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Assignment Questions

Cryptography and Network Security:

Principles and Practice
Eighth Edition

Chapter 1

Information and Network Security

Concepts

Cybersecurity (1 of 3)

Cybersecurity is the collection of tools, policies, security

concepts, security safeguards, guidelines, risk management

approaches, actions, training, best practices, assurance, and

technologies that can be used to protect the cyberspace

environment and organization and users’ assets.

Organization and users’ assets include connected computing

devices, personnel, infrastructure, applications, services,

telecommunications systems, and the totality of transmitted

and/or stored information in the cyberspace environment.

Cybersecurity (2 of 3)

Cybersecurity strives to ensure the attainment and

maintenance of the security properties of the organization

and users’ assets against relevant security risks in the

cyberspace environment. The general security objectives

comprise the following: availability; integrity, which may

include data authenticity and nonrepudiation; and

confidentiality

Cybersecurity (3 of 3)

Information Security

• This term refers to preservation of confidentiality, integrity,

and availability of information. In addition, other properties,

such as authenticity, accountability, nonrepudiation, and

reliability can also be involved

Network Security

• This term refers to protection of networks and their service

from unauthorized modification, destruction, or disclosure,

and provision of assurance that the network performs its

critical functions correctly and there are no harmful side

effects

Security Objectives (1 of 2)

• The cybersecurity definition introduces three key

objectives that are at the heart of information and network

security:

– Confidentiality: This term covers two related

concepts:

▪ Data confidentiality: Assures that private or

confidential information is not made available or

disclosed to unauthorized individuals

▪ Privacy: Assures that individuals control or

influence what information related to them may be

collected and stored and by whom and to whom

that information may be disclosed

Security Objectives (2 of 2)

• Integrity: This term covers two related concepts:

– Data integrity: Assures that data and programs are changed only

in a specified and authorized manner. This concept also

encompasses data authenticity, which means that a digital object

is indeed what it claims to be or what it is claimed to be, and

nonrepudiation, which is assurance that the sender of information

is provided with proof of delivery and the recipient is provided with

proof of the sender’s identity, so neither can later deny having

processed the information

– System integrity: Assures that a system performs its intended

function in an unimpaired manner, free from deliberate or

inadvertent unauthorized manipulation of the system

• Availability: Assures that systems work promptly and service is not

denied to authorized users

Figure 1.1 Essential Information and

Network Security Objectives

Computer Security Challenges

• Security is not simple

• Potential attacks on the security

features need to be considered

• Procedures used to provide

particular services are often

counter-intuitive

• It is necessary to decide where

to use the various security

mechanisms

• Requires constant monitoring

• Is too often an afterthought

• Security mechanisms typically

involve more than a particular

algorithm or protocol

• Security is essentially a battle of

wits between a perpetrator and

the designer

• Little benefit from security

investment is perceived until a

security failure occurs

• Strong security is often viewed as

an impediment to efficient and

user-friendly operation

O S I Security Architecture

• Security attack

– Any action that compromises the security of information

owned by an organization

• Security mechanism

– A process (or a device incorporating such a process) that is

designed to detect, prevent, or recover from a security

attack

• Security service

– A processing or communication service that enhances the

security of the data processing systems and the information

transfers of an organization

– Intended to counter security attacks, and they make use of

one or more security mechanisms to provide the service

Threats and Attacks

Threat

A potential for violation of security, which exists when there

is a circumstance, capability, action, or event that could

breach security and cause harm. That is, a threat is a

possible danger that might exploit a vulnerability.

Attack

An assault on system security that derives from an intelligent

threat; that is, an intelligent act that is a deliberate attempt

(especially in the sense of a method or technique) to evade

security services and violate the security policy of a system.

Figure 1.2 Key Concepts in Security (1 of 2)

Figure 1.2 Key Concepts in Security
(2 of 2)

Security Attacks

• A means of classifying security attacks, used both in X.800

and R F C 4949, is in terms of passive attacks and active

attacks

• A passive attack attempts to learn or make use of

information from the system but does not affect system

resources

• An active attack attempts to alter system resources or

affect their operation

Passive Attacks

• Are in the nature of

eavesdropping on, or

monitoring of,

transmissions

• Goal of the opponent is to

obtain information that is

being transmitted

• Two types of passive

attacks are:

– The release of message

contents

– Traffic analysis

Active Attacks

• Involve some modification of the

data stream or the creation of a

false stream

• Difficult to prevent because of the

wide variety of potential physical,
software, and network

vulnerabilities

• Goal is to detect attacks and to

recover from any disruption or

delays caused by them

• Masquerade

– Takes place when one entity

pretends to be a different entity

– Usually includes one of the other

forms of active attack
• Replay

– Involves the passive capture of a

data unit and its subsequent

retransmission to produce an

unauthorized effect
• Data Modification

– Some portion of a legitimate

message is altered, or messages

are delayed or reordered to

produce an unauthorized effect
• Denial of service

– Prevents or inhibits the normal use

or management of communications

facilities

Figure 1.3 Security Attacks

Authentication (1 of 2)

