1
Computer and Information
Security
Chapter 1
Introduction

Overview
• Security Goals
• The need for security
• OSI Security Architecture
• Attacks, services and mechanisms
• Security attacks
• Security services
• Methods of Defense
• A model for Internetwork Security
• Internet standards and RFCs

Security Goals
Integrity
Confidentiality
Avalaibility

Security Goals
• Confidentiality
– Concealment of information or resources
– protecting precious business data from
unauthorized persons
• Integrity
– Trustworthiness of data or resources
• Availability
– Ability to use information or resources

Confidentiality
• prevents unauthorized users from
accessing information to protect the
privacy of information content.
Confidentiality is maintained through
access restrictions.
• Access mechanisms, such as
cryptography, support confidentiality
– Example: encrypting income tax return

Integrity
• Ensures the authenticity and accuracy of
information. Integrity is maintained by
restricting permissions for editing or the
ability to modify information.
• Include prevention mechanisms and detection
mechanisms
• Includes both correctness and trustworthiness

Availability
• Ensures that authorized users can reliably
access information.
• Availability is maintained through
continuity of access procedures, backup or
duplication of information, and maintenance
of hardware and network connections.
• Attempts to block availability, called denial
of service attacks are difficult to detect.

The Need for Security
• Computer Security - the collection of
tools designed
– to protect data and
– to thwart hackers
• Network security or internet
security- security measures needed
to protect data during their
transmission

Security
• Motivation: Why do we need security?
• Increased reliance on Information technology with or with
out the use of networks
• The use of IT has changed our lives drastically.
• We depend on E-mail, Internet banking, and several other
governmental activities that use IT
• Increased use of E-Commerce and the World wide web on
the Internet as a vast repository of various kinds of
information (immigration databases, flight tickets, stock
markets etc.)

Security Concerns
• Damage to any IT-based system or activity can
result in severe disruption of services and losses
• Systems connected by networks are more prone
to attacks and also suffer more as a result of the
attacks than stand-alone systems (Reasons?)
• Concerns such as the following are common
– How do I know the party I am talking on the network is
really the one I want to talk?
– How can I be assured that no one else is listening and
learning the data that I send over a network
– Can I ever stay relaxed that no hacker can enter my
network and play havoc?

Concerns continued…
• Is the web site I am downloading
information from a legitimate one, or a
fake?
• How do I ensure that the person I just did
a financial transaction denies having done it
tomorrow or at a later time?
• I want to buy some thing online, but I don’t
want to let them charge my credit card
before they deliver the product to me

That is why…
• ..we need security
– To safeguard the confidentiality, integrity,
authenticity and availability of data
transmitted over insecure networks
– Internet is not the only insecure network in
this world
– Many internal networks in organizations are
prone to insider attacks
– In fact, insider attacks are greater both in
terms of likelihood of happening and damage
caused

7 Layer Model
Layer Functions
7 Application How application uses network
6 Presentatio
n
How to represent & display data
5 Session How to establish communication
4 Transport How to provide reliable delivery (error
checking, sequencing, etc.)
3 Network How addresses are assigned and packets
are forwarded
2 Data Link How to organize data into frames &
transmit
1 Physical How to transmit “bits”

Security Architecture
• OSI Security architecture focuses on :-
• Security Attack: Any action that
compromises the security of information.
• Security Mechanism: A mechanism that is
designed to detect, prevent, or recover
from a security attack.
• Security Service: A service that enhances
the security of data processing systems
and information transfers. A security
service makes use of one or more security
mechanisms

Security Attacks
• A security attack is an unauthorized attempt
to steal, damage, or expose data from an
information system such as your
websiteThe security attacks aim to
compromise the five major security goals for
network security:-
• Confidentiality,
• Availability,
• Authentication,
• Integrity and Nonrepudiation

Security Attacks

Security Attacks
• Interruption: This is an attack on
availability
– Disrupting traffic
– Physically breaking communication line
• Interception: This is an attack on
confidentiality
– Overhearing, eavesdropping over a
communication line

Security Attacks (continued)
• Modification: This is an attack on
integrity
– Corrupting transmitted data or
tampering with it before it reaches its
destination
• Fabrication: This is an attack on
authenticity
– Faking data as if it were created by a
legitimate and authentic party

Threats and Attacks
• Threat - is a condition/circumstance which can cause
damage to the system/asset.
• A potential for violation of security or a possible
danger that might exploit a vulnerability
• A vulnerability is a weakness in a system that can be
easily exploited if found by an attacker.
• Attack - is an intended action to cause damage to
system/asset
• An attack on system security- an intelligent act that
is a deliberate attempt to avoid security services and
violate the security policy of a system.
• Attack (or exploit). An action taken to harm an asset

Threats
• Disclosure – unauthorized access to
information
• Deception – acceptance of false data
• Disruption- interruption or prevention
of correct operation
• Usurpation- unauthorized control of
some part of a system

