Security and Privacy in Computer Networks

Due to the wide spread use of PCs and Developments in networks connecting PCs to company's Mainframe computers, there has been an increase in the chances of feeding undesirable data deliberately outsiders.  A person with a PC at a remote place can use a phone line and illegally collect information without leaving any clues. Individual users can copy confidential data from a company's computer or other details from a remote station connected via a communication network.


Note:-  The collection of tools  designed to protect data and thwart hackers is known as computer security.

Security means preventing the network communication system fall in the hands of unauthorized people. The sender of data may wish to be assured that only the intended party actually receives designated data. The receiver must authenticate first that it is the one who is authorized to receive data and thereafter the sender exchanges data.

Hence, we need to take such steps so as to protect data during transmissions and guarantee that these transmissions are by authorized persons only. The network security methods adopted must address the following issues.

1. Information in a computer system should only be accessed by authorized persons.
2. The shareable resources must be available only for use by authorized members.
3. Unauthorized persons should not be able to insert spurious messages or records into a file being transmitted in a network.
4. It should not be possible for an unauthorized party to perform wiretapping in order to capture data or illicitly copy files and programs.

What is an Algorithm?

We saw above that planning a program involves defining its logic (the correct sequence of instructions needed to solve the problem at hand).The term algorithm is often used to refer to the logic of a program. It is step-by step description of how to arrive at the solution of the given problem. It may be formally defined as a sequence of instruction, designed in a manner that, if the instruction is executed in the specified sequence, the desired results will be obtained. In order to qualify as an algorithm, a sequence of instructions must possess the following characteristics:

1.    Each and every instruction should be precise and unambiguous.
2.    Each instruction should be such that it can be performed in a finite time
3.    One or more instructions should not be repeated infinitely. This ensures that the algorithm will ultimately terminate.
4.    After performing the instruction, that is, after the algorithm terminate, the desired results must be obtained.

Sample Algorithms

To gain insight in to algorithms, let us consider some simple examples

Examples:-

50 students in a class appeared in their final examination.Their mark sheets have been given to yo.The division column of the mark sheet contains the division(FIRST,SECOND,THIRD or FAIL) obtained by the student.Write an algorithm to calculate and print the total number of students who passed in FIRST  division.

Algorithm:-
Step:- 1  Initialize Total_First_Division and Total_Marksheets_Checked to zero.
Setp:- 2 Take the mark sheet of the next student.
Step:- 3 Check the division column of the mark sheet to see if it is FIRST.If no,go to Step 5.
Step:- 4 Add 1 to Total_First_Division
Step:- 5 Add 1 to Total_Marksheets_Checked.
Step:- 6 Is Total_Marksheets_Checked= 50? If no, go to Step2.
Step:- 7 Print Total_First_Division.
Step:- 8 Stop

10 Security Design Principle for your Computer

We have seen that security is guarding use’s data and programs against interface by entities external to a system like unauthorized person. Thus security designs provide need special emphasis.

In general, security measures include control and monitoring of physical access to the computer premises as well as the internal, computer system security. External or physical security includes the standard techniques of fencing, surveillance, authentication, and attendance monitoring. Additional access restriction may be imposed in special areas, such as the computer center and storage areas for backup volumes Physical security may also include measures for disaster recovery. Which often amount of replication of critical data and equipment at geographically dispersed locations to minimize exposure to the consequences of disasters such as fire or flood .Seltzer and Schroeder (1975) have identified the following general design principles for protection mechanisms.

1. Least privilege

 Every subject should use the least set of privileges necessary to complete its task. This principle limits the damage from Trojan horse attacks. It effectively advocates support for small protection domains and switching of domains when the access needs change.

2. Separation of privilege

When possible, access to objects should depend on satisfying more than one condition.

3.Least common mechanism

This approach advocates minimizing the amount of mechanism common to and depended upon by multiple users, Design implication, include the incorporation of techniques for separating users, such as logical separation via virtual machines and physical separation on different machines in distributed systems

4.Economy of mechanism

Keeping the design as simple as possible facilitates verification and correct implementations.

5.Complete mediation

Every access request for every object should be checked for authorization, the checking mechanism should be efficient because it has a profound influence on system performance.

6.Fall-safe default

Access rights should be acquired by explicit permission only, and the default should be back of access.

7.Open design

The design of the security mechanism should not be secret, and it should not depend on the ignorance of attackers, this implies the use o cryptographic system where the algorithms are known but the keys are secret.

8.User acceptability

The mechanism should provide case of use so that it is applied correctly and not circumvented by users.

9.User Friendlily

Computer System security mechanism include authentication, access control, flow control auditing and cryptography.

