Intrusion Detection System
An IDS is a device (or application) that monitors network and/or system activities for malicious activities or policy violations and produces reports to a Management Station. 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.
IDPSs typically record information related to observed events, notify security administrators of important observed events, and produce reports. Many IDPSs can also respond to a detected threat by attempting to prevent it from succeeding. They use several response techniques, which involve the IDPS stopping the attack itself, changing the security environment (e.g., reconfiguring a firewall), or changing the attack’s content.
 IDS Terminology
- Alert/Alarm- A signal suggesting that a system has been or is being attacked.
- True Positive- A legitimate attack which triggers an IDS to produce an alarm.
- False Positive- An event signaling an IDS to produce an alarm when no attack has taken place.
- False Negative- A failure of an IDS to detect an actual attack.
- True Negative- When no attack has taken place and no alarm is raised.
- Noise- Data or interference that can trigger a false positive.
- Site policy- Guidelines within an organization that control the rules and configurations of an IDS.
- Site policy awareness- The ability an IDS has to dynamically change its rules and configurations in response to changing environmental activity.
- Confidence value- A value an organization places on an IDS based on past performance and analysis to help determine its ability to effectively identify an attack.
- Alarm filtering- The process of categorizing attack alerts produced from an IDS in order to distinguish false positives from actual attacks.
 Types of Intrusion-Detection systems
There are two main types of IDS's: network-based and host-based IDS.
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 a host-based system, the sensor usually consists of a software agent, which monitors all activity of the host on which it is installed, including file system, logs and the kernel. Some application-based IDS are also part of this category.
- Network intrusion detection system (NIDS)
- It is an independent platform that 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.
- Host-based intrusion detection system (HIDS)
- It consists of an agent on a host that identifies intrusions by analyzing system calls, application logs, file-system modifications (binaries, password files, capability/acl databases) and other host activities and state. An example of a HIDS is OSSEC.,
Intruders: Intruders are attackers who try to find the way to hack information by breaking the privacy of a network like LAN or internet.
Masquerader: A user who does not have the authority to a system, but tries to access the information as an authorized user. They are generally outside users.
Misfeasor: They are commonly internal users and can be of two types: 1.An authorized user with limited permissions. 2.A user with full permissions and who misuse his powers.
Clandstine user:A user who acts as a supervisor and tries to use his privileges so as to avoid being captured.
Intrusion detection systems can also be system-specific using custom tools and honeypots.
 Passive system vs. reactive system
In a passive system, the intrusion detection system (IDS) sensor detects a potential security breach, logs the information and signals an alert on the console and or owner. In a reactive system, also known as an intrusion prevention system (IPS), the IPS responds to the suspicious activity by resetting the connection or by reprogramming the firewall to block network traffic from the suspected malicious source. This can happen automatically or at the command of an operator.in reactive intrusion detection system is one in which if the intruder or attacks is detected it does not alert the user rather responds to the illegant activity for shows a strict reaction.
Though they both relate to network security, an intrusion detection system (IDS) differs from a firewall in that a firewall looks outwardly for intrusions in order to stop them from happening. Firewalls limit access between networks to prevent intrusion and do not signal an attack from inside the network. An IDS evaluates a suspected intrusion once it has taken place and signals an alarm. An IDS also watches for attacks that originate from within a system. This is traditionally achieved by examining network communications, identifying heuristics and patterns (often known as signatures) of common computer attacks, and taking action to alert operators. A system that terminates connections is called an intrusion prevention system, and is another form of an application layer firewall.
The term IDPS is commonly used to refer to hybrid security systems that both "detect" and "prevent" for sure.
 Statistical anomaly and signature based IDSes
All Intrusion Detection Systems use one of two detection techniques: statistical anomaly based and/or signature based.
Statistical anomaly based IDS- A statistical anomaly-based IDS establishes a performance baseline based on normal network traffic evaluations. It will then sample current network traffic activity to this baseline in order to detect whether or not it is within baseline parameters. If the sampled traffic is outside baseline parameters, an alarm will be triggered
Signature-based IDS- Network traffic is examined for preconfigured and predetermined attack patterns known as signatures. Many attacks today have distinct signatures. In good security practice, a collection of these signatures must be constantly updated to mitigate emerging threats.
