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Need help with setting up full disk encryption (FDE) where /home is on another drive. (lemmy.world)

submitted 3 days ago* (last edited 3 days ago) by mazzilius_marsti@lemmy.world to c/linux@lemmy.ml

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Any distro would do, but for my case, it is Arch because I have more control over the partitions. I would like the OS, so root, swap and others on 1 drive. The /home should be on a separate drive. The tricky thing is to have everything encrypted, except /boot and /efi of course.

Now, here is what I can do

FDE on 1 drive. This is easy: you create /efi, /boot and then create a large LUKS partition. From there, you create LVM on that LUKS partition and get your: /, /home and swap. Then mount everything correctly and install.

In the grub config, you only need to set it so it knows the LUKS partitom and where the root is. For eg, if your LUKs partition is /dev/sda3, you do:

cryptdevice=UUID=<uuid of the /dev/sda3>: cryptlvm rootfs=/dev/vg/root.

Unencrypted /home on another drive. This is like 1) but /home is mounted on a separate drive. Still need to do the grub config, but nothing is needed for /home. It is automatically mounted when you login.

Now for my case: Encrypt /home

The encryption and mount part is easy. But how to get the OS to recognize it? The Arch wiki has this weird thing where you create an encryption key, they called it home.key, using cryptsetup. You then store the key in /etc and then in your /etc/crypttab, you specifiy the drive with /home and location of the key. No need for any passphrase.

The problem I have with this is that keys are stored in root. So if my root system is corrupted, I cant even decrypt home....

Any advice is welcome..

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[–] mazzilius_marsti@lemmy.world 2 points 1 day ago* (last edited 1 day ago)

Well thanks everyone. I finally managed to get it to work on Arch. System has separate encrypted root and swap in LVM, and a separate encrypted home. It can suspend and hibernate. Below are my steps

DISK PREP

partition the main drive for your swap and root first. For me, it is a boot partition + an EFI + a LUKS container with LVM on top. Create your volumes. I use Arch, so format and mount them appropriately before pacstrap. Leave out mount point for /home.
Go to your other drive, follow: https://www.cyberciti.biz/hardware/cryptsetup-add-enable-luks-disk-encryption-keyfile-linux/

to create a LUKS container that is encrypted with: a keyfile and a password. Test both to make sure you can open the locked drive. Format and mount it at /mnt/home or where you want the /home to be.

Pacstrap and then genfstab.
Important: Make sure to copy the keyfile from your archiso environment to your chroot environment aka your system. Otherwise, when reboot, the keyfile is gone. I put it in /root and set permission so only root can read.

AUTOMATIC UNLOCK

First, fstab. When you do genfstab, things should be fine. But just double check the UUID is correct for /home. Note in fstab, the UUID is the unlocked one: so the one with /dev/mapper/home. Change to noatime if you desire.
Second, crypttab. Assume you decrypt your LUKS home as "home". Add this:

home uuid of the unencrypted home drive location of the keyfile luks

The link above said to just use /dev/sda, but imo UUID is safer if you have a removable drive.

Third, grub. Edit your /etc/default/grub and append the following to GRUB_CMD_LINUX:

"rd.luks.uuid=UUID of the locked luks home drive"

FOR HIBERNATION

For some reasons, hibernation doesnt work out of the box. It works when I have everything in 1 drive, i.e 1 boot, 1 efi, 1 lvm on luks for /home, swap and /. The fix is simple:

add "resume" to /etc/mkinitcpio.conf. Add before "filesystems" . Rebuild your initramfs with mkinitcpio -P.
add to /etc/default/grub: "resume= uuid of the unlocked swap partition". Or if you do LVM, just use "resume=/dev/vg/swap".

Special thanks to bodaciousFern@lemmy.dbzer0.com and Lemmchen@feddit.org for giving me correct ideas about "rd.luks.uuid" and that LUKS can do both pass and keyfile.