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6

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Communications, Networks, &
Safeguards

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6.1 From the Analog to the Digital
Age

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Digital


Computers use digital signals
--
0s and 1s, off and on.


All the data that a computer processes is a series of 0s
and 1s.


Each signal is a bit.


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6.1 From the Analog to the Digital
Age



Analog


But most phenomena in life are analog.


Analog signals use wave variations.


Sound, light, and temperature are analog forms.


Traditional TV and radio use analog signals.


Humans’ vision operates in analog mode.


But analog data can be converted into digital form. Even
though digital data is not as exact as analog data, it is
easier to manipulate.


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6.1 From the Analog to the Digital
Age


For data transmission over telephone lines and cables,
modems are needed to convert analog data into digital
data that computers can use.


Modem is short for modulate/demodulate. Modems
modulate (convert) a computer’s digital data to analog
data, transmit it, then demodulate (reconvert) it back to
digital data for the receiving computer.


Modems can convert data by modulating either a
analog wave’s amplitude or its frequency.

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6.1 From the Analog to the Digital
Age

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6.1 From the Analog to the Digital
Age

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6.1 From the Analog to the Digital
Age


Converting Reality to Digital Form
--
Sampling


Tape recorders, voices, and musical instruments are
analog; CDs are digital


To burn a CD, the digital recording equipment must
convert from analog to digital


The analog
-
to
-
digital converter
samples

the sound and
converts the height of the wave to a number


Samples of the sound wave are taken at regular intervals


about 44,100 times each second


Because the digital samples are played back faster than our
ears can react, it sounds to us like a single continuous
sound wave

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6.1 From the Analog to the Digital
Age


Digital sampling is similar to showing movies.


Movies show still pictures (frames)


But they show them so fast that our eyes can’t react in time


So to us the series of still pictures look like continuous
motion

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6.2 Networks


What’s a Network?


A system of interconnected computers, telephones,
and/or other communications devices that can
communicate with one another and share applications
and data

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6.2 Networks


Benefits of Networks


Share peripheral devices, such as printers, scanners, disk
drives


Share programs and data


Better communications, including email


Security of information, because of improved backup
systems


Access to shared databases

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6.2 Networks

Category

Description

WAN


Wide Area Network

Covers a wide geographic area, such as a
country or the world; largest WAN is the internet

MAN


Metropolitan Area Network

Covers a city or a suburb

LAN


Local Area Network

Connects computers and devices in a limited
geographic area such as an office, a building, or
a group of nearby buildings

HAN


Home Area Network

Uses wired, cable, or wireless connections to
link a household’s digital devices

PAN


Personal Area Network

Uses short
-
range wireless technology to connect
an individual’s personal electronics, such

as

cellphone, PDA, MP3 player, notebook PC, and
printer

Home Automatic Network

Relies on very inexpensive, very short
-
range,
low
-
power wireless

technology to link switches
and sensors around the house and outdoors

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6.2 Networks


How Networks Are Structured: Two Principal
Structures


1. Client/Server


Consists of clients, which are computers that request data,
and servers, which are computers that supply data


File servers act like a network
-
based shared disk drive


Database servers store data but don’t store programs


Print servers connect one or more printers and schedule
and control print jobs


Mail servers manage email

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6.2 Networks


How Networks Are Structured: Two Principal
Structures (
continued
)


2. Peer
-
to
-
Peer (P2P)


All computers on the network are “equal” and communicate
directly with one another, without relying on servers



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6.2 Networks

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6.2 Networks


Intranets, Extranets, & VPNs


Intranets

use infrastructure and standards of the
internet and the web, but for an organization’s internal
use only


Extranets

similar to intranets but allows use by selected
outside entities, such as suppliers


VPNs

virtual private networks: use a public network
(usually the internet) plus intranets and extranets to
connect an organization’s various sites) but on a private
basis, via encryption and authentication; regular internet
users do not have access to the VPN’s data and
information

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6.2 Networks


Network Components


Wired/Wireless Connections


wired = twisted
-
pair, coaxial cable, fiber
-
optic cable


wireless = infrared, microwave, Wi
-
Fi, satellite


Hosts and Nodes: Client/server network has a host
computer, which controls the network; a node is any
device attached to the network.


