Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.



Published on

A seminar of CAPTCHA

/* A very kind request to the viewers, please don't try to download it and just edit the name. Just take the idea from the presentation and add your innovation to it */

I hope it will be helpful to you all :)
Good Luck :)

Published in: Technology


  1. 1. CAPTCHA<br />Telling Humans and Computers Apart Automatically<br />Presented by: Preetam Kajal Rout<br />
  2. 2. Definition<br />History<br />Application of CAPTCHA<br />Types of CAPTCHA<br />Breaking CAPTCHA<br />Reference<br />Agenda<br />
  3. 3. CAPTCHA (Completely Automated Public Turing Test To Tell Computers and Humans Apart).<br />The P for Public means that the code and the data used by a CAPTCHA should be publicly available.<br />T for “Turing Test to Tell” is because CAPTCHAs are like Turing Tests.<br />What is CAPTCHA??<br />
  4. 4. CAPTCHA is a program that protects websites against bots by generating and grading tests that humans can pass but current computer programs cannot. For example, humans can read distorted text as the one shown below, but current computer programs can't.<br />What is CAPTCHA??<br />Continues…<br />
  5. 5. CAPTCHA was first used by “AltaVista” in 1997.<br /><ul><li>Reduced Spam by 95% for a small period of time.</li></ul>Yahoo! Chat room problem.<br /><ul><li>In September 2000, UdiManber of Yahoo! described this "chat room problem" to researchers at CMU:'bots' were joining on-line chat rooms and irritating the people there by pointing them to advertising sites. How could all 'bots' be refused entry to chat rooms?</li></ul>CMU’s CAPTCHA research.<br /><ul><li>The term CAPTCHA coined in 2000 by Luis von Ahn, Manuel Blum, Nicholas Hopper and John Langford of Carnegie Mellon University.</li></ul> History Behind CAPTCHA<br />
  6. 6. Preventing Comment Spam in Blogs.<br />Protecting website registration.<br />Protecting email addresses from scrapers.<br />Online Polls.<br />Preventing dictionary attacks.<br /> Application of CAPTCHA<br />
  7. 7. Text Based CAPTCHA<br /><ul><li>Gimpy
  8. 8. ReCAPTCHA
  9. 9. Gimpy-r, Google CAPTCHA</li></ul>Graphics Based CAPTCHA<br /><ul><li>Bongo</li></ul>Audio Based CAPTCHA<br />Types of CAPTCHA<br />
  10. 10. Text Based CAPTCHA<br />GIMPY<br /><ul><li>Gimpy works by selecting seven words out of a dictionary.
  11. 11. Then renders a distorted image containing the words.
  12. 12. Then presents a test to its user, which consists of the distorted image and the directions: “type three words appearing in the image.”</li></ul>Type three words appearing in the image.<br />
  13. 13. Some Screenshots ofText Based CAPTCHA<br />Pictures of CAPTCHA implemented by some popular websites.<br />
  14. 14. Graphics Based CAPTCHA<br />Bongo<br /><ul><li>BONGO asks the user to solve a visual pattern recognition problem.
  15. 15. It displays two series of blocks, the left and the right. The blocks in the left series differ from those in the right, and the user must find the characteristic that sets them apart.
  16. 16. After seeing the two series of blocks, the user is presented with a single block and is asked to determine whether this block belongs to the left series or to the right.</li></ul>To which side does the block on the bottom belong?<br />
  17. 17. Some Screenshots of Graphics Based CAPTCHA<br />GIMPY CAPTCHA<br />b. PIX CAPTCHA<br />
  18. 18. The program picks a word or a sequence of numbers at random, renders the word or the numbers into a sound clip and distorts the sound clip.<br />It then presents the distorted sound clip to the user and asks users to enter its contents.<br />This CAPTCHA is based on the difference in ability between humans and computers in recognizing spoken language.<br /> Audio Based CAPTCHA<br />
  19. 19. Insecure implementation<br /><ul><li>exploiting bugs in the implementation that allow the attacker to completely bypass the CAPTCHA</li></ul>Computer character recognition<br /><ul><li>improving character recognition software</li></ul>Human solvers<br /><ul><li>using cheap human labor to process the tests</li></ul> How to Defeat CAPTCHA?<br />
  20. 20. Wikipedia(<br />Carnegie Mellon School of Computer Science Web site (<br />“Telling Humans and Computers Apart” by Luis von Ahn and colleagues.<br />Xerox Palo Alto Research Center ( istl/projects/captcha/)<br />References<br />
  21. 21. THANK YOU !!!<br />
  22. 22. ANY QUERIES ???<br />