A system for authentication and execution of a transaction at a self-service terminal. The system has a first computerized unit (PINSRV) which, in correspondence to a first data set comprising first elements (0, 1, 2, 3, . . . 9) from which the identification data (PIN) are derived, generates a second set of data with second elements (A, B, C, . . . , J), each of which is unambiguously assigned to one of the first elements. A monitor (DISP) is structurally connected to the self-service terminal (ATM) and displays the unambiguous assignment of the second elements to the first elements. A user terminal (MD) is structurally separated from the self-service terminal (ATM), and assigned to a user (CSM) and displaying the second elements (A, B, C, . . . , J) thus to allow the user to enter the input data (#PIN) at the user terminal (MD).