Packets


fixed
-
length blocks of data for transmission;
reassembled after transmission; a packet is also called a
datagram, a segment, a block, a cell, or a frame,
depending on the protocol.

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6.2 Networks


Network Components (
continued
)


Network Linking Devices


Protocol

set of conventions, or rules, governing the exchange of
data between hardware and/or software components in the
network; built into the hardware or software you are using


Hub

Common connection point for devices on a network; has
multiple ports and can send to all connected devices


Switch

Device that connects computers to a network; sends only
to intended recipients


Bridge

Interface that connects same type of networks


Gateway

Interface that connects dissimilar networks

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6.2 Networks


Network Components (
continued
)


Network Linking Devices(
continued
)


Router

Special computer that directs messages among several
networks


Backbone

The main internet highway that connects all networks
in an organization; includes gateways, routers, etc.


NIC

Network interface card; inserted in a slot on the
motherboard, enables computer to operate as part of a network


NOS

network operating system; the system software that
manages network activity


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Components of Networks

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6.2
Networks


Topologies: Bus, Ring, Star


Bus


all nodes are connected to a single wire or cable

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6.2 Networks


Topologies


Ring


all nodes are

connected in a

continuous loop

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6.2 Networks


Topologies


Star


all nodes are

connected through a

central host


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6.2 Networks


Packet Collision Schemes (Protocols)


Collisions happen when two data packets are going
opposite directions on shared media


Ethernet


deals with LAN collisions


All devices send data at once


Collisions happen regularly


Data is resent until it arrives


Token ring


avoids LAN collisions


Devices take turns sending data


Token is sent around the ring


Wait to get the token, then send data

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6.3 Wired Communications Media


Communications media carry signals over a
communications path


Twisted
-
Pair Wire


2 strands of insulated copper wire twisted around each
other


Twisting reduces interference (crosstalk) from electrical
signals


Data rates are 1


128 Megabits per second


Coaxial Cable


Insulated copper wire wrapped in a metal shield and then in
an external plastic cover


Used for cable TV and cable internet electric signals


Carries voice and data up to 200 megabits per second

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6.3 Wired Communications Media


Communications media (
continued
)


Fiber
-
optic cable


Dozens or hundreds of thin strands of glass or plastic that
transmit pulses of light, not electricity


Can transmit up to 2 gigabits per second


Have lower error rate than twisted
-
pair or coax


More expensive than twisted
-
pair or coax


Lighter and more durable than twisted
-
pair or coax


More difficult to tap into than twisted
-
pair or coax

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6.3 Wired Communications Media


For The Home


Ethernet


Pull Cat5 cables through the house


Connect to PC’s Ethernet network interface card (NIC)


For several PCs, get a hub or switch to connect them all


10 or 100 megabits per second


HomePNA


Uses existing telephone wiring and jacks


Requires HomePNA NIC in your PC


Speeds of about 320 megabits per second


Homeplug


Uses existing home AC electrical lines


Speeds of 200 megabits per second

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6.4 Wireless Communications
Media


Electromagnetic spectrum of radiation is the basis of all
telecommunications signals, wired and wireless


Radio
-
frequency (RF) spectrum is the part of the
electromagnetic spectrum that carries most
communications signals

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6.4 Wireless Communications
Media

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6.4 Wireless Communications
Media

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6.4 Wireless Communications
Media


Bandwidth: range (band) of frequencies that a
transmission medium can carry in a given period of
time


Analog bandwidth is expressed in hertz, digital bandwidth
usually in bits per second (bps)


Narrowband (Voiceband): used for regular telephone
communications


Transmission rate 1.5 megabits per second or less


Broadband: For high
-
speed data and high
-
quality audio
and video


Transmission rate 1.5 megabits per second to 1 gigabit per
second or more

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6.4 Wireless Communications
Media


