Imports System.IO
Imports system.IO.Path
Imports System.Security.Cryptography
Imports System.Runtime.Serialization.Formatters.Binary
Imports System.Text

'Sicheres Speichern von Passwörtern

Namespace Michaels

  Public Class SaltHash

   'Der Pfad für die Serialisation
  Private mySaltHashFile As String = _
          Combine(Application.UserAppDataPath, "mySaltHash.dat")
   'Der für new und check gleiche Salt
  Private mySalt As Byte() = New Byte() {0, 1, 2, 3, 4, 5, 6, _
          241, 240, 238, 33, 34, 69}
  Private iterationCounts As Integer = 2000

  Friend Sub newPassword(ByVal pw As String)

    Try
      Dim ua As New Rfc2898DeriveBytes(pw, mySalt, iterationCounts)
      Dim hash As Byte() = ua.GetBytes(32)

      Dim stream As New FileStream(mySaltHashFile, FileMode.Create)
      Dim converter As New BinaryFormatter()
      converter.Serialize(stream, hash)
      stream.Close()

    Catch ex As ArgumentException
      MsgBox(ex.Message)
    End Try

  End Sub

  Friend Function checkPassword(ByVal pw As String) As Boolean
    Try
      Dim ua As New Rfc2898DeriveBytes(pw, mySalt, iterationCounts)
      Dim newHash As Byte() = ua.GetBytes(32)

       'Deserialisierung:
      Dim stream As New FileStream(mySaltHashFile, FileMode.Open)
      Dim converter As New BinaryFormatter()
       'Den origHash aus File auslesen
      Dim origHash As Byte() = _
          CType(converter.Deserialize(stream), Byte())

      stream.Close()

       'Textsensitiver Vergleich der HashStrings
      Dim i As Int32

      i = String.Compare(ByteArrayToString(origHash), _
      ByteArrayToString(newHash))
      If i <> 0 Then
        Return False
      Else
        Return True
      End If

    Catch ex As ArgumentException
      MessageBox.Show(ex.Message)
    End Try
  End Function

  'Hilfsfunktion ByteArrayToString
  Private Function ByteArrayToString(ByVal arrInput() As Byte) _
          As String
    Dim i As Integer
    Dim sOutput As New StringBuilder(arrInput.Length)

    For i = 0 To arrInput.Length - 1
      sOutput.Append(arrInput(i).ToString("X2"))
    Next
    Return sOutput.ToString()
  End Function

  End Class
End Namespace