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.

Operating System : Types of System Calls

Types of System Calls are:-

1. Process Control

• end, abort
• load, execute
• create process, terminate process
• allocate and free memory
• get process attributes, set process attributes

2. File management

• Create file, delete file
• Open, close
• Read, write, reposition
• Get file attributes, set file attributes

3. Device management

• Request device, release device
• Logically attach and detach devices
• Read, write, reposition
• Get device attributes, set device attributes

4. Communication

• Create, delete communication connections
• Send, receive messages
• Transfer status information
• Attach or detach remote devices

Operating System: System Calls and System Programs

System Calls and System Programs

System calls provide an interface between the process and the operating system. System calls allow userlevel processes to request some services from the operating system which process itself is not allowed to do. For example, for I/O a process involves a system call telling the operating system to read or write particular area and this request is satisfied by the operating system.

System programs provide basic functioning to users so that they do not need to write their own environment for program development (e.g. editors, compilers) and program execution (shells). In some sense, they are bundles of useful system calls.

Types of System Calls are: Click Here

Operating System: Open Source & Distributed Systems

Open Source Operating System:-
The distribution of original source materials that can be studied, altered and built upon with the result once again freely distributed are called Open source.

Distributed Systems Operating System:-
A distributed system is a collection of physically separate, possibly heterogeneous computers systems that are networked to provide the users with access to the various resources that the system maintains. A Network is a communication path between two or more systems. Distributed system depends on networking for their functionality.

Application Interface & User Interface of Operating Systems os

Application Interface & User Interface of Operating

Application Interface of Operating Systems os

APIs lets application programmers use functions of the computer and OS without having to directly keep track of all the details in the CPU’s operation.

User Interface of Operating Systems os
A user interface (UI) brings structure to the interaction between a user and the computer.

Tasks of OS Operating System

Tasks of an OS Operating System

1. Process Management:-

The operating system manages many kinds of activities ranging from user programs to system programs. Each of these activities is encapsulated in a process. There are many processes can be running the same program. The five major activities of an operating system in regard to process management are

• Creation and deletion of user and system processes.
• Suspension and resumption of processes.
• A mechanism for process synchronization.
• A mechanism for process communication.
• A mechanism for deadlock handling.

2. Memory Management:-

• Keeping track of which parts of memory are currently being used and by whom.
• Deciding which processes (or parts thereof) and data to move into and out of memory.
• Allocating and deallocating memory space as needed.

3. Device Management:-

• The assembling-disassembling of I/O peripherals devices are managed by the OS.

4. Storage Management:-
The three major activities of an operating system in regard to secondary storage management are:

• Managing the free space available on the secondary-storage device.
• Allocation of storage space when new files have to be written.
• Scheduling the requests for memory access.

Transition from User Mode to Kernel Mode

Operating System (OS) Operations

Operating System OS has two modes of Operation:-

1. User mode
2. Kernel mode (Supervisor mode, system mode or privileged mode)

A bit called mode bit is added to the hardware of the computer to indicate the current mode: kernel (0) or user (1). With the mode bit, we are able to distinguish between a task that is executed on behalf of the OS and one that is executed on behalf of the user.

Transition from User to Kernel Mode

When the computer system is executing on behalf of a user application, the system is in user mode. However, when a user application requests a service from the OS (via system call), it must transition from user to kernel mode to fulfill the request

At boot time, the hardware starts in kernel mode. The OS is then loaded and starts user
application in user mode.

What is Timer / What do you mean by Timer interrupt

Timer / Timer Interrupt

To prevent a user program from getting stuck in an infinite loop or not calling system services and never returning control to the OS, a timer is used. A timer can be set to interrupt the computer after a specified period.

Transition from User to Kernel Mode

The OS sets the counter and this counter is decremented every time the clock ticks. When the counter reaches 0, an interrupt occurs which transfers control automatically to the OS.

OS Operations : Operating System Operations

Operating System (OS) Operations

Operating System OS has two modes of Operation:-

1. User mode
2. Kernel mode (Supervisor mode, system mode or privileged mode)

A bit called mode bit is added to the hardware of the computer to indicate the current mode: kernel (0) or user (1). With the mode bit, we are able to distinguish between a task that is executed on behalf of the OS and one that is executed on behalf of the user.

