This document provides an overview of cryptography and network security concepts from the textbook "Cryptography & Network Security" by William Stallings. It covers topics like confidentiality, integrity, availability, security threats/attacks, security services, security mechanisms, and the OSI security architecture. The document includes chapter objectives, definitions of key terms, descriptions of security concepts, examples, and review questions. The overall purpose is to introduce fundamental cryptography and network security principles.

1. 2020 - 2021
Odd Semester
14ITT71
Cryptography and Network Security

2. 14ITT71-CryptographyandNetworkSecurity
Roadmap
01 Introduction &
Number Theory
02 Symmetric Key
Cryptography
03 Hash Function
& Digital Signature
04 Security Practice
& System Security
05 E Mail Security
• OSI security
architecture
• Classical Encryption
techniques
• Number theory
• DES
• AES
• RSA
• DH Exchange
• ECC
• MAC
• MD5
• SHA
• HMAC
• CMAC
• Digital Signature
• Kerberos
• Firewalls
• Trusted Systems
• IDS
• Virus and Threats
• PGP
• S/MIME
• IP Security
• Internet Key
Exchange
• Web Security
Understand OSI security
architecture and classical
encryption techniques
Acquire knowledge in
symmetric and public key
cryptography
Know about hash function
and digital signatures
Recognize security practice
and system security
Gain knowledge in email and
web security
Cryptography & Network Security - William Stallings
6th Edition

3. 14ITT71-CryptographyandNetworkSecurity
Chapter 1
Computer and Network Security Concepts

4. 14ITT71-CryptographyandNetworkSecurity
Learning Objectives
After studying this chapter, you should be able to:
1. Describe the key security requirements of confidentiality, integrity, and
availability.
2. 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.
3. Summarize the functional requirements for computer security. Describe
the X.800 security architecture for OSI.

5. 14ITT71-CryptographyandNetworkSecurity
Computer Security
The field of network and Internet security consists of measures to deter, prevent, detect, and correct security
violations that involve the transmission of information.
C
A B
Employee
Manager
Server
Fired
Invalidate Employees Account
Confirmation ?

6. 14ITT71-CryptographyandNetworkSecurity
Computer Security
The NIST Computer Security Handbook defines the term computer
security as:
“ the protection afforded to an automated information system in
order to attain the applicable objectives of preserving the integrity,
availability and confidentiality of i n f o r m a t i o n s y s t e m
resources” (includes hardware, software, firmware, information/
data, and telecommunications)

7. 14ITT71-CryptographyandNetworkSecurity
Three key objectives that are
at the heart of computer security
• Confidentiality
• Integrity
• Availability Figure 1.1 Essential Network and Computer Security Requirements
Data
and
services
Availability
Integrity
Accountability
Authenticity
Confidentiality

8. 14ITT71-CryptographyandNetworkSecurity
CIA triad
• Confidentiality: Preserving authorised restrictions on information access and
disclosure, including means for protecting personal privacy and proprietary
information. A loss of confidentiality is the unauthorised disclosure of
information.
• Integrity: Guarding against improper information modification or destruction,
including ensuring information nonrepudiation and authenticity. A loss of
integrity is the unauthorised modification or destruction of information.
• Availability: Ensuring timely and reliable access to and use of information. A
loss of availability is the disruption of access to or use of information or an
information system.

9. 14ITT71-CryptographyandNetworkSecurity
CIA triad + AA
• Authenticity: The property of being genuine and being able to be verified and
trusted; confidence in the validity of a transmission, a message, or message
originator. This means verifying that users are who they say they are and that
each input arriving at the system came from a trusted source
• Accountability: The security goal that generates the requirement for actions of
an entity to be traced uniquely to that entity. This supports nonrepudiation,
deterrence, fault isolation, intrusion detection and prevention, and after- action
recovery and legal action. Because truly secure systems are not yet an
achievable goal, we must be able to trace a security breach to a responsible
party. Systems must keep records of their activities to permit later forensic
analysis to trace security breaches or to aid in transaction disputes.

10. 14ITT71-CryptographyandNetworkSecurity
The loss could be expected to have a severe or catastrophic adverse effect
on organizational operations, organizational assets, or individuals
The loss could be expected to have a serious adverse effect on
organizational operations, organizational assets, or individuals
The loss could be expected to have a limited adverse effect on
organizational operations, organizational assets, or individuals
High
Moderate
Low
Breach of Security & its Impacts

11. 14ITT71-CryptographyandNetworkSecurity
Security is not simple
Potential attacks on the security
features need to be considered
Security mechanisms typically involve more
than a particular algorithm or protocol
Security is essentially a battle of wits
between a perpetrator and the designer
Procedures used to provide particular
services are often counter-intuitive
Little benefit from security investment is
perceived until a security failure occursIt is necessary to decide where to use the
various security mechanisms
Requires constant monitoring
Is too often an afterthought
Strong security is often viewed as an
impediment to efficient and user-friendly
operation
Computer Security Challenges

12. 14ITT71-CryptographyandNetworkSecurity
OSI Security Architecture
1. Security attack
• Any action that compromises the security of information owned by an
organisation
2. Security mechanism
• A process (or a device incorporating such a process) that is designed to
detect, prevent, or recover from a security attack
3. 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

