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Improved Mathematical Captcha | My Soft Parade. Www.mysoftparade.com / blog / improved-mathematical-captcha A week ago I published MathCaptchaForm that I use in my blog for preventing spam. Malcolm Tredinnick and then other people noticed that solution don't protect from replay attacks and once solved question can be used by spam bots on different web-sites. So I added protection against replay attacks and implemented it without database usage. It was original requirement to keep MathCaptchaForm as lightweight as possible.

I removed from the form captha_question and added new field captcha_token that holds a hash from question, answer, settings.SECRET_KEY , settings.SITE_URL and expires time (1 hour by default). As you see captcha_token contains hash and question with expires time in plain form, but don't contain the answer. When form is submitted, from above fields and user answer is built new hash that we compare with old hash. If captcha is expired, we reset it and generate new captcha. Brains-N-brawn.com. Breaking a Visual CAPTCHA. Summary This is the homepage of the Shape Contexts based approach to break Gimpy, the CAPTCHA test used at Yahoo! To screen out bots. Our method can successfully pass that test 92% of the time. The approach we take uses general purpose algorithms that have been designed for generic object recognition.

The same basic ideas have been applied to finding people in images, matching handwritten digits, and recognizing 3D objects. News Articles Human or Computer? Quick links: BackgroundOur ApproachResultsRelated Links Picture of a CAPTCHA in use at Yahoo. Background A CAPTCHA is a program that can generate and grade tests that: Most humans can pass, BUT Current computer programs can't pass CAPTCHA stands for "Completely Automated Public Turing test to Tell Computers and Humans Apart".

EZ-Gimpy and Gimpy, the CAPTCHAs that we have broken, are examples of word-based CAPTCHAs. Gimpy is a more difficult variant of a word-based CAPTCHA. Our Approach Results EZ-Gimpy Gimpy Links Back to Greg Mori's page. Samuel Hocevar - CV (français)