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Old 09-26-2013, 03:51 PM   #1
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Is partition 4 safe to zero?

At http://wiki.mobileread.com/wiki/Kind...ing#Partitions it says this about partition 4:

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Partition 4 (FAT32, 3.3 GB (KT) / 1.4 GB(PW)): This is where your documents go. In normal operations, it is mounted as /mnt/us, and this is the partition you get to modify when you mount the Kindle via USB. You can delete the contents if you can afford to lose your documents; the device will still work. [Do not delete /diagnostic_logs/device_info.xml from a USB Drive exported from the diagnostic recovery menu screen, or it will be difficult to reboot to the main partition.]
Couple questions about this.

My goal is to make a good attempt at secure-erasing this partition before passing on my stock (i.e. not jailbroken) Kindle Touch to someone else. If I'm understanding everything I've read correctly, this partition is actually an entire disk image containing a MBR, partition table, and then the FAT32 partition exposed to over USB Drive Mode.

Is it safe to zero out the entire exposed disk (since it should just be the contents of partition 4)? Or at least the FAT32 partition-within-a-partition? i.e. will the Touch recreate the partition if it detects it has been zeroed?
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Old 09-26-2013, 08:21 PM   #2
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Answered my own question—sort of—with further reading.

It may or may not be safe to exit USB Drive Mode with the drive zeroed. But it is definitely OK to erase specifically the filesystem part (skipping the MBR and partition table) using an overwrite erase tool of some kind (dd, OS X Disk Utility) followed by a FAT format.
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Old 09-26-2013, 08:37 PM   #3
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Quote:
Originally Posted by zigg View Post
Answered my own question—sort of—with further reading.

It may or may not be safe to exit USB Drive Mode with the drive zeroed. But it is definitely OK to erase specifically the filesystem part (skipping the MBR and partition table) using an overwrite erase tool of some kind (dd, OS X Disk Utility) followed by a FAT format.
Except of course, this is an eMMC (flash based) device.
What you write to is **NOT** the same eraseblock that previously held the data.
Your information can still be recovered from the "idle pool" of erase blocks on the device.

Doing a truly secure erase of a flash device takes more than user-land tools.
The diags "erase all" menu entry will do it.
But it will also do just what it says - blank the entire device.
Which can be a PITA to recover from.
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Old 09-26-2013, 08:55 PM   #4
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Why not just unregister it and then [Reset to Factory Defaults]? Wouldn't that wipe out everything and overwrite everything with a fresh configuration?

If I understand correctly (HAH!) the personal information re login and One Click purchasing is on partition 3 anyway, not partition 4... right?
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Old 09-26-2013, 09:02 PM   #5
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Quote:
Originally Posted by knc1 View Post
Except of course, this is an eMMC (flash based) device.
What you write to is **NOT** the same eraseblock that previously held the data.
Your information can still be recovered from the "idle pool" of erase blocks on the device.
Of course. But as I understand it, that is something that only the Flash controller can do, no? I'm not totally familiar with the driver, though, maybe it is available from software.

Quote:
Originally Posted by knc1 View Post
Doing a truly secure erase of a flash device takes more than user-land tools.
The diags "erase all" menu entry will do it.
But it will also do just what it says - blank the entire device.
Which can be a PITA to recover from.
Heh, yes, I can imagine.

Quote:
Originally Posted by SampleAndy View Post
Why not just unregister it and then [Reset to Factory Defaults]? Wouldn't that wipe out everything and overwrite everything with a fresh configuration?

If I understand correctly (HAH!) the personal information re login and One Click purchasing is on partition 3 anyway, not partition 4... right?
Reset Device looks like it clears things out, but is no better than a "quick format" from the partition 4 perspective.
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Old 09-26-2013, 09:12 PM   #6
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would not kubrick be a decent option.
Just a thought.

Although I fail to see what is so sensitive about the data.
You said "Stock" what on earth would you put on a Stock Device that would be that important?
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Old 09-26-2013, 10:32 PM   #7
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Quote:
Originally Posted by twobob View Post
would not kubrick be a decent option.
Just a thought.

Although I fail to see what is so sensitive about the data.
You said "Stock" what on earth would you put on a Stock Device that would be that important?
Company proprietary documents.
Just a single document could make or break a companies revenue stream.

- - - -

But who would put that sort of thing on a Kindle without encryption? Duh....
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Old 09-27-2013, 05:14 AM   #8
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I misread stock as an implication of something else.
As an academic exercise I suppose this knowledge has value at the very least.

Shutting up.
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Old 09-27-2013, 05:18 AM   #9
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Just do a low-level format of the partition from Windows (or whatever o/s you're using).
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Old 09-27-2013, 08:59 AM   #10
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If the situation is similar to having company proprietary information on the kindle -

I would not try to clean the kindle -
Shred and burn is probably best choice (destroy the whole device).

Simply compare the cost of a Kindle to the potential loss if the information is compromised.
That should make the choice obvious.

Diags -> Erase All
Shred
Burn
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