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Captcha

Captcha. Introduction Objectives Motivation History Types Application Process Breaking Captcha Re-Captcha Conclusion. Introduction. C ompletely A utomated P ublic T uring tests to tell C omputers and H umans A part.

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Captcha

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  1. Captcha

  2. Introduction Objectives Motivation History Types Application Process Breaking Captcha Re-Captcha Conclusion

  3. Introduction Completely Automated Public Turing tests to tell Computers and Humans Apart. Captcha is a challenge response test used in computing to ensure that the response is not generated by computer.

  4. Introduction Captcha is a program that protect website against bots by generating and grading test that -Human can pass but -Computer program can’t

  5. Introduction Captcha requires that the user types letters or digits from distorted image appears on screen. If correct solution is entered than system assumes that response is generated -by user. else -by bots & access denied.

  6. Introduction Captcha word comes from capture. it is also known as reverse turning test. About 200 million CAPTCHAs are solved by humans around the world every day

  7. Objective In the March 2005 College Mathematics Journal Dr. Edward Aboufadel along with students Julia Olsen and Jesse Windle published an article entitled “Breaking the Holiday Inn Priority Club CAPTCHA.” Our objective was to report on their method and reproduce their results.

  8. Motivation The general motivation for decoding CAPTCHAs is financial gain e.g. through spamming. However, another motivation for decoding CAPTCHAs is improvement of Object Character Recognition.

  9. History First developed by Alta Vista in 1997. The term coined in 2000 by Luis von Ahn, Manuel Blum and Nicholas j. Hopper of Carnegie Mellon university and john Langford of IBM.

  10. Types of CAPTCHAs Text based • Gimpy, ez-gimpy • Gimpy-r, Google CAPTCHA • Simard’s HIP (MSN) Graphic based • Bongo • Pix Audio based

  11. Text Based CAPTCHAs Gimpy, ez-gimpy • Pick a word or words from a small dictionary • Distort them and add noise and background Gimpy-r, Google’s CAPTCHA • Pick random letters • Distort them, add noise and background Simard’s HIP • Pick random letters and numbers • Distort them and add arcs

  12. Text Based CAPTCHAs Gimpy, Ez-Gimpy Gimpy-r,Google’s CAPTCHA Simard’s HIP (MSN)

  13. Graphic Based CAPTCHAs Bongo • Display two series of blocks • User must find the characteristic that sets the two series apart • User is asked to determine which series each of four single blocks belongs to Difference? thick vs. thin lines

  14. Graphic Based CAPTCHAs PIX • Create a large database of labeled images • Pick a concrete object • Pick four images of the object from the images database • Distort the images • Ask the user to pick the object for a list of words

  15. Graphic Based CAPTCHAs Pool Dog

  16. Audio Based CAPTCHAs Pick a word or a sequence of numbers at random Render them into an audio clip using a TTS software Distort the audio clip Ask the user to identify and type the word or numbers

  17. Application Online polls In November 1999,htttp://slashdot.com Released an online poll asking which was the best graduate school in computer science!. students at Carnegie Mellon found a way to stuff the ballots by using programs that voted for CMU thousands of times. CMU's score started growing rapidly. The next day, students at MIT wrote their own voting program and the poll became a contest between voting “bots". MIT finished with 21,156 votes, Carnegie Mellon with 21,032 and every other school with less than 1,000. To solve this captcha is used

  18. Application Protecting Website Registration Several companies offer free email services. Up Until a few years ago most of these services suffered from a a specific type of attack:”bots” that would sign up for thousands of email accounts every minuite.The solution to this problem was to use CAPTCHAs to ensure that only humans obtain free accounts.

  19. Application Preventing Comment spam in Blogs Most Bloggers are familiar with programs that submit bogus comments usually for the purpose of raising search engine ranks of some website.This is called comment spam.By using a CAPTCHA only humans can enter comments on a blog.There is no need to make users sign up before they enter a comment,and no legitimate comments are over lost!

  20. Application Preventing Dictionary attacks CAPTCHA can also be used to prevent dictionary attacks in password systems.The idea is simple:prevent computer from being able to iterate through the entire space of passwords by requiring it to solve a CAPTCHA after a certain number of unsuccessful logins.

  21. The Process Generate CAPTCHA Align CAPTCHA Cut CAPTCHA Transform CAPTCHA Decode CAPTCHA

  22. Generate CAPTCHA CAPTCHA generated with our Mathematical code.

  23. Align CAPTCHA Remove gridlines. Undo angle of rotation.

  24. Align CAPTCHA Crop CAPTCHA.

  25. Cut CAPTCHA Cut CAPTCHA cut into 5 pieces.

  26. Transform CAPTCHA Perform the HWT on each of the 5 pieces.

  27. Decode CAPTCHA

  28. Mathematics involved Perform linear regression on the CAPTCHA to find the line of best fit for the data points that make up the CAPTCHA. Matrix multiplication using the rotation matrix to undo the angle of rotation. Three iterations of the Haar Wavelet Transform on each of the cut pieces. Each cut letter is compared to the canonical letters by comparing the Norms.

  29. Breaking CAPTCHAs Most text based CAPTCHAs have been broken by software • OCR • Segmentation Other CAPTCHAs were broken by streaming the tests for unsuspecting users to solve.

  30. Re-Captcha Free captcha service that helps to digitize books, newspaper and old time radio shows. Recaptcha improves the process of digitizing books by sending words that can’t be read by computers to the web in form of captchas for human to decipher

  31. Working of Re-Captcha Two words are shown, one word is known as control word and another one is known as a questionable word System assumes that if human types the control word correctly, then the questionable word is also correct

  32. Re-Captcha Image

  33. New unbreakable Captcha used at http://www.yuniti.com/register.php

  34. Conclusion -Captchas are an effective way to and reduce spam. -They serves dual purpose- help advance AI knowledge. -Applications are varied from stopping bots to character reorganization and pattern matching

  35. Thank You……..

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