Unleash the power of .NET with encryption

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Introduction

Unleash the power of .net with encryption

Source code: encr.zip

Introduction

Security is the prime issue for personal documents. How can we protect personal files and folders from malicious users? Is there any other method apart from the password protection of folder? Well we can encrypt our documents to provide better protection .Once we encrypt our document it is difficult for other user to read it’s content .Even if they add or append any thing to the document nothing harm will happened to the main content as when we will decrypt the same we will get the content in text format except the newly added part which will be displayed in some non formal text.

Ex. All files with .txt extension. This article depicts in detail how to encrypt and decrypt file or folder with “RIJNDAEL” encryption method. You can use this method to encrypt .txt, .bmp, .jpg, .mdb, .wav, MP3 files etc.

Create a new Windows Application project in Visual Studio.NET. The Form will contain five buttons, four textboxes, one imagelist, one treeview and three labels. Add controls to the Form with the following settings:

Code:

Now it’s time to delve into the code. First add the following import statements

Imports System.Security.Cryptography

Imports System.Security

Imports System.IO

Imports System.Text 'TO GET ASCII CONVERSION

Imports System.Drawing.Drawing2D 'TO GET ALL BRUSHES

Imports System.Drawing.Graphics

Imports System.Drawing

Imports System.Security.Permissions

First two import statements are required for encryption and decryption process. Last import statement is required for Code Access Security (CAS).

Next we will create a subroutine for encryption. This subroutine is called from bttnencrypt.

    Sub encrypt(ByVal encr As SymmetricAlgorithm)

        Dim fs, key, ivfile As FileStream

        Dim cs As CryptoStream

        Dim fileperm As New FileIOPermission(PermissionState.Unrestricted)

        Dim regperm As New RegistryPermission(PermissionState.Unrestricted)

        Dim uiperm As New UIPermission(PermissionState.Unrestricted)

        Dim newperm As New PermissionSet(PermissionState.None)

        newperm.AddPermission(fileperm)

        newperm.AddPermission(regperm)

        newperm.AddPermission(uiperm)

        newperm.PermitOnly()

        Try

            fs = New FileStream(txtfilepath.Text.ToString, FileMode.Open, FileAccess.ReadWrite)

        Catch my As Exception

            MsgBox("Following Errors Occured: " & vbCrLf & my.Message & vbCrLf & my.Source)

            Exit Sub

        End Try

        Dim bytes(CInt(fs.Length) - 1) As Byte

        key = New FileStream("C:\key.enc", FileMode.OpenOrCreate)

        ivfile = New FileStream("C:\ivfile.enc", FileMode.OpenOrCreate)

        Try

            encr.Key = keygen()

            key.Write(encr.Key, 0, encr.Key.Length)

            ivfile.Write(encr.IV, 0, encr.IV.Length)

            cs = New CryptoStream(fs, encr.CreateEncryptor(encr.Key, encr.IV), CryptoStreamMode.Write)

            Dim i As Integer

            Dim ascii As Encoding = Encoding.ASCII

            For i = 0 To fs.Length - 1

                bytes(i) = fs.ReadByte

            Next

            TextBox1.Text = "BEFORE ENCRYPTION YOUR FILE CONTAINS :" & vbCrLf & ascii.GetChars(bytes)

            fs.SetLength(0)

            MsgBox("CHECK FILE", MsgBoxStyle.OKOnly)

            cs.Write(bytes, 0, bytes.Length)

        Catch my As Exception

            MsgBox(my.Message)

        Finally

            If Not key Is Nothing Then

                key.Close()

            End If

            If Not ivfile Is Nothing Then

                ivfile.Close()

            End If

            If Not cs Is Nothing Then

                cs.Close()

            End If

            If Not fs Is Nothing Then

                fs.Close()

            End If

        End Try

This subroutine will create two files key.enc and ivfile.enc at “C:\ “. These two file are essentials for decryption. Please save it in proper place. Otherwise you will be in trouble during decryption. After encryption one message will be displayed like “check file..” so that if you wish you can check the encrypted content of your file. Next I have used a function called keygen () which will take password for encryption and return byte ().

Function keygen() As Byte()

        Dim password As String = txtpasswd.Text

        Dim add() As Byte = {3, 45, 78, 123, 9, 77}

        Dim pwd As New PasswordDeriveBytes(password, add)

        Dim pwdbytes() As Byte = pwd.GetBytes(24)

        Return pwdbytes

    End Function

Declare another subroutine called decrypt which will take two arguments for decryption. This subroutine is called from the click event of bttndecrypt.

Sub decrypt(ByVal encr As SymmetricAlgorithm, ByVal include As Boolean)

        Dim fout, key, ivfile As FileStream

        Dim cs As CryptoStream

        Dim readbyte, newbyte As Integer

        fout = New FileStream(txtfilepath.Text.ToString, FileMode.Open, FileAccess.ReadWrite)

        Dim bytes1(CInt(fout.Length) - 1) As Byte

        key = New FileStream("C:\key.enc", FileMode.Open, FileAccess.ReadWrite)

        ivfile = New FileStream("C:\ivfile.enc", FileMode.Open, FileAccess.ReadWrite)

        If include Then

            Dim key1(key.Length - 1) As Byte

            Dim iv(ivfile.Length - 1) As Byte

            key.Read(key1, 0, key.Length)

            encr.Key = key1

            ivfile.Read(iv, 0, iv.Length)

            encr.IV = iv

        End If

        Try

            cs = New CryptoStream(fout, encr.CreateDecryptor(encr.Key, encr.IV), CryptoStreamMode.Read)

