There are two types of authentication methods in the 802.11 protocol: Open System and Shared Key. Open System (sometimes called Null Authentication) does not utilize a password. Under Open System, a client simply requests to be authenticated and the AP grants access. This is useful in environments like public hotspots, where free and open access is intentional.
Shared key, however, requires knowledge of the WEP key. That's right: The WEP key used to encrypt data (see Chapter 3 for more details) is also used to authenticate clients and access points. It works like this: