Network Security and its applications in

• Basics of Networking
• Network Security
• Encryption standards & Algorithms
• Network security devices
• Attack types
• Firewalls

The Computer Network
 A computer network is a group of computers/devices(Nodes)
that use a set of common communication protocols over digital
interconnections for the purpose of sharing resources located on
or provided by the network nodes.
 The nodes of a computer network may include personal
computers, servers, networking hardware, or other specialised or
general-purpose hosts.
 The interconnections between nodes are formed from a broad
spectrum of telecommunication network technologies, based on
physically wired, optical, and wireless technologies.
 A communication protocol is a set of rules for exchanging
information over a network. physically wired, optical, and
wireless

The Network Diagram
(Click on the Words Below and Learn More About Each Component)
The Internet
Other LANS
Firewall
Router
Fiber Optic Network Cable
Server
PC
Wireless Network
Wired Network
Switch

Components Of Computer Network
1. NIC Card
2. Repeater
3. Hub
4. Switch
5. Bridge
6. Router
7. Gateway
8. Firewall

1. Network Interface Card
 NIC is used to physically
connect host devices to the
network media.
 A NIC is a printed circuit board
that fits into the expansion slot of
a bus on a computer
motherboard.
 It can also be a peripheral
device. NICs are sometimes
called network adapters.
 Each NIC is identified by a
unique code called a Media
Access Control (MAC) address.
 This address is used to control
data communication for the host
on the network.

2. Repeaters
 A repeater is a network device used to
regenerate a signal.
 Repeaters regenerate analog or digital
signals that are distorted by transmission
loss due to attenuation.
 A repeater does not make an intelligent
decision concerning forwarding packets

3. Hubs
 Hubs concentrate on connections.
 In other words, they take a group of
hosts and allow the network to see
them as a single unit. This is done
passively, without any other effect
on the data transmission.
 Active hubs concentrate hosts and
also regenerate signals.

4. Bridges
 Bridges convert network data
formats and perform basic data
transmission management.
 Bridges provide connections
between LANs.
 They also check data to
determine if it should cross the
bridge. This makes each part of
the network more efficient

5. Switches
 Switches add more intelligence to data transfer management.
 They can determine if data should remain on a LAN and
transfer data only to the connection that needs it.
 Another difference between a bridge and switch is that a
switch does not convert data transmission formats

6. Routers
 Routers have all the capabilities listed
above.
 Routers can regenerate signals,
concentrate multiple connections, convert
data transmission formats, and manage
data transfers.
 They can also connect to a WAN, which
allows them to connect LANs that are
separated by great distances.

7. Gateway
 A gateway is a piece of networking
hardware used in
telecommunications for
telecommunications networks that
allows data to flow from one discrete
network to another.
 Gateways are distinct from routers or
switches in that they communicate
using more than one protocol to
connect a bunch of networks

8. Firewall
 A firewall is a network device or
software for controlling network
security and access rules.
 Firewalls are inserted in connections
between secure internal networks and
potentially insecure external networks
such as the Internet.
 Firewalls are typically configured to
reject access requests from
unrecognized sources while allowing
actions from recognized ones.

Features of Computer Network
A list Of Computer network features is
given below.
• Communication speed
• File sharing
• Back up and Roll back is easy
• Software and Hardware sharing
• Security
• Scalability
• Reliability

Computer Network Architecture
Two types of Computer Network Architecture
• Peer-To-Peer network
• Client/Server network
Peer-To-Peer network is a network in which
all the computers are linked together with
equal privilege and responsibilities for
processing the data.
Client/Server network is a network model
designed for the end users called clients, to
access the resources such as songs, video,
etc. from a central computer known as
Server.

Transmission Media
The function of the media is to carry a flow of information through a LAN.
A. Wired Media:- A widely adopted family that uses copper and fiber media in
local area network (LAN) technology are collectively known as Ethernet
1. Copper Cable
a. Coaxial Cables
b. Shielded Twisted Pair(STP)
c. Unshielded Twisted Pair
2. Fibre Optic Cable
B. Wireless Media:- use the atmosphere, or space, as the medium.

