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LUKS decrypt at boot over SSH? (lemmy.world)

submitted 3 days ago by clif@lemmy.world to c/linux@lemmy.ml

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I've done a little research but curious about first hand experience.

I've got a little home server that is full disk encrypted with LUKS (+LVM, of course). It's headless (no display, no keyboard, etc) and just lives attached to the back of my desk, out of the way.

If it gets rebooted due to a power outage, I can plug in a keyboard, wait long enough for it to get to the LUKS password prompt, enter password, hit enter, and assume it worked if I see the disk activity light blinking. Worst case scenario, I can move it to a monitor and plug it in to get display too.

Because lazy, I'd prefer to be able to enter the decrypt password remotely. "Dropbear" seems to be a common suggestion but I haven't tried it yet.

So, asking for your experience or recommendations.

I'll start. Recommendation #1 - get a UPS : D ... But besides that.

Addendum: either way, I currently need to be home to do this because I access it remotely via tailscale along with my desktop. Since both are full disk encrypted, neither will boot to the point of starting tailscale without intervention. But, I might repurpose a nonencrypted RPi with SSHd to act as a "auto restarts with tailscale so I can SSH to it, then SSH to server to enter the LUKS password" jump point.

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[–] just_another_person@lemmy.world 1 points 3 days ago* (last edited 3 days ago) (2 children)

Clevis with TPM+Tang is the most secure you're going to get as far as automated unlocking goes.

https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/8/html/security_hardening/configuring-automated-unlocking-of-encrypted-volumes-using-policy-based-decryption_security-hardening

Dropbear is still a thing, but going to be more problematic.

[–] data1701d@startrek.website 3 points 3 days ago

+1 for Clevis. I’ve been using it on my laptop for a year and it works like a charm. Sometimes, you need to update bindings after kernel updates, but it’s overall quite smooth.

[–] clif@lemmy.world 1 points 2 days ago (1 children)

If I'm reading the docs correctly, Clevis can rely on a separate Tang server for retrieving the decryption key, right? So in that scenario I'd need to have another machine for Tang that can also auto-boot without entering a boot/LUKS password. Otherwise, if both machines (server+clevis and Tang server) were in the same room and restarted due to power loss, neither would be able to boot if both were encrypted... or did I misunderstand something important?

And I don't think I actually want "automatic" unlocking. I just want to be perform the unlock (enter LUKS password) remotely. I realize that comes with manual intervention (entering the password remotely) but I'm okay with that. I should probably have clarified that by "home server" I mean a machine the serves nice to have stuff, nothing mission critical. Plus I'm really the only one who uses it currently so I'll notice it's down when something doesn't work and can then initiate the remote unlock/boot : D

Clevis is interesting but I don't think it matches my specific situation. Glad I know about it now though, thanks for the info.

[–] just_another_person@lemmy.world 3 points 2 days ago (1 children)

If you just want to remotely interact with LUKS to unlock it, I think dropbear-initramfs module is your only option.

Clevis+Tang is essentially the same thing but automatic, and yes it does require a separate machine and network access to that machine.

[–] clif@lemmy.world 2 points 2 days ago

Great, thanks for checking my understanding of it.