Noise - Noise can severely limit an Intrusion detection systems effectiveness. Bad packets generated from software bugs, corrupt DNS data, and local packets that escaped can create a significantly high false-alarm rate.
Too few attacks- It is not uncommon for the number of real attacks to be far below the false-alarm rate. Real attacks are often so far below the false-alarm rate that they are often missed and ignored.
Signature updates - Many attacks are geared for specific versions of software that are usually outdated. A constantly changing library of signatures is needed to mitigate threats. Outdated signature databases can leave the IDS vulnerable to new strategies.
 IDS evasion techniques
Intrusion detection system evasion techniques bypass detection by creating different states on the IDS and on the targeted computer. The adversary accomplishes this by manipulating either the attack itself or the network traffic that contains the attack.
A preliminary concept of an IDS began with James P. Anderson and reviews of audit trails. An example of an audit trail would be a log of user access.
Dorothy E. Denning, assisted by Peter G. Neumann, published a model of an IDS in 1986 that formed the basis for many systems today. Her model used statistics for anomaly detection, and resulted in an early IDS at SRI International named the Intrusion Detection Expert System (IDES), which ran on Sun workstations and could consider both user and network level data. IDES had a dual approach with a rule-based Expert System to detect known types of intrusions plus a statistical anomaly detection component based on profiles of users, host systems, and target systems. Lunt proposed adding an Artificial neural network as a third component. She said all three components could then report to a resolver. SRI followed IDES in 1993 with the Next-generation Intrusion Detection Expert System (NIDES).
The Multics intrusion detection and alerting system (MIDAS), an expert system using P-BEST and LISP, was developed in 1988 based on the work of Denning and Neumann. Haystack was also developed this year using statistics to reduce audit trails.
Wisdom & Sense (W&S) was a statistics-based anomaly detector developed in 1989 at the Los Alamos National Laboratory. W&S created rules based on statistical analysis, and then used those rules for anomaly detection.
In 1990, the Time-based Inductive Machine (TIM) did anomaly detection using inductive learning of sequential user patterns in Common LISP on a VAX 3500 computer. The Network Security Monitor (NSM) performed masking on access matrices for anomaly detection on a Sun-3/50 workstation. The Information Security Officer's Assistant (ISOA) was a 1990 prototype that considered a variety of strategies including statistics, a profile checker, and an expert system. ComputerWatch at AT&T Bell Labs used statistics and rules for audit data reduction and intrusion detection.
Then, in 1991, researchers at the University of California, Davis created a prototype Distributed Intrusion Detection System (DIDS), which was also an expert system. The Network Anomaly Detection and Intrusion Reporter (NADIR), also in 1991, was a prototype IDS developed at the Los Alamos National Laboratory's Integrated Computing Network (ICN), and was heavily influenced by the work of Denning and Lunt. NADIR used a statistics-based anomaly detector and an expert system.
The Lawrence Berkeley National Laboratory announced Bro in 1998, which used its own rule language for packet analysis from libpcap data. Network Flight Recorder (NFR) in 1999 also used libpcap. APE was developed as a packet sniffer, also using libpcap, in November, 1998, and was renamed Snort one month later, and has since become the world's largest used IDS/IPS system with over 300,000 active users.
The Audit Data Analysis and Mining (ADAM) IDS in 2001 used tcpdump to build profiles of rules for classifications.
In 2003 Dr. Wenke Lee argues for the importance of IDS in networks with mobile nodes.
 See also
- Anomaly-based intrusion detection system
- Application protocol-based intrusion detection system (APIDS)
- Artificial immune system
- Autonomous Agents for Intrusion Detection
- Host-based intrusion detection system (HIDS)
- Inhep Digital Security (IDS)
- Intrusion prevention system (IPS)
- Network intrusion detection system (NIDS)
- Protocol-based intrusion detection system (PIDS)
 Free Intrusion Detection Systems
 External links
- Guide to Intrusion Detection and Prevention Systems (IDPS), NIST CSRC special publication SP 800-94, released 02/2007
- Softpanorama: Intrusion Detection (General Issues)
- Intrusion Detection/Prevention Systems classification tree (PDF, SVG, Freemind)