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Note for Cryptography And Network Security - CNS by kishan chandra

  • Cryptography And Network Security - CNS
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  • Computer Science Engineering
  • B.Tech
  • 6 Topics
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1.Introduction about Network and Network Security Network :- A network is defined as a group of two or more computer systems linked together. Why Network ? Computer networks allow the user to access remote programs and remote databases either of the same organization or from other enterprises or public sources. Computer networks provide communication possibilities faster than other facilities. Because of these optimal information and communication possibilities, computer networks may increase the organizational learning rate, which many authors declare as the only fundamental advantage in competition. Types Of Network  local-area networks (LANs): The computers are geographically close together (that is, in the same building).  wide-area networks (WANs): The computers are farther apart and are connected by telephone lines or radio waves.  campus-area networks (CANs): The computers are within a limited geographic area, such as a campus or military base.

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 metropolitan-area networks MANs): A data network designed for a town or city.  home-area networks (HANs): A network contained within a user's home that connects a person's digital devices. Network Characteristics In addition to these types, the following characteristics are also used to categorize different types of networks:  topology : The geometric arrangement of a computer system. Common topologies include a bus, star, and ring..  protocol : The protocol defines a common set of rules and signals that computers on the network use to communicate. One of the most popular protocols for LANs is called Ethernet. Another popular LAN protocol for PCs is the IBM token-ring network .  architecture : Networks can be broadly classified as using either a peer-topeer or client/server architecture. Computers on a network are sometimes called nodes. Computers and devices that allocate resources for a network are called servers. Computer Security The meaning of the term computer security has evolved in recent years. Before the problem of data security became widely publicized in the media, most people‟s idea of computer security focused on the physical machine. Traditionally, computer facilities have been physically protected for three reasons:  To prevent theft of or damage to the hardware  To prevent theft of or damage to the information  To prevent disruption of service Strict procedures for access to the machine room are used by most organizations, and these procedures are often an organization‟s only obvious computer security measures. Today, however, with pervasive remote terminal access, communications, and networking, physical measures rarely provide meaningful protection for either the information or the service; only the hardware is secure. Nonetheless, most computer facilities continue to protect their physical machine far better than they do their data, even when the value of the data is several times greater than the value of the hardware.

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Why Do We Need Security? In the ever changing world of global data communications, inexpensive Internet connections, and fast-paced software development, security is becoming more and more of an issue. Security is now a basic requirement because global computing is inherently insecure. As your data goes from point A to point B on the Internet, for example, it may pass through several other points along the way, giving other users the opportunity to intercept, and even alter it. It does nothing to protect your data center, other servers in your network, or a malicious user with physical access to your EnGarde system. Security Models 1. No Security In this simplest case, the approach could be a decision to implement no security at all. 2. Security through Obscurity In this model, a system is secure simply because nobody knows about its existence and contents. This approach cannot work for too long, as there are many ways an attacker can come to know about it. 3. Host Security In this scheme, the security for each host is enforced individually. This is a very safe approach, but the trouble is that it cannot scale well. The complexity and diversity of modem sites/organizations makes the task even harder. 4. Network Security Network security is the security provided to a network from unauthorized access and risks. It is the duty of network administrators to adopt preventive measures to protect their networks from potential security threats. Computer networks that are involved in regular transactions and communication within the government, individuals, or business require security. The most common and simple way of protecting a network resource is by assigning it a unique name and a corresponding password. In this modern era, organizations greatly rely on computer networks to share information throughout the organization in an efficient and productive manner. Organizational computer networks are now becoming large and ubiquitous. Assuming that each staff member has a dedicated workstation, a large scale company would have few thousands workstations and many server on the network.

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It is likely that these workstations may not be centrally managed, nor would they have perimeter protection. They may have a variety of operating systems, hardware, software, and protocols, with different level of cyber awareness among users. Now imagine, these thousands of workstations on company network are directly connected to the Internet. This sort of unsecured network becomes a target for an attack which holds valuable information and displays vulnerabilities. In this chapter, we describe the major vulnerabilities of the network and significance of network security. In subsequent chapters, we will discuss the methods to achieve the same. Physical Network A network is defined as two or more computing devices connected together for sharing resources efficiently. Further, connecting two or more networks together is known as internetworking. Thus, the Internet is just an internetwork – a collection of interconnected networks. For setting up its internal network, an organization has various options. It can use a wired network or a wireless network to connect all workstations. Nowadays, organizations are mostly using a combination of both wired and wireless networks. Wired & Wireless Networks In a wired network, devices are connected to each other using cables. Typically, wired networks are based on Ethernet protocol where devices are connected using the Unshielded Twisted Pair (UTP) cables to the different switches. These switches are further connected to the network router for accessing the Internet. In wireless network, the device is connected to an access point through radio transmissions. The access points are further connected through cables to switch/router for external network access.

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