Abstract or Summary:
To address the limitations of static challenge question based fallback authentication mechanisms (e.g., easy predictability), recently, smartphone based autobiographical authentication mechanisms have been explored where challenge questions are not predetermined and are instead generated dynamically based on users’ day-to-day activities captured by smartphones. However, as answering different types and styles of questions is likely to require different amounts of cognitive effort and affect users’ performance, a thorough study is required to investigate the effect of type and style of challenge questions and answer selection mechanisms on users’ recall performance and usability of such systems. Towards that, this paper explores seven different types of challenge questions where different types of questions are generated based on users’ smartphone usage data. For evaluation, we conducted a field study for a period of 30 days with 24 participants who were recruited in pairs to simulate different kinds of adversaries (e.g., close friends, significant others). Our findings suggest that the question types do have a significant effect on user performance. Furthermore, to address the variations in users’ accuracy across multiple sessions and question types, we investigate and present a Bayesian classifier based authentication algorithm that can authenticate legitimate users with high accuracy by leveraging individual response patterns.