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Encrypted SD Card removed before factory reset

Discussion in 'Android Devices' started by meridius, Dec 17, 2021.

  1. meridius

    meridius Member
    Thread Starter

    Well I was going to get caught out one day on encryption and it seems that this has happened now.

    I first removed an encrypted SD Card before factory resetting my Samsung Galaxy J2 Core. The phone had also been set to Secure startup. After the factory reset I attached the SD Card and the phone will not decrypt the SD Card. I thought the encryption key of the SD Card may be the same as the four digits that are used to enter the phone.

    I have copied the relevant file I need to Windows (which is Contacts.vcf) but cannot seem to find a free app to try to decrypt it. Any ideas and if this is possible at all?

    In the worst case that there is no solution, I have only lost two months of backed up contacts, which is less bad than losing all of them. But it also makes me wonder what would happen in a scenario where a phone is completely damaged beyond repair and is unable to work at all, therefore encrypting an SD Card is linked to the phone itself and dependent on it in its current state.

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  2. mikedt

    mikedt 你好

    It's not. The encryption key is pseudo-randomly generated when the card is encrypted. And that key was securely erased when the phone was reset. You can still have encrypted storage even if there's no PIN or password lock on the device itself.

    FYI the SD is encrypted using AES256, which was invented by Uncle Sam. And there are no free apps to break it. Even the feds might have difficulty with AES.
    "At present, there is no known practical attack that would allow someone without knowledge of the key to read data encrypted by AES when correctly implemented."

    Your best friend is backup, backup, backup!! ...either to local storage, or to the cloud, or both. Because even if it wasn't encrypted, and the phone with SD went missing, broke, or was trashed....
    #2 mikedt, Dec 17, 2021
    Last edited: Dec 17, 2021
  3. puppykickr

    puppykickr Android Expert

    Encrypting an SD card basically makes it part of the device that it is encrypted on.

    This makes it so that the card will not be able to be read by other devices.

    By resetting, you erase the user data on a device, and the encryption key is part of that.

    To unencrypt the SD card, is to reformat it- which will erase everything on it.

    You would of had to send the data from the card to an entirely different storage before the reset happened.
  4. meridius

    meridius Member
    Thread Starter

    Thanks for letting me know. I could have had a much harder lesson as I backed up my contacts in October so am only missing 2 months or so of them.

    However I'm not sure I'm going to encrypt the SD Card again so this doesn't happen once more! My phone is offline so the best policy is probably to regularly copy the .vcf files to my PC.
    puppykickr likes this.
  5. Dannydet

    Dannydet Extreme Android User

    If you have a Gmail account use the Google contacts app.
    Now your contacts are automatically saved to the cloud and available to you on any device you want.
    No vcf file to transfer to your computer
    ocnbrze likes this.
  6. meridius

    meridius Member
    Thread Starter

    For my online phone it's a good idea, but this phone is offline so vcf is likely the best option.
    puppykickr and ocnbrze like this.

Samsung Galaxy J2 Forum

The Samsung Galaxy J2 release date was September 2015. Features and Specs include a 4.7" inch screen, 5MP camera, 1GB RAM, Exynos 3475 Quad processor, and 2000mAh battery.

September 2015
Release Date

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