Method for generating a broadcast challenge value

A method and system for synchronously updating binary numbers used by a plurality of base stations to authenticate a plurality of mobile subscriber units in a cellular system. The method includes applying a first updating algorithm to a plurality of most significant bits of the binary number for each of the plurality of base station operating on a plurality of least significant bits of the binary number for each of the plurality of base stations with a second updating algorithm, and synchronizing across the plurality of base stations, update values of the binary numbers that result from the applying and operating steps.