Easily switch on/off keyless reboot for ext4 Linux systems with LUKS encryption
Home page: https://github.com/jikamens/keyless-entry
LUKS filesystem encryption on Linux is great, but sometimes you want to be able to reboot your system without needing to enter a decryption key on reboot, e.g., if you need to reboot it remotely. This script helps you do that.
The mechanism of this script is based on the approach that Tobias outlined in https://askubuntu.com/a/997668. Thank you to Tobias for leading the way!
This script is only known to work with ext4 filesystems, and probably does not work with ZFS. Pull requests to remedy that will be gratefully accepted.
Copy the file keyless-entry to somewhere in your root filesystem, e.g., /usr/local/bin, and make sure it is executable.
You also need the cryptsetup utility to be installed, and you
probably also need the cryptsetup integration with initramfs. In
recent Ubuntu releases, you get these by installing the
cryptsetup-bin and cryptsetup-initramfs packages. You may need
other packages on other Linux distributions. If you know what's needed
for another OS, feel free to submit a PR to update this README.
After installing the script, run it from its installed location with
one argument, configure. It will prompt you for your existing
decryption key once for every encrypted filesystem listed in
/etc/crypttab. After doing this your system is not yet configured
to reboot without a key being typed.
To do that, run the script again, this time with the argument
enable-once or enable-always. As these names suggest, if you
specify enable-once then no key will be required for the next reboot
but subsequent reboots will require it.
You can specify --default-kernel with enable-once or
enable-always to only enable for the default kernel that grub will
use the next time it boots, or you can specify --kernel-version one
or more times to specify one or more kernel versions to enable for.
Otherwise enable and disable impact all installed kernels. The reason
why you would want to only enable for a subset of installed kernels is
because it makes enable and disable faster since fewer initial RAM
disks need to be rebuilt, and in the case of enable-once, this also
makes the next reboot finish faster (as noted below).
To disable keyless entry, run the script again with the argument
disable. To remove the configuration from your system as if you had
never set it up, run the script with the argument unconfigure.
If you end up in a bad state where keyless entry is partially enabled
and you want to restore a known state, run the script with the
argument recover, which disables keyless entry even if it isn't
fully enabled and rebuilds all the initial RAM disks.
-
Your initial ramdisks are regenerated as part of the reboot process, so while the next reboot will not require a key to be entered by hand, the reboot will take somewhat longer than usual.
-
Because the script configures
/etc/rc.localto invoke itself during reboot, it's important to run the script from its installed location as specified above.
Thank you to John Hancock <john.m.hancock@gmail.com> for helping to make the script more secure by adding logic to use a temporary key when enabling keyless entry along with a permanent key that's only accessible on the encrypted filesystem.
Copyright 2022 Jonathan Kamens <jik@kamens.us>.
This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>.