An authentication device for securing interaction of a user with a computer based application comprising: a memory component adapted to store a secret key; a data processing component adapted to generate a dynamic credential by cryptographically combining said secret key with the value of a dynamic variable; a Near-Field Communication, NFC, interface to couple the authentication device to an NFC transfer device; and a user input interface (140, 150) for capturing an input from said user; the authentication device adapted to: present itself to said NFC transfer device as an NFC tag; make said generated dynamic credential available to said NFC transfer device by including said dynamic credential in first data contents of said NFC tag that can be read by said NFC transfer device using NFC mechanisms for reading data contents of NFC tags; wherein the authentication device is further adapted to require a specific input from said user as a condition for at least one of said generating said dynamic credential or said making said generated dynamic credential available to said NFC transfer device, and to be activated by the user by said user input interface, the authentication device being characterized in that it is further adapted to present itself to said NFC transfer device as an NFC tag only after the user has activated the authentication device by using said user input interface. a memory component adapted to store a secret key; a data processing component adapted to generate a dynamic credential by cryptographically combining said secret key with the value of a dynamic variable; a Near-Field Communication, NFC, interface to couple the authentication device to an NFC transfer device; and a user input interface (140, 150) for capturing an input from said user; the authentication device adapted to: present itself to said NFC transfer device as an NFC tag; make said generated dynamic credential available to said NFC transfer device by including said dynamic credential in first data contents of said NFC tag that can be read by said NFC transfer device using NFC mechanisms for reading data contents of NFC tags; wherein the authentication device is further adapted to require a specific input from said user as a condition for at least one of said generating said dynamic credential or said making said generated dynamic credential available to said NFC transfer device, and to be activated by the user by said user input interface, the authentication device being characterized in that it is further adapted to present itself to said NFC transfer device as an NFC tag only after the user has activated the authentication device by using said user input interface. present itself to said NFC transfer device as an NFC tag; make said generated dynamic credential available to said NFC transfer device by including said dynamic credential in first data contents of said NFC tag that can be read by said NFC transfer device using NFC mechanisms for reading data contents of NFC tags; wherein the authentication device is further adapted to require a specific input from said user as a condition for at least one of said generating said dynamic credential or said making said generated dynamic credential available to said NFC transfer device, and to be activated by the user by said user input interface, the authentication device being characterized in that it is further adapted to present itself to said NFC transfer device as an NFC tag only after the user has activated the authentication device by using said user input interface.