How to Crack WEP Key With Backtrack 5 [wifi hacking]

As announced before we would be writing related to wifi attacks and security,This post is the second part of our series on wifi attacks and Security,In the first part we discussed about various terminologies related to wifi attacks and security and discussed couple of attacks.This post will also show you how one can easily crack WEP keys in no time.

Security Issues With WEP

WEP (Wired Equivalent Privacy) was proved full of flaws back in 2001,WEP protocol itself has some weakness which allows the attackers to crack them in no time.The biggest flaw probably in a WEP key is that it supports only 40bit encryption which means that there are 16million possibilities only.

For more information on WEP flaws, kindly read the WEP flaws section here.

Requirements :-
Here is what you would require to crack a WEP key:

1. Backtrack or any other Linux distro with aircrack-ng installed

2. A Wifi adapter capable of injecting packets , For this tutorial I will use Alfa AWUS036H which is a very popular card and it performs well with Backtrack

You can find compatible wifi card lists here.

Procedure :-
First Login to your Backtrack / Linux distro and plug in your Wifi adpter , Open a new konsole and type in the following commands

ifconfig wlan0 up

where wlan0 is the name of the wireless card ,it can be different .To see all wireless cards connected to your system simply type in " iwconfig ".

Putting your WiFi Adapter on Monitor Mode

To begin, you’ll need to first put your wireless adapter into monitor mode , Monitor mode is the mode whereby your card can listen to every packet in the air , You can put your card into monitor mode by typing in the following commands

airmon-ng start (your interface)

Example :- airmon-ng start wlan0

 
 Now a new interface mon0 will be created , You can see the new interface is in monitor mode by entering "iwconfig mon0" as shown

Finding a suitable Target

After putting your card into monitor mode ,we need to find a network that is protected by WEP. You can discover the surrounding networks by entering the following command

airodump-ng mon0

Bssid shows the mac address of the AP, CH shows the channel in which AP is broadcasted and Essid shows the name broadcasted by the AP, Cipher shows the encryption type.

Now look out for a wep protected network In my case i’ll take “linksys “ as my target for rest of the tutorial

Now look out for a wep protected network In my case i’ll take “linksys “ as my target for rest of the tutorial
 
Attacking The Target
Now to crack the WEP key you'll have to capture the targets data into a file, To do this we use airodump tool again, but with some additional switches to target a specific AP and channel. Most importantly, you should restrict monitoring to a single channel to speed up data collection, otherwise the wireless card has to alternate between all channels .You can restrict the capture by giving in the following commands

airodump-ng mon0 --bssid -c (channel ) -w (file name to save )

As my target is broadcasted in channel 6 and has a bssid "98:fc:11:c9:14:22" ,I give in the following commands and save the captured data as "RHAWEP"

airodump-ng mon0 --bssid 98:fc:11:c9:14:22 -c 6 -w RHAWEP

Using Aireplay to Speed up the cracking
 Now you’ll have to capture at least 20,000 data packets to crack WEP .This can be done in two ways, The first one would be a (passive attack ) wait for a client to connect to the AP and then start capturing the data packets but this method is very slow, it can take days or even weeks to capture that many data packets

The second method would be an (active attack )this method is fast and only takes minutes to generate and inject that many packets .

In an active attack you'll have do a Fake authentication (connect) with the AP ,then you'll have to generate and inject packets. This can be done very easily by entering the following commands

aireplay-ng - 1 3 -a (bssid of the target ) (interface)

In my case i enter the following commands

aireplay-ng -1 3 -a 98:fc:11:c9:14:22 mon0


After doing a fake authentication ,now its time to generate and inject Arp packets . To this you'll have to open a new Konsole simultaneously and type in the following commands

aireplay-ng 3 -b (bssid of target) -h ( Mac address of mon0) (interface)

In my case i enter
aireplay-ng 3 -b 98:fc:11:c9:14:22 -h 00:c0:ca:50:f8:32 mon0

If this step was successful you'll see Lot of data packets in the airodump capture as shown

Wait till it reaches 20000 packets , best would be to wait till it reaches around 80,000 to 90,000 packets .Its simple more the packets less the time to crack .Once you’ve captured enough number of packets, close all the process's by clicking the into mark which is there on the terminal

Cracking WEP key using Aircrack

Now its time crack the WEP key from the captured data, Enter the following commands in a new konsole to crack the WEP key

aircrack-ng (name of the file )

In my case i enter
aircrack-ng RHAWEP-0.1-cap

With in a few minutes Aircrak will crack the WEP key as shown

Once the crack is successful you will be left with the KEY! Remove the colons from the output and you’ll have your WEP Key.Hope You Enjoyed this tutorial ,For further Doubts and clarifications please pass your comments.