However users often need to give detail instructions

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Unformatted text preview: the other Usually, a common key (K) is used for both enciphering and deciphering. For security, it is important that the ke of a symmetric cryptosystem be easily alterable and must always be kept secret. This implies that the key i known only to authorized users. Symmetric cryptosystems are also known as shared-key or private-key cryptosystems. In an asymmetric cryptosystem, on the other hand, the decryption key (K d) is not equal to the encryption key (Ke Furthermore, it is computationally impractical to derive Kd from Ke. Because of this property, only K d needs to b kept secret and K c is made publicly known. Asymmetric cryptosystems are also known as public-he cryptosystems. The Data Encryption Standard (DES) cryptosystem is the best known and the most widely used symmetric cryptosystem today. On the other hand, the Rivest-ShamirAdleman (RSA) cryptosystem is the first published and practically the most satisfactory asymmetric cryptosystem today. COMMAND INTERPRETATION The command interpretation module (known as command interpreter) of an operating system serves as an interface for the user to communicate with the computer via its operating system. It provides a set of commands using which the user can give instructions to the computer for getting some job done by it. The commands supported by the command interpretation module are known as system calls. When a user gives instructions to the computer by using these system calls, the command interpreter takes care of interpreting these commands and directing the system resources to handle the requests. Thus the command interpreter hides the hardware details of the system from the user. In this manner, it greatly contributes to the 'ease of use' objective of an operating system. The two broad categories of user interfaces supported by various operating systems are command-line interface and graphical user interface. They are briefly described below. Command-line Interface This is the textual user interface in which the user gives instructions to the computer by typing commands. That is, to enter a command, the user uses the keyboar...
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This document was uploaded on 04/07/2014.

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