This preview shows page 1. Sign up to view the full content.
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
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.
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
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
View Full Document
This document was uploaded on 04/07/2014.
- Spring '14