Evaluation of user authentication methods in the gadget-free world

In an ideal gadget-free environment the user is interacting with the environment and the services through only "natural" means. This imposes restrictions on many aspects of the interaction. One key element in this is user authentication, because it assures the environment and related services of the legitimacy of user's actions and empowers the user to carry out his tasks. We present five high-level categories of features of user authentication in the gadget-free world including security, privacy and usability aspects. These are adapted and extended from earlier research on web authentication methods. We survey existing authentication methods together with some emerging technologies and evaluate these according to the features in our categories. Our results show, that no single authentication method can realise all these requirements for authentication. In conclusion, we give future research directions and open problems that stem from our observations. Especially, finding combinations of authentication factors and methods that achieve all requirements is an interesting problem in the gadget-free scenario.