decrypt("C:\test.abc", "123", "C:\test.txt", 4096)

    Public Function decrypt(ByVal cryptfile As String, ByVal password As _
      String, ByVal decryptfile As String, Optional ByVal BufferSize As Long = _
      4096)
 
        Try
            Dim sKey As Byte() = (New UnicodeEncoding).GetBytes( _
              password.PadRight(8, "*"))
 
            Dim OldFileStream As New FileStream(cryptfile, FileMode.Open)
 
            Dim NewFileStream As New FileStream(decryptfile, FileMode.Create)
 
            Dim RijndaelManaged As New RijndaelManaged
 
            Dim CryptoStream As New CryptoStream(OldFileStream, _
              RijndaelManaged.CreateDecryptor(sKey, sKey), _
              CryptoStreamMode.Read)
 
            Dim Data(BufferSize) As Byte
 
            Dim Buffer As Long
 
            Dim BufferCount As Long
 
            Dim FileLen As Long = OldFileStream.Length
 
            Do
 
                If BufferCount >= FileLen - BufferSize Then
 
                    ReDim Data(FileLen - BufferCount)
 
                    Buffer = CryptoStream.Read(Data, 0, FileLen - BufferCount)
 
                    'NewFileStream.Write(Data, 0, Buffer)
 
                    Exit Do
 
                End If
 
                Buffer = CryptoStream.Read(Data, 0, BufferSize)
 
                BufferCount += Buffer
 
            Loop
 
            NewFileStream.Write(Data, 256, Data.Length - 256)
 
            NewFileStream.Close()
 
            CryptoStream.Close()
 
            OldFileStream.Close()
 
        Catch ex As Exception
 
            MsgBox(ex.ToString)
 
        End Try
 
    End Function