maknyos

Meeting 9
Computer Network
Definition of
computer networks
A computer network is a group of
interconnected computers. Networks may be
classified according to a wide variety of
characteristics. The benefit of a computer
network are: Sharing hardware resources easily
and Sharing information easily.
A network is a collection of computers
connected to each other. The network allows
computers to communicate with each other and
share resources and information. The Advanced
Research Projects Agency (ARPA) designed
"Advanced Research Projects Agency Network"
(ARPANET) for the United States Department of
Defense. It was the first computer network in the
world in late 1960's and early 1970's.
Types of computer networks
1. Local-area networks (LANs): The computers
are geographically close together (that is, in the
same building).
2. Wide-area networks (WANs): The computers
are farther apart and are connected by
telephone lines or radio waves.
3. Campus-area networks (CANs): The
computers are within a limited geographic area,
such as a campus or military base.
4. Metropolitan-area networks (MANs): A data
network designed for a town or city.
5. Home-area networks (HANs): A network
contained within a user's home that connects a
person's digital devices.
The following characteristics are used to categorize
different types of networks:
1. topology: The geometric arrangement of a computer
system. Common topologies include a bus, star, and
ring.
2. protocol: The protocol defines a common set of rules
and signals that computers on the network use to
communicate. Two of the most popular protocols for
LANs is called Ethernet and the IBM token-ring network.
3. architecture: Networks can be broadly classified as
using either a peer-to-peer or client/server architecture.
Computers on a network are sometimes called nodes.
Computers and devices that allocate resources for a
network are called servers.
Networks Topology
www.webopedia.com
What do we need to create
a computer network?
There are many kinds of devices to create a
computer network. For a basic computer
network we would need:
1. Network Interface Cards
A network card, network adapter or NIC
(network interface card) is a piece of computer
hardware designed to allow computers to
communicate over a computer network
NIC can be identified easily. It has a special port
called RJ-45. RJ means Registered Jack. And also a led
to indicate a data is being transferred.
2. Repeaters
A repeater is an electronic device that receives a signal
and retransmits it at a higher power level, or to the other
side of an obstruction, so that the signal can cover
longer distances without degradation.
3. Hub
A hub contains multiple ports. When a
packet arrives at one port, it is copied to all the
ports of the hub for transmission. When the
packets are copied, the destination address in
the frame does not change to a broadcast
address. Below is a picture of 4-port ethernet
hub.
Above is a network switch
Task 1
Which words in the slides have the
opposite meaning to the following?
1. Narrow
2. Disadvantage
3. Hard/difficult
4. The last
5. Few
6. Sends
7. Single port
8. Above
9. Disconnected
10. Shorter
Task 2
Answer these questions based on
slide 2-5.
1. What is meant by a network?
2. What are the advantages of a network?
3. How do we create a basic network?
4. Who create the first network?
5. How to categorize different types of
networks?
COMPUTER TERMS
• Network is a set of items connected together into one
unit
• Port in a hub or switch is a slot to connect a hub or
switch to other network device
FURTHER READINGS
• http://en.wikipedia.org/wiki/Computer_networks
• http://en.wikipedia.org/wiki/Network_hub
• http://en.wikipedia.org/wiki/Repeater
• http://www.webopedia.com/TERM/N/network.html
• http://www.uaf.edu/toolik/Reports/Report03/CommsSlid
es-SRI.ppt
• http://www.cs.ucr.edu/~weesan/cs6/03_basic_computer
_network.ppt




Steganography
What is steganography
Steganography is the art and science
of writing hidden messages in such a way
that no-one apart from the sender and
intended recipient even realizes there is a
hidden message, a form of security
through obscurity. By contrast,
cryptography obscures the meaning of a
message, but it does not conceal the fact
that there is a message.
Generally, a steganographic message will appear
to be something else: a picture, an article, a shopping
list, or some other message. This apparent message
is the covertext. For instance, a message may be
hidden by using invisible ink between the visible lines
of innocuous documents.
