Tutorial: Full disk encryption on Librem5

With the disclaimer that I did not do this …


Yes, this.

But not just any 32 MB that is free. I believe it has to be the last 32 MB that is free.

Not applicable.

That’s half correct. There’s no new partition. There is an effective adjustment to the size of the existing partition - but whatever happens you don’t have to make that adjustment because the command does it for you. The existing partition is reduced automatically by that command (in order to allow space for the LUKS header). So you don’t have to change the size of the partition.

(Actually, the 32 MB free space at the end, apart from allowing room for the LUKS header, may also allow the process to be done “in place” - because it is using that free space as part of rewriting the entire plaintext partition while not stuffing it up. But I don’t know the details of the implementation. Might have to read sources.)

PS To save you having to mess around further, you may want to choose the key slot encryption parameters at the time of first encryption. That is, if you use the example command as shown then you are taking default parameters for both the disk encryption and the key slot encryption. The default for disk encryption will likely be appropriate (based on recent testing, and only in my opinion of course) but the default for key slot encryption may not be ideal for the Librem 5 (although “ideal” is in the eye of the beholder). Refer e.g. Our LUKS fde may not be enough anymore - #66 by Loki and discussion around that post.

However it’s not that big a deal. While (re-)encrypting the entire disk is going to be slow, changing the encryption of the key slot after the fact is quite quick.


sudo cryptsetup reencrypt --encrypt --type luks2 --reduce-device-size 32m /dev/plaintext_device

took about 50min, however on reboot mobian was stuck on the screen showing all the device mapping warts (like gnss etc.), the LUKS passphrase entry window never showed.

sudo cryptsetup reencrypt --decrypt --header detached-luks2-header /dev/plaintext_device

took about 50min, now it is back to normal and booting.

I encrypted the main usable partition ~32GB in /dev/sdx2, I wonder if I should have encrypted the entire eMMC /dev/sdx instead, though I don’t think so. Maybe I will try to do the default type or LUKS1 encryption, maybe that works better, I remember having used that in the past without issues.

I think just the individual (root) partition. But then:

I don’t think you mentioned that little detail.

You would need to know what Mobian expects! Assuming that it expects an unencrypted boot partition, you would need to know whether you have to change anything in the boot partition in order to handle an encrypted root partition and you would need to know what specific encryption support it has.

Unless this is a test phone, I would not put LUKS1 on it. LUKS1 lacks important features that contribute to security (hence the existence of LUKS2). LUKS1 is much better than plaintext but if you really find that Mobian only has support for LUKS1 then I think you are driving yourself into a corner. Alternatively, maybe it is possible to upgrade Mobian before even starting this exercise so that it does have full support for LUKS2. You would need to investigate Mobian’s documentation.

Regardless of any of the above … after the reencrypt --encrypt it can be helpful to verify the encrypted partition on the host computer i.e. by opening it and mounting it on the host. If it all looks fine on the host then that is a good sign that adding encryption did at least work. I appreciate that you have now reverted the change and hence can’t immediately do that.

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I looked at it and it was fine, cryptsetup did it’s job as expected, so most likely mobian boot order or setup not knowing what to do with encrypted root.

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If the expectation is to encrypt the root/OS disk/partition then boot into that encrypted root/OS disk/partition, then there are some additional steps required.

At the very least, you’ll need to add an entry for the disk/partition within /etc/crypttab, you’ll also need to provide some mechanism to allow for entering the passphrase for the encrypted device during boot. With these in place you’ll also need to regenerate the boot image (update initramfs) to include the additional config.

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Mobian has support for LUKS2 and has done (as far as I’m aware) since it’s inception.

Mobian doesn’t require any special consideration over any other OS, the Librem 5 images offered up by Mobian have separate boot and root partitions making things relatively straightforward.

Personally, I wouldn’t bother with convert plain to encrypted on device (the disk I/O performance of the Librem 5 makes this quite a painful experience for me) I’d just create and prepare the LUKS container offline before pushing it to the device.

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Yes, looking at information recorded by me for my own messing around, I think this would be an overall win in terms of time i.e. (using Jumpdrive) copy Librem 5 disk contents to local disk image, encrypt on the much faster desktop/laptop, copy disk image back. Can even do the mucking around with the boot partition while on the desktop/laptop.

The win would be amplified if there are failures (as occurred here) so that things have to be done more than once.

That said, I chose not to do this (encrypt in place contents) anyway, instead flashing the LUKS variant from scratch and then re-establishing my environment.

Thank you so much for all the valuable input. I figured out how to setup the crypttab. The key is to install osk-dl, which isn’t installed on mobian (maybe it has a different osk to point to) and have it point to that so you actually get a OSK to input the password. In addition to adding the mapped LUKS UUID. I used the pureos format that had crypttab setup properly as a guide and Ubuntu as well where I have an encrypted volume, but also a hardware keyboard so don’t need the osk-dl.

Unfortunately the encryption had issues the second time I tried (over jumpdrive with device attached) and wasn’t able to open the encrypted volume due to superblock bad, some other fs errors. So it is a dud after all with LUKS2, something might have gone wrong.

The general takeaway is then take the .img downloaded file mount it on your computer, encrypt, setup crypttab with osk, and afterwards flash to device.

That would also be my preference, it is typically a more straightforward process, but if there is no LUKS variant image for the given OS then it’s not an option.

I gave converting the latest plain Mobian Trixie image to LUKS2 to check if there is currently some issue with LUKS2, plus it gave me an opportunity to try unl0kr instead of osk-sdl, it was a bit of a dance but ultimately, it works fine…

On boot it’ll confirm it’s waiting for the LUKS container with a quick flash of a message that it’s “Waiting for encrypted device” before throwing up unl0ckr to accept passphrase and then you’ll then get the LUKS container set up confirmation message, before getting to user login then desktop.


nice for unl0kr do you mind sharing the /etc/crypttab line configured to use that?

unl0kr runs in keyscript mode, for crypttab you just need to provide the full path to the unl0kr keyscript to the keyscript parameter.

I installed the unl0kr package from the trixie repo, the package includes the required keyscript and it’s installed by default to /usr/share/initramfs-tools/scripts/unl0kr-keyscript

The full entry in /etc/crypttab would be similar (changing UUID to match your setup) to…

crypt_root UUID=32cc891d-58b7-4b40-adaf-349b8018e8cc none luks,discard,keyscript=/usr/share/initramfs-tools/scripts/unl0kr-keyscript,initramfs

The only additional config change I made was to /etc/unl0kr.conf to change the default theme variant from light to dark, within the file there is a [theme] section specifying…


I just swapped the default and alternate values.

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I realize that the post I’m referring to (#29) is a year and a half old, but I would very much like to read your article on the Github Wiki. The link in your post is now broken. Is the article still available anywhere? Thanks.


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No, the Wayback Machine does not have a snapshot of it, and the GitHub account seems to be deleted or unlisted.

OK. Thanks for responding!

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