1. Copper Cable
 The most common, easiest, quickest,
and cheapest form of network media to
install.
 The disadvantage of sending data over
copper wire is that the further the signal
travels, the weaker it becomes.

a. Coaxial Cable
 It can be run longer distances than Twisted pair Cables.
• Speed: 10-100Mbps
• Cost: Inexpensive
• Media and connector size: Medium
• Maximum cable length: 500m

b. Shielded Twisted Pair(STP)
• Speed: 0-100Mbps
• Cost: Moderate
• Media and connector size: Medium to large
• Maximum cable length: 100m

c. Unshielded Twisted Pair
 UTP is a four-pair wire
medium used in a variety of
networks.
 Each of the eight copper wires
in the UTP cable is covered by
insulating material
Speed: 10-100-1000 Mbps*
Cost: Least Expensive
Media and connector size: Small
Maximum cable length: 100m * (Depending
on the quality/category of cable)

UTP Implementation
 EIA/TIA specifies an RJ-45 connector for
UTP cable.
 The letters RJ stand for registered jack.

Fiber Optic Cable
 Glass fiber carrying light pulses, each
pulse a bit.
 Based on the Total Internal Reflection of
Light.
 High-speed point-to-point
transmission 10-100’s Gbps
 low error rate:
 repeaters spaced far apart
 immune to electromagnetic
noise

Communication Protocols
Internet Protocol Suite
 Also called TCP/IP, is the foundation of all modern networking.
 It defines the addressing, identification, and routing specifications
for IPv4 and for IPv6.
 It is the defining set of protocols for the Internet.
IEEE 802
 It is a family of IEEE standards dealing with local area networks
and metropolitan area networks.
 They operate mostly at levels 1 and 2 of the OSI model.
Ethernet
 It is a family of protocols used in wired LANs, described by a set
of standards together called IEEE 802.3

Communication Protocols
Wireless LAN
 It is standardized by IEEE 802.11 and shares many properties with wired
Ethernet.
SONET/SDH
 Synchronous optical networking (SONET) and Synchronous Digital
Hierarchy (SDH) are standardized multiplexing protocols that transfer
multiple digital bit streams over optical Fibre using lasers.
Asynchronous Transfer Mode(ATM)
 It uses asynchronous time-division multiplexing and encodes data into
small, fixed-sized cells.
 Good choice for a network that handle both traditional high-throughput
data traffic, and real-time, low-latency content such as voice and video.

Types of Networks
1. Personal Area Network (PAN)
2. Local Area Network (LAN)
3. Campus Area Network (CAN)
4. Metropolitan Area Network (MAN)
5. Wide Area Network (WAN)
6. Storage-Area Network (SAN)
7. Virtual Private Network (VPN)
8. Client Server Network
9. Peer to Peer Network (P2P)

1. Personal Area Network
1. Personal Area Network (PAN) is a
computer network used for data
transmission amongst devices such
as computers, telephones, tablets
and personal digital assistants.
2. Also Known as HAN (Home Area
Network)
3. PANs can be used for
communication amongst the
personal devices themselves
(interpersonal communication), or
for connecting to a higher level
network and the Internet (an uplink)
where one "master" device takes up
the role as internet router.

2. Local Area Network
 Xerox Corporation worked in
collaboration with DEC and Intel
to create Ethernet, which is the
most pervasive LAN
architecture used today.
 Ethernet has evolved and has
seen significant improvements
in regard to speed and
efficiency.
 An upside of a LAN is fast data transfer with data speed that can reach
up to 10Gbps.
 Other significant LAN technologies are Fiber Distributed Data Interface
(FDDI) and token ring.

3. Campus Area Network
 Larger than LANs, but smaller
than metropolitan area networks
these types of networks are
typically seen in universities,
large K-12 school districts or
small businesses.
 They can be spread across
several buildings that are fairly
close to each other so users can
share resources

4. Metropolitan Area Network
1. A MAN is larger than a LAN but smaller than or equal in size to a WAN.
2. The size range anywhere from 5 to 50km in diameter.
3. MANs are typically owned and managed by a single entity.
4. This could be an ISP or telecommunications company that sells its services
to end-users in that metropolitan area.
5. For all intents and purposes, a MAN has the same characteristics as a WAN
with distance constraints.

5. Wide Area Network
• A Wide Area Network exist over a large area
• Data travels through telephone or cable lines
• Usually requires a Modem
• The world’s largest Wide Area Network in the Internet

6. Storage Area Network
 SAN may be referred to as a Sub network or special purpose network.
 Its special purpose is to allow users on a larger network to connect
various data storage devices with clusters of data servers.
 SANs can be accessed in the same fashion as a drive attached to a
server.

