For human eyes only: security and usability evaluation

This paper presents 'For Human Eyes Only' (FHEO), our Firefox extension that enables one to conveniently post online messages, such as short emails, comments, and tweets in a form that discourages automatic processing of these messages. Similar to CAPTCHA systems, FHEO distorts the text to various extents. We provide a security analysis of its four default distortion profiles as well as a usability analysis that shows how these profiles affect response time and accurate understanding. Our results illustrate the security/usability tradeoffs that arise in the face of adversaries that use current, off-the-shelf optical character recognition technology in order to launch a variety of attacks. Two profiles, in particular, achieve a level of protection that seems to justify their respective usability degradation in many situations. The 'strongest' distortion profile, however, does not seem to provide a large additional security margin against the adversaries we considered.