Will this onion make you cry? A Usability Study of Tor-enabled Mobile Apps

In 2013, more than half a million users relied on Tor, the second generation Onion Routing system, daily to protect their privacy [1]. Users hide among other users in the Tor network to achieve anonymity, so the degree of anonymity grows as more users successfully participate in the network [3]. A user who makes mistakes while installing or using Tor software jeopardizes both her own privacy and that of other users in the network [2]. Accordingly, in order to attract more users, ensure their successful participation in the network, and improve privacy, the usability of Tor tools is considered “a security requirement” [3]. A poor user interface may lead to dangerous errors, and can leave users unknowingly unprotected with a false sense of security that can be especially harmful [4]. Whitten et al. [4] performed both a cognitive walkthrough (CW) and a user study on PGP 5.0 and used their results to introduce general principles for designing usable security UIs that are now widely accepted. Clark et al. [2] used CW for studying the usability of different Tor tools on desktop computers. The authors defined a set of representative tasks, then evaluated them against usability guidelines compiled specifically for Tor-enabled tools. To the best of our knowledge, we present the first usability study of Tor mobile apps.