10. Other

To which the user is supposed to apply a secret transformation,such as squaring and incrementing the value.Failure to do so may be used to detect unauthorized users.

What is Computer Processor

Processors are now being built with even faster ratings. With all other parameters being equal (although they never are) a CPU operating at 500 MHz can process data five times as fast as one operating at 100 MHz

Types of Processors

CISC Processors

One of the earlier goals of CPU designers was to provide more and more instructions in the instruction set of a CPU, to ensure that the CPU directly supports more features, making it easier to translate high level language programs to machine language, and to ensure that the machine language programs run more effectively. Of course every additional instruction in the instruction set of a CPU requires the necessary hardware circuitry to handle that instruction, adding more complexity to the CPU’s hardware circuitry. Another goal of CPU designers was to optimize the usage of expensive memory. To achieve this, the designers tried to pack more instruction in memory, by introduction the concept of variable-length instructions such as half word, one and half word, etc.

For example and operand in an immediate instruction needs fewer bits, and can be designed as half word instruction. Additionally, CPU,s were designed to support a variety of addressing modes .CPUs with large instruction set, variable  length instructions and a variety of addressing modes are said to employ CISC(Complex instruction set computer) architectures, Since  CISC processors posses so many processing features, they make the job of machine language programmers easier. However they are complex and expensive to produce. Most personal computers of today use CISC processors.

RISC Processors

In early 1980;s Some CPU designers discovered that several of the instruction supported by a CISC-based CPU are rarely used. Hence they came out with an idea that the complexity of CPU design can be greatly reduced, by implementing only a bare minimum basic set of instructions, plus some of the more frequently used instructions in the hardware circuitry of the CPU. Other complex instructions need not to be supported in the instructions set of the CPU, because they can always be implemented in software, by using the basis set of instructions.

 While working on simpler CUP design. These designers also came up with the idea of making .All the instructions of uniform length, so that the decoding and execution of all instructions become simple fast. Furthermore, to speed up computation, and to reduce the complexity of handling a number of addressing modes, they decided to design all the instructions in such a way that they retrieve operands stored in registers in CPU, rather than from memory. These design ideas resulted in producing faster and less expensive processors. CPUs with a small instruction set, fixed-length instructions, and reduced reference to memory to retrieve operands, are said to employ RISC(Reduced Instruction Set Computers)architure, Since RISC processors have a small instruction set, they place extra demand on programmers, who must consider how to implement complex computations by combining simple instructions. However, due to simpler design, RISC processors are faster for most application, less complex and less expensive to produce than CISC processors.

EPIC Processors

The Explicitly Parallel Instruction Computing (EPIC) technology breaks through the sequential nature of conventional processor architectures, by allowing the software to communicate explicitly to the processor, when operations can be done in parallel. For this, it uses tighter coupling between the complier and the processor, and enables the compiler to extract maximum parallelism in the original code, and explicitly describe it to the processor. Processors based on EPIC architecture are simpler and more powerful than traditional CISC or RISC processors. These processors are mainly targeted to next-generation, 64-bit high-end server and workstation market (not for personal computer market).

What is Registers in Computer Architecture

Registers

As the instructions are interpreted and executed by the CPU, there is a movement of information between the various units of the computer system. In order to handle this process satisfactorily, and to speed up the rate of information transfer, the computer uses a number of special memory units, called registers. These registers are used to hold information on temporary basis, and are part of the CPU (not main memory).
The length of a register equals the number of bits it can store. Hence, a register that can store 8 bits is normally referred to as 8-bit register. Most CPU sold today, have 32-bit or 64-bit registers. The size of the registers is sometimes called the world size. The bigger the world size, the faster the computer can process a set of data. With all other parameters being same, a CPU with 32-bit registers, can process data twice as fast as one with 16-bit registers.

Although, the number of registers varies from computer to computer, there are some registers, which are common to all computers. The functions of these registers are described below.

Memory Address Register (MAR)

- It holds the address of the active memory location. It is loaded from the program control register, when an instruction is read from memory.

Memory Buffer Register (MBR)

- It holds the contents of the memory world read from, or written in, memory. An instruction world placed in this register is transferred to the instruction register. A data word placed in this register is accessible for operation with the accumulator register, or for transfer to the I/O register.A word to be stored in memory location must first be transferred to the MBR, from where it is written in memory.

Program Control Register (PC)

- It holds the address of the next instruction to be executed Normally, the instructions of a program are stored in consecutive memory location, and read and executed in sequence, unless a branch instruction is encountered. A branch instruction is an operation, which calls for a transfer to a non-consecutive instruction. The address part of a brands instruction is transferred to the PC register, to become the address of the next instruction.

