WPF

byte[] bytBuffer = new byte[4096]; //holds a block of byte for process.
               long lngBytesProcessed = 0; //running count of byte processed.
               long lngFileLength = fsInput.Length; //the input file is lenght.
               int intBytesIncurrentBlock; //current bytes being processed.

               CryptoStream csCryptoStream;

               //Declare your CryptoServiceProvider.
               System.Security.Cryptography.RijndaelManaged cspRijndael = new System.Security.Cryptography.RijndaelManaged();

               //Setup Progress bar.
               pbStatus.Value = 0;
               pbStatus.Maximum = 100;

               //Determine if encryption or decryption and set setup CryptoStream.

               switch (Direction)
               {
                   case CryptoAction.ActionEncrypt: 
                    csCryptoStream = new CryptoStream(fsOutput, cspRijndael.CreateEncryptor(bytKey, bytIV), CryptoStreamMode.Write);
                    break;

                   case CryptoAction.ActionDecrypt:
                       csCryptoStream=new CryptoStream(fsOutput, cspRijndael.CreateDecryptor(bytKey, bytIV), CryptoStreamMode.Write);
                       break;
                       
               }

               //Use While to loop until all of the file is processed.

               while (lngBytesProcessed<lngFileLength){
                   //Read file with the input filestream.
                   intBytesIncurrentBlock = fsInput.Read(bytBuffer, 0, 4096);

                   //Write output file with the crytostreamm.
                   csCryptoStream.Write(bytBuffer, 0, intBytesIncurrentBlock);

                   //Update lngBytesProcessed.
                   lngBytesProcessed = lngBytesProcessed + long.Parse(intBytesIncurrentBlock);

                   //Update progress bar
                   pbStatus.Value = int.Parse((lngBytesProcessed/lngFileLength)*100);

               }

<Window.Resources>
    <HierarchicalDataTemplate DataType="{x:Type model:PartDescriptionUpdateModel}"
                              ItemsSource="{Binding Path=Descriptions}">
        <StackPanel Orientation="Horizontal">
            <Image Source="/Abtech.Spares.UI;component/Media/Graphics/lancard_enabled_128x128.png"
                   Height="16"
                   Width="16"
                   Margin="0,0,3,0"/>
            <TextBlock Text="{Binding Path=PartNo}"/>
            <Label Content=" - "/>
            <TextBlock Text="{Binding Path=Description}"/>
        </StackPanel>

    </HierarchicalDataTemplate>

</Window.Resources>


<Grid>

    <Grid.RowDefinitions>
        <RowDefinition Height="Auto"></RowDefinition>
        <RowDefinition Height="Auto"></RowDefinition>
        <RowDefinition Height="*"></RowDefinition>
        <RowDefinition Height="Auto"></RowDefinition>
    </Grid.RowDefinitions>
    <Grid.ColumnDefinitions>
        <ColumnDefinition></ColumnDefinition>
    </Grid.ColumnDefinitions>

    <!--List of part info-->
    <ListBox x:Name="lstParts"
             Grid.Row="2"
             Margin="5"
             ItemsSource="{Binding PartsData}"/>

</Grid>