Patent ID: 7752441

Claim:
A method, comprising: establishing, at a mobile unit, an uplink counter for a security association between the mobile unit and a first base first base station that has established a downlink counter for the security association, wherein the uplink counter is incremented prior to each message transmitted to the first base station and the downlink counter is incremented prior to each message transmitted to the mobile unit; receiving, at the mobile unit, a message authentication code from the second base station, the message authentication code being formed using values of the uplink counter and the downlink counter provided to the second base station by a key distributor; and mutually authenticating the mobile unit and a second base station by comparing values of the uplink counter and the downlink counter stored in the mobile unit to values of the uplink counter and the downlink counter provided to the second base station in response to the mobile unit handing off from the first base station to the second base station and determining, at the mobile unit, that the value of the downlink counter received from the second base station is larger than the value of the downlink counter stored by the mobile unit.