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Thread: Wiping sensitive data in QML

  1. #1
    Join Date
    Mar 2012
    Qt products
    Unix/X11 Windows

    Default Wiping sensitive data in QML


    I am looking for a way to wipe properties of objects once the property is not needed any more. Reassigning unfortunately doesn't work (value is changed, but you can still find original values in memory, until the area is re-used by something else). Basically I'm looking for an equivalent of QByteArray::fill, but as I can't get to the properties themselves (only the copies), original values still dangle around the memory. Any ideas (on C++ or QML side) would be very welcome.
    Last edited by Buldozer; 6th November 2019 at 16:15.

  2. #2
    Join Date
    Mar 2012
    Qt products
    Unix/X11 Windows

    Default Re: Wiping sensitive data in QML

    To answer my own question (and help anyone else looking for an (ugly) solution to the same problem):

    In the end the problem actually turned out to be - how to modify QVariant string data directly. Turns out the biggest problem was in-place rewriting of QString data. I came up with a solution (though I don't really like it and would prefer something cleaner):

    Qt Code:
    1. Q_INVOKABLE void wipe(QVariant value)
    2. {
    3. void *valuePtr = value.d.is_shared ?>ptr : static_cast<void *>(&(;
    4. if ((value.type() == QMetaType::QString) && valuePtr) {
    5. QString *text = reinterpret_cast<QString *>(valuePtr);
    6. QChar* txtPtr = const_cast<QChar*>(text->constData()); //yes, const_cast constData(), as data() creates a modifiable copy
    7. for (int x = 0; x < text->size(); x++)
    8. *(txtPtr++) = QChar(0);
    9. }
    10. }
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