This description is given of a use-authorization device for security-related applications, in particular access control to secure areas or securing vehicles with a user operated key unit for generating consecutive, alternating user code information which exhibits a sequence of consecutive function values v.sub.i+1=F(v.sub.i, const) for i=0, . . . , N through the repeated use of a one-way function F(.sub.vi, const), which function values are used in inverse order to the sequence formation to create the consecutive user code information, and an application-sided processing unit for determining actual authorization information which is dependent upon the user code information received from the key unit and for performing a use-authorization checking process by comparing this actual authorization information with target authorization information saved in the application, as well as for generating use-release information depending on the result of the comparison, wherein the target authorization information has a function value v; which has been transferred from the user code information processed during the previous positive use-authorization operation. The special feature of the invention is that there is a certain number of levels G provided, with at least one support point and one intermediate value, from which a certain number of iterative function value calculations can be performed in each level by means of the one-way function F(v.sub.i,const) wherein there are G=L(N)/b levels, with N as the starting value, L(N) as the number of bits required for representing N in the dual system and b as the basis.