I was really intrigued when I heard openSUSE Aeon would be defaulting to automatic TPM unlocking. I thought it would be nice, it just boots into my login screen and that’s handy since I’d just have to write one password.

Then I realized I can just set my account to autologin and I’ll still have to write just one password (encryption) with the added benefit that it doesn’t automatically unlock the system. Oh well

Microsoft uses TPM PCRs 7+11 for BitLocker which is more secure than the Linux implementations mentioned in the article.

PCR 7 is the Secure Boot measurement which means it can’t be unlocked unless every signed boot component has not been tampered with up to the point of unlock by the EFI bootloader. PCR 11 is simply flipped from a 0 to a 1 by the bootloader to protect the keys from being extracted in user land from an already booted system.

The article is correct that most Linux implementations blindly following these kinds of “guides” are not secure. Without additional PCRs, specifically 8 and 9 measuring the grub commands (no single-user bypass) and initrd (which is usually on an unencrypted partition), it is trivial to bypass. But the downside of using these additional PCRs is that you need to manually unlock with a LUKS2 password and reseal the keys in TPM whenever the kernel and or initrd updates.

Of course to be really secure, you want to require a PIN in addition to TPM to unlock the disk under any OS. But Microsoft’s TPM-only implementation is fairly secure with only a few advanced vulnerabilities such as LogoFAIL and cold boot attacks.

it has been known for years that the defaults on windows are insufficient, and they don’t make it easy to switch to a password prompt at boot time (though it is possible)