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Question About TPM Autodecrypt
(mander.xyz)
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this post was submitted on 27 Oct 2023
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on my laptop I have tpm to decrypt my drive and I've also enabled secure boot and set a bios password, so if someone steals my laptop it's basically bricked,
secure boots there to prevent any potential tampering if someone were to take the drive out then put it back in
I feel this setup is secure enough for me, if you've got some nation state after you, or some guy with a wrench theres probably nothing you can do
My laptop has an option to demand a bios password if a storage unit is removed and if the bottom of the laptop is removed.
Very useful.
I was wondering what security does the TPM password provides. If I understand correctly, it will prevent attacker from getting the data on the disk.
However, theoretically, attacker can boot the laptop and disconnect the disk to get a decrypted disk. Realistically, I think my laptop will shutdown when the chasis is opened (unless configured otherwise in the bios). So it should be safe?
This is not how this works. The bits are never decrypted on your disk / partition. If that was the case, a power loss would leave your device decrypted as well, and that is something a potential attacker might have control over.
What actually happens is that encrypted data is read from disk by the CPU, decrypted by the CPU and then written to RAM unencrypted. Unencrypted data should NEVER be written to non-volatile memory (the necessary exceptions, like the boot image, apply).
Oh! That makes much more sense! Thanks!
Then I guess there is not much point in encrypting both the full disk and the home dir together then (if I trust gnome login screen cannot be by-passed), since the data is always encrypted when they are on the disk.
In a single user context where the only user is also the administrator, full disk encryption has no disadvantages to home directory encryption AFAIK.