[Q] TA partition, DRM keys, what's the full story?
I'm hoping to use this thread to get the full story on the whole DRM keys issue that comes with unlocking your bootloader. For myself to get a clear picture, but also for others who are interested.
So far I've only been able to find bits and pieces about what exactly the DRM keys do, and how to handle them, I'll start off by writing what I (think I) know, please correct me if I'm wrong:
What do the DRM keys do?
So far I found out they're needed to run the Walkman app, which is understandable as it involves music purchases which are DRM protected.
Personally, I couldn't care less about this app not working anymore, your opinion might differ.
I also heard they're needed for the 'Bravia engine', now this is something that concerns me more, so far I haven't been able to find out what exactly is this 'bravia engine', I would go on a limb and say it's the screen rendering engine, and removing the DRM keys could completely mess up the colors or something, but this is a pure guess, and could be completely wrong. This is the first point which needs clarification.
Can the DRM keys be backed up?
Until recently, no, since the DRM keys reside in the 'TA partition', backing them up was something which required root access, and then again root access was something that could only be obtained by unlocking the bootloader, which in turn wipes the 'TA partition' before you could back it up.
However, since recently, there's a way:
Thanks to our famous friend geohot
, we have recently got the ability to root our tablet using his 'towelroot' app. It works by breaking into a kernel vulnerability present on the stock ROM, and inserting root access that way, thus not touching the bootloader (which effectively remains locked). Since we now have root access I was able create a backup of my TA partition, which I've safely backed up to google drive, just in case.
Here are the threads I used to get me this far:
So now I have a rooted stock ROM, XZDualRecovery (which includes TWRP recovery which I prefer), and backed up TA partition.
Can the DRM keys be restored?
According to Install XZDualRecovery
"]the thread of the 'TA Backup tool'[/URL] , yes. I haven't tried this out myself, so no personal experience here.
It also says that restoring the keys effectively re-locks your bootloader, which brings you back to zero off course...
Note: The thread explicitly says that trying to restore a 'TA backup' which was created on another device, will effectively hard-brick your device!
For this boils down to 2 options:
- Either you can live with a locked bootloader, and have the DRM keys in place
- Or you unlock it, and use the device without DRM keys
Off course to make this choice, we have to fully understand what exactly stops working when DRM keys are removed.