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...

Abstract: CAPTCHA-Systeme sind weit verbreitete Schutzsysteme, um auf OnlinePlattformen menschliche Benutzer von automatischen Bots zu unterscheiden. Dabei kommen verschiedene Varianten zum Einsatz, die sich in Art und Interaktionsmodus sowie im Schwierigkeitsgrad der Lösung unterscheiden. In der vorliegenden Studie werden Kriterien der Benutzbarkeit von CAPTCHA-Systemen aufgestellt. Zudem werd...

Internet services designed for human use are being abused by programs. We present a defense against such attacks in the form of a CAPTCHA (completely automatic public Turing test to tell computers and humans apart) that exploits the difference in ability between humans and machines in reading images of text. CAPTCHAs are a special case of ‘human interactive proofs,’ a broad class of security pr...

Research on CAPTCHA has led CAPTCHA design into adopting almost exclusively graphical implementations that deal mostly with character recognition. This has reached an exhaustion point, where new approaches are vital to the survival of the technique. This paper discusses the early stages of a research that intends to solve the open problem of a CAPTCHA in the text domain offering, this way, inno...

Herein, we propose generating CAPTCHAs through random field simulation and give a novel, effective and efficient algorithm to do so. Indeed, we demonstrate that sufficient information about word tests for easy human recognition is contained in the site marginal probabilities and the site-to-nearby-site covariances and these quantities can be embedded into KNW conditional probabilities, designed...

In this paper we present a new CAPTCHA system (Completely Automated Turing Test To Tell Computers and Humans Apart). This proposal, SemCAPTCHA, is motivated by an increasing number of broken OCR-based CAPTCHA systems and it is based not only on text recognition but also on text understanding. We describe SemCAPTCHA from both user’s perspective and system’s perspective and compare it to some cur...

CAPTCHA is a completely automated program designed to distinguish whether the user is a computer or human. As the problems of Internet security are worsening, it is of great significance to do research on CAPTCHA. This article starts from the recognition of CAPTCHAs, then analyses the weaknesses in its design and gives corresponding recognition proposals according to various weaknesses, finally...

The malware attacks attempt to deplete the cloud services with bogus request which is a major threat in cloud. A mechanism to intensify the login security in cloud is suggested. The concept of CaPGP – CAPTCHA as Puzzle and Graphical Password is introduced because CAPTCHA is one way to discriminate human and malware apart. The computations at the client side are made intensive than on the server...

In this paper we present a new CAPTCHA system (Completely Automated Turing Test To Tell Computers and Humans Apart). The proposal of SemCAPTCHA is motivated by an increasing number of broken OCR-based CAPTCHA systems and it is based not only on text recognition but also on text understanding. We describe both, the user’s and the system’s perspective of SemCAPTCHA and compare it with some curren...

We argue that a set of usability heuristics are needed for easy and quick evaluation of Captchas implementations. With this set of heuristics we contribute to sustain the Captcha Mantra: “Easy for humans, hard for machines”. In particular, the usability of Captcha schemes change radically when utilized on mobile environments. We are developing a set of heuristics for use by practitioners wishin...