By Steven Baker CAPTCHA Roadmap What is a

By: Steven Baker CAPTCHA

Roadmap � What is a CAPTCHA? � History of CAPTCHA � Applications of CAPTCHAs � Accessibility � Examples of CAPTCHAs � re. CAPTCHA � Vulnerabilities � Conclusion

What is a CAPTCHA? � Completely Automated Public Turing test to tell Computers and Humans Apart � The goal: To create an automated test that is easy for a human to pass but difficult for a computer � Optical character recognition (OCR) is a difficult problem for computers to solve Take advantage of the fact that humans are good at recognizing patterns that computers have trouble with � The most common form of CAPTCHAs are images of text that are distorted:

History of CAPTCHA � Verification of a human in the loop, or identification via the Turing Test Journal from 1996 by Moni Naor, an Israeli Computer Scientist First work published detailing ideas behind modern day CAPTCHA � Mark D. Lillibridge, Martin Abadi, Krishna Bharat, and Andrei Z. Broder Used CAPTCHAs for Alta. Vista in 1997 to prevent bots from adding to their search engine Patented their process in 1998 although they didn’t use the term CAPTCHA � Luis von Ahn, Manuel Blum, Nicholas J. Hopper, and John Langford First to coin the term CAPTCHA in 2000 at CMU when they developed the first CAPTCHA used by Yahoo

Applications of CAPTCHAs �Protect website registration �Online Polls �Prevent comment spam on blogs �Prevent worms and spam �Search engine bots �Prevent dictionary attacks

Accessibility � While you want to stop unwanted bots, you don’t want to keep legitimate users out � Section 508 in the US requires federal agencies to make information technology accessible to those with disabilities � Problem: Visually impaired users will not be able to solve image based CAPTCHAs � Like OCR, speech recognition is also a difficult problem for computers to solve � Solution: Provide an audio alternative for human verification

Examples of Different CAPTCHAs � Distorted text with audio option � Picture identification � Simple Math CAPTCHA � 3 D CAPTCHA

re. CAPTCHA � Developed by Luis von Ahn, Ben Maurer, Colin Mc. Millen, David Abraham, and Manuel Blum at CMU Acquired by Google in September 2009 �Assists in digitizing the text of books Requires user to enter two words ▪ One is the test word that is known by the system ▪ The other is a word from the scan of a digitized text that a computer was unable to recognize �Used to digitize the archives of the New York Times and books from Google Books

Vulnerabilities �Images that use undistorted text or a consistent font are vulnerable Image processing techniques are able to read the text if it is not distorted enough �Some companies sell CAPTCHA breaking services Employ actual humans to solve CAPTCHAs as a job

Conclusion � What is a CAPTCHA? � History of CAPTCHA � Applications of CAPTCHAs � Accessibility � Examples of CAPTCHAs � re. CAPTCHA � Vulnerabilities � Any questions?

References �http: //www. google. com/recaptcha/captcha �http: //en. wikipedia. org/wiki/CAPTCHA �http: //www. captcha. net/captcha_crypt. pdf �http: //www. findexamples. com/5 -examples-of- different-types-of-captchas/ �http: //www. captcha. net/Breaking_Audio_CAPT CHAs. pdf