1 CASA : A Framework for Context-Aware Scalable Authentication

We introduce context-aware scalable authentication (CASA) as a way of balancing security and usability for authentication. Our core idea is to combine a number of passive factors for authentication (e.g., a user’s current location) with appropriate active factors. In this paper, we provide a probabilistic framework for dynamically selecting an active authentication scheme that satisfies a security requirement given passive factors about a user. We also present the results of two user studies evaluating the feasibility and users’ receptiveness of our concept. Our results suggest that location data has good potential as a passive factor, and that users can reduce up to 68% of the number of user authentication when using the user authentication system designed with CASA compared to an authentication system that requires a fixed active authentication consistently. Furthermore, more than half of the participants who tested our prototype preferred to use our user authentication system on their phones.