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While cleaning I've found an old cellphone. This phone does not turn on, and I'm not sure if contains personal data.

I would like to throw away this phone, but I'm concerted if this data can be recovered some way.

What could be the best way to securely destroy it?

Not sure if relevant, it's an iPhone 3G.

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    Who are your adversaries? What is the time frame in which access would be dangerous? What would the fallout be if they got access to it? You need to specify your threat model before anyone can tell you what you need to do.
    – forest
    Nov 28 '18 at 9:53
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    microwave oven :) Nov 28 '18 at 9:53
  • @SoufianeTahiri That actually wouldn't do very much...
    – forest
    Nov 28 '18 at 9:54
  • @forest It's personal data (not professional). In that case I assume that threats are people that get this phone on the dumping site, and some way, can turn on phone or remove hard drive and get my personal data. I cannot remember which personal data is, at least could be personal photos and videos, maybe passwords (althouth I assume that most could be expired).
    – user674887
    Nov 28 '18 at 9:57
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    @user674887 The only dangerous thing is the battery (which should be removed). If you can open the device, locate the flash memory and break it. If you only care about some casual snoop who finds it later, then simply removing it and putting a hole in it is more than enough. If you want to avoid a sophisticated attacker with a laboratory to access data, you'd need to sand it down into dust.
    – forest
    Nov 28 '18 at 10:03
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You could disassemble the phone and drive a nail through the NAND. But since some companies (like DriveSavers) can rebuild flash chips on a certain extent, you might want to further destroy it by smashing the chip to bits.

(Note here that I do not know how "recoverable" a NAND flash is once there is physical damage. I just know that there are specialist equipment that can reconstruct NAND flashes off of SSDs. Granted, these SSDs are brought in with a cell failure rather than actual deformation, but if you think your data is that sensitive you have bigger problems.)

Here is a link to the iPhone 3G iFixit teardown that reveals where the chip resides. It's the Toshiba TH58G6D1DTG80 chip found on the back of the logic board, step 20. (I didn't post it here because of copyright.) Be sure not to puncture the battery as it might cause fire, smoke, and start leaking nasty chemicals.

Finally, if you can afford to wait it out, NAND flashes usually wear down with time if there is no power supplied to it. If you don't want to physically break your phone, you could lock it in a safe and preserve it for a couple of years. Some sources say you only need to wait two years (or even one year) under ideal conditions (high temperatures) for the data to become corrupt, while other sources claim it's false and NAND flashes can retain data for long periods of time. (The articles talk about SSDs, but the same could be applied to NAND flash because SSDs use NAND to store data.) Note that newer advances in the field could help retain data more than old chips, but I don't know how much that can impact data retention. So depending on how sensitive your data is, this might not be feasible, but could be the option if you want to preserve your phone, maybe for sentimental purposes.

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    "for the data to become corrupt" only means that a small fraction of the bits are gone. Very different from keeping all (or at least enough to make the remainder unintelligible) secret.
    – Ben Voigt
    Nov 29 '18 at 20:18
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    So instead of putting a nail through the chip, use a grinder to turn it to dust (vacuum that dust as you work, as you don't want to breathe it).
    – Ben Voigt
    Nov 29 '18 at 20:19
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I had the same problem with a personal device that I used before. The device would not turn on, and there was personal information. If there is a micro USB, you could plug the phone into anything that is running Linux or something that is running shred. Shred is used to securely delete files that can only be recovered with great difficulty with specialized hardware, if at all. If you do not have shred installed you could smash the phone to bits, or use something that would destroy it without anyway of recovering it.

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  • Unfortunately, the shred command only works on files saved locally on a physical hard drive. It will not work on flash-based solid state drives, and certainly not cell phones as shred cannot figure out where the file is located and overwrite on top of it.
    – so5user5
    Dec 14 '18 at 22:20

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