7. Virtual Private Network
 VPN is a private network that can
access public networks remotely. VPN
uses encryption and security protocols
to retain privacy while it accesses
outside resources.
 When employed on a network, VPN
enables an end user to create a virtual
tunnel to a remote location. Typically,
telecommuters use VPN to log in to
their company networks from home.
 Authentication is provided to validate the identities of the two peers.
 Confidentiality provides encryption of the data to keep it private from
prying eyes.
 Integrity is used to ensure that the data sent between the two devices or
sites has not been tampered with.

8. Client/Server Network
In a client/server arrangement,
network services are located on a
dedicated computer called a server.
 The server responds to the requests
of clients.
The server is a central computer that
is continuously available to respond
to requests from clients for file, print,
application, and other services.
 Most network operating systems adopt the form of a client/server
relationship.
 Typically, desktop computers function as clients, and one or more
computers with additional processing power, memory, and specialized
software function as servers.

9. Peer to Peer Network
 Usually very small networks
 Each workstation has equivalent capabilities and responsibilities
 Does not require a switch or a hub.
 These types of networks do not perform well under heavy data
loads.

Network Topologies
Network topology defines the structure of the network.
A. Physical topology:- It define the actual layout of the wire or media.
1. Bus
2. Ring
3. Star
4. Tree(Hierarchical)
5. Mesh
B. Logical topology:- It defines how the hosts access the media to send data.
1. Broadcast
2. Token passing
C. Hybrid Topology

1. Bus Topology
T
T
All devices are connected to a central
cable, called bus or backbone.
There are terminators at each end of
the bus that stops the signal and
keeps it from traveling backwards.
Disadvantages:
1. It is possible that more than one station may
attempt transmission simultaneously (collision or
contention).
2. Difficult reconfiguration and fault isolation.
3. A fault or break in the bus cable stops all
transmission, even between devices on the same
side of the problem.
4. The damaged area reflects signals in the direction
of origin, creating noise in both directions
Advantages:
1. There is no central controller.
2. Control resides in each station
3. The less interconnecting wire is
required.
4. Ease of installation.
5. Backbone cable can be laid along the
most efficient path, and then
connected to the nodes by drop lines
of various lengths

2. Ring Topology
• All devices are connected to one another in the shape
of a closed loop.
• Each device is connected directly to two other devices,
one on either side of it.
Advantages:
1. Avoids the collisions that are possible in the bus topology.
2. Each pair of stations has a point-to-point connection.
3. A signal is passed along the ring in one direction, from device to
another, until it reaches its destination.
4. Each device incorporates a repeater.
5. Relatively easy to install and reconfigure.
6. Fault isolation is simplified.
Disadvantages:
1. A break in the ring (such as station disabled) can disable the entire
network.
2. Unidirectional traffic.

3. Star Topology
• All devices are connected to a central hub.
• Nodes communicate across the network by passing data
through the hub or switch.
Advantages:
1. Easy to install and reconfigure.
2. Robustness, if one link fails; only that link is affected. All other
links remain active.
3. Easy fault identification and isolation. As long as the hub is
working, it can be used to monitor link problems and bypass
defective links.
Disadvantages:
1. The devices are not linked to each other.
2. If one device wants to send data to another, it sends it to the
controller, which then relays the data to the other connected device.

4. Tree/Hierarchical Topology
Advantages:
1. It allows more devices to be attached to a
single central hub and can therefore increase
the distance a signal can travel between
devices.
2. It allows the network to isolate and prioritize
communications from different computers.
Disadvantages:
1. The devices are not linked to each other.
2. If one device wants to send data to another,
it sends it to the controller, which then relays
the data to the other connected device.
3. The addition of secondary hubs brings two
further advantages.

