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PAPER PRESENTATIONPAPER PRESENTATION
ONON
‘CAPTCHA’‘CAPTCHA’
Presented By:Presented By:
EduTechLearnersEduTechLearners
www.edutechlearners.comwww.edutechlearners.com

OVERVIEWOVERVIEW
CAPTCHACAPTCHA
Completely AutomatedCompletely Automated
Public Turing Test toPublic Turing Test to
tell computers andtell computers and
Humans ApartHumans Apart

INTRODUCTIONINTRODUCTION
 Computers and Humans are apart , a technique usedComputers and Humans are apart , a technique used
by a computer to tell if it is interacting with human orby a computer to tell if it is interacting with human or
some other computer.some other computer.
 It is needed because activities such as onlineIt is needed because activities such as online
commerce transactions, search engine submissions,commerce transactions, search engine submissions,
Web polls, Web registrations, free e-mail serviceWeb polls, Web registrations, free e-mail service
registration and other automated services are subjectregistration and other automated services are subject
to software programs, or bots, that mimic theto software programs, or bots, that mimic the
behavior of humans in order to skew the results of thebehavior of humans in order to skew the results of the
automated task or perform malicious activities, suchautomated task or perform malicious activities, such
as gathering e-mail addresses for spamming.as gathering e-mail addresses for spamming.

BASCILLY WHAT A ‘CAPTCHABASCILLY WHAT A ‘CAPTCHA
DO ?DO ?
 In order to validate the digital transaction, using theIn order to validate the digital transaction, using the
CAPTCHA system the user is presented with aCAPTCHA system the user is presented with a
distorted word typically placed on top of a distorteddistorted word typically placed on top of a distorted
background. The user must type the word into a fieldbackground. The user must type the word into a field
in order to complete the process. Computers have ain order to complete the process. Computers have a
difficult time decoding the distorted words whiledifficult time decoding the distorted words while
humans can easily decipher the text. Somehumans can easily decipher the text. Some
CAPTCHAs now use pictures instead of words whereCAPTCHAs now use pictures instead of words where
the user is presented with a series of pictures andthe user is presented with a series of pictures and
asked what the common element among all of theasked what the common element among all of the
pictures is. By entering that common element, thepictures is. By entering that common element, the
user validates the transaction and the computer knowsuser validates the transaction and the computer knows
it is dealing with a human and not a bot.it is dealing with a human and not a bot.

A stack of images called from theA stack of images called from the
CAPTCHA program on YahooCAPTCHA program on Yahoo
groups.groups.

BASIC TRMINOLOGYBASIC TRMINOLOGY
 Artificial intelligence.Artificial intelligence.
 Strong artificial intelligence.Strong artificial intelligence.
 Weak artificial intelligence.Weak artificial intelligence.
 Bot.Bot.
 Turing test.Turing test.
 Challenge response test.Challenge response test.
 Spam.Spam.

ARTIFICIAL INTELLIGENCEARTIFICIAL INTELLIGENCE
 Artificial intelligence, also known as machineArtificial intelligence, also known as machine
intelligence, is defined as intelligenceintelligence, is defined as intelligence
exhibited by anything manufactured byexhibited by anything manufactured by
humans or systems .It is usually hypotheticallyhumans or systems .It is usually hypothetically
applied to general-purpose computers.applied to general-purpose computers.
 It is concerned with systems that think likeIt is concerned with systems that think like
humans, systems that act like humans, systemshumans, systems that act like humans, systems
that think rationally or systems that actthat think rationally or systems that act
rationally.rationally.

STRONG ARTIFICIALSTRONG ARTIFICIAL
INTELLIGENCEINTELLIGENCE
 Strong artificial intelligence research deals with theStrong artificial intelligence research deals with the
creation of some form of computer-based artificialcreation of some form of computer-based artificial
intelligence that can truly reason and solve problems;intelligence that can truly reason and solve problems;
a strong form of AI is said to be self-aware. In theory,a strong form of AI is said to be self-aware. In theory,
there are two types of strong AI:there are two types of strong AI:
 Human-like AI, in which the computer programHuman-like AI, in which the computer program
thinks and reasons much like a human mind.thinks and reasons much like a human mind.
 Non-human-like AI, in which the computer programNon-human-like AI, in which the computer program
develops a totally non-human sentience, and a non-develops a totally non-human sentience, and a non-
human way of thinking and reasoninghuman way of thinking and reasoning

