Machine Learning
Comparison of Texture Features Based on Gabor Filters
ICIAP '99 Proceedings of the 10th International Conference on Image Analysis and Processing
Cryptanalysis of a Cognitive Authentication Scheme (Extended Abstract)
SP '07 Proceedings of the 2007 IEEE Symposium on Security and Privacy
Asirra: a CAPTCHA that exploits interest-aligned manual image categorization
Proceedings of the 14th ACM conference on Computer and communications security
Proceedings of the 9th workshop on Mobile computing systems and applications
A low-cost attack on a Microsoft captcha
Proceedings of the 15th ACM conference on Computer and communications security
LIBSVM: A library for support vector machines
ACM Transactions on Intelligent Systems and Technology (TIST)
Recognizing objects in adversarial clutter: breaking a visual captcha
CVPR'03 Proceedings of the 2003 IEEE computer society conference on Computer vision and pattern recognition
Leveraging the CAPTCHA problem
HIP'05 Proceedings of the Second international conference on Human Interactive Proofs
Applications of SAT solvers to cryptanalysis of hash functions
SAT'06 Proceedings of the 9th international conference on Theory and Applications of Satisfiability Testing
What's up CAPTCHA?: a CAPTCHA based on image orientation
Proceedings of the 18th international conference on World wide web
Balancing usability and security in a video CAPTCHA
Proceedings of the 5th Symposium on Usable Privacy and Security
ACM SIGGRAPH Asia 2009 papers
Exploiting the human-machine gap in image recognition for designing CAPTCHAs
IEEE Transactions on Information Forensics and Security
Proceedings of the 2nd ACM workshop on Security and artificial intelligence
Streamlining attacks on CAPTCHAs with a computer game
IJCAI'09 Proceedings of the 21st international jont conference on Artifical intelligence
An automated reverse turing test using facial expressions
HSI'09 Proceedings of the 2nd conference on Human System Interactions
Scene tagging: image-based CAPTCHA using image composition and object relationships
ASIACCS '10 Proceedings of the 5th ACM Symposium on Information, Computer and Communications Security
CAPTCHA smuggling: hijacking web browsing sessions to create CAPTCHA farms
Proceedings of the 2010 ACM Symposium on Applied Computing
Leveraging cognitive factors in securing WWW with CAPTCHA
WebApps'10 Proceedings of the 2010 USENIX conference on Web application development
Attacks and design of image recognition CAPTCHAs
Proceedings of the 17th ACM conference on Computer and communications security
Attacking image recognition CAPTCHAS: a naive but effective approach
TrustBus'10 Proceedings of the 7th international conference on Trust, privacy and security in digital business
Proceedings of the 26th Annual Computer Security Applications Conference
CAPTCHA phishing: a practical attack on human interaction proofing
Inscrypt'09 Proceedings of the 5th international conference on Information security and cryptology
Proceedings of the 4th ACM workshop on Security and artificial intelligence
Text-based CAPTCHA strengths and weaknesses
Proceedings of the 18th ACM conference on Computer and communications security
SEMAGE: a new image-based two-factor CAPTCHA
Proceedings of the 27th Annual Computer Security Applications Conference
Do cognitive styles of users affect preference and performance related to CAPTCHA challenges?
CHI '12 Extended Abstracts on Human Factors in Computing Systems
Security and usability challenges of moving-object CAPTCHAs: decoding codewords in motion
Security'12 Proceedings of the 21st USENIX conference on Security symposium
Fluxing botnet command and control channels with URL shortening services
Computer Communications
A survey and analysis of current CAPTCHA approaches
Journal of Web Engineering
A User-friendly Image-Text Fusion CAPTCHA for Secure Web Services
Proceedings of International Conference on Information Integration and Web-based Applications & Services
DeepCAPTCHA: an image CAPTCHA based on depth perception
Proceedings of the 5th ACM Multimedia Systems Conference
FaceDCAPTCHA: Face detection based color image CAPTCHA
Future Generation Computer Systems
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The Asirra CAPTCHA [EDHS2007], proposed at ACM CCS 2007, relies on the problem of distinguishing images of cats and dogs (a task that humans are very good at). The security of Asirra is based on the presumed difficulty of classifying these images automatically. In this paper, we describe a classifier which is 82.7% accurate in telling apart the images of cats and dogs used in Asirra. This classifier is a combination of support-vector machine classifiers trained on color and texture features extracted from images. Our classifier allows us to solve a 12-image Asirra challenge automatically with probability 10.3%. This probability of success is significantly higher than the estimate of 0.2% given in [EDHS2007] for machine vision attacks. Our results suggest caution against deploying Asirra without safeguards. We also investigate the impact of our attacks on the partial credit and token bucket algorithms proposed in [EDHS2007]. The partial credit algorithm weakens Asirra considerably and we recommend against its use. The token bucket algorithm helps mitigate the impact of our attacks and allows Asirra to be deployed in a way that maintains an appealing balance between usability and security. One contribution of our work is to inform the choice of safeguard parameters in Asirra deployments.