Transition from User to Kernel Mode

When the computer system is executing on behalf of a user application, the system is in user mode. However, when a user application requests a service from the OS (via system call), it must transition from user to kernel mode to fulfill the request

At boot time, the hardware starts in kernel mode. The OS is then loaded and starts user
application in user mode.

Types of Operating System (OS) :-

There are four types of OS categorized based on the types of computers they control and the sort of applications they support.

1. Real-time OS (RTOS): -They are used to control machinery, scientific instruments and industrial systems. It has a little user interface capability. The very important property of RTOS is managing the resources of the computer so that a particular operation executes in precisely the same amount of time every time it occurs.
2. Single-User, Single Task:- This OS is designed to manage the computer so that one user can effectively do one thing at a time. Example: Palm OS for Palm handheld computers.
3. Single-user, Multi-tasking:- It let a single user have several programs in operation at the same time. Windows and Apple’s MacOS are example of such OS.
4. MultiUser:- It allows multiple users to take advantage of the computer’s resourcessimultaneously. It must make sure that the requirements of various users are balanced, and that each of the programs they are using has sufficient and separate resources so that a problem with one user doesn’t affect the entire community of users.

History of OS/ Different Generations of Operating System OS

Different Generations of Operating System OS

1940’s (First Generation) :- programming languages were unknown; earlies electronic digital computers had no OS.

1950’s (Second Generation):- Introduction of punch cards; first OS is IBM 701 which runs one job at a time.

1960’s (Third Generation):- concept of multiprogramming in which several jobs are in memory at once and the processor is switched from job to job as needed; time sharing technique in which each user has an on-line terminal and the computer system responds quickly to user requests.

From 1970’s (Fourth Generation):- development of LSI(large scale integration) circuits, chips, OS; personal computer and workstation age; multiprocessor technology evolved; DOS and UNIX were dominated OS .

Classification of OS (Operating System)

Classification of Operating System

Multiuser :- It allows for multiple users to use the same computer at the same time and /or different times. Example: Linux, UNIX, Win 2000.

Multiprocesing :- It is that type of OS that is capable of supporting and utilizing more than one computer processor. Example: UNIX, Win 2000.

Multitasking :- This OS is capable of allowing multiple software processes to run at the same time. Allows more than one program to run concurrently. Example: UNIX, Win 2000.

Multithreading :- It allow different parts of a single software to run concurrently. Example: Linux, UNIX, Win 2000

Functions of OS, Common OS and Goals/Objective of OS:

Functions of OS:

1. Implementing the user interface.
2. Sharing hardware among users.
3. Facilitating input/output.
4. Recovering from errors.
5. Facilitating parallel operations.

Common OS:

1. Windows(Win 98,XP,Vista,Windows 7)
2. Macintosh OS X
3. LINUX and UNIX
4. i5/OS (IBM iSeries)
5. z/OS (IBM z series mainframes)

Goals/Objective of OS:

1. To hide details of hardware by creating abstraction (used to reduce complexity, to enforce
2. security).
3. To allocate resources to processes.
4. To provide a pleasant and effective user interface.

Job Management:- It controls the order and time in which programs are run.

Task Management:- Multitasking, which is the ability to simultaneously execute multiple programs.

Data Management:- It keeps track of the data on disk, tape and optical storage devices. The application program deals with data by file name. The OS’s file system knows where that data are physically stored.

Device management:- It controls peripheral devices by sending them commands in their own propriety language. The software routine that knows how to deal with each device is called a “driver” and the OS requires drivers for the peripherals attached to the computer.

What is an Operating System

Operating System :

• It is a software program that enables the computer hardware to communicate and operate with computer hardware.
• It acts as an intermediate layer between application softwares and computer hardware.

Application Softwares

OS

Hardware

• It is a platform on which application programs executes and interacts with hardware.
• It performs tasks such as recognizing input from the keyboard, sending output the screen, Keeping track of files and directories on the disk and controlling peripheral devices such as disk drives and printers