CAPTCHA

1
CAPTCHA

• What humans can do,
• But computers can not.

2
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?

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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

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Turing Test (2)

• If the Tester isnt able to tell whos the Human
  and whos the Computer
• gt Then the computer must be as (or even more)
  intelligent as the human being.
• CAPTCHA The Tester doesnt need to be human if
  it knows the correct answers

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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 dont want computers to
  do something

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Can we know that no computer can pass this test?

• Its wrong to believe, no computer will ever pass
  this tests
• BUT
• Its 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

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Hard Problem of the AI?

• What is a hard problem of the AI?
• A problem, the AI-Community is aware of, but
  wasnt able to solve
• So it is very hard to develop a program for it
• gt If a CAPTCHA-breaking program can be used to
  solve a hard problem of the AI, it is very hard
  to break a CAPTCHA

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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

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What kinds of CAPTCHAS exist? (1)

• Gimpy a text-based CAPTCHA

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What kinds of CAPTCHAS exist? (2)

• Bongo a shape-based CAPTCHA

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What kinds of CAPTCHAS exist? (3)

• Pix a picture-based CAPTCHA
• Eco a sound-based CAPTCHA

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Bad Computers use humans!

• Relink CAPTCHAs to human-users
• Let humans do the work, and tell them its a game!

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Resumee

• Good to secure from bad programs
• Although wanted to be broken
• gt Use new / unbroken Captchas
• Captcha A wanted race with AI-Specialists
  covered as Hackers

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Last Sentence

• Who knows, maybe one day WE arent allowed
  anymore to create an
• E-Mail-Account, because we are not
• intelligent enough...
• Thank You for your Interest!

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List of Sources

• 1 Luis von Ahn, Manuel Bluhm und John Langford.
  The Captcha Project Homepagehttp//www.captcha.n
  et
• 2 Luis von Ahn, Manuel Bluhm und John Langford.
  Telling Humans and Computers Apart
  (Automatically)http//www.cs.cmu.edu/biglou/cap
  tcha.pdf
• 3 Andrew Hodges. The Alan Turing Internet
  Scrapbookhttp//www.turing.org.uk/turing/scrapbo
  ok/test.html
• 4 Luis von Ahn. The ESP Gamehttp//www.espgame
  .org