Captcha

 

                              

CAPTCHAs (Completely Automated Public Turing test to tell Computers and Humans Apart) SUBMITTED BY : Niharjyoti Sarangi Regd . No . 0601101232 Information Technology

TOPICS PRESENTED INTRODUCTION ORIGIN OF CAPTCHAS APPLICATIONS OF CAPTCHAS EXAMPLES OF CAPTCHAS CHARACTERISTICS OF CAPTCHAS CRITICISMS CONCLUSION

INTRODUCTION 

A CAPTCHA is a program that can generate and grade tests that:

 Most humans can pass ,but Current computer programs can’t pass.  

Such a program can be used to differentiate humans from computers.

CAPTCHA tests are dynamically generated by

computers , in contrast to the standard Turing test which is administered by a human.

 This characteristic allows them to be widely used for

practical security reasons.

ORIGIN OF CAPTCHAS 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. 

APPLICATIONS ONLINE POLLS FREE EMAIL SERVICES SEARCH ENGINE BOTS SHOPPING AGENTS

EXAMPLES OF CAPTCHAs 1.Based on difficulty of reading distorted text



e.g.1:Gimpy  Selects 7-10 words out of a dictionary and renders a distorted image of the words. The test can be passed by recognizing any 3 of the words. 



Based on difficulty of reading distorted text (contd..) e.g.2:EZ-Gimpy  Simplified version of Gimpy where the test can be passed by recognizing the distorted image of a single word  

2. Based on pattern recognition e.g. Bongo  Two series of blocks with different patterns are presented. The test is passed by recognizing which one of the two series a given block belongs to. 





3. Based



on sound recognition

The program picks a word or a sequence of numbers at random, renders the word or the numbers into sound clip and distorts the sound clip. It then presents the distorted sound clip to its user and asks them to enter the contents of the sound clip.

CHALLENGES IN CAPTCHAS 

Reading-based CAPTCHAS challenges typically comprises:





Segmentation challenges  Recognition challenges 

CHARACTERISTICS OF CAPTCHAS

Fully automated requiring little human maintenance or intervention in administering the test. Algorithms used to create CAPTCHAs are made public. Discovery of the algorithm cannot be used to break it. 

P stands for PUBLIC.WHY? Hackers : Once a hacker breaks into the system

and finds this secret data , the captcha ceases to be secure forever. Reverse Engineering and Analysis: If the code weren’t public, The Adversary could still earn how a captcha works by simply taking many of the tests generated by it. We’re doing AI:. If a captcha is broken, then a previously unsolved AI problem is solved.

CRITICISMS Visually impaired people may not be able to pass the

test even though they are eligible users. Accessibility is greatly reduced as the CAPTCHAs become more complex. Some CAPTCHAs lose their readability. In the case of using logic puzzles, users with cognitive disabilities may have trouble. In heuristic methods, if pattern-matching algorithms can't find good heuristics, then this is not a good solution.  

LAUNDRY ATTACKS  A laundry attack takes advantage of unsuspected

users who will eventually solve a CAPTCHA in favor of the attacker, while they think that the CAPTCHA is solved for their own service.

 The laundering of a CAPTCHA can be implemented

by using the bots as intermediates.

SOLUTION TO LAUNDRY ATTACKS Current forms of CAPTCHAs are subject to laundry

attacks because of their static nature. They are pictures that contain the puzzle and the user has to complete the answer to a text field outside the puzzle .That is the solution of the CAPTCHA is static and can be transferred between nodes. What we need to take is to transform a CAPTCHA test from a static picture to a dynamic application. That is, the answer must be completed inside the puzzle.

CONCLUSION CAPTCHAs prove a good security measure if they are

strong enough and more accessible. There is still room for improvement in the non-visual type of CAPTCHAs. A CAPTCHA implies a win-win situation: either the CAPTCHA is not broken and there is a way to differentiate humans from computers, or the CAPTCHA is broken and a useful AI problem is solved.

REFERENCES www.wikipedia.org Telling Humans and Computers Apart by Luis von

Ahn, Manuel Blum. Enhanced CAPTCHAS by Elias Athanasopoulos and Spiros Antonatos. CAPTCHA: Using Hard AI Problems For Security by Luis von Ahn, Manuel Blum.

THANK YOU QUERIES?