Jul 05 2009

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tor on a vps

I value my privacy – and I dislike the increasing tendency of every commercial website under the sun to attempt to track and/or profile me. Yes, I know all the arguments in favour of advertising, and well targeted advertising at that, but I get tired of the Amazon style approach which assumes that just because I once bought a book about subject X, I would also like another book about almost the same subject. I don’t much like commercial organisations profiling me (and, incidentally, I find it highly ironic that we in the UK seem to make a much bigger fuss about potential “big brother” Government than we do about commercial data aggregation, but hey).

Sure, I routinely bin cookies, block adware and irritating pop up scripts, and use all the, now almost essential, firefox privacy plugins, but even there we still have a problem. I don’t know who wrote those plugins, I just have to trust them. That worries me. Some of the best known search engines are even more scary if you think carefully about the aggregate information they have about you.

Sometimes I care about the footprint I leave, sometimes I don’t, but the point is that I should be in control of that footprint. Increasingly that is becoming difficult. Besides being tracked by sites I visit, last year’s controversy about BT’s use of phorm is also worrying. If my ISP can track everything I do, then I face another level of difficulty in protecting my fast vanishing privacy.

Besides using a locked down browser, DNS filtering which blocks adware, cutting cookies and all the other tedious precautions I now feel are necessary to make me feel comfortable, I often use anonymous proxies when I don’t want the end site to know where I came from. But even that now looks problematic. If you use a single anonymising proxy, all you are doing is shifting the knowledge about your browsing from the end site to an interrmediary. That intermediary may (indeed should) have a very strict security policy. Ideally, it should log absolutely nothing about transit traffic. But if that intermediary does log traffic data and then sells that data to a third party, you may be in an even worse position than if you had not attempted to become anonymous. Back in january of this year, Hal Roberts of Harvard University, posted a blog item about GIFC selling user data. If sites such as Dynaweb are prepared to sell user data, then the future for true anonymity looks problematic. As Doc Searle said in this blog posting,

We live in a time when personalized advertising is legitimized on the supply side. (It has no demand side, other than the media who get paid to place it.) Worse, there’s a kind of gold rush going on. Even in a crapped economy, a torrent of money is flowing into online advertising of all kinds, including the “personalized” sort. No surprise that companies in the business of fighting great evils rationalize the committing of lesser ones. I’m sure they do it it the usual way: It’s just advertsing! And it’s personalized, so it’s good for you!

No, as Searle well knows, it is not good for you.

What to do? Enter tor and privoxy.

I first used tor some years ago in its earlier incarnation as “the onion router” (hence its name) and until recently had used it only sporadically since. The main drawback of the early tor network was its speed, or lack of it. Tor gets is strength (anonymity) from the way it routes traffic.


Tor traffic passes through a series of nodes before exiting at a node which cannot be linked back to the original source. So tor performance depends on a large number of both fast intermediate relays and a large number of exit nodes. Since not all tor users are prepared to run relays, let alone an exit node (it can be bandwidth expensive and in the case of an exit node can lead to your system being mistaken for a hostile, or compromised, site) tor can be slow, at times painfully slow. But recently tor has been getting faster as more relay and exit nodes are added. It is now at a state which is probably usable most of the time, so long as you are prepared to wait a little longer than is customary for some web pages to load (and you don’t use youtube…..).

When using tor recently I have tended to follow the well trodden path of local installation alongside privoxy. Because I believe in giving something back to the community if I am gaining benefit, I also set my local configuration to run as a relay. But that caused some difficulty. If we assume that my tor usage was fairly representative of the majority of tor users out there, then the fact that my relay was only operational when my client system was up and running meant that the relay would be seen by the tor network as unstable and probably slow, Indeed, the fact that I had to throttle tor usage to the minimum to stop the network from impacting unduly on my ADSL bandwidth, meant that I was not entirely happy with the setup. So I stopped relaying. But that leaves me feeling that I am taking advantage of a free good when I could be contributing to that good.

Some while back I bought myself a VPS from Bytemark (an excellent, technically savvy, UK based hosting company) to run a couple of webs and an MTA. I use it now largely as a mail server (running postfix and dovecot) and the traffic is relatively low volume. That VPS is pretty small (though actually way better specced than some real servers I have run in the past) but I reasoned that I could easily run a tor relay on that machine and then connect to it remotely from my client system. I did, and it worked fine. But I soon found that the tor network seems to have a voracious appettite for bandwidth, Even with a fairly strict exit policy (no torrents allowed!) and some tight bandwidth shaping, I still found that I was using about 2 Gig of traffic per day (vnstat is useful here). Any more than that would start to encroach on my bandwidth allowance for my VPS and possibly impact on the main business use of that server. Monthly rates for VPSs are now less than I pay for my mobile phone contract (and arguably more useful than a phone contract too) so I decided to specialise and buy another VPS just for tor. I now run an exit node on a VPS with 384 MB of RAM and 150 Gig monthly traffic allowance. That server is currently throttled to about 2 Gig of traffic per day, but I will double that very shortly.

Now one of the nicest things about running a tor relay is the fact that your own tor usage is masked and you may get better anonymity. I therefore run privoxy on my tor relay and proxy through from my client to that proxy which in turn chains to tor internally on my relay. However, if you simply configure your local client to proxy through to your relay in clear you are allowing your ISP (and anyone else who cares to look) to see your tor requests – not smart. So I tunnel my requests to the tor relay through ssh. My local client has an ssh listener which tunnels tor requests through to the relay and connects to privoxy on port 8118 bound to localhost on the relay. I also have a separate browser on my desktop which has as its proxy the ssh listener on my client system. For a good description of how to do this see tyranix’s howto on the tor wiki site. Now whenever I want to use tor myself I simply switch browser (and that browser is particularly dumb and stripped, and has no plugins or toolbars which could leak information). Of course, should I get really paranoid, I could always run the local browser in a VM on my desktop and reload the VM after each session.

But I’m not that paranoid.

Permanent link to this article: http://baldric.net/2009/07/05/tor-on-a-vps/


  1. Chris Samuel

    Interesting stuff, do you do anything to counter/spot the people who do MITM attacks on the Tor exit nodes that they run ? Just run https over it and keep an eye on certificate checks ?

  2. Mick


    I routinely check SSL certs on sites I really care about regardless of whether I’m using tor (OK, maybe I am paranoid).


  3. Peter

    I actually route all the interesting stuff through a VPN – as the tail of that VPN is someone who nukes logfiles, and as he has plenty of other customers my stuff drowns in the noise, provided I browse in private mode with changed OS and browser identity, and stop browser LSOs.

    Having said that, it is starting to *seriously* annoy me that I have to fight so hard to keep my privacy – something that is so basic you find it defined in the Human Rights (#13, to be exact).

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