A method for determining an access code comprising a predetermined number of input symbols. The access code is determined from input symbols and the position thereof when inputted. The number of possible input positions for the input symbols is greater than the predetermined number of input symbols. An input device detects the input symbols and the positions thereof in an input field. An access code is determined therefrom and compared in a comparator with a references access code. If compatibility is established, access to the system is authorized.