在Windows应用商店应用中加密和解密本地图像

Question

I'm building a Windows Store App including a local folder of Images.

I want to protect all the Images so they can't be accessed from:

C:\Users[username]\AppData\Local\Packages\LocalState\Settings\settings.dat

I know I should encrypt and decrypt the Images using the DataProtectionProvider class, but the documentation only shows how to encrypt/decrypt strings...

How should I convert a Bitmap image into a byte array? or should I encode it with Base64 ? Is there any tutorial or sample using this process?

Answer 1

It's easiest if the images you want to encrypt are loaded from files and written back out to files. Then you can do:

async void EncryptFile(IStorageFile fileToEncrypt, IStorageFile encryptedFile)
{
    IBuffer buffer = await FileIO.ReadBufferAsync(fileToEncrypt);

    DataProtectionProvider dataProtectionProvider = 
        new DataProtectionProvider(ENCRYPTION_DESCRIPTOR);

    IBuffer encryptedBuffer = 
        await dataProtectionProvider.ProtectAsync(buffer);

    await FileIO.WriteBufferAsync(encryptedFile, encryptedBuffer);
}

DataProtectionProvider.ProtectStreamAsync is another alternative if you can get stream instances from your inputs and outputs. For example, if you have a byte[] containing your image data then you can create an in-memory input stream from it:

byte[] imageData = ...
using (var inputMemoryStream = new MemoryStream(imageData).AsInputStream())
{
    ...
}

Edit: Then for example to decrypt the file and display it in an Image control you could do:

var encryptedBuffer = await FileIO.ReadBufferAsync(encryptedFile);

var dataProtectionProvider = new DataProtectionProvider();

var buffer = await dataProtectionProvider.UnprotectAsync(encryptedBuffer);

var bmp = new BitmapImage();
await bmp.SetSourceAsync(buffer.AsStream().AsRandomAccessStream());
imageControl.Source = bmp;

Answer 2

        public async void Protect()
        {
            for (int i = 1; i < 24; i++)
            {
                string imageFile = ImagePages[i];
                var fileToEncrypt = await Windows.ApplicationModel.Package.Current.InstalledLocation.GetFileAsync(imageFile);
                var encryptedFile1 = await ApplicationData.Current.LocalFolder.CreateFileAsync("encryptedPage" + i);

                var encryptedFile2 = await EncryptFile(fileToEncrypt, encryptedFile1);
                IBuffer buffer = await DecryptFile(encryptedFile2);
                //(2.) It goes here and throw the 'System.ArgumentException' having the encryptedFile's ContentType=""

                var bmp = new BitmapImage();
                await bmp.SetSourceAsync(buffer.AsStream().AsRandomAccessStream());

                //Fill the List responsible for the Portrait View
                MyPortrait mp = new MyPortrait();
                mp.onlyImage = bmp;
                PImageList.Add(mp);
            }
        }    

        public async Task<IStorageFile> EncryptFile(IStorageFile fileToEncrypt, IStorageFile encryptedFile)
        {
            IBuffer buffer = await FileIO.ReadBufferAsync(fileToEncrypt);
            //I have no more exceptions here

            DataProtectionProvider dataProtectionProvider = new DataProtectionProvider("LOCAL=user");

            IBuffer encryptedBuffer = await dataProtectionProvider.ProtectAsync(buffer);
            //(1.) After arriving here when deploying it goes to (2.)

            await FileIO.WriteBufferAsync(encryptedFile, encryptedBuffer);

            return encryptedFile;
        }

        public async Task<IBuffer> DecryptFile(IStorageFile encryptedFile)
        {
            var protectedBuffer = await FileIO.ReadBufferAsync(encryptedFile);

            var dataProtectionProvider = new DataProtectionProvider();

            var buffer = await dataProtectionProvider.UnprotectAsync(protectedBuffer);

            return buffer;
        }