A Closer Look at Pure-Text Human-Interaction Proofs

Human-interaction proofs (HIPs) are used to mitigate automated attacks. Security and usability have always been a critical problem for HIPs, especially when "accessibility" is a system requirement. Pure-text HIPs are more favorable from the usability perspective, but they are not secure. Audio HIPs usually cannot reliably distinguish attacks from legitimate use; they are either easy, and can be automatically solved, or hard, even for humans. In this study, we first compare the usability of a currently used pure-text HIP service, textCAPTCHA, against Google's re-CAPTCHA. After analyzing the results, we propose a new HIP system (SMARTCHA). In this system, by using human computation we generate around 21 000 HIP tests. We conduct a user study among 31 visually impaired users to compare SMARTCHA against the latest version of audio reCAPTCHA HIPs. The study results show that SMARTCHA takes less time and is more enjoyable to solve, which suggests that pure-text HIPs could be a promising solution for secure, usable, and accessible HIPs.