WEAK ARTIFICIALWEAK ARTIFICIAL
INTELLIGENCEINTELLIGENCE
 Weak artificial intelligence research deals with theWeak artificial intelligence research deals with the
creation of some form of computer-based artificialcreation of some form of computer-based artificial
intelligence that can reason and solve problems onlyintelligence that can reason and solve problems only
in a limited domain.in a limited domain.
 To date, much of the work in this field has been doneTo date, much of the work in this field has been done
with computer simulations of intelligence based onwith computer simulations of intelligence based on
predefined sets of rules. Very little progress has beenpredefined sets of rules. Very little progress has been
made in strong AI. Depending on how one definesmade in strong AI. Depending on how one defines
one's goals, a moderate amount of progress has beenone's goals, a moderate amount of progress has been
made in weak AI.made in weak AI.

BOTBOT
 AA botbot is common parlance on the Internet for ais common parlance on the Internet for a
software program that is a software agent. Botssoftware program that is a software agent. Bots
interact with other network services intended forinteract with other network services intended for
people as if it was a real person. .people as if it was a real person. .
 Some bots communicate with other users of InternetSome bots communicate with other users of Internet
based services, for example via Instant Messenger orbased services, for example via Instant Messenger or
Internet Relay Chat. These chatterbots may allowInternet Relay Chat. These chatterbots may allow
people to ask questions in plain Englishpeople to ask questions in plain English
 The term bot is used frequently in videogames,The term bot is used frequently in videogames,
referring to computer controlled enemies in areferring to computer controlled enemies in a
multiplayer game that simulate the actions of amultiplayer game that simulate the actions of a
human player. These bots are used in training, beforehuman player. These bots are used in training, before
playing over Internet.playing over Internet.

TURING TESTTURING TEST
 In 1950, the mathematician Alan Turing suggested that aIn 1950, the mathematician Alan Turing suggested that a
computer could earn the label "intelligent" if it could foolcomputer could earn the label "intelligent" if it could fool
a person into thinking he or she was communicating witha person into thinking he or she was communicating with
another person instead of a machine.another person instead of a machine.
 It's become a major problem on the Internet, as has theIt's become a major problem on the Internet, as has the
use of 'bots to register for e-mail addresses that are lateruse of 'bots to register for e-mail addresses that are later
used to send unwanted advertisements, or spam, to e-mailused to send unwanted advertisements, or spam, to e-mail
users.users.
 In a 1950 paper, he described what he called the ImitationIn a 1950 paper, he described what he called the Imitation
game, now known as the Turing Test, in which a persongame, now known as the Turing Test, in which a person
tries to distinguish between human and computer testtries to distinguish between human and computer test
subjects by asking them each a series of questions. If thesubjects by asking them each a series of questions. If the
person can't distinguish between the computer and theperson can't distinguish between the computer and the
human, the computer is deemed to be intelligent. There is ahuman, the computer is deemed to be intelligent. There is a
prize of $100,000 for a computer that can pass the Turingprize of $100,000 for a computer that can pass the Turing
Test.Test. www.edutechlearners.comwww.edutechlearners.com

CHALLENGE RESPONSE TESTCHALLENGE RESPONSE TEST
 AA challenge-response testchallenge-response test is a test involving a set ofis a test involving a set of
questions (or "challenges"), that the person or otherquestions (or "challenges"), that the person or other
entity has to answer in order to pass the test. If theentity has to answer in order to pass the test. If the
person or entity provides an adequate response to theperson or entity provides an adequate response to the
challenges, then it is seemed that this person or entitychallenges, then it is seemed that this person or entity
has passed the test.has passed the test.
 The Turing test for artificial intelligence is a goodThe Turing test for artificial intelligence is a good
example of challenge-responseexample of challenge-response
 One real world example would be as in movies whereOne real world example would be as in movies where
in order to gain access to a certain location the door-in order to gain access to a certain location the door-
man says something and the person attempting toman says something and the person attempting to
gain access has to say the adequate response.gain access has to say the adequate response.

SPAMSPAM
 Spamming is the act of sending unsolicited electronicSpamming is the act of sending unsolicited electronic
messages in bulk. In the popular eye, the most commonmessages in bulk. In the popular eye, the most common
form of spam is that delivered in e-mail as a form ofform of spam is that delivered in e-mail as a form of
commercial advertising.commercial advertising.
 One of the strengths of electronic communications media isOne of the strengths of electronic communications media is
that it costs virtually nothing to send a message. Electronicthat it costs virtually nothing to send a message. Electronic
messaging is cheap and fast. It is also easy to automate:messaging is cheap and fast. It is also easy to automate:
computer programs can send out millions of messages viacomputer programs can send out millions of messages via
e-mail, instant message (IM), in minutes or hours at nearlye-mail, instant message (IM), in minutes or hours at nearly
no labour cost.no labour cost.
 Sending bulk messages in this fashion, to recipients whoSending bulk messages in this fashion, to recipients who
have not solicited them, has come to be known ashave not solicited them, has come to be known as
spamming, and the messages themselves as spam.spamming, and the messages themselves as spam.

