Most Big Tech efforts to secure the boot process give the vendor control over what software you are allowed to boot on your laptop, with keys they control.
With PureBoot Restricted Boot, you can lock down your boot firmware to only boot trusted, signed executables both on a local disk and USB, so you control the keys. Let’s see how you tighten down your boot security with Restricted PureBoot in this video.
Restricted Boot is disabled by default to give you maximum flexibility in what OSes you can boot, but once you enable it, an attacker can’t disable it without triggering a tamper warning.
To enable restricted boot, ensure you’re running at least version 23 of PureBoot. If you need to upgrade, follow along with this video.
For those running an older version of PureBoot:
Flash or update the BIOS->
Flash the firmware with a new ROM and retain BIOS settings.
mkdir ~/updates cd ~/updates wget https://source.puri.sm/coreboot/utility/raw/master/coreboot_util.sh -O coreboot_util.sh sudo bash ./coreboot_util.sh
Have a look at this video for a deep dive into how the Librem Key works with PureBoot, or continue on to enable PureBoot restricted boot.
With the latest Pureboot installed, head to
Change Configuration Settings ->
Enable Restricted Boot.
Save changes to the running BIOS
After rebooting, you can still boot into your system as normal, but you’ll no longer be allowed to ignore any tamper warnings and boot into failsafe mode. This also disables options like the recovery shell.In this mode, your computer will outright refuse to boot when your boot files aren’t signed with your paired Librem Key.
During normal use, when you update your OS while Restricted Boot is enabled, it will behave much like you expect. If your kernel changes, you will be prompted to re-sign files in /boot using your Librem Key and once you do, you will be able to boot into your OS as normal.
In this mode, you can also boot pre-approved signed distros via USB. Instead of imaging directly to a USB, copy the ISO and the corresponding .asc GPG signature file the vendor provides. This will allow you to boot from ISOs on USB disks, as long as their signature matches one of the trusted public keys in PureBoots ISO keyring. By default, we include public keys for Arch Linux, Qubes, Tails, and PureOS. Later on, we’d like to add a feature that lets you modify the approved keys from within the GUI itself, but that feature didn’t make it for this first release.
To disable Restricted boot, go back to
Change Configuration Settings and select
Disable Restricted Boot
To prevent someone from disabling this without detection, once you select this option, your TPM will be reset.
This will notify the proper user of tampering once they try to boot their computer again.
PureBoot provides flexible security measures, with defaults that balance security with ease of use. Restricted Boot allows you to tighten down boot security even further, while still having full control over your own system.
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