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L. Tahani Al jehani
Information security :
 Before
the widespread use of data processing
equipment, the security of information felt to be
valuable to an organization was provide primarily by
physical and administrative means.
 An example of the former is the use of rugged filing
cabinets with a combination lock for storing sensitive
computer security (cyber security)
With the introduction of the computer, the need for
automated tools for protecting files and other
information stored on the computer became evident.
Especially the case for a shared system, such as a timesharing system, and for systems that can be accessed
over a public telephone network, data network, or the
Internet. (server)
The generic name for the collection of tools designed to
protect data is computer security.
Computer security
"Security is the ability of a system to protect
information and system resources with respect to
confidentiality , availability, and integrity." Note
that the definition includes system resources, which
include CPUs, disks, and programs, in addition to
Challenges of computer and network security
Challenges of computer and network security:
Security is not simple as it might first appear to the
novice: we need to consider potential attacks .
Security mechanisms typically involve more than a
paticular algorithm.
Having designed various security mechanisms, it is
necessary to decide where to use them (physical and
logical sense). What points in a network are certain
secured mechanisms needed? What layer or layers
of our architecture should mechanisms be placed?
Key Security Concepts
Computer security is frequently associated with
three core areas, which can be conveniently
summarized by the acronym "CIA“
Confidentiality -- Ensuring that information is not
accessed by unauthorized persons
Integrity -- Ensuring that information is not altered
by unauthorized persons in a way that is not
detectable by authorized users
Authentication -- Ensuring that users are the
persons they claim to be
A strong security protocol addresses all three of
these areas. Take, for example, Netscape's SSL
(Secure Sockets Layer) protocol. It has enabled an
explosion in ecommerce which is really about trust
(or more precisely, about the lack of trust). SSL
overcomes the lack of trust between transacting
parties by ensuring confidentiality through
encryption, integrity through checksums, and
authentication via server certificates
Computer security is not restricted to these three broad concepts.
Additional ideas that are often considered part of the taxonomy of
computer security include:
Access control -- Ensuring that users access only those resources and
services that they are entitled to access.
Nonrepudiation -- Ensuring that the originators of messages cannot
deny that they in fact sent the messages
Availability -- Ensuring that a system is operational and functional
at a given moment, usually provided through redundancy; loss of
availability is often referred to as "denial-of-service"
Privacy -- Ensuring that individuals maintain the right to control what
information is collected about them, how it is used, who has used it,
who maintains it, and what purpose it is used for
Network security
The second major change that affected security is the
introduction of distributed systems (telecommunication ,
internet , wireless sensors network ) and the use of
networks and communications facilities for carrying
data between terminal user and computer and between
computer and computer.
Network security measures are needed to protect data
during their transmission
Protecting network and telecommunications equipment,
protecting network servers and transmissions,
combatting eavesdropping, controlling access from
untrusted networks, firewalls, and detecting intrusions
Scenario of massage interception in
User A transmits a file to user B. The file contains
sensitive information that is to be protected from
disclosure. User C, who is not authorized to read the
file, is able to monitor the transmission and capture
a copy of the file during its transmission.
Security Trends
In 1994, the Internet Architecture Board (IAB) issued
a report entitled "Security in the Internet
The report stated that the Internet needs more and
better security.
the need to secure the network infrastructure from
unauthorized monitoring and control of network
traffic and the need to secure end-user-to-end-user
traffic using authentication and encryption .
The OSI model is a layered model that describes
how information moves from an application running
on one networked computer to an application
running on another networked computer
Security Architecture for OSI
Security Architecture for OSI defines systematic
way to :
Defining the requirements for security
 Characterizing the approaches to satisfying those
Examples of Security Requirements
confidentiality – student grades
integrity – patient information
availability – authentication service
Security Architecture for OSI
The OSI security architecture focuses on security attacks,
mechanisms, and services.
• Security attack: Any actions that compromises the
security of information owned by an organization (or a
• 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
the data processing systems and the information transfers
of an organization. The services make use of one or more
security mechanisms to provide the service
Security attacks
Passive attack: aims to learn or make use of
information from the system but does not affect
system resources.
 Like
eavesdropping on, or monitoring of, transmissions.
The goal is to obtain information that is being
Active attack: attempts to alter system resources
or affect their operation
Passive Attacks
Passive Attacks :
 the
release of message contents
A telephone conversation, an electronic mail message,
and a transferred file may contain sensitive or
confidential information. We would like to prevent an
opponent from learning the contents of these
 Traffic analysis also encrypted data can be read
the release of message contents
Traffic analysis
Passive attacks
Passive attacks are very difficult to detect, because
they do not involve an alteration of the data.
Typically, the message traffic is sent and received in
an apparently normal fashion, and neither the
sender nor receiver is aware that a third party has
read the messages or observed the traffic pattern.
Active Attacks
Active attacks involve some modification of the data
stream or the creation of a false stream and can be
subdivided into four categories:
 Masquerade.
 Replay.
 modification
of messages.
 denial of service.
A masquerade attack usually includes one of the
other forms of active attack.
For example, authentication sequences can be
captured and replayed after a valid authentication
sequence has taken place, thus enabling an
authorized entity with few privileges to obtain extra
privileges by impersonating an entity that has those
Replay involves the passive capture of a data
unit and its subsequent retransmission to produce
an unauthorized effect
Modification of messages
Modification of messages simply means that
some portion of a legitimate message is altered,
or that messages are delayed or reordered, to
produce an unauthorized effect
For example, a message meaning “Allow John
Smith to read confidential file accounts” is modified
to mean “Allow Fred Brown to read confidential file
denial of service
prevents or inhibits the normal use or management
of communications facilities
the disruption of an entire network, either by
disabling the network or by overloading it with
messages so as to degrade performance.
denial of service
Network security can provide one of the five
services as shown in Figure. Four of these services
are related to the message exchanged using the
network: message confidentiality, integrity,
authentication, and nonrepudiation.
The fifth service provides entity authentication or
Message Confidentiality
Message confidentiality or privacy means that the
sender and the receiver expect confidentiality. The
transmitted message must make sense to only the
intended receiver. To all others, the message must
be garbage. When a customer communicates with
her bank, she expects that the communication is
totally confidential.
Message Integrity
Message integrity means that the data must arrive
at the receiver exactly as they were sent. There
must be no changes during the transmission, neither
accidentally nor maliciously.
For example, it would be disastrous if a request for
transferring $100 changed to a request for
$10,000 or $100,000.
The integrity of the message must be preserved in a
secure communication.
Message Authentication
Message authentication is a service beyond
message integrity. In message authentication the
receiver needs to be sure of the sender'sidentity
and that an imposter has not sent the message.
Message Nonrepudiation
Message nonrepudiation means that a sender must
not be able to deny sending a message that he or
she, in fact, did send. The burden of proof falls on
the receiver. For example, when a customer sends a
message to transfer money from one account to
another, the bank must have proof that the customer
actually requested this transaction.
Entity Authentication
In entity authentication (or user identification) the
entity or user is verified prior to access to the
system resources(files(
For example, a student who needs to access her
university resources needs to be authenticated
during the logging process. This is to protect the
interests of the university and the student.
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.
Confidentiality requirements:
the communication channel between the ATM and the bank must be encrypted
the PIN must be encrypted (wherever it is stored)
Integrity requirements:
the actions performed via the ATM must be associated to the account
associated with the card
Availability requirements:
the system must be able to serve at least X concurrent users at any given time
the system must be available 99.9% of the time
Choose one of internet protocol (TCP/IP , UDP ,..)
Then give an example of integrity , availability and