We propose a new construct, the Text-Graphics Character (TGC) CAPTCHA, for preventing dictionary attacks against password authentication systems allowing remote access via dumb terminals. Password authentication is commonly used for computer access control. But password authentication systems are prone to dictionary attacks, in which attackers repeatedly attempt to gain access using the entries...

Abuse of free Internet resources and services from false account creation, to spam, to identity theft, excessive bandwidth usage, or even vote stuffing online polls is a big problem. The Completely Automatic Public Turing Test to tell Computers and Humans Apart (CAPTCHA) controls access to resources but automated systems are increasingly adept at overcoming them. In this paper a method of acces...

A CAPTCHA is a test that can, automatically, tell human and computer programs apart. It is a mechanism widely used nowadays for protecting web applications, interfaces, and services from malicious users and automated spammers. Usability and robustness are two fundamental aspects with CAPTCHA, where the usability aspect is the ease with which humans pass its challenges, while the robustness is t...

Any Web user is a potential knowledge contributor, but it remains a challenge to make them devote their time contributing to some purpose. In order to align individual with social interests, we selected the CAPTCHA Web resource protection application to embed knowledge elicitation within the users' main task of accessing a Web resource. Consequently, unlike previous knowledge acquisition approa...

Web access is affected by a great amount of accessibility issues that do not allow some users to access all information presented. Therefore, Web accessibility is an important issue because everybody should access Web content independently of their access features. Among these accessibility issues, a Web content element that interferes with Web accessibility is a CAPTCHA. A CAPTCHA is a challen...

CAPTCHAs are a widely deployed mechanism to distinguish a legitimate human user from a computerized program trying to abuse online services. Attackers, however, have devised a clever and an economical way to bypass the security provided by CAPTCHAs by simply relaying CAPTCHA challenges to remote human-solvers. Most existing varieties of CAPTCHAs are completely vulnerable to such relay attacks, ...

A CAPTCHA is a widely used security mechanism to prevent automated access to webpages by malicious users such as internet bots. Introducing elements such as distortion, distracting backgrounds and noise are some ways to make it harder for computer vision algorithms to break them. However, making CAPTCHAs complex by increasing the intensity of these properties has a direct adverse impact on thei...

This paper proposes a public-key cryptosystem and a short password encryption mode, where traditional hardness assumptions are replaced by specific refinements of the CAPTCHA concept called Decisional and Existential CAPTCHAs. The public-key encryption method, achieving 128-bit security, typically requires from the sender to solve one CAPTCHA. The receiver does not need to resort to any human a...

CAPTCHA is an acronym that stands for Completely Automated Public Turing Test to tell Computers and Humans Apart (CAPTCHA), it a good example of authentication system can be used determine the true identity any user. It serves as security measure prevent attack caused by web bots (automatic programs) during online transaction. come text-based or image-based depending on project programmer. The ...