Imports System
Imports System.Windows.Controls
Imports System.Windows.Input
Imports System.IO
Imports System.IO.IsolatedStorage
Imports System.Security.Cryptography
Imports System.Security.Permissions
Imports System.Text
Class MainPage
    Inherits UserControl
    Private Shared encryptedFiles As String = ""
    Private Shared store As IsolatedStorageFile = IsolatedStorageFile.GetUserStoreForApplication()
    Private Const PasswordSalt As String = "PasswordSalt"
    Private Shared sourceFilePath As String = ""
    Private Shared signedFilePath As String = ""

    Public Sub New()
        InitializeComponent()
        AddHandler Me.inputBox.KeyDown, AddressOf inputBox_KeyDown
        AddHandler Me.passwordBox.KeyDown, AddressOf passwordBox_KeyDown
        AddHandler Me.decodePassWordBox.KeyDown, AddressOf decodePassWordBox_KeyDown
        AddHandler Me.deleteBox.KeyDown, AddressOf deleteBox_KeyDown
        AddHandler Me.decodeBox.KeyDown, AddressOf decodeBox_KeyDown

        store.CreateDirectory("MyFiles")

        ' Create subdirectory under MyFiles.
        encryptedFiles = System.IO.Path.Combine("MyFiles", "EncryptedFiles")
        store.CreateDirectory(encryptedFiles)
        ListFiles()
        inputBox.Focus()

    End Sub 'New   
    Private Sub inputBox_KeyDown(ByVal sender As Object, ByVal e As EventArgs)
        If CType(e, System.Windows.Input.KeyEventArgs).Key = Key.Enter Then
            CreateFile()
            Me.passwordBox.Focus()
        End If

    End Sub 'inputBox_KeyDown   
    Private Sub decodeBox_KeyDown(ByVal sender As Object, ByVal e As EventArgs)
        If CType(e, System.Windows.Input.KeyEventArgs).Key = Key.Enter Then
            Dim store As IsolatedStorageFile = IsolatedStorageFile.GetUserStoreForApplication()
            signedFilePath = System.IO.Path.Combine(encryptedFiles, "signedFile.txt")
            Me.decodePassWordBox.Focus()
        End If

    End Sub 'decodeBox_KeyDown    
    Private Sub ListFiles()
        Dim searchpath As String = System.IO.Path.Combine(encryptedFiles, "*.*")
        Dim filesInSubDirs As String() = store.GetFileNames(searchpath)
        Dim sb As New StringBuilder()
        ' List files in MyFiles\EncryptedFiles.
        sb.AppendLine("Files in MyFiles\EncryptedFiles:")
        Dim fileName As String
        For Each fileName In filesInSubDirs
            sb.AppendLine(" - " + fileName)
        Next fileName
        sb.AppendLine()
        outputBlock.Text = sb.ToString()

    End Sub 'ListFiles   
    Private Sub deleteBox_KeyDown(ByVal sender As Object, ByVal e As EventArgs)

        If CType(e, System.Windows.Input.KeyEventArgs).Key = Key.Enter Then
            store.DeleteFile(encryptedFiles + "\" + deleteBox.Text)
            ListFiles()
            Me.passwordBox.Focus()
        End If

    End Sub 'deleteBox_KeyDown   
    Private Sub passwordBox_KeyDown(ByVal sender As Object, ByVal e As EventArgs)
        If CType(e, System.Windows.Input.KeyEventArgs).Key = Key.Enter Then
            Try
                ' Create a random key using a random number generator. This would be the
                '  secret key shared by sender and receiver.
                Dim secretkey() As Byte = New [Byte](63) {}
                Dim deriveBytes As 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 ex As Exception
                outputBlock.Text = ex.Message
            End Try
            Me.decodePassWordBox.Focus()
        End If

    End Sub 'passwordBox_KeyDown    
    Private Sub decodePassWordBox_KeyDown(ByVal sender As Object, ByVal e As EventArgs)
        If CType(e, System.Windows.Input.KeyEventArgs).Key = Key.Enter Then
            Try
                ' Create a random key using a random number generator. This would be the
                '  secret key shared by sender and receiver.
                Dim secretkey() As Byte = New [Byte](63) {}
                Dim deriveBytes As New Rfc2898DeriveBytes(passwordBox.Password, Encoding.UTF8.GetBytes(PasswordSalt))
                secretkey = deriveBytes.GetBytes(64)

