Applied cryptography Part 2: a tool to encrypt files on your HDD

• Download demo project - 31.1 Kb

Introduction

Do you need to keep some of your files unreadable to others? Do you want to be sure that when you leave your workplace your files are secure?

CryptoSafe is a tool that enables you to encrypt your private files so that no one else can read them.

Key features of CryptoSafe:

• Rijndael encryption algorithm.
• Secure key creation from given password using PasswordDeriveBytes method.
• Using Isolated Storage for storing per-user configuration.
• Extracting icons associated with files, using Win32 shell.

The algorithm - RijndaelManaged

Why RijndaelManaged? As written in part 1: because it is strong, fast, and managed, what ensures to run on every machine with .NET framework installed.

The Application

There are very few steps you have to do for using CryptoSafe:

• Enter password for encryption.
• Define folders you want to protect (in Folders tab).
• Select active folder to work with.
• Encrypt files selected in left listbox by clicking "move right" button.
• Decrypt files by clicking "move left" (or double clicking) encrypted files in right listbox.

You can refresh file list by clicking "re" button if necessary (when folder contents change).

The Code

Creating file list with proper icons

void refreshFileList()
{
    listView1.Items.Clear();
    listView2.Items.Clear();

    if (workingDirectory == null || workingDirectory.Length == 0)
        return;
    this.Cursor = Cursors.WaitCursor;
    try
    {
        string[] files = Directory.GetFiles(workingDirectory);
        int imageIndex = 0;
        imageList1.Images.Clear();
        SHFILEINFO shinfo = new SHFILEINFO();
        listView1.BeginUpdate();
        listView2.BeginUpdate();
        foreach (string s in files)
        {
            FileInfo fi = new FileInfo(s);
            if (fi.Extension.ToLower() == ".enc")
            {
                ListViewItem lvi = new ListViewItem(fi.Name);
                lvi.SubItems.Add(fi.Length.ToString());
                lvi.Tag = fi.FullName;
                lvi.ImageIndex = 0;
                listView2.Items.Add(lvi);
            }
            else
            {
                //extract file icon
                IntPtr hImgSmall = MyShell.SHGetFileInfo(s, 0, 
                    ref shinfo,(uint)Marshal.SizeOf(shinfo),
                    MyShell.SHGFI_ICON |
                    MyShell.SHGFI_SMALLICON);
                //The icon is returned in the hIcon member of the shinfo
                //struct
                System.Drawing.Icon myIcon = 
                    System.Drawing.Icon.FromHandle(shinfo.hIcon);
                imageList1.Images.Add(myIcon);

                ListViewItem lvi = new ListViewItem(fi.Name);
                lvi.ImageIndex = imageIndex++;
                lvi.SubItems.Add(fi.Length.ToString());
                lvi.Tag = fi.FullName;
                listView1.Items.Add(lvi);
            }
        }
        listView1.EndUpdate();
        listView2.EndUpdate();
    }
    catch(IOException ex)
    {
        MessageBox.Show("refreshFileList IOexception: "+ex.Message);
    }
    finally
    {
        this.Cursor = Cursors.Arrow;
    }}

Save settings in isolated storage

void saveSettings()
{
    // Retrieve an IsolatedStorageFile
    // for the current Domain and Assembly.
    try
    {
        IsolatedStorageFile isoFile = 
          IsolatedStorageFile.GetStore(IsolatedStorageScope.User |
          IsolatedStorageScope.Assembly |
          IsolatedStorageScope.Domain , null,null);

        IsolatedStorageFileStream fs = new 
          IsolatedStorageFileStream("cryptoSettings.txt", 
          FileMode.Create,FileAccess.Write);
        StreamWriter sw = new StreamWriter(fs);
        foreach (string fname in lbFolders.Items)
            sw.WriteLine(fname);
        sw.Close();
        isoFile.Close();
        
    }
    catch (IsolatedStorageException ex)
    {
        MessageBox.Show(ex.Message);
    }
    catch (IOException ex)
    {
        MessageBox.Show(ex.Message);
    }
}

Load settings from isolated storage

void loadSettings()
{
    // Retrieve an IsolatedStorageFile for the current Domain and Assembly.
    try
    {
        lbFolders.Items.Clear();
        IsolatedStorageFile isoFile = 
          IsolatedStorageFile.GetStore(IsolatedStorageScope.User |
          IsolatedStorageScope.Assembly |
          IsolatedStorageScope.Domain , null,null);

