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