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CAPTCHAs are employed as a security measure to differentiate human users from bots. A new sound-based CAPTCHA is proposed in this paper, which exploits the gaps between human voice and synthetic voice rather than relays on the auditory…

Cryptography and Security · Computer Science 2013-06-13 Haichang Gao , Honggang Liu , Dan Yao , Xiyang Liu , Uwe Aickelin

Completely Automated Public Turing Test To Tell Computers and Humans Apart (CAPTCHA) is a type of challenge-response test widely used in authentication systems. A well-known challenge it faces is the CAPTCHA farm, where workers are hired to…

Cryptography and Security · Computer Science 2023-12-19 Rui Jin , Yong Liao , Pengyuan Zhou

CAPTCHAs or reverse Turing tests are real-time assessments used by programs (or computers) to tell humans and machines apart. This is achieved by assigning and assessing hard AI problems that could only be solved easily by human but not by…

Human-Computer Interaction · Computer Science 2014-02-05 A. K. B. Karunathilake , B. M. D. Balasuriya , R. G. Ragel

CAPTCHAs have long been essential tools for protecting applications from automated bots. Initially designed as simple questions to distinguish humans from bots, they have become increasingly complex to keep pace with the proliferation of…

Cryptography and Security · Computer Science 2025-02-25 Ziqi Ding , Gelei Deng , Yi Liu , Junchen Ding , Jieshan Chen , Yulei Sui , Yuekang Li

Crowdsourcing human-solving or online typing attacks are destructive problems. However, studies into these topics have been limited. In this paper, we focus on this kind of attacks whereby all the CAPTCHAs can be simply broken because of…

Cryptography and Security · Computer Science 2019-04-30 Jianyi Zhang , Xiali Hei , Zhiqiang Wang

We introduce GOTCHAs (Generating panOptic Turing Tests to Tell Computers and Humans Apart) as a way of preventing automated offline dictionary attacks against user selected passwords. A GOTCHA is a randomized puzzle generation protocol,…

Cryptography and Security · Computer Science 2013-10-07 Jeremiah Blocki , Manuel Blum , Anupam Datta

To this date, CAPTCHAs have served as the first line of defense preventing unauthorized access by (malicious) bots to web-based services, while at the same time maintaining a trouble-free experience for human visitors. However, recent work…

Cryptography and Security · Computer Science 2020-11-05 Dorjan Hitaj , Briland Hitaj , Sushil Jajodia , Luigi V. Mancini

To enhance the security of text CAPTCHAs, various methods have been employed, such as adding the interference lines on the text, randomly distorting the characters, and overlapping multiple characters. These methods partly increase the…

Cryptography and Security · Computer Science 2023-08-17 Ran Jiang , Sanfeng Zhang , Linfeng Liu , Yanbing Peng

The rapid evolution of GUI-enabled agents has rendered traditional CAPTCHAs obsolete. While previous benchmarks like OpenCaptchaWorld established a baseline for evaluating multimodal agents, recent advancements in reasoning-heavy models,…

Machine Learning · Computer Science 2026-02-10 Jiacheng Liu , Yaxin Luo , Jiacheng Cui , Xinyi Shang , Xiaohan Zhao , Zhiqiang Shen

Bots constitute a significant portion of Internet traffic and are a source of various issues across multiple domains. Modern bots often become indistinguishable from real users, as they employ similar methods to browse the web, including…

Machine Learning · Computer Science 2024-12-04 Jan Kadel , August See , Ritwik Sinha , Mathias Fischer

Traditional CAPTCHA (Completely Automated Public Turing Test to Tell Computers and Humans Apart) schemes are increasingly vulnerable to automated attacks powered by deep neural networks (DNNs). Existing adversarial attack methods often rely…

Computer Vision and Pattern Recognition · Computer Science 2025-07-02 Xia Du , Xiaoyuan Liu , Jizhe Zhou , Zheng Lin , Chi-man Pun , Cong Wu , Tao Li , Zhe Chen , Wei Ni , Jun Luo

The gaming industry has experienced substantial growth, but cheating in online games poses a significant threat to the integrity of the gaming experience. Cheating, particularly in first-person shooter (FPS) games, can lead to substantial…

Cryptography and Security · Computer Science 2025-11-18 Jiayi Zhang , Chenxin Sun , Yue Gu , Qingyu Zhang , Jiayi Lin , Xiaojiang Du , Chenxiong Qian

For nearly two decades, CAPTCHAs have been widely used as a means of protection against bots. Throughout the years, as their use grew, techniques to defeat or bypass CAPTCHAs have continued to improve. Meanwhile, CAPTCHAs have also evolved…

Cryptography and Security · Computer Science 2023-07-25 Andrew Searles , Yoshimichi Nakatsuka , Ercan Ozturk , Andrew Paverd , Gene Tsudik , Ai Enkoji

Deep learning technology has made it possible to generate realistic content of specific individuals. These `deepfakes' can now be generated in real-time which enables attackers to impersonate people over audio and video calls. Moreover,…

Cryptography and Security · Computer Science 2023-01-10 Lior Yasur , Guy Frankovits , Fred M. Grabovski , Yisroel Mirsky

In recent years, the rapid development of artificial intelligence (AI) especially multi-modal Large Language Models (MLLMs), has enabled it to understand text, images, videos, and other multimedia data, allowing AI systems to execute…

Cryptography and Security · Computer Science 2025-04-02 Lehao Lin , Ke Wang , Maha Abdallah , Wei Cai

Preventing abuse of web services by bots is an increasingly important problem, as abusive activities grow in both volume and variety. CAPTCHAs are the most common way for thwarting bot activities. However, they are often ineffective against…

Cryptography and Security · Computer Science 2020-07-22 Yoshimichi Nakatsuka , Ercan Ozturk , Andrew Paverd , Gene Tsudik

CAPTCHAs are a defense mechanism to prevent malicious bot programs from abusing websites on the Internet. hCaptcha is a relatively new but emerging image CAPTCHA service. This paper presents an automated system that can break hCaptcha…

Cryptography and Security · Computer Science 2022-03-08 Md Imran Hossen , Xiali Hei

For the last ten years, CAPTCHAs have been widely used by websites to prevent their data being automatically updated by machines. By supposedly allowing only humans to do so, CAPTCHAs take advantage of the reverse Turing test (TT), knowing…

Computer Vision and Pattern Recognition · Computer Science 2014-09-04 Ahmad B. A. Hassanat

How to detect and mitigate deceptive AI systems is an open problem for the field of safe and trustworthy AI. We analyse two algorithms for mitigating deception: The first is based on the path-specific objectives framework where paths in the…

Artificial Intelligence · Computer Science 2023-06-27 Ismail Sahbane , Francis Rhys Ward , C Henrik Åslund

Human-like agents are an increasingly important topic in games and beyond. Believable non-player characters enhance the gaming experience by improving immersion and providing entertainment. They also offer players the opportunity to engage…

Artificial Intelligence · Computer Science 2025-06-11 Maciej Swiechowski , Dominik Slezak