Remotely unlocking an encrypted hard disk

mmh0000

This has been a "need" for a long time for home users with FDE. The go-to software solution for Linux has been: https://github.com/gsauthof/dracut-sshd

kotaKat

I'm vaguely reminded of some of the third party disk encryption/preboot management utilities that exist in the Windows space that leverage similar technology. Authentication is done against an online source, and only then is the key sent back to the local machine to unlock the disk. The Bitlocker key is kept nowhere near the local TPM. I've only seen it on some paranoid-level devices in industry (typically devices handling biometric identity verification services). IIRC this one is a Linux image that boots up, unlocks the normal Bitlocker partition via whatever mechanism you need, then hands control back to the Windows bootloader to continue onwards. https://winmagic.com/en/products/full-disk-encryption-for-wi...

ycombinatrix

FYI your decryption key can be MITMed during this process by anyone with physical access to the system, which defeats the purpose of encrypting the disk in the first place. Just use dm-verity for remote servers.

wildzzz

A long time ago, I built my own crashcart adapter with a raspberry pi and a teensy to do something similar. I would sometimes get weird mdadm errors that would hang the boot process and other times, a reboot or power loss wouldn't actually cause the PC to boot back up. The teensy did USB HID emulation for keyboard inputs. I added the ability to push the power button with a fet and some resistors. I had a cheap VGA to composite adapter going into a USB composite capture device so I could at least get screenshots for any weird boot messages. I built a small webpage using flask to display the screenshot, allow for text input, control inputs, and to push the power button. It was a lot of fun building but a basement flood completely wrecked it. Server was sitting on a 6in platform but the crashcart had fallen off the top of the case and was laying on the ground. Oops.

hrtk

I recently ported the WiFi hook to support systemd based initramfs so you could autoconnect via your WiFi to unlock your device. Give it a go: https://aur.archlinux.org/packages/mkinitcpio-wifi

idorosen

There is an old but still reasonable solution with mkinitcpio hooks encrypt/sd-encrypt + ssh, which is very easy to set up with EFI or grub2 onward. Tailscale is probably overkill for this use case, given that you're already exposing pre-/early- boot to the network by setting up interfaces that early. This became much more hermetic with secureboot and TPMs, too.

Scramblejams

I'd love to see this in the bootloader, along with a selection of binaries useful for recovery. Might sound silly but over the years I have had many a remote system get to the bootloader and then no further after an upgrade. Nowadays we've usually got a nicely sized EFI partition, why not stuff it all in there? Gimme a full Linux userspace from the bootloader, it would feel luxurious when I'm up at 3 am trying to recover a broken system halfway across the country. Or is there already a solution to this that I've been missing? (Yeah, KVM/IPMI/etc, I know, but not all hosters make it easy to get to that.)

teddyh

If you want to be able to reboot remotely, and non-interactively (i.e. while you sleep), I (and one other person) created Mandos for this purpose: < https://www.recompile.se/mandos >. It gets the password over the network. If this seems insecure to you, read the FAQ: < https://www.recompile.se/mandos/man/intro.8mandos > Mandos works with initramfs images created by both initramfs-tools and Dracut, and is present in Debian since 2011, so no need to use a third-party package.

Calzifer

> Because initramfs is just a (mostly) normal Linux system, that means it has its own init PID 1. On Arch, that PID is in fact just systemd. Debian has (or had; at least my Devuan still has) a simple shell script as first init. Was an interesting read and helped me understand were to add my remote rootfs decryption. https://salsa.debian.org/kernel-team/initramfs-tools/-/blob/...

epistasis

Glad to see another example of this! Remote unlocking of your personal server's encrypted hard drive is PITA. Other options that I've investigated that involve having a second server: * A second server with Tang, and Clevis in the initramfs OS * Keylime Putting tailscale in the initramfs, and then updating the certs on a frequent enough schedule, seems risky to me. I've already played around with limine enough that I know I don't want to install much in the initramfs...

convivialdingo

Man, that's pretty excellent! I once built a demo-ish encrypted network boot system using similar initrd techniques. It's a fun hack working in the preboot environment.

XorNot

I currently have dropbear-ssh presenting the LUKS password prompt on my home server, but that has the very annoying quality that there's no way to do it from the console if you set that up too. It's not a huge problem but it certainly means some recovery scenarios would be painful.

bitbasher

Not sure how relevant it is, but I use dropbear to remote unlock over ssh: https://www.cyberciti.biz/security/how-to-unlock-luks-using-...

WorldPeas

back before tailscale got good, I used to use tor to remote-unlock on my nixos tower. It worked quite well! https://nixos.wiki/wiki/Remote_disk_unlocking

abound

I have a very similar setup to the author, but instead of running Tailscale in my initramfs, I have a Raspberry Pi sitting next to the home server (which is on my Tailscale network) and I use it like a bastion host. Process is something like: 1. SSH into the Pi 2. Issue the Wake-on-LAN packet to boot the server 3. Tunnel that server's SSH port to my laptop 4. SSH into the initramfs SSH server (I use TinySSH), enter the decryption key 5. Wait for server to come up, then access via Tailscale This is more complicated than the author's setup in that it requires another device (the Pi), but it's simpler in that you don't need to have the initramfs on your Tailnet.

jcul

I have something similar set up to unlock the drives on my home server. Just the SSH in initramfs though, tailscale is pretty cool. I've done stuff with mkinitcpio / initramfs on arch before, can't remember exactly what for. I still run arch on my main laptop. I'm running nixos on my home server though, and adding something like this is so easy by comparison.

varispeed

And me was thinking about having a monitor, camera pointed at monitor and robot arm that I could type password in controlling it remotely.

fennec-posix

Aside from enrolling a token with the TPM to unlock the LUKS volume, this is actually a pretty novel idea. Perfect for older hardware without TPM. I guess it depends on your use-case.

nembal

is it just me, or feels scary that it is happening