Abstract
An automated public Turing test to distinguish between computers and humans known as CAPTCHA is a widely used technique on many websites to protect their online services from malicious users. Two fundamental aspects of captcha considered in various studies in the literature are robustness and usability. A widely accepted standard benchmark, to guide the text-based captcha developers is not yet available. So this paper proposes a benchmark for designing usable-secure text-based captchas based on a community driven evaluation of the usability and security aspects. Based on this benchmark, we develop four new textbased captcha schemes, and conduct two separate experiments to evaluate both the security and usability perspectives of the developed schemes. The result of this evaluation indicates that the proposed benchmark provides a basis for designing usable-secure text-based captchas.
Highlights
Distinguishing computers from humans is a key issue for website security
This paper proposes a benchmark for designing a usable-secure captcha based on a community driven evaluation of security and usability features
The Easy and Secure schemes were completed with an average of 95% accuracy in 6.3 seconds. These results demonstrated the usability of the proposed schemes
Summary
Distinguishing computers from humans is a key issue for website security. EBay must stop bots from flooding its website with scams and Gmail must prevent abuse by automated spammers. A captcha, which is a Completely Automated Public Turing test to tell Computer and Human Apart [1], allows websites to make an automatic assessment. There are different types of captchas [2, 3] such as text-based, video-based and image-based, to name but a few. Due to its many advantages [4], the text-based captcha is the most commonly deployed type currently used by websites. The text-based type prompts users to recognize text, which state-of-the-art text recognition programs cannot do. The term captcha refers to text-based schemes only
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