Communication method for radio communication system

PURPOSE: To reduce the communication quantity by devising the method such that an authentification section authenticates only a radio terminal and a ciphering key between a base station and the radio terminal is shared in common. CONSTITUTION: A radio terminal sends an authentication number PSi to a base station and the base station generates a random number R1 and sends it to the radio terminal. The radio terminal receives it to generate a random number R2, an authentication information generating means 103 synthesizes the numbers R1, R2 and secret information Sppi to obtain an authentication number σps and it is sent to the base station together with the random number R2. The random numbers R1, R2, the authentication number PSi and the authentication number σps are given to an authentication information check means 105, which authenticates the radio terminal as the terminal having the PSi when the result of check is OK, ad the radio terminal and the base station generate a common ciphering key by common share means 106a, 106b. Thus, a random number required for mutual authentication consists of key common share information and a function in the device to reduce number of random numbers to be converted thereby reducing the communication quantity. COPYRIGHT: (C)1993,JPO&Japio