DEFINITIONDEFINITION
 AA CAPTCHACAPTCHA (an acronym for "(an acronym for "ccompletelyompletely
aautomatedutomated ppublicublic tturing test to telluring test to tell ccomputersomputers
andand hhumansumans aapart") is a type ofpart") is a type of challenge-challenge-
response testresponse test used in computing to determineused in computing to determine
whether or not the user is human.whether or not the user is human.
A CAPTCHA is a program that can generateA CAPTCHA is a program that can generate
and grade tests that:and grade tests that:
 Most humans can pass, butMost humans can pass, but
 Current computer programs can't passCurrent computer programs can't pass

HOW DOES A CAPTCHAHOW DOES A CAPTCHA
WORKS?WORKS?
A CAPTCHA imageA CAPTCHA image
shows a random stringshows a random string
which the user has to typewhich the user has to type
to submit a form. This is ato submit a form. This is a
simple problem forsimple problem for
humans, but a very hardhumans, but a very hard
problem for computersproblem for computers
which have to usewhich have to use
character recognition,character recognition,
especially, because theespecially, because the
displayed string isdisplayed string is
alienated in a way, whichalienated in a way, which
makes it very hard for amakes it very hard for a
computer to decode.computer to decode.

HOW ARE IMAGES INTEGATEDHOW ARE IMAGES INTEGATED
Both your web server and our CAPTCHA server needBoth your web server and our CAPTCHA server need
a common secret key. The picture is integrated quitea common secret key. The picture is integrated quite
similar to page counters. As a parameter you have tosimilar to page counters. As a parameter you have to
send a random string within the link. The secret keysend a random string within the link. The secret key
and the random string are used to generate theand the random string are used to generate the
password. Both strings are needed to compute thepassword. Both strings are needed to compute the
password. The password is computed by thepassword. The password is computed by the
CAPTCHA server to generate the image and by yourCAPTCHA server to generate the image and by your
server to validate itserver to validate it

CHARACTERISTICSCHARACTERISTICS
 They areThey are completely automatedcompletely automated. This avoids the. This avoids the
necessity for human maintenance or intervention innecessity for human maintenance or intervention in
the test, with obvious benefits in cost and reliability.the test, with obvious benefits in cost and reliability.
 The algorithm used is madeThe algorithm used is made publicpublic, though it may be, though it may be
encumbered by a patent. This is stipulated so as toencumbered by a patent. This is stipulated so as to
require that breaking a captcha requires the solutionrequire that breaking a captcha requires the solution
of a hard problem in the field of artificial intelligenceof a hard problem in the field of artificial intelligence
(AI) rather than just the discovery of the (secret)(AI) rather than just the discovery of the (secret)
algorithm, which could be obtained through otheralgorithm, which could be obtained through other
techniques.techniques.

VARIOUS TEST OFVARIOUS TEST OF
CAPTCHACAPTCHA
 GIMPYGIMPY
 BONGOBONGO
 PIXPIX
 SOUNDSOUND

GIMPYGIMPY
GimpyGimpy is our mostis our most
reliable system. It wasreliable system. It was
originally built for (andoriginally built for (and
in collaboration with)in collaboration with)
Yahoo!Yahoo!

BONGOBONGO
Bongo is a program that asksBongo is a program that asks
the user to solve a visualthe user to solve a visual
pattern recognition problem.pattern recognition problem.
In particular, Bongo displaysIn particular, Bongo displays
two series of blocks, the lefttwo series of blocks, the left
and the right series. Theand the right series. The
blocks in the left series differblocks in the left series differ
from those in the right, andfrom those in the right, and
the user must find thethe user must find the
characteristic that sets thecharacteristic that sets the
two series aparttwo series apart

PIXPIX
PixPix a program that has aa program that has a
large database oflarge database of
labeled images. All oflabeled images. All of
these images arethese images are
pictures of concretepictures of concrete
objects (a horse, a table,objects (a horse, a table,
a house, a flower, etc).a house, a flower, etc).

