From http://wirelessdefence.org/Contents/coWPAttyMain.htm:

coWPAtty is designed to audit the pre-shared key (PSK) selection for WPA networks based on the TKIP protocol. - Joshua Wright.

Since I had problems installing/compiling cowpatty, I had to modify the Makefile and several include-lines in some files. Currently I’m using NetBSD/Amd64. Feel free to modify the files at your needs. Download here!

Edit: As stated here, there is a newer version, 4.3. I edited the Makefile and created a new tarball. make -D __NETBSD__ should do the work.