Airsnort is a tool for wireless lans which recovers encryption keys by passively monitoring transmissions, computing the encryption key when enough packets have been gathered. Works on both 40 and 128 bit encryption. Many weaknesses in the WEP 802.11 protocol are discussed here. Once enough packets have been gathered, AirSnort can guess the encryption password in under a second. Tested on Linux kernel v2.4.
You can download it from the following link: https://packetstormsecurity.com/files/download/29756/airsnort-0.2.1b.tar.gz
Source: https://packetstormsecurity.com/files/29756/airsnort-0.2.1b.tar.gz.html