Hacking Wifi: Cracking WEP with Kali Linux

Theory

WEP, short for wired equivalent privacy, is one of several encryption schemes used to secure wireless networks. At the time of conception, WEP was believed to be secure. However, a security flaw was found in the IV headers of data packets that makes it possible to crack WEP if enough IV headers are collected. The attacks shown in this tutorial take advantage of this weakness in the initialization vectors of wireless packets to crack WEP.
When enough packets have been collected, the key for the WEP-secured network can be cracked by using wifi-hacking tools, such as aircrack-ng. Kali Linux includes aircrack-ng among one of its top 10 security tools for testing vulnerability of computer networks. In this post, I’ll demonstrate how a WEP key can be easily found using the aircrack-ng tools in Kali Linux. However, a problem may arise when there are multiple keys in use instead of just one.

What You Need To Follow The Steps In This Tutorial

You need Kali Linux and basic knowledge of Linux. Kali Linux is a Debian-based Linux distribution for testing network security. Kali Linux currently supports PC’s and ARM-powered machines.
Then, boot your computer with the Kali Linux DVD. Hopefully, you’ll be automatically presented with a nice and dark GUI screen of GNOME desktop.

Let’s Crack WEP

First off, I will say that I use Alfa USB Wifi Cards. They work great, have long range, and you can use them in Kali right out of the box. There are many options when it comes to plugging in external antennas and arrays for Alfa Wifi Adapters. It is my highest recommendation to click on the picture to the right and pick yourself up an Alfa Wifi USB adapter!
Open a Terminal window and type ifconfig to see if your wifi card is running. It will have a designation such as wlan0, wlan1, etc…
If you have no wlan, you may need to type the command for loading a driver for your wireless network card or USB WiFi adapter. You may have to put required firmware in /lib/firmware before trying to load the driver because Kali Linux lacks firmware for some drivers. For example, to load b43 driver, type:

modprobe -r b43
modprobe b43

If the WiFi driver is working, then the network traffic in the top right corner of the screen will show available wireless networks when you click on it.

Use kismet to find information about the WEP-secured wireless network that you want to crack. You need such information as:

• Name of the wireless network (ESSID)
• MAC address of the access point (BSSID)
• Channel of the wireless network
• MAC address of wireless clients

In Kismet, WEP-secured networks are marked with W under the C column of network list.
Type the following commands to put your wireless device wlan0 in monitoring mode.

airmon-ng stop wlan0
airmon-ng start wlan0

Change the MAC address of your wireless network card. This may or may not work depending on the hardware used. In the example, the text in red is the new MAC address for your wireless card. Usually, this MAC is the actual MAC address of an existing wireless client associated with the target network. With the fake MAC, we’re going to trick the access point with one of the following attacks.

ifconfig wlan0 down
ifconfig wlan0 hw ether 6C:83:36:6C:65:CD
ifconfig -a

Start airodump-ng which will sniff wireless traffic of the target network and collect good IV’s (initialization vectors, part of WEP encryption data). The logfile will be used later to find the WEP key. The number after -c option is the channel of the wireless network to listen to. The screen will show wireless networks and associated clients, if any, with a set of numbers increasing. Don’t stop airodump-ng or close the terminal yet. Just leave the terminal open.

airodump-ng -w logfile -c 6 –ivs wlan0

In the following attacks, we are going to use aireplay-ng. Aireplay-ng is a handy tool for generating more wireless traffic in order to collect sufficient amount of good IV’s. It does so by injecting or replaying captured packets to fool the access point into giving us what we need. Open another tab in GNOME Terminal. This attack will associate the target wireless client with the access point.

aireplay-ng -1 30 -e WIFINET -a 00:23:97:26:66:A3 -h 6C:83:36:6C:65:CD wlan0

The -e option specifies the network name, the -a option specifies the MAC address of the AP, and the -h option specifies the MAC address of the wireless client. You can use macchanger to view and change your MAC address, for example, macchanger -s wlan0. Then, you can associate your wireless adapter when there are no clients connected to the wireless network in the first place.
ARP injection is slow but always works. While airodump-ng is listening, open another tab in GNOME Terminal and start the ARP injection attack.

aireplay-ng -3 -b 00:23:97:26:66:A3 -h 6C:83:36:6C:65:CD wlan0

The -b option specifies the MAC address of the AP and -h specifies MAC address of the associated client. Let it run and airodump-ng will pick up traffic. If no client is connected, we can create one by fake authentication described above.
This attack generates traffic by asking the access point to resend data packets. Open another tab in GNOME Terminal and start the interactive packet replay attack.

aireplay-ng -2 -b 00:23:97:26:66:A3 -h 6C:83:36:6C:65:CD -n 160 -p 0841 -c FF:FF:FF:FF:FF:FF wlan0

The -b option specifies the MAC address of the AP and -h specifies MAC address of the associated client.
After enough packets have been collected and saved, aircrack-ng can be used to crack the WEP key.

aircrack-ng -a 1 -b 00:23:97:26:66:A3 -n 64 logfile-01.ivs

Replace the filename with your log file that was previously generated with airodump-ng. Also, specify the access point’s MAC address with -b option. The -n option specifies whether the WEP strength is 64-bit or 128-bit. The -a 1 option specifies that we’re cracking WEP.
If you still can’t crack WEP with tons of IV’s, increase the fudge factor with -f N option (N>=2). It’ll take much longer to crack but you’ll have a better chance at success.