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Decrypt file before loading

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  • hskoglundH Offline
    hskoglundH Offline
    hskoglund
    wrote on last edited by
    #8

    Another alternative is that you create a new, small disk partition D: which you format with the builtin encryption in NTFS.

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    • C ChrisW67

      @Roberrt said in Decrypt file before loading:

      It states that QFile is used to read the files from the Qt resources, I'll try put a debug in some of these functions and see if one of them are being used to load the stylesheet files.

      The first part is largely irrelevant since you are not using the Qt resource system.
      The way you are using it, the provided path is transformed to native separators and passed to the underlying C/C++ libraries and operating system.

      QFile knows nothing of what purpose a file may have in your application: an icon image being accessed by a stylesheet is just the same as a cat video to QFile. If you want to impact only files referenced from stylesheets then you need to intercept that much earlier.

      If you really want to change the entire file handling behaviour for anything that uses QFile then you probably want to be looking at qfsfileengine* in the IO code. The decision between native file and resource system occurs in qfilesystemengine.cpp. The handling for the resource system lives in qresource* in the same location.

      R Offline
      R Offline
      Roberrt
      wrote on last edited by
      #9

      @ChrisW67

      If you want to impact only files referenced from stylesheets then you need to intercept that much earlier.

      This is my goal, impact any file being referenced from stylesheets the QPushButton on my previous post was just an example.

      If you really want to change the entire file handling behaviour for anything that uses QFile

      Not exactly, I don't want to change files handled by QFile, I'm trying to find in which function the stylesheet URL file is loaded, then I could decrypt and return the file decrypted.

      Thank you for pointing these files, I'm reading the functions of qfsfileengine_win.cpp , i think its probably one of these?

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      • kkoehneK Offline
        kkoehneK Offline
        kkoehne
        Moderators
        wrote on last edited by
        #10

        This sounds like a use case of QQuickImageProvider, at least if you have control over the code loading the image, so that you can use a different scheme.

        Director R&D, The Qt Company

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        • R Offline
          R Offline
          Roberrt
          wrote on last edited by Roberrt
          #11

          kkoehne i would like to hardcode the decryption into the sources, then I wouldn't need to care about coding anything else in the project as mostly of the pictures are added using stylesheet.

          I have added some OutputDebugString into the functions under qfsfileengine_win.cpp, but none of them got called.

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          • R Roberrt

            kkoehne i would like to hardcode the decryption into the sources, then I wouldn't need to care about coding anything else in the project as mostly of the pictures are added using stylesheet.

            I have added some OutputDebugString into the functions under qfsfileengine_win.cpp, but none of them got called.

            D Offline
            D Offline
            DerReisende
            wrote on last edited by
            #12

            @Roberrt If you want to read encrypted images, why don‘t you „define“ your own file format and write a Image I/O plugin which can decrypt these files?

            JonBJ 1 Reply Last reply
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            • D DerReisende

              @Roberrt If you want to read encrypted images, why don‘t you „define“ your own file format and write a Image I/O plugin which can decrypt these files?

              JonBJ Offline
              JonBJ Offline
              JonB
              wrote on last edited by
              #13

              @DerReisende That looks like a good approach indeed (provided it works)!

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              • JonBJ JonB

                @DerReisende That looks like a good approach indeed (provided it works)!

                D Offline
                D Offline
                DerReisende
                wrote on last edited by
                #14

                @JonB Don‘t know as I never used it. But in my small ideal plugin world I would decrypt to a temp file (or byte array of this works), use QImage or whatever to read the decrypted file (which can now be handled by the qt image format plugins), return it and discard the temp file.

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                • JoeCFDJ Offline
                  JoeCFDJ Offline
                  JoeCFD
                  wrote on last edited by JoeCFD
                  #15

                  I need this feature as well. It would be nice if Qt can provide this function. The idea of DerReisende is not bad. But if the file is big and loading takes long, the tmp file can be copied and encryption does not make sense anymore.

                  JonBJ 1 Reply Last reply
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                  • JoeCFDJ JoeCFD

                    I need this feature as well. It would be nice if Qt can provide this function. The idea of DerReisende is not bad. But if the file is big and loading takes long, the tmp file can be copied and encryption does not make sense anymore.

                    JonBJ Offline
                    JonBJ Offline
                    JonB
                    wrote on last edited by JonB
                    #16

                    @JoeCFD
                    So try it using memory instead of external file.

                    Goodness knows what you guys are trying to encrypt to hide from the user, an image that you're presumably going to show anyway. You would be talking about a symmetric encryption/decryption algorithm, right? So between that, and whether it be Qt's code or your code both likely to be publicly visible, isn't it likely that a user who wants to see the image file decrypted could do so anyway?

                    JoeCFDJ 1 Reply Last reply
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                    • R Offline
                      R Offline
                      Roberrt
                      wrote on last edited by
                      #17

                      Well I didn't expect it was going to be a 'hard' task, the reason to encrypt is to avoid easily copy of icons, personal art, logo, etc

                      JonBJ JoeCFDJ D jsulmJ C 5 Replies Last reply
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                      • R Roberrt

                        Well I didn't expect it was going to be a 'hard' task, the reason to encrypt is to avoid easily copy of icons, personal art, logo, etc

                        JonBJ Offline
                        JonBJ Offline
                        JonB
                        wrote on last edited by
                        #18

                        @Roberrt
                        OK, but then for you the issue @JoeCFD raised about unencrypting to a temporary file (if it is even needed) should not be an issue.

