I will say, that word sequence"Crack WPA"is very loudly...
http://www.securityfocus.com/news/11537
http://www.theregister.co.uk/2008/11/08/wi_fi_protected_access_attack/
This is a TKIP flaw... and Tews-Becker attack is based on old fashioned Korek's chopchop inductive packet guess idea. Idea is realized in aircrack-ng -4 tool against WEP (DWEP) an is very impressive: don't look for encryption key itself, find out short keystream to perform packet injectiion with arp(icmp) packets afterward.
TKIP utilize RC4 encryption with MIC(michael) packet integrity. In WEP case, if inductive guess is correct, AP answer is positve, in TKIP case, if packet guess is correct, but MIC fails, AP respond with: wait a 1 minute.
And so, there are 14 unknown arp packet bytes, and less than 15 minutes need to discover full arp packet.
Attack is very limited and employed in DoS attacks with arp(icmp ) packet injection.
Recommendation: move to WPA2 + CCMP