CAPTCHACAPTCHA: ARE U A HUMAN: ARE U A HUMANSORRY I HAD TO SORRY I HAD TO

ASKASK

Pranaya Priyankar Mishra

B.Tech(CSE)Roll:06165GITA

AGENDAAGENDAWhat is CAPTCHA?Types of CAPTCHAWhere to use CAPTCHAs?Guidelines when making a

CAPTCHAWays to break CAPTCHAsreCAPTCHAHuman Computation Games

AGENDAAGENDAWhat is CAPTCHA?Types of CAPTCHAWhere to use CAPTCHAs?Guidelines when making a

CAPTCHAWays to break CAPTCHAsreCAPTCHAHuman Computation Games

CAPTCHACAPTCHA

Completely Automated Public Turing test to tell Computers and Humans Apart

BEGININGS. . . . .BEGININGS. . . . .

Created in 2000 for Yahoo to prevent automated e-mail account registration,

by Luis von Ahn, Manuel Blum, Nicholas Hopper and John Langford in Carnegie Mellon University.

LUIS VON AHN (LUIS VON AHN (1978 1978 - )- )

What is CAPTCHA?What is CAPTCHA?

A program that can tell whether its user is a human or a computer.

It uses a type of challenge-response test to determine that the response is not generated by a computer.

TURING TESTTURING TEST

„Standard Interpretation"

player C, the interrogator, is tasked with trying to determine which player - A or B - is a computer and which is a human.

REVERSE TURING TESTREVERSE TURING TEST

A CAPTCHA is sometimes described as a reverse Turing test, because it is

administered by a machine and targeted to a human.

So, CAPTCHA is…So, CAPTCHA is…

A program that can generate and grade tests that:

Most humans can pass;Current computer programs cannot

pass.

AGENDAAGENDAWhat is CAPTCHA?Types of CAPTCHAWhere to use CAPTCHAs?Guidelines when making a

CAPTCHAWays to break CAPTCHAsreCAPTCHAHuman Computation Games

TYPE:EARLY CAPTCHATYPE:EARLY CAPTCHAGenerated by the EZ-Gimpy and

Gimpy programUsed previously on Yahoo!

Type: Improved Type: Improved CAPTCHA CAPTCHA

high contrast for human readability; medium, per-character perturbation; random fonts per character; low background noise;

Type: A modern Type: A modern CAPTCHACAPTCHA

rather than attempting to create a distorted background and high levels of warping on the text;

focus on making segmentation difficult by adding an angled line;

Type: A modern Type: A modern CAPTCHACAPTCHA

another way to make segmentation difficult is to crowd symbols together;

this can be read by humans but cannot be segmented by bots;

Other Types of Other Types of CAPTCHACAPTCHAAnimated CAPTCHAs

3D CAPTCHA

ASCII art

Reverse CAPTCHA "Leave this field blank"

OTHER………OTHER………

Distinguish pictures of dogs from catsVisual Puzzle(BONGO)Choose a word that relates to all the

images(PIX)Trivia questions Math and word problems 3D Object CAPTCHASolve failed OCR inputs(reCAPTCHA)Audio CAPTCHAVideo CAPTCHA

Other: Distinguish Other: Distinguish picturespictures Microsoft Asirra (Animal Species Image

Recognition for Restricting Access); KittenAuth Project .

OtherOther: : Mathematical Mathematical CAPTCHA CAPTCHA

Other: 3D Object Other: 3D Object CAPTCHACAPTCHA

You must enter them in the exact sequence listed:

• The Head of the Walking Man,

• The Vase,• The Back of the

Chair.

