If you've forgotten the password of your WiFi network you can use a simple application to recover it. We're talking about Password WiFi with which you can do it provided that you still use your router's default password.
Get hold of the password for any wireless network
This WiFi password recovery tool for Android allows us to recover our passwords in a matter of seconds. It's ready to work with the following types of wireless networks:
But this is just for a private use, at home... if you intend to crack a WiFi network and steal passwords, take into account that it will always be under your own responsibility.