Captcha

CAPTCHA

CAPTCHA A CAPTCHA is a type of challenge – response

Test that response is generated by a human being or computer

CAPTCHA – Completely Automated Public Turing test to tell Computers & Humans Apart.

Why captcha was needed?

Online Polls Protecting Web Registration E–Ticketing Email Spam

Turing Test :-

To test a machine’s level of intelligence CAPTCHA employs a reverse Turing test

judge = CAPTCHA program

participant = user

if user passes CAPTCHA, he is human

if user fails , it is a machine

Types of CAPTCHAs :-

Texts CAPTCHAsGimpyEz – GimpyMSNs Passport Service CAPTCHAsAudio CAPTCHAs

Texts CAPTCHAs :-

Simple, normal questions like: What is twenty minus three?

What is the third letter in UNIVERSITY? If yesterday was a Sunday, what is today?

Gimpy :-

Designed by Yahoo & CMU(Carnegie Mellon University) Picks up 10 random words from dictionary, and

displaying them in a distorted and overlapped manner.

User has to recognize at least 3 words. If the user is correct, then he is admitted.

Ez – Gimpy :-

A modified version of Gimpy. Yahoo used this version in Messenger. Randomly picks a single word from a dictionary and

applies distortion to the text.

MSNs Passport Service CAPTCHAs :- Provided for Microsoft’s MSN services. Eight characters(upper case) and digits.  Warping is used to distort. Very strong implementation, hasn’t been broken.

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Audio CAPTCHAs :-

Consists of downloadable audio clip. User listens & enters the spoken word. Google’s audio enabled CAPTCHA

reCAPTCHA :-

Used in Google books project.

Two words are shown, the program knows the first word.

If the user enter the first word correctly, it assumes that the second unknown word will also be entered correctly.

API Key for reCAPTCHA:-

Login www.recaptcha.net with your Gmail account.

Domain Name – localhost.com

It will generate public key and private key

Public Key:6LfAIuASAABBBAl2TAmrFWlGUQyols8bqcVvI1c6

Use this in the JavaScript code that is served to your users

Private Key: 6LfAIuASAABBBFHNHH--MitbQPqnezzg3XftrX5k

Use this when communicating between your server and our server. Be sure to keep it a secret.

https://developers.google.com/recaptcha/docs/display

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