping TPM.)

You would not be safe if they did a bus listening attack or if your shell pwd is not safe. If that is your threat vector this may not be a good option for you.