Abstract: A mobile device (16) includes a transceiver (40) for mobile communication and a controller (44) configured to execute an authentication function for authenticating a registered user of the device, in which the device (16) has only a single operating element (48), the functionality of the single operating element (48) is limited to activating and deactivating the authentication function, the authentication function has the transceiver logged-on to a mobile communications network and enabling a detection of an active state and/or a location of the mobile device via the mobile network, and the operating element (48) and the transceiver (40) constitute the only data input and output ports of the controller (44).

Abstract: A method of authenticating a user to a transaction at a terminal (10), wherein a user identification is transmitted from the terminal (10) to a transaction partner (12) via a first communication channel (14), and an authentication device (18) uses a second communication channel (20) for checking an authentication function that is implemented in a mobile device (16) of the user, and, as a criterion for deciding whether the authentication to the transaction shall be granted or denied, the authentication device (18) checks whether a predetermined time relation exists between the transmission of the user identification and a response from the second communication channel, and the authentication function is normally inactive and is activated by the user only preliminarily for the transaction, the response from the second communication channel (20) includes the information that the authentication function is active, and the authentication function is automatically deactivated.

Abstract: A mobile device (16) includes a transceiver (40) for mobile communication and a controller (44) configured to execute an authentication function for authenticating a registered user of the device, in which the device (16) has only a single operating element (48), the functionality of the single operating element (48) is limited to activating and deactivating the authentication function, the authentication function has the transceiver logged-on to a mobile communications network and enabling a detection of an active state and/or a location of the mobile device via the mobile network, and the operating element (48) and the transceiver (40) constitute the only data input and output ports of the controller (44).

Abstract: A method of authenticating a user to a transaction at a terminal (10), wherein a user identification is transmitted from the terminal (10) to a transaction partner (12) via a first communication channel (14), and an authentication device (18) uses a second communication channel (20) for checking an authentication function that is implemented in a mobile device (16) of the user, and, as a criterion for deciding whether the authentication to the transaction shall be granted or denied, the authentication device (18) checks whether a predetermined time relation exists between the transmission of the user identification and a response from the second communication channel, and the authentication function is normally inactive and is activated by the user only preliminarily for the transaction, the response from the second communication channel (20) includes the information that the authentication function is active, and the authentication function is automatically deactivated.