Text Encrypter VB.NET

Public Function SimpleCrypt( _
       ByVal Text As String) As String
  ' Encrypts/decrypts the passed string using
  ' a simple ASCII value-swapping algorithm
  Dim strTempChar As String, i As Integer
  For i = 1 To Len(Text)
    If Asc(Mid$(Text, i, 1)) < 128 Then
      strTempChar = _
CType(Asc(Mid$(Text, i, 1)) + 128, String)
    ElseIf Asc(Mid$(Text, i, 1)) > 128 Then
      strTempChar = _
CType(Asc(Mid$(Text, i, 1)) - 128, String)
    End If
    Mid$(Text, i, 1) = _
        Chr(CType(strTempChar, Integer))
  Next i
  Return Text
End Function