the present invention discloses a method used by an authenticator of a wireless lan . the authenticator is capable of communicating wirelessly with a supplicant of the wireless lan . the authenticator holds a plurality of candidate keys whereas the supplicant holds one key . the key held by the supplicant is included in the plurality of candidate keys held by the authenticator . the method includes determining which one of the plurality of candidate keys is the key held by the supplicant and communicating with the supplicant wirelessly according to the determined key held by the supplicant .