PRESENTED BY
ASMITA A. JADHAV.
VANDANA P. SHARMA

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ABSTRACT
The world is surging towards a digital revolution where computer networks mediate every aspect of modern life. Not many years ago, most computers were carefully guarded mainframes, held tightly in the hands of skilled professionals. The systems and their guardians combined to provide ironclad protection of the organization’s all important data. Today the world is scary, anyone can get their hands on to the personal computers and even page link into networks!
Today the threat to the information on the network has grown to the greatest extent. Information is the most vital aspect of every organization. Network security has become sufficiently important. The object of security is to protect valuable or sensitive organizational information while making it readily available. Attackers and hackers try to harm a system and disrupt information exploiting vulnerabilities by using various techniques, methods, and tools. Security aims to develop measures and policies to protect assets and limit their vulnerabilities.
This first half of the paper deals with need for network security measures, threats to the network, steps towards network security, implementation policies of security and communication security: firewalls. The second half of paper deals with principles of cryptography, symmetric key algorithms, public key algorithms and digital signatures.
INTRODUCTION
Computers and networks originally were built to ease the exchange of information. Information is the key asset in most organizations. Inside the network the world is scary. There are links that eavesdropper can listen in on. Information needs to be forwarded through packets switches, and these switches can be reprogrammed to listen or to modify data in transit. A network is vulnerable to intruders and misuse. Network security means to protect information across the network. It deals with the prevention and detection of authorized actions by users of a network. Security forces must protect critical information while it is being ever more widely shared. Setting security aims at providing security where needed and to provide easy access for those who need information. The organizational control in security policy should define exactly who is authorized to what and under which conditions. Except for physical Security, nearly all security is based on cryptography. In Internetworking cryptography has emerged as the only alternative to protect Internet data. Cryptography can reformat and transform data making it safer on its trip between computers. Cryptography can take the data and transform it into a bunch of numbers known as ciphertext. The ciphertext is unintelligible gibberish except to someone who knows the secret to reversing the transformation. Cryptography also allows us to disguise our data so that eavesdroppers gain no information from listening to the information as transmitted. Cryptography also allows us to create an unforgettable message and detect if it has been modified in transit. Another important issue in communication security is firewalls. A firewall is simply a group of components that collectively form a barrier between two networks. Security is strongest if done end-to-end.
NETWORK SECURITY
Today’s security challenge is to share information with the right people without also sharing it with the wrong people. Information drives the modern organization.
Network security means to protect information from unauthorized disclosure while allowing authorized disclosure. It is also important to keep this information accurate and uncorrupted, even while it races around the network.
• Need for security
A network should not allow anyone to see confidential information without authorization. This requires a reliable way to identify the users. Network security needs protection for confidential information, reliable performance and data integrity. Important element of security is to protect the system’s integrity, security measures must include features like validation systems to screen out errors, both deliberate and accidental.
• Security threats
The object of security is to protect valuable or sensitive information while making it readily available. Attackers trying to harm a system exploit vulnerabilities by using various techniques, methods and tools.
A network can suffer several types of vulnerability
i) Physical threats
ii) Natural threats
iii) Mechanical breakdowns
iv) Electronic signals
v) Human threats
Natural calamities like earthquakes, hurricanes, floods, lightning, and fire can cause severe damage to the computer systems. Information can be lost and damage to hardware can disrupt other essential services. Other threats such as riots, wars, and terrorist attacks, like the bombing of the World Trade Center, can cause disasters to the network. The best approach is to have disaster recovery plans and contingency plans in place.
All mechanical devices will eventually fail, for e.g. the hard disk of a PC. Its failure will take a lot of valuable data with it. Electric components like power supplies can also fail. Network sends out electronic signals wherever cables run. Electronic signals can be intercepted to steal information. Shielded cables, fiber optic cables can be used to protect signals from being intercepted. Fiber cables provide better protection.
The most serious threat is human sources. Human threats may be from insiders, also called as malicious threat. Insiders are one who know many of the codes and security measures that are already in place. Insiders can plant viruses, worms and they can browse through the file system. Human threats can be from non-malicious threats. Non-malicious threats comes from employees who are untrained in computers and are unaware of security threats and vulnerabilities. The primary threat to data integrity comes from authorized users who are not aware of the actions they are performing. Errors and omissions can lose, damage, or alter valuable data.
• Steps towards network security
The basic goals of network security are
 To protect information from accidental destruction or modification.
 To protect information from deliberate destruction or modification.
 Make sure the data is available to authorized users, when they need it and in a form they can use.
Network security has been extended to include privacy, confidentiality, and integrity. This implies that we have to know the information and the value of that information in order to develop protective measures.
Classification of protective measures in computer security are:
 Prevention: Measures must be taken to prevent information from being damaged, altered or stolen.
 Detection: Measures must be taken to allow to detect when and how information has been damaged, altered or stolen and who caused the damage.
 Reaction: Measures that allow recovery of information, even if information is lost or damaged.
In order to take measures to protect the information following components should be examined:
i. Confidentiality: It is to prevent unauthorized disclosure of information.
ii. Integrity: It is to prevent erroneous modification of information. Storing incorrect data within the system can lose data. Malicious attackers also can modify, delete, or corrupt information that is vital.
iii. Availability: It is to prevent unauthorized withholding of information or resources. Information should be as freely available as possible to authorized users.
iv. Authentication: It is the process of verifying that users are who they claim to be when logging onto a system. It proves who you are.
v. Authorization: It is the process of allowing only authorized users access to sensitive information.
• Implementation policies
 Create usage policy: The first step, creating usage policy statements that outline users' roles and responsibilities with regard to security. Second step, Explain any specific acts that have been identified as security attacks and actions that will be taken to detect security attacks. Lastly, create an administrator acceptable use statement to explain the procedures for user account administration, policy enforcement, and privilege review.
Conduct a risk analysis: A risk analysis should identify the risks to your network, network resources, and data. The intent of a risk analysis is to identify portions of your network, assign a threat rating to each portion, and apply an appropriate level of security. This helps maintain a workable balance between security and required network access.
Assign each network resource one of the following three risk levels:
Low Risk Systems or data if data viewed by unauthorized personnel, data corrupted, or data lost would not disrupt the information.
Medium Risk Systems or data if data viewed by unauthorized personnel, data corrupted, or data lost would cause a moderate disruption.
High Risk Systems or data if data viewed by unauthorized personnel, data corrupted, or data lost would cause an extreme disruption