Imports System
Imports System.IO
Imports System.Text
Imports System.Security.Cryptography
 
Public Class AESCrypt
 
    Public Function EncryptString(ByVal Klartext As String) As String
        ' Erzeugen einer neuen RijndaelManaged-Instanz samt Schlüssel und IV
        Dim AESEncrypt As New RijndaelManaged
 
        ' Erzeugen des Verschlüsslers 
        Dim Encryptor As ICryptoTransform = AESEncrypt.CreateEncryptor( _
          AESEncrypt.Key,  AESEncrypt.IV)
 
        ' Wandelt einen String in ein ByteArray um  
        Dim Converter As New ASCIIEncoding
 
        ' Verschlüsselt den Klartext und weist ihm ein ByteArray zu
        Dim CryptS As Byte() = Encryptor.TransformFinalBlock(Converter.GetBytes( _
          Klartext), 0, Klartext.Length)
 
        Return Converter.GetString(AESEncrypt.Key) & Converter.GetString( _
          AESEncrypt.IV) & Converter.GetString(CryptS)
    End Function
 
    Public Function DecryptString(ByVal CryptString As String) As String
        ' Wandelt Strings in ein beliebiges Format um
        Dim Converter As New ASCIIEncoding
 
        ' Die im String entahltenen Verschlüsselung Keys auslesen und entfernen
        Dim Key As Byte() = Converter.GetBytes(CryptString.Substring(0, 32))
        Dim IV As Byte() = Converter.GetBytes(CryptString.Substring(32, 16))
        CryptString = CryptString.Remove(0, 48)
 
        ' Erzeugen einer neuen RijndaelManaged-Instanz samt Schlüssel und IV
        Dim AESEncrypt As New RijndaelManaged
 
        ' Entschlüsseln des Strings
        Dim Decryptor As ICryptoTransform = AESEncrypt.CreateDecryptor(Key, IV)
        Dim Klartext As Byte() = Decryptor.TransformFinalBlock( _
          Converter.GetBytes(CryptString), 0, CryptString.Length)
 
        Return Converter.GetString(Klartext)
    End Function
End Class

    Sub Main()
        Dim AES As New AESCrypt
        Dim CryptS As String = AES.EncryptString("TEST")
        MsgBox(AES.DecryptString(CryptS))
    End Sub