BMS Institute of Technology&

Management

Presentation On

CAPTCHAPresented by:Sachin JainMCA 1st sem

Guided by:Mr. GaneshAsst prof. Department of MCABMSIT&M

AGENDA

• Introduction• Origin• How to generate CAPTCHA• Types• Applications• Advantages• Disadvantages• Conclusion• References

INTRODUCTION CAPTCHA-Completely Automated Public Turing

test to tell Computer and Human Apart A CAPTCHA is a type of challenge response test

used in computing to ensure that response is not generated by a computer.

A common type of CAPTCHA requires that the user type letters or digits from the distorted image that appears on the screen.

ExamplesExamples

ORIGIN The most common type of CAPTCHA was first

invented in 1997 by Mark D. Lillibridge, Martin Abadi , Krishna Bharat, and Andrei Z. Broder.

This form of CAPTCHA requires that the user type the letters of a distorted image, sometimes with the addition of an obscured sequence of letters or digits that appears on the screen.

The term was coined in 2003 by Luis von Ahn, Manuel Blum, Nicholas J. Hopper, and John Langford.

HOW TO GENERATE

Picks a random string of letters:

o m a g

Renders it to a distorted image:-

TYPE THE CHARACTERS THAT APPEAR IN THE IMAGE

..... and generates a test

o Text Based CAPTCHAs

Gimpy Ez-gimpy Baffle text Simard’s HIP (MSN)

oGraphics Based CAPTCHAs

Bongo Pix

oAudio or Sound Based CAPTCHAs

TYPES OF CAPTCHA

Gimpy: Originally designed by Yahoo and CMU. Based on human ability to read heavily

distorted and corrupted text. Picks up 10 random words from dictionary

and distorts. User has to recognize at least 3 words. If user is correct, he is admitted.

Fig:-Gimpy CAPTCHA[1]

Ez-Gimpy:A modified version of Gimpy. Used in Yahoo Messenger Service.It contains only one random character string.The word is random and not picked from the

dictionary.

Fig:- Ez-Gimpy CAPTCHA[2]

Its provided for Microsoft MSN services.

Uses 8 characters.

Wraping is used to distort.

It is very strongly implemented and hasn’t been

broken.

MSN CAPTCHA

Fig:- MSN CAPTCHA[3]

Following steps are followed in BONGO CAPTCHAS as:

a)Display two series of blocksb)User must find the characteristic that sets the two series apartc)User is asked to determine which series each of four single blocks belongs to.

To which side does the block on the bottom belong?

BONGO

Fig:- Bongo CAPTCHA[4]

Uses a large database of labeled imagesIt shows a set of images, user has to recognize the

common feature among those.

Ex:- Pick the common characteristic among the following four pictures

PIX

Fig:- pix CAPTCHA[5]

Applications

Protecting Web Registration Preventing comment spam Search engine bots Preventing Dictionary Attacks

• Distinguishes between a human and a machine

• Makes online polls more genuine.• Reduces spam and viruses• Makes online shopping safer.• Diminishes abuse of free email account

services.

• Sometimes very difficult to read.• Are not compatible with users with disabilities.• Time-consuming to decipher.• Technical difficulties with certain internet

browsers.

Advantages

Disadvantages

CAPTCHAs are an effective way to counter bots and reduce spam.Some issues with current implementations represent challenges for future improvements.

Conclusion

References

[1] http://www.slideshare.net/search/slideshow?searchfrom=header&q=captcha [2] http://www.slideshare.net/search/slideshow?searchfrom=header&q=captcha [3] http://www.slideshare.net/search/slideshow?searchfrom=header&q=captcha [4] http://www.slideshare.net/search/slideshow?searchfrom=header&q=captcha [5] http://www.slideshare.net/search/slideshow?searchfrom=header&q=captcha [6] https://en.wikipedia.org/wiki/CAPTCHA [7] http://www.nytimes.com/2002/12/10/science/human-or-computer-take-this-test.html [8] http://www.captcha.net/captcha_cacm