what is Masquerade Attacks

Masquerade Attacks : takes place when one entity pretends to be a different entity . 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 privileges.

what is replay attacks

Replay attacks : An attack in which a service already authorized and completed is forged by another duplicate request" in an attempt to repeat authorized commands.

what is 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 accounts.“

what is Denial of Service Dos Attacks

Denial of Service: prevents or inhibits the normal use or management of communications facilities. This attack may have a specific target; for example, an entity may suppress all messages directed to a particular destination (e.g., the security audit service). 

Another 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.

Types of 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, and denial of service.

Masquerade Attacks : takes place when one entity pretends to be a different entity . 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 privileges.

replay attacks : An attack in which a service already authorized and completed is forged by another duplicate request" in an attempt to repeat authorized commands.

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 accounts.“

Denial of Service: prevents or inhibits the normal use or management of communications facilities. This attack may have a specific target; for example, an entity may suppress all messages directed to a particular destination (e.g., the security audit service). Another 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.

Explain TermThreat & Attack in Security perspective

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.


A useful means of classifying security attacks, used both in X.800 and RFC 2828, 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. An active attack attempts to alter system resources or affect their operation

Security Mechanism the specific means of implementing one or more security services

• 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

Note these mechanisms span a wide range of technical components, but one aspect seen in many is the use of cryptographic techniques.

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

Security Services provided by (X.800)

The OSI security architecture is useful to managers as a way of organizing the task of providing security. Furthermore, because this architecture was developed as an international standard, computer and communications vendors have developed security features for their products and services that relate to this structured definition of services and mechanisms.

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

The role of a security service

Consider the role of a security service, and what may be required.

• 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

Note both similarities and differences with traditional paper documents, which for example:

  have signatures & dates;

  need protection from disclosure, tampering, or destruction;

  may be notarized or witnessed;

  may be recorded or licensed

Also have a couple of definition of “security services” from relevant standards.

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 2828:“a processing or communication service provided by a system to give a specific kind of protection to system resources”

Passive Attacks

Have “passive attacks” which attempt to learn or make use of information from the system but does not affect system resources.

passive attacks

By eavesdropping on, or monitoring of, transmissions to:

+ obtain message contents (as shown above in Stallings Figure 1.3a), or

+ monitor traffic flows

Are difficult to detect because they do not involve any alteration of the data.

• Passive attacks are in the nature of eavesdropping on, or monitoring of, transmissions. The goal of the opponent is to obtain information that is being transmitted. Two types of passive attacks are release of message contents and traffic analysis.
• 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. However, it is feasible to prevent the success of these attacks, usually by means of encryption. Thus, the emphasis in dealing with passive attacks is on prevention rather than detection.

Active Attacks

Active Attacks:Also have “active attacks” which attempt to alter system resources or affect their operation.

By modification of data stream to:
+ masquerade of one entity as some other
+ replay previous messages (as shown above in Stallings Figure 1.4b)
+ modify messages in transit
+ denial of service

Active attacks present the opposite characteristics of passive attacks. Whereas passive attacks are difficult to detect, measures are available to prevent their success. On the other hand, it is quite difficult to prevent active attacks absolutely, because of the wide variety of potential physical,software,and network vulnerabilities. Instead, the goal is to detect active attacks and to recover from any disruption or delays caused by them.

• 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, and denial of service.

Security Attack: Expand on definition and use of “security attack”,

Security Attacks:

• 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
• often threat & attack used to mean same thing
• have a wide range of attacks
• can focus of generic types of attacks
• passive
• active

3 aspects of information security

consider 3 aspects of information security:

• security attack
• security mechanism
• security service

 The OSI security architecture focuses on security attacks,mechanisms,and services. These can be defined briefly as follows:

• Security attack: Any action that compromises the security of information owned by an organization.

• 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: A processing or communication service that enhances the security of the data processing systems and the information transfers of an organization.The services are intended to counter security attacks, and they make use of one or more security mechanisms to provide the service.

OSI Security Architecture

• 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

To assess effectively the security needs of an organization and to evaluate and choose various security products and policies, the manager responsible for security needs some systematic way of defining the requirements for security and characterizing the approaches to satisfying those requirements. This is difficult enough in a centralized data processing environment; with the use of local and wide area networks,the problems are compounded. ITU-T Recommendation X.800, Security Architecture for OSI, defines such a systematic approach. The OSI security architecture is useful to managers as a way of organizing the task of providing security.

Security Trends from 1990 to 2001

Discuss observed security trends (Stallings section 1.1 & Figure 1.2 above), noting growth in sophistication of attacks contrasting with decrease in skill & knowledge needed to mount an attack.

Security Trends from 1990 to 2001

Definitions Computer Security, Network Security, Internet Security

Here are some key definitions of Computer Security, Network Security, Internet Security , note boundaries between them are blurred.

• Computer Security - generic name for the collection of tools designed to protect data and to thwart hackers
• Network Security - measures to protect data during their transmission
• Internet Security - measures to protect data during their transmission over a collection of interconnected networks

our focus is on information Security which consists of measures to deter, prevent, detect, and correct security violations that involve the transmission & storage of information

Cryptography and Network Security”, 4/e, by William Stallings,

Cryptography and Network Security Background

• Information Security requirements have changed in recent times
• traditionally provided by physical and administrative mechanisms
• computer use requires automated tools to protect files and other stored information
• use of networks and communications links requires measures to protect data during transmission

The requirements of information security within an organization have undergone two major changes in the last several decades. Before the widespread use of data processing equipment,the security of information felt to be valuable to an organization was provided primarily by physical (eg. rugged filing cabinets with locks) and administrative mechanisms (eg. Personnel screening procedures during hiring process).

Growing computer use implies a need for automated tools for protecting files and other information stored on it. This is especially the case for a shared system, such as a time-sharing system, and even more so for systems that can be accessed over a public telephone network, data network, or the Internet.

The second major change that affected security is the introduction of distributed systems 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.