6. Mesh Topology
Each host has its connections to all other hosts.
Mesh topology is implemented to provide as much
protection as possible from interruption of service.
1. A nuclear power plant might use a mesh
topology in the networked control systems.
2. Although the Internet has multiple paths to any
one location, it does not adopt the full mesh
topology.
Disadvantages:
1. A large amount of cabling required.
2. A large amount of I/O ports required.
3. Installation and reconfiguration are difficult.
4. The sheer bulk of the wiring can be greater
than the available space (in the walls, ceiling,
or floors) can accommodate.
5. The hardware required to connect each
link (I/O ports and cables) can be
prohibitively expensive.
Advantages:
1. The use of dedicated links guarantees that each
connection can carry its data load, thus eliminating
the traffic problems that can occur when links must
be shared by multiple devices.
2. It is robust, if one link becomes unusable, it does
not incapacitate (affect) the entire system.
3. Privacy and Security (every message sent travels
along a dedicated line; only the intended recipient
sees it).
4. Point-to-point links make fault identification and
fault isolation easy.

Wireless Networks
Wireless network is a type of
computer network that uses
wireless data connections for
connecting network nodes.
Example
Bluetooth
Wi-Fi

Bluetooth
 Bluetooth is a short-range
wireless technology standard
used for exchanging data
between fixed and mobile
devices over short distances.
 It is using UHF radio waves in
the ISM bands, from 2.402
GHz to 2.48 GHz.
 The IEEE standardized
Bluetooth as IEEE 802.15.1,
but no longer maintains the
standard.

Wi-Fi
 Wi-Fi Stands for Wireless Fidelity.
 Wi-Fi, is a Local Area Wireless
technology.
 Wi-Fi networks use radio technologies to
transmit and receive data at high speed.
 It is based on the IEEE 802.11 family of
standards.
 Access point: The access point is a wireless
LAN transceiver or “ base station” that can
connect one or many wireless devices
simultaneously to the internet

The Internet
The simplest
definition of
the Internet
is that it's a
network of
computer
networks
How Information Travel Through the Internet
A page on the Internet—whether it's full of words, images or
both—doesn't come to you in one shipment. It's translated
into digital information, chopped into 1500 byte pieces called
PACKETS, and sent to you like a puzzle that needs to be
reassembled. Each part of the packet has a specific
function:
Header
Provides the
complete
destination
address for the
packet
Data Block
The portion of the overall information
carried by the packet
Sequence ID
ID’s where the information
belongs in relation to the rest
of the information
End of Message
ID’s the end of the
packet

The Internet
How Information Travel Through the Internet
When you connect to a Web site through an ISP and start exchanging information,
there isn't a fixed connection between your computer and the Web server computer
hosting the Web site. Instead, information is exchanged using the best possible path
at that particular time. Special computers called routers determine these paths,
avoiding slow links and favoring fast ones.
Your
Computer ISP Routers
Web
Servers

1-1 DATA COMMUNICATIONS
The term telecommunication means communication at a
distance. The word data refers to information presented in
whatever form is agreed upon by the parties creating and
using the data.
Data communications are the exchange of data between
two devices via some form of transmission medium such as
a wire cable or wireless.
1. Delivery → Correct destination
2. Accuracy → Accurate data
3. Timelines → Real-time transmission
4. Jitter → Uneven delay
1.46

Figure 1.1 Five components of data communication
Components
Data Representation
Data Flow
Topics discussed in this section:
Components
2
1
3
4
5
1.47

Data Representation
1. Text
2. Numbers
3. Images
4. Audio
5. Video
Data flow
 Simplex
 Half-duplex
 Full-duplex
1.48

1-5 LAYERED TASKS
 A network model is a layered architecture
 Task broken into subtasks
 Implemented separately in layers in stack
 Functions need in both systems
 Peer layers communicate
 Protocol:
 A set of rules that governs data communication
 It represents an agreement between the communicating devices
1.50

Tasks involved in sending a letter
Sender, Receiver, and Carrier
Hierarchy (services)
1.51

1-5.1 THE OSI MODEL
Established in 1947, the International Standards
Organization (ISO) is a multinational body dedicated
to worldwide agreement on international standards.
An ISO is the Open Systems Interconnection (OSI)
model is the standard that covers all aspects of
network communications from ISO. It was first
introduced in the late 1970s.
1.52

Seven layers of the OSI model
Layered Architecture
Layers
Layer 7. Application
Layer 6. Presentation
Layer 5. Session
Layer 4. Transport
Layer 3. Network
Layer 2. Data Link
Layer 1. Physical Sender
Receiver
1.53

Layered Architecture
 A layered model
 Each layer performs a subset of the required
communication functions
 Each layer relies on the next lower layer to perform
more primitive functions
 Each layer provides services to the next higher layer
 Changes in one layer should not require changes in
other layers
 The processes on each machine at a given layer are
called peer-to-peer process
1.54

