CAPTCHA

04/20/23 Matthias Neubauer

CAPTCHA

What humans can do,

But computers can not.


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?


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


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


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


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“


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


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


What kinds of CAPTCHAS exist? (1)

Gimpy – a text-based CAPTCHA



Bongo – a shape-based CAPTCHA



Pix – a picture-based CAPTCHA

Eco – a sound-based CAPTCHA


„Bad“ Computers use humans!

Relink CAPTCHAs to human-users

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


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


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!


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

CAPTCHA

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Transcript of CAPTCHA