Encrypt And Decrypt Files In Windows Runtime Apps Using Windows Cryptography Technique

Here are the steps: 

Step 1:

Create a simple Windows Runtime Project. Click New Project, Visual C#, Windows 8, Windows, then Blank App (Windows 8.1).

 

Step 2:

Let's add two buttons in MainPage.xaml with click events:

• Encrypt Button
• Decrypt Button

<Page
    x:Class="Encrypt_Decrypt.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:Encrypt_Decrypt"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d">

    <Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
        <Button Content="Encrypt" Name="btn_Encrypt" Height="125" Margin="65,365,0,278" Width="225" Click="btn_Encrypt_Click"></Button>
        <Button Content="Decrypt" Name="btn_Decrypt" Margin="350,365,0,278" Height="125" Width="231" Click="btn_Decrypt_Click"></Button>
    </Grid>
</Page>

Step 3:

Let's add a text file in Solution Explorer for testing purpose. We will copy that file from Installed Location to Local folder and encrypt it.

 

Step 4: Name it ‘OriginalFile.txt’

Step 5:Add some text in this text file.

 

Step 6:

In the code behind: MainPage.xaml.cs, Update your code with this:

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices.WindowsRuntime;
using Windows.ApplicationModel;
using Windows.Foundation;
using Windows.Foundation.Collections;
using Windows.Storage;
using Windows.Storage.Streams;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Controls.Primitives;
using Windows.UI.Xaml.Data;
using Windows.UI.Xaml.Input;
using Windows.UI.Xaml.Media;
using Windows.UI.Xaml.Navigation;


namespace Encrypt_Decrypt
{

    public sealed partial class MainPage : Page
    {
        public MainPage()
        {
            this.InitializeComponent();
        }

        private async void btn_Encrypt_Click(object sender, RoutedEventArgs e)
        {
            //For Copying File from Installed Location to Local Folder
            StorageFolder appFolder = ApplicationData.Current.LocalFolder;
            StorageFile stopfile = await StorageFile.GetFileFromApplicationUriAsync(new Uri("ms-appx:///OriginalFile.txt"));
            await stopfile.CopyAsync(ApplicationData.Current.LocalFolder, "OriginalFile.txt", NameCollisionOption.ReplaceExisting);

            string sourceFileName = "OriginalFile.txt";
            string destinationFileName = "EncryptedFile.txt";

            try
            {
                StorageFile file = await appFolder.GetFileAsync(sourceFileName);
                IBuffer fileStreamBuffer = await FileIO.ReadBufferAsync(file);
                string protectionDescriptor = "LOCAL=user";
                if (fileStreamBuffer.Length != 0)
                {
                    Windows.Security.Cryptography.DataProtection.DataProtectionProvider provider = String.IsNullOrEmpty(protectionDescriptor) ? new Windows.Security.Cryptography.DataProtection.DataProtectionProvider() : new Windows.Security.Cryptography.DataProtection.DataProtectionProvider(protectionDescriptor);
                    IBuffer encryptedBuffer = await provider.ProtectAsync(fileStreamBuffer);

                    StorageFile encryptedFile = await appFolder.CreateFileAsync(destinationFileName, CreationCollisionOption.ReplaceExisting);
                    await FileIO.WriteBufferAsync(encryptedFile, encryptedBuffer);
                }
            }
            catch (Exception ex)
            {
                Debug.WriteLine(ex.ToString());
            }
        }


        private async void btn_Decrypt_Click(object sender, RoutedEventArgs e)
        {
            StorageFolder appFolder = ApplicationData.Current.LocalFolder;
            string sourceFileName = "EncryptedFile.txt";
            string destinationFileName = "DecryptedFile.txt";
            try
            {
                StorageFile file = await appFolder.GetFileAsync(sourceFileName);
                IBuffer fileStreamBuffer = await FileIO.ReadBufferAsync(file);
                string protectionDescriptor = "LOCAL=user";
                if (fileStreamBuffer.Length != 0)
                {
                    Windows.Security.Cryptography.DataProtection.DataProtectionProvider provider = String.IsNullOrEmpty(protectionDescriptor) ? new Windows.Security.Cryptography.DataProtection.DataProtectionProvider() : new Windows.Security.Cryptography.DataProtection.DataProtectionProvider(protectionDescriptor);
                    IBuffer encryptedBuffer = await provider.UnprotectAsync(fileStreamBuffer);

                    StorageFile encryptedFile = await appFolder.CreateFileAsync(destinationFileName, CreationCollisionOption.ReplaceExisting);
                    await FileIO.WriteBufferAsync(encryptedFile, encryptedBuffer);
                }
            }
            catch (Exception ex)
            {
                Debug.WriteLine(ex.ToString());
            }
        }
    }
}

Step 7:

Run the application. Click on Encrypt and Decrypt button. You can see the files being encrypted and decrypted in the Application Local Folder:

This PC, C, Users > [Your User Name] > AppData, Local, Packages > [App package name] > LocalState,

That’s it.

Thanks, Happy Coding!

Read more articles on Windows Runtime Apps:

• WinJS application With Windows Runtime Component To Access Native C# Code
• Asynchronous Programming In WinJS Applications With Windows Runtime Component