 Communication must move downward through the layers on
the sending device, over the communication channel, and
upward to the receiving device
 Each layer in the sending device adds its own information to
the message it receives from the layer just above it and passes
the whole package to the layer just below it
 At the receiving device, the message is unwrapped layer by
layer, with each process receiving and removing the data
meant for it
PEER – TO – PEER PROCESS
1.55

PEER – TO – PEER PROCESS
 The passing of the data and network information down
through the layers of the sending device and backup through
the layers of the receiving device is made possible by interface
between each pair of adjacent layers
 Interface defines what information and services a layer must
provide for the layer above it.
1.56

The interaction between layers in the OSI model
1.57

An exchange using the OSI model
1.58

LAYERS IN THE OSI MODEL
1. Physical Layer
2. Data Link Layer
3. Network Layer
4. Transport Layer
5. Session Layer
6. Presentation Layer
7. Application Layer
1.59

The physical layer is responsible for movements of
individual bits from one hop (node) to the next.
 Function
 Physical characteristics of interfaces and media
 Representation of bits
 Data rate
 Synchronization of bits
 Line configuration (point-to-point or multipoint)
 Physical topology (mesh, star, ring or bus)
 Transmission mode ( simplex, half-duplex or duplex)
Physical Layer
1.60

The data link layer is responsible for moving
frames from one hop (node) to the next.
 Function
 Framing
 Physical addressing
 Flow control
 Error control
 Access control
Data Link Layer
1.62

Example 1
In following Figure a node with physical address 10 sends a frame to a node
with physical address 87. The two nodes are connected by a link. At the data
link level this frame contains physical addresses in the header. These are the
only addresses needed. The rest of the header contains other information
needed at this level. The trailer usually contains extra bits needed for error
detection
1.65

The network layer is responsible for the
delivery of individual packets from
the source host to the destination host.
 Source-to-destination delivery
 Responsible from the delivery of packets from the original
source to the final destination
 Functions
 Logical addressing
 routing
Network Layer
1.66

Source-to-destination delivery
1.68

Example 2
We want to send data from a node
with network address A and
physical address 10, located on
one LAN, to a node with a
network address P and physical
address 95, located on another
LAN. Because the two devices are
located on different networks, we
cannot use physical addresses
only; the physical addresses only
have local influence. What we
need here are universal addresses
that can pass through the LAN
boundaries. The network (logical)
addresses have this characteristic.
1.69

The transport layer is responsible for the delivery
of a message from one process to another.
 Process-to- process delivery
 Functions
 Port addressing
 Segmentation and reassembly
 Connection control ( Connection-oriented or connection-less)
 Flow control
 Error control
Transport Layer
1.70

Transport layer
Segmentation and reassembly
1.71

Reliable process-to-process delivery of a message
1.72

Example 3
Data coming from the
upper layers have port
addresses j and k (j is the
address of the sending
process, and k is the
address of the receiving
process). Since the data size
is larger than the network
layer can handle, the data
are split into two packets,
each packet retaining the
port addresses (j and k).
Then in the network layer,
network addresses (A and
P) are added to each
packet.
1.73

The session layer is responsible for dialog
control and synchronization.
Session Layer
 It establishes, maintains and synchronize the
interaction between communicating system
 Function
 Dialog control
 Synchronization (checkpoints)
1.74

Session layer
Synchronization
1.75

The presentation layer is responsible for translation,
compression, and encryption.
Presentation Layer
 Concerned with the syntax and semantics of the
information exchanged between two system
 Functions
 Translation ( EBCDIC-coded text file  ASCII-coded
file)
 Encryption and Decryption
 Compression
1.76

The application layer is responsible for
providing services to the user.
 Functions
 Network virtual terminal (Remote log-in)
 File transfer and access
 Mail services
 Directory services (Distributed Database)
 Accessing the World Wide Web
Application Layer
1.78

TCP/IP model
•The TCP/IP model was developed prior to the OSI model.
•The TCP/IP model is not exactly similar to the OSI model.
•The TCP/IP model consists of five layers: the application layer, transport layer,
network layer, data link layer and physical layer.
•The first four layers provide physical standards, network interface,
internetworking, and transport functions that correspond to the first four layers
of the OSI model TCP/IP is a hierarchical protocol made up of interactive
modules, and each of them provides specific functionality.

