HMACSHA256 Class

using System;
using System.Windows.Controls;
using System.Windows.Input;
using System.IO;
using System.IO.IsolatedStorage;
using System.Security.Cryptography;
using System.Security.Permissions;
using System.Text;

namespace HMACSHA256Example
{
    public partial class MainPage : UserControl
    {
        // Initialized in Page ctor.
        private static string encryptedFiles = "";
        private static IsolatedStorageFile store = IsolatedStorageFile.GetUserStoreForApplication();
        private const string PasswordSalt = "PasswordSalt";
        private static string sourceFilePath = "";
        private static string signedFilePath = "";
        public MainPage()
        {
            InitializeComponent();
            this.inputBox.KeyDown += new KeyEventHandler(inputBox_KeyDown);
            this.passwordBox.KeyDown += new KeyEventHandler(passwordBox_KeyDown);
            this.decodePassWordBox.KeyDown += new KeyEventHandler(decodePassWordBox_KeyDown);
            this.deleteBox.KeyDown += new KeyEventHandler(deleteBox_KeyDown);
            this.decodeBox.KeyDown += new KeyEventHandler(decodeBox_KeyDown);

            store.CreateDirectory("MyFiles");

            // Create subdirectory under MyFiles.
            encryptedFiles = System.IO.Path.Combine("MyFiles", "EncryptedFiles");
            store.CreateDirectory(encryptedFiles);
            ListFiles();
            inputBox.Focus();
        }
        private void inputBox_KeyDown(object sender, EventArgs e)
        {
            if (((System.Windows.Input.KeyEventArgs)e).Key == Key.Enter)
            {
                CreateFile();
                this.passwordBox.Focus();
            }
            if (((System.Windows.Input.KeyEventArgs)e).Key == Key.Tab)
            {
                CreateFile();
                this.inputBox.Focus();
            }
        }
        private void decodeBox_KeyDown(object sender, EventArgs e)
        {
            if (((System.Windows.Input.KeyEventArgs)e).Key == Key.Enter)
            {
                IsolatedStorageFile store = IsolatedStorageFile.GetUserStoreForApplication();
                signedFilePath = System.IO.Path.Combine(encryptedFiles, "signedFile.txt");
                this.decodePassWordBox.Focus();
            }
        }
        private void ListFiles()
        {
            string searchpath = System.IO.Path.Combine(encryptedFiles, "*.*");
            string[] filesInSubDirs = store.GetFileNames(searchpath);
            StringBuilder sb = new StringBuilder();
            // List files in MyFiles\EncryptedFiles.
            sb.AppendLine(@"Files in MyFiles\EncryptedFiles:");
            foreach (string fileName in filesInSubDirs)
            {
                sb.AppendLine(" - " + fileName);
            }
            sb.AppendLine();
            outputBlock.Text = sb.ToString();
        }
        private void deleteBox_KeyDown(object sender, EventArgs e)
        {

            if (((System.Windows.Input.KeyEventArgs)e).Key == Key.Enter)
            {
                store.DeleteFile(encryptedFiles + "\\" + deleteBox.Text);
                ListFiles();
                this.passwordBox.Focus();
            }
        }
        private void passwordBox_KeyDown(object sender, EventArgs e)
        {
            if (((System.Windows.Input.KeyEventArgs)e).Key == Key.Enter)
            {
                try
                {
                    // Create a random key using a random number generator. This would be the
                    //  secret key shared by sender and receiver.
                    byte[] secretkey = new Byte[64];
                    Rfc2898DeriveBytes deriveBytes = new Rfc2898DeriveBytes(passwordBox.Password, Encoding.UTF8.GetBytes(PasswordSalt));
                    secretkey = deriveBytes.GetBytes(64);

                    // Use the secret key to encode the message file.
                    EncodeFile(secretkey, sourceFilePath, signedFilePath);

                }
                catch (Exception ex)
                {
                    outputBlock.Text = ex.Message;
                }
                this.decodePassWordBox.Focus();
            }

        }
        private void decodePassWordBox_KeyDown(object sender, EventArgs e)
        {
            if (((System.Windows.Input.KeyEventArgs)e).Key == Key.Enter)
            {
                try
                {
                    // Create a random key using a random number generator. This would be the
                    //  secret key shared by sender and receiver.
                    byte[] secretkey = new Byte[64];
                    Rfc2898DeriveBytes deriveBytes = new Rfc2898DeriveBytes(passwordBox.Password, Encoding.UTF8.GetBytes(PasswordSalt));
                    secretkey = deriveBytes.GetBytes(64);

