Wednesday, January 23, 2008

BackTrack

DISCLAIMER: Yes, this will show you how to hack into a wireless network. This is very much ILLEGAL. The purpose of this writeup is for educational purposes only. I am demonstrating the weakness of WEP encryption on my own network. If you wish to try this for yourself, I suggest you buy a wireless router and attempt to crack that.

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I wanted to post a live instructional movie instead of a set of pictures. However, I am still attempting to get my wireless card working in a virtual environment and/or an open source video capturing utility that runs in Back Track 3.

I could list the set of programs I will be using here, but they are listed throughout the blog. I believe it is better to say that I am using Back Track 3 (beta) using a live install and a Linksys WMP11 wireless NIC. You can find details on downloading and installing Back Track 2 and 3 here.

Alright, there are a few things I'm leaving off the beginning. The first is setting your wireless card to monitor mode. I had a little trouble with this at first. I have to extend a thank you to Brian for pointing me in the right direction.

Another is the list of compatible wireless cards. You can find those circulating around the net (at the ubuntu website, the aircrack site, and a few others). I am also leaving off driver installation. Some wireless cards require madwifi drivers to work. You can find out more about this via the Madwifi webpage.

It is actually very easy to set your wireless NIC to monitor mode in Back Track 3. Play around with some of the programs, and if you are still having trouble, try the Remote Exploit Forums.

Okay, so you have your card in monitor mode (or you're just curious and want to read on). The first step is to make certain that your card is in fact running in monitor mode. To do this, open the terminal and type iwconfig Look for your wireless card. The window should be displaying as such:



Notice the second line in eth2? It says "Mode:Monitor." This confirms that the wireless card is set to monitor.

Now, you can do one of two things. The first is run a wireless sniffing program, that will allow you to see hidden SSID's. I will not be demonstrating that in this tutorial. Instead, we will use a program called airodump to capture the packets and create a file that we can use in a cracking program. There are several options you can set when using Airodump.



This may seem overwhelming at first, but its easy to figure out. The options we are interested in right now are: --ivs, -w, and -channel 6.

This is because I already know the target is using channel 6, and don't need to scan any other channels. --ivs will store only captured ivs. Ivs are initialization vectors that preamble the key. There are 16.7 million varieties, which may sound like a lot. However, they are only 3 bytes in size, and so even a weak computer can run an algorithm that checks for patterns and eventually breaks the wep key. For our purposes, we only need to record these. Finally, the -w or write option will write the stored information to a .cap file that we can use at a later time.

So we type in the command airodump-ng -w --ivs -channel 6 eth2

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Alright. Now airodump is running and pulling ivs out of packets. How long does this need to run for? It varies depending on the type of encryption and complexity of the code. In this case, it is a 64 bit hex code using WEP encryption. I'll let it run for 20 minutes, but I could probably do it in as few as 5 if I'm lucky.



Notice that there is a second wireless AP that popped up? Airodump will capture all available information on any selected channel, or even scan every channel within the range specified.

Now that the 20 minutes is up, we can press ctrl+c to stop the dump and exit back to the konsole. The -w command now creates a capture file with all the information we need.



We can see the name of the capture file is ivs-01.cap. Now, in the konsole, type aircrack-ng --help.

This brings up the aircrack options. Aircrack is the program we will use to crack the encryption and discover the code.



We really don't need any of the special options at this point. So simply type aircrack-ng ivs-01.cap. We are now presented with an option. Remember that other AP that came up when airodump was running? It saves all of this information in the file. If there were 10 ap's during the airodump process, there would be 10 ap's to choose from now. We are only interested in the first, which is airwave (the SSID of my router). So we type 1 and press enter.



Congradulations! There is the key to my wireless network. It took about .5 seconds to produce, though it is a very weak key with the worst possible encryption. I will look into cracking 128 bit WEP, and possibly WPA in the future.

3 comments:

IT135SecurityBlog said...
This comment has been removed by the author.
IT135SecurityBlog said...

It might be smart to specify the amount of IV's needed to be captured, not the time. (factor such as distance from AP and such could play a factor)

also, you dont need to use iwconfig for monitor mode, you have them run 'airmon-ng start interfacename' which will save them digging through guides.

pretty decent tutorial

Stephen.King said...

The point was to have them dig through guides, so they can learn more =). And yes, I probably should have mentioned that it takes an average of 500,000 ivs to crack a wep key. Note that this is an average. As you could see in my tutorial, weak keys require less.