Presentation on CAPTCHA by Sachin Jain
Post on 07-Apr-2017
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BMS Institute of Technology&Management
Presentation OnCAPTCHAPresented by:Sachin JainMCA 1st sem
Guided by:Mr. GaneshAsst prof. Department of MCABMSIT&M
AGENDAIntroductionOriginHow to generate CAPTCHATypesApplicationsAdvantagesDisadvantagesConclusionReferences
INTRODUCTIONCAPTCHA-Completely Automated Public Turing test to tell Computer and Human ApartA 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.
The most common type of CAPTCHA was first invented in 1997 by Mark D. Lillibridge, Martin Abadi ,Krishna Bharat, andAndrei 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 byLuis von Ahn,Manuel Blum, Nicholas J. Hopper, andJohn Langford.
HOW TO GENERATEPicks 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
Text Based CAPTCHAs
Gimpy Ez-gimpyBaffle textSimards HIP (MSN)
Graphics Based CAPTCHAs
Audio or Sound Based CAPTCHAsTYPES 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.
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
Its provided for Microsoft MSN services.Uses 8 characters.Wraping is used to distort.It is very strongly implemented and hasnt been broken.
Fig:- MSN CAPTCHA
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
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
Fig:- pix CAPTCHA
ApplicationsProtecting Web RegistrationPreventing comment spamSearch engine botsPreventing Dictionary Attacks
Distinguishes between a human and a machineMakes online polls more genuine.Reduces spam and virusesMakes 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.
CAPTCHAs are an effective way to counter bots and reduce spam.Some issues with current implementations represent challenges for future improvements.Conclusion
References http://www.slideshare.net/search/slideshow?searchfrom=header&q=captcha http://www.slideshare.net/search/slideshow?searchfrom=header&q=captcha http://www.slideshare.net/search/slideshow?searchfrom=header&q=captcha http://www.slideshare.net/search/slideshow?searchfrom=header&q=captcha http://www.slideshare.net/search/slideshow?searchfrom=header&q=captcha  https://en.wikipedia.org/wiki/CAPTCHA http://www.nytimes.com/2002/12/10/science/human-or-computer-take-this-test.html http://www.captcha.net/captcha_cacm