The advantage of steganography over
cryptography alone is that messages do not attract
attention to themselves, to messengers, or to
recipients. An unhidden coded message, no matter
how unbreakable it is, will arouse suspicion and may
in itself be incriminating, as in countries where
encryption is illegal. Often, steganography and
cryptography are used together to ensure security of
the covered message.
Someone who is expert in steganography is
called steganalyst.
History of steganography
The word steganography is of Greek origin
and means "covered, or hidden writing". Its
ancient origins can be traced back to 440 BC.
Herodotus mentions two examples of
steganography in The Histories of Herodotus.
Demaratus sent a warning about a forthcoming
attack to Greece by writing it on a wooden panel
and covering it in wax. Wax tablets were in
common use then as re-usable writing surfaces,
sometimes used for shorthand.
Another ancient example is that of Histiaeus,
who shaved the head of his most trusted slave
and tattooed a message on it. After his hair had
grown the message was hidden. The purpose
was to instigate a revolt against the Persians.
Task 1
Check your understanding.
1. What is steganography for?
2. What is covertext?
3. Why is steganography better than
cryptography?
4. Who sent a warning to Greece by using
steganography?
5. How did Histiaeus apply the
steganography technique?
Some Techniques of Steganography
1. Writing a secret message using invisible ink.
2. Hidden messages on messenger's body: also
in ancient Greece. Herodotus tells the story
of a message tattooed on a slave's shaved
head, hidden by the growth of his hair, and
exposed by shaving his head again.
The message allegedly carried a warning
to Greece about Persian invasion plans.
This method has obvious drawbacks:
a. It is impossible to send a message as quickly
as the slave can travel, because it takes
months to grow hair.
b. A slave can only be used once for this
purpose. (This is why slaves were used: they
were considered expendable).
3. A picture of a message in microdots or
microfilms.
4. In computer era, steganography can be done by
inserting a secret document into other
document. Any document can be used as a
media, for example text file, picture file, or
multimedia file such as mp3 or video file.
Practice
• Prepare an image for cover image.
• Prepare a secret image to be hidden.
• Go to this site
http://incoherency.co.uk/hideimage.php
• Hit button Go!
Task 2
Find the term in the passage which have
meaning of the following (Slide 7-9).
1. Colored liquid material that is hidden or cannot
be seen.
2. So very old
3. Removing hair or beard
4. Must not be known by others
5. A person who is owned by and must served
someone
6. A tiny sized dot
7. Coming to conquest or rule
8. Disadvantage
COMPUTER TERMS
• Cover text = a text or a messages that is displayed to a user
• Encryption = a process converting plain text into cipher text
FURTHER READINGS
• http://www.dmoz.org/Computers/Security/Products_and_Tools/Crypt
ography/Steganography//
• http://petitcolas.net/fabien/steganography/image_downgrading/index
.html
• http://www.fbi.gov/hq/lab/fsc/backissu/july2004/research/2004_03_r
esearch01.htm
• http://www.jjtc.com/Steganography
• http://www.citi.umich.edu/techreports/reports/citi-tr-01-11.pdf
• http://www.spy-hunter.com/stego.html
• http://www.datahide.com/BPCSe/Articles/Ref-6.SPIE98.pdf
• http://blog.maxant.co.uk/pebble/2007/07/19/1184876280000.html



Meeting 11
Cryptography
What is cryptography
The term cryptography is derived from Greek,
kryptos means “hidden” or “secret” and graphy
means “writing”. So, cryptography is the practice
and study of creating a secret information.
Cryptography works by Cryptography is a part of
mathematics and computer science.
Cryptography is used in applications present
in technologically advanced societies; examples
include the security of ATM cards, computer
passwords, and electronic commerce, which all
depend on cryptography. In short we can say that
cryptography is needed to secure a secret
document. A person who is master in
cryptography is called cryptographer.