• Concerned with assuring that a communication is authentic

– In the case of a single message, assures the recipient

that the message is from the source that it claims to be

from

– In the case of ongoing interaction, assures the two

entities are authentic and that the connection is not

interfered with in such a way that a third party can

masquerade as one of the two legitimate parties

• Two specific authentication services are defined in X.800:

– Peer entity authentication

– Data origin authentication

Authentication (2 of 2)

• Peer entity authentication

– Provides for the corroboration of the identity of a peer entity in an

association. Two entities are considered peers if they implement

the same protocol in different systems. Peer entity authentication

is provided for use at the establishment of, or at times during the

data transfer phase of, a connection. It attempts to provide

confidence that an entity is not performing either a masquerade or

an unauthorized replay of a previous connection

• Data origin authentication

– Provides for the corroboration of the source of a data unit. It does

not provide protection against the duplication or modification of

data units. This type of service supports applications like

electronic mail, where there are no ongoing interactions between

the communicating entities

Access Control

• The ability to limit and control the access to host systems

and applications via communications links

• To achieve this, each entity trying to gain access must first

be identified, or authenticated, so that access rights can be

tailored to the individual

Data Confidentiality

• The protection of transmitted data from passive attacks

– Broadest service protects all user data transmitted between

two users over a period of time

– Narrower forms of service includes the protection of a single

message or even specific fields within a message

• The protection of traffic flow from analysis

– This requires that an attacker not be able to observe the

source and destination, frequency, length, or other

characteristics of the traffic on a communications facility

Data Integrity

• Can apply to a stream of messages, a single message, or

selected fields within a message

• Connection-oriented integrity service, one that deals with a

stream of messages, assures that messages are received

as sent with no duplication, insertion, modification,

reordering, or replays

• A connectionless integrity service, one that deals with

individual messages without regard to any larger context,

generally provides protection against message

modification only

Nonrepudiation

• Prevents either sender or receiver from denying a

transmitted message

• When a message is sent, the receiver can prove that the

alleged sender in fact sent the message

• When a message is received, the sender can prove that

the alleged receiver in fact received the message

Availability Service

• Protects a system to ensure its availability

• This service addresses the security concerns raised by

denial-of-service attacks

• It depends on proper management and control of system

resources and thus depends on access control service and

other security services

Security Mechanisms (1 of 2)

• Cryptographic algorithms: We can distinguish between

reversible cryptographic mechanisms and irreversible

cryptographic mechanisms. A reversible cryptographic

mechanism is simply an encryption algorithm that allows data to

be encrypted and subsequently decrypted. Irreversible

cryptographic mechanisms include hash algorithms and

message authentication codes, which are used in digital

signature and message authentication applications.

• Data integrity: This category covers a variety of mechanisms

used to assure the integrity of a data unit or stream of data

units.

• Digital signature: Data appended to, or a cryptographic

transformation of, a data unit that allows a recipient of the data

unit to prove the source and integrity of the data unit and protect

against forgery.

Security Mechanisms (2 of 2)

• Authentication exchange: A mechanism intended to ensure

the identity of an entity by means of information exchange.

• Traffic padding: The insertion of bits into gaps in a data stream

to frustrate traffic analysis attempts.

• Routing control: Enables selection of particular physically or

logically secure routes for certain data and allows routing

changes, especially when a breach of security is suspected.

• Notarization: The use of a trusted third party to assure certain

properties of a data exchange

• Access control: A variety of mechanisms that enforce access

rights to resources.

Figure 1.4 Cryptographic Algorithms

Keyless Algorithms

• Deterministic functions that have certain properties useful

for cryptography

• One type of keyless algorithm is the cryptographic hash

function

– A hash function turns a variable amount of text into a

small, fixed-length value called a hash value, hash

code, or digest

– A cryptographic hash function is one that has additional

properties that make it useful as part of another

cryptographic algorithm, such as a message

authentication code or a digital signature

• A pseudorandom number generator produces a

deterministic sequence of numbers or bits that has the

appearance of being a truly random sequence

Single-Key Algorithms (1 of 3)
• Single-key cryptographic algorithms depend on the use of

a secret key

• Encryption algorithms that use a single key are referred to

as symmetric encryption algorithms

– With symmetric encryption, an encryption algorithm

takes as input some data to be protected and a secret

key and produces an unintelligible transformation on

that data

– A corresponding decryption algorithm takes the

transformed data and the same secret key and

recovers the original data

Single-Key Algorithms (2 of 3)
• Symmetric encryption takes the following forms:

