presentation on captcha by sachin jain
TRANSCRIPT
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