## Increasing anonymity with Tor

Terrified I had to notice, that some of you don’t know Tor!? Here is a little intro, so you don’t have to die stupid.

When you for example request a website, the server that provides this site knows your IP address, with this address it’s able to detect your real location. It also get to know your UserAgent and a lot of other things like that. So the other site of your connection knows quite a lot of you, which system you’re working on, which browser you use, where (which website) do you come from and so on.. But is it essential to let the world know so much about you!? Of course not! By the way, think about the security issue ;)

So what to do!? One option is not to use the internet, only connect to servers you trust. But the better solution is to use Tor! Tor is a software to get anonymous network connection. It works like a big proxy. All around the world are Tor-server. When you try to connect to a webserver you won’t do it directly, but you will connect to a Tor access-node, this node is connecting further nodes, until an exit-node is reached. This exit-node will now send your initial request to the webserver, wait for a response and send this response on a way through the Tor-network back to your machine. The connections between the Tor nodes are encrypted and randomly chosen, so nobody is able to find the way your requests took through the Tor nodes. This process is called onion routing and is much more complicated than I described here, but it’s to much to talk about in detail.

## Setting up Tor

The setup is very easy. Just add the Tor repositories to your sources.list:

I for example added the following to my /etc/apt/sources.list.d/3rdparty.list :

After that add the GPG-Key of this repository:

And install the software:

If you now start Tor with /etc/init.d/tor start it is listening on 127.0.0.1:9050 . You also need a small proxy like privoxy:

It’s configuration is very easy, just tell privoxy to send the packages to Tor with the following in /etc/privoxy/config :

The rest of this file should be configured correctly.

That’s it! Everything that now reaches your proxy is finding its anonymous way through the Tor-network.

## Configuring client software

Now you have to force your software to use the proxy. The most important client software is probably your browser. For example in firefox (or iceweasel) you find the settings in Edit->Preferences->Advanced->Network->Settings and check Manual proxy configuration. Your proxy is 127.0.0.1 (or rather localhost) on port 8118 . Now your more anonymous, just ask a website where you come from. (at the moment I’m using an exit node from Russian Federation and the webserver recognizes me as Windows 7 user with Firefox 3.6 while using a sidux and iceweasel 3.5.11). Here you can verify that you Tor configuration is working. There are also some AddOns for firefox, that makes live easier. For example Torbutton or FoxyProxy. With it you can enable or disable the usage of Tor with a single mouse click.

But Tor is not only designed for browsers. You can configure a lot of software to go through Tor, for example gajim in Edit->Accounts->Your Account->Connection, or in opera with Settings->Preferences->Advanced->Network->Proxy Servers…. Nearly every thing that is able to connect the internet may be able to use your proxy. You can also activate the usage of your proxy by default by including the following line in your .bashrc or .zshrc or what ever:

## Conclusion

Tor is a very nice project, for further reading you may take a look on the projects website. If you hold a server that is contactable for the public you should think about providing an onion node on it! It’s very easy, but you should know about legal stuff.

Ok, when Micha saw my tiny hack he changed his implementation (as promised) and told me I’m not able to hack it again… Micha, your captcha failed again :P

Lets have another look to his code:

First of all he renamed the fields, so of course my last attack will fail :P The next problem is, that the hash for a 7 isn’t the hash for another 7 of a different calculation. Maybe he’s using the arithmetic problem or the time or other things for his hash calculation. So if we don’t know how his calculation for the hash is, the last attack is senseless… Btw he told me that he’s using encryption. If you’re bored, try to break it, it’s to much for me. But Micha bets three beer that I’m not able. So no chance to quit!

In my last post I had another idea to crack the captcha: Parse the formula. Ok, I wrote about parsing the URI to the external server that produces the picture, of course it’s much easier to parse the title - or alt -tag of the image! These fields are human readable to get the site handicapped accessible. Of course worthy that he provides this fields! So, after some reloads I had a small idea with what kind of problems I have to deal with:

Simple calculations
something like: $$\sqrt{49} + 24 - 4^2$$, just calculate the solution
Convertings
like $$x + 82 = 192$$, first convert the formula before calculating the solution
Sums
for example $$\displaystyle\sum^{4}_{n=1} (2 \cdot n + 1)$$, first rewrite the sum-symbol, than calculate the solution

That’s the theory, the code is this time a little bit longer:

As you can see, it’s a little bit tricky and just works for some mathematical formulas that are of interest. If he combines the converting problem with brackets or something like that, this code fails.. But the algorithm is easy to modify for such changes ;)

But respect, to crack my captcha you don’t need that intelligence, it’s feasible in much less code. I hope he doesn’t rewrite his plugin again, don’t want to calculate that stuff by brain…

Micha just implemented an own Captcha-Plugin for wordpress, I just cracked it some minutes later ;)

This version is deprecated, see Cracked next Captcha…

Micha was annoyed of his previous Captcha-Plugin, neither valid nor beautiful, so he decided to write his own tool for killing bots.

When I saw his new captchas I was wondering wheter he will get further comments. His captchas ask for solution of mathematical problems like $$\sqrt{121} + 95$$ or $$228 \div 19$$ or $$\frac{136 - 61}{\sin(\pi \div 2)}$$.. Who the hell wants to calculate that stuff!? Me not! ;)

So I developed a little userscript that solves this problem. When you take a look to the source code of his website you’ll find something like this:

So you see, there is an image created by an external server, an input field where you can put the solution and an input field of the type hidden with a crypt value (seems like a hash^^). The most of you will see several ways to hack this:

1. Parse the string of the image like the external server does to create the $$\LaTeX$$-image. So you’ll get an arithmetic problem, easy to solve.
2. Find out what kind of hash is in the value of the secret hidden input-field and try to find a number that matches that hash, maybe via brute force.
3. Solve one captcha and fake the rest ;)

Of course the last solution is the easiest one. So I solved on captcha, solution was 7 and the secret key was 9ee4251f80923e6239ae66ab50a357daa6039f04 , hack done!

The development of the userscript was more than simple:

I think that this script won’t work for a long time, so there is no download available ;) If you want to use it, copy&paste, you know.

Ähm, before anybody starts to blame me, a similar workaround kills also my captcha-solution… :P

## New logo for Iceweasel

Actually iceweasel is searching for a new logo.

When I updated a PC of our work group I recognized that iceweasel, iceape and icedove are searching for new logos. Micha just created one for iceweasel with xfig, here is a similar one with tikz:

If the maintainer understand something about art they will use one of our creations! ;)

## Tweet-button for website

Yeah, completely in twitter-fever! Just developed a tweet-button.

You can see the button at the end of every post. The button itself of course isn’t my work, I just copied it from twitter, but when you click the link around it you can tweet the actual post directly to twitter! Feel free to try it! ;)

It’s more than easy. All the code you need is (replace […]):

So the code that I wrote in my theme is:

After that just using the \$tweet variable at any position I like ;)