TY  - RPRT
AU  - El Ahmad, Ahmad S
AU  - Yan, Jeff
AU  - Tayara, Mohamad
A2  - 
T1  - The Robustness of Google CAPTCHAs
PB  - School of Computer Science, Newcastle University, UK
AD  - 
PY  - 2011/05
VL  - 
IS  - 
SP  - 
EP  - 
UR  - http://homepages.cs.ncl.ac.uk/jeff.yan/google.pdf
DO  - 
KW  - recognition
KW  - google
KW  - captcha
KW  - character
KW  - image
KW  - ocr
KW  - segmentation
L1  - 
N1  - 
N1  - 
N1  - 
AB  - We report a novel attack on two CAPTCHAs that have been widely deployed on the Internet, one being Google's home design and the other acquired by Google (i.e. reCAPTCHA). With a minor change, our attack program also works well on the latest ReCAPTCHA version, which uses a new defence mechanism that was unknown to us when we designed our attack. This suggests that our attack works in a fundamental level. Our attack appears to be applicable to a whole family of text CAPTCHAs that build on top of the popular segmentation-resistant mechanism of "crowding character together" for security. Next, we propose a novel framework that guides the application of our well-tested security engineering methodology for evaluating CAPTCHA robustness, and we propose a new general principle for CAPTCHA design. 
ER  -