John is able to crack WPA-PSK and WPA2-PSK passwords. Recent changes have improved performance when there are multiple hashes in the input file, that have the same SSID (the routers 'name' string).
Input format is exactly the same as oclHashcat's hccap file described here but need one more step of conversion, with the “hccap2john” tool supplied with John up to 1.7.9-Jumbo-7. In latest git trees (and any released version newer than 1.7.9-Jumbo-7) there is a new tool “wpapcap2john”, that will convert a raw pcap (.cap) file directly into JtR wpapsk input hashes, omitting the hccap step.
You can convert airodump's .cap file to .hccap in one of the following ways:
When you have hccap file you need to convert it to john's input format using hccap2john program. It encodes hccap file to “$WPAPSK$essid#b64encoded hccap”
Example testcase you can get from http://wiki.wireshark.org/SampleCaptures?action=AttachFile&do=view&target=wpa-Induction.pcap or wpa-Induction.tar.gz
From that point you can use john as you always do. The format comes in three flavours:
If “Induction” is in your (by default it is not) password.lst file, john will crack it.
If you are interested in how it works visit this page