                ' Take the encoded file and decode
                DecodeFile(secretkey, signedFilePath)
            Catch ex As Exception
                outputBlock.Text = ex.Message
            End Try
            Me.deleteBox.Focus()
        End If

    End Sub 'decodePassWordBox_KeyDown    
    ' 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 Sub EncodeFile(ByVal key() As Byte, ByVal sourceFile As String, ByVal destFile As String)
        Dim isoStore As IsolatedStorageFile = IsolatedStorageFile.GetUserStoreForApplication()
        Try
            Dim outStream As IsolatedStorageFileStream = isoStore.OpenFile(signedFilePath, FileMode.Open)
            Try
                Try
                    ' Initialize the keyed hash object.
                    Dim myhmacsha256 As New HMACSHA256(key)
                    Dim inStream As IsolatedStorageFileStream = isoStore.OpenFile(sourceFilePath, FileMode.Open)
                    inStream.Position = 0
                    ' Compute the hash of the input file.
                    Dim hashValue As Byte() = 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.
                    Dim bytesRead As Integer
                    ' read 1K at a time
                    Dim buffer(1023) As Byte
                    Do
                        ' Read from the wrapping CryptoStream.
                        bytesRead = inStream.Read(buffer, 0, 1024)
                        outStream.Write(buffer, 0, bytesRead)
                    Loop While bytesRead > 0
                    myhmacsha256.Clear()
                    ' Close the streams
                    inStream.Close()
                    outStream.Close()
                    decodeBox.Text = destFile.Replace(encryptedFiles + "\", "")
                    decodePassWordBox.Focus()
                    Return
                Catch e As Exception
                    outputBlock.Text = e.Message
                End Try
            Finally
                outStream.Dispose()
            End Try
        Finally
            isoStore.Dispose() 'end if-else
        End Try

    End Sub 'EncodeFile
    ' end EncodeFile
    ' Decode the encoded file and compare to original file.
    Public Function DecodeFile(ByVal key() As Byte, ByVal sourceFile As String) As Boolean
        Dim isoStore As IsolatedStorageFile = IsolatedStorageFile.GetUserStoreForApplication()
        Try
            Dim inStream As IsolatedStorageFileStream = isoStore.OpenFile(signedFilePath, FileMode.Open)
            Try
                Try
                    ' Initialize the keyed hash object. 
                    Dim hmacsha256 As New HMACSHA256(key)
                    ' Create an array to hold the keyed hash value read from the file.
                    Dim storedHash(hmacsha256.HashSize / 8 - 1) As Byte
                    ' 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.
                    Dim computedHash As Byte() = hmacsha256.ComputeHash(inStream)
                    ' compare the computed hash with the stored value
                    Dim i As Integer
                    For i = 1 To storedHash.Length - 1
                        If computedHash(i) <> storedHash(i) Then
                            outputBlock.Text = "Hash values differ! Either wrong password or file has changed."
                            Return False
                        End If
                    Next i
                    outputBlock.Text = "Hash values agree -- no tampering occurred."
                    Return True
                Catch e As Exception
                    outputBlock.Text = e.Message
                    Return False
                End Try
            Finally
                inStream.Dispose()
            End Try
        Finally
            isoStore.Dispose()
        End Try
        'end DecodeFile
    End Function 'DecodeFile   
    Public Sub CreateFile()
        Dim store As IsolatedStorageFile = IsolatedStorageFile.GetUserStoreForApplication()
        sourceFilePath = System.IO.Path.Combine(encryptedFiles, "sourceFile.txt")
        signedFilePath = System.IO.Path.Combine(encryptedFiles, "signedFile.txt")
        Dim sourceStream As IsolatedStorageFileStream = store.CreateFile(sourceFilePath)
        Dim sw As New StreamWriter(sourceStream)
        sw.WriteLine(inputBox.Text)
        sw.Close()
        sourceStream.Close()

        Dim signedStream As IsolatedStorageFileStream = store.CreateFile(signedFilePath)
        signedStream.Close()
        decodeBox.Text = "sourceFile.txt"

    End Sub 'CreateFile
End Class 'Page

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";
        }
    }
}