this post was submitted on 28 Sep 2023
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To go back to basics, why is FDE not suitable for your needs?
I second this.
Full disk encryption is entirely practical for everyday use. If you don't already have a dedicated TPM, your motherboard/CPU may provide a software TPM (fTPM?). If so, you don't even have to interact with the machine during boot. It's just a bit slower to start up (by a few seconds), which really isn't a big issue for your average user.
Pardon my ignorance here, but I don't get it how is the whole thing still safe with unlocking from TPM instead of me providing the password at boot time?
Considering now anyone can just boot the machine into the installed system then bruteforce/exploit something to get login/get read permissions and make a plain copy of the data?
Where, without tpm, as long as I do not type in the encryption password myself I have a pretty high guarantee that the data is safe, especially when I am not at the (powered down) computer.
This is what I don't understand either. It seems like with tpm it only protects the data from someone taking or copying the hard drive, but the bigger risk seems like what you describe
plus, using an encryption password and then automatically logging in the user prevents needing to enter two passwords while still keeping the data secure as long as the machine is off
You have a competent grasp of the situation
The idea behind it is that the files are stored encrypted at rest, which is really what you want, because once a system is booted, you have to play by the computer's rules (respect file permissions, policies, etc.).
The TPM provides a secure mechanism to provide a decryption key to the computer during boot, eliminating the need for direct interaction.
Could it be compromised? Probably, but it would take considerably more effort than a man-in-the-middle on your keyboard via a logic analyzer.
This is a common misunderstanding insofar as how encryption works. You can't flick a bit and TURN your storage unencrypted nor can you plausibly make your computer obey restrictions.
If your storage is encrypted it remains encrypted always including the file you have open right now. Your takes a plausibly length usable string and uses it to compute or retrieve the long binary number actually needed to decrypt your files. This number is stored in memory such that encrypted files can be decrypted when read into memory.
Once that key is loaded in memory anyone with 10 minutes and access to google could trivially unlock your computer in several different ways. It is virtually exactly like having no security whatsoever.
If you don't actually enter a passphrase to unlock you have no meaningful security against anything but the most casual unmotivated snooping.
Your little sister might not be motivated enough to read your diary but the dipstick that stole your laptop will definitely be spending your money.
I highly doubt it.
If you have any tips for how I can personally bypass my computer's encryption in 10 minutes without being able to login, I'd love to try my hand at it.
You aren't actually asking to how to bypass encryption because the key is already in memory. You are asking about the much simpler task of compromising a computer with physical access to same. Depending on configuration this can be as ridiculous as killing the lockscreen process or as hard as physically opening the case chilling the contents of ram enough that data survives transfer to different physical hardware. See also the massive attack surface of the USB stack.
That doesn't sound trivial at all.
On most systems you can press a hotkey in grub to edit the Linux command line that will be booted and in about 7 keystrokes gain access to any unlocked filesystem. Asking how you can break into a system you physically control is like asking how many ways you could break into a house supposing you had an hour alone with a crowbar the answers are legion. No machine in someone else's hand which is unlocked can possibly be deemed secure.
Even dumber no installer will create such an insecure configuration because the people that design Linux installers are smarter than you.
I'm not advocating for this right now, but yes that is why when using TPM password, one must insure to enable secure boot, enable bios password, disable boot media, and disable grub editing. That's the recommended proceedure for this setup.
This is essentially how HEADs works too. Some very smart people have worked on TPM boot and it is even built into systemd. You're just wrong here.
Reference:
Whether I would fully rely on the systems proper operation against a state sponsored adversary is a different question though.
Actually, thinking more about this...
Can you give an example of this grub cmdline bypass? If what you're saying is true, this would be a huge issue. I'd switch bootloaders over something like this.
You can disable editing and enable password in grub, done. That's the recommended proceedure for TPM boot.
Finally, someone reasonable.
TPM is only kinda related to FDE, in that it can be used to unlock a LUKS encrypted volume. FDE doesn’t require a TPM.
I also wouldn’t recommend automatically unlocking your root partition on boot using the TPM as this allows access to your data if the device is stolen, which, for an average user, defeats the main purpose of FDE.
How so? The data is still encrypted on the drive after boot, so unless your machine also automatically logs you in, there shouldn't be anything to worry about.
At that point you relying on the fact that nothing running in your machine at boot can be compromised - after all, everything running on your machine has access to your unencrypted data.
If you don’t automatically unlock using the TPM, an attacker only has access to encrypted data.
As others explained: If the FDE key is in RAM, I'm vulnerable. My thread model includes a stolen Laptop with the attackers able to freeze my RAM and reading out the keys.
Thank you for mentioning TPM though. Didn't know of that before. :)
There are plenty of reasons to not want FDE or not want just FDE alone. Shared computer, your data isn't safe if you share the FDE password with another user who needs to share the system. He said he's paranoid, so he is wanting his data encrypted above all. Home directory encryption, especially on top of FDE, while a performance hit, would do well for that. But most importantly, he said FDE isn't practical for him, end of FDE story.
Simple convenience. I usually don't have the time to wait one or two minutes until my full disk is decrypted (I am often late and the only person in a group meeting who brought a laptop for taking minutes).
I also use a weird keyboard layout (Neo 2) and I never got grub to load with that layout. Typing a 40+ passphrase in QWRETZ is just cumbersome to me.
Also: I hate to admit it, but I am a bit vain and simply would like a nice gui for entering my password.
Edit: I forgot to add that I'm playing with the idea of getting a surface tablet and installing linux on it. Then I couldn't count on awlays having a usb keyboard with me.
You can setup FDE that utilizes TPM like Windows does with bitlocker, in such a way that your backup phrase is only necessary if something about your hardware changes.
Last I set it up however, there wasn't any easy/automatic way. Searching "luks TPM" should get you started.
I've been using this guide for ages.
https://fedoramagazine.org/automatically-decrypt-your-disk-using-tpm2/
I have a LUKS-encrypted laptop (1GB SSD), it takes about 10 seconds between typing in the password and the start of the boot process.
Would a FDE with FIDO2 hardware key meet your needs?
I don't think so. There's a high likelihood of both laptop and key ending in the same hands if the laptop is stolen.
The concept of hardware key is precisely to be removed as soon as you are not in front of the device.
In my case, I'm using one this way. It is tethered to myself with a metal chain, so as soon as I'm not in front of my computer, they are separated and my sensitive data protected. Of course it won't prevent someone from threatening to harm me in order to get access to said key, but he might as well do the same to get access to any kind of password.