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Comment by withinboredom | Hacker News Reader

Hmm. Isn’t this what secure boot is for? What is the difference and why isn’t it on the front page?

No. SecureBoot does non of that. SecureBoot is only a signature on the first binary that runs on the system. "Does Microsoft or the alternative CA I added allow this binary to run". That's it. It doesn't say anything about system state; or about the binaries that run after.

Measured boot gives you a holistic view of system state that can be verified by a third party. "What binaries are currently running; which ones ran; did a user unlock the disk with the right password; was the firmware modified; did the latest system update run; are the right users on the system". It's extremely powerful. Combined with TPM policies you can do things like "The secret to my service can only be decrypted after the service has securely authenticated with my mesh network and proven its identity to an attestation server and only after 3rd of february 2024".

If TPM measured boot is implemented correctly; secureboot is actually redundant. SecureBoot is basically just an allow-list of which bootloaders can run and nothing more.

To summarise:

* SecureBoot only works at time T0 with Binary b0. But say you install a compromised apt package after booting secureboot is not gonna help you with that

* Measured boot is supposed to protect against (or make it cryptographically obvious that it happened) compromise for the entire lifetime of the machine. (Which is what you need if you want to attest that your bare metal servers were not tampered with by law enforcement agencies)

Secure Boot also validates UEFI Option ROMs, not just bootloaders.

It sure sounds useful. It also sounds like it could be used to constrain user freedom once and for all.

It also sounds like non-sense. "Measured" boot's core tech is "updating some write only registers in TPM". So as long as you use OS that does not check these registers, you're fine. (Other than the whole "Secure" (should have been called Restricted Boot, but whatever) boot thing, but that's nothing new and still can be disabled on most systems.)

How do you validate that you're on a machine running secure boot? How about when you connect remotely?

> How do you validate that you're on a machine running secure boot?

That sounds suspiciously like a human problem and not a technical one. In other words, humans configured the server, not a machine.

But, humans forget sometimes... and for that `mokutil --sb-state` will save the day.

I don’t know why I am getting downvoted. We are talking about physical machines that someone had to physically connect hardware to and not a vm that can simply be provisioned via cloud init. Maybe it was pxe booted, but you’d have to really try to get homogeneous hardware.

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