US Patent 8176327 Authentication protocol

A method includes sending a first authentication challenge from an authenticator to an access terminal, and receiving, at the authenticator, a first return message from the access terminal that includes an identifier of the access terminal and a response to the first challenge. A second authentication challenge is sent from the authenticator to the access terminal, in which the second authentication challenge is determined by an authentication server based in part on the identifier of the access terminal previously received along with the response to the first challenge. The authenticator receives a second return message from the access terminal that includes a response to the second authentication challenge.