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I plan to sell my old Kindle Keyboard and I want to erase all the Kindle's data ( my books, my personal info, wi-fi passwords...) before. Is it enough to deregister the Kindle and execute a factory reset? Would it completely erase everything?

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2 Answers

Every Kindle has a menu option "Reset to Factory Defaults", which does exactly what you want: It removes all user specific data from the device.

Step by step instructions for factory resets on various Kindle devices

For the paranoid: Most devices will not actually erase your data, but just mark it as "erased". For the user both are the same thing - if you sell your device, the new owner will not see your stuff. For anybody with sufficient knowledge and interest in that piece of information - such as crime scene investigators etc. - it usually is possible to restore data. I have not checked if a Kindle will actually overwrite your data or leave traces behind.

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up vote 1 down vote accepted

After deregistering the device and executing factory reset the Kindle looks empty. It shows none of my earlier books.

I've connected the Kindle to a Linux computer and copied all the information to a huge (3.2GB) file:

dd if=/dev/sdc1 of=afterfactoryreset.dat bs=1M

One of the books I've read on this device is Zendegi ( by Greg Egan ) so I've searched for the string zendegi which appears quite a few times:

$ strings afterfactoryreset.dat | grep -i zendegi
;/mnt/us/documents/Zendegi-asin_B003NE5TVU-type_EBOK-v_0.azwt
;/mnt/us/documents/Zendegi-asin_B003NE5TVU-type_EBOK-v_0.azwt
Zendegi
Zendegi
LAST_BOOK_READ=/mnt/us/documents/Zendegi-asin_B003NE5TVU-type_EBOK-v_0.azw
;/mnt/us/documents/Zendegi-asin_B003NE5TVU-type_EBOK-v_0.azwsq
;/mnt/us/documents/Zendegi-asin_B003NE5TVU-type_EBOK-v_0.mbpsr
</mnt/us/documents/Zendegi-asin_B003NE5TVU-type_EBOK-v_0.apnxsq
;/mnt/us/documents/Zendegi-asin_B003NE5TVU-type_EBOK-v_0.azwsq
...

It was very easy to create a script which lists most of the books previously installed on the device:

$ strings afterfactoryreset.dat | grep -i '^mnt/us/documents' | rev | cut -d "." -f2- | rev | sort | uniq
mnt/us/documents/A Clash of Kings A Song of Ice a-asin_B000FC1HBY-type_EBOK-v_0
...
mnt/us/documents/Zendegi-asin_B003NE5TVU-type_EBOK-v_0

It's not a perfect list but clearly shows that factory reset does not erase all the information.

There are several ways to wipe the empty space of the filesystem. A very simple (not that secure) way is to create a huge files filled with zeroes and delete it:

dd if=/dev/zero of=/path/to/mounted/kindle/hugefile.dat
sync
rm /path/to/mounted/kindle/hugefile.dat

After that the script does not list the previously installed books.

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