METHOD FOR CERTIFYING MOBILE STATION AND SYSTEM THEREWITH

PROBLEM TO BE SOLVED: To prevent a hacker from directly receiving a cryptographic key number, and therefore to prevent the intrusion of the hacker not by transmitting the cryptographic key itself but by specifying the pointers of the plural cryptographic keys with a first random number at the time of communication between a base station and a moving station. SOLUTION: A mobile station 1 selects one of owned N=7 pieces of cryptographic key numbers according to the instruction of a base station 1, and transmits it through the base station 1 to a home center 3, and the cryptographic key is collated with a registered key number, and only when they are made coincident, the mobile station is certified as a proper mobile station. At that time, the cryptographic key number transmitted by the home center 3 is designated with a first random number. The first random numbers are generated to replace with respective numbers corresponding to 7 pieces as moduli when there are 7 pieces of cryptographic key numbers, and the cryptographic key number is selected from among those 7 pieces of cryptographic key numbers according to the number. Moreover, a second random number is also used for the confirmation of the cryptographic key number in the mobile station 1. Then, when the number N of the cryptographic key numbers is the same in all the mobile stations, and then the backer knows the number, probability that the hacker knows the cryptographic key number is increased. Then, the number of the cryptographic key numbers is varied for each mobile station.