Network Access Layer
• A network layer is the lowest layer of the TCP/IP model.
• A network layer is the combination of the Physical layer and Data
Link layer defined in the OSI reference model.
• It defines how the data should be sent physically through the
network.
• This layer is mainly responsible for the transmission of the data
between two devices on the same network.
• The functions carried out by this layer are encapsulating the IP
datagram into frames transmitted by the network and mapping of IP
addresses into physical addresses.
• The protocols used by this layer are ethernet, token ring, FDDI, X.25,
frame relay.

Internet Layer
• An internet layer is the second layer of the TCP/IP model.
• An internet layer is also known as the network layer.
• The main responsibility of the internet layer is to send the
packets from any network, and they arrive at the destination
irrespective of the route they take.

Transport Layer
• The transport layer is responsible for the reliability, flow control,
and correction of data which is being sent over the network.
• The two protocols used in the transport layer are User
Datagram protocol and Transmission control protocol.

Application Layer
• An application layer is the topmost layer in the TCP/IP model.
• It is responsible for handling high-level protocols, issues of representation.
• This layer allows the user to interact with the application.
• When one application layer protocol wants to communicate with another application layer,
it forwards its data to the transport layer.
• There is an ambiguity occurs in the application layer. Every application cannot be placed
inside the application layer except those who interact with the communication system. For
example: text editor cannot be considered in application layer while web browser
using HTTP protocol to interact with the network where HTTP protocol is an application
layer protocol.

Network Security and its applications in

Computer Network Security
• Computer network security consists of measures taken by
business or some organizations to monitor and prevent
unauthorized access from the outside attackers.
• Network Administrator controls access to the data and software
on the network. A network administrator assigns the user ID and
password to the authorized person.

• Privacy: Privacy means both the sender and the receiver expects
confidentiality. The transmitted message should be sent only to the
intended receiver while the message should be opaque for other
users.
• Message Integrity: Data integrity means that the data must arrive at
the receiver exactly as it was sent. There must be no changes in the
data content during transmission, either maliciously or accident, in a
transit.
• End-point authentication: Authentication means that the receiver is
sure of the sender’s identity, i.e., no imposter has sent the message.
• Non-Repudiation: Non-Repudiation means that the receiver must
be able to prove that the received message has come from a specific
sender. The sender must not deny sending a message that he or she
send.

Cryptography
• Encryption/Decryption
• Encryption: Encryption means that the sender converts the
original information into another form and sends the
unintelligible message over the network.
• Decryption: Decryption reverses the Encryption process in
order to transform the message back to the original form.
• The data which is to be encrypted at the sender site is known
as plaintext, and the encrypted data is known as ciphertext. The
data is decrypted at the receiver site.

1. There are two types of Encryption/Decryption techniques:
Privacy with secret key Encryption/Decryption
Privacy with public key Encryption/Decryption

Secret Key
Encryption/Decryption technique
• In Secret Key Encryption/Decryption technique, the same key is
used by both the parties, i.e., the sender and receiver.
• The sender uses the secret key and encryption algorithm to
encrypt the data; the receiver uses this key and decryption
algorithm to decrypt the data.
• The secret key encryption algorithm is also known as symmetric
encryption algorithm because the same secret key is used in
bidirectional communication.
• In secret key encryption/decryption algorithm, the secret code is
used by the computer to encrypt the information before it is sent
over the network to another computer.

Public Key Encryption/Decryption
technique
• here are two keys in public key encryption: a private key and a
public key.
• The private key is given to the receiver while the public key is
provided to the public.
• In public key Encryption/Decryption, the public key used by the
sender is different from the private key used by the receiver.
• The public key is available to the public while the private key is
kept by each individual.
• The most commonly used public key algorithm is known as
RSA.

Digital Signature
• The Digital Signature is a technique which is used to validate
the authenticity and integrity of the message. We know that
there are four aspects of security: privacy, authentication,
integrity, and non-repudiation. We have already discussed the
first aspect of security and other three aspects can be achieved
by using a digital signature.
• The basic idea behind the Digital Signature is to sign a
document. When we send a document electronically, we can
also sign it. We can sign a document in two ways: to sign a
whole document and to sign a digest.