Examples of Threats
• Snooping intercepting information
(“passive”)
• Modification or alteration of
information by “active”
• Masquerading or spoofing
• Repudiation of origin
• Delay or denial of service

Safeguards and
Vulnerabilities
• A Safeguard is a countermeasure to
protect against a threat
• A weakness in a safeguard is called a
vulnerability

Passive and active attacks
• Passive attacks
– No modification of content or fabrication
– Eavesdropping to learn contents or other
information (transfer patterns, traffic flows etc.)
• Active attacks
– Modification of content and/or participation in
communication to
• Impersonate legitimate parties
• Modify the content in transit
• Launch denial of service attacks

Passive Attacks

Passive Attacks

Active Attacks

Active Attacks

Two types of threats
• Information access threats
– Intercept or modify data on behalf of users
who should not have access to that data.
– E.g. corruption of data by injecting malicious
code
• Service threats
– Exploit service flaws in computers to inhibit use
by legitimate uses.
– E.g. disabling authentication

Fundamental threats [McGibney04]
• Information leakage
– Disclosure to unauthorized parties
– Prince Charles mobile phone calls, 1993
• Integrity violation
– Corruption of data or loss of data
– Coca-Cola website defaced with slogans, 1997
• Denial of service
– Unavailability of system/service/network
Illegitimate use
– Morris Internet worm spread to 5% of machines on the
Internet, 1988

Services and Mechanisms
• A security policy is a statement of what is
and what is not allowed.
• A security service is a measure to address
a threat
– E.g. authenticate individuals to prevent
unauthorized access
• A security mechanism is a means to
provide a service
– E.g. encryption, cryptographic protocols

Security Services
• A security service is a service provided by the
protocol layer of a communicating system (X.800)
• Security services implement security policies are
implemented by security mechanisms.
• X.800 divides these services into 5 Categories
– Authentication
– Access Control
– Data confidentiality
– Data Integrity
– Nonrepudiation (and Availability)

Authentication
• The authentication service is concerning with
assuring that a communication is authentic:
• The recipient of the message should be sure that
the message came from the source that it
claims to be
• All communicating parties should be sure
that the connection is not interfered with by
unauthorized party.
Example: consider a person, using online banking
service. Both the user and the bank should be
assured in identities of each other

Access control
• This service controls
• who can have access to a resource;
• under what conditions access can occur;
• what those accessing are allowing to do.
Example: in online banking a user may be
allowed to see his balance, but not allowed
to make any transactions for some of his
accounts.

Data confidentiality
• The protection of data from
unauthorized disclosure (from passive
attacks).
• Connection confidentiality
• Connectionless confidentiality
• Selective field confidentiality
• Traffic-Flow Confidentiality

Data Integrity
• The assurance that data received are
exactly as
sent by an authorized entity, i.e. contain
• no modification
• no insertion
• no deletion
• no replay
• Protection from active attacks
It may be
• integrity with recovery, or
• Integrity without recovery (detection
only)

Nonrepudiation
• Protection against denial by one of the
entities involved in a communication of
having participated in the communication.
Nonrepudiation can be related to
• Origin: proof that the message was sent
by the specified party
• Destination: proof that the message was
received by the specified party
• Example: Imagine a user of online banking
who has made a transaction, but later
denied that. How the bank can protect
itself in a such situation?

Availability service
• Protects a system to ensure its
availability
• Particularly, it addresses denial-of-
service attacks
• Depends on other security services:
access control, authentication, etc

Security Mechanisms
• Security mechanisms are technical
tools and techniques that are used
to implement security services. A
mechanism might operate by itself, or
with others, to provide a particular
service.

Security Mechanisms
Examples
• Two types
– Specific mechanisms existing to provide certain
security services
• E.g. encryption used for authentication
– Pervasive mechanisms which are general
mechanisms incorporated into the system and
not specific to a service
• E.g. security audit trail

Model for Network Security
• Basic tasks
– Design an algorithm that opponent cannot
defeat
– Generate the secret information to be used
with the algorithm
– Develop methods for distributing secret
information
– Specify a protocol to be used
• May need a trusted third part to assist

Model for Network Access
Security
• using this model requires us to:
1. select appropriate gatekeeper
functions to identify users
2. implement security controls to ensure
only authorised users access
designated information or resources
• trusted computer systems may be
useful to help implement this model

Methods of Defense
• Encryption
• Software Controls
– (access limitations in a data base, in operating
system protect each user from other users)
• Hardware Controls
– (smartcard)
• Policies
– (frequent changes of passwords)
• Physical Controls

Internet standards and
RFCs
• The Internet society
– Internet Architecture Board (IAB)
– Internet Engineering Task Force (IETF)
– Internet Engineering Steering Group
(IESG)