Imports System.IO

Public Class Form1
    '
    ' Basic login form
    '   - Username & Password is saved in " C:\PASSWORD1.txt " (change in code if you like)
    '   - Username & Password is stored like this:    USERNAME:PASSWORD_ENCRYPTED
    '     -> Password is encrypted in MD5 (cant decrypt)
    '
    ' You can add as many accounts as you want, if you create an account with a username which is already in use, it will be ignored.


    ' Make sure:
    ' You have textboxes: txtUsername & txtPassword
    ' You have buttons: btnLogin & btnMakeAccount


    Private Sub btnLogin_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnLogin.Click
        Dim strUsername, strPassword, strSavedPassword As String
        Try
            strUsername = txtUsername.Text.Trim
            strPassword = txtPassword.Text.Trim

            If strUsername = "" Or strPassword = "" Then
                Throw New NullReferenceException("The Username & Password field are required!")
            Else
                strSavedPassword = getPassword(strUsername, "C:\PASSWORD1.txt")
                If (strSavedPassword = strToMD5(strPassword)) Then
                    MessageBox.Show("Password correct")
                Else
                    MessageBox.Show("Password NOT correct")
                End If
            End If
        Catch ex As Exception
            MessageBox.Show(ex.Message)
        End Try
    End Sub
    Private Function getPassword(ByVal pUsername As String, ByVal Location As String) As String
        Dim srFileReader As System.IO.StreamReader
        Dim sInputLine As String
        Dim Username As String
        Dim i As Integer = 0
        srFileReader = System.IO.File.OpenText(Location)
        sInputLine = srFileReader.ReadLine()
        Do Until sInputLine Is Nothing
            Username = sInputLine.Split(":")(0)
            If (Username = pUsername) Then
                Return sInputLine.Split(":")(1)
            End If

            sInputLine = srFileReader.ReadLine()
            i = i + 1
        Loop
        srFileReader.Close()
        Return Nothing
    End Function
    Private Sub createAccount(ByVal Username As String, ByVal Password As String, ByVal Location As String)
        Dim objWriter As New System.IO.StreamWriter("C:\PASSWORD1.txt", True)
        objWriter.WriteLine(Username & ":" & strToMD5(Password))

        objWriter.Close()
        MessageBox.Show("Account " & Username & " created !")
    End Sub
    Function strToMD5(ByVal strToCrypt As String) As String
        Dim md5Obj As New Security.Cryptography.MD5CryptoServiceProvider
        Dim bytesToHash() As Byte = System.Text.Encoding.ASCII.GetBytes(strToCrypt)
        bytesToHash = md5Obj.ComputeHash(bytesToHash)
        Dim strResult As String = Nothing
        For Each b As Byte In bytesToHash
            strResult += b.ToString("x2")
        Next
        Return strResult
    End Function

    Private Sub btnMakeAccount_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnMakeAccount.Click
        Dim strUsername, strPassword As String
        strUsername = txtUsername.Text.Trim
        strPassword = txtPassword.Text.Trim
        createAccount(strUsername, strPassword, "C:\PASSWORD1.txt")
    End Sub


End Class