– Block cipher

▪ A block cipher operates on data as a sequence of

blocks

▪ In most versions of the block cipher, known as

modes of operation, the transformation depends not

only on the current data block and the secret key but

also on the content of preceding blocks

– Stream cipher

▪ A stream cipher operates on data as a sequence of

bits

▪ As with the block cipher, the transformation depends

on a secret key

Single-Key Algorithms (3 of 3)

• Another form of single-key cryptographic algorithm is the

message authentication code (M A C)

– A M A C is a data element associated with a data block

or message

– The M A C is generated by a cryptographic

transformation involving a secret key and, typically, a

cryptographic hash function of the message

– The M A C is designed so that someone in possession

of the secret key can verify the integrity of the message

– The recipient of the message plus the M A C can

perform the same calculation on the message; if the

calculated M A C matches the M A C accompanying the

message, this provides assurance that the message

has not been altered

Asymmetric Algorithms

• Encryption algorithms that use a single key are referred to as

asymmetric encryption algorithms

• Digital signature algorithm

– A digital signature is a value computed with a cryptographic

algorithm and associated with a data object in such a way that any

recipient of the data can use the signature to verify the data’s

origin and integrity

• Key exchange

– The process of securely distributing a symmetric key to two or

more parties

• User authentication

– The process of authenticating that a user attempting to access an

application or service is genuine and, similarly, that the application

or service is genuine

Figure 1.5 Key Elements of Network

Security

Communications Security

• Deals with the protection of communications through the

network, including measures to protect against both passive and

active attacks

• Communications security is primarily implemented using

network protocols

– A network protocol consists of the format and procedures

that governs the transmitting and receiving of data between

points in a network

– A protocol defines the structure of the individual data units

and the control commands that manage the data transfer

• W ith respect to network security, a security protocol may be an

enhancement that is part of an existing protocol or a standalone

protocol

Device Security (1 of 2)

• The other aspect of network security is the protection of

network devices, such as routers and switches, and end

systems connected to the network, such as client systems

and servers

• The primary security concerns are intruders that gain

access to the system to perform unauthorized actions,

insert malicious software (malware), or overwhelm system

resources to diminish availability

Device Security (2 of 2)
• Three types of device security are:

– Firewall

▪ A hardware and/or software capability that limits access

between a network and device attached to the network, in

accordance with a specific security policy. The firewall acts as

a filter that permits or denies data traffic, both incoming and

outgoing, based on a set of rules based on traffic content

and/or traffic pattern

– Intrusion detection

▪ Hardware or software products that gather and analyze

information from various areas within a computer or a network

for the purpose of finding, and providing real-time or near-real-

time warning of, attempts to access system resources in an

unauthorized manner

– Intrusion prevention

▪ Hardware or software products designed to detect intrusive

activity and attempt to stop the activity, ideally before it reaches

its target

Trust Model (1 of 2)

• One of the most widely accepted and most cited definitions

of trust is:
“the willingness of a party to be vulnerable to the actions
of another party based on the expectation that the other
will perform a particular action important to the trustor,
irrespective of the ability to monitor or control that other
party”

Trust Model (2 of 2)

• Three related concepts are relevant to a trust model:

– Trustworthiness: A characteristic of an entity that

reflects the degree to which that entity is deserving of

trust

– Propensity to trust: A tendency to be willing to trust

others across a broad spectrum of situations and trust

targets. This suggests that every individual has some

baseline level of trust that will influence the person’s

willingness to rely on the words and actions of others

– Risk: A measure of the extent to which an entity is

threatened by a potential circumstance or event, and

typically a function of 1) the adverse impacts that would

arise if the circumstance or event occurs; and 2) the

likelihood of occurrence

Figure 1.6 Trust Model

The Trust Model and Information

Security
• Trust is confidence that an entity will perform in a way that will not

prejudice the security of the user of the system of which that entity is a

part

• Trust is always restricted to specific functions or ways of behavior and

is meaningful only in the context of a security policy

• Generally, an entity is said to trust a second entity when the first entity

assumes that the second entity will behave exactly as the first entity

expects

• In this context, the term entity may refer to a single hardware

component or software module, a piece of equipment identified by

make and model, a site or location, or an organization

Trustworthiness of an Individual
(1 of 2)

• Organizations need to be concerned about both internal users

(employees, on-site contractors) and external users (customers,

suppliers) of their information systems

• W ith respect to internal users, an organization develops a level of trust

in individuals by policies in the following two areas:

