Barbhuiya, Ferdous Ahmed2015-09-212023-10-202015-09-212023-10-202014ROLL NO. 07610107http://172.17.1.107:4000/handle/123456789/450Supervisors: Sukumar Nandi and Santosh BiswasWith the rapid increase of security threats in Internet, Intrusion Detection System(IDS), a hardware or software that monitors network or host activities for malicious behavior, is an indispensable component of Network Security. Among the two prevalent IDS designing techniques, signature based IDSs can detect known attacks only while anomaly based systems can detect both known and unknown attacks, but generates large number of false alarms. There are classes of attacks like ARP based attack, ICMP based attack, TCP low rate DoS attack etc. which escape detection by both signature and anomaly IDSs. This thesis proposes a Discrete Event System(DES) based approach to design IDS for attacks across di erent network layers. DES models are designed for the system under normal and failure conditions where attacks are mapped to failures. A state estimator called diagnoser is designed which observes sequences of events generated by the system to decide whether the states through which the system traverses correspond to the normal or faulty DES model. The diagnoser acts as the IDS engine. For detecting ARP based attacks, an active probing mechanism based on ARP requests and responses is used. Active DES framework is adopted to model ARP based attacks using a controllable event (ARP probe) which creates di erence in sequence of events for normal or attack condition. Next, to handle network uncertainties due to presence of congestion, for detecting ICMP based attack, I-diagnosis framework of DES has been adopted where diagnosis is tested only in those sequence of states where a fault is followed by a indicator event. Redundant states of diagnoser of I-diagnosis framework are removed and a reduced detector is also proposed to improve complexity. Further, in Induced Low Rate TCP DoS attack, the attack and genuine sequence of state di ers with some probability. So to detect this attack, Stochastic DES framework has been adapted where attack case can be identified with some probability. Lastly, considering the migration from IPv4 to IPv6 addressing in the Internet, detection mechanism for NDP based attacks of IPv6 network is proposed. To tackle the challenge of presence of error in building complex DES model manually for NDP related attacks in IPv6, LTL based DES framework is adopted. All proposed detection mechanisms are implemented in testbed and the results show the e ectiveness of the systems in terms of accuracy and detection rate.enCOMPUTER SCIENCE AND ENGINEERINGThesis