Presented By Vibhute J.B. Class : M.Sc. (CS) CAPTCHA Presented By Vibhute J.B. Class : M.Sc. (CS)

Introduction History Types of Captcha Process of Captcha Breaking Captcha Re-Captcha Benefits Reference

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. Captcha requires that the user types letters or digits from distorted image appears on screen.

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.

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

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

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

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

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

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

The Process Generate CAPTCHA Align CAPTCHA Cut Captcha Transform CAPTCHA Decode CAPTCHA

Generate CAPTCHA CAPTCHA generated with our Mathematical code.

Align CAPTCHA Remove gridlines. Undo angle of rotation

Cut CAPTCHA Cut CAPTCHA cut into 5 pieces.

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

Breaking CAPTCHAs 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.

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

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

Re-Captcha Image

Benefits The database already exists and is public. The database is constantly being updated and maintained. Adding “concrete object” to the dictionary is virtually instantaneous. Distortion prevents caching hacks. Quick expiration limits streaming hacks.

Reference http://www.captcha.net/ http://www.blogtoplist.com/rss/captcha.html http://www.gnu.org/licenses/gpl.html http://www.white-hat-web-design.co.uk/articles/php-captcha.php

Thank You……..