            Dim ascii As Encoding = Encoding.ASCII

            Do

                readbyte = cs.Read(bytes1, 0, bytes1.Length)

                If readbyte = 0 Then Exit Do

            Loop

            TextBox2.Text = "AFTER DECRYPTION YOUR FILE CONTAINS : " & vbCrLf & ascii.GetChars(bytes1)

            fout.SetLength(0)

            For newbyte = 0 To bytes1.Length - 1

                fout.WriteByte(bytes1(newbyte))

            Next

        Catch my As Exception

            MsgBox(my.Message)

        Finally

            If Not key Is Nothing Then

                key.SetLength(0)

                key.Close()

            End If

            If Not ivfile Is Nothing Then

                ivfile.SetLength(0)

                ivfile.Close()

            End If

            If Not fout Is Nothing Then

                fout.Close()

            End If

            If Not cs Is Nothing Then

                cs.Close()

            End If

        End Try

    End Sub

A few codes I have written for bttnrefresh_click event. This is as follows

TextBox1.Text = ""

        TextBox2.Text = ""

        bttnencrypt.Enabled = True

        bttndecrypt.Enabled = True

        txtfilepath.Text = ""

        txtpasswd.Text = ""

Finally, all of the above subroutines are called as follows

Private Sub bttnencrypt_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles bttnencrypt.Click

        If txtfilepath.Text <> "" Then

            Dim encr As Rijndael = Rijndael.Create()

            encrypt(encr)

            bttnencrypt.Enabled = False

            bttndecrypt.Enabled = True

        Else

            MsgBox("Please select path of file or write the physical path of target file")

        End If

    End Sub

Private Sub bttndecrypt_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles bttndecrypt.Click

        Dim encr As Rijndael = Rijndael.Create()

        decrypt(encr, True)

        bttndecrypt.Enabled = False

        bttnencrypt.Enabled = True

    End Sub

Conclusion

This article describes in brief both the encryption and decryption method of rijndael. As I told you earlier if we click bttnencrypt for the first time it will create two files called as key.enc and ivfile.enc. Later decrypt subroutine will use the same file for decryption. Thus the path of these two files is important. Otherwise decryption will not occur. We can avoid such problem in one way by keeping   these two files in a memory location.

 To give a professional look to my software “’NCRYPTOR” I have added one treeview and one imagelist to display the directories and subdirectories of all logical drives. Just create a subroutine called treeview() .This subroutine is called from the click event of bttnpath.

Sub treeview()

        Dim node, childnode, grandchld, grgrandchld As TreeNode

        Dim img As Image

        Dim rootdir, subdir, subdr, fname As String

        TreeView1.Nodes.Clear()

        TreeView1.ImageList = ImageList1

        For Each rootdir In Directory.GetLogicalDrives

            node = TreeView1.Nodes.Add(rootdir)

            If node.Text = "A:\" Then

                node.ImageIndex = 4

                node.SelectedImageIndex = 4

            ElseIf node.Text = "F:\" Then

                node.ImageIndex = 1

                node.SelectedImageIndex = 1

            ElseIf node.Text = "G:\" Then

                node.ImageIndex = 1

                node.SelectedImageIndex = 1

            ElseIf node.Text = "H:\" Then

                node.ImageIndex = 1

                node.SelectedImageIndex = 1

            Else

                node.ImageIndex = 3

                node.SelectedImageIndex = 3

            End If

            Try

                For Each subdir In Directory.GetDirectories(rootdir)

                    childnode = node.Nodes.Add(subdir)

                    For Each subdr In Directory.GetDirectories(subdir)

                        grandchld = childnode.Nodes.Add(subdr)

                        For Each fname In Directory.GetFiles(subdr)

                            grgrandchld = grandchld.Nodes.Add(fname)

                        Next

                    Next

                Next

            Catch my As Exception

                MsgBox(my.Message)

            End Try

        Next

    End Sub

Private Sub TreeView1_AfterSelect(ByVal sender As System.Object, ByVal e As System.Windows.Forms.TreeViewEventArgs) Handles TreeView1.AfterSelect

        Label2.Text = e.Node.Text

        txtfilepath.Text = Label2.Text

    End Sub

    Private Sub bttnpath_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles bttnpath.Click

        treeview()

    End Sub

Last but not least I have written a few codes for background color of the form which is as follows

Private Sub transparent_frame(ByVal sender As Object, ByVal e As PaintEventArgs) Handles MyBase.Paint

        Dim b As New GraphicsPath()

        b.AddRectangle(New Rectangle(0, 0, Me.Width, Me.Height))

        Dim br As New PathGradientBrush(b)

        br.CenterColor = Color.White

        br.CenterPoint = New PointF(120, 30)

        Dim colors() As Color = {Color.Blue, Color.AliceBlue, Color.CornflowerBlue, Color.Azure}

        br.SurroundColors = colors

        Label1.BackColor = Color.Transparent

        bttnencrypt.BackColor = Color.Transparent

        bttndecrypt.BackColor = Color.Transparent

        bttnpath.BackColor = Color.Transparent

        bttnrefresh.BackColor = Color.Transparent

        Panel1.BackColor = Color.Transparent

        Panel2.BackColor = Color.Transparent

        Label2.BackColor = Color.Transparent

        lblfilepath.BackColor = Color.Transparent

        bttncls.BackColor = Color.Transparent

        e.Graphics.FillPath(br, b)

    End Sub

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