SOUNDSOUND
SoundsSounds can be thought of as a sound versioncan be thought of as a sound version
of Gimpy. The program picks a word orof Gimpy. The program picks a word or
a sequence of numbers at random, rendersa sequence of numbers at random, renders
the word or the numbers into a sound clipthe word or the numbers into a sound clip
and distorts the clip. It then presentsand distorts the clip. It then presents
the distorted sound clip to its user and asks thethe distorted sound clip to its user and asks the
user to type in the contents of the sound clip.user to type in the contents of the sound clip.

APPLICATIONSAPPLICATIONS
 Online pollsOnline polls
 Free E-mail servicesFree E-mail services
 Search engine botsSearch engine bots
 Worms and spamsWorms and spams
 Preventing dictionary attacksPreventing dictionary attacks

ONLINE POLLSONLINE POLLS
 In November 1999, http://www.slashdot.com released anIn November 1999, http://www.slashdot.com released an
online poll asking which was the best graduate school inonline poll asking which was the best graduate school in
computer science (a dangerous question to ask over thecomputer science (a dangerous question to ask over the
web!). As is the case with most online polls, IP addresses ofweb!). As is the case with most online polls, IP addresses of
voters were recorded in order to prevent single users fromvoters were recorded in order to prevent single users from
voting more than once. However, students at Carnegievoting more than once. However, students at Carnegie
Mellon found a way to stuff the ballots using programsMellon found a way to stuff the ballots using programs
that voted for CMU thousands of times. CMU's scorethat voted for CMU thousands of times. CMU's score
started growing rapidly. The next day, students at MITstarted growing rapidly. The next day, students at MIT
wrote their own program and the poll became a contestwrote their own program and the poll became a contest
between voting "bots". MIT finished with 21,156 votes,between voting "bots". MIT finished with 21,156 votes,
Carnegie Mellon with 21,032 and every other school withCarnegie Mellon with 21,032 and every other school with
less than 1,000. Can the result of any online poll beless than 1,000. Can the result of any online poll be
trusted? Not unless the poll requires that only humans cantrusted? Not unless the poll requires that only humans can
vote.vote. www.edutechlearners.comwww.edutechlearners.com

FREE E-MAIL SERVICESFREE E-MAIL SERVICES
 Several companies (Yahoo!, Microsoft, etc.)Several companies (Yahoo!, Microsoft, etc.)
offer free email services. Most of these sufferoffer free email services. Most of these suffer
from a specific type of attack: "bots" that signfrom a specific type of attack: "bots" that sign
up for thousands of email accounts everyup for thousands of email accounts every
minute. This situation can be improved byminute. This situation can be improved by
requiring users to prove they are human beforerequiring users to prove they are human before
they can get a free email account. Yahoo!, forthey can get a free email account. Yahoo!, for
instance, uses a CAPTCHA test of our designinstance, uses a CAPTCHA test of our design
to prevent bots from registering for accountsto prevent bots from registering for accounts

SEARCH ENGINE BOTSSEARCH ENGINE BOTS
 It is sometimes desirable to keep web pagesIt is sometimes desirable to keep web pages
unindexed to prevent others from finding them easily.unindexed to prevent others from finding them easily.
There is an html tag to prevent search engine botsThere is an html tag to prevent search engine bots
from reading web pages. The tag, however, doesn'tfrom reading web pages. The tag, however, doesn't
guarantee that bots won't read a web page; it onlyguarantee that bots won't read a web page; it only
serves to say "no bots, please". Search engine bots,serves to say "no bots, please". Search engine bots,
since they usually belong to large companies, respectsince they usually belong to large companies, respect
web pages that don't want to allow them in. However,web pages that don't want to allow them in. However,
in order to truly guarantee that bots won't enter a webin order to truly guarantee that bots won't enter a web
site, CAPTCHA tests are needed.site, CAPTCHA tests are needed.

WORMS AND SPAMSWORMS AND SPAMS
 Tests also offer a plausible solution againstTests also offer a plausible solution against
email worms and spam. A few companies areemail worms and spam. A few companies are
already marketing this idea.already marketing this idea.

PREVENTING DICTIONARYPREVENTING DICTIONARY
ATTACKSATTACKS
 CAPTCHA tests are also used to preventCAPTCHA tests are also used to prevent
dictionary attacks in password systems. Thedictionary attacks in password systems. The
idea is simple: prevent a computer fromidea is simple: prevent a computer from
being able to iterate through the entire spacebeing able to iterate through the entire space
of passwords.of passwords.

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