this post was submitted on 25 Dec 2023
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I'm curious about the possible uses of the hardware Trusted Protection Module for automatic login or transfer encryption. I'm not really looking to solve anything or pry. I'm just curious about the use cases as I'm exploring network attached storage and to a lesser extent self hosting. I see a lot of places where public private keys are generated and wonder why I don't see people mention generating the public key from TPM where the private key is never accessible at all.

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[–] wildbus8979@sh.itjust.works 15 points 11 months ago (9 children)

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.

[–] savvywolf@pawb.social 9 points 11 months ago (8 children)

I've heard that before, but there are two main problems that stick out to me:

  • A lot of the marketing for TPM (at least when I was setting up bitlocker on Windows) suggests that it's used to support decrypting drives without a password on boot. But that doesn't seem to offer any protection from the devices being stolen. The bootloader may be safe but it's not actually verifying that I'm the one booting the device.
  • I can't think of a situation where someone would be able to actually modify the bootloader without also having full access to the files and secrets. Especially in a single-boot environment where every time the system is running, the device is decrypted.

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.

[–] baseless_discourse@mander.xyz 2 points 11 months ago (1 children)

If the device is stolen, your disk is still encrypted at all time. If you believe your OS's login system is reasonably secure, then the attacker should have no way to access your data: they cannot access the data from software because it is blocked by login screen, they cannot access the data from hardware because it is protected by FDE.

One of the misconceptions I had before is that I assumed that the disk will be decrypted when you enter the LUKS password. This is not true, the password is loaded into the ram, and only decrypts necessary parts to RAM. All the data on the disk is never decrypted, even when you are working in your OS.

[–] SpaceCadet@feddit.nl 6 points 11 months ago* (last edited 11 months ago)

they cannot access the data from software because it is blocked by login screen

The system may still be vulnerable to over the network exploits. So for example, if the system is running sshd, and a couple of months from now a root exploit is found (à la heartbleed), the attacker may get inside.

It's somewhat of a long shot, but it's still a much larger attack surface than butting your head against a LUKS encrypted drive that's at rest.

they cannot access the data from hardware because it is protected by FDE.

RAM is not protected by FDE. There are (obviously non-trivial) ways to dump the RAM of a running system (Cold Boot attacks, and other forensic tools exist). So if the attacker is dedicated enough, there are ways.

One of the misconceptions I had before is that I assumed that the disk will be decrypted when you enter the LUKS password. This is not true, the password is loaded into the ram, and only decrypts necessary parts to RAM. All the data on the disk is never decrypted, even when you are working in your OS.

Hah! That would be impractical :) Imagine having to decrypt your entire 32TB drive array everytime you booted your computer.

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