A Comparative Usability Study of Two-Factor Authentication

TLDR

Two‑factor authentication enhances password security by adding a second factor, yet it imposes costs on providers and requires users to perform extra steps. The study explores the usability of two‑factor authentication technologies. The authors first interviewed users to identify common 2F methods and contexts, then surveyed 219 Mechanical Turk participants to compare the usability of token‑generated codes, email/SMS one‑time PINs, and smartphone app authenticators, while recording motivations and contexts. Participants perceived all three 2F solutions as usable, and factor analysis revealed that ease‑of‑use, cognitive effort, and trustworthiness jointly explain usability.

Abstract

Two-factor authentication (2F) aims to enhance resilience of password-based authentication by requiring users to provide an additional authentication factor, e.g., a code generated by a security token. However, it also introduces non-negligible costs for service providers and requires users to carry out additional actions during the authentication process. In this paper, we present an exploratory comparative study of the usability of 2F technologies. First, we conduct a pre-study interview to identify popular technologies as well as contexts and motivations in which they are used. We then present the results of a quantitative study based on a survey completed by 219 Mechanical Turk users, aiming to measure the usability of three popular 2F solutions: codes generated by security tokens, one-time PINs received via email or SMS, and dedicated smartphone apps (e.g., Google Authenticator). We record contexts and motivations, and study their impact on perceived usability. We find that 2F technologies are overall perceived as usable, regardless of motivation and/or context of use. We also present an exploratory factor analysis, highlighting that three metrics – ease-of-use, required cognitive efforts, and trustworthiness – are enough to capture key factors affecting 2F usability.