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this post was submitted on 25 Dec 2023
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Personally, I don't see how a TPM module is more useful than full disk encryption with a password you enter on boot.
I struggle to see how it makes automatic login safer given it does nothing to protect against the really common threat of someone physically stealing your laptop or desktop.
I don't trust any encryption or authentication system that I don't have access to the keys for. Microsoft has also kinda made me feel it's more for vendor lock in, like they did with secure boot.
Still, I'm probably being unreasonably pessimistic about it though - be interested to see any practical use cases of it.
In theory, the TPM can be used to verify that the bootloader, kernel and injtamfs haven't been tampered with, which is very very useful as FDE (in the running machine) is only good if that remains true.
I've heard that before, but there are two main problems that stick out to me:
I'm not saying that it's all just a scam or anything like that, but it really feels like I'm missing something important and obvious.
The bootloader is stored unencrypted on your disk. Therefore it is trivial to modify, the other person just needs to power down your PC, take the hard drive out, mount it on their own PC and modify stuff. This is the Evil Maid attack the other person talked about.
Otherwise you simply have a USB boot partition.
Pretty easy to set up, can be taken out to not be modified at run time unless you want plus not being stolen with the computer itself.
I see only drawbacks with a TPM for a computer system like that. In embedded credentials, mobile applications, cold credential storage, etc... it works very well, but it doesn't solve any problem that someone tech savvy doesn't have a better solution for, in my opinion.
If you are a big enough target for an evil maid attack, you are either good enough to circumvent it better than an embedded TPM, or you are rich enough to hire someone who is.
I can't see that being a reasonable approach for them to take, tbh. One option with TPM is that your system logs in automatically to the desktop, in which case they can just turn it on and use it normally. The other is that it requires a password at some point during startup, to which they could just use a (hardware) keylogger.
It only at most auto logs you into the display manager or more generally into login. Then you still need to get root access to modify anything from there. Login would still be based on user password/key/whatever.