                    // Take the encoded file and decode
                    DecodeFile(secretkey, signedFilePath);
                }
                catch (Exception ex)
                {
                    outputBlock.Text = ex.Message;
                }
                this.deleteBox.Focus();
            }
        }
        // Computes a keyed hash for a source file, creates a target file with the keyed hash
        // prepended to the contents of the source file
        public void EncodeFile(byte[] key, String sourceFile, String destFile)
        {
            using (IsolatedStorageFile isoStore = IsolatedStorageFile.GetUserStoreForApplication())
            using (IsolatedStorageFileStream outStream = isoStore.OpenFile(signedFilePath, FileMode.Open))
            {
                try
                {
                    // Initialize the keyed hash object.
                    HMACSHA256 myhmacsha256 = new HMACSHA256(key);
                    IsolatedStorageFileStream inStream = isoStore.OpenFile(sourceFilePath, FileMode.Open);
                    inStream.Position = 0;
                    // Compute the hash of the input file.
                    byte[] hashValue = myhmacsha256.ComputeHash(inStream);
                    // Reset inStream to the beginning of the file.
                    inStream.Position = 0;
                    // Write the computed hash value to the output file.
                    outStream.Write(hashValue, 0, hashValue.Length);
                    // Copy the contents of the sourceFile to the destFile.
                    int bytesRead;
                    // read 1K at a time
                    byte[] buffer = new byte[1024];
                    do
                    {
                        // Read from the wrapping CryptoStream.
                        bytesRead = inStream.Read(buffer, 0, 1024);
                        outStream.Write(buffer, 0, bytesRead);
                    } while (bytesRead > 0);
                    myhmacsha256.Clear();
                    // Close the streams
                    inStream.Close();
                    outStream.Close();
                    decodeBox.Text = destFile.Replace(encryptedFiles + "\\", "");
                    decodePassWordBox.Focus();
                    return;
                }
                catch (Exception e)
                {
                    outputBlock.Text = e.Message;
                }
            } //end if-else

        } // end EncodeFile
        // Decode the encoded file and compare to original file.
        public bool DecodeFile(byte[] key, String sourceFile)
        {
            using (IsolatedStorageFile isoStore = IsolatedStorageFile.GetUserStoreForApplication())
            using (IsolatedStorageFileStream inStream = isoStore.OpenFile(signedFilePath, FileMode.Open))
            {
                try
                {
                    // Initialize the keyed hash object. 
                    HMACSHA256 hmacsha256 = new HMACSHA256(key);
                    // Create an array to hold the keyed hash value read from the file.
                    byte[] storedHash = new byte[hmacsha256.HashSize / 8];
                    // Create a FileStream for the source file
                    // Read in the storedHash.
                    inStream.Read(storedHash, 0, storedHash.Length);
                    // Compute the hash of the remaining contents of the file.
                    // The stream is properly positioned at the beginning of the content, 
                    // immediately after the stored hash value.
                    byte[] computedHash = hmacsha256.ComputeHash(inStream);
                    // compare the computed hash with the stored value
                    for (int i = 0; i < storedHash.Length; i++)
                    {
                        if (computedHash[i] != storedHash[i])
                        {
                            outputBlock.Text = "Hash values differ! Either wrong password or file has changed.";
                            return false;
                        }
                    }
                    outputBlock.Text = "Hash values agree -- no tampering occurred.";
                    return true;
                }
                catch (Exception e)
                {
                    outputBlock.Text = e.Message;
                    return false;
                }
            }
        } //end DecodeFile
        public void CreateFile()
        {
            IsolatedStorageFile store = IsolatedStorageFile.GetUserStoreForApplication();
            sourceFilePath = System.IO.Path.Combine(encryptedFiles, "sourceFile.txt");
            signedFilePath = System.IO.Path.Combine(encryptedFiles, "signedFile.txt");
            IsolatedStorageFileStream sourceStream = store.CreateFile(sourceFilePath);
            StreamWriter sw = new StreamWriter(sourceStream);
            sw.WriteLine(inputBox.Text);
            sw.Close();
            sourceStream.Close();

            IsolatedStorageFileStream signedStream = store.CreateFile(signedFilePath);
            signedStream.Close();
            decodeBox.Text = "sourceFile.txt";
        }
    }
}

<UserControl x:Class="HMACSHA256Example.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
    Width="1024" Height="768">
    <Grid x:Name="LayoutRoot" Background="White" >
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="550" />
            <ColumnDefinition Width="250" />
            <!--<ColumnDefinition Width="250" />-->
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto" />
            <RowDefinition Height="Auto" />
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
        </Grid.RowDefinitions>

