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An Introduction To Intrusion Detection Systems

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I decided to write my paper on Intrusion Detection Systems (IDS) and Intrusion Prevention Systems (IPS) because professor mentioned these devices several times in class and I am interested in network security therefore it was a good opportunity for me to learn more about these security systems. An intrusion detection system (IDS) generally detects unwanted manipulations to computer systems, mainly through the Internet. The manipulations may take the form of attacks by crackers. An intrusion detection system is used to detect many types of malicious network traffic and computer usage that can't be detected by a conventional firewall. This includes network attacks against vulnerable services, data driver attacks on applications, host based attacks such as privilege escalation, unwanted logins and access to sensitive files, and malware (viruses, Trojan horses, and worms).

Intrusion detection is the process of monitoring the events occurring in a computer system or network and analyzing them for signs of possible incidents, which are violations or imminent threats of violation of computer security policies, acceptable use policies, or standard security practices. Intrusion prevention is the process of performing intrusion detection and attempting to stop detected possible incidents. Intrusion detection and prevention systems (IDPS) are primarily focused on identifying possible incidents, logging information about them, attempting to stop them, and reporting them to security administrators. In addition, organizations use IDPSs for other purposes, such as identifying problems with security policies, documenting existing threats, and deterring individuals from violating security policies. IDPSs have become a necessary addition to the security infrastructure of nearly every organization. An IDS is composed of several components: Sensors which generate security events, a Console to monitor events and alerts and control the sensors, and a central Engine that records events logged by the sensors in a database and uses a system of rules to generate alerts from security events received. There are several ways to categorize an IDS depending on the type and location of the sensors and the methodology used by the engine to generate alerts. In many simple IDS implementations all three components are combined in a single device or appliance.

In a network-based intrusion-detection system (NIDS), the sensors are located at choke points in the network to be monitored, often in the demilitarized zone (DMZ) or at network borders. The sensor captures all network traffic and analyzes the content of individual packets for malicious traffic. In systems, PIDS and APIDS are used to monitor the transport and protocols illegal or inappropriate traffic or constricts of language (say SQL). In a host-based system, the sensor usually consists of a software agent, which monitors all activity of the host on which it is installed. Hybrids of these two systems also exist.

Let's examine the different types of intrusion-detection systems available today. A network intrusion detection system is an independent platform which identifies intrusions by examining network traffic and monitors multiple hosts. Network Intrusion Detection Systems gain access to network traffic by connecting to a hub, network switch configured for port mirroring, or network tap. An example of a NIDS is Snort. A protocol-based intrusion detection system consists of a system or agent that would typically sit at the front end of a server, monitoring and analyzing the communication protocol between a connected device (a user/PC or system). For a web server this would typically monitor the HTTPS protocol stream and understand the HTTP protocol relative to the web server/system it is trying to protect. Where HTTPS is in use then this system would need to reside in the "shim" or interface between where HTTPS is un-encrypted and immediately prior to it entering the Web presentation layer. An application protocol-based intrusion detection system consists of a system or agent that would typically sit within a group of servers, monitoring and analyzing the communication on application specific protocols. For example; in a web server with database this would monitor the SQL protocol specific to the middleware/business-login as it transacts with the database.

I have some experience with the next type of intrusion detection system as I have used one for a couple of years on my Windows PC at home. A host-based intrusion detection system consists of an agent on a host which identifies intrusions by analyzing system calls, application logs, file-system modifications (binaries, password files, capability/acl databases) and other host activities and state. I have used BlackICE, which according to the software maker, scans all inbound



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