TC/IP (Ch. 2) is the protocol for getting wired devices
connected to the internet


WAP (wireless application protocol) gets wireless
handheld devices, such as cellphones, connected to
the internet

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6.4 Wireless Communications
Media


Five Types of Wireless Communications Media


Infrared Transmission


Sends signals using infrared light


Frequencies are too low to see (1
-
16 Mbits per second)


Broadcast Radio


AM/FM, CB, ham, cellphones, police radio


Sends data over long distances using a transmitter and a
receiver (up to 2 Mbits per second)


Cellular Radio


Form of broadcast radio


Widely used in cellphones and wireless modems


Transmits voice and digital messages

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6.4 Wireless Communications
Media


Five Types of Wireless Communications Media
(
continued
)


Microwave Radio


Superhigh
-
frequency radio waves (2.4 gigahertz or higher)


Requires line
-
of
-
sight transmitters and receivers


More than ½ of today’s telephones systems use microwave


Communications Satellites


Microwave relay stations in orbit around the earth


Basis for Global Positioning Systems (GPS)


Cover broad service area


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6.4 Wireless Communications
Media


Communications Satellites (
continued
)


Can be placed at different heights: GEO, MEO, LEO


GEO


geostationary earth orbit


22,300 miles above earth; travel at the same speed as the
earth and so appear to us to be stationary


Always above equator


Transmission delay can make conversations difficult


MEO


medium
-
earth orbit


5,000


10,000 miles up


LEO


low
-
earth orbit


200


1,000 miles up


Has no signal delay

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6.4 Wireless Communications
Media


Long
-
Distance Wireless: One
-
Way Communication


GPS (Global Positioning System)


24 to 32 MEO satellites continuously transmitting timed
radio signals


Each satellite circles earth twice each day at 11,000 miles
up


GPS receivers pick up transmissions from up to 4 satellites
and pinpoint the receiver’s location


Accurate within 3


50 feet, with a norm of 10 feet accuracy



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6.4 Wireless Communications
Media


Long
-
Distance Wireless: One
-
Way Communication (
continued)



One
-
way Pagers


One
-
way pagers are radio receivers that receive data sent from a
special radio transmitter


Radio transmitter sends out signals over the special frequency


Pagers are tuned to that frequency


When a particular pager hears its own code, it receives and
displays the message

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Question: Why do airplane rules require you to turn off pagers and
cellphones during flight?

Answer: Pilots use radar and radio to determine their position and
communicate with ground control. Pager and cellphone signals use
radio, too, and competing signals can interfere with one another.

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6.4 Wireless Communications
Media


Long
-
Distance Wireless: Two
-
Way Communications


1G: First
-
Generation Cellular Service


Analog cellphones


Designed for voice communication using a system of
hexagonal ground
-
area cells around transmitter
-
receiver cell
towers


Good for voice


less effective for data because of handing
off


2G: Second
-
Generation Cellular Service


Uses digital signals


First digital voice cellular network

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6.4 Wireless Communications
Media


Long
-
Distance Wireless: Two
-
Way Communications
(
continued)


3G: Third
-
Generation Cellular Service


3G cellphones are more like PDAs


Broadband technology


Carries data at high speeds


High speed data: 144 kilobits per second up to 2.4 megabits
per second


Accepts e
-
mail with attachments


Displays color video and still pictures


Plays music



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6.4 Wireless Communications
Media


Long
-
Distance Wireless: Two
-
Way Communications
(
continued)


4G: Fourth
-
Generation Cellular Service


A nationwide 4G network in development


Uses the WiMax (Worldwide Interoperability for Microwave
Access) standard


May provide broadband to rural areas


First 4G phone, the EVO, released in March 2010

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Discussion Question: If your cellphone can download and play music,
do you still need an iPod?

