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ACKNOWLEDGEMENT

I would like to express my sincere gratitude and appreciation to everyone who

made this seminar report possible. Most of all, I would like to thank my Seminar

Supervisor, Mr. Amit Kumar Jaiswal, Assistant Professor, Department of Computer

Science and Engineering, Ideal Institute of Technology Ghaziabad and Ms. Sumita

Verma, Lecturer, Department of Computer Science and Engineering, Ideal Institute

of Technology Ghaziabad, for their guidance in the seminar. With their knowledge

and experience, they guided me to successfully achieve my seminar objective.

I sincerely extend my thanks to, Dr. G. P. Govil, (Prof.) and Dr. Sudhir

Dawra, (Associate Prof. & Head) Department of Computer Science and Engineering,

Ideal Institute of Technology Ghaziabad, Uttar Pradesh for their encouragement and

support.

I express my sincere thanks to all my friends, my well-wishers and classmates

for their support and help during the seminar report.

ABHIMANYU SOOD Roll No. 0902810002 B. Tech. (CSE) 3rd Year (A)

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ABSTRACT

We introduce captcha, an automated test that humans can pass, but current

computer programs cannot pass: any program that has high success over a captcha can

be used to solve an unsolved Artificial Intelligence (AI) problem. We provide several

novel constructions of captchas. Since captchas have many applications in practical

security, our approach introduces a new class of hard problems that can be exploited

for security purposes. Much like research in cryptography has had a positive impact

on algorithms for factoring and discrete log, we hope that the use of hard AI problems

for security purposes allows us to advance the field of Artificial Intelligence. We

introduce two families of AI problems that can be used to construct captchas and we

show that solutions to such problems can be used for steganographic communication.

Captchas based on these AI problem families, then, imply a win-win situation: either

the problems remain unsolved and there is a way to differentiate humans from

computers, or the problems are solved and there is a way to communicate covertly on

some channels.

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CONTENTS

Certificate

Acknowledgement -------------------------------------------------------------- i

Abstract ------------------------------------------------------------------------- ii

Content ------------------------------------------------------------------------- iii

List of Figures------------------------------------------------------------------ iv

1. INTRODUCTION --------------------------------------------------------------------- 1

2. TYPES OF CAPTCHAS ------------------------------------------------------------- 5

3. APPLICATION ----------------------------------------------------------------------- 12

4. CONSTRUCTING CAPTCHA ----------------------------------------------------- 15

5. BREAKING OF CAPTCHA -------------------------------------------------------- 24

6. ISSUES WITH CAPTCHA --------------------------------------------------------- 30

Conclusion ------------------------------------------------------------------- 33

Reference --------------------------------------------------------------------- 34

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List of Figures

1. Fig 2.1 Gimpy CAPTCHA ------------------------------------------------------------ 6

2. Fig 2.2 Yahoo’s Ez – Gimpy CAPTCHA ------------------------------------------- 6

3. Fig 2.3 BaffleText examples ---------------------------------------------------------- 7

4. Fig 2.4 MSN Passport CAPTCHA --------------------------------------------------- 7

5. Fig 2.5 Bongo CAPTCHA ------------------------------------------------------------ 8

6. Fig 2.6 First line shows --------------------------------------------------------------- 11

7. Fig 5.1 Breaking CAPTCHAs ------------------------------------------------------- 27

8. Fig 6.1 Usability issues in text based CAPTCHAs ------------------------------- 30