        IsolatedStorageFileStream fs = new 
          IsolatedStorageFileStream("cryptoSettings.txt", 
          FileMode.Open,FileAccess.Read);
        StreamReader sr = new StreamReader(fs);
        while (true)
        {
            string l = sr.ReadLine();
            if (l == null)
                break;
            lbFolders.Items.Add(l);
        }

        sr.Close();
        isoFile.Close();
        
    }
    catch (FileNotFoundException)
    {
        MessageBox.Show("application settings" + 
          " file not found - please set working folders");
    }
    catch (IsolatedStorageException ex)
    {
        MessageBox.Show(ex.Message);
    }
    catch (IOException ex)
    {
        MessageBox.Show(ex.Message);
    }
}

File encryption

public  void EncryptData(String inName, 
        String outName, byte[] rijnKey, byte[] rijnIV)
{    
    FileStream fin = null;
    FileStream fout = null;
    CryptoStream encStream = null;

    try
    {
        //Create the file streams to handle the input and output files.
        fin = new FileStream(inName, FileMode.Open, FileAccess.Read);
        fout = new FileStream(outName, FileMode.Create, FileAccess.Write);
        //fout.SetLength(0);

        //Create variables to help with read and write.

        //This is intermediate storage for the encryption.
        byte[] bin = new byte[bufLen];
        //This is the total number of bytes written.
        long rdlen = 0;
        //This is the total length of the input file.
        long totlen = fin.Length;
        //This is the number of bytes to be written at a time.
        int len;

        RijndaelManaged rijn = new RijndaelManaged();
        encStream = new CryptoStream(fout, 
          rijn.CreateEncryptor(rijnKey, rijnIV), 
          CryptoStreamMode.Write);
        
        fireMessage("Rijndael encrypting...");

        //encrypt test header
        encStream.Write(testHeader,0,testHeader.Length);

        //Read from the input file, then encrypt 
        //and write to the output file.
        while(true)
        {
            len = fin.Read(bin, 0, bufLen);
            if (len == 0)
                break;
            encStream.Write(bin, 0, len);
            rdlen += len;
            fireMessage(inName,(int)totlen,(int)rdlen);
        }
        fireMessage(string.Format("{0} - {1} bytes processed", 
                                                 inName ,rdlen));
    }
    finally
    {
        if (encStream != null)
            encStream.Close();  
        if (fout != null)
            fout.Close();
        if (fin != null)
            fin.Close();                   
    }
}

File decryption

public bool DecryptData(String inName, 
          String outName, byte[] rijnKey, byte[] rijnIV)
{    
    //Create the file streams to handle the input and output files.
    FileStream fin = null;
    FileStream fout = null;
    CryptoStream decStream = null;
    
    try
    {
        fin = new FileStream(inName, FileMode.Open, FileAccess.Read);

        //Create variables to help with read and write.

        //This is intermediate storage for the encryption.
        byte[] bin = new byte[bufLen];
        //This is the total number of bytes written.
        long rdlen = 0;
        //This is the total length of the input file.
        long totlen = fin.Length;
        //This is the number of bytes to be written at a time.
        int len;

        RijndaelManaged rijn = new RijndaelManaged();
        
        decStream = new CryptoStream(fin, 
          rijn.CreateDecryptor(rijnKey, rijnIV), 
          CryptoStreamMode.Read);

        fireMessage("Rijndael decrypting...");

        //decrypt test header
        byte[]test = new byte[testHeader.Length];
        decStream.Read(test,0,testHeader.Length);
        if (BitConverter.ToString(test) != testHeaderString)
        {
            decStream.Clear();
            decStream = null;
            fireMessage("error while decrypting file "+inName);
            return false;
        }

        //create output file
        fout = new FileStream(outName, 
                     FileMode.Create, FileAccess.Write);

        //Read from the encrypted file and write dercypted data
        while(true)
        {
            len = decStream.Read(bin,0,bufLen);
            if (len == 0)
                break;
            fout.Write(bin,0,len);
            rdlen += len;
            fireMessage(inName,(int)totlen,(int)rdlen);
        }
        fireMessage(string.Format("{0} - {1} bytes processed", 
                                                  inName ,rdlen));

        return true;
    }
    finally
    {
        if (decStream != null)
            decStream.Close();
        if (fout != null)
            fout.Close();
        if (fin != null)
            fin.Close();                   
    }
}