Is it possible to block Tor users?

Question

Would it be possible to block Tor users? (https://www.torproject.org/)

Due to the nature of the site I run I should do all I can to stop multiple accounts and block cert

Answer 1

In .NET it's possible and simple. I have implemented it on my site.

Let's say your site has an external IP address of 192.168.0.5 for argument's sake. Real TOR IP address at the time of posting: 95.215.44.97

Imports System.Net
Imports System.Net.Sockets
Imports System.Web

Private Function IsTorExitNode(sIP As String) As Boolean

    ' Reverse your IP (97.44.215.95) then pass to the string, I have just created it as one for this example
    Try
        Dim strTor As String = "97.44.215.95.80.5.0.168.192.ip-port.exitlist.torproject.org"
        Dim host As IPHostEntry = Dns.GetHostEntry(strTor)

        If host.AddressList.Length = 0 Then
            Return False
        Else
            If host.AddressList(0).ToString() = "127.0.0.2" Then
                Return True
            Else
                Return False
            End If
        End If
    Catch ex As SocketException
        Return False
    End Try
End Function

Breakdown

Reversed IP address: 97.44.215.95
Port: 80
Reversed IP address: (your external site IP address)

If the address is a TorExitNode it will return 127.0.0.2.

In your Global.asax file, you can use the Application_Start to check if IP address returns true and then redirect them away from your site:

If IsTorExitNode("97.44.215.95") = True Then Response.Redirect("http://www.google.co.uk")

Now, as soon as they hit your site they are redirected away from it.

TOR has a list of IP addresses, but obviously they change all the time so using my function would be the best way as it's always real-time.