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                        • R Roberrt

                          kkoehne i would like to hardcode the decryption into the sources, then I wouldn't need to care about coding anything else in the project as mostly of the pictures are added using stylesheet.

                          I have added some OutputDebugString into the functions under qfsfileengine_win.cpp, but none of them got called.

                          R Offline
                          R Offline
                          Roberrt
                          wrote on last edited by
                          #19

                          @Roberrt said in Decrypt file before loading:

                          kkoehne i would like to hardcode the decryption into the sources, then I wouldn't need to care about coding anything else in the project as most of the pictures are added using stylesheet.

                          Doing this also would work when testing the UI in qt designer, with encrypted files.

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                          • R Roberrt

                            Well I didn't expect it was going to be a 'hard' task, the reason to encrypt is to avoid easily copy of icons, personal art, logo, etc

                            JoeCFDJ Offline
                            JoeCFDJ Offline
                            JoeCFD
                            wrote on last edited by
                            #20

                            @Roberrt Maybe save the temp files into an invisible dir.

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                            • R Roberrt

                              Well I didn't expect it was going to be a 'hard' task, the reason to encrypt is to avoid easily copy of icons, personal art, logo, etc

                              D Offline
                              D Offline
                              DerReisende
                              wrote on last edited by
                              #21

                              @Roberrt said in Decrypt file before loading:

                              Well I didn't expect it was going to be a 'hard' task, the reason to encrypt is to avoid easily copy of icons, personal art, logo, etc

                              Well AFAIK unless you are using a commercial license of Qt, every modification of Qt source you make must be made available to other users - including your encryption modification. If that is the case you win nothing and your customers may easily decrypt the resources...but I guess it will be a lot easier for them to just make screenshots and edit those.

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                              • JonBJ JonB

                                @JoeCFD
                                So try it using memory instead of external file.

                                Goodness knows what you guys are trying to encrypt to hide from the user, an image that you're presumably going to show anyway. You would be talking about a symmetric encryption/decryption algorithm, right? So between that, and whether it be Qt's code or your code both likely to be publicly visible, isn't it likely that a user who wants to see the image file decrypted could do so anyway?

                                JoeCFDJ Offline
                                JoeCFDJ Offline
                                JoeCFD
                                wrote on last edited by
                                #22

                                @JonB How to use memory for the encrypted files?

                                D 1 Reply Last reply
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                                • JoeCFDJ JoeCFD

                                  @JonB How to use memory for the encrypted files?

                                  D Offline
                                  D Offline
                                  DerReisende
                                  wrote on last edited by
                                  #23

                                  @JoeCFD QImage::loadFromData() with a byte array.

                                  JoeCFDJ 1 Reply Last reply
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                                  • D DerReisende

                                    @JoeCFD QImage::loadFromData() with a byte array.

                                    JoeCFDJ Offline
                                    JoeCFDJ Offline
                                    JoeCFD
                                    wrote on last edited by
                                    #24

                                    @DerReisende said in Decrypt file before loading:

                                    QImage::loadFromData()

                                    Thanks. Then it is doable for images. How about videos?

                                    D 1 Reply Last reply
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                                    • R Roberrt

                                      Well I didn't expect it was going to be a 'hard' task, the reason to encrypt is to avoid easily copy of icons, personal art, logo, etc

                                      jsulmJ Offline
                                      jsulmJ Offline
                                      jsulm
                                      Lifetime Qt Champion
                                      wrote on last edited by
                                      #25

                                      @Roberrt said in Decrypt file before loading:

                                      the reason to encrypt is to avoid easily copy of icons, personal art, logo, etc

                                      One can do a simple screen shot of running app and cut all the icons, personal art, logo. Don't see how encryption can help here...

                                      https://forum.qt.io/topic/113070/qt-code-of-conduct

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                                      • R Roberrt

                                        Well I didn't expect it was going to be a 'hard' task, the reason to encrypt is to avoid easily copy of icons, personal art, logo, etc

                                        C Offline
                                        C Offline
                                        ChrisW67
                                        wrote on last edited by
                                        #26

                                        @Roberrt said in Decrypt file before loading:

                                        Well I didn't expect it was going to be a 'hard' task, the reason to encrypt is to avoid easily copy of icons, personal art, logo, etc

                                        For my money, using the Qt resource system is going to achieve this goal. There is no on-disk file to copy. Anyone savvy enough, and with enough motivation, to find and decompress the image data embedded in your executable or DLL is probably going to be able to subvert this several ways.

                                        @DerReisende 's suggestion is a good one if it is only images involved. This has the benefit of working anywhere the encrypted image is used.

                                        A QImageIOPlugin should be quite quick to produce. The plugin create() method would have to create your QImageIOHandler subclass for *.enc images and ensure it gets a decryption key if one is needed.
                                        The QImageIOHandler may be more involved but could be as simple as the read() method loading the target QIODevice data into a QByteArray, decrypting/de-obfuscating in-place, calling QImage::loadFromData(), and destroying the interim QByteArray.

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                                        • JoeCFDJ JoeCFD

                                          @DerReisende said in Decrypt file before loading:

                                          QImage::loadFromData()

                                          Thanks. Then it is doable for images. How about videos?

                                          D Offline
                                          D Offline
                                          DerReisende
                                          wrote on last edited by
                                          #27

                                          @JoeCFD One guy did it this way with PyQt5.

                                          1 Reply Last reply
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