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[Q] TA partition, DRM keys, what's the full story?

OP vyruz1986

13th July 2014, 11:45 AM   |  #1  
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Hi everyone,

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.
13th July 2014, 12:31 PM   |  #2  
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Hi, i tried alrdy to restore DRM after i flashed castor CM11 on my Tablet, but i softbricked them. I was in hope that this way will give me a chance to use Sony aps etc.
I restored with Flashtool , now is all ok and Running without DRM. I mean the TA Partition mess up with Bootloader so your Device will not Boot after u try to restore them.
Except on Stock ROM..
5th September 2014, 08:31 PM   |  #3  
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ive also came to the same conclusion but heres the thing...ive got an Ultra Z which i had the bootloader unlocked without backing up the TA Partition. Ive installed TWRP, wiped it clean and flashed PA Rom. Then decided to go back to Stock and now everything works as it should. Bravia engine is enabled, walkman app works and the OTA is working as it should. So what am i missing here?
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