• Human resource security

– Sound security practice dictates that information security

requirements be embedded into each stage of the employment life

cycle, specifying security-related actions required during the

induction of each individual, their ongoing management, and

termination of their employment. Human resource security also

includes assigning ownership of information (including

responsibility for its protection) to capable individuals and

obtaining confirmation of their understanding and acceptance

Trustworthiness of an Individual
(2 of 2)

• Security awareness and training

– This area refers to disseminating security information

to all employees, including I T staff, I T security staff,

and management, as well as I T users and other

employees. A workforce that has a high level of

security awareness and appropriate security training

for each individual’s role is as important, if not more

important, than any other security countermeasure or

control

Trustworthiness of an Organization

• Most organizations rely on information system service and information

provided by external organizations, as well as partnerships to accomplish

missions and business functions (examples are cloud service providers and

companies that form part of the supply chain for the organization)

• To manage risk to the organization, it must establish trust relationships with
these external organizations

• N I S T S P 800-39 (Managing Information Security Risk, March 2011) indicates

that such trust relationships can be:

– Formally established, for example, by documenting the trust-related

information in contracts, service-level agreements, statements of work,
memoranda of agreement/understanding, or interconnection security

agreements

– Scalable and inter-organizational or intra-organizational in nature

– Represented by simple (bilateral) relationships between two partners or

more complex many-to-many relationships among many diverse partners

Trustworthiness of Information

Systems
• S P 800-39 defines trustworthiness for information systems as

“the degree to which information systems (including the information

technology products from which the systems are built) can be

expected to preserve the confidentiality, integrity, and availability of

the information being processed, stored, or transmitted by the

systems across the full range of threats”

• Two factors affecting the trustworthiness of information systems are:

– Security functionality: The security features/functions employed

within the system. These include cryptographic and network

security technologies

– Security assurance: The grounds for confidence that the security

functionality is effective in its application. This area is addressed

by security management techniques, such as auditing and

incorporating security considerations into the system development

life cycle

Establishing Trust Relationships

• Validated trust:

– Trust is based on evidence obtained by the trusting organization about the

trusted organization or entity. The information may include information

security policy, security measures, and level of oversight

• Direct historical trust:

– This type of trust is based on the security-related track record exhibited by

an organization in the past, particularly in interactions with the

organization seeking to establish trust

• Mediated trust:

– Mediated trust involves the use of a third party that is mutually trusted by
two parties, with the third party providing assurance or guarantee of a

given level of trust between the first two parties

• Mandated trust:

– An organization establishes a level of trust with another organization

based on a specific mandate issued by a third party in a position of
authority

Standards (1 of 2)
• National Institute of Standards and Technology:

– N I S T is a U.S. federal agency that deals with measurement science,

standards, and technology related to U.S. government use and to the

promotion of U.S. private-sector innovation. Despite its national scope, N I

S T Federal Information Processing Standards (F I P S) and Special
Publications (S P) have a worldwide impact

• Internet Society:

– I S O C is a professional membership society with worldwide organizational

and individual membership. It provides leadership in addressing issues

that confront the future of the Internet and is the organization home for the
groups responsible for Internet infrastructure standards, including the

Internet Engineering Task Force (I E T F) and the Internet Architecture

Board (I A B). These organizations develop Internet standards and related

specifications, all of which are published as Requests for Comments (R F

C s).

Standards (2 of 2)
• I T U-T:

– The International Telecommunication Union (I T U) is an international

organization within the United Nations System in which governments and

the private sector coordinate global telecom networks and services. The I

T U Telecommunication Standardization Sector (I T U-T) is one of the three
sectors of the I T U. I T U-T’s mission is the development of technical

standards covering all fields of telecommunications. I T U-T standards are

referred to as Recommendations

• I S O:

– The International Organization for Standardization (I S O) is a worldwide
federation of national standards bodies from more than 140 countries,

one from each country. I S O is a nongovernmental organization that

promotes the development of standardization and related activities with a

view to facilitating the international exchange of goods and services and

to developing cooperation in the spheres of intellectual, scientific,
technological, and economic activity. I S O’s work results in international

agreements that are published as International Standards

Summary

• Describe the key security requirements of confidentiality, integrity, and

availability

• List and briefly describe key organizations involved in cryptography

standards

• Provide an overview of keyless, single-key and two-key cryptographic

algorithms

• Provide an overview of the main areas of network security

• Describe a trust model for information security

• Discuss the types of security threats and attacks that must be dealt

with and give examples of the types of threats and attacks that apply to

different categories of computer and network assets

Copyright

This work is protected by United States copyright laws and is

provided solely for the use of instructors in teaching their

courses and assessing student learning. Dissemination or sale of

any part of this work (including on the World Wide Web) will

destroy the …

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