about 802.1x

 In 802.11,if 802.1x authentication messages are not be encrypted,user are 
vulnerable

 to denial of service.For example,attackers can send error response to 
authenticator

 before the valid user because of media contention(DCF),so the authenticator 
will set

 controlled-port "unauthorized".


 To encrypt these messages,how to get encryption key before 802.1x 
authentication 

 procedure?