
Originally Posted by
allquixotic
That sounds pretty secure indeed, but requires toggling a switch on the motherboard each time you want to change any files in the operating system. Also, this method does not provide any way to verify that all of the binaries present on the system are genuine: if they were somehow modified through an exploit of some kind, you wouldn't be able to know.
It's like if you send an HTTP request to a remote website without SSL enabled, and a response comes back, you don't know if someone in the middle has messed with the data somehow. You can't verify that it is coming from the endpoint that you sent your request to. But if you send an HTTPS request with SSL or TLS enabled, you are practically guaranteed (barring any vulnerabilities in SSL) that no hosts sitting between you and your endpoint were able to modify the data. If they were, it would immediately fail your message digest check, and your browser would give you a big error message.
This is what secure boot does, but instead of network data, it verifies executable code on disk.