Accumulator Register (A)

- It holds the data to be operated upon, the intermediate results and the results of processing. It is used during the execution of most instructions. The results of arithmetic operations are returned to the accumulator register, for transfer to main memory, through the memory buffer register. In many computers, there are more than one accumulator registers.

Instruction Register (I)

- It holds the current instruction, which is being executed. As soon as the instruction is stored in this register, the operation part and the address part of the instruction are separated. The address part of the instruction is sent to the MAR. While its operation part is sent to the control unit, where it is decoded and interpreted, and ultimately command signals are generated to carry out the task specified by the instruction.

Input/output Register (I/O)

-It is used to communicate with the input/output devices. All input information, such as instructions and data, are transferred to this register by an input device. Similarly, all output information, to be transferred to an output device, is found in this registers.

SL.NO	Name of Register	Function
1	Memory Address(MAR)	Holds the address of the active memory location
2	Memory Buffer(MBR)	Holds information on its way to and from memory
3	Program Control(PC)	Holds the address of the next instruction to be executed
4	Accumulator(A)	Accumulators results and data to be3 operated upon
5	Instruction(I)	Holds an instruction, while it is being executed.
	Input/output(I/O)	Communicates with the I/O devices

What is instruction sets in computer architecture

Every CPU has built-in-ability to execute a set of machine instructions, called instructions set. Most CPUs have 200 or more instructions (such as add, substract, and compare) in instruction set. The machine language designed for a processor (CPU), is based on the list of instructions supported by the CPU in its instructions set. Since each processor (CPU).is based on the list instructions supported by the CPU in its instructions set, Since each processor has a unique instruction set, machine language programs written for one computer will generally not run on another computer, with a different CPU.

CPUs made by different manufacturers have different instructions sets. In fact, different CPU models of the same manufacturer also often have different instructions sets. However, manufacturers tend to group their CPUs into “families”, which have similar instructions sets. When a new CPU is developed, it it ensured that its instructions set includes all the instructions in the instruction set of its predecessor Crumples some new ones. This manufacturing strategy is known as upward compatibility, and the new CPU is said to be upward compatible with its predecessor. This feature allows software written for a computer with a particular CPU, to work on computers with newer processors of the same family. In turn, it allows the users of these computer systems to easily upgrade their system, without worrying about converting all their existing software.NSK2VZ4KNRW6

What is central processing unit (CPU) how it is work

The CPU is the brain of a computer system. All major calculations and comparisons performed by a computer are carried out inside its CPU.

 The CPU is also responsible for activating and controlling the operation of other units of the computer system. Hence, no other single component of a computer determines its overall performance ,as much as the CPU, In order to be able to quickly evaluate any computer capabilities it is important to know how CPU are internally structured how different CPUs differ from each other ,and how CPU speed is evaluated. These and other related concepts about CPU are described below.

The Control Unit.

We saw that the two basic components of a CPU are the control unit and the arithmetic logic unit. The control unit of the CPU selects and interprets program instructions, and then sees that they are executed. It has some special purpose registers (whose functions are described in a latter subsection), and a decoder to perform these activities. The special purpose registers, namely the Instructions register and the program control register, respectively hold the current instruction and the next instruction to be executed, and in this way help the control unit in instruction selection. On the other hand. The decoder has the necessary circuitry to decode and interpret the meaning of every instruction supported by the CPU. Each instruction is accompanied by microcode—very basic directions. Which tell the CPU how to execute the instruction?
Although, the control unit does not perform any actual processing of the data, it acts as a central nervous system for other components of the computer. It manages and coordinates the entire computer system, including the input and output units. It obtains instructions from the program stored in the main memory, interprets the instructions, and issues signal, which cause other units of the system to execute them.

The Arithmetic Logic Unit (ALU)

The ALU of the CPU is the place, where the actual execution of the instructions takes place, during the data procession operation. That is, when the control unit encounters an instruction, which involves an arithmetic operation (such as, add, subtract, multiply, divide), or a logic operation (such as less than, equal to, greater that), it passes control to the ALU. The ALU has some special purpose registers and the necessary circuitry, to carry out all the arithmetic and logic operations, which are included in the instructions supported by the CPU. For example, the arithmetic and logic operations, which are included in the instructions supported by the CPU.For example, the control unit might load two numbers into the registers in the ALU.Then, it might the ALU to add the two numbers (an arithmetic operations), or to check if the two numbers are equal (a logical operation).

In case of a microcomputer, the entire CPU (both the control unit and the ALU) is contained on a single tiny silicon chip, called a microprocessor.