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					  CAPTCHA


             What humans can do,
             But computers can not.



30.09.2011           Matthias Neubauer
Introduction

      What does CAPTCHA mean?
            “Completely Automated Public Turing
             Test to Tell Computers and Humans
             Apart“
            Founded by Luis von Ahn, Manuel
             Bluhm, Nick Hopper and John Langford
             from Carnegie Mellon School of
             Computer Science
      What is a Turing Test?
30.09.2011                Matthias Neubauer
Turing Test (1)

      Turing: „One day, computers will be as
       intelligent as humans“
      Created a Test to prove it:
            A Tester (für Turing a person)
            2 Contestians (1 Computer, 1 Human) in
             another room than the tester
            Tester asks questions in text-form
            Answers are returned in text-form

30.09.2011                Matthias Neubauer
Turing Test (2)

      If the Tester isn`t able to tell who`s the
       Human and who`s the Computer
      => Then the computer must be as (or
       even more) intelligent as the human
       being.
      CAPTCHA: The Tester doesn`t need
       to be human if it knows the correct
       answers
30.09.2011             Matthias Neubauer
What is CAPTCHA for?

      Helps blocking automated creations of
       email-accounts
      Blocks Computers to vote
       automatically in online-polls
      Blocks Search-Engine-Bots
      and anything where humans don`t
       want computers to do something
30.09.2011           Matthias Neubauer
Can we know that no
computer can pass this test?

      It`s wrong to believe, no computer will ever
       pass this tests
      BUT:
            It`s hard do develop a computer program for
             modern machines that can pass this tests
            „Any program that can be used to break a
             CAPTCHA, can be used to solve an unsolved
             problem of the Artificial Intelligence“


30.09.2011                   Matthias Neubauer
Hard Problem of the AI?

      What is a „hard“ problem of the AI?
            A problem, the AI-Community is aware
             of, but wasn`t able to solve
            So it is very hard to develop a program
             for it
            => If a CAPTCHA-breaking program can
             be used to solve a hard problem of the
             AI, it is very hard to break a CAPTCHA

30.09.2011                 Matthias Neubauer
Why public?

      The developers WANT the hackers to
       break their CAPTCHAs
      „This is how lazy cryptographers to AI“
      The results are good, and some text-
       based CAPTCHAs are already broken



30.09.2011            Matthias Neubauer
What kinds of CAPTCHAS
exist? (1)
      Gimpy – a text-based CAPTCHA




30.09.2011           Matthias Neubauer
What kinds of CAPTCHAS
exist? (2)

      Bongo – a shape-
       based CAPTCHA




30.09.2011            Matthias Neubauer
What kinds of CAPTCHAS
exist? (3)

      Pix – a picture-based CAPTCHA




      Eco – a sound-based CAPTCHA

30.09.2011            Matthias Neubauer
„Bad“ Computers use humans!

      Relink CAPTCHAs to human-users

      Let humans do the work, and tell them
       it`s a game!




30.09.2011           Matthias Neubauer
Resumee

      Good to secure from „bad“ programs
            Although wanted to be broken
            => Use new / unbroken Captchas



      Captcha – A wanted race with AI-
       Specialists covered as Hackers

30.09.2011                Matthias Neubauer
Last Sentence

      Who knows, maybe one day WE
       aren`t allowed anymore to create an
       E-Mail-Account, because we are not
       intelligent enough...


Thank You for your Interest!

30.09.2011           Matthias Neubauer
List of Sources
      [1] Luis von Ahn, Manuel Bluhm und John Langford. The
       Captcha Project Homepage:
       http://www.captcha.net

      [2] Luis von Ahn, Manuel Bluhm und John Langford. Telling
       Humans and Computers Apart (Automatically):
       http://www.cs.cmu.edu/~biglou/captcha.pdf

      [3] Andrew Hodges. The Alan Turing Internet Scrapbook:
       http://www.turing.org.uk/turing/scrapbook/test.html

      [4] Luis von Ahn. The ESP Game:
       http://www.espgame.org


30.09.2011                    Matthias Neubauer

				
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