Decrypt file before loading

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.

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?

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

JonB

@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.

Roberrt

@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.

JoeCFD

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

DerReisende

@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.

JoeCFD

@JonB How to use memory for the encrypted files?

DerReisende

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

JoeCFD

@DerReisende said in Decrypt file before loading:

QImage::loadFromData()

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

jsulm

@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...

ChrisW67

@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.

DerReisende

@JoeCFD One guy did it this way with PyQt5.