        <TextBlock Grid.Row="0"  Grid.Column="0" FontSize="14" Text="Enter data for source file, press Enter to create the file"/>
        <TextBlock Grid.Row="1" Grid.Column="0" FontSize="14" Text="Enter password and press Enter to create a signed copy" />
        <TextBlock Grid.Row="2" Grid.Column="0" FontSize="14" Text="Enter file to check" />
        <TextBlock Grid.Row="3" Grid.Column="0" FontSize="14" Text="Enter password and press Enter to check" />
        <TextBlock Grid.Row="4" Grid.Column="0" FontSize="14" Text="Enter file name to delete" />
        <TextBox x:Name="inputBox" Grid.Row="0" Grid.Column="1" TabIndex="0" FontSize="12" IsReadOnly="False"  BorderThickness="5" Height="40"  Width="160" HorizontalAlignment="Center" />
        <PasswordBox x:Name="passwordBox" Grid.Row="1" Grid.Column="1" TabIndex ="1" FontSize="12"  BorderThickness="5" Height="40"  Width="160" HorizontalAlignment="Center" />
        <TextBox x:Name="decodeBox" Grid.Row="2" Grid.Column="1" TabIndex="2" FontSize="12" IsReadOnly="False"  BorderThickness="5" Height="40"  Width="160" HorizontalAlignment="Center" />
        <PasswordBox x:Name="decodePassWordBox" Grid.Row="3" TabIndex="3" Grid.Column="1" FontSize="12" BorderThickness="5" Height="40"  Width="160" HorizontalAlignment="Center" />
        <TextBox x:Name="deleteBox" Grid.Row="4" Grid.Column="1" TabIndex="4" FontSize="12" IsReadOnly="False"  BorderThickness="5" Height="40"  Width="160" HorizontalAlignment="Center" />
        <TextBlock x:Name="outputBlock" Grid.Row="5" Grid.Column="0" FontSize="12" TextWrapping="Wrap">
        </TextBlock>
    </Grid>
</UserControl>

<UserControl x:Class="HMACSHA256Example.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
    Width="1024" Height="768">
    <Grid x:Name="LayoutRoot" Background="White" >
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="550" />
            <ColumnDefinition Width="250" />
            <!--<ColumnDefinition Width="250" />-->
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto" />
            <RowDefinition Height="Auto" />
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
        </Grid.RowDefinitions>

        <TextBlock Grid.Row="0"  Grid.Column="0" FontSize="14" Text="Enter data for source file, press Enter to create the file"/>
        <TextBlock Grid.Row="1" Grid.Column="0" FontSize="14" Text="Enter password and press Enter to create a signed copy" />
        <TextBlock Grid.Row="2" Grid.Column="0" FontSize="14" Text="Enter file to check" />
        <TextBlock Grid.Row="3" Grid.Column="0" FontSize="14" Text="Enter password and press Enter to check" />
        <TextBlock Grid.Row="4" Grid.Column="0" FontSize="14" Text="Enter file name to delete" />
        <TextBox x:Name="inputBox" Grid.Row="0" Grid.Column="1" TabIndex="0" FontSize="12" IsReadOnly="False"  BorderThickness="5" Height="40"  Width="160" HorizontalAlignment="Center" />
        <PasswordBox x:Name="passwordBox" Grid.Row="1" Grid.Column="1" TabIndex ="1" FontSize="12"  BorderThickness="5" Height="40"  Width="160" HorizontalAlignment="Center" />
        <TextBox x:Name="decodeBox" Grid.Row="2" Grid.Column="1" TabIndex="2" FontSize="12" IsReadOnly="False"  BorderThickness="5" Height="40"  Width="160" HorizontalAlignment="Center" />
        <PasswordBox x:Name="decodePassWordBox" Grid.Row="3" TabIndex="3" Grid.Column="1" FontSize="12" BorderThickness="5" Height="40"  Width="160" HorizontalAlignment="Center" />
        <TextBox x:Name="deleteBox" Grid.Row="4" Grid.Column="1" TabIndex="4" FontSize="12" IsReadOnly="False"  BorderThickness="5" Height="40"  Width="160" HorizontalAlignment="Center" />
        <TextBlock x:Name="outputBlock" Grid.Row="5" Grid.Column="0" FontSize="12" TextWrapping="Wrap">
        </TextBlock>
    </Grid>
</UserControl>