' Dialog erzeugen und Einstellungen setzen
Dim dlg As New SaveFileDialog()
With dlg
   .Title = "Datei verschlüsseln..."
   .InitialDirectory = Environment.SpecialFolder.MyDocuments
   .Filter = "Verschlüsselte Dateien|*.sef|Alle Dateien|*.*"
End With
 
If dlg.ShowDialog() = DialogResult.OK Then
   ' Algorithmus anlegen, hier Rijndael
   Dim rm As New RijndaelManaged()
 
   ' IV und Key generieren
   rm.GenerateIV()
   rm.GenerateKey()
 
   ' IV und Key speichern
   Dim iv() As Byte = rm.IV
   Dim key() As Byte = rm.Key
   SaveKeys(iv, key)
 
   ' Quelltext in Byte-Array umwandeln		
   Dim source() As Byte = Encoding.Unicode.GetBytes(Me.txtInput.Text)
 
   ' Benötigte Streams erzeugen
   Dim fsIn As New MemoryStream(source)
   Dim fsOut As New FileStream(dlg.FileName, FileMode.Create, _
   FileAccess.Write, FileShare.None)
 
   ' Cryptostream erzeugen
   Dim crypter As ICryptoTransform = rm.CreateEncryptor(key, iv)
   Dim cs As New CryptoStream(fsIn, crypter,CryptoStreamMode.Read)
 
   ' Hilfsvariablen
   Dim buffer(4096) As Byte
   Dim read As Integer
 
   ' In dieser Schleife findet die eigentliche Verschlüsselung statt
   Do
      read = cs.Read(buffer, 0, 4096)
      fsOut.Write(buffer, 0, read)
   Loop While read > 0			
 
   ' Resourcen freigeben
   fsOut.Close()
   cs.Close()
   fsIn.Close()
   crypter.Dispose()
   rm.Clear()			
End If
 
' Resourcen des Dialogs freigeben
dlg.Dispose()

Ralf