Internet firewalls
Internet firewallsInternet Firewalls:
Introduction
The Internet is a complex web of interconnected servers and workstations that span the globe, linking millions of people and companies. But there is a dark side: The convenient availability of valuable and sensitive electronic information invites severe misuse in the form of stolen, corrupted, or destroyed data found therein. Compounding this problem is the unfortunate fact that there are ample opportunities to intercept and misuse information transmitted on the Internet. For example, information sent across telephone lines can not only be seen, but also can be easily manipulated and retransmitted, or software can be developed to do something as fundamental as deny Internet service. Preventing unauthorized access is a cost that should be factored into every Internet equation. What follows is an explanation of Internet security and the concept of Firewalls.
What Makes the Internet Vulnerable?
Let's look at some of the most common security threats:
Impersonating a User or System - To authenticate Internet users, a system of user-Ids and passwords is used. Anyone intent on gaining access to the Internet can repeatedly make guesses until the right combination is found, a simple but time consuming process made all the easier by programs which systematically try all character combinations until the correct one is eventually generated. User-IDs and passwords can also be trapped by finding security holes in programs; a person looking to abuse the Internet finds these holes and uses the information leaked through them for his or her own personal agenda. Even someone who has been entrusted with high-level network access, such as a system administrator, can misuse his or her authorization to gain access to sensitive areas by impersonating other users.
Eavesdropping - By making a complete transcript of network activity, sensitive data such as passwords, data, and procedures for performing certain functions can be obtained. Eavesdropping is can be accomplished through the use of programs that monitor the packets of information transmitted across the network; or, less often, by tapping network circuits in a manner similar to telephone wiretapping. Regardless of technique, it is very difficult to detect the presence of an intruder.
Packet Replay - The recording of transmitted message packets over the network is a significant threat for programs requiring authentication sequences because an intruder saves and later replays (retransmits) legitimate authentication sequences to gain access to a system.
Packet Modification - This significant integrity threat involves one system intercepting and modifying a packet destined for another system; more significantly, in many cases, packet information can be just as easily destroyed as it can be modified.
Denial of Service - Multi-user, multi-tasking operating systems are subject to denial of service attacks where one user can render the system unusable by hogging a resource or by damaging or destroying resources so that they cannot be used. Service overloading, message flooding, and signal grounding are three common forms of denial-of-service attacks. While system administrators must protect against these types of threats...
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