13. 14ITT71-CryptographyandNetworkSecurity
Threats vs Attacks

14. 14ITT71-CryptographyandNetworkSecurity
Security Attacks

15. 14ITT71-CryptographyandNetworkSecurity
Security Attacks
A passive attack attempts to learn or make use of
information from the system but does not affect
system resources
(a) Passive attacks
Alice
(b) Active attacks
Figure 1.2 Security Attacks
Bob
Darth
Internet or
other comms facility
Bob
Darth
Alice
Internet or
other comms facility
1 2
3
An active attack attempts to alter system resources
or affect their operation

16. 14ITT71-CryptographyandNetworkSecurity
Passive Attacks
Two types of passive attacks are:
• The release of message contents
• Traffic analysis

17. 14ITT71-CryptographyandNetworkSecurity
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
• Takes place when one entity
pretends to be a different entity
• Usually includes one of the other
forms of active attack
Masquerade
• Involves the passive capture of a
data unit and its subsequent
retransmission to produce an
unauthorized effect
Replay
• Some portion of a legitimate
message is altered, or messages
are delayed or reordered to
produce an unauthorized effect
Modification of
messages
• Prevents or inhibits the normal
use or management of
communications facilities
Denial of
service

18. 14ITT71-CryptographyandNetworkSecurity
Security Services
• Defined by X.800 as:
•A service provided by a protocol layer of communicating open systems and
that ensures adequate security of the systems or of data transfers
• Defined by RFC 4949 as:
•A processing or communication service provided by a system to give a specific
kind of protection to system resources

19. 14ITT71-CryptographyandNetworkSecurity
Security
Services
(X.800)
(This table is found on page
18 in textbook)

20. 14ITT71-CryptographyandNetworkSecurity
Authentication
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

21. 14ITT71-CryptographyandNetworkSecurity
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 indentified, or
authenticated, so that access rights can be tailored to the individual

22. 14ITT71-CryptographyandNetworkSecurity
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

23. 14ITT71-CryptographyandNetworkSecurity
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

24. 14ITT71-CryptographyandNetworkSecurity
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

25. 14ITT71-CryptographyandNetworkSecurity
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

26. 14ITT71-CryptographyandNetworkSecurity
Security Mechanisms (X.800)
Specific Security Mechanisms
•Encipherment
•Digital signatures
•Access controls
•Data integrity
•Authentication exchange
•Traffic padding
•Routing control
Pervasive Security Mechanisms
•Trusted functionality
•Security labels
•Event detection
•Security audit trails
•Security recovery

27. 14ITT71-CryptographyandNetworkSecurity
Security
Mechanisms
(X.800)
(This table is found on pages
14-15 in textbook)

28. 14ITT71-CryptographyandNetworkSecurity
Relationship Between Security Services and
Mechanisms

29. 14ITT71-CryptographyandNetworkSecurity
Model for Network Security
Information
Channel
Security-related
transformation
Sender
Secret
information
Message
Message
Secure
message
Secure
message
Recipient
Opponent
Trusted third party
(e.g., arbiter, distributer
of secret information)
Figure 1.5 Model for Network Security
Security-related
transformation
Secret
information

30. 14ITT71-CryptographyandNetworkSecurity
Network Access Security Model
Computing resources
(processor, memory, I/O)
Data
Processes
Software
Internal security controls
Information System
Gatekeeper
function
Opponent
—human (e.g., hacker)
—software
(e.g., virus, worm)
Figure 1.6 Network Access Security Model
Access Channel

31. 14ITT71-CryptographyandNetworkSecurity
Review Questions
• What is the OSI security architecture?
• What is the difference between passive and active security threats?
• List and briefly define categories of passive and active security attacks.
• List and briefly define categories of security services.
• List and briefly define categories of security mechanisms.

32. 14ITT71-CryptographyandNetworkSecurity
Review Questions
1. Consider an automated teller machine (ATM) in which users provide a personal
identification number (PIN) and a card for account access. Give examples of
confidentiality, integrity, and availability requirements associated with the system
and, in each case, indicate the degree of importance of the requirement.
2. Consider a desktop publishing system used to produce documents for various
organizations.
• Give an example of a type of publication for which confidentiality of the stored
data is the most important requirement.
• Give an example of a type of publication in which data integrity is the most
important requirement.
• Give an example in which system availability is the most important requirement.

33. 14ITT71-CryptographyandNetworkSecurity
Review Questions
1. Draw a matrix similar to Slide No 28 that shows the relationship between security services and
attacks.
2. For each of the following assets, assign a low, moderate, or high impact level for the loss of
confidentiality, availability, and integrity, respectively. Justify your answers.
a. An organization managing public information on its Web server.
b. A law enforcement organization managing extremely sensitive investigative
information.
c. A financial organization managing routine administrative information (not
privacy-related information).
d. An information system used for large acquisitions in a contracting organization
contains both sensitive, pre-solicitation phase contract information and routine administrative
information. Assess the impact for the two data sets separately and the information system as a whole.
e. A power plant contains a SCADA (supervisory control and data acquisition) system controlling the
distribution of electric power for a large military installa- tion. The SCADA system contains both
real-time sensor data and routine admin- istrative information. Assess the impact for the two data sets
separately and the information system as a whole.