How cryptography works
For example someone has a secret
document to secure. Any document can be
secured using cryptography. For example we
have to secure the word “Read” using
cryptography. The word “Read” in cryptography
is called Plain text. Using a set of rule called
algorithm, the plain text is changed into cipher
text. This process is called encryption. The result
of this encryption process is the word “Uhdg”.
This is the cipher text.
A set of rule (algorithm) that is used in
encryption can be different. There are
many algorithm used in encryption. At the
above example we use Caesar Cipher
algorithm that is used by Julius Caesar to
secure his document.
The reverse process of encryption is called
decryption. The input is a cipher text. And the
result of decryption process is plain text.
Task 2
Show whether the followings statements
are true or false (T/F) from Slide 2 - 5.
1. Cryptography is the practice and study of
creating a secret information.
2. Not all document can be secured using
cryptography.
3. Using a set of rule called algebra, the plain
text is changed into cipher text.
4. The word “kryptos” is a Latin origin.
5. The reverse process of encryption is called
decryption.
History of cryptography
Cryptography is already used since ancient
era. Julius Caesar used cryptography to secure
his message from his enemy. He replaced a
character with its next three character. For
example a character ‘A’ in alphabet will be
replaced by character ‘D’. And so on. See the list
below of Julius Caesar algorithm.
• Plain text : a b c d e f g h I j k l m n o p q r
s t u v w x y z
• Cipher Text : d e f g h I j k l m n o p q r s t u
v w x y z a b c
In the era of World War II,
German Nazi was also used
cryptography to secure its
message. Nazi used a machine
called Enigma to encrypt and
decrypt the messages. In this
way Nazi thought its message
would be difficult to break by US
and its allies. Below is a picture
of Enigma used by Nazi.
Unfortunately the algorithm of Enigma can
be broken by US army.
In computer technology, cryptography
is still used to secure a computer data or
document. For example in ATM machine,
computer passwords, and also in
electronic commerce. Using computer
technology someone can use many
sophisticated algorithm for example RSA,
DES, and PGP.
COMPUTER TERMS
• Plain text = a text that can be read by anybody.
This text is not secured yet.
• Cipher text = a secret text resulting from
encryption process.
• Algorithm = a set of rule to encrypt a document.
• Enigma = a machine like typewriter that is used
by Nazi during World War II to secure
a document before transmitted.
• Cryptographer = a person who is master in
cryptography.
Task 2
Figure out this message.
“BRX KDYH MXVW GLVFRYHUHD WKH
DQFLHQW VHFUHW FRGLQJ FDOOHG
MXOLXV FDHVDU DOJRULWKP”
What does it say?
___________________________________
___________________________________
mhtirogla raseaC suiluJ esU
FURTHER READINGS
• http://en.wikipedia.org/wiki/Cryptography
• http://en.wikipedia.org/wiki/Cryptography_Classification
• http://en.wikipedia.org/wiki/Encyclopedia_of_Cryptography_and_Security
• http://en.wikipedia.org/wiki/Japanese_cryptology_from_the_1500s_to_Meiji
• http://en.wikipedia.org/wiki/List_of_important_publications_in_computer_science#Cry
ptography
• http://www.merriam-webster.com/dictionary/cryptology/
• http://www.csrc.nist.gov/publications/fips/fips197/fips-197.pdf
• http://www.cesg.gov.uk/site/publications/media/notense.pdf
• http://citeseer.ist.psu.edu/cache/papers/cs/22094/http:zSzzSzeprint.iacr.orgzSz2001z
Sz056.pdf/junod01complexity.pdf
• http://www.rsasecurity.com/rsalabs/node.asp?id=2152
• http://www.ieee-security.org/Cipher/Newsbriefs/1996/960214.zimmerman.html
• http://www.schneier.com/crypto-gram-0006.html#DES
• http://scholar.google.com/url?sa=U&q=http://www.springerlink.com/index/K54H077N
P8714058.pdf
• http://www.cacr.math.uwaterloo.ca/hac/
• http://www.cryptool.org/download/CrypToolPresentation-en-1_4_20.pdf
• http://www.rsasecurity.com/rsalabs/node.asp?id=2152
• http://www.pawlan.com/Monica/crypto/
• http://www.nsa.gov/kids/



Meeting 12
The Internet
Internet stands for: Internetworked Networks
The Internet is a worldwide connection of
millions of computers connected to thousands of
different networks. These computers
"communicate" that is, share, exchange, and
transmit data to another computer on the same
or another network.
