Text-based captcha strengths and weaknesses Text-based captcha strengths and weaknesses
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Text-based captcha strengths and weaknesses

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Conference Computer and Communications Security
Authors Elie Bursztein , Matthieu Martin , John C. Mitchell
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@inproceedings{ BURSZTEIN2011TEXT-BASED,title = {Text-based captcha strengths and weaknesses},author = {"Elie, Bursztein" and "Matthieu, Martin" and "John C., Mitchell"},booktitle = {Computer and Communications Security},year = {2011},organization = {ACM}}

Warning:the attack techniques and design guidelines describedin this paper are obsolete due to the invention of generalized techniques to break text captchas as described in this paper.

We carry out a systematic study of existing visual CAPTCHAs based on distorted characters that are augmented with anti-segmentation techniques. Applying a systematic evaluation methodology to 15 current CAPTCHA schemes from popular web sites, we find that 13 are vulnerable to automated attacks. Based on this evaluation, we identify a series of recommendations for CAPTCHA designers and attackers, and possible future directions for producing more reliable human/computer distinguishers.

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