Electronic Thesis and Dissertation Repository


Doctor of Philosophy


Electrical and Computer Engineering


Dr. Abdelkader Ouda


Cloud systems, also known as cloud services, are among the primary solutions of the information technology domain. Cloud services are accessed through an identity authentication process. These authentication processes have become increasingly vulnerable to adversaries who may perform denial-of-service (DoS) attacks to make cloud services inaccessible. Several strong authentication protocols have been employed to protect conventional network systems. Nevertheless, they can cause a DoS threat when implemented in the cloud-computing system. This is because the comprehensive verification process may exhaust the cloud resources and shut down cloud’s services. This thesis proposes a novel cloud-based secure authentication (CSA) protocol suite that provides a smart authentication approach not only for verifying the users’ identities but also for building a strong line of defense against the DoS attacks. CSA protocol suite offers two modules, CSAM-1 and CSAM-2. The decision of which module of CSA to be utilized depends on the deployment nature of the cloud computing.

CSAM-1 is designed to prevent external risks of DoS attacks in private and community cloud computing. CSAM-1 utilizes multiple techniques that include the client puzzle problem and utilization of unique encrypted text (UET). Therefore, these techniques can distinguish between a legitimate user’s request and an attacker’s attempt.

CSAM-2 is designed to prevent internal risks of DoS attacks in public and hybrid cloud computing. CSAM-2 combines an extended unique encrypted text (EUET) application, client puzzle problem, and deadlock avoidance algorithm to prevent DoS risks that occur from inside cloud computing systems. The authentication process in both modules is designed so that the cloud-based servers become footprint-free and fully able to detect the signs of DoS attacks.

The reliability and scalability of these two modules have been measured through a number of experiments using the GreenCloud simulation tool. The experiments’ results have shown that the CSA protocol suite is practically applicable as a lightweight authentication protocol. These experiments have verified the ability of the CSA to protect the cloud-based system against DoS attacks with an acceptable mean time to failure while still having the spare capacity to handle a large number of user requests.