Try
                fOut.SetLength(0)
 
                Dim totalFileLength As Long = fIn.Length    'Set Source File 
                ' Size
 
                'cryptostream object, DES Encryption
                'Will write encypted data into output file
                Dim crStream As New CryptoStream(fOut, _
                  objDES.CreateEncryptor(TheKey, Vector), _
                  CryptoStreamMode.Write)
                'Encrypt data into output file.'
                'Cut Source file in 4096 Packet
                While totalBytesWritten < totalFileLength
                    'Read 4096 Byte
                    packageSize = fIn.Read(bufPacket, 0, 4096)
                    'Encrypt and write data into output file
                    crStream.Write(bufPacket, 0, packageSize)
                    'Update totalBytesWritten
                    totalBytesWritten = Convert.ToInt32(totalBytesWritten + _
                      packageSize / objDES.BlockSize * objDES.BlockSize)
                End While
 
                'Close all file stream object
                crStream.Close()
                fIn.Close()
                fOut.Close()
 
                If DeleteSourceFile = True Then
                    System.IO.File.Delete(inName)
                End If
 
 
            Catch ex As Exception
                Throw New ApplicationException(ex.Message)
 
                fIn.Close()
                fOut.Close()
            End Try
 
        Catch ex As Exception
            Throw New ApplicationException("Input and/or Output File are" & _
              "invalid.")
        End Try
    End Function
 
    Public Function FileDecrypt(ByVal inName As String, ByVal outName As _
      String, ByVal DeleteSourceFile As Boolean)
        Dim bufPacket(4096) As Byte    'Create packet separator buffer (4096 
        ' Byte / Packet)
        Dim totalBytesWritten As Long = 8  'Written Bytes Cmptr
        Dim packageSize As Integer    'Set number of byte to be write at same 
        ' time
 
        Try
            'Input File Stream, to be decrypted (Source)
            Dim fIn As New FileStream(inName, _
            FileMode.Open, FileAccess.Read)
 
            'Output File Stream, decrypted 
            Dim fOut As New FileStream(outName, _
            FileMode.OpenOrCreate, FileAccess.Write)
 
 
            Try
                fOut.SetLength(0)
 
                Dim totalFileLength As Long = fIn.Length    'Input File Size
 
                'cryptostream object, DES Encryption
                'Will write decrypted data into output file
                Dim crStream As New CryptoStream(fOut, _
                  objDES.CreateDecryptor(TheKey, Vector), _
                  CryptoStreamMode.Write)
 
 
                'Decrypt data into output file.'
                'Cut Source file in 4096 Packet
                While totalBytesWritten < totalFileLength
                    packageSize = fIn.Read(bufPacket, 0, 4096)
                    crStream.Write(bufPacket, 0, packageSize)
                    totalBytesWritten = Convert.ToInt32(totalBytesWritten + _
                      packageSize / objDES.BlockSize * objDES.BlockSize)
                End While

Mit freundlichen Gr??en

Peter