Fern Wifi Cracker is a Wireless security auditing and attack software program written using the Python Programming Language and the Python Qt GUI library, the program is able to crack and recover WEP/WPA/WPS keys and also run other network based attacks on wireless or ethernet based networks.
> Open BackTrack 5 R3.
> Go to Applications > BackTrack > Exploitation Tools > Wireless Exploitation Tools > WLAN Exploitation > fern-wifi-cracker.
> Select Wireless Interface.
> Scan for Access points.
> Click WEP cracking button.
> A new dialog box will open where you can select the wep network, the attack method etc.
> Click Attack.