Abstract: An apparatus for providing authentication of a mobile station in a wireless communication system. The present invention takes the number dialed by the mobile station user and computes the 24 bit number (AUTH.sub.-- DATA) for authentication in accordance with a hashing function that has the following characteristics. The hashing function takes as its input at least the entire dialed digit string contained in the request for service and the number of digits. In a preferred embodiment, the ordering of the digits affects the result, as well as, the values of the digits. The preferred embodiment of the hashing function also accepts some or all of the mobile station identifier data. The function provides as output a number of suitable size for input to a second calculation of an authentication signature, such as the 24 bits required for AUTH.sub.-- DATA. The output number is created in such a way that there is a minimum likelihood that other sets of dialed digits may create the same result.