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6.4 Wireless Communications
Media


Short
-
Range Wireless: Two
-
Way Communications


Local Area Networks


Range 100


228 feet


Include Wi
-
Fi (802.11) type networks


Wi
-
Fi n is the latest and fastest Wi
-
Fi technology


Personal Area Networks


Range 30


32 feet


Use Bluetooth, ultra wideband, and wireless USB


Home Automation networks


Range 100


150 feet


Use Insteon, ZigBee, and Z
-
Wave standards

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6.4 Wireless Communications
Media


Short
-
Range Wireless: Two
-
Way Communications
(
continued
)


Wi
-
Fi b, a, g, and n networks


Named for variations on the IEEE 802.11 standard
(802.11b, 802.11a, 802.11a)


Data ranges: 11 megabits per second up to 126 feet
indoors (Wi
-
Fi b) to 54 megabits per second up to 120
feet (Wi
-
Fi a and g)


Wi
-
Fi n with MIMO extends range of Wi
-
Fi using multiple
transmitting and receiving antennas


100
-

320
megabits per second for up to 228 ft

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6.4 Wireless Communications
Media


Short
-
Range Wireless: Two
-
Way Communications
(
continued
)


Wi
-
Fi Security


A person with a $50 antenna can eavesdrop on
everything your computer sends over wireless from a
block or two away; this is called “wardriving.” Make sure
to turn your Wi
-
Fi software off when you are not using it.

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6.4 Wireless Communications
Media


Short
-
Range Wireless: Two
-
Way Communications
(
continued
)


Personal Area Wireless


Bluetooth


Short
-
range wireless standard to link cellphones, PDAs,
computers, and peripherals at distances usually up to 30 ft


Transmits up to 3 megabits per second


When Bluetooth devices come into range of each other, they
negotiate. If they have information to exchange, they form a
temporary wireless network

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6.4 Wireless Communications
Media


Short
-
Range Wireless: Two
-
Way Communications
(
continued
)


Personal Area Wireless (
continued)



Ultra Wideband (UWB)


Developed for military radar systems


Operates in 480 megabits per second, range up to 30 ft


Uses a low power source to send out millions of bursts of radio
waves each second


Wireless USB


USB is the most used interface on PCs


Range of 32 ft and maximum data rate of 480 megabits per
second; used in game controllers, printers, scanners, cameras,
MP3 players, hard disks, and flash drives

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6.4 Wireless Communications
Media


Short
-
Range Wireless: Two
-
Way Communications
(
continued
)


Short
-
Range Wireless for Home


Insteon


Combines electronic power line and wireless technology


Can send data at 13.1 kilobits per second with 150 ft range


ZigBee


Entirely wireless sensor technology


Can send data at 128 kilobits per second with 250 ft range


Z
-
Wave


Entirely wireless power
-
efficient technology


Can send data at 127 kilobits per second to range of 100 ft


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6.5 Cyberthreats, Hackers, &
Safeguards


Problem: Internet was begun to foster collaboration
among universities and scientists. They trusted each
other. No security was built into the internet.


Problem: The internet is open
-
access and is used by
criminals who take advantage of the lack of built
-
in
safeguards.


Problem: Most people connect to the internet and use
their computers in LANs. All it takes is one computer
on a LAN that has been compromised for all computers
on it to be vulnerable.

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6.5 Cyberthreats, Hackers, &
Safeguards


Cyberthreats


Denial of Service Attacks


Consist of making repeated requests of a computer or
network device, thereby overloading it and denying access
to legitimate users


Used to target particular companies or individuals

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6.5 Cyberthreats, Hackers, &
Safeguards


Cyberthreats (
continued
)


Worms (Malware)


A program that copies itself repeatedly into a computer’s
memory or disk drive


May copy itself so much it crashes the infected computer


Primarily target PCs running Microsoft Windows

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6.5 Cyberthreats, Hackers, &
Safeguards


Cyberthreats (
continued
)


Viruses (Malware)


Deviant program that hides on a disk, in an e
-
mail, or in a
web link that causes unexpected effects such as destroying
or corrupting data