AGENDAAGENDAWhat is CAPTCHA?Types of CAPTCHAWhere to use captchas?Guidelines when making a

CAPTCHAWays to break CAPTCHAsreCAPTCHAHuman Computation Games

WHERE TO USE CAPTCHAsWHERE TO USE CAPTCHAs

Worms and SpamPreventing Comment Spam in BlogsProtecting Email Addresses From

ScrapersOnline PollsProtecting Website RegistrationPreventing Dictionary AttacksSearch Engine BotsBook Digitization

AGENDAAGENDA

What is CAPTCHA?Types of CAPTCHAWhere to use CAPTCHAs?Guidelines when making a

CAPTCHAWays to break CAPTCHAsreCAPTCHAHuman Computation Games

GUIDELINES……GUIDELINES……

Image SecurityScript Level Security.Security Even After Wide-Spread

AdoptionAccessibility.(Implement Audio

Captcha)

GUIDELINES:GUIDELINES: ACCESIBILITYACCESIBILITYWorst CAPTCHAs:

AGENDAAGENDAWhat is CAPTCHA?Types of CAPTCHAWhere to use CAPTCHAs?Guidelines when making a

CAPTCHAWays to break CAPTCHAsreCAPTCHAHuman Computation Games

Ways to break CAPTCHAsWays to break CAPTCHAs

Exploiting bugs in the implementation that allow the attacker to completely bypass the CAPTCHA;

Improving Character Recognition software (OCR – Optical Character Recognition );

Using cheap human labor to process the tests (sweatshops).

BreakBreak: Character : Character RecognitionRecognition

Programs that have the following functions:◦Extraction of the image from the web page ◦Removal of background clutter, for

example with color filters and detection of thin lines;

◦Segmentation, i.e. splitting the image into regions each containing a single letter;

◦Identifying the letter for each region.

Attacks – Attacks – EZ-Gimpy EZ-Gimpy 20002000 Yahoo's early CAPTCHA called "EZ-Gimpy“; The program picks a word from a

dictionary, and produces a distorted and noisy image of the word;

Algorithm for breaking EZ-Gimpy (92%):

1. Locate possible letters at various locations;

2. Construct graph of consistent letters;

3. Look for plausible words in the graph.

Attacks – Attacks – EZ-Gimpy 2000EZ-Gimpy 2000

EZ-Gimpy

Possible Letters

Graph of Letters

Plausible Words

Attacks – Attacks – SimpleOCR Engine SimpleOCR Engine 20022002

AGENDAAGENDAWhat is CAPTCHA?Types of CAPTCHAWhere to use CAPTCHAs?Guidelines when making a

CAPTCHAWays to break CAPTCHAsreCAPTCHAHuman Computation Games

reCAPTCHA(2007)reCAPTCHA(2007)New form of CAPTCHA that also

helps digitize books;The words displayed to the user

come directly from old books that are being digitized;

Words that OCR could not identify;

reCAPTCHAreCAPTCHA Pairs an unknown word with a known one; Distorts them both and puts a line through

them and then sent them to be proofread; Respondent answers both elements:

• half of effort validates the challenge; • the other half is captured as work.

reCAPTCHAreCAPTCHA

AGENDAAGENDA

What is CAPTCHA?Types of CAPTCHAWhere to use CAPTCHAs?Guidelines when making a

CAPTCHAWays to break CAPTCHAsreCAPTCHAHuman Computation Games

HUMAN COMPUTATION HUMAN COMPUTATION GAMESGAMES

ESP GameTag A Tune GameMatchin GameSquigl GameVerbosity Game

ESP GAMEESP GAMEPlayer 1

Guessing: CARGuessing : HATGuessing: KIDSuccess!You agree on CAR

Player 2

Guessing : BOYGuessing : CARSuccess!You agree on CAR

TAG A TUNE GAMETAG A TUNE GAME

MATCHIN GAMEMATCHIN GAME

SQUIGL GAMESQUIGL GAME

VERBOSITY GAMEVERBOSITY GAME

REFERANCESREFERANCES

www.captcha.netwww.recaptcha.netwww.howstuffworks.comwww.youtube.com

PREDICTIONS……PREDICTIONS……

The CAPTCHA spam arms race will lead to the creation of ARTIFICIAL INTELLIGENCE……

QUERIES ? QUERIES ?