Doing a simple crypter without use library

Sub Activity_Create(FirstTime As Boolean)
   Log (Encrypt("sdfsdfsdfsdf"))
End Sub

Sub Encrypt(str As String) As String
   Dim su As StringUtils
   Dim result As StringBuilder
   result.Initialize
   Dim key, c, keyChar As String
   key = "a      "
   For i = 0 To str.Length - 1
      c = str.CharAt(i)
      Dim start As Int
      start = (key.Length + (i Mod key.Length) - 1) Mod key.Length
      keyChar = key.CharAt(start)
      c = Chr(Asc(c) + Asc(keychar))
      result.Append(c)
   Next
   Return su.EncodeUrl(su.EncodeBase64(result.ToString.GetBytes("UTF8")), "UTF8")
End Sub