How Secure Is Your Wireless Network? Safeguarding Your Wi-Fi LAN

Brute Force Attacks

Another approach to determining the WEP key is to use brute force. The shared secret portion of the WEP key is either 40 bits or 104 bits, depending on which key strength you are using. Security researcher Tim Newsham discovered that the key generators from some vendors are flawed. A brute force attack on a 40-bit key using a weak key generator could take less than a minute to crack.

Key generators enable a user to enter a simple pass phrase to generate the key, instead of entering the key manually with hexadecimal numbers. A 40-bit WEP key shared secret would require 10 hexadecimal numbers; a 104-bit WEP key shared secret would require 26 hexadecimal numbers. As a convenience, some vendors allow you to enter a pass phrase ...