Extraordinary how Linux continues to be 20 years behind Microsoft and Apple when it comes to FDE. This is a hilariously stupid level of complexity for something that should have a universal solution across distros by now.
This is literally a one click process in Windows (plus a couple shell commands to enable TPM+PIN).
I'm not disparaging the author in any way — he's merely documenting the stupidity.
On both my Fedora laptop and on my MacBook, I have to enter a password at boot to unlock the hard drive, and both had similar complexity to set it up (in Fedora I clicked a button and entered a password during the install, on Mac I clicked a button and wrote down a backup key after the install).
I think this is specifically for the TPM2 integration, which isn’t required for FDE. But I assume it makes it smoother. System updates that requires multiple reboots for example are more annoying on Fedora, since every reboot requires re-entering the password, while on Mac I just login after the final reboot.
What problem is this solving though? The post says they're doing this to avoid typing passphrases. Why would you want the private key hidden in the tpm chip of that device? How will you decrypt if the laptop goes bust or if you move the drive elsewhere?
The TPM generates a strong, non-exportable key in hardware that is far less susceptible to brute-force attacks.
As opposed to accidentally creating your own key of "4", for instance.
A PIN can be used to protect the TPM from unlocking. Even if you set a PIN of "1234" — it would still be far more secure if the disk and laptop were ever to become separated, because the TPM will have generated a strong key anyway.
The TPM is basically a smart card soldered to the motherboard.
> How will you decrypt if the laptop goes bust or if you move the drive elsewhere
Windows and Apple both generate a recovery key as part of the enrollment process which you can store offline.
When you format LUKS you can add multiple decryption keys in case the TPM is hosed for some reason like the mobo failing. Can even use a Yubikey instead of a TPM. Or both. Or none. It's really up to you.
Has nothing to do with distros. This is you encrypting your disk for the kernel to open during boot. It literally prompts you normally when it hits the step where it attempts to mount the main partition. The way Linux does it is far more flexible and secure because the keys aren't sent to some third party and no one can unlock it without your keys. You are free to use anything to sign the LUKS partition besides a TPM or some silly pin like a Yubikey or whatever the hell you want.
Sealing to a reasonable subset of PCRs (ie, not just 7 like the article) is reasonably strong against point-in-time evil maid, no?
Like, in Evil Maid Scenario 1, where the Evil Maid only has one-time access, if you've sealed to say 0,2,4,7,9 , or 7 and 15 with a reasonable setup for what gets extended into 15, the Evil Maid's Fake PIN Entry Software would _not_ validate in the secured boot configuration and couldn't actually unseal the TPM, only coerce you into entering your PIN. Then the Evil Maid would have to physically return to your "correct" boot state with the PIN to unseal the disk, no?
(this is all modulo firmware and early boot exploits, of course, since in that case the attestation could also be forged also)
No, I think this is a valid threat model and a good rebuttal. The evil maid steals the original laptop, replaces it with a second laptop with a look-alike PIN entry screen without an attestation. You enter your PIN, it is transmitted to the evil maid with the first laptop, and your data is unlocked. You would notice, but your data would be exposed.
Now, to be clear, I don't think this negates TPM-sealed disk encryption or TPM-and-PIN sealed disk encryption; they're still meaningfully better than the alternatives (with a passphrase alone, your data is already compromised regardless in this invented scenario, and all scenarios are equally variable to the swiss-cheesiness of UEFI firmware unless it is replaced). But it is a valid model.
What does it matter if it doesn't unlock the disk? It's a different device with a logger. The purpose of the maid is to be evil and steal your pin. The maid has your real device. The only way to prevent this is by you authenticating the device before you enter anything. Look at the heads project (https://github.com/linuxboot/heads).
tpm2totp used to do this, and it also eliminated the need to divulge the secret used to unlock the TPM, I now see that it has not seen a commit in 2 years.
I also hear mjg59 is looking into encrypted swap hibernation support, so there's a slim chance there will be some development on the system-attestation front.
You have no idea what is inside the TPM chip and its vulnerabilities.
This is literally a one click process in Windows (plus a couple shell commands to enable TPM+PIN).
I'm not disparaging the author in any way — he's merely documenting the stupidity.
I think this is specifically for the TPM2 integration, which isn’t required for FDE. But I assume it makes it smoother. System updates that requires multiple reboots for example are more annoying on Fedora, since every reboot requires re-entering the password, while on Mac I just login after the final reboot.
As opposed to accidentally creating your own key of "4", for instance.
A PIN can be used to protect the TPM from unlocking. Even if you set a PIN of "1234" — it would still be far more secure if the disk and laptop were ever to become separated, because the TPM will have generated a strong key anyway.
The TPM is basically a smart card soldered to the motherboard.
> How will you decrypt if the laptop goes bust or if you move the drive elsewhere
Windows and Apple both generate a recovery key as part of the enrollment process which you can store offline.
Windows and macOS both can do FDE with good UI/UX compared to Linux.
Like, in Evil Maid Scenario 1, where the Evil Maid only has one-time access, if you've sealed to say 0,2,4,7,9 , or 7 and 15 with a reasonable setup for what gets extended into 15, the Evil Maid's Fake PIN Entry Software would _not_ validate in the secured boot configuration and couldn't actually unseal the TPM, only coerce you into entering your PIN. Then the Evil Maid would have to physically return to your "correct" boot state with the PIN to unseal the disk, no?
(this is all modulo firmware and early boot exploits, of course, since in that case the attestation could also be forged also)
You're in here shitting on TPM but don't seem to understand the threat model at all.
Now, to be clear, I don't think this negates TPM-sealed disk encryption or TPM-and-PIN sealed disk encryption; they're still meaningfully better than the alternatives (with a passphrase alone, your data is already compromised regardless in this invented scenario, and all scenarios are equally variable to the swiss-cheesiness of UEFI firmware unless it is replaced). But it is a valid model.
I also hear mjg59 is looking into encrypted swap hibernation support, so there's a slim chance there will be some development on the system-attestation front.