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  1. #1
    Regular Contributor
    Join Date
    Jun 2007
    Jakarta, Indonesia

    secure delete file

    Hi FN

    I want to be able to secure delete a file from the disk, so the file can not be undelete. Is there any API to do this?

  2. #2
    Super Contributor
    Join Date
    Mar 2004

    Re: secure delete file

    As far as i know there is no Undelete API in Symbian.C++. So just delete a file and you can't recover.

  3. #3
    Nokia Developer Champion
    Join Date
    Mar 2003

    Re: secure delete file

    It depends. If the file is on a memory card, it might just be marked as deleted, but the contents are still accessible (and there are file recovery tools that can help with it).

    A better way might be first to overwrite the contents of the file with garbage, and only then delete it. However, I think with flash memory there is a limited number of writes that a given memory location can handle, so overwriting might appear to be to the same memory location, but in reality might be done to a different location still leaving the data there. However, I could be mistaken, as I'm no flash memory behaviour expert.

    If you want to be safer, then also store everything in encrypted form, and then unencrypt the data in memory. That way the written data in a file is even harder to recover.

    In any case, for files in phone memory, usually just deleting is enough to prevent most people from being able to undelete it.

  4. #4
    Regular Contributor
    Join Date
    May 2008

    Re: secure delete file

    Quote Originally Posted by strike_noir View Post
    Hi FN

    I want to be able to secure delete a file from the disk, so the file can not be undelete. Is there any API to do this?
    relatively secure way is to overwrite with AA55... and later with 55AA.. pattern and then delete it. So even if someone trys to recover it by removing memory card etc, it will be safe.

    Refer to Gutmann overwrite method wikipedia


  5. #5
    Super Contributor
    Join Date
    Nov 2004
    Wiltshire, UK

    Re: secure delete file

    Actually NAND flash cards employ a levelling algorithm which means that any writes to a sector will result in a different sector being written. Whether or not the original sector is cleared immediately is up to the driver.

    In addition to the levelling algorithm there is also a block erasure issue in that blocks tend to be quite big so partial pages will not be cleared when the file is rewritten.

    More information can be found in the devkit by looking for the UniStore II drivers if you are a devkit licencee.
    Download Symbian OS now! [url]http://developer.symbian.org[/url]

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