This document provides an overview of information security and network security. It discusses security attacks like passive attacks (release of message contents, traffic analysis) and active attacks (masquerade, replay, modification, denial of service). It also covers security mechanisms, services (authentication, access control, data confidentiality, data integrity, nonrepudiation), and basic encryption terminology (plaintext, ciphertext, cipher, encryption, secret key, decryption, cryptanalysis). The document is a lecture on security that outlines these key concepts and issues.

1. SECURITY
Lec 1
Dr. Hassan Shaban

2. CONTENTS
Security Attacks
Security Mechanisms
Security Services
Part 1: Information Security
• Substitution Techniques
• Hill algorithm
• Play fair algorithm
• Transposition Techniques
• DES
• RSA
Part 2: Network Security
• Networking Security Concepts
• Common Security Threats
• Fundamentals of IP Security
• Virtual Private Networks (VPN)
• Securing Layer 2 Technologies
• Network Foundation Protection

3.  Information security is: concerned with protecting information in all its forms, whether written,
spoken, electronic, graphical, or using other methods of communication.
 Network security is concerned with protecting data, hardware, and software on a computer network.
 Access: An object’s ability to use, manipulate, modify, or affect another object. Authorized
users have legal access to a system, whereas hackers have illegal access to a system.
 Asset: The organizational resource that is being protected. An asset can be logical, such as a
Web site, information, or data; or an asset can be physical, such as a person, computer
system, or other tangible object. Assets, and particularly information assets, are the focus of
security efforts; they are what those efforts are attempting to protect
 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

4. SECURITY ATTACKS
A useful means of classifying security attacks, 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.
Passive attacks are very difficult to detect because they do not involve any
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.
Passive attacks can be subdivided into two categories: Release of
message contents-read content of the message and Traffic Analysis-
observe pattern of the messages

6.  Active attack - attempts to alter system resources or affect their operation.
It can be subdivided into four categories: masquerade, replay, modification, and denial of
service (DoS).
masquerade takes place when one entity pretends to be a different entity
Replay takes place when a different entity capture the message from the source and
later replay message to the destination

7. 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
denial of service prevents the normal use or management of communications facilities. form
of service denial is the disruption of an entire network, either by disabling the network or by
overloading it with messages so as to degrade performance.

8. THE OSI SECURITY ARCHITECTURE
The OSI security architecture focuses on security attacks, mechanisms, and services.
● Security attacks
●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

9. SECURITY SERVICES
AUTHENTICATION- the function of the authentication service is to assure the recipient
that the message is from the source that it claims to be from.
ACCESS CONTROL - The prevention of unauthorized use of a resource (i.e., this
service controls who can have access to a resource, under what conditions access can
occur, and what those accessing the resource are allowed to do).
DATA CONFIDENTIALITY - The protection of data from unauthorized disclosure.
DATA INTEGRITY - The assurance that data received are exactly as sent by an
authorized entity (i.e., assures that messages are received with no modification, no
insertion, no deletion, or no replay).
NONREPUDIATION - Nonrepudiation prevents either sender or receiver from denying
a transmitted message. Thus, when a message is sent, the receiver can prove that
the alleged sender in fact sent the message. Similarly, when a message is received,
the sender can prove that the alleged receiver in fact received the message.

10. SECURITY MECHANISMS
• Specific Security Mechanisms: May be incorporated into the appropriate
protocol layer in order to provide some of the OSI security services.
• Encipherment - The use of mathematical algorithms to transform data into a form that is not
readily intelligible. The transformation and subsequent recovery of the data depend on an
algorithm and zero or more encryption keys.
• Digital Signature - Data appended to 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 (e.g., by the
recipient).
• Routing Control -Enables selection of particular physically 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.
• Pervasive Security Mechanisms - Mechanisms that are not specific to any
particular OSI security service or protocol layer.

11. Basic terminology
• Plaintext - the original message
• Ciphertext - the coded message (coded plaintext)
• Cipher - algorithm for transforming plaintext to ciphertext
• Encryption - performs various substitutions and transformations on the
plaintext, converting plaintext to ciphertext
• Secret key: The secret key is also input to the encryption algorithm. The
key is a value independent of the plaintext and of the algorithm. The
algorithm will produce a different output depending on the specific key
being used at the time. The exact substitutions and transformations
performed by the algorithm depend on the key.
• Decryption - reconverting ciphertext to plaintext
• Cryptanalysis (code breaking) - the study of principles and methods of
deciphering ciphertext without knowing key