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Topic # 175032 15-Jun-2015 10:41
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Hello guys!


I know many people asked this same question over and over but novice like me don't even know how to search answer in our great forum.


Can anyone tell me how to completely wipe internal storage so I can sell my old phone with peace of mind?


Do I need to get aftermarket program to root?


Thanks in advance!!

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  Reply # 1324830 15-Jun-2015 10:47
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To search the forum, you type words relating to what you want to find in to the "search" box at the top right of the page. Perhaps try searching for "erase phone" or "erase android"or something similar.

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  Reply # 1324833 15-Jun-2015 10:53

Encrypt it, then re-flash the stock ROM with ODIN. Or wipe just data from recovery mode after encrypting the device if you haven't had experience with ROM flashing or the ODIN tool before.

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  Reply # 1324965 15-Jun-2015 13:34
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You can't, or not to a 100% reliable standard anyway.

All flash memory is over-provisioned: i.e. is says <X> GB 'on the tin', but there's actually <X + a bit> GB actually there and 'a bit' is a number proportional to the quality, sometimes up to 100%.
This is because flash memory is wear-limited, you can only write to each cell so many times beore it fails. In order to make sure you dn't see a failure before the expected life, the flash memory controller implements 'wear levelling', so when you re-write a block, the original is marked as 'available' and the information is written to a pseudao-random different physical place on the flash chip(s).
Note I said the flash memory controller, this is waay below what the Operating System can see, let alone an app. As user, you have absolutely no access to or control over this mechanism.

So, no matter how many time you 'erase' or 'over-write' data in flash memory, some or all of it may be recoverable by a sufficiently determined opponent.

The only way to avoid this would be to encrypt everything all the time from very first to very last use of the phone, using rock-solid encryption (AES-256 might be good enough) and an unguessable and very long key phrase - the longer the better, "Password1" is obviously broken, but "This is My passw0rd, and I don't think ya'll c4n guess it in a meeeelion years" is probably getting close wink.
However today's reports that Snowden's raw data treasure trove has been decrypted by the Russian and/or Chinese governments shows the outer limit of this approach

Hence, it's a matter of probability: If your data is so interesting that you're trying to keep it out of the hands of a well-resourced technically astute opponent, then just toss the phone in the crucible of a nice hot (e.g. 1500 degrees Celsius) furnace. Problem solved. If on the other hand, you're one of the 99.9% whose most 'interesting' data is maybe a selfie taken in a reduced-clothing state, or a drunken text message that you now deeply regret, then following NikT's excellent advice to encrypt all your data, then factory-reset the device, is most likely 'good enough'

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