Docstoc

CAPTCHA (PowerPoint)

Document Sample
CAPTCHA (PowerPoint) Powered By Docstoc
					CAPTCHA   What humans can do,
          But computers can not.
CAPTCHA, the Acronym
     Completely
     Automated
     Public
     Turing Test to Tell
     Computers and
     Humans
     Apart
CAPTCHA – literal meaning
     Completely--- Whole
     Automated--- made by machine
     Public--- universally known also easy
      for hackers to break it
     Turing Test to Tell--- test presented
      by Alan Turing
     Computers and
     Humans
     Apart
CAPTCHA Origins
     1997: Andrei Broder at AltaVista
      wanted to prevent bots from
      automatically submitting sites for
      indexing
     He decided to add a test to the
      submission page
     He reversed Brother scanner OCR
      optimization techniques
     2000: Luis von Ahn, Manuel Blum &
      John Langford at CMU coined term
      CAPTCHA
CAPTCHA: Deciding Human or Bot?
     A puzzle or problem that is easy for
      humans to solve and very difficult for
      computers
     If the puzzle is solved correctly, you
      are considered human and can
      continue
Basic two types
     Printed CAPTCHA




     H-CAPTCHA
Printed CAPTCHA
     Printed CAPTCHA is difficult to break
     Lots of algorithms are available to
      generate these
     Humans cannot identify these very
      easily
     Two major types are there viz. Baffle
      text,Pessimal print.
Baffle Text image
      Developed by Monica Chew and
       Henry Baird
      Uses pronounceable English
       characters with masking that are not
       present in English dictionary
Pessimal Print Image
      Developed by Allison Coates and
       Henry Baird and Richard Fateman
      Uses the degradation model
       simulating physical defects caused by
       printing and scanning of printed text
Handwritten CAPTCHA
     less frequently used because human
      can easily identify the handwriting
      rather than text images
     Use of transformations by adding
      lines,arcs,circles etc.
Example showing H-CAPTCHA
Types of Printed CAPTCHA
      GIMPY
      BONGO
      PIX
      KittenAuth
      Face Recognition
      Audio
      Logic Puzzles
GIMPY
    Randomly chooses 7 words from a
     dictionary
    Distorts the words using a variety of
     techniques
    Human must correctly type 3 of the
     words to pass the test
    In the real world, most applications
     only test for a single word (EZ-Gimpy)
GIMPY Examples


                      EZ-GYMPY




                 R-GIMPY
BONGO
    A visual recognition problem
    Two sets of shapes with a
     distinguishing characteristic
    Must choose which set the shape
     belongs to
PIX
       A database of labeled images of
        recognizable objects
       Randomly chooses an object and
        displays N pictures of it
       Must correctly identify the object
       Pictures are distorted
KittenAuth
      “The Cutest Human Test”
      A 3x3 matrix of cute animals
      Choose the 3 kittens
      Strategy is to use
       animals that look
       similar to kittens
Face Recognition CAPTCHA
Audio CAPTCHA
     Pick a word or a sequence of numbers
      at random
     Render them into an audio clip using a
      TTS software
     Distort the audio clip
     Ask the user to identify and type the
      word or numbers
Logic Puzzles
      Easy trivia questions
      Example: Which of the following is a
       bird? Elephant, Tiger or Robin,Cons
          Difficult to create a big enough database
           of these questions
          Difficult for ESL users / international
           users
Breaking CAPTCHA
       Most text based CAPTCHAs have been
        broken by software
         OCR
         Segmentation




       Other CAPTCHAs were broken by
        streaming the tests for unsuspecting
        users to solve.
Uses of CAPTCHA
     Online polls
     Free e-mail services
     Search engine bots
     Prevention to Worms and spams
     Preventing dictionary attack
      etc.
Properties
        CAPTCHA should be automatically generated
         and graded
        Test can be taken quickly and easily by human
         users
        Test will accept virtually all human users and
         reject software agents
        Test will resist automatic attack for many years
         despite the technology advances and prior
         knowledge of algorithms
Free Email Registration
      Hotmail Registration




      Yahoo! Registration
Final Thoughts
     They  are crucial to preventing bot
      attacks
     Hopefully, they will become more
      user-friendly to people with
      disabilities (visual, mental)
     CAPTCHA’s are mainly produced from
      AJAX and PHP technology
     Various algorithms are present
     Use of XML
Different CAPTCHA’s
                    PHP

•PHP – originally known as Personal Home Page
•It’s a Hypertext Preprocessor
•It is a scripting lang. Used to create dynamic web
pages.
•With syntax from C,JAVA,perl etc PHP code is
embedded within HTML pages for server side
execution.
                  OCR
(Optical Character Recognition) The machine
recognition of printed characters. OCR systems can
recognize many different OCR fonts, as well as
typewriter and computer-printed characters.
Advanced OCR systems can recognize hand printing.
When a text document is scanned into the computer, it
is turned into a bitmap, which is a picture of the text.
OCR software analyzes the light and dark areas of the
bitmap in order to identify each alphabetic letter and
numeric digit. When it recognizes a character, it
converts it into ASCII text. Hand printing is much
more difficult to analyze than machine-printed
characters. Old, worn and smudged documents are
also difficult. Scanning documents and processing
them with OCR is sometimes as much an art as it is a
OCR
      Segmentation

It is nothing but Image Processing
Pixel based Segmentation
Model based Segmentation
Multi-scale Segmentation
Semi-automatic Segmentation
            Validators

Types of validators :
1) Mark up : checks web documents in format like
   HTML,XHTML etc.
2) Link validator : checks hyperlinks,useful to
   find broken links
3) CSS validator : checks stylesheet
4) RDF validator : checks RDF documents
5) Feed validator
6) P3P validator : related to protocols
Etc.
    Session Management
•Process of keeping tracks of user’s activity
across the sessions of interaction of user with
comp sys.
•When user opens some web pages and does not
do anything on that, session gets xpired.
•E.g : score watch on web site
•So after certain time when user re-login to the
page then previously xpired session gets restored.
•E.g: if user opened yahoo acc in two windows,
and after some time he\ she logged off from one
window.then user cannot use same acc from
other window, session gets xpired. User have to
re-login to acc.
 Session Management

There are types :
1) Desktop management
2) Browser management


Mainly useful for web applications

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:23
posted:3/21/2012
language:English
pages:34