Viruses are released at the rate of about one per day


To see what the latest ones are, go to

www.symantec.com/avcenter/vinfodb.html


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6.5 Cyberthreats, Hackers, &
Safeguards


Cyberthreats (
continued
)


Trojan Horses (Malware)


Programs that pretend to be a useful program such as a
free game or a screensaver but that carry viruses or
malicious instructions that damage your computer or install
a backdoor or spyware


Backdoors and spyware allow others to access your
computer without your knowledge

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6.5 Cyberthreats, Hackers, &
Safeguards


Cyberthreats (
continued
)


How they spread


Via e
-
mail attachments


By infected disks


By clicking on infiltrated websites


By downloading infected files from websites


Through infiltrated Wi
-
Fi hotspots


From one infected PC on a LAN to another


What can you do about it?


Install antivirus software and subscribe to the
manufacturer’s automatic antivirus update service

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6.5 Cyberthreats, Hackers, &
Safeguards


Cyberthreats (
continued
)


Cellphone Malware


Spread via internet downloads, MMS attachments, and
Bluetooth transfers


Usually show up disguised as applications such as games,
security patches, add
-
on functionalities, erotica, and free
programs


Protect your phone:


Turn off Bluetooth discoverable mode


Check security updates to learn about filenames to
watch out for


Install security software

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6.5 Cyberthreats, Hackers, &
Safeguards


Cyber Villains


Hackers are either


Computer enthusiasts, people who enjoy learning about
programming and computers


People who gain unauthorized access to computers or
networks, often for fun or just to see if they can


Two types:


Thrill
-
seeker hackers: do it for the challenge


White
-
hat hackers: do it to expose security flaws that can be
fixed

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6.5 Cyberthreats, Hackers, &
Safeguards


Cyber Villains


Crackers


Malicious hackers who break into computers for malicious
purposes


Script kiddies are technically unsophisticated teenagers who
use downloadable software for perform break
-
ins


Hacktivists are hacker activists who break into systems for a
political purpose


Black
-
hat hackers are those who break into computers to steal
or destroy information or to use it for illegal profit


Cyberterrorists attack computer systems so as to bring physical
or financial harm to groups, companies, or nations

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6.5 Cyberthreats, Hackers, &
Safeguards


Online Safety


Use antivirus software, and keep it current


Install a firewall to monitor network traffic and filter out
undesirable types of traffic and undesirable sites


Don’t use the same password for multiple sites


Don’t give out any password information


Use robust passwords:


Minimum 8 characters with letters, numbers, characters


4cats is not a good password; f0UrK@tTz is safer

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6.5 Cyberthreats, Hackers, &
Safeguards


Online Safety (
continued
)


Install antispyware software


Encrypt financial and personal records so only you can
read them


Back up your data, so if your PC is attacked and must be
reformatted, you can restore your data


Never download from a website you don’t trust


Consider biometric authentication



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6.5 Cyberthreats, Hackers, &
Safeguards


Online Safety (
continued
)


Biometrics: science of measuring individual body
characteristics


Used in security devices


Examples; hands, fingerprints, iris recognition, face
recognition, voice recognition


Now available on laptops


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6.5 Cyberthreats, Hackers, &
Safeguards


Online Safety (
continued
)


Encryption


Process of altering readable data into unreadable form to
prevent unauthorized access


Uses powerful mathematical ciphers to create coded
messages that are difficult to break


Unencrypted messages are known as plain text


Encrypted text is known as cybertext


Either private keys or public keys are used to encrypt
and send and then to receive and decrypt messages

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6.5 Cyberthreats, Hackers, &
Safeguards


Online Safety (
continued
)


Private Key encryption means the same secret key is
used by both the sender and receiver to encrypt and
decrypt a message


Public Key encryption means that two keys are used; the
recipient’s public key is given to the sender to encrypt the
message; the receiver uses a private key to decrypt it

© 2011 The McGraw
-
Hill Companies, Inc. All rights reserved.