ReCAPTCHA.net Now Vulnerable to Algorithmic Attack

n3ond4x writes "reCAPTCHA.net algorithms have been developed to solve the current CAPTCHA at an efficacy of 30%. The algorithms were disclosed at DEFCON 18 over the weekend and have since been made available online. Also available is a video demonstration of random reCAPTCHA.net CAPTCHAs being subjected to the algorithms." There's probably an excellent Firefox plugin to render this page's color scheme more bearable. Note: the PowerPoint presentation linked opens fine in OpenOffice, and the video speaks for itself.

Comments

Re:Speaking about re-captcha

[icebraining]

Currently, we are helping to digitize old editions of the New York Times and books from Google Books.

http://www.google.com/recaptcha/learnmore

Re:colours

[electrostatic]

"...an excellent Firefox plugin to render this page's color scheme more bearable."

Yep. Color Toggle

https://addons.mozilla.org/en-US/firefox/addon/9408/

I have it set so Ctl-Shift-Z set light yellow background, black text, and blue links.

Re:Offtopic

[Anonymous Coward]

No, Firefox addons used to be called extensions, plugins are still plugins.

Re:far from it

[hydrofix]

Since both words need to be correct "solve the current CAPTCHA at an efficacy of 1%" would be closer to the truth.

Actually, that is incorrect. The other word is already positively known by the OCR, and serves as a control, while the other is the one that the OCR could not read. It will of course only check the one that it knowns, and assumes the other one is then correct as well. So, if you get one of the words correct AND this is the same word that as their OCR identified correctly (which is very likely the case), then you pass, but most of the time (99%) give a bad answer for the harder, non-OCR word. Sadly, this leads to pollution of their database in the long run.

Re:far from it

[Jorl17]

This is not informative. As many have said. If You read: http://www.google.com/recaptcha/learnmore , you'll get it.

Here is the deal: reCAPTCHA presents two words. One is picked by it and is previously known. The other one is a word from a book that has been scanned. Said word is unknown to the reCAPTCHA system. When the user enters both words, reCAPTCHA checks to see if the known word has been properly recognized. If that is the case, then reCAPTCHA can assume that a human is answering. Given that a human is answering, then the second unknown word given by the human is most likely correct, because he/she will be able to recognize it as well. Using this system, reCAPTCHA works as a CAPTCHA (spam prevention) mechanism and also helps transforming old books/papers into digital format, such as the New York Times.

So, in practice, only one word has to be correct -- the word that reCAPTCHA knows. What's sad is that bots may contribute incorrect second words...

Next time, get informed before going all crazy.

And here is the relevant info, quoted from the aforementioned website:

reCAPTCHA improves the process of digitizing books by sending words that cannot be read by computers to the Web in the form of CAPTCHAs for humans to decipher. More specifically, each word that cannot be read correctly by OCR is placed on an image and used as a CAPTCHA. This is possible because most OCR programs alert you when a word cannot be read correctly. But if a computer can't read such a CAPTCHA, how does the system know the correct answer to the puzzle? Here's how: Each new word that cannot be read correctly by OCR is given to a user in conjunction with another word for which the answer is already known. The user is then asked to read both words. If they solve the one for which the answer is known, the system assumes their answer is correct for the new one. The system then gives the new image to a number of other people to determine, with higher confidence, whether the original answer was correct.