Aircrack is a free application available from the Cydia store for jailbroken iPhones. You can download the application to the home screen of your device directly from Cydia. Aircrack allows you to crack the password for secured Wi-Fi networks using your iPhone. You should, however, only use this application to crack a Wi-Fi network that you own or have the owner's permission to use. Jailbreaking will also void the terms of your iPhone's warranty.
Tap the "Cydia" icon on your jailbroken iPhone.
Tap the "Manage" icon.
Tap the "Sources" button.
Tap the "Edit" button.
Tap the "Add Button."
Enter "http://cydia.myrepospace.com/wontonsipodhelp/" in the search bar and tap the "Add Source" button.
Tap the "wontonsipodhelp" option.
Tap the "Aircrack" option.
Tap the "Install" icon.
Tap the "Confirm" button. The Aircrack application will download to the home screen of your iPhone.