Many web-based services such as email, search engines, and polling sites are being abused by spammers via computer programs known as bots. This problem has bred a new research area called Human Interactive Proofs (HIP) and a testing device called CAPTCHA, which aims to protect services from malevolent attacks by distinguishing bots from human users. In the past decade, researchers have focused ...

CAPTCHAs are computer generated tests that humans can pass but current computer systems cannot. CAPTCHAs provide a method for automatically distinguishing a human from a computer program, and therefore can protect web services from bots. Most CAPTCHAs consist of distorted images, usually text, for which a user must provide some description. Unfortunately, visual CAPTCHAs limit access to the mil...

CAPTCHA stands for “Completely Automated Public Turing test to tell Computers and Humans Apart” and has received much attention since it first began appearing on websites. It requires the deciphering of distorted texts, mostly in English which is something that computers still cannot do well. It is also helpful in preventing the abuse of online services. The current text-based CAPTCHA requires ...

We explore authenticated group key agreement in data-sharing Peer-to-Peer networks. We first propose a novel password-based authenticated group key agreement protocol with key confirmation. We present a formal statement of its security in a variant of the Bresson et al. security model adapted for the password-based setting. A discussion of the limitations of our protocol in the case where the g...

In this paper the elements of the CAPTCHA usability are analyzed. CAPTCHA, as a time progressive element in computer science, has been under constant interest of ordinary, professional as well as the scientific users of the Internet. The analysis is given based on the usability elements of CAPTCHA which are abbreviated as user-centric approach to the CAPTCHA. To demonstrate it, the specific typ...

CAPTCHA is widely used security technique employed to avoid automated form submissions or verify user as human. An alternative CAPTCHA method based on pattern matching and number recognition ability is proposed in this paper, which verifies user as human and prevents bots to intervene and spam applications or services. This method is based on user gestures which make it unique and secure. The b...

We present a technique for using a content-based video labeling task as a CAPTCHA. Our video CAPTCHAs are generated from YouTube videos, which contain labels (tags) supplied by the person that uploaded the video. They are graded using a video’s tags, as well as tags from related videos. In a user study involving 184 participants, we were able to increase the average human success rate on our vi...

Human Interactive Proofs (HIPs) are automatic reverse Turing tests designed to distinguish between various groups of users. Completely Automatic Public Turing test to tell Computers and Humans Apart (CAPTCHA) is a HIP system that distinguish between humans and malicious computer programs. Many CAPTCHAs have been proposed in the literature that text-graphical based, audio-based, puzzle-based and...