Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As _
  System.EventArgs) Handles MyBase.Load
 
        Dim sser As String = getSer(1234)
        Debug.WriteLine(sser)
        Debug.WriteLine(checkSer(sser))
 
        sser = getSer(123456)
        Debug.WriteLine(sser)
        Debug.WriteLine(checkSer(sser))
 
        sser = getSer(134)
        Debug.WriteLine(sser)
        Debug.WriteLine(checkSer(sser))
 
        Debug.WriteLine(checkSer("001234-0232219638"))
        Debug.WriteLine(checkSer("000134-0789468709"))
 
    End Sub
 
    Private Function getSer(ByVal ser As Integer) As String
        Dim md5 As New System.Security.Cryptography.MD5CryptoServiceProvider
 
        If ser < 0 Or Len(CStr(ser)) > 6 Then Throw New _
          System.ArgumentOutOfRangeException("ser")
 
        Dim hash() As Byte = md5.ComputeHash(BitConverter.GetBytes(ser))
        Dim ser1 As Integer = BitConverter.ToInt32(hash, 0)
        Return Format(ser, "000000") + IIf(ser1 < 0, "", "-") + Format(ser1, _
          "0000000000")
 
    End Function
 
    Private Function checkSer(ByVal sser As String) As Boolean
        Dim md5 As New System.Security.Cryptography.MD5CryptoServiceProvider
 
        Try
            Dim ser As Integer = CInt(sser.Substring(0, 6))
            Dim hash() As Byte = md5.ComputeHash(BitConverter.GetBytes(ser))
            Dim ser1 As Integer = BitConverter.ToInt32(hash, 0)
            Return sser = Format(ser, "000000") + IIf(ser1 < 0, "", "-") + _
              Format(ser1, "0000000000")
        Catch
            Return False
        End Try
 
    End Function