How to check file is Tempering or not with existing file

 

We can see if the file is tempering or not using Cryptography

Code:

Imports System.IO

Imports System.Security.Cryptography

Public Class Form1

   

    Private Sub Button5_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button5.Click

        Application.Exit()

    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

        OpenFileDialog1.Title = "Open File"

        OpenFileDialog1.Filter = "Files (*.*)|*.*"

        If OpenFileDialog1.ShowDialog = Windows.Forms.DialogResult.Cancel Then

            Exit Sub

        End If

        Dim sFilePath As String = OpenFileDialog1.FileName

        If System.IO.File.Exists(sFilePath) = False Then

            sFilePath = ""

            Exit Sub

        Else

            TextBox1.Text = sFilePath

        End If

    End Sub

    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click

        OpenFileDialog1.Title = "Open File"

        OpenFileDialog1.Filter = "Files (*.*)|*.*"

        If OpenFileDialog1.ShowDialog = Windows.Forms.DialogResult.Cancel Then

            Exit Sub

        End If

        Dim sFilePath As String = OpenFileDialog1.FileName

        If System.IO.File.Exists(sFilePath) = False Then

            sFilePath = ""

            Exit Sub

        Else

            TextBox2.Text = sFilePath

        End If

    End Sub

    Private Sub Button4_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button4.Click

        Dim myHash As HashAlgorithm

        myHash = HashAlgorithm.Create()

        If TextBox2.Text = String.Empty Or Me.TextBox1.Text = String.Empty Then

            MessageBox.Show("Set all form fields prior to initiating a test", _

            "Missing Form Data", MessageBoxButtons.OK)

        End If

        Dim fs1 As New FileStream(TextBox2.Text, FileMode.OpenOrCreate)

        Dim fs1Bytes As Byte() = New Byte(fs1.Length) {}

        fs1.Read(fs1Bytes, 0, fs1.Length)

        Dim arr1() As Byte = myHash.ComputeHash(fs1Bytes)

        fs1.Close()

        Dim fs2 As New FileStream(TextBox1.Text, FileMode.OpenOrCreate)

        Dim fs2Bytes As Byte() = New Byte(fs2.Length) {}

        fs2.Read(fs2Bytes, 0, fs2.Length)

        Dim arr2() As Byte = myHash.ComputeHash(fs2Bytes)

        fs2.Close()

        If BitConverter.ToString(arr1) = BitConverter.ToString(arr2) Then

            MessageBox.Show("The file examined has not been tampered with.", "Hash" & _

            "Test Passed")

            'display comparison

            MessageBox.Show("Original Hash: " & Environment.NewLine &

            BitConverter.ToString(arr1) & _

            Environment.NewLine & _

            "Test Hash: " & Environment.NewLine & _

            BitConverter.ToString(arr2), "Hash Test Results")

        Else

            MessageBox.Show("The file examined has been tampered with.", "Hash Test Failed")

            'display comparison

            MessageBox.Show("Original Hash: " & Environment.NewLine &

            BitConverter.ToString(arr1) & _

            Environment.NewLine & _

            "Test Hash: " & Environment.NewLine & _

            BitConverter.ToString(arr2), "Hash Test Results")

        End If

    End Sub

    Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click

        'Dim myhash As Byte

        'Dim fs1 As New FileStream(TextBox2.Text, FileMode.OpenOrCreate)

        'Dim fs1Bytes As Byte() = New Byte(fs1.Length) {}

        'fs1.Read(fs1Bytes, 0, fs1.Length)

        'Dim arr1() As Byte = myhash.CompareTo(fs1Bytes)

        'fs1.Close()

        Dim fs1 As New FileStream(TextBox2.Text, FileMode.OpenOrCreate)

        Dim fs1Bytes As Byte() = New Byte(fs1.Length) {}

        fs1.Read(fs1Bytes, 0, fs1.Length)

        fs1.Close()

        Dim fs2 As New FileStream(TextBox1.Text, FileMode.OpenOrCreate)

        Dim fs2Bytes As Byte() = New Byte(fs2.Length) {}

        fs2.Read(fs2Bytes, 0, fs2.Length)

        fs2.Close()

        Dim i As Integer = 0

        For i = 0 To fs1Bytes.Length - 1

            If Not fs1Bytes(i) = fs2Bytes(i) Then

                MessageBox.Show("The file examined has been tampered with at position " & _

                i.ToString(), "Byte Test Failed")

                Exit Sub

            End If

        Next

        MessageBox.Show("The file examined has not been tampered with.", "Byte Test Passed")

    End Sub

End Class