A captcha is a program that can generate and grade tests that: (A) most humans can pass, but (B) current computer programs can’t pass. Such a program can be used to differentiate humans from computers and has many applications for practical security, including (but not limited to)

1. What Computers
Cannot Do
Which Humans
Can Do???

2. Can’t Can’t Calculate Can’t Teach
A B C
Can’t Read
Distorted Text
Secret Answer D
D

3. This
INABILITY
of Computers
was seen as an
OPPORTUNITY
to solve
Big Problems

4. WEB APPLICATION SECURITY
USING
Presented by :
Komal Jadhav

5. Agenda
OBJECTIVES AND SCOPES
PROBLEM DEFINITION
TYPES OF CAPTCHA
ADVANTAGES AND DISADVANTAGES
HARDWARE AND SOFTWARE
REQUIREMENTS
APPLICATIONS
WORKFLOW
INTRODUCTION
LITERATURE SURVEY

7. CAPTCHA – literal meaning
• Completely --- Whole
• Automated --- made by machine
• Public --- universally known also easy
for hackers to break it
• Turing Test to --- test presented by Alan
Tell Turing
• Computers and
• Humans
• Apart

8. ORIGIN
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.
Primitive CAPTCHAs seem to have been developed in 1997 by
Andrei Broder, Martin Abadi, Krishna Bharat, and Mark
Lillibridge to prevent bots from
adding URLs to their search engine.
Luis von Ahn
Manuel Blum

10. Why CAPTCHA was needed???
To prevent the following :-
• Multiple votes in online polls
• Worms and Spam e-mails
• Search engine BOTs
• Preventing dictionary attacks(password
cracking)
• Tampering with rankings on recommendation
systems (e.g. e-bay, amazon etc.)

11. Online Poll In 1999-
MIT- 21156 voted
CMU – 21036 voted
AND……
Every Other College with less than
1000……….!!!!!!

13. Turing Test
„Standard Interpretation"
player C, the interrogator,
is tasked with trying to
determine which player
- A or B - is a computer
and which is a human.

14. Reverse Turing Test
A CAPTCHA is
sometimes described
as a reverse Turing
test, because it is
administered by a
machine and
targeted to a human.

15. So, CAPTCHA is…
A program that can generate and
grade tests that:
• Most humans can pass;
• Current computer programs
cannot pass.

17. TEXT BASED CAPTCHA
IMAGE BASED CAPTCHA
In this CAPTCHA we are Combining
numbers ,
alphabets and also special character in
which we use various fonts.
Using combination of all these we
generate a CAPTCHA which is difficult
for machine to identify
In these CAPTCHA ,user has to choose
image
based on the question ask by system
captcha

18. AUDIO BASED CAPTCHA
In these we provide audio to user by
which user has enter the text
according to voice.
VIDEO BASED CAPTCHA
In these we provide video in which
there are some hidden word or
number is present . User has to
enter this words.

19. PUZZLE BASED CAPTCHA
In these CAPTCHA puzzle is divided into
chunks . User is suppose to combine this
chunks so as to they fit into a given
appropriate chunks of the puzzle.
MATH BASED CAPTCHA
In these various math problems are
given using basic fundamentals . And
user has to give correct answer.

20. GIMPY CAPTCHA
FACE BASED CAPTCHA
In these three and four words are combine
with each other and user has to choose
two or three proper word from that image.
In these we provide face image and
user has to click on same images
given in captcha.

21. DEVNAGRI CAPTCHA
In these we provide image in
which 2 words are provide and
user has to check correct word

23. Advantages:
•Distinguishes between a human and a machine
•Makes online polls more legitimate
•Reduces spam and viruses
•Makes online shopping safer
•Diminishes abuse of free email account services
Disadvantages:
•Sometimes very difficult to read
•Are not compatible with users with disabilities
•Time-consuming to decipher
•Technical difficulties with certain internet browsers
•May greatly enhance Artificial Intelligence

25. HARDWARE REQUIRED :
1. Minimum 1GB Ram
2. Processor 1.2 GHz
3. Internet connection
4. 16GB hard disk
SOFTWARE REQUIRED :
1. Language java
2. OS – windows , Linux
3. IDE-Eclipse
4. Database-Sqlserver 2008

29. Access to the website
1.
Captcha
phprandom
values
5.
User submit the
challenge code
7.
Valid code
redirects to the
website services
2.Send session values
3.Call image
php/GD library
function
4.Display secure form/captcha challnge
6.Failed or refresh page go to step 2
Redirect to the next stage
CAPTCHA FRAMEWORK :

30. Gimpy based captcha
Holistic algorithm :
In this algorithm, two to three words are mixed with each
other and form a patch.
User has to choose that correct words from the patch
Given in captcha.
In this we construct shape contexts that are eliptical in shape
with some word with cahnged fonts.
This can be possibly done only by human not by machine.
this is the main motive of holistic algorithm.
This can give better security.

31. START
Vary the size and font of words and
form a patch
Combination of two-three words
Convert code into image with
background
Associate random query with
code
Answer of code & query is stored in session variable

32. If user
input=session
Successfull
y Login
STOP
Ask user to provide input for test
yes No
Display code & corresponding query
in same session

33. Video based captcha algorithm :
CANNY EDGE DETECTION ALGORITHAM
Canny edge detection is a technique to extract useful structural
information from different vision objects and dramatically reduce
the amount of data to be processed.
In these we used Noise reduction by smoothing and Finding
Gredients.

34. Start
Pass video
Frame Creation
Apply threshold over selected point
Pass same video again
Frame Extract
If point is
matched
Proceed to transaction
stop
Bot
Discard Transaction
No
No
Yes

36. Usability issues:
• W3C mandates Web to be accessible to all people.
• Some CAPTCHAs are inaccessible to visually impaired,
cognitively challenged people
Compatibility issues:
• JavaScript may need to be activated in browsers.
• Some may need Adobe Flash plugin installed

37. INTERESTING FACTS
• Alta vista first used a crude CAPTCHA in
their Sites.
• Resulted in 95% spam reduction.
• Yahoo partnered CMU to counter these
threats in Messenger chat service
.
• AI knowledge is advanced if CAPTCHAs are
broken.