Nobody owns or controls the Internet. It is a
global information system similar in some
respects to telephone networks that allow
anybody to call any other number anytime,
anywhere.
a. Internet Services
The Internet has several component applications. These
include:
1. Telnet - terminal emulation - Allows a user on one
computer to log onto a remote computer and run
software on that remote computer as if it were on the
user's local computer
2. FTP – File Transfer Protocol - Allows users to upload
and download files from other computers
3. EDI – Electronic Data Interchange - Allows for
electronic transfer of data between companies over
the Internet
4. IRC – Internet Relay Chat - Allows people connected
over the Internet to participate in discussions. It allows
people to converse in "real time," people may actually
see you type your questions and responses.
6. Email – Electronic Mail, allows people to send and
receive electronic messages.
7. Newsgroup - This is the Internet equivalent of a
discussion group or an electronic bulletin board. There
are newsgroups for every conceivable topic and more,
from educational technology and Brazil culture to stamp
collecting and mountaineering. Computer newsgroups
start with comp as in comp.apps.spreadsheets. while
recreational newsgroups start with rec as in
rec.arts.cinema. The others are alt for alternate, soc for
social, sci for science, and news for news.
8. World Wide Web is a vast, ever-expanding collection
of online documents and information formatted in
Hypertext Markup Language (HTML) distributed over
the Internet. It is a software application that uses the
Internet.
b. Internet address domain
Each computer on the Internet is called an Internet
host or a host machine. Each host machine has a
special Internet protocol address (IP address) that
uniquely identifies that computer. IP addresses were
never designed to be seen by human eyes. They are an
address that is interpreted by a computer. An example of
an IP address is:
205.213.164.10
Since numbers are easy for a computer to work with but
difficult for humans, most host machines have a Domain
Name Service (DNS) address. For instance, the domain
name service address of the IP address listed above is:
depts.alverno.edu
The most common Top Level Domains (TLD)
are:
TLD Name Type of Organization
.com A commercial organization in
.edu An educational site in the US
.gov A government agency in the US
.mil A military site in the US
.net A network site
.org A nonprofit organization
Other TLD names identify geographical
locations by country – such as:
TLD Name Location by country
.au Australia
.ca Canada
.dk Denmark
.fr France
.de Germany
.uk Great Britain
.hk Hong Kong
.hu Hungary
.ie Ireland
.id Indonesia
Newly added Top-Level Domains
include:
TLD Name Type of
Organization
.biz Businesses
.info For all users
TLD scheduled to be added soon include:
TLD Name Type of Organization
.aero For the air-transport
industry
.coop For cooperatives
Top-Level Domain Names help the user to
identify what type of site they are visiting.
.museum For museums
.name For individuals
.pro For professionals
c. Netiquette
There are guidelines on how one must
behave in cyberspace. In the Internet
these responsibilities are defined by what
is called Netiquette. There are different
versions of Netiquette on the Web, the
following is an example of netiquette.
10 Commandments of Computer Use
by Computer Ethics Institute in
Washington D.C.
1. Thou shalt not use a computer to harm
other people
2. Thou shalt not interfere with other
people's computer work
3. Thou shalt not snoop around in other people's computer
files
4. Thou shalt not use a computer to steal
5. Thou shalt not use a computer to bear false witness
6. Thou shalt not copy or use proprietary software for
which you have not paid
7. Thou shalt not use other people's computer resources
without authorization or proper compensation
8. Thou shalt not appropriate other people's intellectual
output
9. Thou shalt think about consequences of the program
you are writing or the system you are designing
10. Thou shalt always use a computer in ways that ensure
consideration and respect for your fellow humans.
