Install

Table of contents

Prerequisites

You should have at least 2GB of free memory available.

You need the unlocked variant of one of the supported devices, not a locked carrier specific variant.

It's best practice to update the stock OS on the device to make sure it's running the latest firmware before proceeding with these instructions. This avoids running into bugs in older firmware versions. It's known that the early Pixel 2 and Pixel 2 XL bootloader versions have weird quirks with unlocking. There aren't known issues on other devices, but this is still a good idea. You can either do this via over-the-air updates or sideload a full update from their full update package page.

You need an updated copy of the fastboot tool and it needs to be included in your PATH environment variable. You can run fastboot --version to determine the current version. It should be at least 28.0.0. Don't proceed with the installation process until this is set up properly in your current shell. A very common mistake is using an outdated copy of fastboot from a Linux distribution package not receiving regular updates. Make sure that the fastboot found earliest in your PATH is the correct one if you have multiple copies on your system. The fastboot --version output includes the installation path for the copy of fastboot that's being used. Older versions of fastboot do not have support for current devices and OS versions. Very old versions of fastboot from several years ago are still shipped by Linux distributions like Debian and lack the compatibility detection of modern versions so they can soft brick devices.

Obtaining signify

To verify the download of the OS beyond the security offered by HTTPS, you need the signify tool. If you don't have a way to obtain signify from a trusted package repository, such as on Windows, skip the additional verification. This is an important step, but it only makes sense if you can chain trust from your existing OS install.

On many distributions, signify is available via a signify package in the official repositories. On Debian-based distributions, the package and command name were renamed to signify-openbsd. Following Debian tradition, the signify package and command are an unmaintained legacy mail-related tool for generating signatures.

Enabling OEM unlocking

OEM unlocking needs to be enabled from within the operating system.

Enable the developer settings menu by going to Settings ➔ System ➔ About phone and pressing on the build number menu entry until developer mode is enabled.

Next, go to Settings ➔ System ➔ Advanced ➔ Developer settings and toggle on the 'Enable OEM unlocking' setting. This requires internet access on devices with Google Play Services as part of Factory Reset Protection (FRP) for anti-theft protection.

Unlocking the bootloader

First, boot into the bootloader interface. You can do this by turning off the device and then turning it on by holding both the Volume Down and Power buttons.

The bootloader now needs to be unlocked to allow flashing new images:

fastboot flashing unlock

The command needs to be confirmed on the device.

Obtaining factory images

The initial install will be performed by flashing the factory images. This will replace the existing OS installation and wipe all the existing data.

Download the factory images public key (factory.pub) in order to verify the factory images.

This is the content of factory.pub:

untrusted comment: GrapheneOS factory images public key
RWQZW9NItOuQYJ86EooQBxScfclrWiieJtAO9GpnfEjKbCO/3FriLGX3

The factory.pub has a detached signature made with the previously used GPG key to verify that this is an authorized key rotation. The public key has also been published via the official @GrapheneOS Twitter account, the /u/GrapheneOS Reddit account and is available on GitHub. When the current signing key is replaced, the new key will be signed with it.

Download the factory images for the device from the releases page.

Verify the factory images using the signature:

signify -Cqp factory.pub -x crosshatch-factory-2019.06.23.05.zip.sig && echo verified

Flashing factory images

Reboot into the bootloader interface to begin the flashing procedure.

Next, extract the factory images and run the script to flash them. Note that the fastboot command run by the flashing script requires a fair bit of free space in a temporary directory, which defaults to /tmp:

unzip crosshatch-factory-2019.06.23.05.zip
cd crosshatch-pq3a.190605.003
./flash-all.sh

Use a different temporary directory if your /tmp doesn't have enough space available:

mkdir tmp
TMPDIR="$PWD/tmp" ./flash-all.sh

Wait for the flashing process to complete and for the device to boot up using the new operating system.

You should now proceed to locking the bootloader before using the device as locking wipes the data again.

Locking the bootloader

Locking the bootloader is important as it enables full verified boot. It also prevents using fastboot to flash, format or erase partitions. Verified boot will detect modifications to any of the OS partitions (vbmeta, boot/dtbo, product, system, vendor) and it will prevent reading any modified / corrupted data. If changes are detected, error correction data is used to attempt to obtain the original data at which point it's verified again which makes verified boot robust to non-malicious corruption.

In the bootloader interface, set it to locked:

fastboot flashing lock

The command needs to be confirmed on the device since it needs to perform a factory reset.

Unlocking the bootloader again will perform a factory reset.

Disabling OEM unlocking

OEM unlocking can be disabled again in the developer settings menu within the operating system after booting it up again.

Verifying installation

Verified boot authenticates and validates the firmware images and OS from the hardware root of trust. Since GrapheneOS supports full verified boot, the OS images are entirely verified. However, it's possible that the computer you used to flash the OS was compromised, leading to flashing a malicious verified boot public key and images. To detect this kind of attack, you can use the Auditor app included in GrapheneOS in the Auditee mode and verify it with another Android device in the Auditor mode. The Auditor app works best once it's already paired with a device and has pinned a persistent hardware-backed key and the attestation certificate chain. However, it can still provide a bit of security for the initial verification via the attestation root. Ideally, you should also do this before connecting the device to the network, so an attacker can't proxy to another device (which stops being possible after the initial verification). Further protection against proxying the initial pairing will be provided in the future via optional support for ID attestation to include the serial number in the hardware verified information to allow checking against the one on the box / displayed in the bootloader. See the Auditor tutorial for a guide.

After the initial verification, which results in pairing, performing verification against between the same Auditor and Auditee (as long as the app data hasn't been cleared) will provide strong validation of the identity and integrity of the device. That makes it best to get the pairing done right after installation. You can also consider setting up the optional remote attestation service.

Replacing GrapheneOS with the stock OS

Installation of the stock OS via the stock factory images is the same process described above. However, before locking, there's an additional step to fully revert the device to a clean factory state on modern devices with Android Verified Boot 2.0 (AVB) like the Pixel 2, Pixel 2 XL, Pixel 3, Pixel 3 XL, Pixel 3a and Pixel 3a XL. It isn't necessary for devices with legacy verified boot like the Pixel and Pixel XL.

The GrapheneOS factory images flash a non-stock Android Verified Boot key which needs to be erased to fully revert back to a stock device state. After flashing the stock factory images and before locking the bootloader, you should erase the custom Android Verified Boot key to untrust it:

fastboot erase avb_custom_key