Imports System.Security.Cryptography
Imports System.IO
Imports System.Text
 
Public Class VerschlüsselnKlasse
    Inherits System.Windows.Forms.Form
 
    Function verschlüsseln(ByVal text As String)
        Dim rd As New RijndaelManaged
        Dim md5 As New MD5CryptoServiceProvider
        Dim key() As Byte = md5.ComputeHash(Encoding.UTF8.GetBytes(text))
 
        md5.Clear()
        rd.Key = key
        rd.GenerateIV()
 
        Dim iv() As Byte = rd.IV
        Dim ms As New MemoryStream
 
        ms.Write(iv, 0, iv.Length)
 
        Dim cs As New CryptoStream(ms, rd.CreateEncryptor, _
          CryptoStreamMode.Write)
        Dim data() As Byte = System.Text.Encoding.UTF8.GetBytes(text)
 
        cs.Write(data, 0, data.Length)
        cs.FlushFinalBlock()
 
        Dim encdata() As Byte = ms.ToArray()
        Return Convert.ToBase64String(encdata)
        cs.Close()
        rd.Clear()
    End Function
 
    Function entschlüsseln(ByVal text As String)
        MsgBox(text)
        Dim rd As New RijndaelManaged
        Dim rijndaelIvLength As Integer = 16
        Dim md5 As New MD5CryptoServiceProvider
        Dim key() As Byte = md5.ComputeHash(Encoding.UTF8.GetBytes(text.Trim))
 
        md5.Clear()
 
        Dim encdata() As Byte = Convert.FromBase64String(text.Trim)
        Dim ms As New MemoryStream(encdata)
        Dim iv(15) As Byte
 
        ms.Read(iv, 0, rijndaelIvLength)
        rd.IV = iv
        rd.Key = key
 
        Dim cs As New CryptoStream(ms, rd.CreateDecryptor, _
          CryptoStreamMode.Read)
 
        Dim data(ms.Length - rijndaelIvLength) As Byte
 
        Dim i As Integer = cs.Read(data, 0, data.Length)
 
        Return System.Text.Encoding.UTF8.GetString(data, 0, i)
        cs.Close()
        rd.Clear()
    End Function
End Class

Public Class Form1
 
    Inherits System.Windows.Forms.Form
 
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles Button1.Click
        TextBox3.Text = VerschlüsselnKlasse.verschlüsseln(TextBox1.Text)
    End Sub
 
    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles Button2.Click
        TextBox1.Text = VerschlüsselnKlasse.entschlüsseln(TextBox3.Text)
    End Sub
 
End Class

Dim i As Integer = cs.Read(data, 0, data.Length)