الفهرس 
Enhancement of prevention technique for distributed denial of service attacks
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Abstract
DDoS attack has become a nightmare for the online businesses and the critical Internet sites (CIS). Imagine having a state of denial where you are not able to access your bank accounts, e-mail, e-government, e-trading, or e-commerce for hours, or days. Over the past years, the Internet was heavily used for day-to-day activities; from e-banking, e-ticketing and e-commerce to e-governments and the whole cyberspace. Distributed denial of service (DDoS) attack is one of the most rapidly increasing threats to the Internet eco-system. It has been increasing almost exponentially leaving the servers always wanting more bandwidth. Nowadays, DDoS attacks may be more than 100 Gbps which is 10 times the size of most internet backbone pipes. In this thesis, two models to thwart and defend DDoS attack are proposed. These models use the concept of Proof of Work to detect the malicious users and punish them. The first model 2DDoS-KaPoW3 uses two metrics to calculate the difficulty of the puzzle provided to the users. While the second model 2Z-PoW3 uses six metrics. Z-PoW model is considered as an enhancement and an improvement for DDoS-KaPoW model. A simulation program was developed using NetBeans development environment and XAMPP. The proposed models and 2KaPoW Guestbook3 which is a model proposed before by Feng, Ed Kaiser and Wu chang, to defend DoS attacks, were all simulated using the same environment. The proposed models DDoS-KaPoW and Z-PoW were evaluated and compared together. Then, they were evaluated in comparison with KaPoW guestbook