Could one seperate the kdf from the disk? Actually, not have any kdf?
Where the disk only has a fully secure huge random key, not generated by a kdf but supplied whole by usb or something.
Protecting that external component is a problem, but it's a seperate problem, and having a copy of the drive, and everything else in your posession, and all the ram and gpus in aws doesn't get you into that drive.
The external part doesn't have to be a thumb drive right on your person. It could be stored anywhere on-line and/or on paper, and you just know where it is and how to get it.
You might have to re-create some kind of thumb drive for conveient use, but you could also intentionally lose/destroy it any time and not have it on your person during travel or sitting in a drawer at home. You would only recreate it when & where you decided it was safe to.
I guess that's what tpm aims to do. It's physically on-board but not accessible, as long as you trust the chip maker.
Obviously I've spent about 5 entire minutes thinking about this. Please excuse.
However I don't recall if the keyfile is then used to decrypt a header stored on disk to get the key that's actually used to en/decrypt the drive contents in the same way that passwords are.
To be specific, LUKS supports up to 8 slots. Slots can be used by different decryption mechanisms such as passwords (either typed in, or read from a keyfile), or something like clevis+tang to decrypt the disk on the correct network.
Each of these slots can then decrypt the main key to decrypt the drive data. This is done for a few reasons. This allows you to change "your disk encryption password" - or rather, passwords used for password based slots - without re-encrypting the (arbitrarily large) disk (for an arbitrarily long time). You just change an encrypted master key for a different ciphertext of the same master key.
You could enter a password using the Yubikey instead, provided there's a way to input a password. That might make brute-forcing a little challenging especially if you added tamper evidence and heat-sensitive fuses that blow if someone tries to open the case and modify the device. At that point you might be stuck brute forcing with a pen plotter.
Where the disk only has a fully secure huge random key, not generated by a kdf but supplied whole by usb or something.
Protecting that external component is a problem, but it's a seperate problem, and having a copy of the drive, and everything else in your posession, and all the ram and gpus in aws doesn't get you into that drive.
The external part doesn't have to be a thumb drive right on your person. It could be stored anywhere on-line and/or on paper, and you just know where it is and how to get it.
You might have to re-create some kind of thumb drive for conveient use, but you could also intentionally lose/destroy it any time and not have it on your person during travel or sitting in a drawer at home. You would only recreate it when & where you decided it was safe to.
I guess that's what tpm aims to do. It's physically on-board but not accessible, as long as you trust the chip maker.
Obviously I've spent about 5 entire minutes thinking about this. Please excuse.