Task 1
Answer these questions.
1. In a network, computers ‘communicate’ with
each other. What does it mean?
2. If you want to upload and download files from
other computers, what component application do
you need?
3. What is the guidelines on how someone must
behave in cyberspace called?
4. Can we copy paste other people’s intellectual
output and claim it as our idea?
5. www.spiegel.de/international/business
www.kompass.ie
In what country is the location of the website?
Challenge!
Match the top level domain with the correct
description in 10 seconds!
____1) .com A. US Educational institution
____2) .gov B. A non-profit or not-for-profit
institution
____3) .org C. US Governmental agency
____4) .mil D. A company or business
____5) .edu E. US Military
Task 2
Take home assignment
In a group, translate the 10
Commandments of Computer Use by
Computer Ethics Institute in
Washington D.C.
Further readings
• http://en.wikipedia.org/wiki/Internet
• http://www.comptechdoc.org/basic/basictut
/
• http://dragon.ep.usm.edu/~it365/module/In
ternet/Internet.htm
• http://depts.alverno.edu/cil/mod1/webtutori
al/internet.html



Meeting 13
E-mail
Electronic mail, often abbreviated as email,
email, or eMail, is any method of
creating, transmitting, or storing primarily
text-based human communications with
digital communications systems. Unlike
conventional mail, email is much faster
(conventional mail is sometimes called
"snail mail" by email users).
Email has both similarities and
differences with more conventional postal
services. First, messages are posted
electronically to individuals at specific
addresses much like conventional mail.
The address denotes the computer that
the individual employs as a mail server. A
mail server is like a local post office: it is a
computer that sends and receives
electronic mail for a specific network.
This is how email works
An email message is made up of several
parts. They include:
header - It contains information about the
sender, the routing and the time of the message.
The header always contains a subject line. This
is a very important part of the message and
you should always include a subject line. Some
folks sort their messages by subject, so it is rude
to not include a subject! The subject line
indicates the purpose or content of the message
message body, where you write your message
signature, which identifies the sender. This part
is optional and must be set up inside of your
email software
Header fields
The message header usually includes at least the
following fields:
From: The e-mail address of the sender
To: The e-mail address of recipient
Subject: Topic of message
Date: The local time and date when the message was
written
Cc: carbon copy, adopted from business
communication protocol when typewriters ruled the
day
Bcc: Blind Carbon Copy, when recipient
does not need to know who else got a copy
of the message. May or may not appear in
sender's file copy depending on e-mail
software used
A picture of an email page
The usefulness of e-mail is being threatened
by four phenomena:
a. E-mail bombardment, an e-mail bomb is a
form of net abuse consisting of sending huge
volumes of e-mail to an address in an attempt
to overflow the mailbox or overwhelm the
server.
b. spamming, unsolicited commercial (or bulk) email
results in information overload for many
computer users who receive such email each
day
c. phishing, process of attempting to
acquire sensitive information such as
usernames, passwords and credit card
details by masquerading as a trustworthy
entity in an electronic communication.
d. E-mail worms use e-mail as a way of
replicating themselves into vulnerable
computers.
Task 1
Show whether the followings statements
are true or false (T/F).
1. Conventional mail is another name for email.
2. Electronic mail is human communication
method based on text.
3. The post office is like a mail server to an email.
4. A traditional mail is often called snail mail by
computer users.
5. The “Subject” field indicates the recipient of the
mail.
6. Email Bomb means sending a very big
volume of emails.
7. A subject line identifies the sender.
8. Phishing is a technique used to gain
personal information for purposes of
identity theft, using fraudulent e-mail
messages.
