  The Denial-of-service (DoS) attack is considered one of the largest threats
to the availability of cloud-computing services. Due to the unique architecture
of cloud-computing systems, the methods for detecting and preventing DoS
attacks are quite different from those used in traditional network systems. A
main target for DoS attackers is the authentication protocol because it is
considered a gateway to accessing cloud resources. In this work, we propose a
cloud-based authentication protocol - one that securely authenticates the cloud
user and effectively prevents DoS attack on the cloud-computing system-by
involving the user in a high computation process. Then, we analyze the protocol
via Syverson and Van Oorschot (SVO) logic to verify the authentication process
of the protocol in a cloud-computing system.
