A user authentication method and system which maintains reliable security using a low cost storage medium in place of cryptocards, wherein the system comprises control equipment and an operating section connected to the control equipment, and wherein the method comprises the steps of the operating section reading a storage medium that stores specific parameters, creating a user authenticaly code using a specific function from the specific parameters and other parameters provided by the control equipment, and supplying the created user authentication code to the control equipment, wherein the user authentication code sent from the operating section is compared with another code computed using a specific function generated by the control equipment, and when both codes are found to coincide, the control equipment causes information to be interchanged between the control equipment and the operating section. Advantageously, the invention method provides reliable security combined with low cost.