Unlocking your Robot¶
The first step in your new adventure is unlocking your robot and transforming it from a normal Vector to and OSKR enabled Vector where you will be able to directly access all internals.
What is Unlocking? Why do we do it?¶
By default the operating system of Vector is secure and unchangeable with digital signatures to ensure system integrity. The security starts with encryption keys baked in to the hardware itself and works its way down to the final operating system image. In each phase of the boot process the previous system verifies the next system loads. If even one bit, byte, letter, etc change in any of the phases then the system will stop loading and come to a halt. This is done for:
Security We want to make sure a malicious user hasn’t modified the code to do something that it shouldn’t be doing, like sending spam emails. Even if a hacker or bot network is somehow able to access the Vector they won’t be able to make any changes to turn it in to the wrong kind of bot.
Reliability We don’t want mistakes to break the device. There are currently hundreds of thousands of Vectors out there, and we’re hoping for millions and billions. At that level even small problems can add up quickly. Ensuring the Operating System hasn’t been changed ensures reliability.
At boot time the following verification happens.
The hardware chip itself verifies the cryptographic signature on the low level ABOOT partition. It is for all practical purposes impossible to override this check.
The ABOOT partition has another security key baked in that it uses to verify the BOOT partition and load it. The BOOT partition is a skeleton linux operating system to bootstrap the main system.
The BOOT partition loads the appropriate SYSTEM partition which is the final software to run.
In the case of a normal Vector the SYSTEM partition is protected by an Android-specific system called
dm-verityto ensure that this partition isn’t modified.
Development Vectors used internally by the company, and now OSKR Vectors do not enforce
dm-veritysecurity on the system partition allowing development of new features.
In addition to these layers of cryptographic security a new Vector comes with a recovery filesystem installed for reliability purposes. This has been loaded on at the factory and is the boot system of last resort when no other software will load.
We then set aside two slots for day-to-day software usage called A and B. When you install an OTA update the system:
Downloads the update.
Performs some basic verification to see if the image ‘fits’ with the current configuration.
Decides if the A or B slot is the available one.
Copies the new filesystems on to the slot.
Flags the new slot as the ‘good’ one.
Reboots and loads the software. If the software fails to load it marks the slot as invalid.
If there is a previously valid slot, such as A after an update to B was installed, it reverts to that.
If there is now good A or B slot it reverts back to the recovery filesystem so you can try to install again. This is important. No matter how bad the running system gets messed up we should always be able to fall back to the recovery filesystem
So what does all this mean? We’ve got two conflicting goals:
Normal Vectors should have all the security and reliability that are expected for a consumer electronic device and need to remain locked down.
OSKR Vectors should have some ability to lock down the software installed but some ability to modify software for development.
Because of this each type of robot need to enforce different requirements each needs a different set of cryptographic signatures so that a normal Vector behaves the way it should and a OSKR unit behaves the way it should.
To accomplish this and unlock a OSKR robot we need to:
Reprogram the ABOOT image with a new cryptographic signature.
Sign the new BOOT images with this signature.
Create new recovery filesystems signed by the new keys because the old ones will be considered ‘bad’ when we swap out the signatures.
This is where things get tricky. The normal assumption is that the ABOOT and recovery filesystems get installed directly at the factory and physically written directly to the chips before final assembly of the robot, and never touched again.
But to do this outside of the factory we need to do this with our OTA (Over The Air) update scripts. And we need to modify software partitions that were never expected to be written in an environment much less reliable than a factory with physical connections to the hardware. So we must be very careful to make sure that we generate correct images, and the installation process completes without interruption.
But enough of the theory let’s dive in to the process…