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Cryptography and Network Security Chapter 1. Fifth Edition by William Stallings. Security : is ensuring the (Secrecy) confidentiality, data integrity and availability of components of computing system. Cryptographic algorithms and protocols can be grouped into four main areas:. Definitions.

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Cryptography and Network Security Chapter 1

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Cryptography and Network SecurityChapter 1

Fifth Edition

by William Stallings

Security:is ensuring the (Secrecy) confidentiality, data integrity and availability of components of computing system.

Cryptographic algorithms and protocols can be grouped into four main areas:


  • Network Security - measures to protect data during their transmission

  • Internet Security - measures to protect data during their transmission over a collection of interconnected networks

The field of network and Internet security consists of:

Computer Security

  • the protection afforded to an automated information system in order to attain the applicable objectives of preserving the integrity, availability and confidentiality of information system resources (includes hardware, software, firmware, information/data, and telecommunications)

Key Security Concepts

Levels of Impact

  • can define 3 levels of impact from a security breach

    • Low

    • Moderate

    • High

Goals of computer security

• To protect computer assets from:

– Human errors, natural disasters, physical and electronic maliciousness.

• Confidentiality, Integrity, Availability

Confidentiality ( Secrecy, Privacy).

  • 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

      (Ensuring that the system is only accessible by authorized parties.)


  • Data integrity

    • Assures that information and programs are changed only in a specified and authorized manner

  • System integrity

    • Assures that a system performs its intended function in an unimpaired manner, free from deliberate or inadvertent unauthorized manipulation of the system


• Assures that systems work promptly and service is not denied to authorized users

  • Ensuring that authorized parties are not

    denied access to information and resources

    • Ensuring that the computer works when it

    is supposed to work and that it works the

    way it should.

    (access tocomputing resources without difficulties.)


Other goals

  • Non-repudiation

    – Ensuring that communication parties can't

    later deny that the exchange took place (or

    when the exchange took place).

  • Legitimate use

    – Ensuring that resources are not used by

    unauthorized parties or in unauthorized ways.

    – Examples:

  • Printer and disk quotas.

  • Spam-filters in E-mail servers..

Kinds of Security breaches

  • Exposure: . A form of possible loss or a harm in computing system . Examples :

    Unauthorized disclosure of data ,modification of data or Denial legitimate access to computing

  • Vulnerability: is a weakness in the security system that might be exploited to cause loss or harm

    • Attack: an assault on system security, a deliberate attempt to evade security services

    (Attempt to exploit a vulnerability.)


  • Threat:-a potential for violation of security

  • Physical threats - weather, natural disaster, bombs, power etc.

  • Human threats - stealing, trickery, spying, sabotage, accidents.

  • Software threats - viruses, Trojan horses, logic bombs.

  • Network Security

    Network Security

    Normal Flow:

    Network Security

    • Four types of possible attacks are:

    • Interruption: services or data become unavailable, unusable, destroyed, and so on, such as lost of file, denial of service, etc.

    Cut wire lines,

    Jam wireless signals,

    Drop packets,

    • 2. Interception: an unauthorized subject has gained access to an object, such as stealing data, overhearing others communication, etc.

    Wiring, eavesdrop

    3.Modification:unauthorized changing of data or tempering with services, such as alteration of data, modification of messages, etc.

    Replaced info


    4. Fabrication: additional data or activities are generated that would normally no exist, such as adding a password to a system, replaying previously send messages, etc.

    Also called impersonation

    Security Trends

    OSI Security Architecture . OSI : Open System Interconnection . ITU : International Telecommunication Union

    • ITU-T X.800 “Security Architecture for OSI”

    • defines a systematic way of defining and providing security requirements

    • for us it provides a useful, if abstract, overview of concepts we will study

    Aspects of Security

    • consider 3 aspects of information security:

      • security attack

      • security mechanism

      • security service

    Security Attack

    • any action that compromises the security of information owned by an organization

    • information security is about how to prevent attacks, or failing that, to detect attacks on information-based systems

    • can focus of generic types of attacks

      • passive

      • active

    Passive AttacksA passive attack attempts to learn or make use of information from the system but does not affect system resources

    Passive Attacks

    • Two types of passive attacks are:

      • The release of message contents

      • Traffic analysis

    Are in the nature of eavesdropping on, or monitoring of, transmissions

    Goal of the opponent is to obtain information that is being transmitted

    ActiveAttacksAn active attack attempts to alter system resources or affect their operation

    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

    Security Service

    • enhance security of data processing systems and information transfers of an organization

    • intended to counter security attacks

    • using one or more security mechanisms

    • often replicates functions normally associated with physical documents

      • which, for example, have signatures, dates; need protection from disclosure, tampering, or destruction; be notarized or witnessed; be recorded or licensed

    Security Services

    • X.800:

      “a service provided by a protocol layer of communicating open systems, which ensures adequate security of the systems or of data transfers”

    • RFC 4949 :

      “a processing or communication service provided by a system to give a specific kind of protection to system resources”

    Security Services (X.800)

    • Authentication - assurance that the communicating entity is the one claimed

      There are two specific authentication services defined in X.800:

    • Peer entity authentication:- Provides for the corroboration of the entity of a peer entity in association.

    • Data origin authentication:- provides for the corroboration of the source of a data units.

    Security Services (X.800)

    • Access Control - prevention of the unauthorized use of a resource

    • Data Confidentiality –protection of data from unauthorized disclosure

    • Data Integrity - assurance that data received is as sent by an authorized entity

    • Non-Repudiation - protection against denial by one of the parties in a communication

    Security Mechanism

    • feature designed to detect, prevent, or recover from a security attack

    • no single mechanism that will support all services required

    • however one particular element underlies many of the security mechanisms in use:

      • cryptographic techniques

    • hence our focus on this topic

    Security Mechanisms (X.800)

    • specific security mechanisms:

      • encipherment, digital signatures, access controls, data integrity, authentication exchange, traffic padding, routing control, notarization

    • pervasive security mechanisms:

      • trusted functionality, security labels, event detection, security audit trails, security recovery

    Model for Network Security

    Model for Network Security

    • using this model requires us to:

      • design a suitable algorithm for the security transformation

      • generate the secret information (keys) used by the algorithm

      • develop methods to distribute and share the secret information

      • specify a protocol enabling the principals to use the transformation and secret information for a security service

    Model for Network Access Security

    Model for Network Access Security

    • using this model requires us to:

      • select appropriate gatekeeper functions to identify users

      • implement security controls to ensure only authorised users access designated information or resources

    • trusted computer systems may be useful to help implement this model


    • have considered:

      • definitions for:

        • computer, network, internet security

    • X.800 standard

    • security attacks, services, mechanisms

    • models for network (access) security

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