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CAPTCHA
Your security partner
Contributors:
Jakir Hossain
Md.Tanvir Hossain
Department of Computer Science and Engineering
Daffodil International University-DIU
Dhaka, Bangladesh
Agenda:
■ Introduction
■ History behind CAPTCHAs
■ Types of CAPTCHA
■ Where to use CAPTCHAs
■ Re-Captcha
■ Benefit of using CAPTCHAs
■ Conclusion
Introduction
■ Completely Automated PublicTuring test to tell Computers and
HumansApart.
■ A program that can tell whether its user is a human or a computer.
Example: Filling out a form
Google uses CAPTCHA forGmail accounts:
History behind CAPTCHA
■ Captcha word comes from capture.
■ it is also known as reverse turing test.
■ About 200 million CAPTCHAs are solved by humans around the world
every day.
■ First developed byAltaVista in 1997.
■ The term coined in 2000 by Luis von Ahn, Manuel Blum and Nicholas j.
Hopper of Carnegie Mellon university and john Langford of IBM.
Types of CAPTCHAs
■ Early CAPTCHAs
■ Improved CAPTCHA
■ Modern CAPTCHA
■ Animated CAPTCHA
■ 3D CAPTCHA
Types Of CAPTCHAs
■ ASCIIArt
■ Distinguish pictures
■ MathematicalCAPTCHA
■ 3D Object CAPTCHA
Where to use CAPTCHAs
■ Preventing Comment Spam in Blogs.
■ Protecting Email Addresses From Scrapers: Mechanism to hide your email address,
require users to solve a CAPTCHA before showing your email address
■ Online Polls: You cannot trust the results of an online roll because anybody could just
write a program to vote for their favorite option thousands of times.
Where to use CAPTCHAs
■ Protecting Website Registration: (E-mail services:Yahoo, Microsoft, Google)
■ Preventing Dictionary Attacks (in password systems): Prevent a computer to iterate
through the entire space of passwords by requiring it to solve a CAPTCHA after a
certain number of unsuccessful logins.
■ Search Engine Bots: It is sometimes desirable to keep webpages unindexed to
prevent others from finding them easily.
Re-Captcha
■ Free captcha service that helps to digitize books, newspaper and old time radio shows.
■ Two words are shown, one word is known as control word and another one is known as
a questionable word.
■ System assumes that if human types the control word correctly, then the questionable
word is also correct.
Benefits
■ The database already exists and is public.
■ The database is constantly being updated and maintained.
■ Adding “concrete objects” to the dictionary is virtually instantaneous.
■ Distortion prevents caching hacks.
■ Quick expiration limits streaming hacks.
Conclusion
■ Captchas are an effective way to and reduce spam
■ They serves dual purpose- help advance AI knowledge
■ Applications are varied from stopping bots to character reorganization
and pattern matching.
ThankYou

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Captcha

  • 3. Contributors: Jakir Hossain Md.Tanvir Hossain Department of Computer Science and Engineering Daffodil International University-DIU Dhaka, Bangladesh
  • 4. Agenda: ■ Introduction ■ History behind CAPTCHAs ■ Types of CAPTCHA ■ Where to use CAPTCHAs ■ Re-Captcha ■ Benefit of using CAPTCHAs ■ Conclusion
  • 5. Introduction ■ Completely Automated PublicTuring test to tell Computers and HumansApart. ■ A program that can tell whether its user is a human or a computer.
  • 6.
  • 7. Example: Filling out a form Google uses CAPTCHA forGmail accounts:
  • 8. History behind CAPTCHA ■ Captcha word comes from capture. ■ it is also known as reverse turing test. ■ About 200 million CAPTCHAs are solved by humans around the world every day. ■ First developed byAltaVista in 1997. ■ The term coined in 2000 by Luis von Ahn, Manuel Blum and Nicholas j. Hopper of Carnegie Mellon university and john Langford of IBM.
  • 9. Types of CAPTCHAs ■ Early CAPTCHAs ■ Improved CAPTCHA ■ Modern CAPTCHA ■ Animated CAPTCHA ■ 3D CAPTCHA
  • 10. Types Of CAPTCHAs ■ ASCIIArt ■ Distinguish pictures ■ MathematicalCAPTCHA ■ 3D Object CAPTCHA
  • 11. Where to use CAPTCHAs ■ Preventing Comment Spam in Blogs. ■ Protecting Email Addresses From Scrapers: Mechanism to hide your email address, require users to solve a CAPTCHA before showing your email address ■ Online Polls: You cannot trust the results of an online roll because anybody could just write a program to vote for their favorite option thousands of times.
  • 12. Where to use CAPTCHAs ■ Protecting Website Registration: (E-mail services:Yahoo, Microsoft, Google) ■ Preventing Dictionary Attacks (in password systems): Prevent a computer to iterate through the entire space of passwords by requiring it to solve a CAPTCHA after a certain number of unsuccessful logins. ■ Search Engine Bots: It is sometimes desirable to keep webpages unindexed to prevent others from finding them easily.
  • 13. Re-Captcha ■ Free captcha service that helps to digitize books, newspaper and old time radio shows. ■ Two words are shown, one word is known as control word and another one is known as a questionable word. ■ System assumes that if human types the control word correctly, then the questionable word is also correct.
  • 14. Benefits ■ The database already exists and is public. ■ The database is constantly being updated and maintained. ■ Adding “concrete objects” to the dictionary is virtually instantaneous. ■ Distortion prevents caching hacks. ■ Quick expiration limits streaming hacks.
  • 15. Conclusion ■ Captchas are an effective way to and reduce spam ■ They serves dual purpose- help advance AI knowledge ■ Applications are varied from stopping bots to character reorganization and pattern matching.