1 / 17

CAPTCHA

CAPTCHA. Presented By Sayani Chandra (Roll - 09127106017). What is CAPTCHA ?. CAPTCHA is …. C ompletely A utomated P ublic T uring test to tell C omputers and H umans A part.

thina
Télécharger la présentation

CAPTCHA

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. CAPTCHA Presented By Sayani Chandra (Roll - 09127106017)

  2. What is CAPTCHA ?

  3. CAPTCHA is … • Completely Automated Public Turing test to tell Computers and Humans Apart. • Created in 2000 for Yahoo to prevent automated e-mail account registration,by Luis von Ahn, Manuel Blum, Nicholas Hopper and John Langford, Carnegie Mellon University.

  4. Introduction …

  5. A program that can tell whether its user is a human or a computer. • It uses a type of challenge-response test to determine that the response is not generated by a computer. • Generic CAPTCHAs distort letters and numbers. • Distorted characters are presented to user. • User has to recognize the distorted letters. • If the guessed letters are correct, the user is inferred to be a human and allowed access. • Else, user is a bot and denied access. • Humans can read the distorted and noisy text. • Current OCRs cannot read them.

  6. Background …

  7. In November 1999, slashdot.com released a poll to vote for the best CS College in the US. • Students from the CMU and the MIT created bots that repeatedly voted for their respective colleges. • This incident created the urge to use CAPTCHAs for such online polls to ensure that only human users are able to take part in the polls. • Altavista first used a crude CAPTCHA in their sites. • Resulted in 95% spam reduction. • Yahoo partnered CMU to counter these threats in Messenger chat service. • Luis von Ahn and Manuel Blum of CMU trademarked CAPTCHA in 2000.

  8. Why CAPTCHA was needed ? • Sabotage of online polls. • Spam emails. • Abusing free online accounts. • Tampering with rankings on recommendation systems (like EBay, Amazon).

  9. So, CAPTCHA is … • A program that can generate and grade tests that: • Most humans can pass. • Current computer programs cannot pass.

  10. What is Turing test?

  11. Turing test is … • Proposed by Alan Turing. • To test a machine’s level of intelligence. • Human judge asks questions to two participants, one is a machine, he doesn’t know which is which. • If judge can’t tell which is the machine, the machine passes the test. • CAPTCHA employs a reverse Turing test, • judge = CAPTCHA program, • participant = user, • if user passes CAPTCHA, he is human. • if user fails, it is a machine.

  12. Classification …

  13. CAPTCHA are of … 3 types :- CAPTCHA Text Based Audio Based Graphics Based MSN Passport Service Bongo PIX Gimpy Ez-Gimpy

  14. Text Based CAPTCHA …

  15. Simple, normal language questions: • What is sum of three and thirty-five? • If today is Saturday, what is day after tomorrow? • Which of mango, table, water is a fruit? • Very effective, needs a large question bank. • Cognitively challenged users find it hard.

  16. Gimpy … • Designed by Yahoo and CMU. • Picks up 10 random words from dictionary and distorts, fills with noise. • User has to recognize at least 3 words. • If user is correct, he is admitted.

More Related