Ubiquity needs support for fscrypt

[Redsandro]

Home encryption using ecryptfs was removed in Ubuntu 18.04 for reasons. Full disk encryption was recommended as an alternative, and set as the one-size-fits-all solution in ubiquity.

Not everyone agrees that encrypting the entire disk is the best alternative. Some prefer a more lightweight solution. Others have families and like to share a laptop, perhaps even with an unprivileged password-less guest account, and family members want to encrypt their home with a personal password.

Can we re-introduce (an option to choose) home encryption using fscrypt? Not only was this suggested (prematurely) by the Ubuntu 18.04 release notes, it's also feature-complete now with v2 kernel encryption policy patches merged in kernel 5.4, which is the default kernel on Ubuntu 20.04 LTS.

Setup
-----

Steps that would need to be scripted in ubiquity are as simple as:

```
apt install fscrypt libpam-fscrypt
fscrypt setup
fscrypt setup /
fscrypt setup /home ## only if home is on a separate partition
fscrypt encrypt /home/$USERNAME
```

For the rest you can probably re-use the ubiquity widgets and detection code from the ecryptfs days.

Keep in mind that the fscrypt packages on the Ubuntu repositories are outdated. See: https://bugs.launchpad.net/ubuntu/+source/fscrypt/+bug/1882993

Resources
---------

Fscrypt ext4 native encryption documented on Kernel.org
https://www.kernel.org/doc/html/v5.4/filesystems/fscrypt.html

Build instructions
https://github.com/ebiggers/fscrypt#fscrypt-

Fscrypt on Arch Linux
https://wiki.archlinux.org/index.php/Fscrypt

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Tim Ritberg (xpert-reactos)]

Yes, please. Goog idea.

[Redsandro (redsandro)]

Please give this issue some love too:
https://bugs.launchpad.net/ubuntu/+source/fscrypt/+bug/1882993

[wysiwyg31 (wysiwyg31)]

I think some problem has to be considered: as far as I understood, the folder /.fscrypt shall not be deleted (risk to loose access to your data?)
if yes, it's a bit risky in case you re-install system on / with a separated encrypted /home that you want to keep.

I also would like to add an other issue of full disk encryption: it need to enter password at boot on the machine...it cannot be done remotely.
So if you need remote connexion to a powered-off device (with wake on lan) or a rebooted device (for example due to power interruption), it's not possible.

[Redsandro (redsandro)]

> I think some problem has to be considered: as far as I understood, the folder /.fscrypt shall not be deleted (risk to loose access to your data?)
> if yes, it's a bit risky in case you re-install system on / with a separated encrypted /home that you want to keep.

When you set up your encrypted home using the fscrypt tool and it detects that /home is not the same as /, it will offer to create a recovery protector. This creates a file in your home called fscrypt-recovery-passphrase.txt (or something like that) that needs to be written down (similar to ecryptfs). This protector is stored on /home/.fscrypt.

This means you can unlock the directory on a different (or new) system, and once unlocked, you can create a new login protector.

I assume ubiquity can be scripted to detect a pre-existing user home was encrypted using fscrypt, query for the recovery protector passphrase, unlock the directory, and add add a login protector.

> I also would like to add an other issue of full disk encryption: it need to enter password at boot on the machine.

I hadn't even thought about that because I never use full disk encryption. Some will argue that this is the point as it is more secure, but I would argue that you should have the choice to use your computer in a more versatile manner while still being able to protect your personal files from raw disk reading with a bootable usb stick. Options could be presented:

Encryption options:

* Full Disk Encryption - (Recommended) Best security. Suitable for single user hardware.
* Home Encryption - Good security. Suitable for shared family computers and WoL.
* No Encryption - No security. Good for guests and internet cafes.

[Redsandro (redsandro)]

Note that the above was added in fscrypt 0.2.6 (january 2020), and it is described here:
https://github.com/google/fscrypt/pull/167

Ubuntu still packages 0.2.5 (september 2019)

[Thiago Martins (martinx)]

I do want home-based encryption but, what about the new `systemd-homed`?

[Redsandro (redsandro)]

That's a "no" on Ubuntu 22.10?