Signing the Whole Document
• In Digital Signature, a public key encryption technique is used to
sign a document. However, the roles of a public key and private
key are different here.
• The sender uses a private key to encrypt the message while the
receiver uses the public key of the sender to decrypt the
message.
In Digital Signature, the private key is used for encryption while
the public key is used for decryption.
• Digital Signature cannot be achieved by using secret key
encryption.

Signing the Digest
• Public key encryption is efficient if the message is short. If the
message is long, a public key encryption is inefficient to use.
The solution to this problem is to let the sender sign a digest of
the document instead of the whole document.
• The sender creates a miniature version (digest) of the
document and then signs it, the receiver checks the signature of
the miniature version.
• The hash function is used to create a digest of the message.
The hash function creates a fixed-size digest from the variable-
length message.
• The two most common hash functions used: MD5 (Message
Digest 5) and SHA-1 (Secure Hash Algorithm 1). The first one
produces 120-bit digest while the second one produces a 160-
bit digest.

PGP
• PGP stands for Pretty Good Privacy (PGP) which is invented by Phil
Zimmermann.
• PGP was designed to provide all four aspects of security, i.e.,
privacy, integrity, authentication, and non-repudiation in the sending
of email.
• PGP uses a digital signature (a combination of hashing and public
key encryption) to provide integrity, authentication, and non-
repudiation.
• PGP uses a combination of secret key encryption and public key
encryption to provide privacy.
• PGP is an open source and freely available software package for
email security.
• PGP provides authentication through the use of Digital Signature.
• It provides confidentiality through the use of symmetric block
encryption.

• Following are the steps taken by PGP to create secure e-mail at
the sender site:
• The e-mail message is hashed by using a hashing function to
create a digest.
• The digest is then encrypted to form a signed digest by using
the sender's private key, and then signed digest is added to the
original email message.
• The original message and signed digest are encrypted by using
a one-time secret key created by the sender.
• The secret key is encrypted by using a receiver's public key.
• Both the encrypted secret key and the encrypted combination of
message and digest are sent together.

• Following are the steps taken to show how PGP uses hashing
and a combination of three keys to generate the original
message:
• The receiver receives the combination of encrypted secret key
and message digest is received.
• The encrypted secret key is decrypted by using the receiver's
private key to get the one-time secret key.
• The secret key is then used to decrypt the combination of
message and digest.
• The digest is decrypted by using the sender's public key, and
the original message is hashed by using a hash function to
create a digest.
• Both the digests are compared if both of them are equal means
that all the aspects of security are preserved.

Network Attack
• A network attack is an attempt to gain unauthorized access to an
organization’s network, with the objective of stealing data or perform
other malicious activity. There are two main types of network attacks:
• Passive: Attackers gain access to a network and can monitor or
steal sensitive information, but without making any change to
the data, leaving it intact.
• Active: Attackers not only gain unauthorized access but also
modify data, either deleting, encrypting or otherwise harming it.

Types of Network Attacks
• 1. Unauthorized access
Unauthorized access refers to attackers accessing a network
without receiving permission.
• 2. Distributed Denial of Service (DDoS) attacks
Attackers build botnets, large fleets of compromised devices,
and use them to direct false traffic at your network or servers.
• 3. Man in the middle attacks
A man in the middle attack involves attackers intercepting
traffic, either between your network and external sites or within your
network.
• 4. Code and SQL injection attacks
Many websites accept user inputs and fail to validate and
sanitize those inputs. Attackers can then fill out a form or make an API
passing malicious code instead of the expected data values.
• 5. Privilege escalation
Once attackers penetrate your network, they can use privilege
escalation to expand their reach.
• 6. Insider threats
A network is especially vulnerable to malicious insiders, who
already have privileged access to organizational systems

FIREWALL
• A firewall can be defined as a special type of network security device or a software
program that monitors and filters incoming and outgoing network traffic based on a
defined set of security rules.
• It acts as a barrier between internal private networks and external sources (such as
the public Internet).
• The primary purpose of a firewall is to allow non-threatening traffic and prevent
malicious or unwanted data traffic for protecting the computer from viruses and
attacks.
• A firewall is a cybersecurity tool that filters network traffic and helps users block
malicious software from accessing the Internet in infected computers.

Functions of Firewall
• Network Threat Prevention
• Application and Identity-Based Control
• Hybrid Cloud Support
• Scalable Performance
• Network Traffic Management and Control
• Access Validation
• Record and Report on Events

Network Security and its applications in

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