Further readings
• http://depts.alverno.edu/cil/mod2/whatisem
ail.html
• http://en.wikipedia.org/wiki/E-mail
• http://dragon.ep.usm.edu/~it365/module/B
asics/Basics.htm


Meeting 14
a. Website
A website is a site (location) contains a
collection of pages on the World Wide
Web. Each Web site contains a home
page, which is the first document users
see when they enter the site.
Home page, as the name suggests, is
the main or opening page of a website.
You will notice that several websites use
the word "Home" or an image of a house
to guide surfers back to the main page.
The URL or Uniform Resource Locator
is the specific address of a webpage, like
http://geocities.com/toe6000/www1.html
The site might also contain additional
documents and files. Each site is owned
and managed by an individual, company
or organization.
Web page is a document written in
Hypertext Mark-up Language (HTML)
code that contains text and links to other
pages, files, or parts of the document. The
earliest Web pages were all-text
documents and at present there are still
text-based browsers like Lynx. Although
Tim Berners-Lee also wrote the first
multimedia browser in 1990, graphical
user-interface (GUI), browsers didn't
become popular until Mosaic came along
in 1993.
Task 1
Is it true or false (T/F)?
1. Each Web site contain a house page.
2. Tim Berners-Lee also wrote the first
multimedia browser in 1991.
3. Home page, as the name suggests, is
the main or opening page of a website.
4. No one owns and manages each site in
the Internet.
5. Mosaic is one of internet browsers.
b. Search engine
Search Engine is a program that
searches documents for specified
keywords and returns a list of the
documents where the keywords were
found. Although search engine is really a
general class of programs, the term is
often used to specifically describe systems
like Google, Alta Vista and Excite that
enable users to search for documents on
the World Wide Web and USENET
newsgroups.
In a simpler way, a Web search
engine is a tool designed to search for
information on the World Wide Web.
Information may consist of web pages,
images, information and other types of
files. Search engines operate
algorithmically or are a mixture of
algorithmic and human input.
There are basically three types of
search engines: Those that are powered
by robots (called crawlers; ants or spiders)
and those that are powered by human
submissions; and those that are a hybrid
of the two.
The following description explains how
Crawler-based search engines works.
Typically, a search engine works by
sending out a spider to fetch as many
documents as possible. Another program,
called an indexer, then reads these
documents and creates an index based on
the words contained in each document.
Each search engine uses a proprietary
algorithm to create its indices such that,
ideally, only meaningful results are
returned for each query.
Did You Know...
The first tool for searching the Internet,
created in 1990, was called "Archie". It
downloaded directory listings of all files located
on public anonymous FTP servers; creating a
searchable database of filenames. A year later
"Gopher" was created. It indexed plain text
documents. "Veronica" and "Jughead" came
along to search Gopher's index systems. The
first actual Web search engine was developed
by Matthew Gray in 1993 and was called
"Wandex".
Examples of three search engines
Task 2
Check your understanding.
1. How many tools to search the Internet ever
created from 1990-1993? Name them.
2. How do surfers back to the main page?
3. What is website?
4. What is search engine?
5. Mention types of search engines.
Further readings:
• http://dragon.ep.usm.edu/~it365/module/In
ternet/Internet.htm
• http://www.webopedia.com/DidYouKnow/I
nternet/2003/HowWebSearchEnginesWor
k.asp
• http://www.webopedia.com/quick_ref/Inter
net_Search_Engines.asp
Task 3
Google Search Tips:
a. You can search for a phrase by using quotations
["like this"] or with a minus sign between words [likethis].
b. You can search by a date range by using two dots
between the years [2004..2007].
c. When searching with a question mark [?] at the end
of your phrase, you will see sponsored Google
Answer links, as well as definitions if available.
In groups translate the
following!
d. Google searches are not case sensitive.
e. By default Google will return results which include
all of your search terms.
f. Google automatically searches for variations of your
term, with variants of the term shown in yellow
highlight.
g. Google lets you enter up to 32 words per search
query.