Method for the secure input of identification data of a user of a self-service terminal for the authentication of a transaction that is performed by means of the self-service terminal, which terminal is connected to multiple computer-aided units (PINSRV, SRV) via secure channels, wherein the multiple computer-aided units (PINSRV, SRV) comprise at least a first computer-aided unit (PINSRV) and a second computer-aided unit, characterized by the following steps: for a first volume of data having first elements, which comprise key values (0, 1, 2, 3,... 9) of a numerical keypad, from which key values the identification data are formed, the first computer-aided unit (PINSRV) is used to form a second volume of data having second elements, which comprise components (A, B, C,.... J) of a prescribable scheme, which are each uniquely associated with one of the first elements (0, 1, 2, 3,... 9), as a result of which input data (#PIN) can be generated from the second elements, which input data correspond to a bijective mapping of the identification data, wherein the second elements are different from the first elements and wherein the association between the second volume of data and the first volume of data is formed afresh, by means of a pseudorandom association between the second elements (A, B, C,... J) and the first elements (0, 1, 2, 3,.....9), prior to each performance of a new transaction, wherein the first computer-aided unit (PINSRV) generates a permutation of the first elements (0, 1, 2, 3,...9) and sends it to the self-service terminal; the unique association between the second elements (A, B, C,....J) and the first elements (0, 1, 2, 3,....9) is displayed on a screen (DISP) that is physically connected to the self-service terminal (step 107); a mobile user terminal, which is physically separate from the self-service terminal, which is connected to the second computer-aided unit via secure channels of a mobile communication link, and which is associated with the user of the self-service terminal, is used to display the second elements (A, B, C,...J) rather than the first elements (0, 1, 2, 3,....9) by virtue of an application program implemented on the mobile user terminal (step 108); the mobile user terminal is used by the user to input the input data (#PIN) (step 109); and the input data (#PIN) that are generated from the second elements are transmitted by means of the application program to the computer-aided units (PINSRV; SRV) connected to the self-service terminal via the secure network channels (step 110), wherein the second computer-aided unit performs the authentication of the transaction and wherein the first computer-aided unit (PINSRV), which manages the unique association between the second elements (A, B, C,....J) and the first elements (0, 1, 2, 3,...9), checks the input data (#PIN) (step 111). for a first volume of data having first elements, which comprise key values (0, 1, 2, 3,... 9) of a numerical keypad, from which key values the identification data are formed, the first computer-aided unit (PINSRV) is used to form a second volume of data having second elements, which comprise components (A, B, C,.... J) of a prescribable scheme, which are each uniquely associated with one of the first elements (0, 1, 2, 3,... 9), as a result of which input data (#PIN) can be generated from the second elements, which input data correspond to a bijective mapping of the identification data, wherein the second elements are different from the first elements and wherein the association between the second volume of data and the first volume of data is formed afresh, by means of a pseudorandom association between the second elements (A, B, C,... J) and the first elements (0, 1, 2, 3,.....9), prior to each performance of a new transaction, wherein the first computer-aided unit (PINSRV) generates a permutation of the first elements (0, 1, 2, 3,...9) and sends it to the self-service terminal; the unique association between the second elements (A, B, C,....J) and the first elements (0, 1, 2, 3,....9) is displayed on a screen (DISP) that is physically connected to the self-service terminal (step 107); a mobile user terminal, which is physically separate from the self-service terminal, which is connected to the second computer-aided unit via secure channels of a mobile communication link, and which is associated with the user of the self-service terminal, is used to display the second elements (A, B, C,...J) rather than the first elements (0, 1, 2, 3,....9) by virtue of an application program implemented on the mobile user terminal (step 108); the mobile user terminal is used by the user to input the input data (#PIN) (step 109); and the input data (#PIN) that are generated from the second elements are transmitted by means of the application program to the computer-aided units (PINSRV; SRV) connected to the self-service terminal via the secure network channels (step 110), wherein the second computer-aided unit performs the authentication of the transaction and wherein the first computer-aided unit (PINSRV), which manages the unique association between the second elements (A, B, C,....J) and the first elements (0, 1, 2, 3,...9), checks the input data (#PIN) (step 111).