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I've had a Samsung Galaxy filled with thousands of sensitive financial documents, which I've been using as a pocket computer pretty much, in order to reference them each time I need to throughout the day.

It's heavily debloated, de-Googled, I've had the Secure Startup device encryption enabled in case I'd lose it and a firewall (NetGuard) installed to prevent data leak for when it had to connect to the internet.

I wish to sell this phone now (or rather, give it away for free to someone who might). So, that means decrypt it and hard reset it.

Is there anything I can do programmatically (e.g., via ADB) to further wipe data? Something we would do to a computer hard drive, for instance, like secure wipe/zero out its data?

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  • What Galaxy phone are you talking about (ai don't thing you are talking about the original Samsung Galaxy)? You don't need to decrypt the device. Just perform a factory reset. This will erase the decryption key and all the encrypted data will be unrecoverable. You can check that after factory reset the files are gone.
    – Robert
    Jun 27, 2021 at 18:18
  • @Robert It's an S9+ and apparently there's another S8 that I was using for the same purpose, like a year ago, forgotten in a drawer. Basically, what you are saying is keep them encrypted and simply perform a hard reset? That will do?
    – yin8219
    Jun 30, 2021 at 13:22
  • Yes. If you are unsure, perform the factory reset from within running Android (not via recovery) and then after factory reset skip most of the first start wizard and check if you can see any files. Because of the encryption if the files are no longer to be seen they are unrecoverable gone after a factory reset.
    – Robert
    Jun 30, 2021 at 14:06
  • @Robert Can you explain why I should reset from within the Settings menu and not via Recovery? In the past, I've always used Recovery for this purpose. Specifically, I'd use Wipe cache partition, then Wipe data/factory reset and finally Reboot system now.
    – yin8219
    Jun 30, 2021 at 20:09
  • Search the internet for "factory reset protection" (FRP) and you will know why.
    – Robert
    Jul 1, 2021 at 1:42

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